Evaluation of Wear Behavior of Ni-P-Ag Composite Coating at High Temperature

In this research, wear mechanisms and tribological properties of Ni-P and Ni-P-Ag electroless coatings at high temperatures have been studied. At First, the surface of carbon steel samples were prepared and then they were entered into the Nickel phosphorus electroless bath (with and without silver particles) to deposit Ni-P-Ag and Ni-P coatings on the substrates. After heat treatment at 400 °C, the hardness of the coatings was measured using a microhardness tester and the tribological tests were implemented by Pin on disc method at 500 °C. The microstructure of the coatings was also evaluated by XRD analysis and the surface morphology, cross-section and wear scars of the coatings were studied by using an optical microscope a scanning electron microscope equipped with EDS analyzer. The results showed that the co-deposition of silver particles in Ni-P coating led to the self-lubricating property as the result of the formation of silver rich tribofilms. It can be related to the diffusion of silver toward the sliding surface of Ni–P–Ag coating at high temperatures. Also, abrasive wear, surface oxidation and the plastic deformation were also recognized as the high temperature wear mechanisms in Ni-P-Ag coating.