It was noted that, during the high-temperature deformation of polycrystalline materials, interaction between neighboring grains gave rise to grain shape changes, grain-boundary sliding and grain rotation. There was some debate as to whether sliding made a direct contribution to strain or whether it merely accommodated shape changes. In principle, it was possible to deduce any direct sliding contribution by comparing the overall strain with grain strain. Such attempts were often blocked, however, by the existence of grain rotation. In a previous paper, rotation which occurred via interfacial diffusion had been analyzed. It could also occur by lattice diffusion, and this was the subject of the present work, where a numerical method was used to treat the rotation of a bicrystalline configuration. The method was checked by using it to solve a related problem; that of lattice diffusion creep. The predictions were shown to agree with known analytical solutions. The rate of rotation was calculated as a function of the bending moment, grain dimensions and grain aspect ratio. The steady-state vacancy concentration and diffusion fluxes within the bicrystal were determined. The fluxes at the free surfaces were shown to lead to apparent boundary grooving and mounding effects at the tensile and compressive ends of the interface. The method could be further adapted to solve the diffusion creep problem for a bamboo structure, and this gave rise to important new results. It permitted diffusion fluxes at the free surfaces to be calculated for the first time, and the variation in the creep constant to be determined as a function of the grain aspect ratio. Reported measurements of enhanced grain-boundary grooving could be explained by these results.

Lattice-Diffusion-Controlled Rotation of Crystals about a Common Interface. B.Burton: Philosophical Magazine, 2003, 83[23], 2715-31