Classification of Laser Cladding Material Powder and its Advantages and Disadvantages

The laser fusion technique refers to the coating of the selected coating alloy powder on the surface of the substrate, using high-energy beam irradiation, which is used the surface of the substrate, rapidly melting, expanding and coagulating on the surface of the substrate, and then forming a layer of coating with the base material. The newly formed layer can significantly improve and even reconstruct the matrix material, allowing it to achieve wear resistance, heat resistance, corrosion resistance, antioxidant and its target characteristics.

Laser fusion technology is a complex physical and chemical metallurgical process, and the setting of laser parameters has a large effect on the quality of the coating. In addition, the selection of alloy powder is also an important factor. The material composition of laser alloy powder is divided into self-melting alloy powder, composite powder and ceramic powder. In this paper, the self-melting alloy powder is studied and applied most in reality.

One. Self-melting alloy powder

Self-melting alloy powder can be divided into iron base (Fe), nickel base (Ni), cobalt base (Co) alloy powder, its main characteristics are containing boron (B) and silicon (Si), so it has self-deoxidation and slagging properties; Also contains high chromium, their priority and oxygen in the alloy powder and workpiece surface oxide fused together to generate low melting borosilicate covered in molten pool surface, such as to prevent excessive oxidation of liquid metal, thus improve the melt to the substrate metal wetting ability, reduce the inclusion and oxygen in the cladding layer and improve the process of forming performance of cladding layer, Therefore, it has excellent corrosion resistance and oxidation resistance. It has good adaptability to carbon steel, stainless steel, alloy steel, cast steel and other substrates, and can obtain the cladding layer with low oxide content and small porosity. However, for sulfur-containing steel, due to the presence of sulfur, a brittle phase with a low melting point is easy to form at the interface, which makes the cladding easy to peel off, so it should be carefully selected.

a. Iron base (Fe) self-melting alloy powder

Fe-based self-melting alloy powder is suitable for parts requiring local wear resistance and easy deformation. The matrix is mostly cast iron and low-carbon steel. The biggest advantages of Fe-based self-melting alloy powder are wide material sources, low cost and good wear resistance.?The disadvantages are high melting point, poor oxidation resistance, easy cracking of the cladding layer, easy-to-produce pores, etc. In the iron base alloy powder composition, the hardness of the coating is adjusted by adjusting the alloying element content, and the hardness, cracking sensitivity and residual austenite content of the cladding layer are improved by adding other elements, so as to improve the wear resistance and toughness of the cladding layer. There are two types of iron-based self-melting alloy powders for laser cladding: austenitic stainless steel and high chromium cast iron.

In recent years, the research of laser cladding, many people around the iron base powder to add other components to the experiment. The RESULTS SHOW that THE addition of rare earth can improve the anti-SPalling ability of the passivation film on the surface of the cladding layer, reduce the corrosion weight loss of the material in different degrees, and improve the corrosion resistance of the cladding layer.

b. Nickel base (Ni) self-melting alloy powder

Ni-based self-melting alloy powder has been studied and widely used in laser cladding materials due to its good wettability, corrosion resistance, high-temperature self-lubrication and moderate price.

Under the condition of serious sliding, impact wear and abrasive wear of nickel base (Ni) self-melting alloy powder, the simple self-melting alloy powder is no longer competent to use the requirements, at this time, various carbide, nitride, boride and oxide ceramic particles with a high melting point can be added to the self-melting alloy powder to make the metal composite coating.

c. Cobalt base (co) self-melting alloy powder

Cobalt-based (Co) self-melting alloy powder has excellent heat resistance, corrosion resistance, wear resistance, impact resistance and high-temperature oxidation resistance, which is often used in the petrochemical, electric power, metallurgy and other industrial fields of wear resistance, corrosion resistance and high temperature and other occasions. Co-based self-melting alloy has good wettability, and its melting point is lower than that of carbide. After being heated, Co element is first in the melting state, and when the alloy is solidified, it is the first to form a new phase with other elements, which is very beneficial to the strengthening of the cladding layer. At present, the main alloying elements used in cobalt-based alloys are nickel, carbon, chromium and iron. Among them, nickel element can reduce the thermal expansion coefficient of the cobalt-based alloy cladding layer, reduce the melting temperature interval of the alloy, effectively prevent the cracks in the cladding layer, and improve the wettability of the cladding alloy to the matrix.

