The effects of Cr2O3 particles on the microstructure and wear-resistant properties of electrodeposited CoNiP coatings

In this paper, CoNiP and CoNiP/Cr2O3 composite coatings were successfully electrodeposited onto Cr-Ni-Mo-V steels substrate by using direct current (DC). The effects of Cr2O3 particle contents and heat treatment on the microstructures, coating compositions, microhardness and wear resistance properties of the coatings were investigated by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Vickers hardness tester and ball-on-disk tribometer. The results showed that the coatings transformed from amorphous to crystalline structures by heat treatment at 350 °C, and their microhardness significantly increased. The contents of Cr2O3 particles in the coatings reached a stable value for the coatings deposited in the plating bath with concentration of Cr2O3 higher than 15 g/L, meanwhile the coating deposited in the plating bath of 15 g/L Cr2O3 (CoNiP-15 g/L Cr2O3) possessed the highest microhardness. Wear test results at room temperature, 200, 300, 400 and 500 °C showed that the wear resistance of the coatings was improved by the addition of Cr2O3 particles, and the CoNiP-15 g/L Cr2O3 coating had the lowest coefficient of friction and wear loss among all the samples.