Part II: tribological performance of Cr3C2-25% NiCr reactive plasma sprayed coatings deposited at different pressures

The present work has been undertaken to determine the sliding wear behavior of plasma sprayed coatings deposited using different pressure conditions, ranging from 300–1200 mbars, in a nitrogen atmosphere using a controlled atmosphere plasma spray system (CAPS). The spraying distance and the substrate temperature during deposition were also varied. Sliding wear tests were performed against WC-6% Co balls using a pin-on-disc tribometer. The highest sliding wear resistance was obtained for the samples processed at a pressure of 1200 mbar, a spraying distance of 120 mm and substrate heating to 600°C, for which an average value for the specific wear coefficient, k, of 5.72 E-07 mm3/N m was determined. An increase in the spraying distance from 120 to 140 mm, keeping all the other parameters constant produced an increase in the wear volume of 33%. However, for the same spraying pressure and distance, cooling the substrate resulted in an increase in the wear volume of nearly 1125% when compared to the coating produced with optimum conditions. In addition, a decrease in wear resistance of 83% occurred when the pressure was varied between 1200 to 300 mbar, which was attributed to a decrease in the carbide deposition efficiency, ξ, defined as the relationship between the (Cr3C2) coating/(Cr3C2) powder. This new material, consisting of chromium carbide, Ni–Cr, carbo-nitride phase and graphitic carbon had excellent sliding wear resistance that was approximately 23 times better than that reported for conventional HVOF Cr3C2–25NiCr coatings.