Laser cladding technology refers to the process method of placing the selected coating material on the surface of the coated substrate in different filler ways, melting a thin layer on the surface of the substrate at the same time by laser irradiation, and forming a surface coating with very low dilution and metallurgical combination of the substrate material after rapid solidification, so as to significantly improve the wear resistance, corrosion resistance, heat resistance, oxidation resistance and electrical characteristics of the surface of the matrix material.
Laser cladding technology is a new technology with high economic benefits, which can prepare high-performance alloy surfaces on cheap metal substrates without affecting the properties of the matrix, reducing costs and saving precious and rare metal materials.
The lasers used in laser cladding mainly include CO2 lasers and solid-state lasers, mainly including disk lasers, fiber lasers and diode lasers.
Process characteristics of laser cladding technology
Laser cladding can be divided into two categories according to the different powder feeding processes: powder presetting method and synchronous powder feeding method. The effect of the two methods is similar, and the synchronous powder feeding method has the advantages of easy automatic control, high laser energy absorption rate, and no internal porosity, especially the cladding cermet, which can significantly improve the anti-cracking performance of the cladding layer, so that the hard ceramic phase can be evenly distributed in the cladding layer.
1. Laser cladding has the following characteristics:
(1) The cooling rate is fast (up to 106K/s), which belongs to the rapid solidification process, and it is easy to obtain fine grain structure or produce new phases that cannot be obtained in the equilibrium state, such as unstable phase, amorphous state, etc.
(2) The dilution rate of the coating is low (generally less than 5%), and the matrix is firmly metallurgically bonded or interfacial diffusion, through the adjustment of laser process parameters, a good coating with low dilution rate can be obtained, and the coating composition and dilution are controllable.
(3) The heat input and distortion are small, especially when high power density rapid cladding is adopted, the deformation can be reduced to the assembly tolerance of the part.
(4) There are hardly any restrictions on powder selection, especially for depositing high melting point alloys on low melting point metal surfaces.
(5) The thickness range of the cladding layer is large, and the thickness of a single powder feeding is 0.2~2.0mm.
(6) It can be used for selective deposition, with less material consumption and excellent performance-to-price ratio.
(7) Beam aiming can make inaccessible areas deposition.
(8) The process is easy to automate. It is very suitable for the wear repair of common wear parts in the oilfield.
2. Similarities and differences between laser cladding and laser alloying
Laser cladding and laser alloying are both alloy cladding with completely different compositions and properties formed on the surface of the substrate by using a rapid melting process generated by a high-energy-density laser beam. The process of the two is similar, but there are essential differences, the main differences are as follows:
(1) The cladding material in the laser cladding process is completely melted, and the matrix melting layer is extremely thin, so it has little impact on the composition of the cladding layer, while laser alloying is to add alloying elements to the surface molten composite layer of the substrate to form a new alloy layer based on the substrate.
(2) Laser cladding essentially does not melt the metal on the surface layer of the matrix as a solvent, but melts the alloy powder that is otherwise configured to make it the subject alloy of the cladding layer, and at the same time, the matrix alloy also has a thin layer of melting to form a metallurgical bond. The preparation of new materials by laser cladding technology is an important basis for the repair and remanufacturing of failed parts under extreme conditions and the direct manufacturing of metal parts, which has been highly valued by scientific circles and enterprises around the world.
Evaluation of laser cladding effect
To evaluate the quality of laser cladding layer, there are two main considerations. First, macroscopically, the shape, surface unevenness, cracks, porosity and dilution rate of the cladding channel are investigated; The second is to examine whether a good organization is formed and whether it can provide the required performance. In addition, the types and distribution of chemical elements of the surface cladding layer should also be determined, attention should be paid to analyzing whether the transition layer is metallurgically combined, and if necessary, the quality life test should be carried out.
The research work focuses on the research and development of cladding equipment, melt pool dynamics, alloy composition design, crack formation, propagation and control methods, and the adhesion between the cladding layer and the matrix.
The main problems faced by the further application of laser deposition technology are:
(1) The main reason why laser cladding technology has not been fully industrialized in China is the instability of the quality of cladding layer. Due to the difference in the temperature gradient and thermal expansion coefficient of the cladding layer and the base material, a variety of defects may occur in the cladding layer, mainly including porosity, cracks, deformation and surface unevenness.
