Low carbon steel due to low production costs, in the defense industry, aerospace and daily life plays an irreplaceable role, but its low hardness and wear resistance, easy to make mechanical equipment wear failure or damage, resulting in severe economic losses, rough estimates, the world every year due to wear caused by about 40% of the material loss, Due to wear and tear, mechanical equipment, components and engineering structural parts fail and scrap up to about 80%. How to reduce the wear of materials has become the focus of researchers.
As a "green" remanufacturing technology with high productivity and low pollution, laser cladding can produce a coating with high performance on the surface of a cheap and low performance matrix material, reduce resource waste and reduce production cost. Because laser cladding has interatomic bonding, it has higher bonding force than other surface treatment methods, so that the surface of the matrix has better resistance to friction and wear, corrosion resistance, cavitation corrosion resistance, high temperature oxidation resistance and so on. Therefore, laser cladding technology has more and more extensive research and application in high-performance coating preparation, remanufacturing of ineffective parts and other aspects, and the market prospect is quite considerable.
Laser cladding process parameters
Laser cladding involves many disciplines such as materials, physics, chemistry and metallurgy, and the process is quite complex. In addition to the properties of the laser system, matrix materials and cladding materials that have been determined, The technical parameters of laser cladding process, the feeding mode of cladding material and the scanning mode of laser beam will have an important influence on the macroscopic quality, microstructure and serviceability of laser cladding layer. The selection of process parameters has an important effect on the macroscopic quality, microstructure and properties of the cladding layer. The process parameters of laser cladding mainly include laser power, spot size, scanning speed, bonding rate and powder feeding speed or thickness of pre-coated powder. During the cladding process, the process parameters can be adjusted according to the composition of the cladding alloy powder and the required performance. According to the specific cladding conditions, the optimization of technical parameters is an important guarantee for the preparation of high-quality cladding layers.
The best parameters of laser cladding process were obtained by using the width, height and depth of the cladding layer. It is also pointed out that the scanning speed is the most important factor, followed by the laser power, and the defocus is the least important factor. For different cladding materials and substrates, there is a critical specific energy value to achieve good forming of laser cladding. When the specific energy used in the cladding process is greater than the critical specific energy, the cladding layer with good metallurgical bonding can be prepared. For the same cladding material and matrix, when the specific energy is similar, low power and small scanning speed are generally used. The heating speed of this process is slow, the heating time is longer, the temperature difference between the cladding layer and the matrix metal is small, the thermal stress is small, and the cracking tendency is small.
Cladding material
Laser cladding mainly improves the performance by improving the physical and chemical properties of the substrate material surface. The composition determines the performance, and the composition of the cladding layer is mainly determined by the type of cladding material used. Cladding material is a key factor affecting the performance of cladding layer. At present, the main cladding powders used are self-fusible alloy powder, ceramic powder, and gold based composite materials.
1. Self-fluxing alloyed powder
Self-fluxing alloy powder refers to the powder of adding B and Si elements in iron, cobalt and nickel-based alloys. B and Si play the functions of self-deoxidation and slagging in the laser cladding process. The slag with small specific gravity covers the surface of the cladding layer to protect the molten pool and prevent excessive oxidation of the molten pool. This kind of material has a good adaptability to ordinary carbon steel, the prepared coating surface is smooth, fewer defects, and can form an excellent combination with the matrix. At present, the commonly used self-fusible alloy powders mainly include three kinds of powders: Ni-based self-fusible alloy, Co-based self-fusible alloy and Fe-based self-fusible alloy. Co based, Ni based self-fluxing alloy powder and matrix materials have good wettability, strong corrosion resistance, has a certain self-lubricating effect under high temperature conditions, because the cost is relatively high, generally used in aerospace and petroleum and other industrial fields require fatigue resistance, corrosion resistance, wear resistance and high-temperature resistance of precision parts; Fe-based self-fluxable alloy powder has certain wear resistance and low price, but the alloy coating is prone to cracking, oxidation and porosity defects in the laser cladding process, which is widely used in the workpiece with certain wear resistance requirements, and the matrix material is mostly cast iron and low carbon steel.
2. Ceramic powder
Ceramic powder materials are regarded as the best choice for preparing special performance coatings because of their high hardness and strength, excellent wear resistance, corrosion resistance and high-temperature stability. However, ceramic materials have very low toughness, greater brittleness and greater thermal expansion coefficient, and the coating is easy to crack. In order to solve this problem, some researchers reduce the cracking tendency of the coating by adding an intermediate transition layer or even adding TiO2 and CaO oxides with high expansion series number to the ceramic material, but the research results are still unsatisfactory and need further research.
3. Composite powder
The composite powder is developed to overcome the serious cracking that may occur between the ceramic coating and the substrate due to their own property differences. It refers to a new cladding material system formed by adding a variety of hard materials with high hardness to the metal or alloy powder and mixing evenly. The hard material is used as the strengthening phase in the laser cladding layer, and the metal or alloy powder mainly acts as the bonding phase and the transition layer, which can promote the good transition between the hard material and the metal matrix, so that the cladding layer is well formed and has a high hardness. Hard materials are mainly composed of ceramic materials with high melting point and high hardness. Metal alloy powder is mainly Fe base, Ni base and Co base three kinds of self-fluxing alloy powder. The method of adding hard materials: first, the hard material powder is directly added to the metal alloy powder and mixed evenly; The other is in the form of alloy powder coated with hard materials. According to the actual application conditions, the metal base alloy powder matched with the corresponding hard reinforcement can be uniformly mixed to form the required composite powder. The ceramic reinforced metal matrix composite coating is prepared on the selected matrix material by laser cladding technology, which not only makes the cladding layer have high strength and toughness, but also makes full use of the hard hardening phase to improve the performance of the matrix metal material, which has become a hot research topic.
Xi'an Guosheng Laser Technology Co., Ltd. is a high-tech enterprise specializing in R&D, manufacturing and sales of automatic laser cladding machine, high-speed laser cladding machine, laser quenching machine, laser welding machine and laser 3D printing equipment. Our products are cost-effective and sold domestically and abroad. If you're interested in our products, please contact us at bob@gshenglaser.com.