Relationship between annealing time and the mechanical, tribological and corrosion properties of Ni–Mo/diamond coatings

The relationship between structure and mechanical, tribological and corrosion properties of coatings is investigated by adjusting the annealing time (750 °C for 1–10 h). Results exhibit that the coatings mainly consist of Ni(Mo) and Mo2C, and MoC is formed after long time annealing (≥4 h). The hardness of coatings decreases from 9.3 GPa to 5.9 GPa with the extension of annealing time, and the inversion relationship between strength and toughness (0.19–0.17) is observed owing to the decline of elastic recovery. The highest wear rate of coatings is about 13.6 × 10−6 mm3 N−1 m−1, and most of them under the applied load of 1.96 N and 3.92 N are in the range of 2.1–6.3 × 10−6 mm3 N−1 m−1. Meanwhile, the wear resistance of coatings annealed for 1–4 h is better than those annealed for longer time (6–10 h), and the change of it is proportional to the hardness and elasticity recovery. In addition, the corrosion resistance of coatings in 3.5 wt% NaCl solution decreases with annealing time due to the grain growth, the uneven distribution of composition and the increase of porosity.