This article reviews the research progress of laser cladding technology, covering the basic principles of laser cladding, material selection, process parameter control, equipment configuration and industrial application. Laser cladding has great application prospects in improving the surface performance of materials due to its small heat-affected zone and high bonding strength. The article outlines the selection criteria of laser cladding materials, the research and development status of metal/ceramic/composite materials, analyzes the optimization strategy of laser/scanning/gas protection parameters, discusses the development direction of equipment such as lasers/nozzles/control systems, and lists application examples in aerospace, automobile, metallurgy and other fields. Further innovation of laser cladding technology and equipment will promote the important role of this technology in reducing life cycle costs and improving product reliability.
Laser cladding technology is a technology that uses high-power laser as a heat source to melt the cladding material and then deposit it on the surface of the cladding material to generate a cladding layer. Compared with traditional cladding technology, laser cladding has the advantages of small heat-affected zone, high bonding strength, and almost no pretreatment of the cladding material, which can achieve local precision repair. The laser cladding layer has a gradient structure with the substrate, which is conducive to reducing thermal stress and residual stress and improving bonding strength. Since the laser cladding technology was proposed in the 1960s, with the development of laser technology and materials science, it has become a key technology widely used in the field of surface engineering.
Compared with gas torch cladding, laser cladding has a narrow heat-affected zone, small residual stress, and little thermal effect on the substrate. Compared with plasma spraying, the laser cladding layer is firmly welded to the substrate and has high bonding strength. Compared with electron beam cladding, laser cladding can be operated without vacuum and is easy to automate. In general, laser cladding combines the advantages of high power density, strong collimation, and high control flexibility of lasers during the cladding process, making it have obvious advantages in material surface modification.
Laser cladding technology can form a coating with specific composition and properties on the surface of metal or non-metal materials, and achieve unique wear resistance, corrosion resistance, oxidation resistance, high temperature resistance, fatigue resistance and other multi-functions of the material surface, which greatly expands the application range of the material. Laser cladding technology has been widely used in many industrial fields such as aerospace, automobiles, molds, metallurgy, machinery, chemicals, photovoltaics, biomedicine, etc., which is of great significance to improving product performance and life.
1 Research on laser cladding materials
1.1 Selection and characteristics of laser cladding materials
Selecting suitable cladding materials is crucial to obtaining high-quality cladding layers. Generally, excellent laser absorption performance is required, and parameters such as the melting point, density, diffusivity, and residual stress of the material are considered. Commonly used materials include metal powders (cobalt-based, nickel-based, etc.), ceramic powders (aluminum oxide, silicon carbide, etc.), and pre-alloyed compounds or mixtures made of the above materials. Functional gradient materials can also be designed using different materials.
In addition to good laser absorption performance, cladding materials also need to have a moderate melting point, high stability, good wettability and metallurgical coupling with the substrate. Metal cladding materials can provide good ductility and density, while ceramic cladding materials have high hardness and chemical stability. By rationally selecting materials, a composite cladding layer with multiple properties can be obtained.
1.2 Functions and performance of laser cladding materials
By selecting different laser cladding materials, excellent hardness, wear resistance, corrosion resistance, thermal fatigue resistance, oxidation resistance, high temperature resistance, biocompatibility, etc. can be obtained, giving the surface of the cladding material comprehensive excellent performance. The performance of the cladding layer is closely related to factors such as material composition and the magnitude of the components, laser process parameters, etc. For example, by selecting metal-ceramic composite materials such as WxC-NiCrBSi, a wear-resistant cladding layer with both metal ductility and high ceramic hardness can be obtained. Using Inconel 718 alloy cladding materials, a high-temperature corrosion-resistant and oxidation-resistant cladding layer can be obtained. Boron nitride cladding materials can provide very high surface hardness. Titanium alloy cladding materials can obtain excellent biocompatible cladding layers.
1.3 Research status and development trend of laser cladding materials
The material composition of laser cladding is a very important factor affecting the performance of cladding coatings. As the application environment of engineering parts becomes more and more complex and harsh, the coating functions are required to be more and more diverse and the performance is getting better and better. Therefore, a single coating material can no longer meet the application requirements. The composite of coating materials has become a very important way for people to solve this problem.
At present, the commonly used laser cladding material formulas are: self-fluxing alloy materials, carbide dispersion or composite materials, composite ceramic materials, etc. This type of material has excellent wear resistance, corrosion resistance, high temperature resistance and other properties, and is widely used in metallurgy, marine equipment, aerospace, nuclear power and other fields. Therefore, the research on laser cladding material formulas has received close attention from scholars at home and abroad.
