APPLICATION OF ADVANCED CERAMICS IN THE FIELD OF WEAR RESISTANT MATERIALS
Wear-resistant and corrosion-resistant industries is a branch of surface treatment industry. It is an emerging industry for preventive care and remanufacturing technology services in order to solve the wear and corrosion problems of equipment and work-pieces in power, steel, chemical mining, cement and other industries. wear-resistant and corrosion-resistant industry has strong vitality. Through the wear and corrosion protection of industrial equipment, its service life can be greatly improved, and the consumption of steel and other materials caused by its maintenance or replacement can be reduced to save resources. The wear-resistant and corrosion-resistant industries are important measure to save resources, protect environment and promote circular economy. They are also powerful assistant for enterprise to achieve energy saving, emission and cost reduction, and economic efficiency improvement. The wear-resistant and corrosion-resistant industries have the characteristics of cross cutting, marginal and multidisciplinary.
The core of wear-resistant and corrosion-resistant industries is the application of new materials and technologies in related industries. It mainly includes wear-resistant ceramic technology, thermal spraying, surfacing and wear-resistant plate, laser cladding, corrosion-resistant and wear-resistant coating technology, corrosion-resistant technology, wear-resistant material technology, etc.
Application of Advanced Ceramics in the Field of Wear resistant Materials
According to statistics, friction consumes about 1/3 of the disposable energy in the world, and about 80% of machine parts fail due to wear. The wear failure of mechanical parts is closely related to the selection of friction pair materials and service conditions. Generally, the materials used under friction and wear conditions with small wear amount are called wear-resistant materials; The material with small friction coefficient is called antifriction material; The material with large friction coefficient is called friction material. It is very important to correctly select and use appropriate materials for different working conditions and the friction and wear properties required by mechanical components. For example, it is generally appropriate to select high manganese steel as wear-resistant material in high impact environment, but in small impact load environment, high manganese steel cannot play the advantage of deformation hardening of high manganese steel, while high chromium cast iron is more appropriate. In addition, both antifriction materials and friction materials hope to have good wear resistance at the same time. The good wear resistance of materials can not only prolong the service life of mechanical parts, reduce the replacement of parts and labor intensity of workers, but also save energy and material resources. Therefore, according to different working conditions and mechanical parts performance requirements, it is of great significance to correctly select wear-resistant materials in improving mechanical equipment performance and saving energy.
What are the types of wear-resistant materials?
There are many kinds of wear-resistant materials, which can be divided into metal wear-resistant materials, ceramic wear-resistant materials, polymer wear-resistant materials and wear-resistant composites according to their chemical composition; According to the material structure, it can be divided into integral wear-resistant materials and surface wear-resistant materials; The wear-resistant materials can be divided into normal temperature wear-resistant materials and high temperature wear-resistant materials according to different service temperatures.
① Metallic materials. Metal materials can also be divided into wear-resistant steel and wear-resistant cast iron. Commonly used are wear-resistant alloy steel, high manganese steel, bearing steel and tool steel. Except for the high manganese steel, which improves the wear resistance by deformation hardening, other wear resistant steels mainly improve the hardness and wear resistance of steel by adding carbide forming elements and forming carbides with carbon. At present, the development trend of wear-resistant steel is microalloying (such as adding B, Ti, Nb, V, etc.) strengthening, rare earth modification and composite strengthening. These trace elements form compounds in steel, such as adding B and other trace elements in steel to form boride, and adding Ti, Nb, V, etc. to form high hardness carbide to improve the wear resistance of steel. WC and AlO are added in the casting process. The steel matrix composite is formed by strengthening the steel matrix with equal particles.
② Ceramic materials. The materials used as wear-resistant ceramics mainly include oxide ceramics, carbide ceramics and nitride ceramics. Typical wear-resistant ceramics include alumina, silicon carbide, silicon nitride, etc. Ceramic materials are very brittle, so the toughening of wear-resistant ceramic materials is the main research direction. Cemented carbide, also known as cermet, is a WC or TiC particle reinforced Co based alloy, which is commonly used as tools, abrasives and other parts requiring very high wear resistance.
③ Polymer wear-resistant materials. The polymer wear-resistant materials mainly include nylon, polyurethane, epoxy resin and rubber. The disadvantages of polymer materials are low hardness and low service temperature, so ceramic particles or fibers are often used to strengthen them to improve their strength and wear resistance.
