Effect of Severe Surface Plastic Deformation on Tribological Properties of CoCrWNi Super Alloys

The effect of severe surface plastic deformation on the microstructure and tribological properties of CoCrWNi super alloy L605 was investigated. The surface of the annealed alloy was frictionally processed by a tungsten carbide tool with a tip radius of 5 mm under different sliding speeds of 500, 800, 1100, 1400, 1700, and 2000 mm/min for 2, 5, 10, 20, and 30 passes. Based on the results, applying friction hardening (FH) promoted the formation of the Ɛ-HCP (martensite) phase in the surface structure of the ɣ-FCC alloy up to a depth of about 500 m. The maximum surface hardness was observed at the sliding speed of 1700 mm/min and 30 passes, where the surface hardness increased by almost 100% (from about 320 HV to more than 635 HV). Pin-on-disk wear tests were carried out at room temperature, under applied pressures of 0.25, 0.5, and 1 MPa, for a sliding distance of 1000 m. According to the results, under low applied pressures, i.e. 0.25 MPa, the maximum wear resistance was observed in the sample FH-processed for 30 passes at 1700 mm/min. However, due to the formation of lateral microcracks on the surface of samples processed by high number of FH passes, under the applied pressure of 1 MPa, the lowest wear was observed in the 5-pass processed sample (1700 mm/min). The wear rate and average friction coefficient (AFC) of this sample were about 45% and 30% lower than those of the base (annealed) sample, respectively.