A two-step brazing method for improving the joint strength of m42 steel and pcbn ceramic by using solid solution brazing

Abstract

The application relates to a two-step brazing method for improving the joint strength of M42 steel and PCBN ceramic by using solid solution brazing, and belongs to the field of ceramic-metal brazing. The application aims to solve the problems of the existing M42 steel and PCBN ceramic brazing difficulty and low mechanical property. The method comprises the following steps: 1, ball milling mixing; 2, bonding the mixed powder after ball milling on the surface of the M42 steel; 3, heating to the mixed powder on the surface of the M42 steel to fully melt; 4, polishing, cleaning and drying; 5, placing Ti foil between the PCBN ceramic and the M42 steel which is pretreated and covered with a molten layer to obtain a to-be-welded piece; and 6, keeping the temperature at the connecting temperature. The application is used for the two-step brazing for improving the joint strength of M42 steel and PCBN ceramic by using solid solution brazing.

Description

Technical Field

[0001] This invention belongs to the field of ceramic-metal brazing. Background Technology

[0002] M42 steel (W2Mo9Cr4VCo8) is a cobalt-containing high-speed tool steel with high hardness, good wear resistance, and impact resistance, especially good red hardness, making it widely used in the manufacture of saw blades, stamping dies, high-speed cutting tools, and friction stir welding heads. However, with the development of modern industry, the emergence of increasingly difficult-to-machine materials has placed higher demands on the precision and efficiency of cutting tools and friction stir welding heads. After prolonged machining of copper alloys or high-temperature alloys, cutting tools or friction stir welding heads made of M42 steel often experience severe wear, thus shortening their service life. To solve this problem, methods such as nitriding, laser hardening, and special heat treatments are commonly used to improve the surface hardness and wear resistance of the steel; however, these methods are often complex. Joining M42 steel with ceramics, which have better wear resistance, to create ceramic-metal composite cutting tools can effectively improve the steel wear problem. Among them, PCBN (polycrystalline cubic boron nitride) ceramic is a material with high hardness and excellent wear resistance, and has broad application potential in cutting, grinding, and other fields. Composite cutting tools and friction stir welding heads made by joining M42 steel with PCBN ceramic can meet even more stringent usage requirements. Brazing is a common method for joining ceramics and metals, but the significant differences in the physicochemical properties of M42 steel and PCBN ceramics make brazing them quite difficult. PCBN ceramics are chemically stable, and only by using active solders can their surfaces be wetted. AgCuTi solder is the most commonly used solder for brazing ceramics and metals, but Ag-based solder joints have a low operating temperature, which cannot meet the high-temperature service requirements of cutting tools. When using Cu-based or Ni-based solders, at higher brazing temperatures, the active elements in the solder (such as Ti) react violently with the alloying elements in M42 steel, leading to the precipitation of carbides and the formation of numerous brittle intermetallic compounds. These continuous intermetallic compounds result in significant residual stress in the brazed joint, severely limiting the mechanical properties of the joint. Summary of the Invention

[0003] This invention aims to solve the problems of difficult brazing of M42 steel and PCBN ceramic and low mechanical properties, and provides a two-step brazing method to improve the joint strength of M42 steel and PCBN ceramic by utilizing solid solution brazing seam.

[0004] A two-step brazing method for improving the strength of M42 steel and PCBN ceramic joints using solid solution brazing seams is performed as follows:

[0005] 1. Mix Cu powder and Ni powder to obtain a mixed powder. Place the mixed powder in a ball mill and grind it to obtain a ball-milled mixed powder.

[0006] The mass percentage of Cu powder in the mixed powder is 80% to 86%.

[0007] 2. Using a binder, the ball-milled mixed powder is coated onto the surface of M42 steel and dried to obtain M42 steel with the mixed powder on the surface;

[0008] 3. Place the M42 steel with the mixed powder on its surface in a vacuum brazing furnace and heat it until the mixed powder on the surface of the M42 steel is fully melted. Finally, cool it with the furnace to obtain M42 steel with a molten layer.