For economic purposes, modern enterprises usually adopt high-speed technology. The efficiency of the factory is determined by the following parameters: equipment characteristics and durability; Investment cost, operation cost, maintenance and repair cost, among which the most important is safety and reliability in production and reduction of maintenance. Therefore, it is very important to reduce wear and corrosion of high-speed running equipment. Because of the outstanding characteristics of ceramic materials, the use of ceramics can solve the problems of wear resistance and corrosion resistance required in many applications. Compared with metal materials and polymers, ceramics have better wear resistance, corrosion resistance and thermal insulation.
Common types of wear-resistant ceramics?
Oxide ceramics
1. Alumina ceramics
Alumina ceramics usually refer to α- Ceramic materials with alumina as the main crystalline phase. According to the different alumina content, there are 75 porcelain, 85 porcelain, 90 porcelain, 95 porcelain and 99 porcelain. with α- Ceramic materials with aluminum oxide as the main crystalline phase have high hardness and mechanical strength, good abrasion resistance, thermal conductivity, high electrical strength and insulation resistance, low dielectric loss, stable electrical performance with temperature and frequency changes, and are widely used as electrical insulation materials because of their convenient manufacturing, uniform and flat surface. Up to now, more than ten kinds of Al2O3 crystal structures have been found, but there are mainly three kinds. At temperatures above 1300 ℃, other crystal phases are almost completely transformed into α-Al2O3.
Alumina ceramic materials are widely used in industry due to their wide source, low price and good wear resistance. The results show that the erosion wear resistance of 95% Al2O3 ceramic material is more than 5 times that of high chromium cast iron (Cr15Mo3). For friction and wear, when the alumina content is low, the alumina content has an impact on the wear resistance of alumina ceramics. With the increase of Al2O3 content, the wear resistance is improved, and the effect is more significant in wet grinding.
2. Zirconia ceramics
Zirconia grinding medium has high density (the specific gravity of alumina ball is about 3.6g/cm3, and the specific gravity of zirconia ball is about 6.0g/cm3), high strength and toughness, so it has excellent wear resistance and very high grinding efficiency, and can prevent material pollution. It is especially suitable for wet grinding and dispersion. At present, it has been widely used in ceramics, magnetic materials, coatings, inks, medicine and food industries. For example: advanced car paint, mobile phone paint, ink-jet ink, advanced cosmetics, etc. Zirconia grinding beads have become the most widely used grinding media in the market by virtue of their high specific gravity (the specific gravity of alumina balls is about 3.6g/cm3, and the specific gravity of zirconia balls is about 6.0g/cm3), high toughness, and excellent wear resistance.
In the powder engineering, in addition to being used as the grinding medium, zirconia is also used as an accessory of the sand mill. Everyone is familiar with the sand mill. Its task is grinding. An excellent sand mill needs to have the advantages of high grinding efficiency, stable equipment performance and high product quality. In order to ensure these advantages, it is necessary to put forward requirements for its accessories: first, it has wear resistance, that is, it has low wear rate when grinding, and will not cause serious pollution to the grinding products; 2、 The hardness is large enough to ensure the high efficiency of grinding. Among the ceramic parts, zirconia is the most mature ceramic part used in the sand mill and has a wide range of applications. Among the four most mature diamond materials, zirconia, alumina, silicon carbide and silicon nitride, zirconia has the best toughness. In high-speed rotating sand mills, it has more obvious advantages as a rotor. Because in the process of high-speed rotation, the contact grinding process between the rotor and materials will easily lead to cracks in ceramic parts, which will lead to fracture of ceramic parts over time. Only zirconia ceramics can meet the use toughness of this special working condition. The application of ceramic rotors meets the requirements for the preparation and application of many high-purity ultrafine powders without ferromagnetic pollution.
3. Zirconia alumina aluminum composite ceramics
Alumina ceramic ball is widely used because of its high hardness, stable chemical properties and suitable price; Zirconia grinding balls are also used in many markets because of their large ratio and good toughness. However, the brittleness of Al2O3 ceramics seriously hinders the application and development of alumina ceramics. In recent years, researchers have tried to improve the mechanical properties of alumina ceramics by adding second phases.
