Tribological properties of spark plasma sintered NiCr-Cr₂AlC composites at elevated temperature

In this work, layered ternary Cr₂AlC powders with high purity and a size of 0.5-1 μm were synthesized by solid-state reaction method. NiCr-Cr₂AlC composites have been prepared by spark plasma sintering (SPS) process. The composites' tribological properties were evaluated against alumina ball under dry sliding condition from room temperature to 600 °C. Compared with unmodified NiCr alloy, Cr2AlC addition has an effect on reduction of friction coefficient of NiCr-Cr₂AlC composites at the temperatures up to 400 °C. Especially, in comparison with NiCr alloy, the wear rates of NiCr-Cr₂AlC composites significantly decrease from 10^-4 mm³/(N·m) to 10^-5-10^-6 mm³/(N·m) from room temperature to 600 °C (except for 200 °C). The NiCr-20 wt % Cr2AlC composite exhibited excellent tribological properties with a friction coefficient of 0.3-0.4 and a wear rate of about 10^-6 mm³/(N·m) from 400 °C to 600 °C. Through the analysis of scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS), it is clarified that effective improvement of tribological properties of NiCr-Cr₂AlC composites is attributed to a glaze layer consisting of NiO, Cr₂O₃, Al₂O₃, and NiCr₂O₄, which is formed by tribo-oxidation during wear process.