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Vacuum Brazing of Diamond and Carbide

Polycrystalline diamond compact (PCD) not only has the high hardness and wear resistance of diamond, but also has the toughness and weldability of cemented carbide. In recent years, it has been widely used in the processing of non-ferrous metals and non-metallic materials. , has become one of the key cutting tool materials researched and developed by countries all over the world.

The heat-resistant temperature of the PCD composite sheet is generally lower than 720°C, and low-temperature vacuum brazing is required. The vacuum brazed joints formed in this way have many defects and low shear strength, which is easy to cause desoldering. Researchers have done a lot of research work in the field of PCD composite sheet vacuum brazing.

Firstly, the surface of the PCD composite sheet and the sipe to be welded is treated to remove the oxide film and degreasing; then, the paste flux is applied in the cutter body sipe, and the solder and the PCD composite sheet are placed in turn, and the brazing filler metal Then apply a layer of flux between PCD composite sheet; finally, carry out vacuum brazing on high-frequency induction heating equipment (self-made heating induction coil), and use induction heating fuzzy control and synchronous data acquisition system to control the heating temperature. The process parameters of vacuum brazing are: heating temperature θp=690℃, holding time th=16s.

Due to the high activation energy of the cemented carbide surface, the wetting ability of the brazing filler metal to it is worse than that of the 45 steel cutter body, resulting in low welding strength between the PCD composite sheet and the cemented carbide cutter body, and the tool is easy to desolder during use. Under the condition of constant solder, further improving its wettability to cemented carbide is the key to solve the problem of low welding strength of cemented carbide. A reasonable combination of brazing material and flux can improve the wetting and spreading behavior of the brazing material on the cemented carbide and the microstructure of the vacuum brazed joint, and improve the bonding strength of the vacuum brazed joint of the PDC tool. In addition, choosing a reasonably matched brazing flux can also reduce the requirements on the performance of the solder, which can significantly reduce the production cost of the tool manufacturer and improve the cost performance of the PDC tool.

Improvement of PDC Tool Vacuum Brazing Process

At present, in view of the problem that cemented carbide is difficult to wet, many scholars have conducted a lot of research on the surface modification of cemented carbide. In this paper, the re-welding process is used to explore an effective way to improve the welding strength of PCD composite sheets. The re-welding process in the test is to first vacuum braze a layer of solder on the surface of the polished and cleaned test piece, and then vacuum braze according to the above-mentioned welding specifications. The results show that the bonding strength of PCD composite sheet and YG8 cemented carbide vacuum brazing joint is improved by adopting the rewelding process, and the vacuum brazing strength of brazing material and flux is even increased by 1.5 times. This is because a layer of solder is vacuum brazed on the surface of the YG8 cemented carbide cutter body, and the alloy elements of the solder diffuse with the components in the cemented carbide to play a role of solid solution strengthening; at the same time, it will also change the surface structure of the cemented carbide. , During re-welding, the wettability of the brazing material is enhanced, which indirectly increases the vacuum brazing area, so re-welding can improve the shear strength of the vacuum brazed joint.

Diamond and Carbide Vacuum Brazing Conclusions

(1) Under the test conditions, the high-frequency induction vacuum brazing of PCD composite sheet and YG8 cemented carbide, the shear strength of the vacuum brazed joint with No. 1 brazing filler metal containing Mn is higher than that of No. 2 brazing filler metal containing Cd Joint shear strength; when No. 1 solder and QJ102 flux are combined, the shear strength of vacuum brazed joints is the highest, reaching more than 220MPa; while the combination of No. 2 solder and QJ102 flux has the lowest shear strength of vacuum brazed joints, the average The shear strength is only 77.96MPa; at the same time, the thickness of the weld seam of the specimen using No. 1 solder is smaller than that of the specimen using No. 2 solder, and the appearance is beautiful.

(2) The welding seam obtained by matching No. 1 brazing filler metal with QJ102 brazing flux has a smooth appearance and uniform structure, and there is an obvious transition layer between the brazing filler metal and the cemented carbide; the bonding interface of Cu elements, Ni elements, and Mn elements on the cemented carbide side Aggregation, [CuNi], [CuMn] and [NiMn] metallurgical reactions may have occurred.

(3) The re-welding process can significantly improve the bonding strength of the vacuum brazed joint. The low-cost No. 2 brazing material can greatly increase the strength of vacuum brazing by adopting the re-welding process, which can meet the strength requirements of PDC tools, and can reduce production costs, and is suitable for the production of small batches of PDC tools.