Laser Cladding Overview
Laser cladding is a process that uses different filling methods to deposit selected coating materials onto the surface of a substrate.
The material is melted onto the surface of the substrate with a thin layer after being irradiated by a laser, and then quickly solidified to form a surface coating with minimal dilution and metallurgical bonding with the substrate material.
This significantly improves the surface's resistance to wear, corrosion, heat, oxidation and improves its electrical properties in the base material.
Laser cladding is a cost-effective technology that can create high-performance alloy surfaces on inexpensive metal substrates without changing substrate properties. This reduces costs and conserves precious and rare metal materials.
The lasers used in laser cladding are mainly CO 2 lasers and solid-state lasers such as disk lasers, fiber lasers and diode lasers.
Features of the laser cladding process
Laser cladding can be divided into two categories based on different powder feeding processes: powder presetting method and synchronous powder feeding.
The two methods are similar, but synchronous powder feeding has advantages such as easy automation and control, high laser energy absorption and no internal porosity. This is particularly beneficial for metal ceramic coating, as it significantly improves the anti-crack properties of the coating layer and allows for uniform distribution of the hard ceramic phase throughout the coating layer.
1 . Laser cladding has the following characteristics
- Fast cooling rate (up to 106K/s), which is part of the rapid solidification process, facilitating the obtaining of fine crystalline structures or the production of new phases that cannot be obtained through an equilibrium state, such as non-stationary phases and amorphous states.
- Low coating dilution rate (generally less than 5%) with a tightly metallurgical or interfacial diffusion bond to the substrate. Good coatings with low dilution rates can be obtained by adjusting the laser process parameters, and the coating composition and the degree of dilution can be controlled.
- Reduced heat input and distortion, especially when high power density fast plating is used, with distortion maintained within part assembly tolerances.
- Few restrictions on powder choice, particularly for deposition of high melting point alloys on low melting point metals.
- Wide range of coating layer thicknesses, with single channel powder coating thickness ranging from 0.2mm to 2.0mm.
- Selective deposition with low material consumption and excellent performance/price ratio.
- Ability to merge inaccessible areas through beam aiming.
- Easy to automate.
Laser cladding is highly suitable for repairing commonly worn parts in oil fields due to its wear resistance.
two . Differences and similarities between laser cladding and laser alloying
Both laser cladding and laser alloying use high-energy density laser beams to form an alloy cladding layer on the surface of a substrate, which is fused with the substrate and has unique composition and properties.
The two processes are similar but fundamentally different, with the following key differences:
(1) In laser cladding, the coating material is completely melted with an extremely thin matrix fusion layer, causing minimal impact on the coating composition. In laser alloying, alloying elements are added to the surface of the base material in the molten composite layer, forming a new alloy layer based on the base material.
(2) Laser cladding does not rely on molten metal from the surface layer of the substrate as a solvent, but instead melts a pre-set alloy powder to create the alloy in question from the coating layer. At the same time, the matrix alloy also has a thin fusion layer, leading to the formation of a metallurgical bond.
Laser cladding is a crucial basis for the repair and remanufacturing of defective parts under extreme conditions and for the direct manufacturing of metal parts. It has received significant attention from the scientific community and companies around the world for its ability to prepare new materials.
Assessment of the effect of laser fusion
Assessing the quality of laser cladding involves two main aspects: macroscopic and microscopic.
The macroscopic aspect examines the shape of the melt channel, surface irregularities, cracks, porosity and dilution rate. Microscopically, it analyzes the formation of a good organization and the provision of necessary properties.
In addition, the type and distribution of chemical elements in the surface coating layer must be determined, attention must be paid to the analysis of the transition layer for metallurgical bonding, and, if necessary, quality of life tests must be carried out.
Research efforts focus on the development of coating equipment, weld pool dynamics, alloy composition design, methods of crack formation, propagation and control, and bonding forces between the coating layer and the substrate.
The main challenges faced by the further application of laser deposition technology are:
- The instability of the coating layer quality is the main reason why laser cladding technology has not yet been fully industrialized in China. During the laser cladding process, defects such as porosity, cracks, deformation and surface irregularities may occur in the coating layer due to differences in the temperature gradient and thermal expansion coefficient between the coating layer and the base material.
