Ti(C,N)-based cermet is a kind of granular composite material, which is a new type of cermet developed on the basis of TiC-based cermet. Ti(C,N)-based cermets have a series of excellent comprehensive properties such as high hardness, wear resistance, oxidation resistance and corrosion resistance. They exhibit high red hardness and strength during processing, and they have high wear resistance at the same hardness. It is a WC Co cemented carbide with a density of only 1/2 of that of cemented carbide. Therefore, Ti(C,N)-based cermet tools can be successfully used as tool materials in many processing applications to replace WC-based cemented carbides, filling the gap between WC-based cemented carbide and Al2O3 ceramic tool materials. . China's metal cobalt resources are relatively scarce, and as a strategic precious metal, the price of cobalt has continued to rise in recent years. Therefore, the research and development and wide application of Ti(C,N)-based cermet tool materials can not only promote China's hard The upgrading of alloy materials is also of great significance in improving the level of national resource security.
We have developed Ti(C,N)-based cermets with TiN added. Since TiC has higher hardness and wear resistance than WC, the addition of TiN can refine grains, so Ti(C,N)-based cermets can exhibit more than WC-based or TiC-based cemented carbides. For superior overall performance. The wide application of this new type of cermet tool material is based on its successful connection technology. At home and abroad, many studies have been carried out on the connection of ceramics and metals, but there are few studies on the technology of cermet and metal connection. It limits the wide application of Ti(C,N)-based cermet materials in industrial production. Commonly used methods of joining ceramics and metals are vacuum electron beam welding, laser welding, vacuum diffusion welding, and brazing. Among these connection methods, the brazing and diffusion welding connection methods are relatively mature and widely used, and new connection methods and processes such as transition liquid phase connection are under research and development. On the basis of summarizing various ceramic and metal welding methods, this paper makes a preliminary discussion on the welding technology of cermet and metal. At the same time, it introduces various techniques suitable for cermet and metal welding, and points out its advantages and disadvantages and needs to be solved. The problem is to promote the research of cermet and metal welding technology, and then promote the application of this advanced tool material in the industrial field.
Performance characteristics and application status of Ti(C,N)-based cermets
Ti(C,N)-based cermets are a new class of tooling materials developed on the basis of TiC-based cermets. According to its composition and performance, it can be divided into: TiC-based alloy with TiC Ni Mo; 2 Titanium-based alloy with other carbides (such as WC, TaC, etc.) and metal (such as Co); TiC TiN (or TiCN) based alloy; 4 TiN based alloy with TiN as the main component.
The performance characteristics of Ti(C,N)-based cermets are as follows:
(1) High hardness, generally up to HRA 91 ~ 93.5, some up to HRA94 ~ 95, that is, to achieve the hardness level of non-ceramic tools.
(2) It has high wear resistance and ideal resistance to crater wear. It has extremely low wear rate when cutting steel at high speed, and its wear resistance can be 3-4 times higher than that of WC-based cemented carbide.
(3) It has high anti-oxidation ability. Generally, the temperature of cemented crater wear begins to be 850-900 °C, while the Ti(C,N)-based cermet is 1100-1200 °C, which is 200-300 °C higher. The TiO2 formed by the oxidation of TiC has a lubricating effect, so the degree of oxidation is about 10% lower than that of the WC-based alloy.
(4) It has high heat resistance, and the high temperature hardness, high temperature strength and high temperature wear resistance of Ti(C,N)-based cermets are better, and cutting can be performed at a high temperature of 1100 to 1300 °C. The general cutting speed can be 2 to 3 times higher than that of WC-based cemented carbide, and can reach 200 to 400 m/min.
(5) The chemical stability is good. When cutting Ti(C,N)-based cermet tools, Mo2O3, nickel molybdate and titanium oxide films are formed on the contact surface between the cutter and the chip and the workpiece. They can all be used as dry lubricants. Reduce friction. The Ti(C,N)-based alloy and the steel are not easily bonded, and no adhesion is observed at 700 to 900 ° C, that is, the built-up edge is less likely to occur, and the surface roughness value is low.
