Microstructural and mechanical properties of advanced HVOF-sprayed WC-based cermet coatings

The aim of this research was to investigate the microstructural and mechanical properties of WC-FeCrAl and WC-NiMoCrFeCo coatings deposited by high velocity oxygen fuel (HVOF) spraying. Microstructural characterizations of feedstock powders and coatings were carried out using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analysis. Image analysis techniques were utilized to measure the porosity level of the coatings, the volume fraction of different phases and the carbide grain size in the powders and coatings. Microhardness and indentation fracture toughness measurements were executed to evaluate the mechanical properties of the coatings. For comparison, the same experiments were performed on conventional WC-Co coating deposited by similar HVOF spraying parameters. WC-NiMoCrFeCo coating showed the maximum W2C/WC peak ratio of 40.42% in comparison to WC-FeCrAl (12.48%) and WC-Co (9.14%) coatings indicating a larger extent of W2C phase precipitated during solidification of WC-NiMoCrFeCo coating. The highest porosity level of 5.1 vol% was observed in the case of WC-FeCrAl coating due to the lower temperature of the powder particles causing the FeCrAl matrix not to be fully melted. The microhardness of WC-FeCrAl coating was found to be 1498 HV0.3 indicating higher value as compared to WC-Co and WC-NiMoCrFeCo coatings with 1305 and 1254 HV0.3, respectively. Moreover, a mean fracture toughness of 5.9 MPam1/2 was obtained for WC-Co, which was substantially greater than that for both WC-FeCrAl and WC-NiMoCrFeCo coatings with 3.1 and 2.8 MPam1/2, respectively.