Grain-boundary grooving of the electropolished surfaces of polycrystalline samples, annealed at 1350C, was studied. Atomic force microscopic images of the grooves were obtained, at the same locations, after various annealing times. The profiles of the grooves which developed between unfaceted grains were in qualitative agreement with Mullins’ theory of grooving by surface diffusion mass transport. The predicted secondary maxima, next to the main groove maxima, were often observed. Surface faceting strongly affected the grooving kinetics and groove shapes. Grooves which developed between faceted and unfaceted grains were often asymmetrical, with unusual growth kinetics. The observations suggested that certain faceted grains exhibited negligible surface diffusion coefficients, and that the surface fluxes at the associated groove root were non-zero. Numerical simulations which assumed an anisotropy of the surface diffusion coefficient (high diffusion coefficient on the unfaceted side, negligible diffusion coefficient on the faceted side of the groove) were performed. The qualitative agreement between simulated

and observed groove shapes showed that groove asymmetry could be explained by a surface diffusion anisotropy.

Effect of Faceting on the Thermal Grain-Boundary Grooving of Tungsten. P.Sachenko, J.H.Schneibel, W.Zhang: Philosophical Magazine A, 2002, 82[4], 815-29

 Table 9

 Diffusivity of B in Zr46.8Be27.5Ti8.2Cu7.5Ni10