Wear of thermal spray deposited low carbon steel coatings on aluminum alloys

Sliding wear behavior of low carbon steel coatings deposited on 319 Al alloy substrates using a plasma transfer wire arc (PTWA) thermal spraying process was studied. The coatings had a layered microstructure consisting of steel splats and FeO veins (0.5-3.0 μm thick) between them. Wear tests were performed using a pin-on-disc type wear tester within a load range of 10-75 N and a sliding speed range of 0.2-2.5 m/s against tool steel pins in a dry air atmosphere (7-10% RH). The wear rates, frictional forces, and surface temperatures were measured as a function of the applied load and sliding speed. In constant load tests, the wear rates decreased with increasing sliding velocity. The worn surfaces and the wear debris were characterized with optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and microhardness. It was found that the wear rates and mechanisms could be divided between four loading and velocity conditions. At low load and velocity, oxidation (formation of Fe₂O₃) was the main wear mechanism. The highest wear rates were associated with severe deformation of the steel splat tips and eventually splat fracture and fragmentation and also formation of a mixture of iron oxides that occurred at low velocities and high loads. At high loads and velocities the wear rates decreased, this was associated with the formation of thick protective oxide film and hardening of the sliding surface.