Actually, you do not need to worry about decarbonizing of tungsten carbide. It has very little to do with layer quality. These are only theories that have nothing in common with real coating technology. If you think that decarbonizing means a loss in layer hardness, then it is wrong. The real layer hardness is always significantly smaller than the hardness as well as grains from WC as also grains from W2C.

The properties of real layers are determined by a thousand different things, and the degree of decarbonation is one of the most unimportant factors. The most important are the four: particle size, particle temperature, particle velocity and gas atmosphere (oxidizing or reducing).

Thank you Mr. Verlotski, actually i was wondering because the WC particlues show a big changement and the ' lamellas ' arround the WC particlues become more and more importante by moving away from the substrate interface.

I think the following article can help you reduce the decarburization of WC.

Dear Haibin Wang,

In your work, you explore the coatings obtained by the HVOF method from WC-Co powders, sintered at different temperatures. The result was the fact that coatings sprayed from powders sintered at higher temperatures result in better quality. This is a correct observation, but it is completely incorrect to tie this observation to the degree of decarburization of tungsten carbide!

The WC-Co powders, sintered at low temperatures, have very porous agglomerates (you made excellent photos that prove this) and it is this porosity of agglomerates that causes a deterioration in the quality of HVOF coatings.

The high porosity of the agglomerates leads to the fact that the coating is looser, with weak boundaries of individual particles and a large proportion of oxides. It is the weak boundary of the particles that leads to a lower wear resistance of such coatings as compared to coatings sprayed from dense agglomerates. A side effect of spraying porous agglomerates is decarburization due to the oxidation of small carbide particles with flame oxygen (it is oxidation, not thermal decomposition, as many believe!). Indeed, it formally turns out that a poor coating has a lower content of higher tungsten carbide (WC) than a good one, but to say that the quality of the coating depends on the degree of carburization - this is a substitution of concepts.

The reason for the poor quality of HVOF-coatings from powders sintered at low temperatures is porous agglomerates, and decarburization is not the cause, but one of the consequences.

very clear answer, thanks!

Dear Vadim Verlotski,

Thanks so much for your comments on our work. I agree partly with your viewpoints. After spraying, the porous agglomerates can also become a dense coating layer because of the melting and impacting effects on the substrate. A higher porosity of the feedstock powder will definitely cause a higher decarburization in the coating. This can be ascribed to the higher oxygen concentration inside the feedstock particles and relatively higher melting degree of the surface area during thermal spraying.

In our recent work, we prepared a series of WC-Co feedstock powders containing different amounts of carbon. These powders were sintered at the same temperature to obtain a similar dense structure. Results show that the decarburization degree of coatings increases with the decrease in carbon content of the initial powders. However, the wear rate of the coatings first decreases and then increases with the increase of carbon content (i.e. decrease of decarburization ). The wear mechanisms change from brittle fracture to abrasive wear in a ploughing mode with the decrease of decarburization. This result proves that the decarburization has a significant effect on the wear resistance of WC-Co coatings. But it is true that the coating with a suitable amount of decarburization has the best wear resistance.

Use electron microscope (EBSD) .