Laser cladding is a novel coating technology involving multiple disciplines such as optics, mechanics, electronics, materials science, and detection and control. It is a crucial supporting technology for advanced laser manufacturing, capable of solving problems that traditional manufacturing methods cannot address, and is a high-tech field strongly supported and promoted by the state. Currently, laser cladding technology has become an important means for new material preparation, rapid direct manufacturing of metal parts, and green remanufacturing of failed metal parts, and is widely used in industries such as aerospace, petroleum, automotive, machinery manufacturing, shipbuilding, and mold making. To promote the industrialization of laser cladding technology, researchers worldwide have conducted systematic research on the key technologies involved, achieving significant progress. Numerous research papers, conference papers, and patents both domestically and internationally introduce laser cladding technology and its new applications, including research on laser cladding equipment, materials, processes, monitoring and control, quality inspection, and process simulation. However, to date, laser cladding technology has not yet been widely industrialized. The reasons for this include government guidance, limitations in the maturity of the laser cladding technology itself, and the level of public acceptance of laser cladding technology. Therefore, for laser cladding technology to achieve comprehensive industrial application, it is essential to increase promotional efforts, be market-demand oriented, focus on overcoming key factors hindering development, and solve critical technologies involved in engineering applications. It is believed that in the near future, the application areas and intensity of laser cladding technology will continue to expand.
Below are some application examples of laser cladding: The focused power density of the laser beam can reach 10¹⁰~12 W/cm², achieving a cooling rate of up to 10¹² K/s on materials. This comprehensive characteristic not only provides a strong foundation for the growth of new disciplines in materials science but also provides an unprecedented tool for realizing new materials or new functional surfaces. The rapid cooling conditions created by laser cladding, far from equilibrium under high temperature gradients, lead to the formation of a large number of supersaturated solid solutions, metastable phases, and even new phases in the solidified structure, as confirmed by numerous studies. It provides entirely new thermodynamic and kinetic conditions for manufacturing functionally graded in-situ self-generated particle-reinforced composite layers. Simultaneously, the preparation of new materials using laser cladding technology is a crucial foundation for the repair and remanufacturing of failed components under extreme conditions and the direct manufacturing of metal parts, receiving high attention and extensive research from the scientific community and enterprises worldwide. Currently, laser cladding technology can be used to prepare metal-based composite materials such as iron-based, nickel-based, cobalt-based, aluminum-based, titanium-based, and magnesium-based materials. Functionally, it can produce coatings with single or multiple functions, such as wear resistance, corrosion resistance, high-temperature resistance, and special functional coatings. In terms of the material system constituting the coating, it has evolved from binary alloy systems to multi-component systems. The alloy composition design and multifunctionality of multi-component systems are important development directions for the future preparation of new materials by laser cladding. New research shows that steel-based metal materials dominate engineering applications in my country. Meanwhile, most failures of metal materials (such as corrosion, wear, and fatigue) occur on the working surfaces of components, requiring surface strengthening. Using large-scale in-situ self-generated particle-reinforced steel-based composite materials to meet the service conditions of workpieces is not only wasteful of materials but also extremely costly. On the other hand, from a biomimetic perspective, natural biomaterials have a dense outer layer and a sparse inner layer, exhibiting a hard outer layer and a tough inner layer. Furthermore, the density-sparseness and hardness-toughness gradient from the outside to the inside of natural biomaterials gives them excellent performance characteristics.
Based on the specific service conditions and performance requirements of materials in engineering, there is an urgent need to develop novel surface metal matrix composites with strong and tough bonds and graded performance variations. Therefore, the preparation of graded functional in-situ self-generated particle-reinforced metal matrix composites with metallurgical bonding to the substrate using laser cladding is not only an urgent need in engineering practice but also an inevitable trend in the development of laser surface modification technology. While the preparation of in-situ self-generated particle-reinforced metal matrix composites and functionally graded materials using laser cladding technology has been reported, most studies remain at the stage of microstructure and performance analysis and process parameter control. The size, spacing, and volume ratio of the reinforcing phases are still not controllable. Gradient functionality is formed through multi-layer coating, inevitably resulting in weak interfacial bonding between layers, indicating a long way to go before practical application. The preparation of metal matrix surface composites with controllable particle size, quantity, and distribution, appropriately matched strength and toughness, and integrating graded functionality and in-situ self-generated particle reinforcement using laser cladding technology is an important future development direction. The research content involves:
1. The techniques, methods, and principles of cladding material composition, microstructure, and performance design, as well as the control technology for process implementation.
2. Establishment of thermodynamic and kinetic models for the precipitation, growth, and strengthening of particle-reinforcing phases in functionally graded in-situ self-generated particle-reinforced metal matrix composites prepared by laser cladding.
3. Biomimetic design of particle-reinforcing phase morphology, structure, function, and composite composition, and control technology for size, quantity, and distribution.
4. Research on the principles, key factors, and process methods for gradient control of coating composition, microstructure, and properties.
5. Observation, analysis, control, and characterization of macroscopic and microscopic interfaces; analysis and testing of the conventional properties of functionally graded in-situ self-generated particle-reinforced metal matrix composites, as well as wear behavior and failure mechanisms under different working conditions. Breakthroughs in these research areas may solve the problem of coating-matrix compatibility mismatch and easy cracking, and promote the expansion of the application fields of laser cladding technology.