Microstructure and correlated mechanical properties study of Ni-(Fe, Co)-Mn-(Al, In) as-spun ribbons
The Ni-Mn-based shape memory alloys as a promising candidate of elastocaloric material has been reported in many literatures, especially on bulk samples. The as-spun ribbon, which has a larger surface area and is more efficient for heat transfer, is rarely studied and hence of importance. In the present work, we succeeded in producing very long as-spun Ni-Fe-Mn-(Al, In) ribbons, with around 300 mm in length. The microstructure and mechanical properties of these as-spun ribbons were thoroughly investigated by scanning electron microscopy / electron backscattered diffraction (SEM/EBSD), nanoindentation and 3-points bending experiments. Through SEM/EBSD analyses, the microstructure and texture of the as-spun ribbons were studied. A gradient in microstructure exists along the thickness direction (TD) of the ribbon, which is induced by the temperature gradient during fast rate solidification, resulting in fine equiaxed grains along the surface contacted with the rotating wheel in melt spinning process and elongated grains, respectively. Both equiaxed and elongated grains possess a strong {001} fiber texture (<001>//TD). Nanoindentation analyses show little variation of hardness between the two different microstructures. The ductility index of both Ni-Fe-Mn-Al and Ni-Fe-Mn-In ribbons are within the range of intermetallic materials. The substitution of In by Al allows to increase very slightly the ductility index, which can reach 0.75. The fine equiaxed grains show better tensile resistance than the elongated grains in 3-points bending test. The substitution of In by Al improves the maximum bending strain by a factor of 3. The maximum strain for Ni-Fe-Mn-Al as-spun ribbons can reach 3 % before fracture. Fractography shows that the intergranular fracture is the main damage mechanism in these as-spun ribbons.