Thermal grain boundary grooving with anisotropic surface free energies

Abstract We study the effect of anisotropic surface free energy on thermal grain boundary grooving profiles under surface diffusion using modeling, simulation and experiments with tungsten. Based on Herring’s [W.E. Kingston (Ed.), The Physics of Powder Metallurgy, McGraw-Hill, New York, 1951, p. 143] model we show that when the anisotropy is mild, the groove profiles are self-similar in the evolution but are often not in proportion to those developed under isotropic material properties. The grooving kinetics obey power laws with the exponent 1/4. When the anisotropy is critical surface faceting occurs. And, when it is severe the facets coarsen in the evolution. We exhibit the groove profiles in evolution under different degrees of anisotropy. We observe in the experiments that the {1 1 0} and {1 1 1} oriented grains develop small surface facets during annealing, as in the severely anisotropic cases, whilst those grains without crystalline orientation tilted at about 45° to the sample surface do not.