Influence of long heat treatments on hardness and tribological behaviour of HVOF sprayed WC-CoCr and Cr3C2-25NiCr coatings

Thermally sprayed tungsten and chromium carbide-based coatings are widely applied in several industrial applications and in harsh environments where the tribological resistance is required, such as in many components for oil &gas or petrochemical industries. The microstructural stability of the coatings is a key feature for improving the working life of components exposed at high temperature during service. While WC and Cr 3C2 -based coatings are known to be suitable materials for low and high temperature, respectively, there is the need to know their behavior at intermediate temperature to make a proper selection in these cases. In the present study two different coatings, WC-10Co-4Cr and Cr 3C2 -25NiCr, were deposited by HVOF and analyzed comparing the as received conditions with the aged conditions after isothermal treatments. The effect of aging at temperatures in the range 250-40 as evaluated focusing on hardness behaviour in function of aging time and temperature. Furthermore, wear tests measurements were performed, before and after aging, for evaluating the exposure effect on the tribological properties of both coatings.