Synthesis and characterization of electroless Ni-P-ZrO2-TiO2 coating on Steel substrate

In this study, the effects of zirconia and titania particles on the abrasion behavior and hardness of Ni-P and Ni-P-ZrO2 coatings on ST37 substrate by electroless technique were investigated. For this purpose, Ni-P-ZrO2 composite coatings were precipitated at five different concentrations of 1 to 5 g/l of reinforcing particle, and then, after examining the best specimen in terms of hardness, the effect of TiO2 particles in five concentrations of 1 to 5 g/l was studied as a booster alongside ZrO2 particles. The coatings were heat-treated for 1 hour at 400 °C. Resistance to wear and friction coefficient of coatings were evaluated by pin on disk test. The surface and cross-section of coatings, as well as the abrasion lines, were examined using a scanning electron microscope (SEM) equipped with an EDS test. The X-ray diffraction (XRD) test was also used to examine the coprecipitation of the reinforcing particles and phase transformations in the coatings. The results showed that the heat treatment resulted in increased hardness. Also, increasing the concentration of ZrO2 particles in the bath from 1 g/l to 3 g/l resulted in improved hardness of the coating and the use of TiO2 up to 2 g/l along with ZrO2 resulted in improved Ni-P-ZrO2 coating hardness, so that increasing TiO2 concentration to 2 g/l resulted in an increase in the hardness from 702 HV0.1 in the Ni-P-ZrO2 (3 g/l) sample to 813 HV0.1 in the Ni-P-ZrO2 (3 g/l) -TiO2 (2 g/l) sample.