Improvement in tribological properties of plasma-sprayed Cr 3C 2–NiCr coating followed by electroless Ni-based alloy plating

Abstract

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 Cr 3C 2–NiCr coating. The tribological properties of these electroless-plated coatings against the as-sprayed Cr 3C 2–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 Cr 3C 2–NiCr coating. Especially when the Cr 3C 2–NiCr coatings plated with Ni–Co and Ni–Mo coatings were against the as-sprayed Cr 3C 2–NiCr coating as sliding pairs, friction coefficients of 0.10 to 0.13 and coefficients wear coefficients less than 10 −6 mm 3·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 Cr 3C 2–NiCr coating may be attributed to the transformation of wear mechanism and the formation of CrO 3 on the worn surfaces.