Surface energy anisotropy of tungsten

Field-ion microscopy was used to study the faceting behavior and/or surface energy anisotropy of tungsten in vacuum and in hydrogen. In vacuum below 1700 K the activation energy for {110} facet growth agreed with values previously reported for surface diffusion on tungsten. The observed anisotropy values at 0.5 T_m, where T_m is the absolute melting temperature of tungsten (～3680 K), were different from those previously reported at higher temperatures and more nearly agreed with broken bond calculations based on Mie potential using m = 5, n = 8, and a 1.5% lattice expansion. Hydrogen appeared to have a negligible effect on surface energy anisotropy, but did preferentially increase surface diffusion rates on {310} regions.