Research on low temperature relaxation characteristics in Fe-Mn-Si-based SMA

The low temperature relaxation characteristics of two different FeMnSi based alloys have been systematically studied by means of XRD analysis, TEM observation and measurement of recovery stress. Results show that the degree of low temperature relaxation of FeMnSi based alloy increases with decreasing the temperature. With increase of phase transformation driving force at low temperature, the stress-induced $\varepsilon$-M and $\alpha'$-M transformations by recovery stress will occur in the alloy, which are the essential causes for low temperature relaxation. The more stress induced $\varepsilon$-M and $\alpha'$-M exist, the more serious relaxation arises. The low temperature relaxation degree will reduce when carbide elements such as Zr, V, Nb etc added into the alloy. This is owing to the carbide grains, dispersion separated out while recovery heating, can restrain the stress induced martensitic transformation