2001 Volume 42 Issue 5 Pages 833-837
The effect of WC particle size and fuel/oxygen (F/O) ratio on the characteristics of HVOF-sprayed WC–17 mass%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 \\micron mean particle size varied from 0.82 to 0.89 \\micron depending on F/O ratio, and the unmelted WC particle size in the coatings manufactured with 6.3 \\micron mean particle size ranged from 2.87 to 3.03 \\micron depending on F/O ratio. The sintered WC–17 mass%Co powder for thermal spraying consisted of WC, fcc-Co and Co3W3C phases, but the HVOF-sprayed coatings consisted of WC, W2C 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 W2C 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 W2C phase was preferable but the W phase was detrimental to the hardness of the coatings.
