Tribological characteristic of atmospheric plasma sprayed NiAl coatings with addition of nanostructured MoO3/Bi2O3 binary oxides as high temperature lubricant

Abstract

The MoO3–Bi2O3 binary oxides with higher ion potential difference, lower interaction parameters and lower melting points were selected as the high temperature lubricants for NiAl-based coating to further improve the tribological properties in wide temperature range. The friction and wear performance at low and medium temperatures (400–600 °C) is significantly improved compared to previous works. The NiAl-nanostructured MoO3/Bi2O3 composite coatings were fabricated via atmospheric plasma spraying (APS). The impact of the ratio of the MoO3/Bi2O3 binary oxides on the mechanical and tribological properties at high temperatures was investigated. The results show that the friction coefficients and wear rates of composite coating with a MoO3:Bi2O3 ratio of 1:1 were significantly reduced from room temperature to 800 °C compare with our previous work, where, the friction coefficient and wear rate were reduced to lower than 0.22 and 2.8 × 10−5 mm3·(N·m)-1 at 400–800 °C. The decrease of friction coefficient at room temperature is due to the lower melting points of MoO3 and Bi2O3 than that of other oxides. While above 400 °C, the improved friction and wear performance was attributed to the formation of new easy-to-shear ternary oxides as NiMoO4, Bi2Mo3O12 and Bi2MoO6 on the worn surfaces through tribo–chemical reactions, which works synergistically to reduce the friction coefficients and wear rate.