[0009] IV. Polish, clean and dry the M42 steel with the molten layer in sequence to obtain pretreated M42 steel with the molten layer.

[0010] 5. Place the Ti foil between the PCBN ceramic and the pretreated M42 steel coated with a molten layer, and then apply pressure to the surface of the PCBN ceramic to obtain the workpiece to be soldered;

[0011] 6. Place the parts to be welded in a vacuum brazing furnace, keep them at the connection temperature, and finally cool them to room temperature. This completes the two-step brazing method of improving the strength of the M42 steel and PCBN ceramic joint by utilizing the solid solution brazing seam.

[0012] The beneficial effects of this invention are:

[0013] I. This joining method utilizes eutectic reaction to join ceramics and metals, allowing for controllable interfacial reactions and reducing the formation of continuous brittle intermetallic compounds;

[0014] 2. This connection method uses a two-step brazing process, which increases the proportion of metal matrix solid solution in the brazed seam, alleviates residual stress in the brazed joint, and increases the shear strength of the joint to 150MPa~250MPa.

[0015] Third, this joining method introduces a CuNi cladding barrier layer, which avoids excessive reaction between Ti and M42 steel and reduces the precipitation of carbides in the steel;

[0016] IV. This connection method forms a Cu-Ni-Fe solid solution through the interdiffusion between the CuNi cladding layer and M42 steel, which greatly improves the high-temperature mechanical properties of the brazed joint. It can maintain a shear strength of 60MPa~70MPa under a high-temperature test environment of 900℃.

[0017] This invention relates to a two-step brazing method for improving the strength of M42 steel and PCBN ceramic joints by utilizing solid solution brazing seams. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the two-step brazing method for improving the strength of the M42 steel and PCBN ceramic joint using solid solution brazing seams in Example 1;

[0019] Figure 2 The image shows the XRD pattern of the cladding layer in the pretreated M42 steel with a cladding layer prepared in step four of Example 1.

[0020] Figure 3 The images shown are scanning electron microscope (SEM) images of the cross-section of the M42-PCBN brazed joint prepared in Example 1. (a) is an overall morphology of the joint interface, (b) is a magnified view of a local area of ​​the PCBN-brazing seam, and (c) is a magnified view of a local area of ​​the M42-brazing seam.

[0021] Figure 4 To compare the cross-sectional scanning electron microscope images of the M42-PCBN joint brazed with AgCuTi solder in the experiment, (a) is the overall morphology of the joint interface, (b) is a magnified view of a local area of ​​the PCBN-brazing seam, and (c) is a magnified view of a local area of ​​the M42-brazing seam.

[0022] Figure 5 The following are EDS elemental surface scan analysis images of the M42-PCBN brazed joint cross section prepared in Example 1: (a) is the overall morphology of the joint interface, (b) is N element, (c) is Al element, (d) is Ti element, (e) is Cu element, (f) is Ni element, (g) is Fe element, (h) is Co element, and (i) is Cr element.

[0023] Figure 6 The transmission electron microscope (TEM) images of the M42-PCBN brazed joint prepared in Example 1 located on the PCBN-brazing seam side are shown in (a), where (a) is a bright field image on the PCBN-brazing seam side and (bg) are electron diffraction spots of each phase in (a).

[0024] Figure 7 The high-resolution analysis images of the M42-PCBN solder joint prepared in Example 1 are located on the PCBN-solder seam side. (a) is a bright field image of the TiN layer and a high-resolution image of the interface. 1, 2 and 3 are high-resolution images of interfaces 1, 2 and 3 marked in (a). (b) is a bright field image of the TiB layer and a high-resolution image of the interface. 4 is a high-resolution image of interface 4 marked in (b). (c) is a bright field image of the TiB2 layer and a high-resolution image of the interface. 5 and 6 are high-resolution images of interfaces 5 and 6 marked in (c).

