Microstructure evolution and tribological properties over a wide temperature range of Ni-based composite coatings with Ti3AlC2 addition

Ti3AlC2 MAX phase incorporated with Ni60A alloy powder in varying concentrations (0, 10 wt.% and 20 wt.%) were coated on S31008 NiCr stainless steel substrate using atmosphere plasma spraying technique in this work. Comparative investigation was conducted to examine the effects of Ti3AlC2 additions on the microstructure evolution, microhardness, and wide temperature range (room temperature to 800 oC) tribological performance of the composite coatings. The findings demonstrated that the composite coatings were composed of γ-Ni, intermetallic hard metal borides, Ti3AlC2 and TiC phases, without any noticeable oxide phases. The 20 wt.% Ti3AlC2 additions to the Ni60A alloy coating exhibited minimum imperfections in microstructure with a porosity drop of 65.8%, and the highest microhardness which was enhanced by 64% to 924 HV0.515. After introducing of Ti3AlC2, the coefficient of friction decreased and appeared to distinguish itself by remaining minimal and stable at low-medium temperatures compared with an increase of more than 70% at high temperatures. Ni60A-10 wt.% Ti3AlC2 coating resulted in the lowest friction coefficient of approximately 0.45 from room temperature to 400 oC and it peaked to 0.78 at 800 oC, reducing by 19.6% and 6% compared to non-composite coating, respectively. The wear resistance of the composite coating was considerably improved with the increment of Ti3AlC2, and the coating with 20 wt.% Ti3AlC2 showed the most significant reduction in wear rate: 18.5% at room temperature, 45.2% at 200 oC, 37.2% at 400 oC, 60% at 600 oC, 90.8% at 800 oC. The lubricate layered Ti3AlC2 phases and the tribo-oxide film predominate composed of derivative NiO, Cr2O3 Al2O3 and TiO2 played a critical role in antifriction and wear resistance. The wear mechanisms were accordingly conducted as abrasion and adhesion wear at low-medium temperature and transferred into tribo-oxidation wear at elevated temperature.