Performance requirements for commonly used bonding primer materials

       Generally speaking, as a bonding bottom spray material, it should have the following four performance characteristics:



1) It has high bonding strength with the surface of the substrate, and can even produce micro-regional metallurgical bonding. Especially for the Ni-Al type composite powder with "self-bonding" effect, in the process of thermal spraying, Ni and Al can chemically react to form intermetallic compounds and release a lot of heat, and even this reaction process can continue until It is still going on when the powder hits the surface of the substrate. This effect is very beneficial to the formation of micro-metallurgical bonds between the deformed particles and the surface of the substrate, thereby improving the bonding strength between the bonding bottom layer and the substrate.



2) It has anti-oxidation and corrosion resistance. Especially as the bonding bottom layer of ceramic coating, when working at high temperature, oxygen and corrosive medium in the environment can penetrate into the bonding bottom layer through the pores of the ceramic coating, which requires the bonding bottom layer to form a dense layer at high temperature. The oxide protective film to protect the base metal from oxidation and avoid the corrosion of environmental media.



3) The coating surface has suitable roughness. This not only provides a good roughened surface for the sprayed working layer, which is beneficial to improve the bonding strength between the working layer and the bonding bottom layer, but also has a direct impact on the surface roughness of the working layer.



4) Have suitable thermophysical properties, especially thermal expansion coefficient, thermal conductivity, etc. It is better to be between the base material and the working layer to reduce the thermal expansion mismatch between the two, reduce the thermal stress and volume stress in the coating, and help improve the service life of the coating.



In view of the importance of bonding the bottom layer, when designing the coating, the thermophysical properties of the substrate and the specific working conditions should be comprehensively considered.