A multiscale study of hot-extruded CoNiGa ferromagnetic shape-memory alloys

0536545 - ÚJF 2021 RIV GB eng J - Journal Article
Samothrakitis, Stavros - Larsen, Camilla Buhl - Woracek, Robin - Heller, Luděk - Kopeček, J. - Gerstein, G. - Maier, H. J. - Rames, M. - Tovar, M. - Šittner, Petr - Schmidt, S. - Strobl, Markus
A multiscale study of hot-extruded CoNiGa ferromagnetic shape-memory alloys.
Materials and Design. Roč. 196, č. 11 (2020), č. článku 109118. ISSN 0264-1275. E-ISSN 1873-4197
R&D Projects: GA MŠMT EF16_013/0001794
Institutional support: RVO:61389005
Keywords : Martensitic transformation * hot-extrusion * Laue three-dimensional neutron diffraction tomography * Co-Ni-Ga * ferromagnetic shape-memory alloy
OECD category: Materials engineering
Impact factor: 7.991, year: 2020
Method of publishing: Open access
https://doi.org/10.1016/j.matdes.2020.109118

Ferromagnetic shape-memory CoNiGa alloys have attracted much scientific interest due to their potential alternative use as high-temperature shape-memory alloys, bearing a high prospect for actuation and damping applications at elevated temperatures. Yet, polycrystalline CoNiGa, due to strong orientation dependence of transformation strains, suffers from intergranular fracture. Here, two multi-grain CoNiGa samples were prepared by a novel hot extrusion process that can promote favourable grain-boundary orientation distribution and improve the material's mechanical behaviour. The samples were investigated by multiple methods and their micro structural, magnetic, and mechanical properties are reported. It is found that a post-extrusion solutionising heat treatment leads to the formation of a two-phase oligocrystalline homogeneous microstructure consisting of an austenitic parent B2 phase and gamma-CoNiGa precipitates. Reconstruction of the full 3D grain morphology revealed large, nearly spherical grains with no low-angle grain boundaries throughout the entire sample volume. The presence of gamma precipitation affects the transformation behaviour of the samples, by lowering the martensitic transformation temperature, while, in conjunction with the oligocrystalline microstructure, it improves the ductility. Controlling the composition of the B2 matrix, as well as the phase fraction of the gamma phase, is thus crucial for the optimal behaviour of the alloys.
Permanent Link: http://hdl.handle.net/11104/0314317