Controlling the porosity to enhance the high-temperature tribological performance of plasma-sprayed NiCr–Cr3C2–BaF2/CaF2 coating by adopting axial feeding

To significantly improve high-temperature tribological properties, plasma-sprayed NiCr–Cr 3 C 2 –BaF 2 /CaF 2 coatings were fabricated by axial feeding (named as A-coating) in present work. The microstructure and tribological behavior at elevated temperature were methodically investigated, with the coatings prepared by radial feeding serving (named as R-coating) as a comparison. Moreover, the influence of thermal exposure at 800 °C on the high-temperature tribological behavior was further discussed. It was found that the density as well as hardness of the coating was obviously improved due to the enhanced melting state and flight speed of particles led by axial feeding. The results also indicated that thermal oxidation took a dual effect on high-temperature tribological performance. The formation of hard oxides resulting from oxidation dramatically improved the hardness, however, it in turn consumed binder phase NiCr in the coatings, degrading cohesion strength. Accordingly, wear rate dramatically increased with the extension of thermal oxidation in the both case of A-coatings and R-coatings. Despite of all of this, wear resistance of A-coatings is 28.1 % better than R-coatings thanks to excellent resistance to thermal oxidation aroused by low porosity. This study systemically shed light on the effect of thermal oxidation on tribological behavior, and meanwhile provided effective methodology for enhancing high-temperature tribological performance.