In-situ TEM observation of γ→ε martensitic transformation during tensile straining in an Fe-Mn-Si shape memory alloy

Through in-situ TEM observation on an Fe-30.3 mass%Mn-6.l mass%Si shape memory alloy under extending at room temperature, it is found that on a lower applied stress level, the epsilon-martensite plates are preferentially formed at interfaces of pre-existing overlapped stacking faults or E-martensites with gamma-phase especially at those near by the stress-concentrated locations e.g. inclusions. It is also observed that the epsilon-martensite is growing by the motion of partial dislocations resulting in the widening and thickening of stacking faults until ir is slopped by another martensite plate or grain boundary. On higher stress level, groups of highly oriented E-martensite plates are formed by an autocatalytic activating mechanism suggested by the present authors.