Analysis of Ceramic Coating Related Technologies and Applications
Ceramic coating, as a general term for inorganic non-metallic coatings, specifically refers to spray coatings made with ceramic materials as the core. Its composition includes four categories: oxide coatings, non oxide coatings, silicate series coatings, and composite ceramic coatings. Among them, the commonly used coating materials for oxide ceramics include Al ₂ O3, TiO ₂, ZrO ₂, Cr ₂ O3, SiO ₂, MgO, BeO, Y ₂ O3, etc; The main categories of carbide ceramics include SiC, WC, BC, TiC, etc; Nitride ceramics are represented by Si ∝ N ₄, TiN, BN, and AlN; TiB and ZrB ₂ are commonly used types in boride ceramics.
From the perspective of functional classification, ceramic coatings mainly include high-temperature insulation coatings, wear-resistant and anti erosion coatings, heat treatment protective coatings, high-temperature lubricating coatings, and atomic energy coatings; Thanks to the special properties of its material itself, this type of coating also has advantages such as wear resistance, corrosion resistance, anti adhesion, high hardness, high temperature resistance, and good biocompatibility. In terms of preparation process, its technical path includes melting and burning coating process, spraying coating process, vapor deposition coating process, electrochemical process coating, sol gel coating and in-situ reaction coating.
Core performance characteristics of ceramic coatings
1. Strong integration of material characteristics: It can flexibly integrate the high temperature resistance, wear resistance, corrosion resistance and other characteristics of ceramic materials with the advantages of high strength, toughness, processability, conductivity and thermal conductivity of metal materials, maximizing the comprehensive value of the two types of materials and meeting the dual requirements of mechanical products for structural performance and environmental adaptability.
2. Flexible material selection and adaptation: There are a wide variety of materials suitable for preparing ceramic coatings, and different materials such as ceramics and ceramics, ceramics and metals, ceramics and plastics can be combined and applied according to actual needs; At the same time, this technology is easy to integrate with existing metal processing tooling conditions, making it convenient for enterprises to carry out technological upgrades and transformations.
3. High controllability of forming and spraying: Ceramic coatings are easy to form, have a fast deposition rate, and can be precisely controlled in coating thickness; It can be sprayed on the surface of thin-walled, hollow, and irregular parts through different sintering processes, as well as achieve local spray strengthening treatment of the product.
4. Wide range of substrate adaptation: Ceramic coatings can be prepared on various substrate surfaces with excellent processing performance. For example, the performance of various inorganic materials such as metals, cement, refractory materials, stone gypsum, plastics, organic materials, as well as wood, cardboard, etc. can be improved by spraying ceramic coatings; After the coating is damaged, if the substrate is not damaged, the metal substrate and other types of substrates can be reused.
5. Material consumption and cost advantages: The thickness of ceramic coatings is usually in the range of tens of micrometers to a few millimeters. In addition, the density of ceramic materials is relatively small, resulting in low overall material consumption. At the same time, the added value of the product is high, and the economy is significant.
6. Unrestricted construction scenarios: The size and shape of the sprayed products are not restricted, and can be completed in the thermal spraying factory or directly operated on site, adapting to different production and maintenance needs.
Performance advantages of nano ceramic coatings
With the continuous development of nanotechnology, the integration of nanotechnology and coating technology can fully leverage the comprehensive advantages of both, enabling materials to exhibit excellent properties in mechanics, thermodynamics, electromagnetics, etc., meeting the high-order requirements of structural performance (strength, toughness, etc.) and environmental performance (wear resistance, corrosion resistance, high temperature resistance, etc.). Nano ceramic coatings have special physical and chemical properties, exhibiting characteristics that conventional materials do not possess in terms of functional protection. Therefore, they have broad application prospects in fields such as thermal insulation, anti-corrosion and rust prevention, insulation protection, self-cleaning and anti fouling, energy absorption and saving, and enclosed high temperature resistance.
Fracture toughness
Fracture toughness is a key indicator for measuring a material’s ability to resist unstable crack propagation. There are two phases inside the nano ceramic coating, one is the matrix phase formed by the melting and solidification of nanoparticles, and the other is the incompletely melted nanoparticles. When cracks propagate to the interface between unmelted or semi melted particles and the matrix, these particles not only absorb the energy required for crack propagation, but also act as obstacles and deflectors to crack propagation. In contrast, the interlayer bonding strength of conventional ceramic coatings is weaker, and cracks are prone to propagate along the interlayer. Therefore, the toughness of nano ceramic coatings is significantly better than that of conventional ceramic coatings.
