What are the characteristics of the structure of thermal spray coating

       Except for flame spray melting and plasma arc powder non-surfacing, the formation mechanism of coatings prepared by other spraying processes is basically the same. The coating structure has the following characteristics:

    (1) The coating is a layered structure, and the formation process of the coating determines that the structure of the coating is layered. Therefore, the physical properties of the coating are directional. For example, the tensile strength is different in the perpendicular and parallel coating directions.

    (2) There is internal stress in the coating. As the coating is formed layer by layer, the tiny stresses in each particle build up together, and since each stress induces a small amount of strain, the entire inner layer of the coating is under compressive stress.

    (3) Inhomogeneity of chemical composition. The inside of the coating contains the oxide of the sprayed metal, and the presence of the oxide often reduces the corrosion resistance and bonding strength of the coating.

    (4) The porosity of the coating. Because the coating is formed by inlaying and quenching of the flattened particles, there are often pores in the coating. The existence of pores in the coating can be divided into three forms; surface pores, closed pores and penetrating pores.

    The pores in the coating will reduce the strength and corrosion resistance of the coating, especially the penetrating pores, which have a greater impact on the corrosion resistance of the coating. However, porosity is often also a desirable property of coatings in some cases, such as heat-resistant ceramic coatings for thermal insulation, where porous coatings have lower thermal conductivity than dense coatings, as in lubricating The pores in the coating have the function of storing lubricating oil.