Basic principles of thermal spray coating design

       The use of thermal spraying technology can not only improve the wear resistance, corrosion resistance, erosion resistance, thermal stability and chemical stability of machinery and equipment, but also endow common materials with special functions, such as high temperature superconducting coatings, biological coatings , diamond coating, solid oxygen fuel cell (SOFC) electrode catalytic coating, etc. Therefore, thermal spraying technology will inevitably attract more and more attention and be more and more widely used in various industrial fields. However, the actual parts vary greatly due to their material, shape, size, application environment, service conditions, etc. To successfully use thermal spray coatings to solve the technical problems faced, a specific process must be followed. The most important are the following five key processes:



1) Accurately analyze the problem and clarify the coating performance requirements.



2) Reasonably carry out coating design, including the correct selection of spraying materials, equipment, processes, and compliance with a strict coating quality evaluation system.



3) Optimize the coating preparation process.



4) Strictly control the coating quality.



5) Economic feasibility analysis of coating technology.



Coating design plays a linking role, is the basis for successfully solving practical problems with thermal spray technology, and is one of the most important links in all aspects. When designing the coating, it is necessary to consider all the links involved in the coating, which has obvious system characteristics. Therefore, in order to obtain a coating that meets the performance requirements, a careful and reasonable coating design must be carried out before spraying.



The main elements of thermal spray coating design include:



①According to the working conditions of the surface of the parts, or the analysis results of the parts that have surface failure, determine the technical requirements for the surface coating or surface coating system of the parts, including bonding strength, hardness, thickness, porosity, resistance abrasion resistance, corrosion resistance, heat resistance or other properties.



②Using the mastered basic knowledge of thermal spraying technology (including spraying materials, spraying process, coating performance, etc.), carry out economic and technical feasibility analysis to meet performance requirements, consider coating economy, and then select appropriate spraying materials , equipment and process methods.



③ Compile a reasonable coating preparation process specification.



④Propose strict coating quality inspection and control standards, parts packaging and transportation conditions, etc.



Now, even stricter requirements include total quality management requirements for manufacturers of coating raw materials.



All of the above content constitutes a complete process of thermal spray coating design.



It should be specially pointed out that although the performance of thermal spray coating mainly depends on the performance of the spray material, it is also significantly affected by the selected spray equipment and spray process. For the same spraying material, when different spraying equipment and different spraying process parameters are used for spraying, the performance of the obtained coating will be very different. In addition, various other steps involved in preparing the coating will determine the final coating properties, such as surface pretreatment, cooling measures, coating processing, etc. Therefore, it is only possible to obtain a coating of stable quality that meets the performance requirements only by comprehensive quality control of each process of preparing the coating.