Effects of load and speed on high-temperature tribological performance of electrodeposited hard Cr coating in trivalent-Cr bath

Abstract

ABSTRACT A chromium (Cr) coating was electrodeposited on 45 steel in trivalent-Cr bath. The morphologies and element distributions of the obtained coating were analysed using a scanning electronic microscope (SEM) and its configured energy dispersive spectrometer (EDS), respectively. The effects of normal load and rotation speed on the tribological performance of Cr coating at 300°C were analysed using a high-temperature friction tester. The results show that the Cr coating is mainly composed of Cr and Cr2O3 phases, and its average bonding force with the substrate is 9.20 N by the scratch method. Under the normal load of 2 N, the average coefficients of friction (COFs) of Cr coating at the rotation speeds of 300, 400 and 500 rpm are 0.70, 0.68 and 0.82, respectively; and the corresponding wear rates are 53.99, 97.38, and 46.17 μm3· N–1·mm–1, respectively, showing that the wear resistance of Cr coating at 500 rpm is the best among the three different rotational speeds. Moreover, the average COFs of Cr coating under the normal loads of 2, 4 and 6 N at 500 rpm are 0.82, 0.58 and 0.55, respectively; and the corresponding wear rates are 46.17, 84.54 and 71.19 μm3·N–1·mm–1, respectively. The wear mechanism of Cr coating at the rotation speeds of 300, 400 and 500 rpm is mainly adhesive wear; while that under the normal loads of 4 and 6 N is dominated by abrasive wear.