Microstructural evolution and deformation mechanism of a Fe-15Mn alloy investigated by electron back-scattered diffraction and transmission electron microscopy

The present studies focus on mechanical properties and microstructure evolution of a Fe-15Mn dual phase alloy during tensile deformation based on the analyses of X-ray diffraction, electron back-scattered diffraction and transmission electron microscopy. The alloy possesses excellent combination of strength and ductility (UTS×TEL=32 GPa•%) and good strain hardening capacity owing to several plastic deformation mechanisms. At earlier stage of tensile deformation, the deformation induced transformation from γ to ε is the main plastic deformation mechanism. In addition, the deformation induced twins within ε-martensite and transformation from ε to αˊ also have contributions to the plastic deformation. With further increasing the strain, the deformation induced transformation from ε→αˊ in combination with the dislocation slip in γ, ε and αˊ become the main plastic deformation mechanisms. During the whole tensile deformation, nearly all αˊ-martensite grains exist within ε-martensite plates, indicating that the deformation induced transformation sequence is ε→αˊ. Moreover, it has been demonstrated that the αˊ-martensite is preferred to nucleate at intersections of two ε-martensite plates, interfaces of γ/ε and ε/ε and low angle grain boundaries within ε-martensite plates. Note that the orientations of some αˊ-martensite grains existing within the same ɛ-martensite plate are not exactly the same.