The austenite to ferrite transformation of Fe-Ni under the influence of a uniaxially applied tensile stress

Differential dilatometry has been employed to study the austenite (γ)-ferrite (α) massive phase transformation of Fe-3.1 at.% Ni upon cooling under the influence of an applied constant uniaxial tensile stress. The applied stress level was chosen to be below the yield stress of the alloy. It was found that an extra length change in the specimens occurs during the transformation as a result of transformation-induced plasticity. The local plastic deformation induced by transformation plasticity results in an anisotropic volume change of the specimen in the longitudinal direction. A phase transformation model, involving site saturation, interface-controlled continuous growth and an appropriate impingement correction, has been employed to extract the velocity of the γ/α interface. The observed scatter in the interface velocity decreases with increasing applied stress due to relaxation of misfit deformation energy by transformation-induced inhomogeneous plastic deformation. The interface velocity remains almost constant during the whole transformation.