Ti(C,N)-based cermets can save valuable rare metal materials such as Co, Ta, and W, which are necessary for ordinary cemented carbides, while having good comprehensive properties. As human resources save resources to promote the "green industry" process, Ti (C, N)-based cermets will become a promising tool material. At present, Ti(C,N)-based cermet materials have been extensively studied in various countries in the world, especially in Japan. Some countries have been actively applying and promoting such tool materials, and all major hard alloy manufacturers in the world have launched commercial brands. Nitrogen-containing cermet. For example, the NX2525 grade ultra-fine particle cermet developed by Mitsubishi Materials Corporation of Japan has a hardness of 92.2HRA and a flexural strength of 2.0GPa, which combines high hardness and high toughness. In the "Eighth Five-Year Plan" period, China has also successfully developed a variety of Ti(C,N)-based cermet tools, which have been launched in batches and have now developed into a series of tool materials for independent series.
Technical method for cermet and metal welding
In industrial processing, there are two ways to connect the cutting tool to the tool holder: welding and machine clamping. The connection between the blade and the tool bar of the tool directly affects the service life of the tool. Song Liqiu and other experimental studies have shown that the tool has high durability when using welded joint blades and shanks, and the tool durability is low when the machine clamp type is selected. Since the Ti(C,N)-based cermet is a brittle material, the melting point is higher than that of the metal, and its linear expansion coefficient is greatly different from that of the metal, so that the residual stress in the joint of the Ti(C,N)-based cermet insert and the shank is welded. Very high, combined with poor compatibility with metals, making the cermet and metal weldability is poor, it is difficult to obtain satisfactory welded joints in general welding methods and processes. Currently, brazing and diffusion welding are used for cermets and metals. The connection has been successful. With the deepening of research, many new methods and processes have emerged. The following describes the various advantages and disadvantages and research directions of cermet and metal welding techniques.
1 fusion welding
Melt welding is the most widely used welding method. It uses a certain heat source to partially melt the joint into a liquid, and then cool and crystallize it into one. Welding heat sources include arcs, laser beams, and electron beams. At present, there are two main problems in the fusion welding of Ti(C,N)-based cermets: First, as the melting temperature increases, the fluidity decreases, which may promote the chemical reaction between the matrix and the reinforcing phase (interfacial reaction). The occurrence of the joint reduces the strength of the welded joint; another problem is the lack of specially developed cermet fusion welding filler material.
1) Arc welding
Arc welding is currently the most widely used welding method in fusion welding. The advantage is that the application is flexible, convenient, adaptable, and simple in equipment. However, this method is very likely to cause a chemical reaction (interfacial reaction) between the matrix and the reinforcing phase when the ceramic is welded to the metal. Since Ti(C,N)-based cermets are electrically conductive and can be directly soldered, experimental studies on Ti(C,N)-based cermets and metal arc welding have shown that it is feasible, but needs to be solved such as interfacial reaction and welding defects ( Cracks, etc.) and low strength of welded joints.
2) Laser welding
Laser welding is an important welding method for welding special and difficult-to-weld materials. Because the energy density of the laser beam is large, the laser welding has the characteristics of large penetration, small melting width, small heat affected zone, reduced residual stress and small deformation after welding, and can manufacture a stable joint at a high temperature. Precise control of the welding quality of the product. Laser welding technology has been successfully applied to powder metallurgy materials sintered in vacuum. According to reports, the Mittweida Laser Application Center has developed a dual laser beam welding method. It works with two lasers, one for preheating the workpiece and the other for welding. This double laser beam welding method enables the connection of various geometries without reducing the strength and high temperature performance of the raw materials, and the welding time takes only a few minutes. The method can effectively prevent the generation of cracks in the heat-affected zone during the welding process, and is suitable for the welding of Ti(C,N)-based cermets and metals, but has high requirements on fixtures, matching precision and pre-weld preparation work, and expensive equipment investment. The operating cost is high, and it is necessary to further improve the process repeatability and reliability.
