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Diamond brazing

High hardness and excellent physical and mechanical properties of diamond make diamond tools become an indispensable tool for machining all kinds of hard materials. The bond of metal matrix based on diamond (diamonds and matrix) is one of the main factors affecting the service life and performance of diamond tools.
Due to high interfacial energy is generally between diamond and metals and alloys, the diamond particles cannot infiltration for low melting point alloy, adhesion is poor, in the traditional manufacturing techniques, to produce diamond particles on matrix contraction after mechanical clamping force is embedded in the metal matrix in the fetal body, but has not formed a strong chemical bonding or metallurgical bonding, resulting in easy separation of diamond particles and matrix metal matrix, greatly reducing the level of life and performance of diamond tools. The utilization ratio of diamond is low in most of the impregnated tool, and a large amount of expensive diamond is lost in the waste. Lin Zengdong pioneered the use of diamond surface metallization technology to give the diamond surface with many new features, such as good thermal conductivity, good thermal stability, improve its physicochemical properties, improve the wettability of metal or alloy solution etc..
Diamond surface metallization in the last century in 70s has caused the domestic and foreign diamond tool manufacturing sector of high attention. A lot of people working on the metal surface of diamond in the sintering process, the matrix material is added to or on the surface of the diamond pre glued strong carbide metal powder (the diamond in the coating did not before heating, and chemical reaction, can only belong to the diamond coating), to expect them to achieve in the sintering process of chemical bond the combination of diamond. Although the literature has demonstrated that some metals such as tungsten (not oxidized) at low temperature (800 DEG C) to form the WC layer on the surface of the diamond, but from the implementation process used in coating diamond point of view, in under the condition of vacuum, heating more than 600 DEG C for 1 hours to get the binding force of the ideal. With the sintering conditions of diamond cutting tools which are commonly used at present, it is not possible to generate a metal layer on the surface of diamond, which is not more than 900 minutes in a non vacuum or low vacuum. Because both the active metal atoms (Ti, V, Cr) according to the diamond surface enrichment or interfacial reaction to the vitrified bond and diamond metallurgy is atomic diffusion process, according to the temperature and pressure in such a short time, this process is not sufficient. In the solid phase sintering conditions (sometimes with a small amount of low strength liquid metal or alloy with low melting point phase), matrix for diamond chemical bonding or metallurgical bonding strength is very weak or no form.
The diamond coating is not the ultimate goal, which is only one of the measures to achieve and matrix metal chemical metallurgy combination. After plating of diamond in sintered saw (drilling) after the tooth, fracture surface exposed on the diamond were lost off the diamond coating, the residual pit surface is very smooth, this phenomenon seems to suggest that the diamond and the matrix also failed to reach the level of chemical package inserts. So even if the surface metallization of diamond, solid powder metallurgy sintering method of traditional could not achieve combination between diamond and matrix materials.
At the end of last century in 80s, people began to explore the technology of brazing for diamond tools. Some of the transition group elements (such as Ti, Cr, W, etc) are deposited on the surface of diamond, and their chemical reactions are formed on the surface of the diamond. Through this layer of carbide, diamond, binder, substrate three can pass brazing for chemical and metallurgical bond, so as to realize the real diamond surface metallization, which is the principle of brazing diamond. From the patent and published articles can be seen, the largest diamond protrusion value reached the size of 2/3 tool life increased 3 times, while the conventional value of less than 1/3, allowing the edge values available edged operations of value to obtain a stable edge. So, is expected to achieve by matrix metal brazing technology (solder) firmly combined with the parent material, diamond and steel substrate.
2 present situation
At present, the production of diamond (or cubic boron nitride) tools have begun to become a hot technology, but only a single tool, for the multi layer to achieve the "pregnancy set" has not yet seen the results published. Study on brazing technology abroad began in late 1980s, but because of the complex are still at the experimental stage, its application is limited to single tool; domestic brazing technology research started late, compared with developed countries, the scope and depth of research is not enough, so the progress is very slow, but with Chinas accession to the WTO, the pace of research will gradually accelerate.
(1) the research status of high temperature brazing diamond tools in foreign countries
Swiss AKChattopadhyay by flame spraying method (oxygen acetylene torch) to solder alloys (72%Ni, 14.4%Cr, 3.5%Fe, 3.5%Si, 3.35%B, 0.5%O2) coating on the steel substrate, and diamond (not coated cloth) in the solder layer, then induction at 1080 DEG C and under argon brazing for 30 seconds the combination of diamond and steel substrate. Cr as a strong carbide element in the solder alloy, the surface metallization of diamond is enriched in the surface of diamond during the brazing process.
The Wiand method is introduced in the United States patent is: (Ni-Cr) metal solder powder and organic binder to brazing paint, coating diamond tool stuck on the steel substrate, and then coated with brazing paint, and then heated to a moderate temperature and heat preservation time to remove volatile substances. In vacuum furnace