Gordon England Surface Engineering Forum



adhesion of coatings

Posted by Alecxei Goncharov (195.96.79.2) on 14:22:37 11/01/06

Hi, I ve read your article Nature of Thermal Spray Coatings with grate interest and with real pleasure. No doubt, it could be recommended as a manual for engineers. As I have dealt for a long period with detonation spraying of coatings, I d like to remark some points at the mentioned text and to make some proposals.
1. Explaining the nature of coating failure, where the tensile stresses exceeds that of the bond strength or cohesive strength, you show two
right pictures, where the bending of the coating is directed to free surface of coating due to its cooling and solidification. I would agree with it, if the heat flow has the same direction, what could be in the case, for instance, if air cooling flow winds to the sprayed surface. In opposite situation, if cooling flow winds to the substrate and it s productivity enough for the heat flow to direct to the substrate, the coating bends tending to snuggle to the substrate. It s clear, that all said concerns to convex form of the substrate, which has to be cooled during spraying to achieve good adhesion strength. In opposite case, if, say, internal cylinder surface has to be coated, the last must be heated just before spraying to enable the initial expansion of the hole, which will follow the shrinkage as well as that of sprayed coating. This procedure of preliminary heating is necessary to avoid the coating detach after spraying.
Best regards


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