The stacking disorder in the face-centred cubic structure of Fe-23Mn-2Si-2Al alloy after tensile testing at -75C was investigated by electron diffraction, using a relationship between the stacking fault probability and the shift of diffraction spots. Shifts of diffraction spots along the [111] direction in the face-centred cubic structure were observed, and the stacking fault probabilities in two selected areas with different densities of stacking faults were determined as α = 0.15 and α = 0.35. The stacking fault probabilities measured by electron diffraction were much larger than average values determined by X-ray diffraction, indicating that the distribution of stacking faults was localized. A mechanism for the γfcc → εhcp transformation was suggested, whereby during deformation the following sequences take place: dissociation of perfect dislocation → localization of stacking faults → evolution from stacking disorder to stacking order → the formation of the perfect hexagonal close-packed martensite (α = 1) or the hexagonal close-packed martensite with stacking faults (α → 1). This proposed mechanism for strain-induced hexagonal close-packed martensite formation should be also applicable to the thermally induced hexagonal close-packed martensite.

Determination of Stacking Fault Probability in FCC Fe-Mn-Si-Al Alloy by Electron Diffraction. X.D.Wang, B.X.Huang, Y.H.Rong, L.Wang: Journal of Applied Physics, 2007, 101[9], 093511