The literature provides different criteria related to coatings which are considered conventional and which one nanoestructurated in relation to grain size. So Is there a single approach to the classification of the WC-Co coatings deposited by thermal spray in terms of sizes of carbide grains in conventional or nanometric coatings?
WC grain size in the coatings WC-Co or WC-Co-Cr equal to the size of the grains of the powders. In turn, the WC grain size of powders WC-Co is equal to the grain size of the starting powder WC, obtained by chemical reduction of the tungsten oxide and the carbonization. All these starting WC powder having a particle size in the range of 0.5-10 microns, that is classified as "micro". Use of the term "nano" with regard to the thermal spraying - no more than advertising.
Generally speaking, the term nanostructured is attributed to sub-micron size of the individual particles that are presented in a powder grain. If this nanostructure remains after spraying the coating can be called nanostructured also. See the attached article from the European Commission for further concept details.
It is very kind of you Carlos. I asked because I found different approaches in terms of size to define nanostructure on cemented carbides, mainly in 200-500 nm. Very interesting the article that you send it to us, it will be very useful for MIguel and the article that you will receive shortly. As always for us will be very useful with your experience and your collaboration. Reiterating my respects. A hug
If we talk about pure nano-WC-Co based powders then WC grain size must be close to 100nm which is very difficult to obtain. These powders are generally very costly 300-400 USD are might contain W2C & Co3W3C pases.The powders having WC grain size 200-500 nm are known as near-nano structured powders are generally cost about 180-250 USD. Near Nanostructuredpowders are generally free from unwanted phases like W2C, W, eta phases which is also good for the developed coatings.
To obtained pure nano-WC-Co coatings these days HVAF process is being adopted and peoples are avoiding plasma as well as HVOF process. You can find research work of L.M. Berger on HVAF coatings.
Very gentle and very interesting your considerations. I meant to do just that, different investigators, different viewpoints. As feared, the true nanostructured compound; below 100 nm. I will review the work of Dr. Berger who with the same courtesy has seen fit to send its research reports. We'll keep in touch. Thank you a lot
What is your application? Why are you focussing on true nanostructured coatings, its not always beneficial to go with pure nano-materials. Some times micron, near nano or multimodal materials work better. Which thermal spray technique you want to use? Kindly share your problem....
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