It can be seen from the comprehensive analysis that the Ni-based or Co-based self-melting alloy powder system has good self-melting, corrosion resistance, wear resistance and oxidation resistance, but the price is high.?Although Fe - based self - melting alloy powder is cheap, it has poor self - melting properties and is easy to crack and oxidation. Therefore, the self-melting alloy powder system should be reasonably selected according to the application requirements.

Two. Composite powder

Composite powder mainly refers to carbide, nitriding, boride, oxide and silicide and other high melting point hard ceramic materials mixed with metal or composite powder system. Composite powder can use laser cladding technique was used to prepare the ceramic particles reinforced metal matrix composite coating, the metal of strong toughness, good manufacturability and ceramic material excellent wear resistance, corrosion resistance, high temperature resistant and antioxidant properties of organic combination, can to a certain extent, make the carbide from oxidation and decomposition, which has high wear resistance and hardness of the coating, This is a hotspot in the field of laser cladding technology. Among them, carbide alloy powder and oxide alloy powder are the most studied and applied, which are mainly used to prepare wear-resistant coatings. The carbide particles in the composite powder can be directly added to the laser molten pool or directly mixed with the metal powder to form a mixed powder, but it is more effective to add in the form of coated powder (such as nickel-coated carbide, cobalt coated carbide).

In the process of laser cladding, the coating metal of the coated powder can effectively protect and weaken the direct effect of high-energy laser and carbide, and can effectively reduce or avoid the burning, carbon loss, volatilization and other phenomena of carbide.

Three. Ceramic powder

Ceramic powder mainly includes silicide ceramic powder and oxide ceramic powder, among which oxide ceramic powder (alumina and zirconia) is the main. Zirconia has lower thermal conductivity and better thermal seismic performance than alumina ceramic powder, so it is often used to prepare thermal barrier coatings. Ceramic powder is often used to prepare high-temperature wear and corrosion-resistant coatings because of its excellent wear resistance, corrosion resistance, high-temperature resistance and oxidation resistance. At present, bio-ceramics materials are a hot research area.

Disadvantages of ceramic powder: compared with matrix metal, the thermal expansion coefficient, elastic modulus and thermal conductivity are quite different, the cladding layer is easy to have cracks and holes and other defects, and it is easy to appear deformation cracking and peeling damage in use.

In order to solve the crack of pure ceramic coating and metal substrate, high strength, some scholars try to use the middle transition layer and ceramic layer with low melting point and high expansion coefficient of CaO, SiO2, TiO2, etc to reduce internal stress, relieve the crack tendency, but the existing research shows that the pure ceramic coating crack and spalling problem has not been well solved, Therefore, it remains to be further studied.

At present, the research of laser cladding bio-ceramics mainly focuses on the laser cladding of hydroxyapatite (HAP), fluorapatite, Ca, Pr and other bio-ceramics on the metal surface of Ti-base alloy and stainless steel. Hydroxyapatite bio-ceramics have good biocompatibility and have been widely paid attention to as human teeth by scholars at home and abroad. Generally speaking, although the research of laser cladding bio-ceramics started relatively late, it develops very rapidly and is a promising research direction.

Four. Other metal powder

In addition to the above types of laser cladding powder material systems, the existing cladding material systems also include copper base, titanium base, aluminum base, magnesium base, zirconium base, chromium base and intermetallic compound base materials. Most of these materials make use of some special properties of the alloy system to achieve wear resistance, friction reduction, corrosion resistance, electrical conductivity, high-temperature resistance, thermal oxidation resistance and other functions.

a. Copper base

Copper base laser cladding materials mainly include Cu-Ni-B-Si, Cu-Ni-Fe-Co-Cr-Si-B, Cu-al2o3, Cu-CuO and other copper base alloy powders and composite powder materials. By taking advantage of the metallurgical properties of copper alloy system, such as liquid phase separation phenomenon, a copper matrix composite powder material for laser cladding of copper matrix self-generated composite material can be designed. The results show that there are a lot of autorigid particles in the laser cladding layer, which has good wear resistance. Based on the liquid phase separation of Cu and Fe and the metallurgical reaction between base metal and surfacing material, Uniji and others prepared the Fe3Si diffusively distributed Copper-base alloy composite cladding layer by laser cladding. The results show that during the laser cladding process, the Fe element which enters the molten pool from the base metal is separated from the Cu alloy in the molten pool in liquid phase. The Fe in the molten pool floats up due to its low density, and reacts with the Si in the molten pool to form Fe3Si, which is distributed in the α-Cu matrix in a diffuse-like gradient in the laser cladding layer.

