Modulus softening during the γ → ɛ martensitic transformation in Fe–25Mn–6Si–5Cr–0.14N alloys

The temperature dependences of internal friction and modulus were measured for the Fe–25Mn–6Si–5Cr–0.14N (wt.%) shape memory alloys. Compared with other Fe–Mi–Si based alloys without nitrogen, a modulus softening of the parent γ phase was observed during the γ → ɛ martensitic transformation, although the rather strong softening has been always recognized to occur during the reverse ɛ → γ transformation, due to the enhanced strength and the increased stacking fault energy of the parent phase by nitrogen alloying. A coupled stacking faulting-modulus softening mechanism is proposed as the modification of the currently accepted faulting mechanism for the ɛ martensite nucleation.