What are the bonding mechanisms of the coating and the substrate?

       1) Mechanical bonding

Mechanical bonding means that the molten particles with a certain function hit the surface of the roughened substrate, and the flat sheets are spread to cover and close to the bumps on the surface of the base material, and shrink and bite the bumps when condensing. (or anchor point), forming a mechanical bond. Mechanical bonding is the main form of bonding between the thermal spray coating and the substrate.

2) Micro-metallurgical bonding

When spraying an exothermic spray material, after the molten particles reach the surface of the substrate, the exothermic reaction can be maintained for several microseconds, and the contact temperature in the micro-region of the substrate surface can be as high as the melting point of the substrate. The substrate is formed into micro-area metallurgical bonding, which improves the bonding performance between the coating and the substrate.

3) Diffusion bonding

When the molten spray material rapidly hits the surface of the substrate to form a close contact, due to deformation, high temperature, etc., there may be slight diffusion between the coating and the substrate, increasing the bonding strength between the coating and the substrate. For example, in When the nickel-clad aluminum composite powder was sprayed on the carbon steel substrate, it was found that the bonding layer was composed of elements such as Ni-AI-Fe, with a thickness of about 0.5

4) Physical bonding

When the surface of the substrate is extremely clean or activated, the substrate and the coating are fully wetted to form intermolecular forces.

The bonding between the spray coating and the substrate is mainly mechanical bonding, and in some cases, micro-metallurgical bonding, diffusion bonding and physical bonding will occur.