Mechanical Property, Tribological Behavior and Oxidation Resistance of Cr-N Gradient Coating Prepared by Low-Temperature Microwave Plasma Nitriding
摘要
The components such as the cylinder piston of automotives are subjected to complex working conditions including friction and oxidation, which impose high requirements on their resistance to friction and oxidation. The Cr coating is usually used as the material for protecting the components of automobile cylinders. In order to further enhance its service performance, microwave plasma nitriding (MPN) was employed to prepare Cr-N gradient coating on the electroplated Cr coating at a low temperature of 700 °C. The mechanical property, tribological behavior and oxidation resistance of the coatings before and after nitriding were systematically characterized, compared and discussed in detail. After MPN treatment, the surface roughness of the coating decreased, with defects and scratches in the pre-nitriding coating repaired. Moreover, the mechanical property of the coating showed significant enhancement, as its hardness remarkably reached 28.68 GPa while the modulus attained an impressive 412.83 GPa. Tribological tests revealed that the Cr-N coating experienced both adhesive and abrasive wear mechanisms, achieving a friction coefficient reduction from 0.543 to 0.359 alongside a substantial decrease in worn volume from 1.36 × 107 to 1.34 × 106 μm3. Oxidation tests demonstrated that the Cr-N coating retained its structural integrity, free from cracks and spalling after being exposed to an Ar/O2 atmosphere at 1000 °C for 3 h, with the cross-sectional oxygen content distinctly lower than that of the Cr coating. Prospectively, the Cr-N coating prepared via MPN exhibits dramatical potential for reinforcing the durability of the substrate, presenting a novel approach for developing advanced coatings with exceptional mechanical strength, wear resistance and oxidation protection.