Preparation and tribological properties of NiCr/Cr3C2 -BaF2·CaF2

BaF2·CaF2 eutectic and Cr3C2 composite powders coated with NiCr alloy were prepared with the technology of hydrogen reduction hydrothermal process combined with a solid state alloying. NiCr/Cr3C2 -BaF2·CaF2 coating was produced by atmospheric plasma spray (APS) using the prepared powders. The microstructure and phase compositions of the powders as well as the deposited coating were analyzed by SEM and XRD, while the friction and wear behavior of the coatings from room temperature to 500C were evaluated using a SRV high temperature tribometer. The NiCr/Cr3C2 -BaF2·CaF2 composite coating exhibited excellent wear-resistant performance by high temperature self-lubrication with high microhardness and cohesive strength. Oxidation, decarburization and ablation of Cr3C2-BaF2·CaF2 during spray were avoided due to the protection by NiCr layer. The friction coefficient of the coating, 0.740.02 at room temperature, gradually decreased with the increase of temperature, a small value of 0.380.03 was achieved as temperature up to 500C, which led to a significant decrease of wear rates of both of the coating and the Si3N4 ball. BaF2·CaF2 eutectic underwent a transition with decrease of shear strength at high temperature from brittle to plastic state, which resulted in the formation on a continuous lubricating layer in the wear track at 500C.