The kinetics of deformation caused by grain-boundary sliding and diffu
sion is discussed for a two-dimensional model polycrystal. It is shown
that boundary sliding is a prerequisite to induce the bulk diffusion.
The sliding must also occur concurrently with the diffusion for a pol
ycrystal to continue diffusional creep. Rate equations for deformation
of the polycrystal are also formulated when both of the bulk and boun
dary diffusions are operative in addition to the boundary sliding. It
is shown that the two diffusional processes are exclusive in general.
Only when boundaries slide extremely fast, the strain rate of the poly
crystal in a steady state becomes the simple sum of the strain rate ac
hieved by the bulk diffusion and that by the boundary diffusion. (C) 1
998 American Institute of Physics.