Laser cladding overview
Laser cladding refers to a process using different filler method on the surface of the coated substrate to place selected coating materials, it melts with a thin layer on the surface of the substrate at the same time after being irradiated by laser, and quickly solidifies to form a surface coating with extremely low dilution and metallurgical bonding with the substrate material, thereby significantly improving the wear resistance, corrosion resistance, heat resistance, oxidation resistance and electrical properties of the surface on the base material.
Laser cladding is a new technology with high economic efficiency, which can prepare high-performance alloy surfaces on cheap metal substrates without affecting the properties of the substrate, reducing costs and saving precious and rare metal materials.
The lasers used in laser cladding are mainly CO2 lasers and solid-state lasers, which mainly include disc lasers, fiber lasers and diode lasers.
Process characteristics of laser cladding
According to the different powder feeding process, laser cladding can be divided into two categories: powder preset method and synchronous powder feeding.
The two methods are similar, synchronous powder feeding has the advantages of easy automation and control, high laser energy absorption, no internal porosity, especially for cladding metal ceramics, which can significantly improve the anti-cracking properties of the cladding layer, so that the hard ceramic phase can be uniformly distributed in the cladding layer and so on.
1. Laser cladding has the following characteristics
(1) Fast cooling rate (up to 106K/s), belonging to the rapid solidification process, it is easy to obtain fine crystalline organization or produce new phases that cannot be obtained by the equilibrium state, such as non-stationary phase and amorphous state etc.
(2) Low coating dilution rate (generally less than 5%), and the substrate was firmly metallurgical bond or interfacial diffusion bond, through the adjustment of the laser process parameters, it can get a good coating with low dilution rate, and the coating composition and dilution degree can be controlled.
(3) Smaller heat input and distortion, especially when high power density rapid cladding is used, and distortion can be reduced to within the assembly tolerances of the part.
(4) There are almost no restrictions on the choice of powder, especially for depositing high melting point alloys on the surface of low melting point metals;
(5) The thickness range of the cladding layer is large, and the thickness of the single-channel powder feed coating is 0.2~2.0mm.
(6) It enables selective deposition with low material consumption and has an excellent performance-to-price ratio.
(7) Beam aiming can fuse inaccessible areas.
(8) The process is easy to automate.
It is very suitable for the wear and tear repair of common wearing parts in oil fields.
2. Differences and similarities between laser cladding and laser alloying
Both laser cladding and laser alloying use the rapid melting process produced by a high-energy density laser beam to form an alloy cladding layer on the surface of the substrate that is fused with the substrate and has a completely different composition and properties.
The two processes are similar, but are fundamentally different, with the main differences being as follows:
(1) The complete melting of the cladding material in the laser cladding process with an extremely thin matrix melting layer makes it have minimal effect on the composition of the cladding.
The laser alloying is to add alloying elements to the surface of the base material in the molten composite layer, the purpose is to form a new alloy layer based on the base material.
(2) Laser cladding is not essentially using the molten metal of the substrate’s surface layer as a solvent, but rather melting the otherwise configured alloy powder to make it the subject alloy of the cladding layer.
At the same time, the matrix alloy also has a thin layer of melting, with the formation of a metallurgical bond.
Laser cladding for the preparation of new materials is an important basis for the repair and remanufacturing of failed parts under extreme conditions and the direct manufacture of metal parts, and has received great attention from the scientific community and enterprises around the world.
Evaluation of the effect of laser melting
Evaluating the quality of laser cladding is based on two main aspects.
The first is macroscopic, examining the shape of the melt channel, surface unevenness, cracking, porosity and dilution rate, etc..
Secondly, microscopically, it is examined whether a good organization is formed and whether it can provide the required properties.
In addition, the type and distribution of chemical elements in the surface cladding layer should be determined, attention should be paid to analyzing the transition layer for metallurgical bonding, and quality life testing should be performed if necessary.
Research efforts focus on the research and development of cladding equipment, melt pool dynamics, design of alloy composition, crack formation, propagation and control methods, and bonding forces between the cladding layer and the substrate.
The main issues facing the further application of laser deposition technology are:
①The main reason why laser cladding technology has not yet been fully industrialized in China is the instability of the quality of the cladding layer.
In the laser cladding process, due to the difference in temperature gradient and thermal expansion coefficient between 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.
