2001 Volume 42 Issue 5 Pages 870-875
This study was performed to investigate the influence of hydrogen-to-oxygen ratio (F/O=3.2, 3.0, 2.8, 2.6) and heat treatment on the characteristics (microstructure, decomposition rate, hardness, and mass loss by erosion) of HVOF (high velocity oxy-fuel)-sprayed coatings using NiCr-coated Cr3C2 composite powder. Decomposition of the Cr3C2 occurred regardless of F/O ratio during spraying. The degree of decomposition of the coatings was increased with decreasing the F/O ratio and with increasing heat-treating temperature. Consequently, after heat treatment at 1000°C about 90% of the coatings adjacent to the surface consisted of Cr7C3 phase and also about 70% of the inner coatings was this phase. Microhardness of the as-sprayed coatings was varied from 987 to 1037 kgf/mm2 with F/O ratio, and the coatings sprayed with F/O=3.0 was the highest (Hv300=1037), and the hardness was increased to 1340 kgf/mm2 after heat treatment at 600°C but it was suddenly decreased after heat treatment from 800 to 1000°C. Erosion resistance was the highest at the coatings sprayed with F/O=3.0. And erosion resistance was improved about 40% than that of as-sprayed coatings after heat treatment at 600°C.
