High entropy shape memory alloys (HE-SMAs) featuring the one-way effect or pseudoelasticity are attractive new materials for many engineering fields. Research and further development in this area is focused on extending the functional range in terms of work-output-density, increasing tolerable stresses as well as extending the transformation temperatures and service life. However, their functional properties are often rapidly degraded due to fatigue mechanisms. Current research often investigates single crystalline materials and promising results were obtained. Yet, these materials are not suited for large-volume production and are of little commercial use. Some polycrystalline HE-SMAs exhibit reversible martensitic transformation at high loads and the recently developed alloys show promising reversibility over many cycles. However, the manufacturing of these materials is usually limited to arc melting and comes with challenges such as decomposition, segregation and dendritic microstructures along with increased pore formation drastically reducing the potential functionality of the materials. Approaches employing pure heat treatments have a marginal benefit in this regard and often do not achieve the desired microstructure. Moreover, subsequent forming is usually necessary for use in technical applications, but this is hardly possible given the brittleness of these material conditions.

In the present study, an approach of a thermo-mechanical forming in a protective hull is presented. In addition to oxidation protection at high temperatures, the hull-aid allows an isostatic forming behavior. It is demonstrated that an elongation of up to 250% can be obtained with a hot-extrusion processes of the HE-SMAs in a protective hull. Moreover, the microstructural analysis has revealed that it is possible to break the dendritic microstructure, and induce recrystallization. The ramifications of the current study for tailoring the microstructure will be discussed with respect to envisaged applications.