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Cermet and metal vacuum brazing
Ti(C,N)-based cermet is a typical cermet developed on the basis of TiC-based cermet; it has many advantages, such as high hardness, high melting point, good oxidation resistance, stability to molten metal, resistance to A series of advantages such as cutting. Due to the outstanding advantages of Ti(C,N)-based cermets, it has been widely used in the processing industry. Based on the wide application of Ti(C,N)-based cermets, strengthening the research on the connection of cermet materials will play a crucial role in the application of cermet materials. Ti(C,N)-based cermets and metals have been successfully connected by vacuum brazing, but the strength of the brazed joints is not high due to residual stress in the cermet at the joint interface. This experiment will try to improve the joint strength to achieve high-quality vacuum brazing of Ti(C,N)-based cermet and 45# steel.
1 Experimental methods and steps
The cermet and metal to be connected are processed into a size of 20mm x 5mm x 5mm by wire cutting, and the brazing filler metal and the intermediate buffer layer are cut into small pieces suitable for the cross section of the cermet and metal. The base metal, buffer layer and brazing filler metal should be cleaned with 400# water sandpaper before entering the furnace, and then ultrasonically cleaned with acetone for about 10 minutes. The form of brazing joint in this test adopts butt joint. During vacuum brazing, the sample assembly from top to bottom is cermet/brazing material/buffer layer/brazing material/metal in the order of flat laying in a vacuum furnace for brazing connection. The degree of medium vacuum is not less than 5×10~3Pa. According to the melting point of the brazing filler metal, the brazing temperature is determined to be 980~1080 °C. There is an interval of 20 °C, a total of 6 brazing temperatures. After determining the optimal brazing temperature, the effect of adding the intermediate layer on the joint performance was studied, and the thickness of the Ni sheet was 0.1, 0.2, 0.3 and 0.4 mm, respectively.
2 Results Analysis and Discussion
2.1 Influence of brazing temperature on joint interface structure
The figure below shows the backscattered microstructure photos of Ti(C,N)-based cermet and 45 steel joints connected by Cu-Mn-Ni solder at different brazing temperatures when the holding time is 15min. It can be seen from the figure that when the brazing temperature is 1000 °C, although the brazing temperature is low, the brazing filler metal and the base metal on both sides are well wetted, and a small amount of solid solution accumulates on the left side of the brazing seam, and the brazing filler metal on the right side diffuses with the cermet. It is not very sufficient; when the connection temperature increases to 1040 °C, the brazing seam and the base metal on both sides diffuse sufficiently, and a dark solid solution is formed near the base metal on both sides, and a dark solid solution is also formed inside the brazing seam. When the temperature is 1080℃, the mutual diffusion between the brazing and the base metal on both sides is very sufficient, and white and dark solid solutions are formed in the brazing joint area, but at the same time, cracks are generated in the brazing joint area. The three-point bending test of the joint shows that the brazed joint has better mechanical properties when the brazing temperature is 1040℃.
2.2 The effect of holding time on the interface structure of joints
In order to analyze the influence of holding time on the interface structure, when the connection temperature is 1040℃, the CU-Mn-Ni brazing filler metal is used to connect Ti(C,N)-based cermet on the back of No. 45 steel joint under different holding time. Scattering microstructure photos, when the holding time is 5min, the inside of the brazing joint is mainly Cu-Mn-Ni solid solution, a small amount of dark solid solution is formed on the 45# steel side, the diffusion of the brazing filler metal and the cermet side is not obvious, when the holding time is extended to At 15min, the brazing filler metal and the base metal on both sides diffuse sufficiently, and a dark solid solution is formed near the base metal area on both sides, and a dark solid solution is also formed inside the brazing joint; when the holding time is 25 minutes, the brazing filler metal has basically been diffused. , The brazing area mainly forms a dark solid solution. The three-point bending test of the joint shows that the brazed joint has the highest strength when the holding time is 15min.
(1) Cu-Mn-Ni solder has good wettability to Ti(C,N)-based cermet and No. 45 steel, and the joint has no welding defects, and the Ni buffer layer is well bonded to the solder.
(2) When the brazing temperature is 1040℃ and the heat preservation is 15min, the performance of the joint is the best.
(3) Using Ni as the buffer layer can improve the joint strength. When the thickness of the buffer layer Ni is 0.1 mm, the joint strength is the highest, the thickness increases, and the joint strength decreases.
Brazing equipment selection: RHVB series vacuum brazing furnaces produced by SIMUWU are high-quality products for vacuum heat treatment of tools and molds. Good temperature control accuracy and uniformity ensure the effective vacuum brazing process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.
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