Application fields of thermal spraying ceramic material coating technology

       Thermal spraying technology is an important part of surface engineering in the field of material science. It is a technology of surface strengthening and surface modification. By spraying a coating on the surface of the metal substrate, the metal has wear resistance, corrosion resistance and high temperature resistance. Oxidation, electric exhaust, heat insulation, radiation protection, wear reduction and sealing properties. Thermal spraying technology is mainly used for pre-protection of high-temperature, wear-resistant, corrosion-resistant components, preparation of functional coatings, and repair of failed components.

Thermal spraying technology is widely used in flame spraying, arc spraying, plasma spraying, explosive spraying and supersonic spraying technology. The flame spraying is realized by a flame spray gun. The spray gun introduces acetylene, oxygen or compressed air respectively through the air valve. After the 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, the mist-like droplets are formed and sprayed onto the surface of the substrate to form a coating. The two wire-shaped material coating materials used in arc spraying are automatically guided by the wire feeder. When a large current is passed between the two wire-shaped materials, an arc will be generated, and the wire-shaped material will melt rapidly under the high temperature of the arc Compressed air acts to form small droplets that are 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 and generates high-temperature and high-speed plasma flame. Explosive spraying is to use the energy provided by the ignition and explosion of the mixture of flammable gas and oxygen to spray powder onto the surface of the substrate to form a coating. The supersonic flame spraying method has improved the bonding strength, hardness, compactness and wear resistance of the coating due to its high particle impact speed.

Most ceramic materials have ionic bond or covalent bond structure, high bond energy, strong interatomic bonding force, and low surface free energy, which endow the ceramic material with high melting point, high stiffness, high chemical stability, and high heat dissipation capability. 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, is difficult to machine, and has high costs. 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 exceptionally superior comprehensive properties of this composite material structure, thermal spraying technology has rapidly expanded from high-end fields to civil industries such as energy, transportation, metallurgy, textile, petrochemical, and machinery.

The characteristics of ceramic coating technology Compared with the overall structure of ceramic materials, ceramic coating technology has the following characteristics:

1. It can organically combine the toughness and ease of processing of metal materials with the high temperature resistance, wear resistance and corrosion resistance of ceramic materials.

2. Reasonable selection of coating materials and suitable spraying process can obtain surface strengthening coatings with various functions.

3. Not limited by the matrix: The matrix 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. Not limited 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 machinability of the ceramic coating is good, and it can be sprayed after the coating is damaged.

The application fields of thermal spraying 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, which are exposed to harsh environments such as high temperature, oxidation, and high-velocity airflow erosion. For gas turbine components that withstand temperatures as high as 1100°C, the temperature limit for nickel-based superalloys (1075°C) has been exceeded. The effective solution is to apply a high melting point ceramic coating with good heat dissipation, called thermal barrier coating. Thermal barrier coatings are mainly used for heating parts of aviation, ships and land gas turbines, as well as civil internal combustion engines, supercharged turbines, oxygen spray guns for metallurgical industries and other devices.

2. High temperature adhesive and wear resistant coating: heat treatment furnace rollers, backup rollers, sintering furnace rollers and other high temperature rollers are mostly operated at high temperature of 800℃-1200℃, using thermal spraying technology to spray special ceramic or cermet coating on the surface of high temperature furnace rollers. It has good high temperature resistance, anti-oxidation, anti-adhesion, anti-nodule and self-cleaning and purification functions, which can not only significantly improve the service life of furnace rolls, but also produce steel with high quality and smooth surface.

3. Wear-resistant and corrosion-resistant coating: The high-pressure reciprocating metering pump plunger used in the chemical plant adopts the spraying Al2O3-TiO2 composite coating instead of the traditional chrome plating process, and its service life is improved by 6 times. Under low-stress sliding wear and abrasive conditions, almost all original chrome-plated products can be replaced by thermal spray ceramic coatings.

4. Functional coating: Plasma sprayed supersonic sprayed 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. The 30μm BaTiO3 coating is sprayed on the 0.1mm iron sheet, and its dielectric constant exceeds 6000, which 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, which meets the requirements of high-temperature electrical isolation. Bioactive ceramics such as 50-75 μm hydroxyapatite are sprayed on the titanium alloy substrate, which provides good chemical compatibility, so 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 coatings will have a wide range of application prospects.