Sliding wear behavior of Cu50Hf41.5Al8.5 bulk metallic glass

Sliding wear behavior of a copper-based bulk metallic glass (Cu50Hf41.5Al8.5) was investigated for both as-cast and annealed samples. The wear resistance increased during isothermal annealing near the glass transition temperature. Nanocrystals developed during the annealing for annealing times up to 300 min. A linear relation between hardness and wear resistance was observed during the early stages of devitrification, but at longer annealing times the wear resistance increased less than the hardness. For the as-cast sample and a sample that was structurally relaxed, nanocrystallites developed during sliding and the wear resistance improved for longer sliding distances when the nanocrystals developed. The transmission electron microscopy analysis of the annealed samples suggests that the deviation from the linear hardness vs. wear resistance relation occurs at a critical volume fraction of the nanocrystals. The improvement in wear resistance with sliding appears to result from an increased surface temperature rather than directly from the sliding-induced nanocrystal formation.