Aluminum oxide has high hardness and zirconia has good toughness. The two materials form excellent composites with high strength and high toughness, which are more widely used. ZTA ceramics have high bending strength and fracture toughness at room temperature, so zirconia toughened ceramics have excellent wear resistance. This composite ceramic material not only shows the characteristics of zirconia ceramics with high toughness and strength, but also retains the advantages of alumina ceramics with high hardness. With the improvement of this comprehensive mechanical property, its wear resistance has also been greatly improved. The specific proportion of the two materials can be adjusted according to the actual use requirements of users. The properties of zirconia toughened alumina ceramics are better than 99 alumina ceramics, and the price is lower than zirconia ceramics. Zirconium aluminum ceramic abrasives/wear-resistant linings are modified and toughened by introducing trace element zirconium, and toughened by phase transformation, forming a polycrystalline structure. The strength and toughness are improved, and the wear resistance is good, which greatly improves the impact toughness of ceramic abrasives/wear-resistant linings.
Carbide ceramics
Carbide ceramics are widely used in high temperature environment with corrosion resistance and wear resistance because of their high hardness, high strength and high wear resistance. High wear resistance ceramics such as silicon carbide and boron carbide are common.
1. Silicon carbide ceramics
Silicon carbide ceramics are widely used in national defense, machinery, metallurgy, electronics and other industrial fields due to their excellent properties. Among many ceramic materials, silicon carbide has been a hot spot in material science research because of its high hardness, high temperature resistance, good thermal stability, low coefficient of thermal expansion and excellent thermal conductivity. Compared with zirconia, silicon carbide has at least several advantages such as fast heat dissipation, low cost, and more wear resistance when applied to the grinding cylinder of the sand mill. The advantage of fast heat dissipation can prevent the agglomeration of materials in the grinding body due to high temperature, thus improving the grinding efficiency. In terms of wear resistance, silicon carbide has excellent performance, but it also has the shortcomings of insufficient toughness and easy fragmentation. It is not easy to make a big barrel.
2. Boron carbide
Hot pressed boron carbide, a non-metallic refractory compound, is one of the hardest substances in artificial abrasives. Hot pressed products have high wear resistance, gray black and shiny. Boron carbide ceramics have good wear resistance, so they have important applications in the field of wear resistance. Nozzles made of boron carbide ceramics have a long service life under severe conditions, which is far higher than those made of aluminum oxide, tungsten carbide and other materials.
In the unit operation of powder engineering, the centrifugal spray dryer is used to prepare ceramic powder, which has the advantages of small pollution, fast drying speed, uniform water content, narrow particle size distribution, good powder fluidity, etc., but many ceramic powders have high hardness, which causes serious wear to high-speed rotating centrifugal nozzles. The use of boron carbide can effectively improve the service life of nozzles.
Nitride ceramics
1. Silicon nitride ceramics
Silicon nitride ceramics have small specific gravity, low coefficient of thermal expansion, good thermal shock resistance, and high fracture toughness. They are widely used in aerospace, automotive engines, machinery, chemical industry and other fields, especially as a new high-temperature structural material, they have obvious advantages.
In the field of powder engineering, the density of the grading wheel of silicon nitride jet mill is 3.2g/m, and its body weight is 2/3 of the metal material. The biggest use feature of silicon nitride grading wheel is to prevent metal pollution. In addition, its proportion is 40% smaller than that of zirconia ceramics, which can not only greatly reduce the energy consumption of the motor, but also has less requirements for the motor. Under the existing motor, it can achieve over frequency to obtain particles with finer particle size.
Silicon nitride, as a new type of grinding medium, has entered the industrial application field. With extremely low wear rate and excellent mechanical properties, it has attracted much attention. Although limited by the cost and processing level of silicon nitride, silicon nitride is not so widely used, and the relatively small proportion of silicon nitride is not conducive to efficient grinding, but the use of grinding medium requires low wear, Silicon nitride is also a potential abrasive material.
2. Aluminium nitride
With high hardness and high temperature strength, aluminum nitride ceramics can be used as cutting tools, grinding wheels, wire drawing dies and raw materials for making tool materials and metal ceramic materials. It also has excellent wear resistance and can be used as wear resistant parts. However, due to its high cost, it can only be used for parts with severe wear. Coating some easily oxidized metal or nonmetal surfaces with AIN coating can improve their oxidation resistance and wear resistance; It can also be used as anti-corrosion coating, such as the processor of corrosive substances and the lining of containers.