Tribological Characteristic of APS NiAl Coatings Inocorparation of Nanostructured MoO ₃/Bi ₂O ₃ at Elevated Temperatures

Abstract

The MoO_3-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 NiAl- nanostructured MoO_3-Bi₂O₃ composite coatings were fabricated via atmospheric plasma spraying (APS). The impact of the ratio of the MoO_3-Bi₂O₃ binary oxides on the mechanical and tribological properties at elevated temperatures was investigated. The results show that the friction coefficients and wear rates of composite coating with a MoO_3-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 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.

Keywords: NiAl Composite Coating, High Temperature, Tribo-Chemical Reaction, Synergistic Lubricating Effect