With the rapid development of the equipment manufacturing industry, the failure and scrapping of many mechanical equipment components in harsh and complex environments has caused huge economic losses and many equipment failures. It is urgent to explore efficient and green emerging manufacturing technologies to strengthen key components of new equipment. Life extension and remanufacturing of obsolete equipment. Ceramic materials are often used as surface protection strengthening materials for metal parts because of their high melting point, high strength, low thermal conductivity, and low thermal expansion coefficient. Ceramic coating can greatly enhance the wear resistance, corrosion resistance, and high-temperature oxidation resistance of the substrate, and is widely used in aerospace, petrochemical, machinery manufacturing, and other fields.
Common ceramic coating preparation techniques include laser cladding, high-temperature self-propagating synthesis, vapor deposition, and thermal spraying. Among them, high-temperature self-propagating synthesis has simple procedures, low energy consumption, and a short production cycle, but requires extremely high-purity powder as raw materials. It is not suitable for large-scale production, and the reaction process is rapid and inconvenient to accurately control; the ceramic coating prepared by vapor deposition has high purity and good density, but the equipment is expensive and the production efficiency is low; thermal spraying ceramic coating has high efficiency and controllable thickness. The process is simple and can be used for spraying complex-shaped workpieces, but there are relatively many defects such as coating pores and low bonding force; laser cladding efficiency is high, and the cladding area is precisely controllable. The preparation of ceramic coatings has performance, cost, Environmental protection, and other advantages, but the prepared ceramic coating may also have defects such as cracks and pores.
Laser cladding technology can melt ceramic materials to overcome their difficult processing characteristics and prepare high-quality ceramic coatings. The ceramic coating obtained by this technology has excellent mechanical properties, physical and chemical properties, which is beneficial to prolong the service life of parts, reduce costs and reduce waste of resources. Surface strengthening and remanufacturing is an important direction of green manufacturing and an effective way to achieve energy saving and emission reduction and promote sustainable economic and social development. With the continuous advancement of laser cladding technology and the replacement of cladding equipment, the preparation of ceramic coatings by laser cladding can strengthen the surface of parts in complex environments and prolong the life of remanufacturing, which is in line with the sustainable development strategy concept advocated by the country. The "Made in China 2025" development plan is getting closer and closer. Laser cladding ceramic coating for remanufacturing belongs to the category of advanced additive manufacturing and green manufacturing and effectively implements the "14th Five-Year" renewable resource development plan.
1 Laser cladding ceramic coating
laser cladding ceramic coatings for surface strengthening and remanufacturing can be divided into composite ceramic coatings, metal-ceramic composite coatings, laser in situ synthetic ceramic coatings, and nanocomposite ceramics according to material composition and forming mechanism coating.
- Composite ceramic coating: Researchers have developed a variety of eutectic types of laser cladding composite ceramic coatings composed of nitrides, borides, carbides, and oxides. These composite materials composed of multi-component ceramics have high mutual solubility and affinity between components, which can effectively reduce the ceramic phase's grain size, improve the coating's strength and toughness, and make the coating more stable than single-phase ceramic coatings. Good thermophysical properties and excellent properties such as wear and corrosion resistance.
- Metal-ceramic composite coating: Metal-ceramic composite coating is a combination of ceramic phase (reinforcing phase) and metal or alloy (bonding phase), so that it can obtain good wettability of metal materials and remarkable hardness of ceramic phase, wear resistance, and corrosion resistance. The rapid heating and solidification during the laser cladding process refines the grains in the metal-ceramic composite coating and evenly distributes the refractory ceramic strengthening phase in the coating in the binder phase, which increases the coating strength. , to obtain the effect of excellent properties of metals and ceramics.
- In-situ synthesis of ceramic coatings: In-situ synthesis of ceramic coatings forms ceramic phase particles by adding different element powders under high-temperature conditions, and due to the formation of the reaction, the ceramic particles will spontaneously nucleate and grow, so the distribution is even, dense structure, enhanced interface bonding, and significantly reduced performance loss, overcomes the defects of poor interface bonding, particle aggregation, cracks and other defects that exist in the direct addition of ceramic phases.
Laser cladding ceramic coatings show extraordinary advantages in the surface modification of new products or the remanufacturing of damaged parts, but in the process of preparing ceramic coatings, there are also common defects such as pores, element segregation, and cracks. Based on the principles and characteristics of coatings prepared by laser cladding, researchers will optimize the quality of ceramic coatings from the aspects of laser cladding process parameters, coating structure, coating material system, and various process-assisted forming.
2 Application direction of laser cladding ceramic coating
In recent years, industries such as machinery manufacturing, transportation, aerospace, petrochemicals, and biomedicine have put forward higher requirements for the load-carrying capacity and fatigue life of workpieces. Aiming at the problems existing in different working conditions, researchers used laser cladding surface strengthening and remanufacturing repair technology to prepare a series of functional coatings to deal with the failure of workpieces. According to the different functions of ceramic materials, ceramic functional coatings prepared by laser cladding can be roughly divided into four types:
- Laser cladding corrosion-resistant ceramic coatings, materials in harsh corrosion environments (such as offshore oil, natural gas drilling platforms, hydropower stations, chemical plants, mines, etc.) need to strengthen the surface of the workpiece and remanufacture damaged parts to resist erosion damage, Corrosion-resistant coatings can increase the service life of the equipment and reduce maintenance costs;
- Laser cladding wear-resistant ceramic coating, wear is the most common failure mode of many engineering materials, friction and wear under harsh working conditions (heavy load, high temperature, high speed, etc.) will shorten the service life of the workpiece. Researchers improve the hardness and wear resistance of workpieces by preparing ceramic coatings with excellent anti-wear and anti-friction properties, thereby prolonging the service life;
- Laser cladding thermal barrier ceramic coating, thermal barrier coating to clad the high temperature resistant, oxidation resistant, and corrosion resistant ceramic material on the substrate, so as to isolate the substrate from the external hot gas, thereby protecting the parts from Corrosion, oxidation, heat protection layer to improve the performance of the substrate and prolong the service life of the parts. This coating has been used in various engineering fields, including internal combustion engines, gas turbine blades of jet engines, thermochemical after-treatment devices, etc.
3 Prospects
- Design of new ceramic coating materials. As the service conditions of equipment become more and more harsh, and the characteristics of ceramic materials and metal materials are quite different, it is necessary to innovate coating material design ideas and introduce material design and performance verification such as first-principle calculations and high-throughput performance tests. method to achieve coating materials with multiple excellent properties at the same time, for example, the combination of MAX phase ceramics and metals can obtain wear-resistant, high-temperature resistant, strong and tough coatings; self-lubricating high-conductivity ceramic materials and hafnium/zirconium ultra-high- temperature ceramics And other materials also have important development and application value. The diversity of material systems can broaden its application range and provide more choices for the use of different working conditions.
- Development of a new laser cladding process. The process has an important influence on the macroscopic morphology and microstructure of the coating. Although the process combination of laser cladding and ultrasonic vibration, electromagnetic assistance, induction heating assistance, and other technologies has been applied, how to reduce the surface roughness of the coating, improve the cladding forming efficiency, improve the fatigue characteristics, and improve the surface quality are still unclear. Need to explore in depth.