Analysis of working condition of thermal sprayed parts

       Part condition analysis is the basis of thermal spray coating design. To obtain an economical, efficient and high-quality coating, the performance requirements and working conditions of the components must be accurately analyzed first to provide a basis for the selection of coating types and materials.



According to failure analysis theory, failure mode analysis is the core content of failure analysis, which is the physical and (or) chemical change process that leads to component failure. In this process, the size, shape, state or performance of the components changes, and thus causes the failure of the whole product, such as wear failure, fatigue failure, corrosion failure, etc. The main factors that determine the failure mode of components include internal factors such as the nature and state of component materials and external factors such as component operating conditions. The external factors that cause the failure of parts, namely stress, environment and time, are the inducing factors of failure, and these factors can be clearly understood through the in-depth analysis of the working conditions of the parts.



1. Stress factor



Force is the condition under which parts work. Different combinations of types, magnitudes and states of stress are important or decisive factors that cause different failure modes. Stress types include persistent, alternating, impact, contact, friction, scouring, etc.; stress states include simple tension, compression, shear, torsion, bending and other stresses, as well as composite effects of tension-bending, compression-bending, bending-torsion, tension Torsion, tensile shear, bending shear, torsion shear and other stresses. Stress factors can act alone or can be coupled with other factors to induce component failure.



2. Environmental factors



Environmental factors mainly include temperature and medium. The working temperature can be generally divided into five categories: low temperature, normal temperature, medium temperature, high temperature and ultra-high temperature; the working medium includes gas phase (vacuum, special gas, rural atmosphere, urban atmosphere, industrial atmosphere, etc.), liquid phase (fresh water, sea water, oil, acid) , alkali, liquid metal, etc.) and solid phase (contact, friction, scouring, etc.). Environmental factors, like stress factors, can act alone or be coupled with other factors to induce component failure.



3. Time factor



Time cannot be used as an independent factor to induce failure. Without the existence of stress and environmental factors, the time factor loses its meaning. However, when the time factor is coupled with stress factors and environmental factors, it becomes a very important factor.



For example, the various external factors mentioned above have different effects on the failure of components, resulting in different failure modes. The relationship between various main failure modes and the most important and typical inducing factors can be found in the relevant information. When designing thermal spray coatings, special attention should be paid to the analysis of the factors that affect the surface failure of parts. These factors may act on components alone or in coupling, and under the action of coupling, the damage to components is much more serious. For example, the surface coating of the plunger of an acetic acid pump, which requires both wear resistance and corrosion resistance under the working conditions The coatings can meet the requirements, but the corrosion resistance of such coatings under the condition of acetic acid are listed as "bad" and "not recommended" coatings. Therefore, considering the overall consideration, this spraying material and process cannot be used to prepare acetic acid. Pump plunger surface coating.



In addition to the above-mentioned external factors, internal factors such as the nature and state of the component material also have an important impact on the failure of the component. Therefore, in the specific analysis, it is possible to design high-quality parts by combining the working conditions and performance requirements of parts, as well as the performance of parts manufactured by different base materials and different processes, and different spraying materials and different spraying processes. , reasonable coating.