Quantitative evaluation of the decarburization and microstructure evolution of WC-Co during plasma spraying

The major hurdle that limits extensive application of thermal sprayed WC-Co coatings is the undesirable phase changes from WC to W ₂C or even W due to loss of carbon. This study investigated quantitatively the decarburization of WC in both in-flight and coating formation stages during atmospheric plasma spraying. The microstructure evolution of WC particles accompanying the decarburization was also investigated. Results showed that decomposition and oxidation of WC to W ₂C predominantly occurred in the in-flight stage (75.82%), while remnant 24.18% occurred during the coating formation stage. Further carbon loss during the coating formation stage of WC-Co droplets is dependent significantly on the temperature of the substrate/pre-coating. Most of the irregular WC particles turned into rounded morphology with a significant decrease in size. W ₂C precipitated from the liquid matrix showed either columnar growth or epitaxial growth on WC substrate.