Why thermal spraying process is generally sealed?

       

Take the common supersonic flame (HVOF) spraying method spraying and the atmospheric plasma spraying (APS) spraying process as an example. The coating is a layered stacked structure formed by numerous deformed particles interlaced in waves. Therefore, there are some pores between the deformed particles in the coating. Pores can be divided into surface pores (open pores), closed pores and penetrating pores (through holes) according to their existing forms. When the coating is used for corrosion resistance, if there are open holes or closed holes in the coating, the corrosive medium cannot directly reach the surface of the substrate, so it cannot directly corrode the substrate; and if there are through holes in the coating, the corrosive medium It will directly reach the surface of the protected substrate through the pores, causing chemical or electrochemical corrosion between the coating and the substrate, and the corrosion products will accumulate at the interface, which will cause the coating to crack and fall off, and ultimately cause the coating to fail. Therefore, in order to prevent the corrosion of the substrate from corrosive media, improve the corrosion resistance of the coating and expand its application in special environments, the coating must be sealed.