3) Electron beam welding
Electron beam welding is a method in which a high-energy density electron beam is used to bombard a weldment to locally heat and melt it. Vacuum electron beam welding is an effective welding method for cermet and metal welding. It has many advantages. It can prevent the pollution of oxygen, nitrogen and the like in the air under vacuum conditions; the electron beam can be focused to form a very small diameter. It can be as small as Φ0.1 to 1.0mm, and its power density can be increased to 107-109W/cm2. Therefore, electron beam welding has the advantages of small heating area, small weld width, deep penetration, and small heat affected zone. However, the disadvantage of this method is that the equipment is complicated, the welding process is strict, and the production cost is high. At present, the electron beam welding technology for Ti(C,N)-based cermets and metals is still in the experimental stage.
2 brazing
Brazing is a welding method in which a material is heated to an appropriate temperature while a brazing material is applied to bond the materials. Brazing methods are usually classified by heat source or heating method. At present, brazing methods with industrial application value include: (1) flame brazing; (2) furnace brazing; (3) induction brazing; (4) resistance brazing; (5) dip brazing; Infrared brazing. Brazing is a major welding method for joining Ti(C,N)-based cermets to metals. The quality of brazed joints depends primarily on the selection of the appropriate solder and brazing process. Li Xianfen et al. conducted a flame brazing test on Ti(C,N)-based cermets and 45 steels using copper-based and silver-based brazing filler metals and brazing tests in an argon gas protection furnace. Under the condition of flame brazing, the average shear strength of joints with H62 as brazing filler metal is 37 MPa, the shear strength of joints with BAg10CuZn as brazing filler metal is 114 MPa, and the average shear strength of joints with BCuZnMn as brazing filler metal is 49 MPa. Under the condition of argon gas protection furnace welding, the average shear strength of the joint with H62 as the brazing material was 37 MPa, and the average shear strength of the joint with Ag72Cu28 as the brazing material was 51 MPa. By observing and analyzing the bonding condition and shear test of the brazed joint, it is shown that the Ti(C,N)-based cermet has good brazability. However, due to the residual stress in the cermet at the joint interface, the shear test is evenly broken on the cermet, and the shear strength of the brazed joint is not high. Zhang Lixia et al. used AgCuZn brazing filler metal to achieve the brazed connection between TiC-based cermet and cast iron. In recent years, a new titanium-containing alloy system, such as Cu Ti and Ni Ti alloy, has been successfully developed using amorphous technology. It can be directly used to braze ceramics and metals. The joint temperature is better than that of brazing with silver-copper solder. Much higher. At present, cermet brazing needs to solve the problem of how to reduce or eliminate the residual stress in the cermet at the interface and improve the strength of the joint.
3 pressure welding
When the pressure welding, the base metal usually does not melt, the welding temperature is lower than the melting point of the metal, and some are heated to the molten state, and the solid phase is combined to form the joint, so that the harmful influence of the high temperature on the base metal can be reduced, and the cermet is improved. The quality of metal welding.
