After that we performed preliminary verification of the mathematical model and numerical algorithm for solution of the three-dimensional problem of metal products manufacturing using plasma deposition of wire materials. For the reference we took the results of the experiment for wire deposition on a metal base using arc surfacing in shielding gases with a tungsten (nonconsumable) electrode as described in the Article [85]. Figure 10a shows the plate in question with the dimensions of 275 х 100 х 12 mm. We build up a metal rib with the length of

The arc deposition process is performed in 2 steps. The first step involves preliminary heating of the base plate that is performed by torch back and forth movement with the speed of vs ¼ 5 mm=s and the impacted area that is 1.5 times larger than the base area of the deposited rib. Power consumption of the torch is W ¼ 2:7 kW, diameter of the spot is Ds ¼ 6mm. Subsequent deposition is performed in 10 layers along a continuous path (the process con-

Figure 10. Product view illustration after the experiment with fixation and sensor systems (a), dimensions of the

4. To implement the ambient temperature, to release the entrapment, to calculate SSS.

165 mm and the cross section showed in Figure 10b on the upper surface of the object.

the model for the impact time of the ray ta.

54 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

time, and hold for twi seconds.

calculate SSS.

tinues backward).

deposited area at the cross section, mm (b) [85].

Figure 11 shows the finite element model of the problem. 20-unit isoparametric Solid 279 elements were used for solution.

The Inconel 718 nickel alloy was used as the material for calculation [86].

Thermal and physical properties of the material were taken from the Article [87]. In addition to the above, according to the data, represented in the Article, the density r ¼ 8170 kg=m3 and thermal conductivity λ ¼ 30 W=ð Þ m K were deemed as constants. Temperature dependence of the enthalpy H Tð Þ is presented in Figure 12. Heat capacity of the material, included in the thermal conductivity equation, was calculated according to the formula c Tð Þ¼ dH Tð Þ=dT. It should be noted that variations at the arc H Tð Þ in the range of 1500–1600 К in Figure 12 arise from heat emission during solidification of the alloy. Heating fraction of the plasma arc capacity K was set to 0.2 for calculation.

Identification of the chosen Anand model (25)–(28) for the material under study was performed according to the data of the stretch experiment with the defined speed at different temperatures represented in the Article [87].

The required constants of the model were defined in several steps by the downhill simplex method in the Matlab package. At that, relative disparity of computational and experimental values of voltage in Diagram σ � ε (Figure 13) was minimized.

As the result, the following values of material constants were obtained by the authors of this publication:

S0 = 2.0447e + 05 Pa, U=R = 2.0864e + 03, ξ = 0.3335, A = 2.5008e + 04, m = 0.4363, h0 = 4.0352e + 06, S1 = 3.2148e + 07 Pa, n = 0.2273, a = 0.4461.

CLTE at the temperature range up to the solidus temperature α is 6.5 � 10�6 К�1

left. Figures 15–17 show graphs of temperature evolution at the given points.

(Figures 16 and 17). The maximum absolute disparity does not exceed 25�С.

ing up process, are included into the Anand model.

sensors in the investigational studies mentioned above.

size of the spot.

Figure 14. The layout of temperature sensors.

shrinkage on the interval between solidus and liquidus temperatures is 0.3% and included in the temperature dependence αð Þ T . Hardening and softening effects, accompanying the build-

The main results of the calculations were given in [88]. Verification was performed using the experimental results obtained in the paper [86, 87]. Figure 14 shows the layout of temperature

In this case sensors No. 2, 3, 5, 6 were placed on the upper surface of the base plate, and No. 1 and 4 were placed on its bottom surface. Initial direction of the torch movement is from right to

The figures show that the qualitatively retrieved data comply with the experiment. The worst quantitative match is observed at points on the down plane of the base close to the heating area (points 1 and 4, Figure 15). In addition, the curves have oscillations and the temperature is below the ambient temperature at some points. All in all, the experimental graphs are below the computational graphs. The oscillations can be explained by proximity of the heating area and, consequently, heavy temperature gradients substantially altering the result at a fairly coarse mesh. Higher heating level in the experiment may be also caused by failure to take account of the torch heat radiation expanded far beyond the computational

Precision of the computational data is substantially higher at other measurement points

. The lineal

57

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Figure 12. Dependence of the enthalpy H(T), kJ/kg, from the temperature T, К, for the alloy Inconel 718.

Figure 13. Comparison of experimental (dots) and computational values of voltage in unconfined stretch tests at the temperatures of 720, 850, 900, 1150С (top-down).

Figure 13 shows that relative error of the calculation does not exceed 10%. The material was considered as isotropic. The Young's modulus of elasticity and the Poisson ratio were equal to 153 GPa and 0.32 respectively and not dependent on temperature [80]. The average value of CLTE at the temperature range up to the solidus temperature α is 6.5 � 10�6 К�1 . The lineal shrinkage on the interval between solidus and liquidus temperatures is 0.3% and included in the temperature dependence αð Þ T . Hardening and softening effects, accompanying the building up process, are included into the Anand model.

The main results of the calculations were given in [88]. Verification was performed using the experimental results obtained in the paper [86, 87]. Figure 14 shows the layout of temperature sensors in the investigational studies mentioned above.

In this case sensors No. 2, 3, 5, 6 were placed on the upper surface of the base plate, and No. 1 and 4 were placed on its bottom surface. Initial direction of the torch movement is from right to left. Figures 15–17 show graphs of temperature evolution at the given points.

The figures show that the qualitatively retrieved data comply with the experiment. The worst quantitative match is observed at points on the down plane of the base close to the heating area (points 1 and 4, Figure 15). In addition, the curves have oscillations and the temperature is below the ambient temperature at some points. All in all, the experimental graphs are below the computational graphs. The oscillations can be explained by proximity of the heating area and, consequently, heavy temperature gradients substantially altering the result at a fairly coarse mesh. Higher heating level in the experiment may be also caused by failure to take account of the torch heat radiation expanded far beyond the computational size of the spot.

Precision of the computational data is substantially higher at other measurement points (Figures 16 and 17). The maximum absolute disparity does not exceed 25�С.

Figure 14. The layout of temperature sensors.

Figure 13 shows that relative error of the calculation does not exceed 10%. The material was considered as isotropic. The Young's modulus of elasticity and the Poisson ratio were equal to 153 GPa and 0.32 respectively and not dependent on temperature [80]. The average value of

Figure 13. Comparison of experimental (dots) and computational values of voltage in unconfined stretch tests at the

temperatures of 720, 850, 900, 1150С (top-down).

Figure 12. Dependence of the enthalpy H(T), kJ/kg, from the temperature T, К, for the alloy Inconel 718.

56 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

Figure 15. The temperature, С in points 1 (red lined) and 4 (black lines). Thin curves show the experiment, thick curves show the calculation.

Figure 17. The temperature, �С in points 3 (red lined) and 5 (black lines). Thin curves—the experiment, thick curves—the

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59

calculation.

Figure 18. Temperature distribution, K (a) t ¼ 291 s, (b) t ¼ 506 s.

Figure 16. The temperature, С in points 2 (red lined) and 6 (black lines). Thin curves—the experiment, thick curves—the calculation.

Figure 17. The temperature, �С in points 3 (red lined) and 5 (black lines). Thin curves—the experiment, thick curves—the calculation.

Figure 18. Temperature distribution, K (a) t ¼ 291 s, (b) t ¼ 506 s.

Figure 15. The temperature, С in points 1 (red lined) and 4 (black lines). Thin curves show the experiment, thick curves

58 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

Figure 16. The temperature, С in points 2 (red lined) and 6 (black lines). Thin curves—the experiment, thick curves—the

show the calculation.

calculation.

Figure 18 shows by way of illustration the temperature fields at the moment of the end of preliminary heating of the base plate (Figure 18a) and of the end of the fourth layer (Figure 18b).

Figure 19 shows the results of solution of the deformable body mechanics problem and residual displacement at central cross sections of the plate. The figure shows that the residual contraction of the structure can be estimated with acceptable accuracy. It was predicted that the plate will be bowl-shaped with the height of the ribs about 1 mm. The minimum computational accuracy is at the cross section where the relative disparity of the height runs up to 20%.

Figure 20 represents the distribution pattern of residual characteristics in the structure.

Figure 20a shows that the longitudinal bend dominates. The transverse bend is almost 10 times lower. The maximum intensity of residual stresses is observed at the contact area of the deposited material and the base.

The stresses are calculated at every step of solution of the quasipermanent boundary deformable solid body problem (Eqs. (21)–(28)). Figure 20b represents distribution of residual stresses, i.e. the stresses observed in the structure at the end of the production process and complete cooldown to the ambient temperature.

The model of thermomechanical behavior of the sample, created by the additive fabrication method, is designed for evaluation of strain-stress state of the sample and its contraction as well as for definition of parameters of the production process ensuring low contraction and residual stress. The model can be combined with other mathematical and numerical models

including the temperature and conversion model specifying distribution of the variable tem-

Figure 20. Vertical displacement in the structure after its cooldown and release, m (a), residual stress intensity, Pa (b).

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61

The model may be included into a computer-aided expert system to forecast the results of

1. We defined the mathematical problem (model) of heat and mass transfer in the process of additive fabrication of products by fusion of wire material using plasma (electric) arc and concentrated energy sources with asymmetrical wire feed. The model describes transient nonequilibrium adjoint heat and mass transfer processes in molten metal with free surface, includes differential equation of viscous fluid movement (Navier-Stokes equations) with

perature field inside the sample.

5. Conclusions

additive fabrication of large-sized components.

Figure 19. Relative residual displacement, mm, at longitudinal (blue lines) and cross (black lines) sections of the plate on its bottom surface. Thin curves show the experiment, thick curves show the calculation.

Figure 20. Vertical displacement in the structure after its cooldown and release, m (a), residual stress intensity, Pa (b).

including the temperature and conversion model specifying distribution of the variable temperature field inside the sample.

The model may be included into a computer-aided expert system to forecast the results of additive fabrication of large-sized components.

## 5. Conclusions

Figure 18 shows by way of illustration the temperature fields at the moment of the end of preliminary heating of the base plate (Figure 18a) and of the end of the fourth layer (Figure 18b). Figure 19 shows the results of solution of the deformable body mechanics problem and residual displacement at central cross sections of the plate. The figure shows that the residual contraction of the structure can be estimated with acceptable accuracy. It was predicted that the plate will be bowl-shaped with the height of the ribs about 1 mm. The minimum computational accuracy is at the cross section where the relative disparity of the height runs up to

60 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

Figure 20 represents the distribution pattern of residual characteristics in the structure.

