Sliding behavior of metallic glass: Part I. Experimental investigations

The unlubricated sliding characteristics of zirconium-based bulk metallic glass disks have been examined in vacuum and in air using sliders made from the same material or from a hard bearing steel (52100). The pin-on-disk test system allowed collection of debris, monitoring of the friction force and, using a Kelvin probe, in situ detection of changes in the structure and chemical composition of the disk surface. Post-test characterization included microhardness testing, X-ray diffraction, SEM and EDS. Examination of worn surfaces, cross-sections and debris confirmed the importance of plastic deformation, material transfer and environmental interactions. When devitrified material was tested, sliding processes caused the near-surface material to re-amorphize. Results from sliding of bulk metallic glass specimens were compared with those from related experiments involving crystalline metals and alloys. Although bulk metallic glasses are reported to have only limited ductility in tensile tests, the friction coefficients and worn surfaces of these materials are typical of ductile materials.