[0025] Figure 8 This is a hardness distribution diagram of the M42-PCBN brazed joint prepared in Example 1;

[0026] Figure 9The following are shear test diagrams of M42-PCBN brazed joints: (a) is a schematic diagram of the shear test; (b) is the strain-shear strength curve at room temperature; 1 is the M42-PCBN brazed part prepared in Example 1; 2 is the M42-PCBN brazed part prepared in the comparative experiment; and (c) is the strain-shear strength curve of the M42-PCBN brazed part prepared in Example 1 at 900℃.

[0027] Figure 10 The fracture surface images of the M42-PCBN brazed joint sample after shear test prepared in Example 1 are shown in (a) and (b) respectively.

[0028] Figure 11 This is a scanning electron microscope (SEM) image of the cross-section of the M42-PCBN brazed joint prepared in Example 2;

[0029] Figure 12 The strain-shear strength curves of the M42-PCBN brazed joint prepared in Example 2 are shown at room temperature and high temperature. (a) is the strain-shear strength curve at room temperature, and (b) is the strain-shear strength curve at 900℃. Detailed Implementation

[0030] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0031] Specific Implementation Method 1: This implementation method is a two-step brazing method for improving the strength of the M42 steel and PCBN ceramic joint using solid solution brazing seams. It is carried out according to the following steps:

[0032] 1. Mix Cu powder and Ni powder to obtain a mixed powder. Place the mixed powder in a ball mill and grind it to obtain a ball-milled mixed powder.

[0033] The mass percentage of Cu powder in the mixed powder is 80% to 86%.

[0034] 2. Using a binder, the ball-milled mixed powder is coated onto the surface of M42 steel and dried to obtain M42 steel with the mixed powder on the surface;

[0035] 3. Place the M42 steel with the mixed powder on its surface in a vacuum brazing furnace and heat it until the mixed powder on the surface of the M42 steel is fully melted. Finally, cool it with the furnace to obtain M42 steel with a molten layer.

[0036] IV. Polish, clean and dry the M42 steel with the molten layer in sequence to obtain pretreated M42 steel with the molten layer.

[0037] 5. Place the Ti foil between the PCBN ceramic and the pretreated M42 steel coated with a molten layer, and then apply pressure to the surface of the PCBN ceramic to obtain the workpiece to be soldered;

[0038] 6. Place the parts to be welded in a vacuum brazing furnace, keep them at the connection temperature, and finally cool them to room temperature. This completes the two-step brazing method of improving the strength of the M42 steel and PCBN ceramic joint by utilizing the solid solution brazing seam.

[0039] This embodiment improves the mechanical properties of the joint by controlling the interfacial reaction in the brazed joint and increasing the proportion of metal-based solid solution in the brazed seam. This embodiment achieves the connection between M42 steel and PCBN ceramic through a eutectic reaction and obtains a high-strength solid solution-based brazed joint by controlling the interfacial reaction.

[0040] The beneficial effects of this embodiment are:

[0041] I. This joining method utilizes eutectic reaction to join ceramics and metals, allowing for controllable interfacial reactions and reducing the formation of continuous brittle intermetallic compounds;

[0042] 2. This connection method uses a two-step brazing process, which increases the proportion of metal matrix solid solution in the brazed seam, alleviates residual stress in the brazed joint, and increases the shear strength of the joint to 150MPa~250MPa.

[0043] Third, this joining method introduces a CuNi cladding barrier layer, which avoids excessive reaction between Ti and M42 steel and reduces the precipitation of carbides in the steel;

[0044] IV. This connection method forms a Cu-Ni-Fe solid solution through the interdiffusion between the CuNi cladding layer and M42 steel, which greatly improves the high-temperature mechanical properties of the brazed joint. It can maintain a shear strength of 60MPa~70MPa under a high-temperature test environment of 900℃.

[0045] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the grinding in step one is specifically carried out as follows: The mixed powder and grinding media are placed in an agate ball mill jar, with the grinding media covering the mixed powder. Under the conditions of a grinding ball to mixed powder mass ratio of (2-2.5):1 and a rotation speed of 250-300 r / min, ball milling is performed using a planetary ball mill for 0.5-2 hours. The grinding media is alcohol. Everything else is the same as in Specific Implementation Method One.

