Improvement in tribological properties of plasma-sprayed Cr3C2–NiCr coating followed by electroless Ni-based alloy plating

Electroless-plated Ni-based alloy coatings, Ni, Ni–Co and Ni–Mo coatings with thickness less than 5 μm were deposited on surfaces of plasma-sprayed Cr3C2–NiCr coating. The tribological properties of these electroless-plated coatings against the as-sprayed Cr3C2–NiCr coating as sliding pairs were investigated with a block-on-ring arrangement in air at room temperature. It was found that all the Ni-based alloy coatings effectively improved the tribological properties of the Cr3C2–NiCr coating. Especially when the Cr3C2–NiCr coatings plated with Ni–Co and Ni–Mo coatings were against the as-sprayed Cr3C2–NiCr coating as sliding pairs, friction coefficients of 0.10 to 0.13 and coefficients wear coefficients less than 10−6 mm3·N−1·m−1 were achieved. Through examination and analysis of the worn surfaces employing scanning electron microscopy and X-ray photoelectron spectrometer, the improvement in tribological properties of the Cr3C2–NiCr coating may be attributed to the transformation of wear mechanism and the formation of CrO3 on the worn surfaces.