Hardness
Hardness is one of the core performance indicators of ceramic coatings. The hardness of nano coatings is less dependent on spraying process parameters and the heterogeneity of coating microstructure, while the refinement effect of grains makes the hardness of nano ceramic coatings significantly higher than that of micro ceramic coatings.
Wear resistance
The improvement of hardness and toughness of nanostructured coatings is the main reason for their enhanced wear resistance. During the wear process, nano ceramic coatings may experience micro convex shear or incomplete melting of particles at the pores, resulting in detachment from the coating surface; These small particles will disperse in the lubricating oil film between the coating and the friction parts, playing the role of “micro bearings”, effectively reducing the friction coefficient of the coating, and thereby improving the wear resistance performance.
Combining strength
The bonding strength of ceramic coatings includes the interfacial bonding strength between the coating and the substrate, as well as the bonding strength of the coating itself. The release effect of unexpanded interlayer cracks on residual stress in coatings, as well as the higher flight speed of nanostructured materials during spraying compared to ordinary powders, all contribute to improving bonding strength; At the same time, after achieving nanoscale spraying of powder, the melting state of particles can be improved, significantly reducing coating pores, and some pores are located inside the deformed particles, further enhancing the bonding strength of the coating.
Porosity rate
The appropriate amount of pores in the coating is beneficial for workpieces that require lubrication, friction, and high-temperature insulation, but not beneficial for workpieces that require corrosion resistance, high-temperature oxidation resistance, and high-temperature erosion resistance. Research has shown that porosity is related to flame temperature and flame velocity, as well as particle velocity – as particle velocity increases, porosity shows a decreasing trend, which can be optimized by adjusting process parameters.
Thermal conductivity
Thermal conductivity is a key indicator for measuring the performance of thermal barrier coatings, and its value decreases as the grain size decreases. This is because when the grain size decreases, the number of micro interfaces inside the coating increases, and the interface spacing decreases, resulting in a shorter average free path of particles during the heat conduction process, which in turn reduces the thermal conductivity of the material, making it more suitable for high-temperature insulation scenarios.
The main application areas of ceramic coatings
High performance thermal barrier coatings
The concept of “thermal barrier coating” was first proposed by a research center in the United States in 1950. In the early 1980s, significant breakthroughs were made in the research and preparation processes of thermal barrier coatings, laying the technical foundation for their application on turbine blades. Ceramic materials have become a commonly used material for preparing thermal barrier coatings due to their excellent high-temperature chemical stability, high melting point, high hardness, and low thermal conductivity.
Thermal barrier coatings (TBCs) are ceramic materials with high melting points and low thermal conductivity, applied to the surface of the metal substrate (mostly nickel based high-temperature alloys) of aircraft engine blades. They can reduce the surface working temperature of the metal substrate in high-temperature environments and protect the substrate from high-temperature oxidation and corrosion. At present, TBCs have become one of the three core technologies for high-performance aircraft engine turbine blades.
The development of TBCs materials has gone through three stages:
- Phase 1: Directly using ZrO ₂ as a thermal barrier coating material, although its insulation temperature can reach around 444K, ZrO ₂ is prone to undergo a phase transition from t-ZrO ₂ to m-ZrO ₂ at high temperatures, generating internal stress and leading to coating cracking and failure;
- Phase 2: Doping 6% to 8% (mass fraction, the same below) of Y ₂ O3 (YSZ) into ZrO ₂ ceramics, achieving partial stability of ZrO ₂ through the doping of rare earth Y ₂ O3, preventing its high-temperature phase transition, and forming point defect structures, obtaining excellent properties such as low thermal conductivity and high thermal expansion, with a long service life, and becoming the most widely used thermal barrier coating material at present. However, YSZ thermal barrier coatings prepared by traditional methods have columnar crystals or porous layered structures, which are susceptible to corrosion and infiltration by molten salts, causing reactions and stress, ultimately leading to coating cracking and detachment;
- Phase 3: Develop new thermal barrier coating materials, such as La ₂ Zr ₂ O ₇, Gd ₂ Zr ₂ O ₇, RE ZrO2 ₂, etc. This type of material has a certain chemical inertness to molten salt corrosion, but its thermal expansion coefficient, mechanical properties, and insulation effect still need to be further improved. With the development of aircraft engines towards higher thrust to weight ratios, combustion chamber temperatures will exceed 2100K, and existing thermal barrier coatings are no longer sufficient to meet the demand. Developing new thermal barrier coatings with ultra-high temperature, high insulation, and long lifespan has become a current research focus.