[0046] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the particle size of the Cu powder and Ni powder mentioned in step one is <50μm. Everything else is the same as in Specific Implementation Method One or Two.

[0047] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the M42 steel mentioned in step two and the PCBN ceramic mentioned in step five are pretreated M42 steel and pretreated PCBN ceramic. The pretreatment is carried out according to the following steps: the surface of the M42 steel to be joined is polished with silicon carbide sandpaper, and the surface of the PCBN ceramic to be joined is polished with a diamond grinding wheel. After polishing, the surface is cut, and then ultrasonically cleaned with acetone solution for 15 to 25 minutes under a power of 200W to 240W. Finally, the surface is dried to obtain the pretreated M42 steel and pretreated PCBN ceramic. Everything else is the same as in Specific Implementation Methods One to Three.

[0048] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the adhesive mentioned in step two is a mixture of polyethylene cellulose and terpineol, and the mass percentage of polyethylene cellulose in the adhesive is 3% to 5%; the coating amount of the adhesive mentioned in step two is 0.15 g / cm³. 2 ~0.3g / cm 2 The drying process described in step two is specifically carried out at a temperature of 50℃ to 60℃. The rest is the same as in specific implementation method four.

[0049] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: in step three, the M42 steel with the mixed powder coating on its surface is placed in a vacuum brazing furnace and heated to 1150℃ to 1180℃ at a heating rate of 20℃ / min to 25℃ / min. Then, under the condition of a melting temperature of 1150℃ to 1180℃, it is heated until the mixed powder on the surface of the M42 steel is fully melted. Finally, it is cooled with the furnace to obtain M42 steel with a molten layer with a thickness of 200μm to 600μm. Everything else is the same as in Specific Implementation Methods One to Five.

[0050] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: in step four, the M42 steel coated with the molten layer is polished smooth with silicon carbide sandpaper, then ultrasonically cleaned with acetone solution for 15 to 25 minutes at a power of 200W to 240W, and finally dried. Everything else is the same as in Specific Implementation Methods One to Six.

[0051] Specific Implementation Method Eight: This implementation method differs from one of Specific Implementation Methods One to Seven in that the thickness of the Ti foil mentioned in step five is 5μm to 10μm. Everything else is the same as in Specific Implementation Methods One to Seven.

[0052] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that a pressure of 0.1 MPa to 0.2 MPa is applied to the PCBN ceramic surface in step five. Everything else is the same as in Specific Implementation Methods One to Eight.

[0053] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: in step six, the workpiece to be soldered is placed in a vacuum brazing furnace and heated to 1000℃ to 1060℃ at a heating rate of 20℃ / min to 25℃ / min. Then, it is held at a connection temperature of 1000℃ to 1060℃ for 15min to 60min, and finally cooled to room temperature at a cooling rate of 5℃ / min to 10℃ / min. Everything else is the same as in Specific Implementation Methods One to Nine.

[0054] The beneficial effects of the present invention are verified using the following embodiments:

[0055] Example 1, combined with Figure 1 Detailed explanation:

[0056] A two-step brazing method for improving the strength of M42 steel and PCBN ceramic joints using solid solution brazing seams is performed as follows:

[0057] 1. Mix Cu powder and Ni powder to obtain a mixed powder. Place the mixed powder in a ball mill and grind it to obtain a ball-milled mixed powder.

[0058] The mass percentage of Cu powder in the mixed powder is 86%, and the mass percentage of Ni powder is 14%.

[0059] 2. Using a binder, the ball-milled mixed powder is coated onto the surface of M42 steel and dried to obtain M42 steel with the mixed powder on the surface;

[0060] 3. Place the M42 steel with the mixed powder on its surface in a vacuum brazing furnace and heat it until the mixed powder on the surface of the M42 steel is fully melted. Finally, cool it with the furnace to obtain M42 steel with a molten layer.

[0061] IV. Polish, clean and dry the M42 steel with the molten layer in sequence to obtain pretreated M42 steel with the molten layer.