Figure 20a shows that the longitudinal bend dominates. The transverse bend is almost 10 times lower. The maximum intensity of residual stresses is observed at the contact area of the

The stresses are calculated at every step of solution of the quasipermanent boundary deformable solid body problem (Eqs. (21)–(28)). Figure 20b represents distribution of residual stresses, i.e. the stresses observed in the structure at the end of the production process and

The model of thermomechanical behavior of the sample, created by the additive fabrication method, is designed for evaluation of strain-stress state of the sample and its contraction as well as for definition of parameters of the production process ensuring low contraction and residual stress. The model can be combined with other mathematical and numerical models

Figure 19. Relative residual displacement, mm, at longitudinal (blue lines) and cross (black lines) sections of the plate on

its bottom surface. Thin curves show the experiment, thick curves show the calculation.

20%.

deposited material and the base.

complete cooldown to the ambient temperature.

1. We defined the mathematical problem (model) of heat and mass transfer in the process of additive fabrication of products by fusion of wire material using plasma (electric) arc and concentrated energy sources with asymmetrical wire feed. The model describes transient nonequilibrium adjoint heat and mass transfer processes in molten metal with free surface, includes differential equation of viscous fluid movement (Navier-Stokes equations) with convective terms in laminar current, takes into account the Marangoni effect on the surface of melt, and allows to calculate volume distribution of temperatures, melt flow speed, pressure, shape and dimensions of the molten pool, shape of the molten metal free surface, shape and dimensions of the deposited bead. We also defined potential uses of the models.

Author details

Dmitriy Trushnikov1

Karuppasamy Poolan Karunakaran5

Vladimir Belenkiy6 and Yurii Schitsyn1

\*Address all correspondence to<EMAIL_ADDRESS>
National Research Polytechnic University, Perm, Russia

University of Science and Technology, Wuhan, China

of Technology Bombay, Mumbai, India

Russia

References

\*, Oleg Smetannikov2

, Anatoly Perminov3

, Petr Maksimov2

1 Department of Welding Production, Metrology and Technology of Material, Mechanical

Mathematics and Mechanics, Perm National Research Polytechnic University, Perm, Russia 3 Department of General Physics, Faculty of Applied Mathematics and Mechanics, Perm

4 State Key Laboratory of Materials Processing and Die and Mould Technology, Huazhong

5 Department of Mechanical Engineering, Rapid Manufacturing Laboratory, Indian Institute

6 Mechanical Engineering Faculty, Perm National Research Polytechnic University, Perm,

[1] Sciaky Inc. Electron Beam Additive Manufacturing (EBAM)—Advantages of Wire AM vs. Powder AM. URL: http://additivemanufacturing.com/2015/10/14/electron-beam-additive-

[2] Sciaky Inc. Electron Beam Additive Manufacturing (EBAM). URL: http://www.sciaky.

[3] Jhavar S, Jain NK, Paul СP. Development of micro-plasma transferred arc (p-PTA) wire deposition process for additive layer manufacturing applications. Journal of Materials

[4] Louvis E et al. Selective laser melting of aluminium components. Journal of Materials Processing Technology. Department of Engineering, The University of Liverpool, Liver-

[5] Campanelli SL et al. Capabilities and Performances of the Selective Laser Melting Process. Polytechnic of Bari, Department of Management and Mechanical Engineering, Viale Japigia, 182 Italy [electronic source]. URL: http://cdn.intechopen.com/pdfs/12285/InTech-

manufacturing-ebamadvantages-of-wire-am-vs-powder-am

Processing Technology. 2014;214(5):1102-1110

pool L69 3GH, United Kingdom. 2011;211:275-284

com/images/pdfs/product-sheets/Sciaky-EBAM-Technology.pdf

Engineering Faculty, Perm National Research Polytechnic University, Perm, Russia 2 Department of Computational Mathematics and Mechanics, Faculty of Applied

, Shengyong Pang4

Modeling of the Plasma 3D Deposition of Wire Materials

http://dx.doi.org/10.5772/intechopen.77153

, Mariia Bartolomey2

,

, Aleksei Kovyazin2

,

63

## Acknowledgements

The work was supported by the Ministry of Education and Science of the Russian Federation (RFMEFI58317X0062) and MOST (No. 2017YFE0100100) under the BRICS project.

## Author details

convective terms in laminar current, takes into account the Marangoni effect on the surface of melt, and allows to calculate volume distribution of temperatures, melt flow speed, pressure, shape and dimensions of the molten pool, shape of the molten metal free surface, shape and dimensions of the deposited bead. We also defined potential uses of the models.

62 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

2. We suggested approximation of the wire feed process by mass inflow on the metal-gas edge. To describe movement of the molten-solid metal interface, one can use any of the two following methods: the Level-Set method or the Arbitrary Lagrangian-Eulerian method

3. We described the heat source when using a plasma arc of various electrical polarity. In the process of deposition with reverse polarity, the plasma source is represented by a combination of the source of the heat, transferred by the plasma flow, with Gaussian distribution and a uniformly distributed source in the area of cathode spots impact. The energy relation between the sources is defined by experiment. We preselected the approximating formulas which describe influence of technological parameters of plasma arcs on distribution of heat

4. We suggested the mathematical 3D-model of the additive product fabrication process by

5. We developed and implemented in the form of an APDL program in the ANSYS package the algorithm for estimation of unsteady temperature fields and strain-stress state of the

6. The experimental information of other authors was used to identify the thermal-physical and thermomechanical properties of the material—the Inconel 718 nickel alloy.

8. The represented example of application of the model and its numerical implementation in the ANSYS package shows that the chosen approach is reasonable and allows to obtain acceptable numerical results properly describing real effects and processes in the objects created by the method of additive volume generation. More accurate verification procedure for the suggested mathematical model showing its accuracy and limits of applicability on the basis of experimental studies of residual stresses and thermoshrinkable deformations of model products manufacturing using the method of additive part fabrication by fusion of wire material with an electric arc and concentrated energy sources will be

The work was supported by the Ministry of Education and Science of the Russian Federation

(RFMEFI58317X0062) and MOST (No. 2017YFE0100100) under the BRICS project.

structure in the process of its generation by arc 3D-deposition of wire materials.

7. Verification of the model showed required accuracy of the results.

(ALE).

flow density in the source.

deposition of wire material.

represented in future studies.

Acknowledgements

Dmitriy Trushnikov1 \*, Oleg Smetannikov2 , Anatoly Perminov3 , Shengyong Pang4 , Karuppasamy Poolan Karunakaran5 , Petr Maksimov2 , Mariia Bartolomey2 , Aleksei Kovyazin2 , Vladimir Belenkiy6 and Yurii Schitsyn1

\*Address all correspondence to<EMAIL_ADDRESS>
1 Department of Welding Production, Metrology and Technology of Material, Mechanical Engineering Faculty, Perm National Research Polytechnic University, Perm, Russia

2 Department of Computational Mathematics and Mechanics, Faculty of Applied Mathematics and Mechanics, Perm National Research Polytechnic University, Perm, Russia

3 Department of General Physics, Faculty of Applied Mathematics and Mechanics, Perm National Research Polytechnic University, Perm, Russia

4 State Key Laboratory of Materials Processing and Die and Mould Technology, Huazhong University of Science and Technology, Wuhan, China

5 Department of Mechanical Engineering, Rapid Manufacturing Laboratory, Indian Institute of Technology Bombay, Mumbai, India

6 Mechanical Engineering Faculty, Perm National Research Polytechnic University, Perm, Russia

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**Chapter 4**

Provisional chapter

**Theory and Technology of Direct Laser Deposition**

DOI: 10.5772/intechopen.76860

Presently the additive technologies in manufacturing are widely developed in all industrialized countries. Replacing the traditional technology of casting and machining with additive technologies, one can significantly reduce material consumption and labor costs. They also allow obtaining products with desired properties. The most promising for manufacturing large-sized products is the additive technology of high-speed direct laser deposition. Using this technology allows to create complex parts and construction to one technological operation without using addition equipment and tools. This technology allows decreasing of consumption of raw materials and decrease amount of waste. Equipment for realization of DLD technology is universal and based on module design principle. DLD is based on layer-by-layer deposition and melting of powder by laser beam from using a sliced 3D computer-aided design (CAD) file. The materials used are powders based on Fe, Ni, and Ti. This chapter presents the results of machine design and research

Keywords: high-speed direct laser deposition, additive manufacturing, stability of

New manufacturing technologies are incorporated into most areas of engineering: aircraft industry, shipbuilding, medicine, engine construction, etc. Existing requirements for its demand are more energy efficient and have environmental compatibility; additive technologies meet both criteria. The intensive development of additive technologies in recent years makes it possible to improve the methods of manufacturing and processing products [1–5]. They allow saving expensive raw materials in comparison with classical production methods, during which up to 90% of the material can be removed. The issue of cost reduction is

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Theory and Technology of Direct Laser Deposition

Gleb Turichin and Olga Klimova-Korsmik

Gleb Turichin and Olga Klimova-Korsmik

http://dx.doi.org/10.5772/intechopen.76860

Abstract

1. Introduction

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

HS DLD technology from various materials.

process, equipment, structure, properties

#### **Theory and Technology of Direct Laser Deposition** Theory and Technology of Direct Laser Deposition

DOI: 10.5772/intechopen.76860

Gleb Turichin and Olga Klimova-Korsmik Gleb Turichin and Olga Klimova-Korsmik

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.76860

#### Abstract

[86] Overfelt RA, Sahai V, Ko YK, Berry JT. Porosity in cast equiaxed alloy 718 Superalloys 718, 625, 706 and Various Derivatives. In: Proceedings of the International Symposium on Superalloys 718, 625, 706 and Various Derivatives, Pittsburg, Pennsylvania; 1994. рp.

70 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

[87] Nowotnik A, Pędrak P, Sieniawski J, Góral M. Mechanical properties of hot deformed Inconel 718 and X750. Journal of Achievements in Materials and Manufacturing Engineer-

[88] Smetannikov OY, Trushnikov DN, Maksimov PV, Bartolomey ML, Kovyazin AV. Modeling of the thermomechanical behavior of the product during process of 3D deposition of wire materials in ANSYS. PNRPU Mechanics Bulletin. 2017;4:154-172. DOI: 10.15593/04

189-200

ing. 2012;50(2):74-80

perm.mech/2017.4.11

Presently the additive technologies in manufacturing are widely developed in all industrialized countries. Replacing the traditional technology of casting and machining with additive technologies, one can significantly reduce material consumption and labor costs. They also allow obtaining products with desired properties. The most promising for manufacturing large-sized products is the additive technology of high-speed direct laser deposition. Using this technology allows to create complex parts and construction to one technological operation without using addition equipment and tools. This technology allows decreasing of consumption of raw materials and decrease amount of waste. Equipment for realization of DLD technology is universal and based on module design principle. DLD is based on layer-by-layer deposition and melting of powder by laser beam from using a sliced 3D computer-aided design (CAD) file. The materials used are powders based on Fe, Ni, and Ti. This chapter presents the results of machine design and research HS DLD technology from various materials.

