Application fields of thermal spray ceramic material coating technology

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Thermal spray 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 a metal substrate, the metal has properties such as wear resistance, corrosion resistance, high temperature oxidation resistance, electrical insulation, heat insulation, radiation protection, wear reduction and sealing. Thermal spray technology is mainly used for pre-protection of high-temperature, wear-resistant, corrosion-resistant and other components, preparation of functional coatings and repair of failed components. The most widely used thermal spraying methods include flame spraying, arc spraying, plasma spraying, explosive spraying and supersonic spraying technology. Flame spraying is achieved through 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. After the introduced powdery or rod-shaped coating material is heated and melted in the flame, it forms mist-like droplets under the action of the flame flow and is sprayed onto the surface of the substrate to form a coating. The coating material of two linear materials used in arc spraying is 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 the compressed air will form small droplets and be 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 thermal energy to produce a high-temperature and high-speed plasma flame. The temperature of the plasma flame can be as high as 50,000°C and can melt all spray materials. Explosive spraying uses the energy provided by the ignition and explosion of a flammable gas and oxygen mixture to spray powder onto the surface of the substrate to form a coating. The supersonic flame spraying method has a high particle impact velocity, which improves the bonding strength, hardness, compactness, and wear resistance of the coating. Most ceramic materials have ionic or covalent bond structures with high bond energy, strong inter-atomic bonding force, and low surface free energy, which give ceramic materials high melting point, high stiffness, high chemical stability, high insulation and thermal insulation capabilities, small thermal expansion coefficient, and small friction coefficient. ； However, compared with metal materials, its plastic deformation ability is poor and it is sensitive to stress concentration and cracks. Obviously, using ceramics as a mechanical structural material has poorer reliability than metal materials, difficult machining, and high cost. However, the use of thermal spraying technology to prepare ceramic coatings on metal substrates can organically combine the characteristics of metal materials and ceramic materials to obtain composite material structures. Due to the extremely superior comprehensive performance of this composite material structure, thermal spraying technology has rapidly expanded its application from high-end fields to energy, transportation, metallurgy, textiles, petrochemicals, machinery and other civilian industrial fields. Characteristics of Ceramic Coating Technology Compared with monolithic structural ceramic materials, ceramic coating technology has the following characteristics:: 1. It can organically combine the strength, toughness and ease of processing of metal materials with the high temperature resistance, wear resistance and corrosion resistance of ceramic materials. 2. By rationally selecting coating materials and appropriate spraying processes, surface-strengthened coatings with various functions can be obtained. 3. Not limited by the matrix: The base 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, paper, etc. 4. Not limited by workpiece size and construction site. 5. The coating deposition rate is fast, the thickness is controllable, and the process is simple. 6. The ceramic coating has good processability and can be sprayed again after the coating is damaged. Thermal spray ceramic coating technology has a wide range of applications, mainly including: 1. Thermal barrier coating. The key components of aeroengines are high-temperature alloy turbine blades and turbine disks. These heated components are exposed to harsh environments such as high temperature, oxidation, and high-speed airflow erosion. For gas turbine components that withstand temperatures up to 1100°C, which has exceeded the temperature limit of nickel-based superalloys (1075°C), an effective solution is to apply a high-melting-point ceramic coating with good thermal insulation properties, called a thermal barrier coating. Thermal barrier coatings are mainly used for heated parts of aviation, ship and land gas turbines, as well as civilian internal combustion engines, supercharged turbines, oxygen spray guns and other devices used in the metallurgical industry. 2. Anti-high temperature adhesive wear coating: High-temperature rollers such as heat treatment furnace rollers, support rollers, and sintering furnace rollers mostly operate at high temperatures of 800°C-1200°C. Thermal spraying technology is used to spray special ceramic or cermet coatings on the surface of high-temperature furnace rollers. They have good high-temperature resistance, anti-oxidation, anti-adhesion, anti-knot and self-cleaning purification functions. It can not only significantly increase the service life of the furnace rollers, but also produce steel with smooth surfaces and excellent quality. 3. Wear-resistant and corrosion-resistant coating: The high-pressure reciprocating metering pump plunger used in chemical plants uses spraying Al2O3-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 abrasive conditions, almost all original chrome-plated products can be replaced with thermal spray ceramic coatings. 4. Functional coating: Plasma spraying and supersonic spraying superconducting ceramic coatings have been successfully applied. Superconducting ceramic coatings show good application prospects in magnetic shielding, microwave components, various transmitters, quantum electronic devices, etc. A 30μm BaTiO3 coating is sprayed on a 0.1mm iron sheet. Its dielectric constant exceeds 6000 and has been widely used in ceramic chip capacitors. When the thickness of the Al2O3 coating formed by plasma spraying is less than 1mm, it can withstand a voltage of more than 2500°C at a high temperature of 1300°C, meeting the requirements for high-temperature electrical insulation. Spraying 50-75 μm hydroxyapatite and other bioactive ceramics on a titanium alloy matrix provides good chemical compatibility, so it can be used as an ideal artificial bone material. In oilfield drilling and production engineering, there are a lot of corrosion and wear problems. It can be expected that thermal spray technology and ceramic coatings will have broad application prospects.