Internationally, the research on traditional metal cladding materials such as nickel-based, cobalt-based, and titanium-based alloys is relatively mature, and is currently committed to the development of high-temperature alloys and functional gradient materials. Traditional ceramic cladding materials such as alumina and silicon nitride have relatively stable performance. Existing research explores high-temperature oxidation-resistant ceramic composites. There are many studies on metal-ceramic composite cladding materials, which have the advantages of metal toughness and ceramic hardness, and there are also attempts to use bioactive materials in the medical field. Technologically advanced countries such as Europe, the United States, Japan and South Korea have conducted research on laser cladding technology earlier. Among them, the Fraunhofer Institute for Laser Technology in Germany has carried out basic research on laser cladding of various metal materials such as titanium alloys, aluminum alloys, chromium alloys, etc.; the Oakridge National Laboratory in the United States is committed to developing efficient and low-cost laser cladding systems; many Japanese companies, such as Sumitomo Heavy Industries and Mitsubishi Heavy Industries, are also engaged in the research and development and production of laser additive manufacturing equipment.
Traditional metal cladding materials are widely used in China. Since 2010, research institutions and universities such as Beijing University of Aeronautics and Astronautics, Northwestern Polytechnical University and Shenyang Institute of Automation of the Chinese Academy of Sciences have made great progress in laser cladding technology. At present, the focus is on industrial applications, and research has been carried out on aircraft engine blade refurbishment, metal functional gradient materials, intermetallic compound coatings, etc., and some technologies have reached the international advanced level. Local companies such as Shenzhen Guangyun Laser are also developing steadily. At present, the localization of ceramic cladding materials has made certain progress, but there is still a gap from high-performance materials; the research on composite cladding materials started late and is developing from simulation to independent design.
Looking to the future, laser cladding materials at home and abroad are developing from traditional to innovative. The research focus is developing from single materials to composite materials, especially metal-ceramic composite materials, to obtain better comprehensive performance. At the same time, new cladding materials suitable for special environments are also being developed, such as high-temperature oxidation-resistant alloys, biocompatible materials, etc.
2 Research on laser cladding process
2.1 Basic principles of laser cladding process
Laser irradiates the cladding material to form a molten pool. The molten cladding material penetrates into the surface of the cladding material through capillary action, and then solidifies rapidly to achieve molten bonding between materials. The cladding process can be divided into three stages: pretreatment, cladding, and post-treatment. The pretreatment includes cleaning the substrate and improving the surface
roughness. The cladding stage is the key step in forming the cladding layer. Post-treatment includes heat treatment to eliminate residual stress, etc.
2.2 Influencing factors and optimization methods of laser cladding process
The main influencing factors of laser cladding process are laser parameters, scanning speed, nozzle parameters, gas protection, etc. The regulation and optimization strategy of laser cladding process parameters is the key to obtaining high-quality cladding layers. For the main process parameters, researchers have proposed many effective adjustment and control strategies. For example, in terms of laser parameters, a more stable molten pool morphology is obtained by optimizing the laser power. The study found that matching the laser wavelength can improve the laser absorption efficiency of specific cladding materials. In terms of scanning trajectory, the effects of different scanning modes on molten pool formation are compared, and the results show that orthogonal scanning can take into account both scanning efficiency and molten pool stability. Regarding gas injection protection, effective atmosphere control is achieved by optimizing gas flow and pressure. Overall, a relatively systematic laser cladding process parameter optimization strategy has been established. Through the coordinated control of key parameters such as laser system, scanning mode, gas protection, etc., the cladding process can be accurately adjusted, and the cladding quality and stability can be significantly improved.
3 Research on laser cladding equipment
Laser cladding equipment refers to special equipment used to perform laser cladding technology. It includes laser source, optical system, spray system, workpiece positioning and moving system, powder spray device, workbench and control system. As the key equipment to realize the laser cladding process, the technological development of laser cladding equipment directly affects the cladding quality and process capability.
Common lasers include CO2 lasers, fiber lasers, semiconductor lasers, etc. As the core light source of laser cladding, the output power, wavelength range, beam quality and operation stability of the laser are the key technical indicators to ensure the cladding quality. In the future, the research and development of lasers will focus on the improvement of output power, the refinement of beam quality, the enhancement of working stability and the expansion of wavelength range to meet the needs of more efficient and refined laser cladding processing.
