Substrate Alloy Elements on Thermodiffused Vanadium Carbide Formation Applied as Intermediate Layer for CVD Diamond Growth

Referencia Apresentador Autores
Felipe Nascimento Araujo da Silva Damm, D.D.(Universidade Federal de São Paulo); Garcez, S.A.(Universidade Estadual de Santa Cruz); Contin, A.(Universidade Federal de Goiás); Andrade, A.E.(Escola Técnica Everaldo Passos); Trava-Airoldi, V.J.(Instituto Nacional de Pesquisas Espaciais); Barquete, D.M.(Universidade Estadual de Santa Cruz); Corat, E.J.(Instituto Nacional de Pesquisas Espaciais); Silva, F.N.(Universidade Estadual de Santa Cruz); Martins, R.L.(Universidade Estadual de Santa Cruz); Pinheiro, R.A.(Instituto Nacional de Pesquisas Espaciais); CVD diamond deposition directly on steel tools with elevated quality and adherence requires an intermediate layer able to act as an excellent diffusional barrier and also to provide an intermediate thermal expansion coefficient (TEC) between diamond and steel. The diffusional barrier had the function to block transition metals from substrate into material surface avoiding graphitic bonds (sp2) formation and also to block carbon diffusivity from gas phase into the substrate which may cause bulk embrittlement. In addition, the interlayer needs to have enough thickness to mitigate CVD diamond thermal residual stress after cooling. Vanadium carbide (VC) was selected by the following features: intermediate TEC (6.06x10-6K-1), high adherence to the carbon steel substrate, hardness of 2200-3600 HV, forms a low-porous film and high corrosion resistance. The coating was deposited by thermo reactive diffusion (TRD) process in the borax salt bath system with the following parameters: process time (3 h), temperature (1050 °C) and powders proportion and composition (68% of Na2B4O7.10H2O, 24% of V2O5 and 8% of B4C). This work has the purpose to analyze and investigate the impact of the alloying elements on the vanadium carbide formation. As substrate were selected the AISI D6, O1, M2 and 1045 as substrate by its elementary composition. The alloy elements as chromium, molybdenum, tungsten and carbon were characterized by X-ray diffraction and scanning electron microscope (SEM). The results showed that the alloy elements impacted mainly the carbon supply at steel surface were TRD deposition occurs and it could change the vanadium carbide phase, thickness and morphology depending of alloy elements composition, proportion and distribution on the substrate surface and cross-section. Diamond was deposited over vanadium carbide coverage by Hot Filament Chemical Vapor Deposition (HFCVD) technique in the following growing conditions: 50torr chain pressure, heating the substrate at 700 °C, 5mm of working distance between filament and substrate surface, process time of 3h, cooling time of 3h, methane (CH4) flow at 2sccm and the hydrogen (H2) flow at 98sccm. The diamond stress state, quality and morphology presented different results for each type of substrate used and were characterized by field emission gun scanning electron microscope (SEM-FEG) and Raman spectroscopy.
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