The neighbour-switching mechanism of superplastic deformation: The constitutive relationship and deformation-enhanced grain growth

Abstract

Grain-boundary rearrangements for superplastic deformation are modelled with cellular dislocation glide and climb in a two-dimensional cellular array. These processes account for the inhomogeneous nature of the microstructural flow. The constitutive relationship is written to consider cellular dislocation motion here. It is analysed and found to predict the nonlinear viscosity (i.e. strain-rate sensitivity) generally exhibited by superplastic materials, if the mobile cellular dislocation density increases with increasing strain rate (or flow stress), as Morral and Ashby suggest. Two models of deformation-enhanced grain growth based on cellular dislocation climb are developed, and semiquantitative predictions are compared with the behaviour exhibited by single-phase (Sn-1% Bi) and quasi-single-phase (A1 alloy 7475) materials.