Reverse transformation behavior of a prestrained MnCu alloy

Prestrained thermoelastic martensite alloys have the characteristics of increased reverse transformation temperature and increased transformation heat by cold deformation. In this study, calorimetric analysis and internal friction (IF) measurements were applied to investigate the reverse phase transformation of a Mn-15 at.% Cu alloy with prestrains up to 18%. The reverse phase transformation temperature increased along with a very small variation in transformation heat with an increase in prestrain. Meanwhile, the IF peak corresponding to the reverse phase transformation increased with prestrain up to 4%, then decreased with an increase in prestrain. Twin boundary reorientation and de-twinning occurred in the prestrained specimens, and the change in the fraction of 90° twin boundaries by the prestrain was similar to that of the reverse phase transformation IF. Based on the stress-induced nucleation model for transformation, the change in the reverse transformation IF by the prestrain could be simulated as a function of both the prestrain and vibration frequency. The twin boundary reorientation and de-twinning caused by the prestrain are thought to influence the reverse phase transformation behavior by affecting the features of the boundaries that are the possible nucleation sites for reverse transformation.