(2) Detection and implementation of automatic control of the light deposition process.
(3) The cracking sensitivity of laser cladding layer is still a difficult problem for researchers at home and abroad, and it is also an obstacle to engineering application and industrialization.
Application of laser cladding technology
The scope of application and application field of laser cladding processing technology is very wide, and it can cover almost the entire machinery manufacturing industry.
At present, laser cladding of self-fusing alloy powders and ceramic phases such as cobalt-based, nickel-based and iron-based on the surface of stainless steel, die steel, malleable cast iron, gray cast iron, copper alloy, titanium alloy, aluminum alloy and special alloys has been successfully carried out.
Laser cladding iron-based alloy powders are suitable for parts that require local wear resistance and are easy to deform. Nickel-based alloy powders are suitable for components that require local wear resistance, thermal corrosion resistance and thermal fatigue resistance. Cobalt-based alloy powders are suitable for parts that require resistance to wear, corrosion and thermal fatigue. The ceramic coating has high strength, good thermal stability and high chemical stability at high temperatures, and is suitable for parts that require wear resistance, corrosion resistance, high temperature resistance and oxidation resistance.
Here are a few typical applications of laser cladding technology:
1. Manufacturing and remanufacturing of mining equipment and its parts
The mining coal machine equipment is large and wears quickly, and the parts are damaged quickly due to its harsh working environment. The parts of coal machinery equipment manufactured and remanufactured by laser include: three machines and one machine.
(1) Shearer: main frame, rocker arm, gear, gear shaft, various bushings, hinged frames, oil cylinders, oil cylinder seats, guide sliding shoes, sprockets, pin wheels, drive wheels, picks, etc.
(2) Roadheader: cylinders, brackets, shafts, various bushings, picks, etc.
(3) Scraper conveyor: middle chute, transition groove, gear box, gear, gear shaft, spiral bevel gear, shaft parts, etc.
(4) Hydraulic support: hinged holes of cylinders, bases and brackets, various bushings, etc.
2. Manufacture and remanufacturing of power equipment and its parts
The power equipment has a large distribution and uninterrupted operation, and the probability of damage to its parts is high. Steam turbine is the core equipment of thermal power generation, due to the special working conditions of high temperature and high heat, it is necessary to regularly repair the damaged unit parts every year, such as spindle shaft diameter, moving blades, etc. Gas turbines are often damaged due to their operation at high temperatures of up to 1300°C. The laser remanufacturing technology is used to repair all the defects and restore its performance, and the cost is only 1/10 of the price of the new unit.
Laser cladding of motor rotor shafts
3. Manufacturing and remanufacturing of petrochemical equipment and its parts
Modern petrochemical industry basically adopts the continuous mass production mode, in the production process, the machine works in a harsh environment for a long time, resulting in damage, corrosion, wear and tear of the components in the equipment, which often have problems with the parts including valves, pumps, impellers, large rotor journals, wheel discs, bushings, bearings, etc., and these components are very expensive, there are many types of parts involved, most of the shapes are very complex, and it is difficult to repair, but because of the emergence of laser cladding technology, None of these problems are a problem.
Laser cladding oil drill pipe, drilling tools and other hard ceramic coatings
4. Manufacture and remanufacturing of railway equipment and its parts
With the rapid development of railway transportation with the growth of social economy, the demand for new railway vehicles is very large, and the number and performance requirements of major components are also increasing. As a new resource reuse technology, remanufacturing technology can be applied to the remanufacturing of wear-prone parts of vehicles. Laser surface strengthening is the core technology and process means of remanufacturing, in which laser surface cladding technology can be applied to the repair and strengthening of the surface of remanufactured parts.
5. Remanufacturing of key parts of equipment in other machinery industries
The remanufacturing of key components of other machinery manufacturing industries, including metallurgy, petrochemical, mining, chemical, aviation, automobile, shipbuilding and machine tools, etc., is used to repair and optimize the performance of precision equipment, large equipment, and valuable parts in these fields of wear, erosion, and corrosion.
Laser-clad steelmaking continuous casting rollers with high wear resistance
Disclaimer: If it involves copyright issues of works, please contact us, we will negotiate copyright issues or remove content as soon as possible! The content only represents the author's personal views, and does not mean that this official account agrees with his views and is responsible for his authenticity.