Keywords: high-speed direct laser deposition, additive manufacturing, stability of process, equipment, structure, properties

#### 1. Introduction

New manufacturing technologies are incorporated into most areas of engineering: aircraft industry, shipbuilding, medicine, engine construction, etc. Existing requirements for its demand are more energy efficient and have environmental compatibility; additive technologies meet both criteria. The intensive development of additive technologies in recent years makes it possible to improve the methods of manufacturing and processing products [1–5]. They allow saving expensive raw materials in comparison with classical production methods, during which up to 90% of the material can be removed. The issue of cost reduction is

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

especially relevant in knowledge-based industries (gas turbine engine construction, aviation, space exploration, etc.). Selective laser melting (SLM) technology has already been implemented in production in many countries of the world [6, 7]. However, SLM technology is limited by its inability to manufacture large-sized products and low productivity.

reason for instabilities is self-oscillations of the weld pool [12–19]. Different experimental data

The stability of surface formation in the process of direct laser deposition is determined by the complex of physical processes occurring on the surface of the molten pool, which moves with high speed along the deposited product at a constant flow of matter to its surface. Hydrodynamic stability of melt flow in semiliquid bath, formed by substrate melting under laser beam heating and powder income, depends on driving force, which leads to melt motion. The main driving force for melt motion relative solid substrate in DLD process is Marangoni effect. Therefore velocity of liquid relative solid phase is determined by the rate of the thermocapillary flow [20]. To make the analysis more clear, it is convenient to confine to analyze practically interesting case, when the molten pool length "L" is much greater than its width "b" and depth "H," which depend on parameters of deposition mode. Then analysis of the equation of continuity of the melt allows us to conclude that the "longitudinal" velocity component vx directed along the axis of the laser beam motion relative to the target is much larger than transverse components vy and vz so we the boundary layer like flow. So that equation of the motion can be written in our case as

> ∂vx ∂t þ vx

∂vx ∂x ¼ � 1 r ∂r ∂x þ v ∂2 vx

∂z z¼H ¼ ∂σ

> η ∂vx ∂z z¼H

∂vx ∂x ¼ � 1 r ∂r ∂x � 3v

At the "bottom" of the molten pool, which coincides with the previous layer surface, the

Assuming that at the front of the melt pool the surface temperature close to the boiling one and the surface tension value close to "0," taking a linear law for the temperature drop to the "tail" of

It is possible to get after a number of transformations that with the consideration of Marangoni

One can use the mass conservation condition to connect the melt velocity vx with position of the melt pool surface. Let ζ be the height of the perturbation on surface. In our case, the mass flux coming to the melt surface with the gas-powder jet must be taken into account. One can denote the incident mass flux density on melt surface as j (x, ζ). Suppose ζ < < H, it is possible

> þ j xð Þ ; 0 Hr þ 1 Hr

¼ σ

vx H2 þ 3σ

∂j xð Þ ∂x

∂z2 (1)

Theory and Technology of Direct Laser Deposition http://dx.doi.org/10.5772/intechopen.76860 73

∂x, where σ is the coefficient of surface tension.

L (2)

2rLH (3)

ζ: (4)

z¼0 ¼ 0; on the surface, the continuity condition of the tangen-

confirm this idea [16, 19].

"sticking" condition is fulfilled vxj

the melt pool, one can write

tial component of the stress tensor is η ∂vx

force, Eq. (1) can be written in the next shape:

to write the continuity condition of the mass flux as

∂vx ∂x ≈ � 1 H ∂ζ ∂t

∂vx ∂t þ vx

The main trend in the development of additive technology is to increase productivity while maintaining the required quality of the product. The most promising technology of product manufacturing is direct laser deposition analogue direct metal deposition (DMD), when the product is formed from a powder, which is supplied by compressed gas-powder jet directly into the laser action zone [8–11]. The jet can be as coaxial and as non-coaxial to focused laser beam, which provides heating and partial melting of the powder and heating the substrate. This technology allows to include a mixture of powders into the gas-powder jet and to change the composition of powders during the process.

The developed technology and equipment have several advantages in comparison with existing analogues. There is a high productivity of DLD process for the manufacture of real parts and products: up to 2.5 kg/h for nickel and iron alloys, up to 1.2 kg/h for titanium alloys. For similar equipment, the productivity is 2–3 times less [12–14]. There are experimental stands with the same high productivity (up to 2 kg/h), preferably [15]. The main feature of the developed equipment is a modular assembly type, which allows to modernize the installation at the customer's request. This is the first Russian technology and equipment for the implementation of additive production.

Complex studies were carried out to understand the relationship between the parameters of the process and the optimization of the technology for obtaining products with specified characteristics. As a result of the research done, the theory and technology of high-speed direct laser deposition are developed. Also a number of machines with various sizes are made for the implementation of this technology. Investigations for powder materials based on iron, nickel, and titanium demonstrated the possibility of obtaining high-quality parts and products. Also, the possibility of working with cermet materials is shown. The research results showed that developed technology of direct laser deposition can replace the currently used technologies, providing multiple increase productivity and material savings, in spite of its technological complexity.

## 2. Theory of high-speed direct laser deposition

The processes that occur during high-speed laser deposition depend on a large number of distributed parameters which effect on the result [8]. An important aspect of the study is the stability of the direct laser deposition process. Previously, the authors studied the root peak formation in welds during the process of laser welding using highly concentrated energy fluxes. According to the present knowledge about the physical nature of these processes, the reason for instabilities is self-oscillations of the weld pool [12–19]. Different experimental data confirm this idea [16, 19].

especially relevant in knowledge-based industries (gas turbine engine construction, aviation, space exploration, etc.). Selective laser melting (SLM) technology has already been implemented in production in many countries of the world [6, 7]. However, SLM technology is limited by its

The main trend in the development of additive technology is to increase productivity while maintaining the required quality of the product. The most promising technology of product manufacturing is direct laser deposition analogue direct metal deposition (DMD), when the product is formed from a powder, which is supplied by compressed gas-powder jet directly into the laser action zone [8–11]. The jet can be as coaxial and as non-coaxial to focused laser beam, which provides heating and partial melting of the powder and heating the substrate. This technology allows to include a mixture of powders into the gas-powder jet and to change

The developed technology and equipment have several advantages in comparison with existing analogues. There is a high productivity of DLD process for the manufacture of real parts and products: up to 2.5 kg/h for nickel and iron alloys, up to 1.2 kg/h for titanium alloys. For similar equipment, the productivity is 2–3 times less [12–14]. There are experimental stands with the same high productivity (up to 2 kg/h), preferably [15]. The main feature of the developed equipment is a modular assembly type, which allows to modernize the installation at the customer's request. This is the first Russian technology and equipment for the imple-

Complex studies were carried out to understand the relationship between the parameters of the process and the optimization of the technology for obtaining products with specified characteristics. As a result of the research done, the theory and technology of high-speed direct laser deposition are developed. Also a number of machines with various sizes are made for the implementation of this technology. Investigations for powder materials based on iron, nickel, and titanium demonstrated the possibility of obtaining high-quality parts and products. Also, the possibility of working with cermet materials is shown. The research results showed that developed technology of direct laser deposition can replace the currently used technologies, providing multiple increase productivity and material savings, in spite of its technological

The processes that occur during high-speed laser deposition depend on a large number of distributed parameters which effect on the result [8]. An important aspect of the study is the stability of the direct laser deposition process. Previously, the authors studied the root peak formation in welds during the process of laser welding using highly concentrated energy fluxes. According to the present knowledge about the physical nature of these processes, the

inability to manufacture large-sized products and low productivity.

72 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

the composition of powders during the process.

2. Theory of high-speed direct laser deposition

mentation of additive production.

complexity.

The stability of surface formation in the process of direct laser deposition is determined by the complex of physical processes occurring on the surface of the molten pool, which moves with high speed along the deposited product at a constant flow of matter to its surface. Hydrodynamic stability of melt flow in semiliquid bath, formed by substrate melting under laser beam heating and powder income, depends on driving force, which leads to melt motion. The main driving force for melt motion relative solid substrate in DLD process is Marangoni effect. Therefore velocity of liquid relative solid phase is determined by the rate of the thermocapillary flow [20]. To make the analysis more clear, it is convenient to confine to analyze practically interesting case, when the molten pool length "L" is much greater than its width "b" and depth "H," which depend on parameters of deposition mode. Then analysis of the equation of continuity of the melt allows us to conclude that the "longitudinal" velocity component vx directed along the axis of the laser beam motion relative to the target is much larger than transverse components vy and vz so we the boundary layer like flow. So that equation of the motion can be written in our case as

$$\frac{\partial v\_{\mathbf{x}}}{\partial t} + v\_{\mathbf{x}} \frac{\partial v\_{\mathbf{x}}}{\partial \mathbf{x}} = -\frac{1}{\rho} \frac{\partial \rho}{\partial \mathbf{x}} + v \frac{\partial^2 v\_{\mathbf{x}}}{\partial \mathbf{z}^2} \tag{1}$$

At the "bottom" of the molten pool, which coincides with the previous layer surface, the "sticking" condition is fulfilled vxj z¼0 ¼ 0; on the surface, the continuity condition of the tangential component of the stress tensor is η ∂vx ∂z z¼H ¼ ∂σ ∂x, where σ is the coefficient of surface tension. Assuming that at the front of the melt pool the surface temperature close to the boiling one and the surface tension value close to "0," taking a linear law for the temperature drop to the "tail" of the melt pool, one can write

$$
\sigma \left. \frac{\partial v\_x}{\partial z} \right|\_{z=H} = \frac{\sigma}{L} \tag{2}
$$

It is possible to get after a number of transformations that with the consideration of Marangoni force, Eq. (1) can be written in the next shape:

$$\frac{\partial v\_x}{\partial t} + v\_x \frac{\partial v\_x}{\partial x} = -\frac{1}{\rho} \frac{\partial \rho}{\partial x} - 3v \frac{v\_x}{H^2} + \frac{3\sigma}{2\rho LH} \tag{3}$$

