Structural changes in Bi-43 wt % Sn eutectic alloy under superplastic deformation

Abstract

Methods of scanning electron microscopy have been used to study the microstructure of superplastically deformed samples of eutectic alloy Bi-43 wt % Sn. The observed specific features of the deformation relief of the samples reveal the active development of the viscous dislocation-diffusion flow under superplasticity conditions. The manifestation of the hydrodynamic mode of deformation has been revealed under these conditions. The opportunity of the realization of viscous mechanisms of the transport of substance and of the manifestation of the effect of superplasticity are explained by the appearance in the material of a state that is characterized by a high dislocation density and low strength properties. An additional increase in the dislocation density and softening under superplasticity conditions are attributed to the occurrence of structural and phase transformations stimulated by deformation, the relaxation of significant internal elastic stresses, and the instability of the structural state of the initially nonequilibrium alloy in the field of mechanical stresses. Factors responsible for the appearance of significant internal elastic stresses in the alloy are analyzed.