An internal variable approach to superplasticity of microduplex Pb-Sn alloys

Abstract

The superplastic deformation behavior of microduplex Pb-Sn alloys has been investigated in this study. The effect of shape and volume fraction of constituent phases was examined within the framework of the recently proposed internal variable theory of structural superplasticity. A series of load relaxation and tensile tests as well as the observation of deformed surface using the technique of in-situ straining in a scanning electron microscope were conducted on Pb-Sn alloys at room temperature. The flow curves obtained from load relaxation tests of the superplastic Pb-Sn eutectic alloy were shown to consist of the contributions from interface sliding (IS) and the accommodating plastic deformation, regardless of grain sizes. The IS behavior could be described as a Viscous flow process characterized by the power index value of M-g = 0.5. From a series of surface observation during tensile tests, it was found that the value of M-g was attributed to the onset of intense phase boundary sliding (PBS). Superplasticity of hypoeutectic alloy (Pb-40 wt.% Sn), which is comparable to that of superplastic eutectic alloy, appeared to be superior to that of hypereutectic alloy (Pb-80 wt.% Sn).