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.