Hillock growth in CuZr metallic glass

While hillock has so far been only observed in crystalline metals, here we show that hillock appeared on the surface of CuZr metallic glass film after annealing treatment. Other than compressive stresses generated upon annealing, surface selective oxidation processes, i.e., preferential oxidation of zirconium arouses the formation of surface ZrO₂ layer and Cu-enriched area in the subsurface, were proposed to play a crucial role in hillock formation in metallic glasses. Cu atoms diffused faster than Zr from the Cu-enriched area towards the film surface, promoting the formation of Cu or Cu-enriched hillocks. Different from the diffusion mechanism in crystal films, the mechanism of atom diffusion to surface with vacancy to relieve compressive thermal stresses dominated the formation of hillocks in CuZr metallic glass films.