Effects of environment on the sliding tribological behaviors of Zr-based bulk metallic glass

The high hardness of bulk metallic glasses (BMGs) makes them promising candidates for high wear applications. This paper focuses on the effects of oxygen on the tribological behavior of a zirconium-based BMG using pin-on-disk wear tests in three different environments, i.e. air, oxygen and argon. It was found that the wear rate of the BMG specimens increased dramatically with increasing oxygen content in the testing environment, i.e. in the order argon, air, oxygen. The pins and disk were examined using X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. A number of cracks and pits were present on the worn surface of the pin tested in oxygen-containing environments, whilst a relatively smooth worn surface and a mixed layer with a thickness of about 2–10 μm were observed in the specimens tested in argon. For the tests in oxygen, abrasive particles induced by oxidation protruded and peeled off from the glassy matrix, resulting in a combination of two-body and three-body abrasion. In an oxygen-free environment, plastic flow took place, presumably accompanied by work-softening, due to frictional heating and local stress concentrations. This led to the formation of the mixed layer on the pin and a material-transfer film on the disk.