The influence of large second phase grains on microstructural evolution during diffusion creep

Abstract

Diffusion creep is a fundamental mechanism by which Earth materials deform, but the way microstructure evolves during diffusion creep remains poorly understood, because the mechanism does not leave behind abundant microstructural indicators. Because most rocks are polyphase, this study used numerical simulations to investigate the influence of large second-phase grains on the microstructural evolution of a fine-grained matrix during diffusion creep in both pure and simple shear. The results of the modelling show that large second-phase grains create stress heterogeneities that focus the effects of diffusion creep, which can lead to a profound drop in strength of a material, and dictate where grain boundary sliding surfaces develop within the fine-grained matrix. Rotations of matrix grains are strongly influenced by the rotation direction and velocity of the large grain, especially those that lie adjacent to it. The rotation direction of large grains is not simply either synthetic or antithetic to the shear direction. Instead, rotation directions of large grains can change due to interactions with the matrix. Such interactions could result in simple strain paths producing complex microstructures which could be misinterpreted to record much more complicated strain histories.