Characteristics of HVOF-sprayed Cr3C2 (20 mass % NiCr) coatings part 2: Effect of heat treatment of the coatings

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) o f HVOF (high velocity oxy-fuel)-sprayed coatings using NiCr-coated Cr3C2 co mposite 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 temperatur e. Consequently, after heat treatment at 1000 degreesC about 90% of the coa tings adjacent to the surface consisted of Cr7C3 phase and also about 70% o f the inner coatings was this phase. Microhardness of the as-sprayed coatin gs was varied from 987 to 1037 kgf/mm(2) with F/O ratio. and the coatings s prayed with F/O = 3.0 was the highest (H-V300 = 1037), and the hardness was increased to 1340 kgf/mm(2) after heat treatment at 600 degreesC but it wa s suddenly decreased after heat treatment from 800 to 1000 degreesC. Erosio n resistance was the highest at the coatings sprayed with F/O = 3.0. And er osion resistance was improved about 40% than that of as-sprayed coatings af ter heat treatment at 600 degreesC.