Stress relaxation behavior of columnar-grained Cu–Al–Mn shape memory alloys

Abstract

Stress relaxation resistance is one of the key properties needed to shape memory alloys (SMAs) in the applications of fasteners, elastic contact components, etc. In this work, the stress relaxation behaviors in the superelastic (SE) and shape memory processes of columnar-grained (CG) Cu–Al–Mn SMAs were investigated under constant strain conditions for 100 h. The effects of loading strain and ambient temperature on the stress relaxation resistance was studied experimentally. The experimental results indicated that the stress relaxation resistance of CG Cu71.3Al17.0Mn11.7 SMAs could reach over 85% and 62% at 25 °C and 60 °C, respectively, at a loading strain of 2%~10%. The SE stress relaxation resistance almost remained constant in the martensite transformation stage; however, it linearly declined with increasing ambient temperature. The stress relaxation resistance for one-way and two-way shape memory effects (OWSME and TWSME) also reached 70% and 66%, respectively, in CG Cu72.7Al16.8Mn10.5 SMAs. The SE, OWSME and TWSME stress relaxation behaviors could be well described by a logarithmic model.