Microstructural design considerations in Fe-Mn-Al-Ni shape memory alloy wires: Effects of natural aging

In this study, FeMnAlNi shape memory alloys are demonstrated to experience room temperature (RT) aging, which manifests itself as a gradual increase in critical transformation stress with time when the sample is kept in a stress-free condition. This effect is sufficient to create superelasticity in the solution treated condition, which does not normally show superelasticity soon after heat treatment. This phenomenon is due to the nucleation and coarsening of nanoprecipitates at room temperature despite the high melting point of the alloy. RT aging also influenced precipitation hardened FeMnAlNi samples by causing an increase in stress hysteresis and hardening rate.