[0062] 5. Place the Ti foil between the PCBN ceramic and the pretreated M42 steel coated with a molten layer, and then apply pressure to the surface of the PCBN ceramic to obtain the workpiece to be soldered;

[0063] 6. Place the workpiece to be soldered in a vacuum brazing furnace, keep it at the connection temperature, and finally cool it to room temperature to obtain the M42-PCBN brazed workpiece.

[0064] The grinding described in step one is carried out in the following steps: the mixed powder and grinding media are placed in an agate ball mill jar, and the grinding media covers the mixed powder. Under the conditions that the mass ratio of grinding balls to mixed powder is 2:1 and the rotation speed is 250 r / min, the mixture is ball-milled for 2 hours using a planetary ball mill; the grinding media is alcohol.

[0065] The average particle size of the Cu powder and Ni powder mentioned in step one is 48 μm, and the purity is 99.9%.

[0066] The M42 steel mentioned in step two and the PCBN ceramic mentioned in step five are pre-treated M42 steel and pre-treated PCBN ceramic. The pre-treatment is carried out according to the following steps: the surface of the M42 steel to be joined is polished with 1500-grit silicon carbide sandpaper, and the surface of the PCBN ceramic to be joined is polished with a 3000-grit diamond grinding wheel. After polishing, the M42 steel and PCBN ceramic are cut, and the size of the cut M42 steel is Φ20×2mm. 3 The PCBN ceramic size is 3×3×3mm. 3 Then, under a power of 200W, the surface is ultrasonically cleaned with acetone solution for 15 minutes, and finally dried to obtain M42 steel with a surface roughness of 2μm to 5μm and PCBN ceramic with a surface roughness of 1μm to 2μm.

[0067] The adhesive described in step two is a mixture of polyethylene cellulose and terpineol, wherein the mass percentage of polyethylene cellulose in the adhesive is 5% and the mass percentage of terpineol is 95%; the coating amount of the adhesive described in step two is 0.3 g / cm³. 2 The drying process described in step two is specifically carried out at a temperature of 60°C.

[0068] In step three, the M42 steel with the mixed powder coating on its surface is placed in a vacuum brazing furnace and heated to 1180°C at a heating rate of 25°C / min. Then, it is heated for 10 minutes at a melting temperature of 1180°C until the mixed powder on the surface of the M42 steel is fully melted. Finally, it is cooled with the furnace to obtain M42 steel with a molten layer with a thickness of 600μm.

[0069] In step four, the M42 steel with the molten layer is polished smooth with silicon carbide sandpaper, then ultrasonically cleaned with acetone solution for 15 minutes at a power of 200W, and finally dried.

[0070] The thickness of the Ti foil mentioned in step five is 10 μm.

[0071] In step five, a pressure of 0.2 MPa is applied to the PCBN ceramic surface.

[0072] In step six, the workpiece to be welded is placed in a vacuum brazing furnace and heated to 1020°C at a heating rate of 25°C / min. Then, it is held at a connection temperature of 1020°C for 30 minutes and finally cooled to room temperature at a cooling rate of 5°C / min.

[0073] Example 2: This example differs from Example 1 in that the connection temperature in step six is ​​1060℃. Everything else is the same as in Example 1.

[0074] Comparative Experiment: This comparative experiment differs from Example 1 in that the solder used is a 100μm thick commercial Ag26.7Cu4.5Ti (wt.%) solder, and the M42 steel surface is not clad with mixed powder. Only one brazing experiment was conducted. Specifically, the AgCuTi solder was placed between the PCBN ceramic and the M42 steel, and a pressure of 0.6 kPa was applied to the PCBN ceramic surface to obtain the workpiece to be soldered. The workpiece was placed in a vacuum brazing furnace and heated to 850℃ at a heating rate of 25℃ / min. Then, it was held at a connection temperature of 850℃ for 10 min, and finally cooled to room temperature at a cooling rate of 5℃ / min. Everything else was the same as in Example 1.

