Tribological characteristics of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass

The sliding characteristics of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass have been examined in vacuum and in air using a pin/disk geometry without lubrication. The counterface material was either the same metallic glass (self-mated) or 52100 steel. Normal load was 0.1-1 kgf The test system was equipped for continuous measurement of friction force. In addition, a Kelvin probe allowed continuous monitoring of changes in the structure and chemistry of the disk surface. Post-test characterization included optical and electron microscopy, X-ray diffraction and EDS of worn surfaces and debris. Friction coefficients in both vacuum and air were typical of those expected for ductile materials, with values ranging from 0.4 to 0.9 (higher values with lower load). Wear rates and average debris size increased with load. Wear rates were larger in air than in vacuum. Wear surface appearance and chemical composition were influenced by plastic deformation, material transfer and environmental interactions. After tests in air, the wear tracks and debris had a granular appearance and oxygen concentrations were high. Changes in the Kelvin probe signal correlated well with visual observations and with concentrations of oxygen detected by EDS.