Tribological characteristics and wear mechanisms of NiMoAl composite coatings in reversible temperature cycles from RT to 900 °C

In an effort to investigate the influence of temperature cycles and of tribo-layers formed at high temperatures on the tribological properties and mechanisms of wide-temperature range lubricating materials at low temperatures, the tribological characteristics of atmospheric plasma sprayed NiMoAl-6Al2O310Ag composite coatings in reversible temperature cycles were investigated. The results indicated that the tribo-layers formed at low temperature have no evident effect on the friction coefficients during subsequent testing at elevated temperatures, while the lubricating film formed at 900 °C decreased the friction coefficient in a subsequent RT test evidently. The lowest friction coefficient at 900 °C was attributed to the formation of lubricating film on the worn surface, which was mainly consisting of NiO and Ag2MoO4 nanoparticles.