Diamond thick film welding tool manufacturing and solder selection
0. Preface
The diamond film has the characteristics of high hardness, wear resistance, low friction coefficient and good thermal conductivity. It is an ideal material for the manufacture of cutting tools for non-ferrous metals and non-metallic materials. There are two types of synthetic diamond film tools: diamond film coated tools, diamond film welding tools. The weaker adhesion is the most prominent problem with diamond coated tools. There are two reasons for the weak adhesion: one is that the chemical vapor deposition (CVD) is attached to the process, which generates a large thermal stress; the other is that the matrix material has many factors that reduce the strength of the joint. In recent years, the difference between the thermal expansion coefficients of the grown matrix metal and the diamond film is large, and the adhesion strength is low. The diamond film is deposited on the substrate. As the substrate cools, the diamond film automatically falls off, and an independent diamond thick film is obtained. In the literature, a plasma film was used to deposit a diamond film on a Mo substrate by a plasma CVD method to obtain an independent diamond thick film (0.3-1.3 mm). The use of this film and the blade material to weld the curtain (the cutting tool has the advantages of both the single crystal diamond tool and the diamond film coated tool, is a new type of tool with extremely broad application prospects.
1. Method for manufacturing diamond thick film welding tool
1-1 diamond thick film forming
Due to the high hardness of the diamond thick film, the wear resistance is good and it is not conductive. Therefore, common mechanical cutting, wire cutting, ultrasonic processing and other processes are not suitable for the cutting of diamond thick film, the common method is laser cutting. Laser cutting not only cuts the diamond thick film into the desired shape and size, but also directly cuts the back angle of the tool and corrects the thick film surface. Generally, the front angle of the diamond turning tool is 0°, and can be selected within the range of +5° as needed. Emphasize the wear resistance of the turning tool and the strength of the sharp knife. A negative rake angle (around -20°) can also be used. The negative relief angle is generally 5°, and can be selected within the range of 2.5 to 10° depending on the conditions of use. The rake angle formed by the rake face and the flank face is 85° or more, and a high-precision tool tip can be obtained.
1-2 tool body properties and welding
Although the blade body material does not directly contact the workpiece in the cutting process, since the matrix body supports the diamond film, it is required to have high rigidity, a thermal expansion coefficient close to the diamond film, and good weldability. At present, commonly used tool materials include cemented carbide (YG3, YG6, YG8, etc.), ceramics (Si3N4, A12O3, etc.), CBN, high-speed steel, etc., and hard alloy is the most promising and currently the most studied tool body material. Cemented carbide is an ideal basic material. Its hardness is high. Because it is a sintered body, it has better red hardness. The hardness at room temperature is generally between HRA 83 and 93. The hardness below 500 ° C remains unchanged. The compressive strength can reach 6000MPa, generally 3400~5600MPa; the room temperature bending strength is between 750~2500MPa, the elastic modulus is high, usually (4~7)×105MPa; the rigidity is better at room temperature, no obvious plastic deformation It can provide a good rigid support for the diamond film.
There are two main methods for connecting the diamond thick film and the blade material: the diamond surface metallization brazing method and the active brazing material welding method. The former uses surface treatment techniques (such as ion beam sputtering) to plate metal (such as Ti, Cr, etc.) on the surface of the diamond to impart metal or metalloid properties to the surface. The surface of the metallized diamond film has good solderability to the Ag-Cu based needle material and can be welded by an intermetallic welding process. This method requires metallization of the diamond film surface, which increases the difficulty of preparation. The active soldering welding method is to add an appropriate amount of an element which can react with carbon atoms on the surface of the diamond film to form carbides in the needle material, and utilize the action of carbide forming elements on the surface to be welded of the diamond film during the needle welding process to make the needle material run. The wet diamond film achieves its brazing process.
1-3 knife body and base metal connection
The obtained diamond thick film cemented carbide composite blade is attached to the base metal, and the connection method is roughly as follows: (1) brazing (2) mechanical reinforcement (3) resin bonding connection (4) hot pressing. Among them, the brazing method is the most used. As the brazing material used for the brazing diamond thick film/hard alloy composite blade, a copper-based needle material, a silver-based needle material, or the like is generally used. However, in consideration of the prevention of oxidation cracks in the oxidation to reduce the tendency of diamond to graphite conversion, it is preferable to use a low melting point solder as much as possible, mainly using a silver-based needle material for hard alloy needle welding. In order to better protect the diamond from conversion to graphite, it is also preferred to weld under vacuum or an inert atmosphere.
