Coating products are widely used in various fields, is a commonly used solid film, can be used for protection, insulation and decoration and other purposes, its preparation method is mainly the use of physical accumulation technology or chemical accumulation technology to coat metal or non-metallic compounds on the substrate material, constitute a coating. However, the manufacture of coatings creates internal stresses that affect the application of coatings. Therefore, it is necessary to take corresponding measures to eliminate or weaken the stress inside the coating structure to avoid various failures caused by stress.
1. Select the appropriate substrate
Choosing a coating and a base material with the same coefficient of thermal expansion will help one to completely remove thermal stress in a coating. The second is to match the measuring or application temperature of the coating with the film-forming temperature. Furthermore, the effect of temperature makes thermal stress, a component of the stress of the film, easily controllable; so, engaging with the intrinsic stress via the change of thermal stress helps to enhance the microscopic stress of the film.
2. Do thermal annealing treatment
The various defects present in the coating are the main causes of intrinsic stress. These defects are generally defects of the balance between right and wrong, so they tend to disappear on their own. However, in order to produce disappearance, the outside world is required to deal with activation energy. When the coating is heat-treated, the external heat energy is applied, and many non-equilibrium defects disappear, so the internal stress of the coating is significantly reduced.
3. Add the center coating
The stress characteristics of the film are the same in the process of coating many layers of high-reflection, anti-reflection or other dielectric films; this will raise the stress of the whole film layer and lead to the coating to break or fall. A layer of film accumulates between the film layers using the strain cancelation concept, and the process is controlled to produce the stress state opposing the structural coating in the film thereby reducing the damage caused by stress.
In addition, when the material properties of the matrix and the coating are very different, that is, the interface properties are inconsistent, their interaction is large, and this force has a tendency to make the two materials interact, so the coating produces a large deformation, constituting internal stress. In this case, the surface treatment of the substrate can be carried out first, that is, sublayers can be added to increase the wettability of the surface, which plays a transitional role in the structure of the coating and the substrate, maintains the continuity of the structure, and then reduces the stress.
4. Modify the process criteria
Changing the process parameters in the process of coating accumulation will directly influence the level of residual stress in the film; hence, the size of the stress in the film can be regulated by modifying the process parameters including substrate temperature, working air pressure, and accumulation rate during coating; even the nature of the stress will be changed.
For example, for sputtering coating, with the increase of sputtering pressure in the reaction chamber, the concentration of high-energy ions (particles) increases, so that the gas molecules collide with each other, and then the energy of the gas molecules is reduced, the atomic shot peening effect is weakened, and the inclined component of the accumulated particle flow is increased, resulting in the loose membrane structure, and the compressive stress becomes smaller and smaller, becoming tensile stress, and the tensile stress increases first and then decreases.
5. Improve stacking skills
The kinetic energy of the stacked atoms also varies and the defect concentration of the interfacial dispersion layer structure and the film layer structure changes in the process of magnetron sputtering stacking coating with variation in RF source power. The residual tensions in the coating therefore change.