Tribological investigation of HVOF-spray Cr3C2-25NiCr and WC-10Co-4Cr coated turbine steel under varied slurry erosion conditions

In this work, high velocity oxy fuel (HVOF) method based spray coatings namely Cr3C2-25NiCr and WC-10Co-4Cr have been deposited on AISI304 turbine steels. An attempt has been made to analyze the coatings under accelerated slurry erosion conditions by employing a laboratory-developed slurry erosion testing set-up. The testing has been performed under varied conditions of slurry concentration, impact velocity and impact angle using the Taguchi approach. The microstructure of coating powder, erodent particles and deposited coatings have been studied using a scanning electron microscope (SEM) analysis. Erosion tests indicated that HVOF-spray Cr3C2-25NiCr and WC-10Co-4Cr coatings have been deposited on AISI304 steel exhibited significant improvements in the erosion resistance of AISI304 steel. The possible reason for such behaviour could be higher microhardness of HVOF-spray coatings in comparison with AISI304 bare steel. From SEM images of the samples taken prior and post slurry erosion tests, it has been observed that Cr3C2-25NiCr coating exhibited mixed (ductile and brittle) behaviour, though the WC-10Co-4Cr coating mostly demonstrated ductile behavior under conditions for erosion from the slurry. Apart from that, an attempt has been made to develop a functional equation based on the regression approach which could be employed to assess the erosion wear rate under a set of conditions. The predicted erosion wear results under varied conditions are in close relationship to experimental values.