Wear resistant ceramic coating
Wear, corrosion, and fracture are the main causes of equipment component failure, which are commonly present in metallurgy, construction, power, machinery, and other fields. Among them, wear has the most serious impact on components – taking transportation equipment as an example, about 80% of component failures are caused by material wear, so wear problems have received widespread attention from the materials science community.
In order to meet the development needs of the manufacturing industry, surface engineering technology has emerged, which can significantly improve material performance with low investment and significant economic benefits. In recent years, the preparation of wear-resistant ceramic coatings on substrate surfaces has become a research hotspot for scholars both domestically and internationally. Ceramic materials have the characteristics of high melting point, high hardness, high strength, high chemical stability, high insulation capacity, low thermal conductivity, and low thermal expansion coefficient. When used as coatings, they can effectively improve the wear resistance, high temperature resistance, corrosion resistance, and high temperature oxidation resistance of the substrate material; At the same time, wear-resistant ceramic coatings combine the advantages of ceramics with the toughness of metal materials. After spraying on the surface of the material, it can combine the strength and toughness of metals with the wear resistance, high temperature resistance, corrosion resistance, and insulation properties of ceramics, which is of great significance for extending the service life of components and improving social and economic benefits.
In specific applications, the power industry is an important scene for wear-resistant ceramic coatings: the service life of wind turbines in thermal power plants can be significantly extended after being coated with wear-resistant ceramic coatings; The large hydraulic engineering hoist adopts piston rods coated with wear-resistant ceramic coatings, which can effectively solve the problems of oil leakage and jamming of traditional piston rods after long-term use. In the electronics industry, high dielectric constant coatings (such as barium titanate coatings) are widely used in the field of capacitors; The high-performance packaging materials for integrated circuit substrates prepared using the high-temperature electrical insulation properties of alumina coatings are also widely used.
Gas barrier ceramic coating
Nuclear fission poses issues of nuclear safety and radioactive contamination from nuclear waste, while nuclear fusion is an ideal clean energy source with advantages such as large energy release, low thermal pollution, safe operation, and pollution-free products. However, the materials used in nuclear fusion reactors are affected by factors such as high temperature, thermal mechanical stress, and strong neutron irradiation during the fusion reaction process. Therefore, the structural materials used in the reactor need to have strong resistance to high temperature oxidation, thermal shock, and radiation. At the same time, low activity materials need to be selected or developed to ensure low radioactivity after service.
In addition, fusion fuel has strong penetration ability in metal structural materials, and can undergo chemical adsorption, desorption, and diffusion phenomena, which can cause damage to the material (such as hydrogen embrittlement). Moreover, the fuel itself is radioactive, and leakage can pollute the environment. Therefore, from the perspectives of radiation safety, environmental protection, and nuclear fuel conservation, materials with low permeability should be selected to reduce gas leakage, optimize gas balance, and reduce the risk of hydrogen embrittlement in containers.
At present, the preferred materials for gas barrier coatings are ceramics and their composite materials – ceramic materials have extremely low solubility for hydrogen isotopes (gases) and can also alleviate magnetohydrodynamic (MHD) effects, reducing corrosion caused by liquid metal proliferators. With the deepening of research, ceramic gas barrier coatings were mainly composed of ceramic materials such as silicides and niobium based materials in the early stage, and have now developed into ceramic gas barrier materials with oxides and their composites as the core.
Anti corrosion ceramic coating
Nano ceramic coatings with soft protection function play an important role in the field of protection. At present, nano ceramic coatings have been used in anti-corrosion scenarios under harsh corrosion conditions, which can effectively protect navigation beacon lamp holders, ships, petrochemical facilities, various storage tanks, bridges, bridge piers, railway culverts, drilling equipment, offshore oilfield facilities, as well as the outer surface of strong acid and alkali production equipment. They can resist the erosion of strong acid and alkali, salt spray, freeze-thaw, mold and other factors for a long time.
