Electrodeposition of nanocrystalline Ni and NiCr alloy coatings: Effects of Cr content on microhardness and wear resistance improvement

Abstract

The safety and reliability of high-speed trains depend on the brake disc. In order to improve the lifetime of brake disc and reduce the waste of resources, a coating with higher microhardness and well wear resistance is urgently needed. The effect of chromium content on the microstructure, microhardness and wear resistance of NiCr coating has been studied. Nano-crystalline Ni and NiCr coatings with superior mechanical properties were successfully prepared on the 30CrNiMo steel substrate by pulse current electrodeposition method. The inclusion of formic acid and sodium citrate was found to significantly expedite the co-deposition of Ni and Cr. The NiCr coatings with various Cr contents were prepared at current densities ranging from 200 to 300 mA/cm2. These coatings significantly enhance microhardness and wear resistance of the substrate. The microhardness of the NiCr coating increased to 603 HV, outperforming pure Ni coating by 119 HV. Additionally, the wear rate of the NiCr coating decreased by 50% at a load of 10 N in comparison to the Ni coating. The high microhardness is attributed to grain refinement and solution strengthening. This study successfully addresses the challenges associated with electrodepositing Ni-based coatings on 30CrNiMo steel substrate and lays a theoretical foundation for the utilization of Ni-based coatings to enhance the tribological properties of materials used in high-speed train brake disc.