Preparation and high-temperature tribological performance of laser clad MoNi coatings with chromium addition

In order to enhance the wear resistance of MoNi matrix coatings at elevated temperature, high-temperature wear resistant MoNi matrix coatings with different Cr contents (3.0 wt%, 7.0 wt% and 11.0 wt%) were prepared on the 718 alloy substrate by laser cladding. The high-temperature tribological performance was investigated sliding against Si3N4 ceramic ball by using ball-on-disk tribo-tester from room temperature to 1000 ?. The effects of chromium addition on the microstructure and the tribological performance of coatings were systematically studied. The coatings with dendritic structure consisted of Mo, Cr9Mo21Ni20 and Cr1.12Ni2.88 phases. The coatings showed a good metallurgical bonding interface with the substrate. There was a critical value of Cr content which could best reinforce the high-temperature wear resistance of MoNi matrix coating. The coating containing 7 wt% Cr had the best wear resistance over a wide temperature range, which was due to the in-situ formed salt compounds, high hardness and oxide lubricating film. The wear mechanism of three coatings transferred from the fatigue wear and abrasive wear to the oxidative wear with the increase in testing temperature.