Effects of V addition on microstructure and pseudoelastic response in Fe-Mn-Al-Ni alloys

Avoiding quench cracks and controlling the formation process of NiAl precipitates are essential to regulate the microstructure and pseudoelastic properties of Fe-Mn-Al-Ni shape memory alloys (SMAs). In this study, we investigated the effect of 1.5 at.%V addition on the quench sensitivity of Fe-Mn-Al-Ni SMAs and the precipitation behavior of NiAl precipitates in air-cooled Fe-Mn-Al-Ni-V SMAs. It is found that the V addition significantly inhibits the precipitation process of non-transforming gamma-phase. Polycrystalline sample of bamboo structure was prepared by abnormal grain growth and tested by incremental strain cycling tensile test at room temperature. The polycrystalline Fe-Mn-Al-Ni-V SMAs obtain fully reversible thermoelastic martensitic transformation without quenching, which also prevents the formation of quenching cracks. Single crystal samples were further prepared by directional recrystallization. High number-density and relatively large-size coherent beta-NiAl precipitates were obtained to strengthen the matrix in the single crystal without aging, resulting in large stress hysteresis and irrecoverable strain. After aging Fe-Mn-Al-Ni-V single crystal for 3 h at 200 degrees C, both the stress hysteresis and irrecoverable strain decreased, thereby achieving good pseudoelasticity in Fe-Mn-Al-Ni-V SMAs.

Automated summary

This study investigates the effect of 1.5 at.%V addition on the quench sensitivity of Fe-Mn-Al-Ni shape memory alloys (SMAs) and the precipitation behavior of NiAl precipitates. The results show that V addition significantly inhibits the precipitation process of non-transforming gamma-phase. Polycrystalline Fe-Mn-Al-Ni-V SMAs achieve fully reversible thermoelastic martensitic transformation without quenching, while single crystal Fe-Mn-Al-Ni-V SMAs obtain high number-density and relatively large-size coherent beta-NiAl precipitates to strengthen the matrix.