The spray system directly affects the conveying efficiency of the cladding material. Nozzle optimization design, process online monitoring and temperature field control are the key technologies of the equipment. New equipment such as new scanning heads and multi-laser coupling are emerging in an endless stream. These technological advances have promoted the development of laser precision cladding. In the future, the research on the spray system will focus on the optimization design of the internal structure, the adoption of high-temperature corrosion-resistant materials, and the development of fast multi-nozzle switching mechanisms to improve the life and adaptability of the nozzles, thereby effectively improving the utilization efficiency of the cladding raw materials.
The intelligence level of the control system is related to the stability and surface quality of the cladding. The development direction of the control system in the future is to build an intelligent closed-loop control mechanism, integrate artificial intelligence algorithms for parameter optimization, strengthen the design of human-computer interaction interfaces, and realize digital and intelligent functions such as remote monitoring and state prediction, so as to achieve precise control and quality optimization of the cladding process.
In summary, the development direction of laser cladding equipment is to improve the laser output power and stability, realize precision nozzle control, and develop intelligent control systems to perform high-quality laser cladding of complex shapes. The collaborative innovation and development of laser technology, spray systems, and control systems will promote the evolution of laser cladding equipment towards high efficiency, stability, and intelligence to meet the future needs of laser cladding applications with higher comprehensive performance requirements.
4 Application and development prospects of laser cladding technology in various fields
Due to its precise and efficient characteristics, laser cladding technology has shown great application advantages and development potential in aerospace, automobile, metallurgy and other fields. In the aerospace field, laser cladding technology can be applied to the surface strengthening of important components such as gas turbine blades, nozzles, and turbine disks to generate high-quality anti-wear and high-temperature corrosion resistant coatings, which significantly improves the service life of components. Compared with traditional processes, laser cladding has the characteristics of small processing heat affected zone and high bonding strength, which is very suitable for precision surface additive manufacturing and repair of aviation components. The further development of this technology will greatly reduce the maintenance cost in the aerospace field.
In the field of automobile manufacturing, laser cladding can be used to strengthen the surface properties of important components such as engine valves, connecting rods, camshafts, etc., and enhance wear resistance and corrosion resistance. The service life and reliability of such key components will be significantly improved, which will help reduce the maintenance frequency and reduce the overall life cycle cost of the vehicle.
In the field of metallurgical industry, laser cladding technology can achieve surface repair and protection, component repair and remanufacturing, surface alloying treatment, manufacturing composite materials, local modification treatment and transformation of traditional materials. In terms of surface repair and protection, laser cladding technology increases the wear resistance and corrosion resistance of materials and extends the service life of equipment by cladding special alloys on damaged surfaces. For the repair and remanufacturing of key components, laser cladding technology can restore the original structure and function by selectively heating and cladding suitable alloy materials, thereby realizing the reuse of components. Surface alloying treatment uses laser cladding technology to clad specific alloy materials on the surface of metal materials, thereby improving the hardness, wear resistance and corrosion resistance of the materials and meeting specific process requirements. The use of laser cladding technology to manufacture composite materials can achieve the comprehensive application of different characteristics by cladding different powder materials, thus broadening the application field of metallurgical materials. At the same time, laser cladding technology can achieve local modification treatments such as hardening, annealing and quenching, providing customized performance for metallurgical materials. In addition, the repair and transformation of traditional materials can also be achieved through laser cladding technology, which significantly improves the performance and life of materials by forming a new alloy layer on the surface of the material.
With the continuous maturity of laser cladding technology and equipment, its application field will also expand to other industrial fields such as petroleum, chemical industry, electric power, rail transportation, etc., and the market prospects are broad. The continuous innovation of this technology will significantly reduce equipment maintenance costs in various industries and improve production efficiency.
5 Conclusion
As a precise and efficient surface modification method, laser cladding technology has shown great application potential and development prospects. Its unique advantages are small heat-affected zone, high bonding strength, flexible process control, etc., which can realize precise functional transformation of material surface. After decades of development, laser cladding technology has been successfully applied in important fields such as aerospace, automobile, metallurgy, etc., greatly improving the service life and reliability of core components.
With the further development of laser technology and equipment manufacturing, laser cladding technology still faces challenges in further reducing equipment costs, realizing multi-layer complex structure cladding, and expanding the scope of application materials. The problem of material system matching and stable and repeatable cladding quality control also need to be continuously optimized. However, the application prospects of this technology are very broad, including the repair of hot section components of aviation engines, surface enhancement of automobile engines, and renovation of hydropower equipment. Laser cladding technology will surely play an important role in improving product reliability and reducing life cycle costs through continuous innovation of equipment and processes.
