“Hybrid” plasma spraying of NiCrAlY+Al2O3+h-BN composite coatings for sliding wear applications

Although the microhardness (≈600 HV0.3) seemed rather insensitive to the composition of the coatings, their sliding wear resistance (tested under ball-on-disk configuration against corundum spheres at various temperatures) improved with increasing contents of Al2O3 and h-BN. The improvement was more significant at room temperature, but some beneficial effect also emerged when testing at 400 °C and 700 °C. Al2O3 and h-BN indeed promote the formation and enhance the mechanical stability of an oxide-based tribofilm, protecting the coating surface from direct contact with the counterbody. Specific tribofilm formation mechanisms however vary with temperature. Overall, coatings containing ≥5 wt% of Al2O3 and h-BN keep a reasonably stable wear rate (<5*10−4 mm3/(Nm)) over a wide temperature range.