What are the requirements for bonding the underlying material (priming material)

       Because ceramic coating materials are quite different from metal materials in chemical bonds, crystal structure and thermophysical properties, when spraying ceramic coatings on metal substrates, it is usually necessary to spray a layer of bonding on the surface of metal substrates first. bottom layer.

There are the following requirements for the bonding base material.

(1) It can form a firm bond with the surface of the metal substrate, preferably metallurgical bond. "Self-bonding" composite powders, such as Ni-AI, NiCr-AI, M(Ni, Co, Fe)CrAIY, etc., at the high temperature of the thermal spray flame, an exothermic chemical reaction occurs between the components to produce intermetallic compounds, And release a lot of heat to supplement the thin layer on the surface of the substrate to a molten state, and promote the formation of micro-area metallurgical bonding between the sprayed molten particles and the surface of the substrate.

(2) It can form a dense anti-oxidation and corrosion-resistant coating to prevent oxygen or corrosive medium from invading through the pores of the ceramic coating at high temperature, and protect the base metal from being oxidized and corroded.

(3) It can form a rough bonding bottom surface, and its surface roughness even exceeds the surface roughness of sandblasting pretreatment, so as to improve the bonding strength between the ceramic surface coating and the bonding bottom layer.

(4) The thermal physical properties of the bonding base material, especially the thermal expansion coefficient, thermal conductivity, etc., are preferably between the base metal material and the surface ceramic coating to reduce the difference and mismatch of thermal expansion and reduce the coating. thermal and volumetric stresses within.