[0075] Figure 2 The image shows the XRD pattern of the cladding layer in the pretreated M42 steel with a cladding layer prepared in step four of Example 1. As can be seen from the image, the cladding layer is mainly a face-centered cubic solid solution.

[0076] Figure 3 The images show scanning electron microscope (SEM) cross-sectional images of the M42-PCBN brazed joint prepared in Example 1. (a) shows the overall morphology of the joint interface, (b) shows a magnified view of a local area of ​​the PCBN-brazed joint, and (c) shows a magnified view of a local area of ​​the M42-brazed joint. As can be seen from the images, the interfaces of the M42-PCBN brazed joint are well-formed, with no obvious pores or cracks. The overall width of the brazed joint is approximately 600 μm. A continuous reaction layer and discontinuous reaction phases are formed at the PCBN interface. The brazed joint mainly consists of a (Cu, Ni, Fe) solid solution, while a diffusion layer of approximately 50 μm is formed at the M42 interface.

[0077] Figure 4 To compare the cross-sectional scanning electron microscope (SEM) images of the M42-PCBN joint brazed with AgCuTi solder in the experiment, (a) shows the overall morphology of the joint interface, (b) shows a magnified view of a local area of ​​the PCBN-brazed joint, and (c) shows a magnified view of a local area of ​​the M42-brazed joint. As can be seen from the figures, when using AgCuTi solder, the brazed joint mainly contains AgCu eutectic structure and large blocks of Cu2Ti intermetallic compounds. In addition, a continuous Ti-Fe-C brittle reaction layer is formed at the M42 interface, and the reaction between Ti and M42 causes carbon precipitation in the steel.

[0078] Figure 5The image shows an EDS elemental surface scan of the joint cross-section of the M42-PCBN brazed component prepared in Example 1. (a) is the overall morphology of the joint interface; (b) represents nitrogen (N); (c) represents al (Al); (d) represents titanium (Ti); (e) represents copper (Cu); (f) represents nitrogen (Ni); (g) represents iron (Fe); (h) represents cobalt (Co); and (i) represents chromium (Cr). As can be seen from the image, the brazed joint mainly contains copper (Cu) and nickel (Ni). Fe from M42 diffuses into the brazed joint, creating an accumulation zone of nickel and iron. Ti is mainly concentrated near the PCBN interface, with a small amount diffusing into the brazed joint.

[0079] Figure 6 The image shows a transmission electron microscope (TEM) image of the M42-PCBN brazed joint prepared in Example 1, located on the PCBN-brazing seam side. (a) is a bright-field image of the PCBN-brazing seam side, and (bg) are electron diffraction spots of each phase in (a). As shown in the image, multiple reaction layers and phases are formed at the PCBN interface. Comparison of the electron diffraction spots confirms that the continuous reaction layer c is TiN, the discontinuous reaction phase f is CuNi2Ti, and the remaining reaction phases include TiB, TiB2, and a Cu-based solid solution. During brazing, Ti contacts Cu and Ni in the cladding layer to form a eutectic liquid phase. Ti gradually dissolves into the liquid phase and reacts with PCBN to generate TiN, TiB, and TiB2. Simultaneously, as Cu and Ni continue to dissolve, CuNi2Ti and TiNi3 gradually precipitate in the liquid phase, consuming a large amount of Ti and Ni and generating a Cu-rich liquid phase. Subsequently, the Cu-rich liquid phase further reacts with TiNi3 to generate CuNi2Ti and a Cu-based solid solution.

