Fretting wear of HVOF Ni–Cr based alloy deposited on SAE 1045 steel

The present study has been carried out in order to investigate the fretting wear performance of a Ni–Cr based alloy, containing B and C, deposited onto a SAE 1045 steel substrate by HVOF thermal spray. Tests were conducted on both the uncoated and coated substrate, under unlubricated dry conditions, at different applied normal loads, cycles and amplitudes in order to analyze the influence of these parameters on the wear behavior. It has been determined that the coated substrate exhibits a very good tribological performance in comparison to the uncoated substrate. The decrease of the wear volume of the coated substrate is of ~ 95–97% of that determined for the uncoated substrate. The increase in the fretting wear resistance provided by the coating has been attributed to the presence of a large amount of dispersed Ni and Cr carbide and/or borides in the Ni–Co matrix. Examination of the fretted surfaces by SEM indicates that the uncoated substrate undergoes an abrasive wear mechanism. On the contrary, it has been observed that the wear mechanism of the coating–substrate system depends on the magnitude of the applied load. At loads of 30 N, a polishing wear mechanism has been determined, whereas between 40 and 50 N, the initiation and propagation of micro-cracks takes place through the coating. The numerical integration of the wear scar depth profile curves employed in the present work allows an estimation of the wear volume which is in good agreement with that determined experimentally by means of 3D profilometry. It has been determined that, at a constant wear amplitude the wear volume increases with the applied normal load and that at under constant load conditions, the wear volume decreases as the wear test amplitude also decreases, becoming insignificant when it is less than ~ 100 µm.