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 the air valve. After acetylene and oxygen are mixed, a combustion flame is generated at the nozzle outlet, and the introduced powder or rod coating material is heated and melted in the flame. Then, under the action of the flame, the mist-like droplets are sprayed onto the surface of the substrate to form a coating. The two linear material coating materials used in arc spraying are automatically introduced by the wire feed wheel. When a large current passes between the two linear materials, an arc will be generated. The linear material will melt rapidly under the high temperature of the arc and will 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 temperature of the plasma flame 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 an ionic bond or covalent bond structure, high bond energy, and atomic The bonding force is strong and the surface free energy is low, which gives the ceramic material the characteristics of high melting point, high stiffness, high chemical stability, high insulation and heat insulation capacity, small thermal expansion coefficient, and small friction coefficient; but compared with metal materials, its plasticity Poor deformability, 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 coating booths 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 from high-end fields to the characteristics and overall structure of ceramic coating technology in civil industries such as energy, transportation, metallurgy, textile, petrochemical, and machinery. Compared with ceramic materials, ceramic coating technology has the following characteristics:
1. It can organically combine the strength and toughness, ease of processing of metal materials with the characteristics of high temperature resistance, wear resistance and corrosion resistance of ceramic materials.
2. Taiwan management chooses coating materials and suitable spraying process to obtain various functional surface strengthening coatings.
3. Not restricted by the substrate: the substrate material used for thermal spraying can be inorganic materials such as metal, ceramics, cement, refractory materials, stone, gypsum, etc., or organic materials such as plastic, rubber, wood, and paper.
4. It is not restricted by the size of the workpiece and the construction site.
5. The coating deposition rate is fast, the thickness is controllable, and the process is simple.
6. The ceramic coating has good machinability, and spraying can be carried out after the coating is damaged.
The application fields of thermal spray ceramic coating technology are very wide, mainly including:
1. Thermal barrier coating. The key components of aero-engines are superalloy turbine blades and turbine disks. These heated components are exposed to harsh environments such as high temperature, oxidation and high-speed air erosion. For gas turbine components that can withstand temperatures as high as 1100°C, which has exceeded the temperature limit (1075°C) used by nickel-based superalloys, the effective solution is to apply a high-melting-point ceramic coating with good thermal insulation, called thermal barrier coating. Thermal barrier coatings are mainly used for heating components of aviation, ships and land-use gas turbines, as well as components such as civil internal combustion engines, turbocharged turbines, and oxygen lances for the metallurgical industry.
2. High-temperature adhesive and abrasion resistant coating: heat treatment furnace rolls, support rolls, sintering furnace rolls and other high-temperature rolls are mostly operated at 800°C and 1200°C. Thermal spraying technology is used to spray special ceramic or cermet coatings on the surface of high-temperature furnace rolls. , It has good high temperature, anti-oxidation, anti-adhesion, anti-nodule and self-cleaning functions, which can significantly increase the service life of furnace rolls and produce steel with good surface smoothness.
3. Wear-resistant and corrosion-resistant coating: The plunger of the high-pressure reciprocating metering pump used in chemical plants uses sprayed al203-tio2 composite coating instead of the traditional chrome plating process, and its service life is increased by 6 times. Under low-stress sliding wear and abrasion conditions, almost all original chrome-plated products can be replaced with thermal spray ceramic coatings. 4 Functional coating: Plasma sprayed supersonic sprayed superconducting ceramic coatings have been successfully applied. Superconducting ceramic coatings have shown good application prospects in magnetic shielding, microwave components, various types of transmitters, and quantum electronic devices. Spraying a 30um ratio3 coating on a 0.1mm iron sheet, its dielectric constant exceeds 6000, which has been widely used in ceramic chip capacitors. When the thickness of the al203 coating formed by plasma spraying is less than 1mm, it can withstand a voltage of over 2500°C at a high temperature of 1300°C, which meets the requirements of high-temperature electrical insulation. Spraying bioactive ceramics such as 50-75um hydroxyapatite on the titanium alloy substrate provides good chemical compatibility. Therefore, it can be used as an ideal artificial bone material. There are a lot of corrosion and wear problems in oilfield drilling and oil production engineering. It can be expected that thermal spraying technology and ceramic coating have a wide range of application prospects.
Article source: China Powder Industry Information Network
