Martensite aging effects on the dynamic properties of Au-Cd shape memory alloys: Characteristics and modeling

We revisit the martensite aging effect in Au-Cd alloys, by studying the evolution of dynamic properties (i.e. storage modulus and internal friction) with aging time. We found that the storage modulus shows a gradual increase while the internal friction shows a gradual decrease with increasing aging time. Moreover, the evolution of dynamic properties with aging time obeys a simple relaxation function with activation energy of 0.46 eV in AuCd_49.5 alloy. The dependence of such evolution on temperature, defect concentration, frequency and displacement amplitude was also well characterized. All the observed characteristics are understood by the gradual stabilization of martensite phase during aging, driven by a symmetry-conforming short-range ordering tendency of point defects. Furthermore, we proposed a homogenous Landau-type model to describe the response of storage modulus during aging by introducing a time-dependent variable coupled with the order parameter. Such systematic investigation on the dynamic properties during martensite aging is crucial for applications under mechanical vibrations.