Characteristics of HVOF-Sprayed WC-Co Cermet Coatings Affected by WC Particle Size and Fuel/Oxygen Ratio

摘要

The effect of WC particle size and fuel/oxygen (F/O) ratio on the characteristics of HVOF-sprayed WC-l7 mass percent Co coatings was investigated. The microstructure of the coatings was dense regardless of F/O ratio, but became slightly inhomogeneous due to incomplete formation of splats with coarsening WC particle size. The unmelted WC particle size in the coatings manufactured with 1.53 #mu#m mean particle size varied from 0.82 to 0.89 #mu#m depending on F/O ratio, and the unmelted WC particle size in the coatings manufactured with 6.3 #mu#m mean particle size ranged from 2.87 to 3.03 #mu#m depending on F/O ratio. The sintered WC-17 mass percent Co powder for thermal spraying consisted of WC, fcc-Co and Co_3W_3C phases, but the HVOF-sprayed coatings consisted of WC, W_2C and W phases. The rate of phase change during spraying was significantly influenced by both raw particle size of WC and F/O ratio. As the amount of the decomposed W_2C phase was more, the hardness of the coatings was higher. 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 that the W_2C phase was preferable but the W phase was detrimental to the hardness of the coatings.