Hot forming of shape memory alloys in steel shells: formability, interface, bonding quality

Abstract

Metal forming of shape memory alloys (SMA) can be challenging since these are very often brittle due to their intermetallic character. However, formability is often needed not only for realising the desired geometry but also for tailoring the microstructure and the functional properties. To investigate whether the encapsulation in a steel shell can improve the formability of shape memory alloys, Co₄₉Ni₂₁Ga₃₀ and Ni_49.5Fe_14.5Mn_4.0Ga_26.0Co_6.0 samples were subjected to tensile tests, upsetting, rolling and extrusion. A ferritic steel (1.0503) was used as the shell material. The shell was employed to curtail the formation of tensile stresses in the core, to maintain high temperatures during processing and to prevent oxidation. With this approach, not only forming of the SMA in the steel shell was possible but also an intensive metallurgical bond between the SMA and the steel shell can be achieved during hot rolling or extrusion.