Thermal spraying process requirements for thermal spraying materials

       In theory, thermal spray processes, especially plasma spray processes, are capable of spraying all solid-state engineering materials. But in fact, not all materials can be used for thermal spraying, and some materials must be modified or specially treated before they can be used, otherwise they cannot be used as thermal spraying materials at all.



Coating materials for thermal spraying must meet the following basic requirements:



1) It must meet the requirements for the use of thermal spray coatings, such as high temperature resistance, wear resistance, corrosion resistance, self-lubrication, insulation, thermal shock, thermal radiation, etc.



2) It has good thermal stability or chemical stability in the high temperature flame flow of spraying flame. There will be no oxidation, volatilization, sublimation and deterioration, and no harmful crystal transformation.



3) No harmful chemical reaction with the base material. Due to the chemical inertness of ceramic materials, ceramic coatings generally do not chemically react with commonly used metal matrix materials. However, for base materials such as high silicon cast iron and silicon steel, since a dense SiO2 film is formed on the surface, harmful chemical reactions will occur if alkaline oxide ceramics such as MgO-Al2O3 are sprayed. For the same reason, acid oxide-based ceramic coatings cannot be sprayed on the surface of alkaline glass substrates.



4) It has a good performance matching and adaptation relationship with the base material or the primer layer. These performance matching relationships include: good wetting ability to the matrix material; relatively close thermophysical properties with the matrix material, such as thermal expansion coefficient, thermal conductivity, etc.; reasonable combination of electrochemical properties with the matrix material, etc.



5) The process performance of thermal spraying materials should meet the requirements of thermal spraying process. The fluidity, particle size and particle size distribution, and bulk density of powdered thermal spray coating materials should meet the requirements of a specific thermal spray process, and the powder should be dry and clean. The wire used for thermal spraying must ensure that the wire diameter is uniform, the surface is smooth and clean, and there is no oil pollution.



6) The toxicity, flammability and explosiveness of thermal spray coating materials must meet the requirements of safety, hygiene and environmental protection.