Superelasticity with excellent temperature stability in Cu-Al-Mn shape memory alloy by gradient high temperature rolling

Abstract

The objective was to enhance the temperature stability of Cu-Al-Mn shape memory alloys (SMAs) across a wide temperature range. To this end, a gradient rolling treatment at 800 °C (HR) and subsequent heat treatment (HT) were employed to create a gradient texture. The objective was to control and reduce the temperature dependence of superelasticity properties, including superelastic stress (σ_M), austenite transformation stress (σ_A), damping coefficient (tanΦ), and so forth, in columnar-grained Cu-Al-Mn SMAs. The results demonstrated that the temperature dependence rate of stress-induced martensitic transformation stress (σ_M) initially increased and then decreased with the reduction in gradient range in the RD direction. The dσ_M/d_T value for HRT-65/68 was 0.369 MPa/K. In the TD direction, the dσ_M/d_T of HRT-60V was only 0.232 MPa/K over a wide range of temperatures, approximately 120 K. The excellent superelastic temperature stability observed in this gradient structure Cu-Al-Mn SMA was superior to that of other reported Cu-Al-Mn SMAs and NiTi SMAs. Following gradient rolling treatment, the alloy retained a strong <001>-oriented texture along the RD direction. However, the strength of this texture was reduced, resulting in the formation of non-high phase transition strain orientation and grains with a gradient size distribution. These characteristics contributed to the development of high superelasticity with excellent temperature stability.