Environment-Dependent Tribological Properties of Bulk Metallic Glasses

The macroscale friction and wear properties of the Zr44Cu10Ni10Ti11Be25 metallic glass were investigated as a function of environmental oxygen concentration and contact force. We found remarkably low and predictable friction when both oxidation and frictional heating (that can lead to thermomechanically-driven crystallization) were supressed. Conversely, oxidation and the formation of a mixed metal-oxide layer was shown to increase the friction coefficient while significantly reducing wear rates. Depending on conditions, the wear rates ranged from values comparable to highly wear-resistant materials like polymer and 2D solid lubricant nanocomposites to those that are found with soft, pure, high-wear metals. These results reveal that the competition between material removal and the deformation-induced mixing of oxide particles can dramatically reduce wear rates, suggesting opportunities for optimization of tribological performance.