[0080] Figure 7High-resolution analysis images of the M42-PCBN solder joint prepared in Example 1, located on the PCBN-solder seam side, are shown. (a) is a bright-field image of the TiN layer and a high-resolution image of the interface. 1, 2, and 3 are high-resolution images of interfaces 1, 2, and 3 marked in (a). (b) is a bright-field image of the TiB layer and a high-resolution image of the interface. 4 is a high-resolution image of interface 4 marked in (b). (c) is a bright-field image of the TiB2 layer and a high-resolution image of the interface. 5 and 6 are high-resolution images of interfaces 5 and 6 marked in (c). As can be seen from the figures, small-angle grain boundaries are formed between the coarse-grained and fine-grained regions of TiN. The TiN generated at the BN interface grows along the (111) crystal plane, exhibiting a 14.3% interface mismatch with the (111) crystal plane of BN. Stacking faults are also present in TiN, indicating significant stress at the interface. The atomic arrangement between TiN and CuNi2Ti is relatively disordered, forming a non-coherent interface. TiB whiskers are distributed in the Cu-based solid solution. The interplanar spacing between the (101) crystal plane of TiB2 and the (112) crystal plane of CuNi2Ti is small, forming a semi-coherent interface with a large number of dislocations. A twin consisting of several atomic layers is formed between TiB2 and TiN, and the (011) crystal plane of TiB2 and the (200) crystal plane of TiN form a coherent interface.

[0081] Figure 8 The figure shows the hardness distribution of the M42-PCBN brazed joint prepared in Example 1. As can be seen from the figure, the hardness in the brazed seam is relatively low (100HV~170HV), while the hardness of the diffusion zone at the M42 interface (200HV~400HV) is between the hardness of the brazed seam and the steel (460HV~510HV).

[0082] According to the GB / T 31541-2015 testing standard; Figure 9Figures show the shear test results of the M42-PCBN brazed joints. (a) is a schematic diagram of the shear test, (b) is the strain-shear strength curve at room temperature, 1 is the M42-PCBN brazed joint prepared in Example 1, 2 is the M42-PCBN brazed joint prepared in the comparative experiment, and (c) is the strain-shear strength curve of the M42-PCBN brazed joint prepared in Example 1 at 900℃. As can be seen from the figures, compared with the shear strength of the joint brazed with AgCuTi (86 MPa), the joint brazed with the solid solution matrix using the two-step method exhibits a higher shear strength (163 MPa). The two-step brazing process can retain more (Cu, Ni, Fe) solid solution within the brazed seam. This solid solution can undergo plastic deformation and hinders the reaction between Ti and steel. Simultaneously, the uneven distribution of Cu and Ni in the solid solution, and the limited eutectic liquid phase, hinder the formation of continuous Ti-Cu or Ti-Ni intermetallic compounds. All these factors contribute to the increased shear strength of the brazed joint. Furthermore, compared to AgCu eutectic, (Cu, Ni, Fe) solid solution has better high-temperature strength, enabling the brazed joint to have a shear strength of 65 MPa under a high-temperature test environment of 900℃.

[0083] Figure 10 The images show the fracture surface of the M42-PCBN brazed joint sample after shear testing, as prepared in Example 1. (a) shows the fracture morphology of the fractured sample, and (b) shows the XRD pattern of the fracture surface. As can be seen from the figures, although the fracture surface is relatively flat, XRD analysis indicates the presence of TiN and solid solution at the fracture site. Due to the good plastic deformation capacity of the (Cu, Ni, Fe) solid solution, under external load, cracks initially initiate near the stress concentration interfaces of BN / TiN and TiN / CuNi2Ti. However, the gradient distribution of coarse and fine grain regions of TiN, as well as the discontinuous distribution of the hard CuNi2Ti phase, effectively suppresses crack propagation. Thus, the crack propagates into the ceramic or solid solution, ultimately leading to fracture of the joint near the ceramic interface, significantly improving the shear strength of the brazed joint.

[0084] Figure 11 The image shows a scanning electron microscope (SEM) image of the cross-section of the M42-PCBN brazed joint prepared in Example 2. As can be seen from the image, the interfaces of the M42-PCBN brazed joint are good, with no obvious pores or cracks. After increasing the connection temperature, the element diffusion is accelerated, and the microstructure in the brazed joint is more uniform, mainly consisting of (Cu, Ni, Fe) solid solution.

[0085] According to the GB / T 31541-2015 testing standard; Figure 12The figures show the room temperature and high temperature strain-shear strength curves of the M42-PCBN brazed joint prepared in Example 2. (a) is the strain-shear strength curve at room temperature, and (b) is the strain-shear strength curve at 900℃. As can be seen from the figures, the room temperature shear strength of the brazed joint is further increased (249 MPa) after increasing the connection temperature, and the brazed joint can maintain a shear strength of 69 MPa under the high temperature test environment of 900℃.