1) diffusion welding
Diffusion welding is a kind of pressure welding. It refers to the surface that is in contact with each other. Under the action of high temperature and pressure, the connected surfaces are close to each other, and plastic deformation occurs locally. After a certain period of time, the bonding atoms between the bonding layers form an integral part. Reliable connection process. Diffusion welding includes diffusion welding without an intermediate layer and diffusion welding with an intermediate layer, and diffusion welding with an intermediate layer is a commonly employed method. The use of an intermediate layer alloy can reduce the soldering temperature and pressure and reduce the total stress level in the welded joint, thereby improving the strength properties of the joint. In addition, in order to reduce the joint stress, in addition to the use of a plurality of intermediate layers, a low modulus compensation intermediate layer may be used. The intermediate layer is composed of fiber metal, which is actually a sintered fiber metal gasket, porosity. Up to 90%, which can effectively reduce the stress generated when welding metal and ceramic. The main advantages of diffusion welding are high joint strength, easy size control, and suitable for joining dissimilar materials. Guan Dehui and other high-temperature vacuum diffusion welding experiments on cermet cutting edges and 40Cr knives show that after cermet welding with 40Cr, the welding of the two materials is quite good, and then the 40Cr is quenched and tempered, the interface has a relatively high strength, the welding interface The tensile strength is 650 MPa and the shear strength is 550 MPa. The main disadvantages of diffusion welding are high diffusion temperature, long time and connection under vacuum, high equipment and high cost. In recent years, some new diffusion welding methods have been developed, such as diffusion welding under high voltage electric field. This method uses a high voltage electric field (above 1000V) and temperature to ionize the dielectric in the ceramic, in the ceramic material adjacent to the metal. A thin layer of polarized regions filled with negative ions is formed therein. In addition, due to the microscopic unevenness of the surface of the material, only a small number of small points are contacted between the ceramic and the metal, and micro-scale gaps are formed in most areas. The ions that are concentrated on both sides of the small gap cause the electric field in these areas to rise sharply, and the applied electric field can be increased by three to four orders of magnitude. Due to the attraction of the opposite charges, the adjacent interfaces of the two materials are brought into close contact (the spacing is smaller than the atomic spacing), and then the metal and the ceramic are connected by means of diffusion.
2) Friction welding
Friction welding is the frictional heat and plastic deformation heat generated by the relative motion between the welding contact end faces and the plastic flow under the action of axial pressure and torque, so that the contact surface and its near region reach a viscoplastic state and produce appropriate macroscopic A pressure welding method that plastically deforms and then quickly upsets to complete the welding. Friction welding is widely used for the connection of similar and dissimilar metals. The friction welding of ceramics and metal joints for different types of materials is still in its infancy.
3) Ultrasonic welding
Ultrasonic welding is an effective method for joining metal to ceramic at room temperature by ultrasonic vibration and pressure. The use of this method to weld aluminum and all types of ceramics has been successful, and the bonding time is only a few seconds. Since the joining energy of the method is ultrasonic vibration, the bonding surface does not need to be surface-treated, the device is simple, and the welding time is shortened, and the cost is greatly reduced compared with the brazing method. The application of this method to the welding of cermets and metals remains to be further studied.
4 Neutral Atomic Beam Irradiation
The neutral atom beam irradiation method uses a neutral atom beam to illuminate the joint surface of the metal and the ceramic to "activate" the atoms on the joint surface. The clean surface of the material has excellent activity, but the surface of the material is often stained with dirt or covered with a very thin oxide film, which reduces its activity. This method mainly applies a low-energy atomic beam of 1000 to 1800 eV to an inert gas such as argon on the joint surface, removes a thin layer of about 20 nm from the surface, activates the surface, pressurizes it, and performs bonding at a normal temperature state by using an excellent reaction degree on the surface. This method can be used for bonding high strength ceramics such as silicon nitride to metals.
