The influence of phase transformations and oxidation on the galling resistance and low friction behaviour of a laser processed Co-based alloy

The effect of oxide formation on the tribological properties of a CO2-laser processed Co-based material (Stellite 21) was investigated under high-load sliding conditions in air and in an oxygen free environment. The tests were carried out by sliding two identical specimens against each other in a load-scanning test. A friction coefficient at a level of about 0.20 was observed for both test environments. However, the wear of the Co base material is accelerated when the sliding is performed in an oxygen free environment. The friction level appears to be controlled by the shearing of hcp {0 0 0 1} planes rather than by the presence of an oxide layer.