Enhancement of wear and corrosion resistance of pulsed electrodeposited Ni–Mo amorphous/nanocrystalline coatings by heat treatment

Abstract

In this study, Ni–Mo coatings with various sodium molybdate concentrations were designed and successfully electrodeposited. The effects of treatment with different temperatures (200 °C,400 °C, 600 °C) on the microstructure and properties of the best-performing coating (4 g/L) were investigated. The surface morphologies, elemental content, and phase structure of the prepared coatings were obtained and analyzed by SEM, EDS, XRD, WFI and TEM. The Ni–Mo coating after heat treatment at 400 °C formed the compact and uniform amorphous/nanocrystalline coating. As shown by the electrochemical and wear test. Heat treatment at 400 °C improved the coating properties, and the corrosion current density was decreased by 66 % to 6.2532 × 10−7 A/cm2. The wear rate reduced from 8.3 × 10−4 mm3/N·m to 3.6 × 10−4 mm3/N·m, and the average friction coefficient minimized to 0.079. Additionally, compared with the as-deposited coating, the microhardness reaches the maximum (1048 HV). The formation of the oxide layer and the intermetallic compound MoNi on the surface of the coating plays a carrying and hindering role, thus the surface of the coating shows excellent wear and corrosion resistance. In addition, the corrosion inhibition mechanism during the heat treatment of Ni–Mo coatings was further explored.