Tailoring the Microstructure in Polycrystalline Co–Ni–Ga High-Temperature Shape Memory Alloys by Hot Extrusion

Co–Ni–Ga alloys represent a new class of promising high-temperature shape memory alloys allowing realization of functional components for applications at elevated temperatures. Single crystals show a fully reversible pseudoelastic response at temperatures up to 500 °C. However, for most industrial applications, the application of polycrystalline material is needed. Polycrystalline Co–Ni–Ga alloys suffer from the anisotropic properties inherent to shape memory alloys, i.e., a strong orientation dependence of transformation strains, and therefore, are prone to intergranular fracture. This drawback can be curtailed by using appropriately textured material with a favorable grain-boundary orientation distribution. The current study discusses the impact of a hot-extrusion process on microstructural evolution and functional properties of polycrystalline Co–Ni–Ga high-temperature shape memory alloys paving the way to their robust application.