b. Titanium base

Titanium-based cladding materials are mainly used to improve the surface biocompatibility, wear resistance and corrosion resistance of matrix metal materials. The titanium base laser cladding powder materials are mainly pure Ti powder, Ti6Al4V alloy powder and Ti-tio 2, Ti-Tic, Ti-WC, Ti-Si and other titanium base composite powders. Zhang Song et al. laser cladding Ti-Tic composite coating on the surface of Ti6Al4V alloy under an argon atmosphere environment, study shows that the composite coating is self-generated and forms tiny TiC particles in situ, and the composite coating has excellent friction and wear properties.

c. Magnesium matrix

Magnesium based cladding material is mainly used for laser cladding of magnesium alloy surface to improve wear resistance and corrosion resistance of magnesium alloy surface. J. Duttamajumdar et al. cladding magnesium-based MEZ powder (composition: Zn: 0.5%, Mn: 0.1%, Zr: 0.1%, RE: 2%, Mg: Bal) on commercial magnesium alloy. The results show that the microhardness of the cladding layer increases from HV35 to HV 85 ~ 100, and the corrosion resistance of the cladding layer in 3.56wt%NaCl solution is greatly improved compared with that of the matrix magnesium alloy due to grain refinement and redistribution of intermetallic compounds.

d. Aluminum base

SorinIgnat et al. used a 3kW Nd∶YAG laser to laterally feed aluminum powder on two kinds of magnesium alloy substrates WE43 and ZE41, and obtained the cladding layer with good binding performance. It was found that the hardness of the coating reached HV0.05120 ~ 200, and the main reason for the increase of hardness was the presence of Al3Mg2 and Al12Mg17 metal compounds. ZMei et al. laser cladding Al-Zn powder on magnesium ZK60/SiC matrix to obtain a good metallurgical cladding layer. The results show that the corrosion potential of the cladding layer is 300mV higher than that of the standard sample, while the corrosion current is at least 3 orders of magnitude lower.

e. Zirconium base

ZrAlNiCu alloy powder was laser cladding on pure titanium matrix and the coating was studied and analyzed. It is found that the coating is composed of intermetallic compounds with high specific strength and high hardness and a small amount of amorphous phase, which has good mechanical properties. When 2wt%B and 2.75wt%Si were added to ZrAlNiCu alloy powder, it was found that the amorphous content of the coating increased and the hardness increased. The highest hardness of the two coatings reached HV909.6 and HV1444.8, respectively.

Five. Conclusion:

The characteristics, prices and properties of different cladding materials are quite different, and the alloy powders with different properties can be selected according to different processing needs in practice.?By laser cladding alloy powder on the surface of the workpiece (laser cladding), high performance alloy surface can be prepared on the cheap metal substrate without affecting the properties of the matrix, effectively reduce the production cost, saving precious and rare metal materials. Compared with traditional surface treatment techniques such as surfacing, thermal spraying and electroplating, laser cladding has the advantages of small dilution, compact structure, good bonding between coating and matrix, more suitable cladding materials, large changes in particle size and content, high processing quality and good controllability (3D automatic machining can be realized).

At present is mainly used in material surface modification, such as hydraulic pillar, roller, gear, gas turbine blades, etc.), product surface repair (such as the failure of the rotor due to abrasion, mould, bearing inner hole, etc.), after repair parts strength can reach more than 90% of the original strength, 1/5 of the cost of repair costs less than new products, more important is to shorten the maintenance time, It effectively solves the problem of quick repair of rotating parts of major complete sets of equipment in large enterprises.

In addition, the service life of the parts can be greatly improved without deformation of the surface of the parts by laser cladding on the surface of the wear and corrosion-resistant alloy. The laser cladding treatment on the mold surface can not only improve the strength of the mold, but also reduce the manufacturing cost by 2/3 and shorten the manufacturing cycle by 4/5.

In general, laser cladding technology is a high-tech surface modification technology and equipment maintenance technology, its research and development has important theoretical significance and economic value.

Laser cladding material is the main factor that restricts the development and application of laser cladding technology. At present, although some progress has been made in the development of laser cladding materials, there is still a long way to quantitatively design the alloy composition according to the properties and application requirements of the designed cladding parts. The laser cladding materials are far from being serialized and standardized, and further research needs to be intensified.