Effect of copper molybdate on the lubricating properties of NiCrAlY laser clad coating at elevated temperatures

The goal of the current work was to prepare a self-lubricating composite coating NiCrAlY/Cr3C2(NiCr)/Cu/MoO3 on GH4169 alloy substrate by laser cladding with hard phase Cr3C2(NiCr) as the reinforcing agent and Cu-MoO3 as the primary fillers. The composition and microstructure of the feedstock powders and corresponding composite coating were examined by scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) and X-ray diffraction. The tribological behavior of the composite coating from 25 °C to 800 °C was performed in air with a ball-on-disk tribometer against Si3N4 ball counterfaces and a dual-mode three-dimensional surface profiler. It has been found that the composite coating shows the most serious abrasion at 200 °C, the friction coefficient was 0.7 and the wear rate was 7.7 × 10− 5 mm3/N · m. Better tribological properties could be found when the temperature higher than 200 °C, and the composite coating got the best wear resistance with the friction coefficient 0.34 and the wear rate was 1.0 × 10− 5 mm3/N · m at 800 °C. The morphology and compositions of the worn surfaces were analyzed by SEM-EDS and Raman spectroscopy. Findings indicate that copper molybdate (CuMoO4) is converted by in situ reaction between Cu and MoO3 during friction at elevated temperatures. The synergetic lubricating effect between CuMoO4 and oxide lubrication (such as MoO3, Cr2O3, CuO, and NiO) is the principal reason for the anti-wear and self-lubricate of the composite coatings. Particularly, composite coating containing CuMoO4 and Cr2O3 exhibits the lowest friction coefficient and smallest wear rate when the temperature above 600 °C. Abrasive wear, plastic deformation, delamination as well as adhesive wear was main wear mechanism of the composite coating during friction at different temperature.