Effect of diamond-like carbon self-lubricant coatings on wear resistance of powder metallurgy products

The iron-based parts with different densities were prepared by powder metallurgy, and then were densified by ultrasonic shot peening. The diamond-like carbon (DLC) self-lubricating coatings were deposited on the sintered and shot peening samples with different densities by physical vapor deposition, and the binding force and tribological properties of DLC coatings were studied. The results show that the matrix with high density has the better binding force with coatings, and the matrix treated with shot peening shows much better binding force, which is about 28.0 N. However, in the process of ultrasonic shot peening, the surface layers of the matrix produce huge compressive stress, and the accumulation of residual stress in the matrix and the coatings may lead to the premature failure of coatings. To reduce the stress accumulation caused by ultrasonic shot peening process, the samples are annealed after shot peening, and show much higher binding force between the matrix and coatings, about 54.5 N. The frictional properties of samples with DLC coating are greatly improved, the friction coefficient of the samples without coatings is about 0.60, and that of the sintered samples with DLC coatings is about 0.15. Compared with the DLC coatings on the matrix after shot peening (friction coefficient 0.13 ~ 0.17), the lubricity of DLC coatings on the annealed matrix is more stable (friction coefficient 0.13).