Laser cladding repair technology is a material surface modification technology. It uses laser high-power density beams and is controlled by the laser processing system under the numerical control to form a thin micro-melting layer on the specified part of the substrate surface, and add self-fluxing alloy powder of specific composition, such as nickel-based, through preset or synchronous mode , Cobalt-based and iron-based alloys, etc., so that they are evenly spread on the surface of the part in a molten state and reach a predetermined thickness, and form a good metallurgical bond with the micro-melted base metal material, and there is only a small degree of dilution between each other. During the solidification process, a functional cladding material layer with predetermined special properties is formed on the surface of the part, which is completely different from that of the substrate, so that the surface properties of the material can be completely changed, and finally the surface of the inexpensive material obtains extremely high wear resistance and corrosion resistance. , High temperature resistance and other properties.
According to the different ways of adding materials, laser cladding methods are divided into preset method and synchronous powder feeding method. The preset method, as the name implies, is to place the material to be coated on the surface of the pretreated substrate by spraying or bonding in advance, and then remelt it by laser beam radiation before performing appropriate heat treatment; synchronous powder feeding is performed in advance After the treatment, the surface of the cladding substrate is sprayed with the powder directly on the moving molten pool formed by laser radiation, and the coating is formed at one time. Synchronous powder feeding is the development trend of laser cladding technology, which can make full use of laser energy, control process parameters, and improve production efficiency and coating quality. However, synchronous powder feeding also has requirements on the particle size and fluidity of the powder, which need to be determined according to the specific situation.
Iron-based alloy powder is suitable for parts that require partial wear resistance and easy deformation.
Cobalt-based alloy powder has good high temperature resistance, wear resistance and corrosion resistance, and is often used in petrochemical and metallurgical fields.
Ceramic materials have high strength at high temperatures, good thermal stability, and high chemical stability. They are often used for parts that require wear resistance, corrosion resistance, high temperature resistance and oxidation resistance.
Because a single material cannot meet the requirements of operating conditions under severe sliding wear, impact wear and abrasive wear. Therefore, the composite use of metal coatings and ceramic coatings has become a research hotspot. There have been researches on laser cladding of various ceramic or cermet coatings on the surface of steel, titanium alloy and aluminum alloy.
Fast cooling rate (up to 10＾6℃/s) belongs to the solidification process, and it is easy to obtain fine-grained structure or produce new phases that cannot be obtained in equilibrium, such as unstable phase and amorphous state;The coating dilution rate is less than 5%, and it is in a strong metallurgical bond or interfacial diffusion bond with the substrate to obtain a good cladding layer with controllable coating composition and dilution to ensure that the performance does not deteriorate;Using high power density cladding, fast heating speed, less heat input, heat affected zone and distortion to the substrate;There are almost no restrictions on the choice of powder, and high melting point alloys can be deposited on the surface of low melting point metals;The thickness and hardness of the cladding layer are wide, and the cladding layer has fewer micro-defects and better performance;The technological process adopts numerical control, non-contact processing, automatic operation, convenient, flexible, and strong controllability.
Laser cladding is a repair and remanufacturing process. The first is to strengthen the function, which can enhance the performance of the substrate through the cladding layer; the second is the repair function, which is mainly reflected in the repair of the holes and cracks on the surface of the material, and restores the geometric dimensions of the worn parts And performance, has great application value for almost the entire machinery manufacturing industry.
In the quarry, chemical, metallurgical, electric power, cement and other mechanical equipment industries, gas turbine rotor journals and blades, roll journals, and steel mills' arches will age and be damaged over time. Due to the long-term endurance of gas high temperature and pressure and corrosive media, coupled with the mechanical stress caused by the volume load, the damage mostly occurs on the surface or the surface, and the failure mode is mainly the chipping and cracking of the internal metal parts, wear or The corrosion is severe to partial peeling. Therefore, the application of laser cladding technology to strengthen the surface properties of parts can effectively extend the service life, and during the periodic maintenance process, the damaged parts can also be remedied by surface remanufacturing technology.
For gas turbines and steam turbines, failures often occur in hot end components such as rotors, blades and nozzles. The fracture that occurs at the root of the blade is irreparable, and the damage that occurs at the end or root of the blade can be reused after repair. Furthermore, the blades used in the generator set are often very expensive. Reinstalling and reusing the repaired blades will greatly reduce the power generation cost of the power plant.
In the automobile manufacturing industry, since the 1980s, countries such as Europe, America, Japan, Russia, and China have begun to use laser cladding to strengthen auto parts. Through this technology, the purpose of saving expensive alloy materials and reducing production costs is achieved. Similarly, failures caused by wear, corrosion, and contact fatigue of automobile molds in use can also be reborn through this technology.
In short, whether it is the surface strengthening of parts before service or the repair of faults after service, the traditional processing methods mainly include surface quenching, surface carburization or nitriding, thermal spraying, and surfacing. With the continuous upgrading and improvement of processing technology, laser mobile remanufacturing technology (laser cladding) has gradually been widely used.
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