②Detection and implementation of automated control of the laser cladding process.
③The cracking sensitivity of laser cladding is still a problem for researchers at home and abroad, as well as an obstacle for engineering application and industrialization,
Although the formation and expansion of cracks have been studied, the control method is still immature.
Application of laser cladding
Laser cladding processing has a wide range of applications and fields, covering almost the entire machinery manufacturing industry.
At present, laser cladding has been successfully carried out on stainless steel, die steel, malleable cast iron, gray cast iron, copper alloys, titanium alloys, aluminum alloys and special alloys, such as cobalt-based, nickel-based, iron-based and other self-fusing alloy powder and ceramic phase on the surface of the laser cladding.
Laser cladding of iron-based alloy powders is suitable for parts that require local wear resistance and are prone to deformation.
Nickel-based alloy powders are suitable for components requiring local abrasion resistance, heat resistance and heat fatigue resistance.
Cobalt-based alloy powders are suitable for parts requiring local abrasion resistance, corrosion resistance and thermal fatigue resistance.
Ceramic coating has high strength under high temperature, good thermal stability and high chemical stability, which is suitable for parts requiring wear resistance, corrosion resistance, high-temperature resistance and oxidation resistance.
The following are a few typical applications of laser cladding：
- Manufacturing and remanufacturing of mining equipment and components
Coal mining equipment uses a lot, so it wears out quickly, and due to its harsh working environment, the parts break down quickly.
Laser manufacture and remanufacture of coal machine equipment parts include: three machines and one support
(1) Coal miner: mainframe, rocker, gear, gear shaft, all kinds of bushings, articulated frame, oil cylinder, cylinder seat, guiding slide shoe, sprocket, pin rail wheel, drive wheel, wrench, etc.
(2) Roadheader: cylinders, brackets, shafts, various bushings, cutters, etc.
(3) Scraper conveyor: central chute, transition groove, gearbox, gears, gear shafts, spiral bevel gears, shaft parts, etc..
(4) Hydraulic support: cylinder, base and bracket articulation hole, various bushings, etc..
Roadheader cutting teeth
Hydraulic support column after cladding
Picks after laser cladding
Manufacturing and remanufacturing of electrical equipment and its components
Power equipment has a large distribution volume with uninterrupted operation, so it has a high probability of damage to its parts.
The 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 repair the damaged parts of the unit regularly every year, such as the main shaft diameter, dynamic vanes, etc.
The gas turbine is often damaged due to its working under the high-temperature condition of 1300℃.
The laser remanufacturing technology is used to repair all the defects and restore the performance, which costs only 1/10th of the price of a new unit.
Laser cladding of motor rotor shaft
Steam turbine rotor repair
Repair of blade wear of powder exhaust fan
- Manufacturing and remanufacturing of petrochemical equipment and its components
The modern petrochemical industry is essentially a continuous mass production model.
During the production process, the machines work in harsh environments for long periods of time, resulting in damage, corrosion, wear and tear of components within the equipment.
Among the parts that often go wrong are valves, pumps, impellers, journals of large rotors, discs, bushings, and shaft tiles.
And these components are very expensive and involve a wide variety of parts, most of which have complex shapes and can be difficult to repair.
But because of the advent of laser melting technology, these problems are no longer a problem.
Laser cladding of hard ceramic coatings on oil drill pipes, drilling tools, etc.
- Manufacturing and remanufacturing of railway equipment and its components
With the rapid development of rail transportation with socio-economic growth, the demand for new rail vehicles is very large, and the number and performance requirements of major parts are also increasing.
As a new resource reuse technology, remanufacturing technology can be applied to the remanufacturing of wearable parts of vehicles.
The laser surface strengthening is the core technology and process means of remanufacturing, in which the laser surface coating technology can be applied to remanufactured parts surface repair and strengthening.
5.Remanufacturing of key components of other machinery industry equipment
The remanufacturing of key components of other machinery manufacturing industries include metallurgy, petrochemical, mining, chemical, aviation, automotive, shipping, machine tools and other fields.
The laser cladding process is used to repair and optimize the performance of precision equipment, large equipment, and valuable parts in these areas where wear, erosion, and corrosion occur.
Laser cladding of worm-gear bars for gantry boring and milling machines
Highly wear-resistant steel continuous casting rolls with laser cladding