Internal friction associated with the premartensitic transformation and twin boundary motion of Ni_50xMn_{25- x}Ga₂₅ (x 0-2) alloys

The internal friction (IF) during the martensitic transformation (MT) has been extensively studied in NiMnGa alloys. In this paper, temperature dependence of the IF associated with the premartensitic transformation (PMT) and twin boundary motion (TBM) was investigated in Ni_50xMn _25-xGa₂₅ (x 0-2) alloys. Both the composition and frequency had no obvious effect on the IF peak position of the PMT and TBM. With increasing frequency from 0.1 Hz to 5 Hz, the IF peak height corresponding to the TBM was significantly decreased, but was kept constant during the PMT. The observed phenomena were discussed in terms of the different microscopic mechanisms of the TBM and PMT.