Tribological properties of HVOF sprayed WC-Cr3C2-Ni coating

The deposition of WC-Cr3C2-Ni coating was done by High velocity Oxy Fuel (HVOF) technique. Microstructural and mechanical properties of coating were measured. Friction and abrasive wear response was evaluated with varying loads and sliding velocities. An increase of 1.6-2 times in friction coefficient (COF) was noted with rise in load and COF reduced by around 15%-20% for rise in sliding velocity. Abrasion wear rate reduced by around 2 times with rise in sliding velocity. The decrease in wear rate and COF at higher sliding velocity was due to lubricating properties of tribo oxides formed due to frictional heating. The composition of tribo oxides on worn surface as indicated by XRD analysis revealed different oxides of tungsten, chromium and nickel such as WO3, W3O8, NiO2, NiWO4, NiCr2O4 and CrO2. With increasing load, carbide pull out, delamination cracking, carbide fracture and inter splat fracture were the dominating mechanisms of material removal, whereas with increasing velocity tribo oxidation leading to oxidative wear was dominant wear mechanism.