Comparison of self-mated hardmetal coatings under dry sliding conditions up to 600 °C

Hardmetal coatings prepared by high velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. In the current systematic study the high-temperature oxidation and unidirectional sliding wear in dry and lubricated conditions were studied. Results for a series of experiments on self-mated pairs in dry conditions as part of that work are described in this paper. Coatings with nominal compositions WC-10%Co4%Cr, WC-(W,Cr)2C-7%Ni, Cr3C2-25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co were prepared with an ethylene-fuelled DJH 2700 HVOF spray gun. Electrolytic hard chromium (EHC) coatings and bulk (Ti,Mo)(C,N)-15%NiMo (TM10) hardmetal specimens were studied for comparison. The wear behaviour was investigated at room temperature, 400 and 600 °C. For the coatings sliding speeds were varied in the range 0.1–1 m/s for a wear distance of 5000 m and a normal force of 10 N. In some cases the WC- and (Ti,Mo)(C,N)-based coatings showed total wear rates (sum of wear rates of the rotating and stationary samples) of less than 10−6 mm3/Nm, i.e., comparable to values typically measured under mixed/boundary conditions. Coefficients of friction above 0.4 were found for all test conditions. The P × V values as an engineering parameter for coating application are discussed. The microstructures and the sliding wear behaviour of the (Ti,Mo)(C,N)-based coatings and the (Ti,Mo)(C,N)-15%NiMo hardmetal are compared.