Characteristics of HVOF-sprayed WC-Co cermet coatings affected by WC particle size and fuel/oxygen ratio

The effect of WC particle size and fuel/oxygen (F/O) ratio on the character istics of HVOF-sprayed WC-17 mass%Co coatings was investigated. The microst ructure of the coatings was dense regardless of F/O ratio, but became sligh tly inhomogeneous due to incomplete formation of splats with coarsening WC particle size. The unmelted WC particle size in the coatings manufactured w ith 1.53 mum mean particle size varied from 0.82 to 0.89 mum depending on F /O ratio, and the unmelted WC particle size in the coatings manufactured wi th 6.3 pm mean particle size ranged from 2.87 to 3.03 mum depending on F/O ratio. The sintered WC-17 mass%Co powder for thermal spraying consisted of WC, fee-Co and Co3W3C phases, but the HVOF-sprayed coatings consisted of WC , W2C and W phases. The rate of phase change during spraying was significan tly influenced by both raw particle size of WC and F/O ratio. As the amount of the decomposed W2C phase was more, the hardness of the coatings was hig her. On the contrary, as the amount of the decomposed W phase was more, the hardness of the coatings was rather lower. Consequently, it was revealed t hat the W2C phase was preferable but the W phase was detrimental to the har dness of the coatings.