2. Research Status of Brazed Diamond Tools
At present, the use of brazing to make diamond (or cubic boron nitride) tools has become a hot spot technology, but it is limited to single-layer tools, and the implementation of "pregnancy" for multiple layers has not yet been published. Foreign brazing technology research began in the late 1980s, but due to the complexity of the work, it still stays in the experimental stage, its application is limited to single-layer tools; domestic high-temperature brazing technology research started late, compared with developed countries Compared with the breadth and depth of research, the progress is very slow, so the progress is very slow, but with China's accession to the WTO, the pace of research will inevitably accelerate.
(1) Research status of foreign high-temperature brazed diamond tools. AK Chattopadhyay et al. used flame spraying (oxygen-acetylene torch) to solder the alloy (72% Ni, 14.4% Cr, 3.5% Fe, 3.5% Si, 3.35%) B, 0.5% O2) was plated on the tool steel substrate, and the diamond (uncoated) cloth was placed on the solder layer, and then brazed for 30 seconds under the protection of argon gas at 1080 ° C to realize the bonding of the diamond to the steel substrate. The Cr in the solder alloy acts as a strong carbide element to enrich the surface of the diamond during brazing to achieve surface metallization of the diamond.
The method described by Wiand et al. in the U.S. patent is: solder (Ni-Cr) metal powder plus organic binder to make a brazing paint, the coated diamond is adhered to the tool steel substrate, and then the brazing paint is applied and heated. Take a moderate temperature and keep it for a certain period of time to remove volatiles. It is heated to about 1100 ° C in a vacuum furnace (vacuum degree: 1.333 × 10-2 Pa) or a dry hydrogen furnace, and kept for 1 hour, and the surface metallization of the diamond is completed while brazing.
In some patents, brazing is also achieved by using Ni-Cr alloy brazing filler metal, and the brazing material also includes Fe, B element or Si, Mo and the like. For example, in the literature [14], Ni-Cr alloy brazing filler metal containing Si or Si and Ti is used for brazing in a vacuum furnace at a brazing temperature of 1126 to 1176 °C; the literature [15] uses a Cu-based inclusion of W and Fe. Brazing diamond grinding wheels such as Cr, B, Si, etc.; [16] used Ag-Mn-Zr silver-based brazing filler metal to braze diamond tools to replace electroplating tools.
In Germany, A Trenker et al. used nickel-based active brazing filler metal and nickel-based brazing filler metal to achieve the combination of diamond and matrix. As can be seen from the comparison with the plating tool, the performance of the high temperature brazed diamond tool is much better than that of the electroplated diamond tool. The initial grinding performance of the brazing tool (using active solder and PDA989, PDA665 diamond) is the plating tool (nickel). More than 3.5 times of the base solder and PDA665 diamond, the life is more than 3 times that of the plating tool; because the brazing tool has a large chip space, the diamond abrasive grain has a large free cutting surface and more space between the abrasive grains. The chip is easily removed, so the brazing diamond tool has good grinding performance.
(2) Research status of domestic high-temperature brazing diamond tools Based on the research of brazing diamonds at home and abroad, the Fourth Military Medical University and Xi'an Jiaotong University adopt the method of high-temperature brazing in a vacuum furnace (vacuum degree: 0.2Pa) to NiCr13P9. The alloy is a brazing filler metal, with a small amount of Cr powder, and is brazed under high temperature (950 ° C) pressure (4.9 MPa), thereby achieving a firm bond between the diamond and the steel substrate. The brazing material is evenly distributed on the surface of the grinding wheel, the diamond has been firmly brazed, and the surface of the touching grinding wheel feels quite sharp and rough. The brazing material is evenly distributed between the diamond abrasive grains, and the diamond cutting edge height is high. Its durability is significantly improved compared to electroplated grinding wheels, and only a small amount of diamonds fall off after work.
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