1-4 diamond thick film cutter sharpening
The sharpening methods of diamond thick film cutters mainly include mechanical grinding (including diamond grinding and diamond grinding). Hot metal plate study, laser beam, ion beam processing and plasma etching. The grinding efficiency of the diamond powder is low, the grinding wheel of the diamond wheel has high grinding efficiency, and the grinding wheel with different particle sizes can be used for rough processing, which is a good surface finish of the diamond thick film cutter. Hot metal disk grinding removes diamond by the principle of graphitizing diamond by reacting iron group elements with diamond under high temperature conditions. In this way, the surface roughness can be ground up to the mirror level. The surface of the thick film is finished by laser, and the processing efficiency is high, but the quality of the processed surface is not high, and it is only suitable for roughing and semi-finishing.
2, active solder composition selection
Active solder brazing method for brazing the active brazing filler metal for diamond and cemented carbide, in addition to considering the wetting conditions of the brazing filler metal to the diamond film and the hard alloy, it is also necessary to consider the joint stress and the composition of the brazing filler metal under vacuum heating conditions. The effect of the state on the brazing process.
2-1 Basic components in solder
Both the diamond film and the cemented carbide are high-hardness and high-strength materials. The linear expansion coefficients of the two materials also have certain differences. The brazing interface between the two materials will generate a large internal stress, which may cause cracking of the diamond film and separation of the interface. . Therefore, the composition of the solder must have a certain deformability under the condition of ensuring strength. Ag-Cu alloy not only has good strength and good wetting of cemented carbide, but also has a lattice structure of Ag-Cu face-centered cubic to make the solid bath alloy have good plasticity. Therefore, Ag-Cu alloy is the preferred matrix component for diamond film and hard alloy brazing.
2-2 active ingredients in the solder
There is a high interfacial energy between the diamond film and the general metal and its alloy, so that the diamond film can not be infiltrated by the general low melting point alloy, and the wettability is poor. Therefore, some strong carbide forming elements must be added to the brazing filler metal as an active metal to improve the wettability between the diamond film and the cemented carbide. However, the addition of strong carbide forming elements also has certain limitations. On the one hand, adding too much carbide forming element may form an excessively thick brittle compound layer between the diamond film and the brazing filler metal, which affects the bonding property. On the other hand, in order to control the melting point of the solder, it is necessary to form a friendship top of the strong carbide in the solder, such as Ti, Cr, Zr, V, B, Mo, W, etc. The melting points of these elements are: 1672 °C, 1863 ° C, 1865 ° C, 1929 ° C, 2300 ° C, 2623 ° C, 3387 ° C. In comparison, Ti, Cr, Zr, and V are more suitable. A small amount of these elements are added to the Ag-Cu based brazing filler metal. Generally, the brazing temperature can be controlled at about 850 ° C, and the process performance is good. .
In addition, a small amount of a low melting point metal such as IN or SN in the brazing material in the brazing material can effectively lower the melting point of the brazing filler metal, but excessively, an embrittlement compound is produced. At the same time, the welding of the diamond film and the blade material is carried out under vacuum, and the solder material should avoid the easy-to-play elements with high vapor pressure such as MN and ZN.
The above selection of elements in the solder is considered from the viewpoints of the melting point, wettability, vapor pressure, thermal expansion of the solder, whether brittle compounds are formed after soldering, and the like. The selection of the active solder composition requires a comprehensive consideration, and the brazing diamond thick film adds a variety of strong carbide forming elements. At present, no commercial diamond solder has been seen at home and abroad, which is generally prepared by the application unit. There are some, Cu-10%Ti, Cu-15%Sn-3%Ti, Ag-15%Ti, Cu-30%Ag-5%Ti, Cu-15%Sn-2%Cr, Cu-1% Solder compositions such as V, Cu-Au, Ag-30%Cu-4%Ti, Ag-26.5%Cu-3%Ti are available.
3. Conclusion
1. The method of brazing between the diamond thick film and the cemented carbide sheet can effectively solve the problem of weak adhesion. 2. In the brazing of diamond thick film and hard alloy sheet, the self-reactive needle material is used for needle welding, and the process method is simple and low in cost. 3. Diamond thick film self-reactive brazing solder can be prepared by adding an appropriate amount of carbide forming elements such as Ti, Zr and Cr to the Ag-Cu alloy needle.