- Automated control of the laser cladding process must be detected and implemented.
- The cracking sensitivity of laser cladding is still a problem for domestic and international researchers and remains an obstacle to engineering application and industrialization. Although the formation and expansion of cracks have been studied, the control method is not yet mature.
Laser cladding application
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 applied to stainless steel, molded steel, malleable cast iron, gray cast iron, copper alloys, titanium alloys, aluminum alloys and special alloys such as cobalt-based, nickel, iron-based and other self-fusing alloy powders and ceramic phases on the surface of the laser cladding.
Iron-based alloy powders are suitable for parts that require local wear resistance and are prone to deformation.
Nickel-based alloy powders are ideal for components that require local abrasion resistance, heat resistance and thermal fatigue resistance.
Cobalt-based alloy powders are suitable for parts requiring local abrasion resistance, corrosion resistance and thermal fatigue resistance.
Ceramic coatings have high high temperature strength, good thermal stability and high chemical stability, making them suitable for parts that require wear resistance, corrosion resistance, high temperature resistance and oxidation resistance.
Some typical laser cladding applications are:
Manufacturing and Remanufacturing of Mining Equipment and Components
Coal mining equipment suffers a lot of wear and tear due to its harsh working environment, leading to frequent parts breakdowns. Laser cladding is used to manufacture and remanufacture these parts, including:
- Coal miner: main frame, rocker arm, gear, gear shaft, bushings, articulated frame, oil cylinder, cylinder seat, guide slide shoe, sprocket, pin rail wheel, driving wheel, wrench, etc.
- Roadheader: cylinders, supports, shafts, bushings, cutters, etc.
- Scraper conveyor: center chute, transition groove, gearbox, gears, gear shafts, spiral bevel gears, shaft parts, etc.
- Hydraulic support: cylinder, base and support articulation hole, bushings, etc.
Roadheader cutting teeth
Hydraulic support column after coating
Choices after laser cladding
Manufacturing and Remanufacturing of Electrical Equipment and its Components
Electrical power equipment has a high distribution volume and must operate continuously, making it vulnerable to damage to its components.
The steam turbine is the heart of thermal power generation, but its demanding working conditions, including high temperatures and heat, lead to regular wear and tear on essential components such as the main shaft and dynamic vanes, which must be repaired annually.
The gas turbine is also subject to damage due to its exposure to high temperatures of up to 1300°C.
Laser remanufacturing technology offers an effective solution for restoring the performance of damaged equipment and is significantly more cost-effective, with a price that is just one-tenth the price of a new unit.
Laser cladding of motor rotor shaft
Steam turbine rotor repair
Repair of dust extractor blade wear
Manufacturing and Remanufacturing of Petrochemical Equipment and its Components
The petrochemical industry operates in a mass production model, which requires the use of machines that work continuously in aggressive environments. Over time, exposure to such conditions results in damage, wear and corrosion of equipment components.
Valves, pumps, impellers, rotor journals, discs, bushings and shaft plates are among the parts most susceptible to failure. These components are not only expensive but also complex in shape, making repairs difficult.
However, the advent of laser melting technology has eliminated these challenges, making it possible to effectively repair and manufacture these parts.
Laser cladding of hard ceramic coatings on oil drilling pipes, drilling tools, etc.
Manufacturing and Remanufacturing of Railway Equipment and Components
The rapid growth of rail transport and its corresponding socio-economic development have resulted in a high demand for new rail vehicles, as well as an increase in the number and performance requirements of key components.
One solution to this demand is the application of remanufacturing technology, which offers the potential for reuse of wearable vehicle parts.
The main technology behind remanufacturing is laser surface strengthening. This process involves applying laser surface coating technology to repair and reinforce the surface of remanufactured parts.
Remanufacturing of key components in other machinery industries
Remanufacturing of key components is not limited to the railway industry and is also applied in a variety of other machinery industries, including metallurgy, petrochemical, mining, chemical, aviation, automotive, marine, machine tools and more.
To repair and improve the performance of precision equipment, large equipment and valuable parts that are susceptible to wear, erosion and corrosion, the laser cladding process is used.
Laser coating of worm gear bars for boring and gantry milling machines
Highly wear-resistant steel continuous casting rollers with laser coating
