During the high-temperature deformation of polycrystalline materials, the interaction between neighboring grains gave rise to grain shape changes, grain-boundary sliding and grain rotation. There was debate on whether sliding makes a direct contribution to strain or whether it merely accommodates the 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 confounded, however, by the existence of grain rotation. In a previous paper, by Burton, rotation occurring by interfacial diffusion was analyzed. It may also occur by lattice diffusion and this was the subject of the present paper. where a numerical method was used to treat the rotation of a bicrystal configuration. The method was validated by adapting it to solve a related problem; that of lattice diffusion creep and predictions were shown to agree with known analytical solutions. The rate of rotation was calculated as a function of 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 has given important new results. It allows 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 may be explained by these results.

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