One can use the mass conservation condition to connect the melt velocity vx with position of the melt pool surface. Let ζ be the height of the perturbation on surface. In our case, the mass flux coming to the melt surface with the gas-powder jet must be taken into account. One can denote the incident mass flux density on melt surface as j (x, ζ). Suppose ζ < < H, it is possible to write the continuity condition of the mass flux as

$$\frac{\partial \mathbf{w}\_x}{\partial \mathbf{x}} \approx -\frac{1}{H} \frac{\partial \zeta}{\partial t} + \frac{j(\mathbf{x}, \mathbf{0})}{H\rho} + \frac{1}{H\rho} \frac{\partial j(\mathbf{x})}{\partial \mathbf{x}} \zeta. \tag{4}$$

The boundary conditions for this task are given by ζ = 0 at x=0, ∂ζ

� �3=2 2 � exp

exp

L � �

> ffiffiffiffiffiffi G H2 r

L � exp �

L � � exp

> ffiffiffiffiffiffi G H2 r

G p L H þ 2

Let us analyze this expression. Depending on the sign of "A," which depends on what is more underestimation of the surface due to thermocapillary acceleration of the melt flow or its overstating caused by the input of a new material with a gas-powder jet; formation of dimple and humps on melt pool surface is possible. The height of the hump, depending on the speed of the process and the length of the melt pool, can significantly exceed the depth of the melt pool H. Such modes are most dangerous from the point of view of unstable surface formation, but it is impossible to analyze this case using the approximations of the "boundary layer" and the smallness of "ζ." This analysis is a theoretical description of the process of forming the profile of the melt pool surface, taking into account the capillary phenomena and the flow of material that the gas-powder jet brings. For the analysis of nonstationary phenomena leading to instability of the growing process, it is necessary to keep the "nonstationary" terms with time deriva-

L � �

> ffiffiffiffiffiffi G H2 r

L � � exp �

ffiffiffiffiffiffi G H2 r

1 � exp

σH2 þ v0j xð Þ ;0 σH .

> G � �3=2 ffiffiffiffi

tives in the equations and to analyze the stability of the "quasi-stationary" behavior.

We derive an equation describing the dynamic behavior of the local excess of the "ζ" melt pool surface above the "quasi-stationary" surface calculated above. We use the nonstationary Navier-Stokes Eq. (5) and the continuity of the flow Eq. (4) for this purpose. Suppose that

ffiffiffiffiffiffi G H2 r

ffiffiffiffiffiffi G H2 r

ffiffiffiffiffiffi G H2 r

L � exp �

ffiffiffiffiffiffi G H2 r

x�

1 � Ch ffiffiffiffi G p L H � �

Sh ffiffiffiffi G p L H

L � exp �

Solution of this problem can be written as

exp

�A H2 G � �3=2

where G ¼ rv0

2H σ , A ¼ � 3

G x þ A H2

G

L � exp �

1 � exp �

exp

2LH þ 3v rv0

ζj

assuming that v1ð Þ x; t ≪ v0ð Þx . Then, obviously,

At the rear part of the melt pool at x = L for the value of ζ, we get

x¼L ¼ A H2

ffiffiffiffiffiffi G H2 r

ζ ¼ A H2

∂x � �

ffiffiffiffiffiffi G H2 r

L � � � �A H2

ffiffiffiffiffiffi G H2 r

L � �

> ffiffiffiffiffiffi G H2 r

� � " # (8)

vxð Þ¼ x; t v0ð Þþ x v1ð Þ x; t (9)

x !

x¼0 ¼ 0, ∂ζ ∂x � � x¼L ¼ 0.

Theory and Technology of Direct Laser Deposition http://dx.doi.org/10.5772/intechopen.76860

> G � �3=2

> > (7)

75

Figure 1. Geometry of the melt pool surface motion.

One can determine the Laplace pressure in the liquid "p" and the additional pressure, which is related to the perturbation of the melt pool surface ζ, taking into account that p = σ/R, where R is the radius of surface curvature (Figure 1).

The one-dimensional model of thermocapillary flow does not allow introducing the effects of the influence of grown wall thickness on change in the shape of its surface. For that, we need to introduce a "transverse" dimension. Analysis of term scales in the continuity equation show that melt velocity in "transverse" direction is negligible but pressure changes can be significant. Therefore, when ζ << H, one can get R ≈ b þ ζ2 2b , and for pressure it is possible to obtain p ≈ σ b � σζ2 2b3 .

Considering it, one can write Navier-Stokes equation in the two-dimensional case as

$$\frac{\partial v\_x}{\partial t} + v\_x \frac{\partial v\_x}{\partial x} = -\frac{\sigma}{\rho} \frac{\partial^3 \zeta}{\partial x^3} - 3v \frac{v\_x}{H^2} + \frac{3\sigma}{2\rho LH} + \frac{\sigma}{\rho b^3} \frac{\zeta \partial \zeta}{\partial x} \tag{5}$$

In the steady-state approximation, with consideration of mass flux conservation, this equation can be simplified as

$$\frac{\partial^3 \zeta}{\partial \mathbf{x}^3} - \frac{\rho v\_0}{\sigma H} \frac{\partial \zeta}{\partial \mathbf{x}} = \frac{3}{2LH} - 3v \frac{\rho v\_0}{\sigma H^2} - \frac{v\_0 j(\mathbf{x}, 0)}{\sigma H} \tag{6}$$

Theory and Technology of Direct Laser Deposition http://dx.doi.org/10.5772/intechopen.76860 75

The boundary conditions for this task are given by ζ = 0 at x=0, ∂ζ ∂x � � x¼0 ¼ 0, ∂ζ ∂x � � x¼L ¼ 0. Solution of this problem can be written as

$$\zeta = A \frac{H^2}{G} \mathbf{x} + A \left(\frac{H^2}{G}\right)^{\frac{\phi}{\phi}} \frac{2 - \exp\sqrt{\frac{G}{H^2}} L - \exp\left(-\sqrt{\frac{G}{H^2}} L\right)}{\exp\sqrt{\frac{G}{H^2}} L - \exp\left(-\sqrt{\frac{G}{H^2}} L\right)} - A \left(\frac{H^2}{G}\right)^{\frac{\phi}{\phi}}$$

$$\frac{1 - \exp\left(-\sqrt{\frac{G}{H^2}} L\right)}{\exp\sqrt{\frac{G}{H^2}} L - \exp\left(-\sqrt{\frac{G}{H^2}} L\right)} \exp\sqrt{\frac{G}{H^2}} \mathbf{x} - \tag{7}$$

$$-A \left(\frac{\mu^i}{c}\right)^{\frac{\phi}{\phi}} \frac{1 - \exp\left(\sqrt{\frac{G}{H^2}} L\right)}{\exp\sqrt{\frac{G}{H^2}} L - \exp\left(-\sqrt{\frac{G}{H^2}} L\right)} \exp\left(-\sqrt{\frac{G}{H^2}} \mathbf{x}\right)$$

where G ¼ rv0 2H σ , A ¼ � 3 2LH þ 3v rv0 σH2 þ v0j xð Þ ;0 σH .

One can determine the Laplace pressure in the liquid "p" and the additional pressure, which is related to the perturbation of the melt pool surface ζ, taking into account that p = σ/R, where R

The one-dimensional model of thermocapillary flow does not allow introducing the effects of the influence of grown wall thickness on change in the shape of its surface. For that, we need to introduce a "transverse" dimension. Analysis of term scales in the continuity equation show that melt velocity in "transverse" direction is negligible but pressure changes can be signifi-

Considering it, one can write Navier-Stokes equation in the two-dimensional case as

2b

vx H2 þ

rv0

In the steady-state approximation, with consideration of mass flux conservation, this equation

2LH � 3v

3σ 2rLH þ

σH2 � v0j xð Þ ; 0

σ rb3 ζ∂ζ

, and for pressure it is possible to obtain

∂x (5)

σH (6)

is the radius of surface curvature (Figure 1).

Figure 1. Geometry of the melt pool surface motion.

p ≈ σ b � σζ2 2b3 .

can be simplified as

cant. Therefore, when ζ << H, one can get R ≈ b þ ζ2

∂vx ∂t þ vx

> ∂3 ζ ∂x3 � rv0

∂vx ∂x ¼ � σ r ∂3 ζ ∂x3 � 3v

74 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

2 σH

∂ζ ∂x ¼ 3 At the rear part of the melt pool at x = L for the value of ζ, we get

$$\zeta|\_{x=L} = A \left(\frac{H^2}{G}\right)^{\frac{\psi}{2}} \left[\sqrt{G}\frac{L}{H} + 2\frac{1 - Ch\left(\sqrt{G}\frac{L}{H}\right)}{Sh\left(\sqrt{G}\frac{L}{H}\right)}\right] \tag{8}$$

Let us analyze this expression. Depending on the sign of "A," which depends on what is more underestimation of the surface due to thermocapillary acceleration of the melt flow or its overstating caused by the input of a new material with a gas-powder jet; formation of dimple and humps on melt pool surface is possible. The height of the hump, depending on the speed of the process and the length of the melt pool, can significantly exceed the depth of the melt pool H. Such modes are most dangerous from the point of view of unstable surface formation, but it is impossible to analyze this case using the approximations of the "boundary layer" and the smallness of "ζ." This analysis is a theoretical description of the process of forming the profile of the melt pool surface, taking into account the capillary phenomena and the flow of material that the gas-powder jet brings. For the analysis of nonstationary phenomena leading to instability of the growing process, it is necessary to keep the "nonstationary" terms with time derivatives in the equations and to analyze the stability of the "quasi-stationary" behavior.

