Antigalling and low friction properties of a laser processed Co-based material

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Abstract
The antigalling and low friction properties of a CO2-laser processed Co-based material (Stellite 21) was investigated under high-load sliding conditions. Dry sliding tests were carried out at both room temperature and at 250 °C. The tests were performed by sliding two identical specimens against each other in a dedicated test. A low and stable friction coefficient at a level of about 0.20, and relatively independent on load and sliding speed, was obtained after a short running-in period. No tendency to galling was observed in any test. During sliding, the superficial face-centered-cubic material transforms to hexagonal-close-packed with the {0001} planes preferentially orientated parallel to the surface of the wear track. Since these planes are easily sheared, and supported by a deformation hardened zone, a surface layer is generated with low friction properties and high resistance to galling. Thus, the laser processed Co-based alloy exhibits the functional ability to generate a surface with unique properties during sliding contact.