Study of microstructure, phase and microhardness distribution of HVOF sprayed multi-modal structured and conventional WC–17Co coatings

Multi-modal structured cermet coating was developed from agglomerated nanostructured WC–17Co powder feedstock by high velocity oxy-fuel (HVOF) spray process. A denser coating structure as compared to the conventional coating was observed. A multi-modal microstructure of very fine nanostructured grains coupled with some micron grains structure was analysed by scanning electron microscope (SEM). X-ray diffractometer (XRD) spectra of the as-sprayed multi-modal structured coatings revealed presence of substantial quantity of amorphous phase which was representative of the nano grains structure observed by the SEM analysis. Weibull analysis revealed bimodal distribution of Vickers microhardness values, under a 10 g indentation load, of the multi-modal structured coating. Such distribution was attributed to the presence of melted and unmelted phases in the resultant coating produced from the nanostructured powder feedstock.