We derive an equation describing the dynamic behavior of the local excess of the "ζ" melt pool surface above the "quasi-stationary" surface calculated above. We use the nonstationary Navier-Stokes Eq. (5) and the continuity of the flow Eq. (4) for this purpose. Suppose that

$$\mathbf{v}\_{\mathbf{x}}(\mathbf{x}, \mathbf{t}) = \mathbf{v}\_0(\mathbf{x}) + \mathbf{v}\_1(\mathbf{x}, \mathbf{t}) \tag{9}$$

assuming that v1ð Þ x; t ≪ v0ð Þx . Then, obviously,

$$
\zeta(\mathbf{x}, \mathbf{t}) = \zeta(\mathbf{x}) + \zeta\_1(\mathbf{x}, \mathbf{t}) \tag{10}
$$

where ζ(x) is given by expression Eq. (7). Taking this into account, we obtain from Eq. (10)

$$\frac{\partial \mathbf{v}\_1}{\partial \mathbf{x}} \approx \frac{1}{H} \frac{\partial \zeta\_1}{\partial t} + \frac{1}{H\rho} \frac{\partial \dot{\jmath}(\mathbf{x})}{\partial \mathbf{x}} \zeta\_1 \tag{11}$$

After substitution of Eqs. (8) and (9) to Eq. (4), taking into account Eq. (10) and the fact that for v0 and ζ expression Eq. (4) is identity, one can obtain an equation for nonstationary addition for flow velocity:

$$\frac{\partial v\_1}{\partial t} + v\_0 \frac{\partial v\_1}{\partial x} + v\_1 \frac{\partial v\_0}{\partial x} = -\frac{\sigma}{\rho} \frac{\partial^3 \zeta\_1}{\partial x^3} + \frac{\sigma}{\rho b^3} \frac{\zeta \partial \zeta\_1}{\partial x} + \frac{\sigma}{\rho b^3} \frac{\zeta\_1 \partial \zeta}{\partial x} - 3v \frac{v\_1}{H^2} \tag{12}$$

By differentiating this equation with respect to (x), taking into account Eq. (11), giving similar and neglecting small terms, we arrive to an equation that describes the dynamic behavior of the excess of the growing surface over a stationary value:

$$\frac{\partial^2 \zeta\_1}{\partial t^2} = \frac{\sigma H}{\rho} \frac{\partial^4 \zeta\_1}{\partial x^4} - \frac{\sigma H^2}{2\rho b^3} \frac{\partial^2 \zeta\_1}{\partial x^2} - \frac{\partial \zeta\_1}{\partial x} \left( 2 \frac{\sigma H^2}{\rho b^3 L} - \frac{v\_0}{\rho} \frac{\partial j}{\partial z} \right) + \zeta\_1 \frac{\partial j}{\partial z} \left( \frac{3v}{H^2 \rho} + \frac{1}{\rho} \frac{\partial v\_0}{\partial x} \right) \tag{13}$$

where L is the length of the melt pool, which is determined from the solution of the heat task.

We use the linear theory of stability and look for the solution of this equation in the form ζ1 ¼ ζ0exp ð Þ ið Þ ωt � kx , where ζ0 is the constant amplitude and ω in turn can be represented as ω ¼ Ω þ iγ, where Ω is the true frequency and γ is the increment (or decrement) of oscillations. Substituting these projects into Eq. (13), we obtain the characteristic equation, which, by neglecting the short-wave capillary ripple in the first approximation, the effect of the viscosity of the melt and the change in its flow velocity due to the thermocapillary effect, we obtain:

$$
\Omega \approx \sqrt{\frac{\sigma}{2\rho}} \frac{\text{Hk}}{\text{b}^{\frac{3}{2}}} \,\text{}\tag{14}
$$

the growing surface. This fact is easy to understand—to stabilize the position of the surface, it is necessary that when it moves upward relative to a stationary value, it would fall under a less dense stream of particles, which would reduce the thickness of the deposited layer, and with shifts downward, under a denser flow, which would increase its thickness and, accordingly,

Theory and Technology of Direct Laser Deposition http://dx.doi.org/10.5772/intechopen.76860 77

Obviously, for the stability of the process, it is also necessary that the length of the zone in which condition Eq. (15) is satisfied should be greater than the thickness of the layer deposited in one pass. In quantitative analysis, it should also be taken into account that not all particles adhere to the growing surface, so it is necessary to have a gradient value somewhat larger than that given by expression Eq. (15). Thus, a linear analysis of the stability of the process of direct laser deposition process allows us to conclude that stable growth is possible only at the position of the grown surface above the waist of the gas-powder jet, and the necessary

Direct laser deposition technology makes it possible to create complex parts and structures in a single technological step without the use of additional equipment, rigging, and adjustment of equipment [8, 21]. It is a complex technology, which is characterized by a multitude of process parameters. All the variety of parameters can be divided into managed and unmanaged [22]. Managed factors include process parameters such as laser power, nozzle type, traverse speed, powder feeding, spot diameter, layer height, powder fraction, selectable path, and rowing thick walls; it is also necessary to take into account the value of their overlap. Process could proceed in high purity Ar atmosphere for sensitive materials as titanium alloys. Also it is possible to get product under local protective atmosphere for less sensitive materials like some stainless steels. Uncontrollable factors include environmental pressure and other physical

would extinguish the perturbations that arise, as shown in Figure 2.

Figure 2. Scheme of stabilization process.

condition for stability is the fulfillment of inequality Eq. (15).

3. Technology and equipment of direct laser deposition process

$$\gamma = -\frac{\mathbf{b}^{\frac{3}{2}}}{\sqrt{\frac{\sigma}{2\rho}}\mathbf{H}} \left( 2\frac{\sigma\mathbf{H}^2}{\rho\mathbf{b}^3\mathbf{L}} - \frac{\mathbf{v}\_0}{\rho}\frac{\partial \dot{\jmath}}{\partial \mathbf{z}} \right) \tag{14}$$

Thus, we come to the conclusion that, for γ <0, an oscillatory instability with frequency Ω and an increment γ occurs at the surface and for γ > 0 the oscillations will decay with the decrement γ. The condition of stability, obviously, is the fulfillment of the inequality:

$$2\frac{\sigma H^2}{v\_0 b^3 L} < \frac{\partial j}{\partial z} \tag{15}$$

Thus, the critical value determining the stability (or instability) of the process of growing is the magnitude of the gradient of the particle flux density in the gas-powder jet along the normal to

Figure 2. Scheme of stabilization process.

ζð Þ¼ x; t ζð Þþ x ζ1ð Þ x; t (10)

ζ1∂ζ ∂x � 3v

þ ζ1 ∂j ∂z

ζ1 (11)

v1

3v H2 r þ 1 r ∂v0 ∂x

, (14)

∂z (15)

� �

H2 (12)

(13)

(14)

where ζ(x) is given by expression Eq. (7). Taking this into account, we obtain from Eq. (10)

After substitution of Eqs. (8) and (9) to Eq. (4), taking into account Eq. (10) and the fact that for v0 and ζ expression Eq. (4) is identity, one can obtain an equation for nonstationary addition for

By differentiating this equation with respect to (x), taking into account Eq. (11), giving similar and neglecting small terms, we arrive to an equation that describes the dynamic behavior of

> 2 σH2 rb3 L � v0 r ∂j ∂z

where L is the length of the melt pool, which is determined from the solution of the heat task. We use the linear theory of stability and look for the solution of this equation in the form ζ1 ¼ ζ0exp ð Þ ið Þ ωt � kx , where ζ0 is the constant amplitude and ω in turn can be represented as ω ¼ Ω þ iγ, where Ω is the true frequency and γ is the increment (or decrement) of oscillations. Substituting these projects into Eq. (13), we obtain the characteristic equation, which, by neglecting the short-wave capillary ripple in the first approximation, the effect of the viscosity of the melt and the change in its flow velocity due to the thermocapillary effect, we obtain:

> ffiffiffiffiffi σ 2r r Hk b 3 2

> > 2 σH2 rb3

Thus, we come to the conclusion that, for γ <0, an oscillatory instability with frequency Ω and an increment γ occurs at the surface and for γ > 0 the oscillations will decay with the decre-

Thus, the critical value determining the stability (or instability) of the process of growing is the magnitude of the gradient of the particle flux density in the gas-powder jet along the normal to

2 σH2 v0b3 L < ∂j

L � v0 r ∂j ∂z

� �

Ω ≈

3 2 ffiffiffiffi σ 2r q H

ment γ. The condition of stability, obviously, is the fulfillment of the inequality:

γ ¼ � b

� �

1 Hr

> σ rb3

ζ∂ζ1 ∂x þ σ rb3

∂j xð Þ ∂x

∂v1 ∂x ≈ 1 H ∂ζ1 ∂t þ

76 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

flow velocity:

∂2 ζ1 ∂t

∂v1 ∂t þ v0

2 ¼ σH r ∂4 ζ1 ∂x4 � σH2 2rb3

∂v1 ∂x þ v1 ∂v0 ∂x ¼ � σ r ∂3 ζ1 ∂x3 þ

the excess of the growing surface over a stationary value:

∂2 ζ1 ∂x2 � ∂ζ1 ∂x

the growing surface. This fact is easy to understand—to stabilize the position of the surface, it is necessary that when it moves upward relative to a stationary value, it would fall under a less dense stream of particles, which would reduce the thickness of the deposited layer, and with shifts downward, under a denser flow, which would increase its thickness and, accordingly, would extinguish the perturbations that arise, as shown in Figure 2.

Obviously, for the stability of the process, it is also necessary that the length of the zone in which condition Eq. (15) is satisfied should be greater than the thickness of the layer deposited in one pass. In quantitative analysis, it should also be taken into account that not all particles adhere to the growing surface, so it is necessary to have a gradient value somewhat larger than that given by expression Eq. (15). Thus, a linear analysis of the stability of the process of direct laser deposition process allows us to conclude that stable growth is possible only at the position of the grown surface above the waist of the gas-powder jet, and the necessary condition for stability is the fulfillment of inequality Eq. (15).

## 3. Technology and equipment of direct laser deposition process

Direct laser deposition technology makes it possible to create complex parts and structures in a single technological step without the use of additional equipment, rigging, and adjustment of equipment [8, 21]. It is a complex technology, which is characterized by a multitude of process parameters. All the variety of parameters can be divided into managed and unmanaged [22]. Managed factors include process parameters such as laser power, nozzle type, traverse speed, powder feeding, spot diameter, layer height, powder fraction, selectable path, and rowing thick walls; it is also necessary to take into account the value of their overlap. Process could proceed in high purity Ar atmosphere for sensitive materials as titanium alloys. Also it is possible to get product under local protective atmosphere for less sensitive materials like some stainless steels. Uncontrollable factors include environmental pressure and other physical conditions of the environment and quality of the raw powder materials. Especially it is necessary to take into account the thermophysical and technological properties of powder alloys.

Direct laser deposition is a multiparameter process; therefore the results of the process are affected by a complex of technological parameters [8, 23]. Among these parameters, it is possible to identify the main characteristics, which primary determine the course of the process [24]. The basic part of process parameters is described in Table 1, where the first four points are the main parameters.

On the basis of theoretical and experimental studies, equipment (Figure 3) was developed, which realizes DLD process. This is the first Russian equipment for realization of direct laser deposition technology.

