Shape memory alloys (SMA) are known for the ability to recover high strains (up to 6-8 %) thanks to a solid-to-solid thermoelastic transition that can be either induced by a change of temperature (shape memory effect, SME) or by a change of load (pseudoelasticity, PE). The resulting mechanical work is frequently exploited in actuation (SME) and in passive damping (PE) [1,2].

The control either active or passive of structures at cryogenic temperatures (below 120 K) through SMA represents a novel and attractive application for extreme environments such as space. Systems like expandable habitats and deployable platforms, solar cells and veils, on demand and adaptive applications, as well as ISRU (In-Situ Resource Utilization) technologies can benefit greatly from these SMA materials.

Figure 1. Resistance vs. Temperature (a), and Stress vs. Strain (Ttest=150 K) (b). Measurements labels: AC_S: as cast and solubilization; HT_S: hot-rolled and solubilization; HT_S_373: hot-rolled, solubilization and annealing at 373 K; HT_S_473: hot-rolled, solubilization and annealing at 473 K.

Starting from the studies of Treheran et al. [3], the present work investigates the cryogenic CuMnAl alloy (nominal: 12.8 at.% Mn, 18.6 at.% Al, Cu bal.) produced via vacuum arc melting. As-cast and hot-rolled specimens were examined through thermal, microstructural and thermo-mechanical analyses, considering as well the effect of solubilization and annealing. Phase transition temperatures Af and Mf (i.e., austenite and martensite finish temperatures) were evaluated through the tangent method applied to the Resistance vs. Temperature measurement graphs.

It was observed that Af and Mf change according to the thermo-mechanical path (Figure 1a). Hot rolling lowers the phase transition temperature range with respect to the as-cast condition: after hot rolling, Mf decreases from 33 K to 20 K and Af from 88 K to 80 K. On the other side, the phase transformation temperatures shift to higher values with the increasing of the annealing temperature. Stable pseudoelastic response was observed at 150 K for hot rolled sample annealed at 473 K (Figure 1b).

References

[1] J.M. Jani, Mater. Des., 2014, 56:1078-1113.

[2] A. Nespoli, Sens. Act. A Phys., 2010, 158:149-160.

[3] W. Trehern, Mater. Letters, 2022, 308, 131246.