Effect of heat treatment on the microstructure, mechanical property and tribological property of plasma-sprayed high temperature lubricating composite coating from nanostructured powder

Abstract

The nanostructured NiCrAlY-Mo-Ag composite coating was prepared by atmospheric plasma spraying (APS). The microstructure, mechanical property and tribological property of composite coatings before and after heat treatment were investigated. The coating had the least pores and cracks, the microstructure became more homogeneous and the precipitated phase increased obviously after 500 °C heat treatment. The size of precipitates became smaller (∼10 nm) and the volume fraction increased. Meanwhile, heat treatment could effectively improve the mechanical property and tribological property of composite coatings. The composite coating had the highest adhesive strength and microhardness of 62.8 MPa and 478.8 HV as well as excellent tribological property over a wide temperature range after 500 °C heat treatment. The friction process promoted the tribo-chemical reaction and formed the Ag2MoO4, Ag2Mo2O7, NiO and NiMoO4 on the worn surface, which could act as the high temperature lubricant and effectively improved the tribological property of composite coating at high temperature.