The technology realized with this equipment solves a number of problems for modern engineering, improves process efficiency by 10 times, and reduces the cost of manufacturing parts by 3–5 times. Benefits of implementing the DLD are:

The equipment is universal, and based on the principle of modular construction, without using accessory devices and bed structures, it is possible to obtain details of any designs and complexity at the request of the customer. The developed equipment can be operated in a chamber filled with protective gas, which completely eliminates the oxidation of metallic

> materials. A technological tool that combines a laser optical head and a powder nozzle is mounted on an industrial robotic manipulator [23]. As a result, the maximum size of the manufactured product is unlimited. The positioner table used for moving the product is also

Theory and Technology of Direct Laser Deposition http://dx.doi.org/10.5772/intechopen.76860 79

During the development of the equipment, special attention was paid to the design of the nozzle [24, 25]. It forms a gas-powder jet and thus has determining effect on DLD process. In the investigations, two types of nozzles were used (Figure 4): axisymmetric (or coaxial) and

The main disadvantage of the lateral nozzle is shape constancy of deposited layer only in one direction, for example, straight line with moving laser head or the body of rotation with rotating substrate (Figure 4a). Therefore, despite its high productivity, it is almost used in the manufacture of equipment. For the developed equipment, the four-jet and annular gap pow-

engaged to increase the technology's capabilities.

Figure 3. Developed equipment for realization of DLD technology.

axially asymmetric (lateral or non-axial).

der nozzles were used.

Table 1. Process parameters of direct laser deposition technology.

Figure 3. Developed equipment for realization of DLD technology.

conditions of the environment and quality of the raw powder materials. Especially it is necessary to take into account the thermophysical and technological properties of powder

78 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

Direct laser deposition is a multiparameter process; therefore the results of the process are affected by a complex of technological parameters [8, 23]. Among these parameters, it is possible to identify the main characteristics, which primary determine the course of the process [24]. The basic part of process parameters is described in Table 1, where the first four

On the basis of theoretical and experimental studies, equipment (Figure 3) was developed, which realizes DLD process. This is the first Russian equipment for realization of direct laser

The technology realized with this equipment solves a number of problems for modern engineering, improves process efficiency by 10 times, and reduces the cost of manufacturing parts

• Productivity of manufacturing parts with complex shapes from intractable materials

The equipment is universal, and based on the principle of modular construction, without using accessory devices and bed structures, it is possible to obtain details of any designs and complexity at the request of the customer. The developed equipment can be operated in a chamber filled with protective gas, which completely eliminates the oxidation of metallic

Laser power Minor Minor Major Minor Major Spot diameter Major Minor Major Minor Major Traverse speed Major Major Major Minor Major Powder feeding Major Major Minor Minor Major Layer height Minor Major Minor Major Minor Shielding gas rate — — Major Minor — Powder fraction Minor — Major Major —

stability

Usage rate

Major Major Major Minor Minor

Roughness Depth

penetration

alloys.

points are the main parameters.

by 3–5 times. Benefits of implementing the DLD are:

• Raw material consumption decreases.

• Full automation and "digitalization" of manufacturing.

• Enhancement of technological and engineering capabilities.

Process parameters Productivity Process

Table 1. Process parameters of direct laser deposition technology.

Distance between Nozzle and focus of gas-

powder jet

deposition technology.

increases.

• Cost saving.

materials. A technological tool that combines a laser optical head and a powder nozzle is mounted on an industrial robotic manipulator [23]. As a result, the maximum size of the manufactured product is unlimited. The positioner table used for moving the product is also engaged to increase the technology's capabilities.

During the development of the equipment, special attention was paid to the design of the nozzle [24, 25]. It forms a gas-powder jet and thus has determining effect on DLD process. In the investigations, two types of nozzles were used (Figure 4): axisymmetric (or coaxial) and axially asymmetric (lateral or non-axial).

The main disadvantage of the lateral nozzle is shape constancy of deposited layer only in one direction, for example, straight line with moving laser head or the body of rotation with rotating substrate (Figure 4a). Therefore, despite its high productivity, it is almost used in the manufacture of equipment. For the developed equipment, the four-jet and annular gap powder nozzles were used.

Figure 4. Lateral nozzle (a), coaxial four-jet nozzle (b), and coaxial annular gap nozzle (c).

Technological heads equipped with coaxial nozzles are characterized by independence of technological parameters from the direction of tool movement. This allows using complex processing trajectories and obtaining products with complex geometry. Multiple jet nozzles have from three up to six separate channels, which form powder jets. Its design is more complex but allows more flexibility for powder jet control (Figure 4b). During processing, the junction area of jets is located near molten pool, which is formed by a laser beam passing through the central hole of the nozzle. Annular gap nozzles are more technologically advanced (Figure 4c). Gas-powder jet is supplied through a gap between two conical surfaces that direct and focus it. Due to the uniform distribution of the powder along the circumference of the annular gap, a high degree of symmetry and isotropy with respect to the direction of motion is achieved. The developed nozzles were used to make a number of machines that realize DLD process.

As a result of the theoretical, technological, and design work, a general principle of constructing the equipment was carried out (Figure 5).

9. Cooling system 10. Control stand

11. The powder feeder

13. Video surveillance system

14. Monitoring system for processing area

of up to 60 mm/s and a productivity of 2.5 kg/h.

4. Structure and properties of manufactured products

Figure 5. The general scheme of equipment for DLD process implementation.

The developed technological complex allowed to manufacture products with a traverse speed

Theory and Technology of Direct Laser Deposition http://dx.doi.org/10.5772/intechopen.76860 81

As a result of the theoretical and experimental studies, the parameters of the process for manufacturing products are carried out, using different metal alloys, which are based on

12. Control system

15. Nozzle

Below the components of the complex for the implementation of the direct laser deposition process are listed:

Figure 5. The general scheme of equipment for DLD process implementation.

9. Cooling system

Technological heads equipped with coaxial nozzles are characterized by independence of technological parameters from the direction of tool movement. This allows using complex processing trajectories and obtaining products with complex geometry. Multiple jet nozzles have from three up to six separate channels, which form powder jets. Its design is more complex but allows more flexibility for powder jet control (Figure 4b). During processing, the junction area of jets is located near molten pool, which is formed by a laser beam passing through the central hole of the nozzle. Annular gap nozzles are more technologically advanced (Figure 4c). Gas-powder jet is supplied through a gap between two conical surfaces that direct and focus it. Due to the uniform distribution of the powder along the circumference of the annular gap, a high degree of symmetry and isotropy with respect to the direction of motion is achieved. The developed nozzles were used to make a number of machines that realize DLD

Figure 4. Lateral nozzle (a), coaxial four-jet nozzle (b), and coaxial annular gap nozzle (c).

80 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

As a result of the theoretical, technological, and design work, a general principle of

Below the components of the complex for the implementation of the direct laser deposition

constructing the equipment was carried out (Figure 5).

process.

process are listed:

3. Laser head

7. The fiber laser

8. Chiller

1. The two-axis positioner

4. The robotic manipulator

5. Preparation and supplying gas system

6. Gas cleaning and drying device

2. Working chamber

The developed technological complex allowed to manufacture products with a traverse speed of up to 60 mm/s and a productivity of 2.5 kg/h.

#### 4. Structure and properties of manufactured products

As a result of the theoretical and experimental studies, the parameters of the process for manufacturing products are carried out, using different metal alloys, which are based on nickel, iron, and titanium [8, 21, 26, 27]. Using optimal parameters of DLD process allows preparing samples without such macrodefects as cracks and pores (Figure 6).

Most often defects are lack of fusion, which have a more negative effect on mechanical characteristics than pores. Small lack of fusion results because of using oxidized powder or contaminated powder. Also, their number increases significantly using local protection, rather than full filling the chamber with shielding gas. Examples of lack of fusion are shown in

Theory and Technology of Direct Laser Deposition http://dx.doi.org/10.5772/intechopen.76860 83

Lack of fusion is also detected at the deposition of thick-walled products. The appearance of such lack of fusion is due to the lack of energy. They are found in the samples grown at low power, a small size of spot diameter. The size of the overlapping layers also affects, but it has less influence and strongly depends on spot diameter. In Figure 9 lacks of fusion in thick-

In the process of deposition, cracks can also appear, especially in those nickel alloys that are prone to their appearance. For all products obtained by direct laser deposition process, the

cracks are an impermissible defect; such products are rejected.

Figure 8. Lacks of fusion in samples, material Ni-based alloy Inconel 625.

Figure 9. Lacks of fusion in thick-walled sample, material Ti-based alloy Grade 5.

Figure 8.

walled samples are shown.

However, in case of violation of the selected modes, porosity, cracks, and lack of fusion may appear. The main reason for the occurrence of large pores (more than 100 μm) is the low quality of the shielding gas or work with local protection. Smaller pores could appear because of low quality of powder [21]. Powders obtained by plasma rotating electrode process (PREP) allow to produce samples of lower porosity as compared with the gas atomization. Powders obtained by gas atomization may contain internal pores. It is also possible for them to form with improperly selected modes, which lead to too high cooling rates. Examples of pores in the samples are shown in Figure 7.

Figure 6. Deposited samples without macrodefects: left—Ti-based alloy and right—Ni-based alloy.

Figure 7. Pores in samples, material Ni-based alloy Inconel 625.

Most often defects are lack of fusion, which have a more negative effect on mechanical characteristics than pores. Small lack of fusion results because of using oxidized powder or contaminated powder. Also, their number increases significantly using local protection, rather than full filling the chamber with shielding gas. Examples of lack of fusion are shown in Figure 8.

Lack of fusion is also detected at the deposition of thick-walled products. The appearance of such lack of fusion is due to the lack of energy. They are found in the samples grown at low power, a small size of spot diameter. The size of the overlapping layers also affects, but it has less influence and strongly depends on spot diameter. In Figure 9 lacks of fusion in thickwalled samples are shown.

In the process of deposition, cracks can also appear, especially in those nickel alloys that are prone to their appearance. For all products obtained by direct laser deposition process, the cracks are an impermissible defect; such products are rejected.

Figure 8. Lacks of fusion in samples, material Ni-based alloy Inconel 625.

nickel, iron, and titanium [8, 21, 26, 27]. Using optimal parameters of DLD process allows

However, in case of violation of the selected modes, porosity, cracks, and lack of fusion may appear. The main reason for the occurrence of large pores (more than 100 μm) is the low quality of the shielding gas or work with local protection. Smaller pores could appear because of low quality of powder [21]. Powders obtained by plasma rotating electrode process (PREP) allow to produce samples of lower porosity as compared with the gas atomization. Powders obtained by gas atomization may contain internal pores. It is also possible for them to form with improperly selected modes, which lead to too high cooling rates. Examples of pores in the

preparing samples without such macrodefects as cracks and pores (Figure 6).

