Decarburization mechanisms of WC–Co during thermal spraying: Insights from controlled carbon loss and microstructure characterization

Investigation on influence of WC–Ni addition on rolling contact fatigue behavior of plasma sprayed Ni-based alloy coating

“…Compared to other carbides, the WC besides with high hardness is easily wetted by other molten metals and alloys (such as Ni metal, Co metal, Nibased alloy, and Co-based alloy). However, it is almost inevitable that partial WC can slightly decarburize to a soft W 2 C phase to influence resistance to wear and contact fatigue during the plasma spraying [30,31].…”

FIB-SEM Sectioning Study of Decarburization Products in the Microstructure of HVOF-Sprayed WC-Co Coatings

“…It is important to note that, as Li et al (Ref 21) demonstrated experimentally, the thermal dissolution of WC is primarily responsible for the occurrence of W 2 C (not oxidation) and that oxidation on the interface of the liquid binder (removal of C and accumulation of W) is necessary to yield metallic W. It is therefore reasonable to suggest that the high-aspect-ratio metallic W crystallites that have been observed in the relevant literature (Ref 4,5,29) can in fact be the fragments of the W-shells formed in-flight and mixed with the binder during the intense plastic deformation during the splat formation, upon the impingement of larger particles. Figure 10 features an exposed splat boundary which is covered by a continuous shell, resembling the morphology that was previously characterized as metallic W. The right part of Fig.…”

“…Ultimately, the thermal dissolution and decarburization of the carbides result in brittle coatings that offer poor structural durability (Ref 2,4,5). The mechanism of thermal dissolution of WC in Co and, ultimately, decarburization of WC-Co has been examined by a number of authors ( Ref 2,[4][5][6][7][8][9][10] and most of the pathways that are responsible have been adequately described. It has been established that the processes of thermal dissolution and oxidation of C are discrete and are both acting in synergy, when the Co binder is able to melt in-flight (Ref 4,11).…”

“…Affected WC grains are typically surrounded by the epitaxially grown semicarbide (W 2 C). Other dissolution-decarburization products are metallic tungsten (Ref 4,6,7) and solid solution g-phases M 6 C (e.g., Co 3 W 3 C) or M 12 C (Co 6 W 6 C) ( Ref 2,5), which are dispersed in the binder. Such g-phases can be formed during post-spray annealing (or equivalent secondary cooling conditions) (Ref [12][13][14] and are brittle, compromising the coating's wear resistance (Ref 5).…”

Microstructure evolution of thermal spray WC–Co interlayer during hot filament chemical vapor deposition of diamond thin films

“…Several dark lines can be found in these figures and nano-phases were distributed along these lines, which is called island boundary. According to Verdon's report [30] , the content of W, C and O along island boundary is higher than binder phase and nano-sized W can be observed near island boundary. This is because the surface of powder particle has the highest temperature and oxygen density.…”