A novel Fe-Mn-Al-Ni-Ta-B superelastic polycrystalline alloy with high stability and low thermal hysteresis

The demand for advanced shape memory alloys, with good processability, high stability, and excellent superelasticity, is highly desirable in widespread practical applications. Here, we demonstrated a novel Fe-34Mn-12.5Al-7.5Ni-2.5Ta-0.05B (at%) polycrystalline alloy (FMAN-Ta-B) with good strain-recovery pseudoelastic behavior (5.68% at a compressive strain of 8%), ultra-low thermal hysteresis (∼81 K), and relatively high stability. In this alloy, highly ordered D03-structured precipitates (Ta-riched Fe3Al) (∼26.3 nm) coupled with B2 precipitates (NiAl) (∼19.6 nm), and dispersive distributed in the A2 (austenitic) matrix. On the one hand, D03-structured precipitates act as a connecting structure between B2 precipitates and the matrix, exhibiting low mismatch with the matrix and inducing a thermoelastic martensitic transformation and good strain recovery in the alloy. On the other hand, D03 nanoprecipitates with high structural and thermal stability limited the growth of B2 precipitates and reduced the size-dependence of the superelasticity for the B2 precipitate, thus elevating the aging temperature and enhancing the thermostability of superelasticity. The drastically improved superelasticity and low thermal hysteresis provide useful insights into the design of high-performance ferrous superelastic alloys.