Room-temperature wear resistance of tungsten carbide composite layers produced on grey cast iron by diffusion-controlled in situ reactions

Abstract

To improve the tribological properties of substrate surfaces, tungsten carbide composite layers were deposited on an iron-based alloy by diffusion-controlled in situ reaction (DIR) at different temperatures. The microstructure, phase composition and worn morphology of the composite layer were characterized by utilizing scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD) and confocal laser scanning microscopy (CLSM). A thin tungsten carbide layer with an interface crack was obtained at 1000 °C. At 1100 °C, the structure of the optimized composite layer contains a thin tungsten plate, a thicker tungsten carbide layer (300 μm) and a broad composite zone (2.5 mm) from top to bottom. The indexed phase composition for the carbide layer includes WC and α-Fe, and the composite zone consists of α-Fe, Fe6W6C, FeC and graphite. The tribological properties and mechanical properties of the composite layers were evaluated by using a ball-on-disk tribometer and a nanoindentation hardness tester. The average nanohardness of the tungsten plate, carbide layer, composite region and substrate is approximately 6.4 ± 1.0 GPa, 24.1 ± 3.4 GPa, 13.5 ± 2.4 GPa and 9.6 ± 1.2 GPa, respectively. Friction wear tests of all samples against GCr15 balls were performed at room temperature under 5, 10, 15 and 20 N normal loads. The carbide layer exhibits an average coefficient of friction of 0.39–0.63, which is higher than that of the substrate under an identical load due to the lubricating effect of the flake graphite phase in the substrate during the wear process. The specific wear rate of the carbide layer with a value of 2.69–4.33 is 18.5–34.3% of that of the substrate. The results of the worn morphology presence of particle deformation, extraction and crushing reveal that abrasive wear is a dominant abrasion mechanism for the carbide layer. For the substrate, adhesive wear plays an important role and is accompanied by abrasive wear.