82 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

Figure 6. Deposited samples without macrodefects: left—Ti-based alloy and right—Ni-based alloy.

Figure 7. Pores in samples, material Ni-based alloy Inconel 625.

samples are shown in Figure 7.

Figure 9. Lacks of fusion in thick-walled sample, material Ti-based alloy Grade 5.

The microstructure of the samples obtained has a finely dispersed, predominantly cast structure. Features of structure formation for the different metal alloys using this technology were studied in detail by the authors. The results of research presented by the

authors in the articles [26–30]. In Figure 10 microstructure of different alloys is

Material Yield strength (0,2% Offset), MPa Ultimate Tensile strength, MPa Elongation, %

Theory and Technology of Direct Laser Deposition http://dx.doi.org/10.5772/intechopen.76860 85

Inconel 625, DLD 489 865 28.5 Inconel 625, cast [31] 310 800 25 Analogue Mar-M200 alloy, DLD 1046 1353 11.5 Analogue Mar-M200 alloy, cast 1075 1108 2.9 Analogue Grade 35 alloy, DLD 882 968 6.6 Analogue Grade 35 alloy, cast 876 951 6.4 Analogue Grade 5 alloy, DLD 1040 1120 8 Analogue Grade 5 alloy, cast — 880 4 316 L, DLD 272.5 570 41 316 L, cast [31] 177 441 25

Comparing with cast samples, the products that are manufactured by direct laser deposition technology have ultrafine structure. It provides high level of mechanical characteristics (Table 2). Mechanical tests were conducted for a greater number of different alloys; the main results are given in Table 2. The materials were tested on uniaxial tension; universal testing

The results of researches show that the developed technology of direct laser deposition, in spite of its technological complexity, can replace the currently used technologies, providing multiple

• Direct laser deposition is technology for manufacturing of details with complex form from powder materials using 3D model. It has potential use for different materials in a single part and obtaining details with gradient properties. Using equipment, which realizes this

• The process productivity is 10 times higher in comparison with layered synthesis technologies like SLM. Mechanical properties of the obtained products are much higher than the characteristics of the cast metal; there are no pores and cracks and is no lack of fusion. • This equipment has a maximum capacity in comparison with existing analogues: up to

• This is the first Russian technology and equipment for the implementation of additive

presented.

5. Conclusions

machine Zwick/Roell Z250 Allround was used.

Table 2. Mechanical characteristics of deposited and cast samples.

increases in productivity and material saving.

2.5 kg/h for metallic materials.

production.

technology, it is possible to produce details of any size.

Figure 10. Microstructure of deposited samples: (a) 316 L steel, (b) Ti-based alloy analog Grade 35, (c) Inconel 625, and (d) Ni-based alloy analogue Mar-M200.

Table 2. Mechanical characteristics of deposited and cast samples.

authors in the articles [26–30]. In Figure 10 microstructure of different alloys is presented.

Comparing with cast samples, the products that are manufactured by direct laser deposition technology have ultrafine structure. It provides high level of mechanical characteristics (Table 2). Mechanical tests were conducted for a greater number of different alloys; the main results are given in Table 2. The materials were tested on uniaxial tension; universal testing machine Zwick/Roell Z250 Allround was used.

## 5. Conclusions

The microstructure of the samples obtained has a finely dispersed, predominantly cast structure. Features of structure formation for the different metal alloys using this technology were studied in detail by the authors. The results of research presented by the

84 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

Figure 10. Microstructure of deposited samples: (a) 316 L steel, (b) Ti-based alloy analog Grade 35, (c) Inconel 625, and (d)

Ni-based alloy analogue Mar-M200.

The results of researches show that the developed technology of direct laser deposition, in spite of its technological complexity, can replace the currently used technologies, providing multiple increases in productivity and material saving.

## Author details

Gleb Turichin\* and Olga Klimova-Korsmik

\*Address all correspondence to<EMAIL_ADDRESS>
State Marine Technical University, Saint-Petersburg, Russian Federation

## References

[1] Gu D. New metallic materials development by laser additive manufacturing. In: Surface Engineering. New-York: Elsevier Ltd; 2015. pp. 163-180

[11] Dutta B, Palaniswamy S, Choi J, Song LJ, Mazumder J. Additive manufacturing by direct

Theory and Technology of Direct Laser Deposition http://dx.doi.org/10.5772/intechopen.76860 87

[12] Renderos M, Girot F, Lamikiz A, Torregaray A, Saintier N. Ni based powder reconditioning

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[14] Saboori A, Gallo D, Biamino S, Fino P, Lombardi M. An overview of additive manufacturing of titanium components by directed energy deposition: Microstructure and mechani-

[15] Zhong C, Gasser A, Kittel J, Wissenbach K, Poprawe R. Improvement of material performance of Inconel 718 formed by high deposition-rate laser metal deposition. Materials

[16] Turichin GA. Hydrodynamic stability aspects of gas-vapour channel at energy beam

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Author details

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Gleb Turichin\* and Olga Klimova-Korsmik \*Address all correspondence to<EMAIL_ADDRESS>
tials, Vol. 26; 2015. pp. 93-98

State Marine Technical University, Saint-Petersburg, Russian Federation

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**Chapter 5**

Provisional chapter

**Processing Parameters for Selective Laser Sintering or**

DOI: 10.5772/intechopen.75832

In this chapter, we present a detailed introduction to the factors which influence laser powder bed fusion (LPBF) on oxide ceramics. These factors can be in general divided in three main categories: laser-related factors (wavelength, power, scanning speed, hatch distance, scan pattern, beam diameter, etc.), powder- and material-related factors (flowability, size distribution, shape, powder deposition, thickness of deposited layers, etc.), and other factors (pre- or post-processing, inert gas atmosphere, etc.). The process parameters directly affect the amount of energy delivered to the surface of the thin layer and the energy density absorbed by the powders; therefore, decide the physical and mechanical properties of the built parts, such as relative density, porosity, surface roughness, dimensional accuracy, strength, etc. The parameter-property relation is hence reviewed for the most studied oxide ceramic materials, including families from alumina, silica, and some ceramic mixtures. Among those parameters, reducing temperature gradient which decreases the thermal stresses is one of the key factors to improve the ceramic quality. Although realizing crack-free ceramics combined with a smooth surface is still a major challenge, through optimizing the parameters, it is possible for LPBF processed ceramic parts to achieve properties close to those of conventionally produced ceramics.

Keywords: LPBF, SLM, SLS, ceramic, additive manufacturing, AM, processing

Laser powder bed fusion (LPBF) is an additive manufacturing process that uses a laser beam to fuse powder particles in a layer-by-layer fashion, which allows production of complex threedimensional (3D) structures. LPBF includes selective laser melting (SLM), where powder is fully melted, and selective laser sintering (SLS) for other cases such as solid state sintering,

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Processing Parameters for Selective Laser Sintering or

**Melting of Oxide Ceramics**

Melting of Oxide Ceramics

Haidong Zhang and Saniya LeBlanc

Haidong Zhang and Saniya LeBlanc

http://dx.doi.org/10.5772/intechopen.75832

Abstract

parameters

1. Introduction

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

#### **Processing Parameters for Selective Laser Sintering or Melting of Oxide Ceramics** Processing Parameters for Selective Laser Sintering or Melting of Oxide Ceramics

DOI: 10.5772/intechopen.75832

Haidong Zhang and Saniya LeBlanc Haidong Zhang and Saniya LeBlanc

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.75832

#### Abstract

[25] Korsmik RS, Turichin GA, Babkin KD. Laser cladding technological machine. Investigation of efficiency of various nozzles design. Journal of Physics: Conference Series. 2017;

88 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

[26] Sklyar MO, Turichin GA, Klimova OG, Zotov OG, Topalov IK. Microstructure of 316L stainless steel components produced by direct laser deposition. Steel in Translation. 2016;

[27] Sklyar MO, Klimova-Korsmik OG, Cheverikin VV. Formation structure and properties of parts from titanium alloys produced by direct laser deposition. Solid State Phenomena.

[28] Klimova-Korsmik OG, Turichin GA, Zemlyakov EV, Babkin KD, Travyanov AY, Petrovskiy PV. Structure formation in Ni superalloys during high-speed direct laser depo-

[29] Klimova-Korsmik OG, Turichin GA, Zemlyakov EV, Babkin KD, Petrovskiy PV, Travyanov AY. Structure formation in Ni superalloys during high-speed direct laser

[30] Turichin GA, Travyanov AY, Petrovskiy PV, Zemlyakov EV, Kovac M, Vondracek S, Kondratiev A, Khvan AV, Cheverikin VV, Ivanov DO, Bazhenova IA, Dinsdale AT. Prediction of solidification behaviour and microstructure of Ni based alloys obtained by casting and direct additive laser growth. Materials Science and Technology. 2016;32(8):

[31] DebRoy T, Wei HL, Zuback JS, Mukherjee T, Elmer JW, Milewski JO, Beese AM, Wilson-Heid A, De A, Zhang W. Additive manufacturing of metallic components—Process,

structure and properties. Progress in Materials Science. 2018;92:112-224

857:4

46(12):883-887

2017;265:535-541

746-751

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deposition. Materials Science Forum. 2017;879:978-983

In this chapter, we present a detailed introduction to the factors which influence laser powder bed fusion (LPBF) on oxide ceramics. These factors can be in general divided in three main categories: laser-related factors (wavelength, power, scanning speed, hatch distance, scan pattern, beam diameter, etc.), powder- and material-related factors (flowability, size distribution, shape, powder deposition, thickness of deposited layers, etc.), and other factors (pre- or post-processing, inert gas atmosphere, etc.). The process parameters directly affect the amount of energy delivered to the surface of the thin layer and the energy density absorbed by the powders; therefore, decide the physical and mechanical properties of the built parts, such as relative density, porosity, surface roughness, dimensional accuracy, strength, etc. The parameter-property relation is hence reviewed for the most studied oxide ceramic materials, including families from alumina, silica, and some ceramic mixtures. Among those parameters, reducing temperature gradient which decreases the thermal stresses is one of the key factors to improve the ceramic quality. Although realizing crack-free ceramics combined with a smooth surface is still a major challenge, through optimizing the parameters, it is possible for LPBF processed ceramic parts to achieve properties close to those of conventionally produced ceramics.

