The working principle of thermal spraying determines that the coating pores are inevitable. When the coating is used to prevent corrosion, the corrosive medium will reach the surface of the substrate through the pores, resulting in failure of protection. Therefore, sealing is an important way to improve the corrosion resistance of coating. In this paper, the methods of coating sealing hole are summarized, the prospect of coating sealing hole technology in the future is prospected, and a new coating sealing agent, glaze, is put forward.

At present, the commonly used methods to reduce the porosity of coating are thermal diffusion remelting, self-sealing coating, improvement and improvement of spraying process, hole sealing agent and so on.

Thermal diffusion remelting

Remelting is a process of reheating and melting the formed coating to make the coating more compact in order to eliminate the pores generated by spraying and improve the corrosion resistance and bonding strength of the coating. During remelting, the components in the coating that are easy to melt are melted, and the liquid phase is generated to help strengthen the diffusion process, permeate the components and slag formation of oxides, so that the coating has a certain shrinkage. The melting results make the bonding zone between the thermal spray coating and the substrate change from the original stacked layer-like structure to the dense and more uniform structure, and the pores decrease or even disappear. The heating methods of coating melting include gas combustion heating, atmosphere control furnace heating and high-frequency induction heating, etc. In recent years, we have developed laser, electron beam, plasma beam, solar energy and other heating methods.

The use of spray material itself to reduce porosity

Improve spraying method and process

When spraying, select appropriate spraying distance, main gas flow and powder feeder flow, gun speed, electrical power, powder particle size and other parameters to reduce the coating porosity and improve the bonding strength is very helpful.

Hole sealing agent for hole sealing treatment

Other ways to reduce porosity

Impregnation of low temperature solder for tungsten carbide coating improves strength and wear resistance. The process is carried out in vacuum at 1000 degrees or hydrogen at 800 degrees. At these temperatures the filler flows into the gap to fill the unmelted carbide and capillary action occurs rapidly, allowing for 12min. It has been confirmed that most lead, tin, silver and copper solders provide satisfactory results.

Mechanical treatment somethermal spray coatingscan be mechanically treated to close pores connected to the surface and improve smoothness. Shot hardening is used on some aeronautical parts. Active metal coatings can be improved by shot hardening and rolling to improve cavitation resistance.

Related link:

http://www.wococarbide.com/Transaction/en_information.html

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