Microstructure and Properties Characterization of WC-Co-Cr Thermal Spray Coatings

Abstract

WC-Co-Cr coatings are widely employed due to their improved wear resistance and mechanical properties, however, the properties and performance of these coatings are compromised by the processing parameters of each spraying technique. Therefore, this study is aimed to evaluate and determine the effect of the deposition parameters on the properties and microstructural characteristics of WC-Co-Cr coatings using a more economical thermal spray technique. In particular, the influence of flame spray parameters on the microstructure, crystal structure, hardness, and sliding wear resistance of WC- Co-Cr coatings was examined. Two parameters were considered: Type of flame (reducing, neutral and oxidizing), and the spray torch nozzle exit area. Results indicated that WC particles undergo considerable degree of decarburization and dissolution during spraying, showing substantial amounts of W 2 C, W, and Co 3 W 3 C, for all the considered conditions. However, the extent of phase transformation depended largely on the flame chemistry. The microstructure of the coatings was mainly affected by the spray nozzle. Regarding the sliding wear behavior, the coatings with uniform distribution of hard particles provided the best wear resistance. The decomposition of WC into W 2 C phase seems to have meaningless significance in the mass loss, nevertheless, the WC phase transformation to metallic tungsten and η-phase (Co 3 W 3 C) produce higher wear rates due to deficiency of carbide particles and embrittlement of the binder phase which induces cracking and delamination of the splats.