Tailoring Micro- and Nanostructures to Optimize the Functional Response of FeMnAlNi-Based Shape Memory Alloys

The present paper focuses on the evolution of micro- and nanostructures during a cyclic heat treatment in a Fe 41 Mn 34.2 Al 14.1 Ni 7.7 Cr 3 (at.-%) shape memory alloy (SMA). Crystallographic orientation and subgrain structures of the obtained single crystal after a cyclic heat treatment have been investigated using optical microscopy and electron backscatter diffraction analysis. Subsequent to the cyclic heat treatment, an aging process (200 °C, 3 h) has been applied to introduce nanosized β-precipitates that are known to enhance the superelastic properties in FeMnAlNi-based SMAs. The precipitates have been analyzed using transmission electron microscopy measurements. To further evaluate their influence on the superelastic properties of the Fe 41 Mn 34.2 Al 14.1 Ni 7.7 Cr 3 (at.-%) SMA, compressive incremental strain tests were carried out, revealing significantly improved recoverable compressive strains after the β-precipitates slightly coarsened . In situ optical microscopy was conducted during the mechanical tests, showing irrecoverable martensite in a not aged condition, rationalizing its inferior superelastic performance. Furthermore, by affecting the substructures, it becomes possible to tailor the superelastic properties of FeMnAlNi-based SMAs for different applications.