An Investigation on the Wear and Corrosion Behavior of HVOF-Sprayed WC-12Co-Al₂O₃ Cermet Coating

The aim of the present study is to develop thermally sprayable WC-12Co and WC-12Co-xAl₂O₃ (x = 10 and 15 wt.%) cermet coatings on steel substrate (SS 304) by high-velocity oxy fuel (HVOF) method. Influence of Al₂O₃ addition on the wear and corrosion behavior of WC-12Co coating has been studied. The microstructure and chemical composition of the coatings were analyzed using field emission scanning electron microscope (FESEM), and phase identification was carried out using x-ray diffraction (XRD) studies. The morphology of the coating appears as coarse granular structure. The XRD studies revealed the presence of hexagonal WC phase along with η-Co₆W₆C phase. It has been observed from the microhardness measurements, that the values gradually increase from 950 to 1300 HK with the addition of Al₂O₃ from 0 to 15 wt.%. The wear rate of WC-12Co-15Al₂O₃ (3.19 × 10⁻⁶ mm³/Nm) and WC-12Co-10Al₂O₃ (5.26 × 10⁻⁶ mm³/Nm) coatings was seen to be one order of magnitude lower than that of WC-12Co (2.9 × 10⁻⁵ mm³/Nm) coating. The polarization studies revealed that WC-12Co-15Al₂O₃ cermet coating showed superior corrosion protection than that of WC-12Co-10Al₂O₃ and WC-12Co coatings. This has been attributed to the gradual decrease in the porosity levels with an increase in Al₂O₃ content which is supported by morphology studies. The microhardness and wear behavior of WC-12Co-Al₂O₃ coatings are equivalent to those of hard chrome suggesting the possibility of its replacement.