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       Superhard abrasive brazing process is the use of active brazing filler metal and ultra-hard abrasive interface formed by the chemical metallurgical combination of abrasive particles to achieve high strength control in the abrasive preparation has been applied and development. Among them, the brazing filler metal has an important influence on the brazing performance and service life of superabrasive grains, and relevant scholars at home and abroad have conducted a great deal of research work on this.

      1 Ag-based solder system

      Ag-based brazing filler metal is commonly used in the preparation of super-abrasive type of solder. The melting point of moderate, good technology, with a certain degree of strength, hardness and corrosion resistance. The traditional Ag-based brazing filler metal can form ternary or multi-element alloys by adding elements such as Ti, Cr, Zn, Cu and the like, which not only reduces the cost of the brazing filler metal but also can effectively control the melting point of the brazing filler metal to improve the brazing performance.

      1.1 brazing properties of Ag-based solder

      Xu Hongjun and other Ag-based brazing filler metal was prepared by single-layer brazed diamond grinding wheel and found that adding a certain amount of active element Cr in Ag-Cu brazing filler metal can significantly improve the substrate holding power of abrasive.

      Zhou Yumei, etc. Addition of Cr-based Ag-based brazing filler metal brazing diamond test, and the abrasive, the matrix and the interface between the solder alloy microstructure and reaction products were observed and analyzed, that the brazing interface generated Cr7C3 Carbide is the main reason for achieving high strength of the substrate on the abrasive.

      Ding and other preclude the use of Ag-Cu-Ti brazing filler metal developed a single layer of brazed CBN grinding wheel, and studied the brazing interface structure and formation mechanism, that B, N and other elements in the Ti alloy layer diffusivity differences caused by interface tissue Layered, and observed preferential aggregation of Ti elements in the abrasive surface to form a needle-shaped compound.

      Lu Guanglin et al studied the brazing properties and microstructure of brazing CBN with Ag-Cu-Ti brazing filler metal. It was found that the content of active element Ti has a great influence on the brazing performance. With the increase of Ti content, the brazing wettability, Brazing joint strength are significantly enhanced.

      Kang Shengjiang prepared Ti-based 1%, 2%, 3%, 4%, 5% (mass fraction) of Ag-based solder, and the diamond film and cemented carbide brazing experiments found that the mass fraction of Ti 1% ~ 3% of the solder with high ductility, suitable for a variety of forming processing, while Ag-based solder was observed in the active ingredient β-Ti and diamond film surface C has a very affinity to achieve the diamond film and the hard High-strength alloy connection.

      1.2 Ag-based brazing process parameters of brazing

      Miab et al investigated the wetting mechanism of Ag-based brazing filler metal on CBN and observed the effect of different holding time (5 ~ 15min) on the brazing CBN performance when the brazing temperature was 920 ℃. It was found that increasing the holding time can promote the Cu- Ti migrates toward the grain boundaries to form a uniform and continuous reaction layer.

      In order to solve the problem of fracture and abrasive breakage caused by large thermal stress in high temperature brazing cooling process, Qin Youqiong etc studied the influence of pressure load on the residual stress of diamond joint when brazing, and found that applying certain pressure to the specimen can be reduced Brazing the maximum residual stress value, improve the shear strength of brazed joints.

      Ding Wenfeng and other finite element method of Ag-Cu-Ti brazing brazing CBN abrasive particles when the joint residual stress simulation and focus on different depth of the brazing filler metal diamond residual stress, the results showed that: When the embedment depth is less than 50%, the maximum residual tensile stress in the abrasive grains decreases with the embedment depth. When the embedment depth is in the range of 60% -80%, the maximum residual tensile stress of the abrasive grains changes less .

      Li et al. Conducted a CBN welding experiment using ultra-high frequency continuous brazing process and explored the brazing performance between the abrasive grains, the Ag-Cu-Ti brazing filler metal and the substrate at different scanning speeds and found that when the scanning speed was 0.5 mm / s , We can get a more suitable interfacial structure of the new compound layer, also pointed out that this combination of local heating and scanning of the brazing form is conducive to reducing the thermal deformation after welding.

      Wulf and so on using Ag-based brazing filler metal on the cemented carbide substrate diamond brazing experiments and explore the substrate surface roughness, brazing temperature and other process parameters on the wetting behavior of the solder and found that with the brazing temperature rise High Ti element diffusion ability increases, the smaller the surface roughness of the substrate, the better the wettability.

      1.3 Ag-based solder elemental study

      In recent years, adding elements to improve the solder composition is a hot research topic. Addition of rare earth, graphite, TiC particles to enhance the same can be further improved solder properties, mainly reflected in the following areas:

      1) regulate the wettability of solder;

      2) adjust the solder melting point;

      3) Grain refinement to improve brazing strength.

      For example, Chen et al. Added brazing CBN to Ag-Cu-Ti brazing filler metal to study brazing CBN. The interface and wear characteristics of the grain were analyzed. It was found that the addition of TiB2 can reduce the violent reaction at the grain boundaries and increase the wear resistance Brazing performance.

      Ding and other nano-TiC particles brazing experiments were carried out and found that the addition of nano-TiC particles can more effectively control the abrasive and the sharp reaction of brazing filler metal refinement of Ag-Cu-Ti alloy layer microstructure.

      Yang and other alloy brazing filler metal rare earth Ce brazing diamond test and found that the addition of Ce promoted the Ag-Cu-Ti brazing alloy alloying, reducing the melting point of the brazing filler metal to refine the organization, when the Ce element is 0.25% ~ 0.5% (mass fraction), and the hardness and shear strength of the brazing filler metal were significantly improved. Subsequently, the mechanical properties and microstructure of the La-modified Ag-Cu-Ti filler metal were studied. It is found that the addition of La has little effect on the melting point of the solder, but significantly increases the microhardness and wettability of the solder.

      Klotz et al. On the basis of Ag-Cu-Ti filler metal, low-melting element In was added and brazing diamond test was carried out on the molybdenum sheet substrate. The results showed that the matrix microstructure including Ag-Cu, Cu- The Ti3InC compound with TiC as a transitional product was formed at the interface of the solder bonding. It is considered that the addition of In element enhanced the wettability and corrosion resistance of the solder.

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