How do ceramic coatings adher to the base substrate and what happens in the small diffusion zone? How are the binding properties?
(Especially between TaC coatings and Graphite as base material)
Thank you.
The maximum possible adhesion of the coating to the substrate cannot be higher than the tensile strength of the substrate itself. In the case of a graphite substrate, this is a very small value (up to 20 MPa). In addition, it is practically impossible to apply coatings on graphite by thermal spraying, since the graphite surface can "withstand" only minimal shear stresses at the boundary between the coating and the substrate, and these stresses cannot be avoided during thermal spraying.
Thanks Vadim Verlotski .
Does this also apply to spraying on an emulsion at room temperature and then procees further with a sinter process (instead of thermal spraying)?
No, the coating obtained by the application of the slurry does not cause such stresses on drying as does thermal spraying. It is quite possible, under normal conditions, to apply a powder or suspension to the surface of the graphite, and then obtain a coating after firing. I do not know whether a tantalum carbide coating on graphite will be obtained in this way, but a coating from a mixture of silicon carbide and silicon is obtained in practice (silicon deposited on graphite must be heated to melting).
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