Effect of Ni-P electroless coating and heat treatment on tribological and corrosion properties of copper substrate

Copper is relatively soft metal and its wear and corrosion are considered to be a major factors of degradation of this metal. For this reason, when the higher wear and corrosion properties are needed, surface properties should be improved with different surface treatments. One of these methods is the applying of Ni-P electroless coating due to good mechanical properties, suitable corrosion resistance and its ability of heat treatment on Cu. In this research after the surface preparation of Cu, which included grinding, degreasing and surface activation, the specimens were dipped into commercial electroless nickel bath (SLOTONIP 70A) for 60 minutes. SEM images and the results of the EDS test confirmed the formation of Ni-P electroless coating (with 10.83 wt.% phosphorus) with a spherical structure. Applying the heat treatment increased the hardness of the coatings from 495 to 880 Vickers. XRD results showed this hardening is due to the formation of Ni crystal and Ni3P phases at this temperature in the coating. The study of wear resistance and corrosion property of coatings was also done using pin-on test and polarization tests, respectively. The results showed that the heat treatment improved the wear resistance of the coating, and the weight loss in the presence of the heat treated coating reduced to 76% due to increasing hardness and roughness of the coating by performing heat treatment. This effect was also quite noticeable in the SEM images of the wear surfaces. The corrosion results illustrated the Ni-P electroless coating significantly improved the Cu substrate corrosion performance, due to the dense spherical structure and without any pores of the coating, and in particular the amorphous phase of the coating, but the heat treatment reduced the corrosion property of the as deposited coating.