Thermal spraying technology is an important part of surface engineering in the field of materials science. It is a surface strengthening and surface modification technology. By spraying a layer of coating on the surface of the metal substrate, the metal has wear resistance, corrosion resistance and high temperature resistance. Oxidation, electrical insulation, heat insulation, radiation protection, anti-wear and sealing properties. Thermal spraying technology is mainly used for the pre-protection of high-temperature, wear-resistant, and corrosion-resistant components, the preparation of functional coatings, and the repair of failed components.
In the thermal spraying process, flame spraying, arc spraying, plasma spraying, explosive spraying and supersonic spraying technology are widely used. Flame spraying is realized by a flame spray gun. The spray gun introduces acetylene, oxygen or compressed air through a gas valve. After acetylene and oxygen are mixed, a combustion flame is generated at the nozzle outlet. The introduced powder or rod coating material is heated and melted in the flame , Under the action of the flame flow, the mist-like droplets are sprayed onto the surface of the substrate to form a coating. The two wire-shaped materials used in arc spraying are automatically introduced by the wire feed wheel. When a large current passes between the two wire-shaped materials, an arc will be generated. The wire-shaped materials will quickly melt under the high temperature of the arc and be compressed The air acts as small droplets and is sprayed onto the surface of the substrate to form a coating. Plasma spraying is suitable for powder coating materials. The plasma spray gun converts electrical energy into heat energy to generate a high-temperature and high-speed plasma flame. The plasma flame temperature can be as high as 50,000 ℃, which can melt all spray materials. Explosive spraying uses the energy provided by the ignition and explosion of a mixture of combustible gas and oxygen to spray powder onto the surface of the substrate to form a coating. The supersonic flame spraying method has a high particle impact speed, which improves the bonding strength, hardness, compactness and wear resistance of the coating.
Most ceramic materials have ionic bond or covalent bond structure, high bond energy, strong bonding force between atoms, and low surface free energy, which endows the ceramic material with high melting point, high stiffness, high chemical stability, high insulation and heat insulation capacity, and thermal expansion Small coefficient, low friction coefficient and other characteristics; but compared with metal materials, its plastic deformation ability is poor, and it is sensitive to stress concentration and cracks. Obviously, using ceramics as mechanical structural materials has worse reliability than metal materials, difficult machining, and high cost. However, the use of thermal spray technology to prepare ceramic coatings on metal substrates can organically combine the characteristics of metal materials with those of ceramic materials to obtain a composite structure. Due to the exceptionally superior comprehensive performance of this composite material structure, thermal spraying technology has rapidly expanded its application from high-end fields to energy, transportation, metallurgy, textile, petrochemical, machinery and other civil industrial fields.
