Tribological properties of cobalt-based alloy coating with different cobalt contents by electro-spark deposition

The cobalt-based alloy coating with different Co contents was deposited on 45 steel by electro-spark deposition with the self-made electrode. The coating has a compact and uniform microstructure with low porosity and no visible microcracks. When Co content increases gradually, oxygen content of coating samples 1-5 decreases first and then increases in the range of 2.52 wt%-3.05 wt%; sample 3 has the lowest oxygen content of 2.52 %. Microhardness of the coating is improved remarkably compared with the substrate (HV 230.18). With Co content increasing, microhardness of the coating samples 1-5 first rises slightly and then declines rapidly in the range of HV 580.61-1052.33. Sample 3 gets the maximum of HV 1052.33, which is about 4.6 times that of the substrate. The coating presents excellent wear resistance, which first increases and then decreases when Co content increases. Sample 3 shows the best wear resistance of about 6.4 times that of the substrate. Main wear mechanism of the coating is abrasive wear and fatigue wear, along with oxidation wear under high speed or heavy load conditions. Cobalt content has an obvious influence on microhardness and tribological properties of cobalt-based alloy coating. When the cobalt content increases, the microhardness and wear resistance of the coating increase firstly and then decrease, the friction coefficient of the coating decreases firstly and then increases.