Effects of solid lubricant content on the microstructure and properties of NiCr/Cr3C2-BaF2•CaF2 composite coatings

NiCr/Cr3C2 and NiCr/BaF2 center dot CaF2 composite powders were prepared with pressurized hydrogen reduction and solid state alloying processes. The NiCr/Cr3C2-BaF2 center dot CaF2 coatings with different contents of BaF2 center dot CaF2 eutectic were fabricated by plasma spray technology using the synthesised powders. The microstructure. mechanical and tribological properties of the coatings were systematically investigated. The results show that the microhardness and tensile strength of the coatings decrease with the increase of BaF2 center dot CaF2 eutectic content. The coating containing 10 wt.% eutectic shows a maximum tribological properties at elevated temperatures, depending on the physical and chemical match between the solid lubricant and the matrix materials as well as fine, dense microstructure of this composite coating, and partially attributed to the protection of NiCr layer of the composite powders which decreased the oxidation, decarburization and ablation of Cr3C2. With further increasing of BaF2 center dot CaF2 content, the wear rates of NiCr/Cr3C2-BaF2 center dot CaF2 coatings increase rapidly, due to the quantitive degradation of mechanical properties. (C) 2009 Elsevier B.V. All rights reserved.