Silicon diffusion coating (silicon-infiltrating coating) is a surface treatment technology widely used in steel and alloy materials. By diffusing silicon elements to the surface of the metal matrix, a hard, oxidation-resistant, corrosion-resistant coating is formed. In this article, we will discuss the properties, preparation processes and practical applications of silicon-infiltrated coatings.
Corrosion resistance
The silica infiltration coating has excellent corrosion resistance, especially in corrosive media such as nitric acid, sulfuric acid, hydrochloric acid, and seawater. It has excellent corrosion resistance in molten aluminium and is particularly suitable for industrial applications that require high corrosion resistance. Although the silica coating will be corroded by infiltration in a boiling acid solution, it will corrode slowly in a dilute acid solution, so it can effectively extend the service life of the metal matrix in a variety of corrosive environments.
Antioxidant properties
The silica infiltration coating significantly improves the oxidation resistance of steel, especially for refractory metals such as molybdenum, tungsten, niobium, etc. In the oxidizing atmosphere of 700~750°C, siliconized steel can effectively resist oxidation and will not form oxide scale, showing lower but still excellent oxidation resistance compared with aluminized and chromeized coatings.
Mechanical properties
Although the silica infiltration coating has low hardness, it has good wear resistance. Its application in iron and steel can effectively improve the wear resistance of materials, especially in 3% NaCl solution, the corrosion fatigue limit can be increased by about 3 times. Silicon infiltration treatment can also improve the fatigue strength of steel, increasing by 15%~20%. However, siliconization reduces the strength limits of steel, especially elongation and impact toughness, and this effect needs to be taken into account when using it.
The silicon-permeable coating reacts the silicon element with the surface of the metal matrix to form a diffusion layer through high-temperature treatment. The specific formation process includes the diffusion of silicon, the reaction of bonding with the metal matrix. The microstructure of a coating usually appears as a multi-layered structure, with the outer layer may contain a certain amount of silicide or compound, while the inner layer is the diffusion area of silicon metal.
The preparation methods of silica infiltration mainly include solid method, liquid method and gas method, among which the solid method is widely used in industry because its process is relatively stable. Solid silicon infiltration forms a uniform silicon diffusion layer by reacting the workpiece with materials such as silicon powder at high temperatures. Liquid and gas silicon, although more efficient, are less common in industrial applications. The selection of penetrating agent, the addition of activator, and the control of silica infiltration time and temperature are key factors in ensuring the quality of the coating.
Siliconized coatings are mainly used to improve the corrosion resistance, high temperature oxidation resistance and wear resistance of metals, and are often used on the surface of workpieces that require high performance.
Corrosion resistance application - improve the corrosion resistance of steel workpieces to seawater, acids, molten salts and molten metals, which are widely used in chemical industry, marine engineering and other fields.
High-temperature oxidation resistance applications – especially for refractory metals in high-temperature environments, such as aerospace, metallurgy, etc.
Wear-resistant and anti-friction applications - silicon-permeated coating has good anti-friction properties and is widely used in automobiles, tractors and other mechanical parts.
Siliconized coatings have significant advantages in improving the corrosion resistance, oxidation resistance and wear resistance of steel materials, especially in extreme environments such as high temperatures, seawater, and acidic solutions. Although the coating has a low hardness, it has a significant improvement in fatigue strength and oxidation resistance, and is widely used in the protection of machinery, automobiles and high-temperature equipment. Its preparation processes include solid method, liquid method and gas method, among which the solid method is more widely used due to its high stability.