The effect of stacking fault configuration on martensitic transformation in Fe-Mn-Si alloys

The stacking fault probability (P-sf) of gamma phase in Fe-Mn-Si alloys was determined by Xray diffraction profile analysis. TEM observations revealed that the distribution of stacking faults formed upon cooling is localized and inhomogeneous, implying an auto-catalytic process in the formation of stacking fault bands. Based on CTEM and HRTEM observations, a possible formation mechanism of thermal-induced hcp(epsilon) martensite was proposed. At temperature above Ms, many stacking faults have been generated and mainly irregularly overlapped to form the fault bands. When cooling down to below Ms, because the stacking fault energy decreases and Delta G(gamma--epsilon) increases as temperature decreases those stacking faults are further widened. Meanwhile, new stacking faults are generated and more regularly overlapped, they form new bands or insert into the previous fault bands, remaining some defects within many epsilon plates.