EXTENSIONS OF THERMAL GROOVING FOR ARBITRARY GRAIN-BOUNDARY FLUX

Groove profiles are computed under isotropic conditions for the intersection of a periodic array of grain boundaries with an external surface, assuming that grain boundary flux I is directed to (I > 0) or away from (I < 0) the surface. When I = 0, the surface assumes an equilibrium (time-independent) profile. For I not equal 0, in a range bounded by upper and lower limits that depend on geometry and material parameters, a global steady-state develops in which the entire surface advances (I > 0) or recedes (I < 0) from its original position at constant velocity. Beyond these limits, the surface near the groove roots becomes diffusively detached from the remaining surface. A rapidly growing ridge (I > 0) or slit (I < 0) then develops along each grain boundary, whose tip ultimately translates at constant velocity in a local steady state, leaving the remaining surface behind. These velocity regimes govern the ultimate stability of polycrystalline materials subjected to large electric (electromigration) or stress (creep) fields, especially in thin films where grain size approximates film thickness. (C) 1995 American Institute of Physics.