5 Self-propagating high-temperature synthetic welding method
Self Propagating High Temperature Synthesis (SHS) technology, also known as Combustion Synthesis (CS) technology, is developed from the method of manufacturing refractory compounds (carbides, nitrides and silicides). . In this method, first, a solid powder capable of burning and releasing a large amount of heat is placed between the ceramic and the metal, and then the powder is locally ignited by an electric arc or radiation to start the reaction, and the heat released by the reaction spontaneously pushes the reaction to continue. Moving forward, the product ultimately formed by the reaction firmly bonds the ceramic to the metal. The remarkable features of the method are low energy consumption, high production efficiency, and little effect on the thermal influence of the base metal. By designing a weld with a gradient of composition gradient to connect the dissimilar materials, the residual stress caused by the difference in thermal expansion coefficient can be overcome. However, gas phase reactions and intrusion of harmful impurities may occur during combustion, resulting in a decrease in the pores and joint strength of the joint. Therefore, the connection is preferably carried out in a protective atmosphere and pressurizes both ends of the ceramic and the metal. Japan's Miyamo to et al. first used the SHS welding technology to study the welding of metal Mo with TiB2 and TiC ceramics. The test used Ti+B or Ti+C powder as the reaction raw material, pre-pressed into a blank and then added between two Mo tablets. The graphite sleeve is energized and heated to initiate the reaction, and the welded joint with complete interface is successfully obtained. He Daihua et al. successfully prepared TiB2 ceramic/metal Fe samples by combustion synthesis technology, and the welding interface was well combined. When the mass percentage of Fe in the middle solder layer was high, the interface bonding was better than the interface with low Fe mass percentage. Combine the situation. Sun Dechao successfully realized the SHS welding of SiC ceramics and GH 4146 alloy with FGM solder (functional gradient material). At present, the research on SHS mechanism is not yet mature, and equipment development and application investment are quite large, so SHS welding has not been engineered.
6 liquid phase transition welding
Liquid phase transition welding (Transient Liquid Phase, abbreviated TLP) is a welding method between solution welding and pressure welding. This technology combines the advantages of brazing technology and diffusion bonding technology to produce high temperature joints with service temperatures not lower than the connection temperature. TLP joining technology process TLP welding and brazing operation steps are similar, both need to put a third material with a melting point lower than the base material between the surface of the base material to be joined (in the TLP is often called the intermediate layer Interlayer, often called brazing in brazing) Fillermetal); then heat and keep warm. However, the degree of diffusion of the two, the way of coagulation, and the composition of the resulting joint, the degree of discontinuity of the tissue are different. Compared with brazing, TLP welding has the following advantages: 1TLP joint has a composition different from that of base metal and filler metal after isothermal solidification is completed, and in some cases can not distinguish the filler metal in the final microstructure; 2TLP joint ratio Generally, the strength of the brazed joint is high; the remelting temperature of the 3TLP joint is higher than that of the brazed joint and the high temperature resistance is good. The above advantages determine that it can be used for the connection of advanced materials, and has broad application prospects in cermet and metal welding technology. Duan Huiping used Ti Cu and Ti Ni composite solder to successfully prepare TiAl/IN718 alloy joint without weld defects by TLP bonding technology.
Ti(C,N)-based cermet is one of the most promising high-speed cutting tool materials. Its welding with metal is one of the key technologies for the development and application of Ti(C,N)-based cermet materials. The key problem of soldering between cermet and metal is interfacial wetting and mitigating residual stress. It is generally possible to change the surface state of the ceramic by selecting the interface between the active element and the cermet to improve the wettability between the two. One of the development directions of the residual thermal stress due to the mismatch of the thermal expansion coefficients between the base metals is that the SHS synthetic functionally graded material (FGM) is used as the solder, so that the residual thermal stress of the welded joint between the cermet and the metal can be greatly alleviated. In summary, although there are many methods for welding Ti(C,N)-based cermets to metals, each method has its own advantages and disadvantages and limitations, such as joint interface using diffusion welding. It is limited and easy to form harmful composite carbides (η phase) in the joint; brazing has problems such as low bonding strength and low use temperature; fusion welding is prone to brittle cracking and lacks suitable welding materials. Some methods are still in the experimental research stage, and it is still difficult to be practical at one time. When selecting the welding method, it is necessary to proceed from the actual situation, that is, from the requirements of the use of cermet and metal composite members, to ensure the quality of the connection and its stability, and to strive to reduce the production cost. Considering welding and process factors, active brazing, diffusion welding, partial instantaneous liquid phase bonding, and SHS welding technology are the most promising research projects in the cermet and metal welding process. The welding of cermet and metal is a brand-new field, and the content is novel and extremely rich. In the future, with the wide application and application range of this kind of material, the research of welding technology methods and processes will become a common concern at home and abroad. Research topics to be solved urgently.
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