Keywords: LPBF, SLM, SLS, ceramic, additive manufacturing, AM, processing parameters

### 1. Introduction

Laser powder bed fusion (LPBF) is an additive manufacturing process that uses a laser beam to fuse powder particles in a layer-by-layer fashion, which allows production of complex threedimensional (3D) structures. LPBF includes selective laser melting (SLM), where powder is fully melted, and selective laser sintering (SLS) for other cases such as solid state sintering,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

liquid state sintering, and partial melting [1]. The main advantages of LPBF are time efficiency and the capability to build geometries that would be unattainable through traditional techniques. LPBF has revolutionized manufacturing by offering great design freedom for 3D structures to be built directly from feedstock powders without additional processing. Introduced in the late 1980–1990s [2–4], the LPBF process was initially applied to metals, and later to polymers, ceramics, and recently, to semiconductors [5, 6].

at high temperatures. These traditional processes involve molding and tooling, have high cost,

Processing Parameters for Selective Laser Sintering or Melting of Oxide Ceramics

http://dx.doi.org/10.5772/intechopen.75832

91

Additive manufacturing on ceramics has been developed in order to overcome some of subtractive manufacturing's shortcomings, especially with respect to high tool wear, size shrinkage, and difficulty creating complex structures. Additive manufacturing includes binder-based, extrusionbased, and powder-based (LPBF) techniques. Among these, LPBF offers the opportunity for fast and direct fusion without costly post treatments and toxic binders which are often required by other techniques. LPBF-produced ceramic parts have potential to impact several applications such as medical and dental components [8–10], metal casting molds [11], thin wall structures,

While LPBF enables rapid manufacturing of ceramic parts with complex structures, there are two technical limitations. First, ceramic powders, as compared with metals, often flow poorly, resulting in imperfect spreading on the powder bed surface. Second, and more importantly, highly localized heating combined with ceramics' intrinsic low thermal conductivity often leads to large temperature gradients that result in residual stresses and deformation. Combined with ceramics' brittleness, the two limitations can result in cracking, lack of fusion, rough surfaces, porosity and less than full density. Due to these challenges, current results for

There are several excellent reviews for SLS/SLM of ceramics [7, 10, 14–23]. However, many of the SLS/SLM processing factors such as laser power, layer thickness, or powder bed preheating are still poorly investigated or need to undergo a systematic review. Key insights about process parameters have not been transferred into industry. This chapter provides an introduction to LPBF of common ceramics. The chapter is organized as follows. The first part introduces the main procedure and tools for LBPF. Following that, the second section introduces laser parameters, powder parameters, and other factors for the LPBF process, as well as a few physical properties concerned in ceramic applications. The third part discusses how the processing parameters and other factors influence the physical properties of the manufactured parts as well as the general rules for parameter selections. Then the fourth part illustrates some of the most widely studied ceramic materials processed by LPBF, including the state of art achievements. The final two sections summarize the perspectives and the common LPBF challenges for ceramics.

A basic LPBF system consists of three parts: laser system, powder bed, and spreading system. The laser system includes a laser and a scanner. In order to heat and melt the material, the laser beam has to focus onto the powder surface and be absorbed by the material. The scanner enables the laser to move in a two dimensional plane. The powder bed is a container for the ceramic powders; it usually has adjustable height to allow laser focusing on the newly formed surface. The spreading system often includes a slot feeder to spread fresh powders and a roller

and limit the device geometry that can be produced.

LPBF of ceramics are far from satisfactory.

2. Processing parameters and characterization

or a scraper blade to flatten the surface.

turbine blades, nozzles [12], and thermal or electrical insulation [13].

This chapter focuses on laser powder bed fusion of ceramic materials. Typical ceramics are strongly bonded inorganic and non-metallic solids such as crystalline oxide, nitride and carbide materials. Sometimes non-crystalline or partially crystalline glass is also referred to as glass-ceramic. Ceramics feature excellent strength and hardness, good abrasion resistance, high melting temperature, high chemical stability, low ductility, and low electrical and thermal conductivities.

A classification of processing techniques for ceramic materials is summarized in Figure 1. Ceramics cannot be shaped by the conventional forging and machining formation. They are usually formed through multi-step processes [7]. The shaping process begins with powder mixtures that contain binders and stabilizers. The next step is shape forming which includes extrusion, slip casting, pressing, tape casting, and injection molding. The last step is sintering

Figure 1. Classification of processing techniques for ceramic materials. Reprinted from [14], with permission of Taylor & Francis Group, LLC.

at high temperatures. These traditional processes involve molding and tooling, have high cost, and limit the device geometry that can be produced.

liquid state sintering, and partial melting [1]. The main advantages of LPBF are time efficiency and the capability to build geometries that would be unattainable through traditional techniques. LPBF has revolutionized manufacturing by offering great design freedom for 3D structures to be built directly from feedstock powders without additional processing. Introduced in the late 1980–1990s [2–4], the LPBF process was initially applied to metals, and later

This chapter focuses on laser powder bed fusion of ceramic materials. Typical ceramics are strongly bonded inorganic and non-metallic solids such as crystalline oxide, nitride and carbide materials. Sometimes non-crystalline or partially crystalline glass is also referred to as glass-ceramic. Ceramics feature excellent strength and hardness, good abrasion resistance, high melting temperature, high chemical stability, low ductility, and low electrical and thermal

A classification of processing techniques for ceramic materials is summarized in Figure 1. Ceramics cannot be shaped by the conventional forging and machining formation. They are usually formed through multi-step processes [7]. The shaping process begins with powder mixtures that contain binders and stabilizers. The next step is shape forming which includes extrusion, slip casting, pressing, tape casting, and injection molding. The last step is sintering

Figure 1. Classification of processing techniques for ceramic materials. Reprinted from [14], with permission of Taylor &

to polymers, ceramics, and recently, to semiconductors [5, 6].

90 Additive Manufacturing of High-performance Metals and Alloys - Modeling and Optimization

conductivities.

Francis Group, LLC.

Additive manufacturing on ceramics has been developed in order to overcome some of subtractive manufacturing's shortcomings, especially with respect to high tool wear, size shrinkage, and difficulty creating complex structures. Additive manufacturing includes binder-based, extrusionbased, and powder-based (LPBF) techniques. Among these, LPBF offers the opportunity for fast and direct fusion without costly post treatments and toxic binders which are often required by other techniques. LPBF-produced ceramic parts have potential to impact several applications such as medical and dental components [8–10], metal casting molds [11], thin wall structures, turbine blades, nozzles [12], and thermal or electrical insulation [13].

While LPBF enables rapid manufacturing of ceramic parts with complex structures, there are two technical limitations. First, ceramic powders, as compared with metals, often flow poorly, resulting in imperfect spreading on the powder bed surface. Second, and more importantly, highly localized heating combined with ceramics' intrinsic low thermal conductivity often leads to large temperature gradients that result in residual stresses and deformation. Combined with ceramics' brittleness, the two limitations can result in cracking, lack of fusion, rough surfaces, porosity and less than full density. Due to these challenges, current results for LPBF of ceramics are far from satisfactory.

There are several excellent reviews for SLS/SLM of ceramics [7, 10, 14–23]. However, many of the SLS/SLM processing factors such as laser power, layer thickness, or powder bed preheating are still poorly investigated or need to undergo a systematic review. Key insights about process parameters have not been transferred into industry. This chapter provides an introduction to LPBF of common ceramics. The chapter is organized as follows. The first part introduces the main procedure and tools for LBPF. Following that, the second section introduces laser parameters, powder parameters, and other factors for the LPBF process, as well as a few physical properties concerned in ceramic applications. The third part discusses how the processing parameters and other factors influence the physical properties of the manufactured parts as well as the general rules for parameter selections. Then the fourth part illustrates some of the most widely studied ceramic materials processed by LPBF, including the state of art achievements. The final two sections summarize the perspectives and the common LPBF challenges for ceramics.

## 2. Processing parameters and characterization

A basic LPBF system consists of three parts: laser system, powder bed, and spreading system. The laser system includes a laser and a scanner. In order to heat and melt the material, the laser beam has to focus onto the powder surface and be absorbed by the material. The scanner enables the laser to move in a two dimensional plane. The powder bed is a container for the ceramic powders; it usually has adjustable height to allow laser focusing on the newly formed surface. The spreading system often includes a slot feeder to spread fresh powders and a roller or a scraper blade to flatten the surface.

Figure 2. Illustration for basic LPBF procedure.

A typical LPBF setup is illustrated in Figure 2. Powders are spread onto the building platform and flattened by a roller, a scraper blade or a combination moving over the surface. The new powder surface moves down one layer thickness to maintain the desired laser focus. The 3D part is decomposed to a number of planes to be processed; each plane consists of a series of basic elements of laser scanning, called vectors. The scan pattern, or the orientation and distance between vectors, is pre-designed. The laser then scans the flat surface of loose or slightly compacted powders following such patterns and selectively melts the illuminated powders. Those powders are quickly solidified after the laser moves away. After that, another layer of powder is deposited and welded, and the process is repeated until a 3D structure in the desired shape and thickness is formed. During the process, unprocessed powder from each layer fills the empty space in the fabrication chamber and supports the part which has been built; afterwards, this powder is recycled. The basic process flow chart is shown in Figure 3. Depending on the materials to be processed, the fabrication chamber is sometimes heated and maintained at a certain temperature to help the sintering or melting process. The Renishaw-AM125 (Renishaw, Wotton-under-Edge, Gloucestershire, UK), and SLM@250HL (SLM Solutions GmbH) are two examples of commercial additive manufacturing machines used to process ceramic powders.

overlapping [28], and continuous or pulsed laser operation. Although most of the parameters have an effect on some aspects of the final product, currently there are not enough experimental data or calculations to relate all the factors. Some parameters are not always adjustable, for example, the wavelength of a certain laser system. As a result, only some of the most important

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parameters will be discussed. Key laser parameters are shown in Figure 4.

Figure 4. SLM process parameters: laser power, scanning speed, hatch spacing, and layer thickness.

Figure 3. Basic process flow chart for LPBF manufacturing.

LPBF can be broadly classified in two types: direct and indirect, depending on whether a binder material is used. An indirect process either mixes binder materials with ceramics or coats the ceramics with a polymer. The mixture can be used as dry powders or as wet slurry from a suspended liquid. The binder materials melt and consolidate the ceramic powders during laser scanning. Then a de-binding process removes the binder, and further sintering of the ceramic part is usually required to increase the final part density. In the direct process, ceramic objects are created by sintering or melting without the aid of any binders. Because of the high melting temperatures of ceramics, indirect processing of ceramics is most common [24].

#### 2.1. Laser parameters

During the LPBF process, many factors affect the final part. The main laser parameters include wavelength, power, scanning speed, hatch distance, scan pattern, vector length [12], ratio of length to width [25], scan angle [25], beam spatial distribution [26], beam spot size [27], point

Figure 3. Basic process flow chart for LPBF manufacturing.