Claims

1. A two-step brazing method for improving the strength of M42 steel and PCBN ceramic joints using solid solution brazing seams, characterized in that... It is done in the following steps:

1. Mix Cu powder and Ni powder to obtain a mixed powder. Place the mixed powder in a ball mill and grind it to obtain a ball-milled mixed powder. The mass percentage of Cu powder in the mixed powder is 80%~86%; the particle size of the Cu powder and Ni powder is <50μm; The grinding process is carried out in the following steps: the mixed powder and grinding media are placed in an agate ball mill jar, with the grinding media covering the mixed powder. Under the conditions that the mass ratio of grinding balls to mixed powder is (2~2.5):1 and the rotation speed is 250r / min~300r / min, the mixture is ball-milled for 0.5h~2h using a planetary ball mill; the grinding media is alcohol.

2. Using a binder, the ball-milled mixed powder is coated onto the surface of M42 steel and dried to obtain M42 steel with the mixed powder on the surface; The adhesive is a mixture of polyethylene cellulose and terpineol, with the polyethylene cellulose comprising 3% to 5% by mass; the adhesive coating amount is 0.15 g / cm³. 2 ~0.3g / cm 2 ; 3. Place the M42 steel with the mixed powder coating on its surface in a vacuum brazing furnace and heat it to 1150℃~1180℃ at a heating rate of 20℃ / min~25℃ / min. Then, heat it to 1150℃~1180℃ at a melting temperature of 1150℃~1180℃ until the mixed powder on the surface of the M42 steel is fully melted. Finally, cool it with the furnace to obtain M42 steel with a molten layer with a thickness of 200μm~600μm. IV. Polish, clean and dry the M42 steel with the molten layer in sequence to obtain pretreated M42 steel with the molten layer.

5. Place the Ti foil between the PCBN ceramic and the pretreated M42 steel coated with a molten layer, and then apply a pressure of 0.1MPa~0.2MPa on the surface of the PCBN ceramic to obtain the workpiece to be soldered; The thickness of the Ti foil is 5μm~10μm; 6. Place the parts to be brazed in a vacuum brazing furnace and heat them to 1000℃~1060℃ at a heating rate of 20℃ / min~25℃ / min. Then, hold them at a connection temperature of 1000℃~1060℃ for 15min~60min. Finally, cool them to room temperature at a cooling rate of 5℃ / min~10℃ / min. This completes the two-step brazing method of improving the strength of the M42 steel and PCBN ceramic joint by utilizing the solid solution brazing seam.

2. The two-step brazing method for improving the strength of M42 steel and PCBN ceramic joints using solid solution brazing seams according to claim 1, characterized in that... The M42 steel mentioned in step two and the PCBN ceramic mentioned in step five are pretreated M42 steel and pretreated PCBN ceramic. The pretreatment is carried out according to the following steps: the surface of the M42 steel to be joined is polished with silicon carbide sandpaper, and the surface of the PCBN ceramic to be joined is polished with a diamond grinding wheel. After polishing, the surface is cut, and then ultrasonically cleaned with acetone solution for 15 min to 25 min under a power of 200W~240W. Finally, the surface is dried to obtain the pretreated M42 steel and pretreated PCBN ceramic.

3. The two-step brazing method for improving the strength of M42 steel and PCBN ceramic joints using solid solution brazing seams, as described in claim 1, is characterized in that... The drying process described in step two is specifically carried out at a temperature of 50℃~60℃.

4. The two-step brazing method for improving the strength of M42 steel and PCBN ceramic joints using solid solution brazing seams according to claim 1, characterized in that... In step four, the M42 steel with the molten layer is polished smooth with silicon carbide sandpaper, and then ultrasonically cleaned with acetone solution for 15 to 25 minutes under a power of 200W to 240W, and finally dried.

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