Continuous Transition of Deformation Modes in Fe-30Mn-5Si-1Al Alloy

Deformation modes at various stages of plastic deformation have been investigated at the same location in an Fe-30Mn-5Si-1Al (mass%) alloy specimen, which exhibits a good shape memory effect associated with the FCC(γ)→HCP(ε) martensitic transformation and a relatively high ductility caused by deformation twinning. The surface relief caused by the γ→ε martensitic transformation, deformation twinning and slip band formation has been analyzed by measuring the surface tilt angles corresponding to each deformation mode by atomic force microscopy. Although the ε-martensitic transformation is the dominant deformation mode at an early deformation stage, a part of the ε-martensite plates changes to deformation twins with increasing tensile strain. Slip deformation also occurs inside the same region under excessive strain. A continuous transition of these deformation modes occurs in other grains as well in the same order: ε martensite → deformation twins → slip bands.