1. Corrosion prevention of chemical thermal fluid transportation pipeline system
Compared to other coatings, the biggest advantage of ceramic coatings is their high temperature resistance. In some hot fluid transportation scenarios containing corrosive media, special protective treatment using nano ceramic coatings on pipelines, valves, storage tanks, and other equipment can significantly enhance the equipment’s corrosion resistance, thereby reducing equipment failure rates, reducing the frequency of equipment downtime for maintenance, improving production efficiency, and ensuring equipment operation safety.
2. Anti corrosion of oil and gas transportation pipeline system
Pipeline transportation is one of the five major modes of transportation, with a development history of over a hundred years worldwide. Currently, the crude oil pipeline transportation volume in developed countries accounts for 80% of their total transportation volume, and the long-distance transportation of refined oil products has basically achieved pipeline transportation. The proportion of natural gas pipeline transportation is as high as 95%. Due to the differences in geological environments in natural gas and oil producing areas, there are many factors that can cause corrosion of oil and gas pipelines and equipment, such as saline alkali land, humid environments, microorganisms, electric currents, etc. (external corrosion), as well as H ₂ S, CO ₂, S, O ₂, H ₂ O, etc. (internal corrosion). Among them, hydrogen sulfide has the most significant destructive effect, which can lead to gas pipeline leakage in mild cases, and pipeline, oil pipe and casing fracture, explosion and other accidents in severe cases. Therefore, pipeline anti-corrosion work is crucial.
Pipeline anti-corrosion usually adopts a combination of anti-corrosion coating and cathodic protection. The anti-corrosion coating is the first barrier for pipeline anti-corrosion, which directly determines the anti-corrosion performance and operating life of the pipeline. Strengthening the research on anti-corrosion coating is of great significance for pipeline corrosion control. At present, organic coatings are mainly used for pipeline anti-corrosion, but organic coatings have problems such as aging and deterioration, poor heat and cold resistance, which limit the service life of pipelines; The nano ceramic coating has anti-aging, temperature resistance, corrosion resistance and other characteristics, which can significantly extend the service life of the pipeline. In addition, using nano ceramic coatings to enhance protection in harsh areas and prone to malfunctions can significantly reduce the incidence of accidents; At the same time, the requirements for the cathodic stripping ability of coatings in oil and gas pipelines are constantly increasing, and the anti cathodic stripping ability of organic coatings is relatively weak, further highlighting the advantages of nano ceramic coatings.
3. Corrosion prevention of marine environmental equipment
In the marine environment, electrochemical corrosion generated in high salt and high humidity conditions can quickly corrode steel hulls into scrap iron. Therefore, equipment protection in marine environments usually adopts a combination of cathodic protection and anti-corrosion coatings to protect ship hulls and other workpieces, equipment or components exposed to corrosive smoke and other environments. The nano ceramic coating has excellent cathodic stripping resistance and can adapt to harsh marine working environments, effectively ensuring equipment lifespan.
4. Anti corrosion of aerospace high-temperature equipment
Space engine equipment is exposed to high-temperature working environments for a long time, and metal alloy turbine blades are susceptible to erosion from substances such as sand and gravel melts. In such harsh working conditions, the use of nano ceramic coatings can meet the protection requirements, protecting turbine blades from erosion and ensuring stable operation of aerospace engines.
Environmentally friendly ceramic coatings and their applications in other fields
Traditional ceramic coatings use hexavalent chromium solution, mainly to achieve high smoothness and rust prevention effect on mechanical components; To replace metal chromium, researchers grind ceramics into ultrafine nanoscale particles, and then form a dense thin film through flow action. By repeatedly adjusting parameters such as the roughness of the ceramic substrate surface, the thickness of the ceramic film, and the hardness of the substrate, a high gloss chromium free ceramic coating is finally formed that is closely adhered to the surface of the component, with high wear resistance and rust prevention performance, greatly improving the environmental friendliness of the coating.
In addition to the above-mentioned fields, ceramic coatings are also widely used in other industries: in the biomedical field, coating ceramic coatings with human biocompatibility on the surface of medical metal alloys can not only prolong the service life of medical materials, but also effectively solve the problem of biocompatibility of medical materials in the human body, making the performance of materials more stable after implantation in the body; In the printing industry, coating ceramic coatings on the surfaces of different types of rollers (such as ink fountain rollers, offset rollers, etc.) can effectively extend the service life of the rollers and reduce the maintenance costs of printing equipment.
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