A method for suppressing Co-depleted regions in WC-Co cemented carbide brazed joints by surface electroplating

Abstract

This invention discloses a method for suppressing Co depletion zones in WC-Co cemented carbide brazed joints through surface electroplating. The method includes the following steps: placing the cemented carbide in a copper plating solution for electroplating, with the anode and cathode composed of a phosphorus-containing copper plate and the cemented carbide, respectively, to obtain a cemented carbide sample with a copper plating layer on its surface; then, uniformly coating the surface of the cemented carbide with brazing paste, followed by vacuum brazing, resulting in a good bond between the WC-Co cemented carbide and steel. This invention, when applied to the joining of WC-Co cemented carbide and steel, offers advantages such as simple process, minimal damage to the base material, high production efficiency, and high shear strength.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide welding technology, and in particular to a process method for suppressing the Co-depletion zone in WC-Co cemented carbide brazed joints by surface electroplating. Background Technology

[0002] Due to rapid technological advancements, traditional materials struggle to meet the high-performance requirements of industrial applications, such as high-temperature resistance, wear resistance, and high strength and hardness. WC-Co cemented carbide, a metal-ceramic material prepared through powder metallurgy, uses the high-melting-point metallic compound WC as its matrix and the transition metal Co as its binder phase. It possesses advantages such as high strength, hardness, excellent wear resistance, and corrosion resistance, earning it the reputation of "industrial teeth." Furthermore, the joints formed by brazing cemented carbide and steel play an irreplaceable role in cutting tools and wear- and corrosion-resistant components in aerospace, machinery, geological exploration, and engineering construction. By fully utilizing the advantages of both cemented carbide and steel, material costs and component specifications are significantly reduced, while performance and lifespan are greatly improved, achieving a synergistic effect greater than the sum of its parts.

[0003] However, during the brazing process of cemented carbide / steel joints, Co in the cemented carbide tends to diffuse into the solder layer, resulting in a Co-depleted region in the cemented carbide near the solder layer. This region is the weak point when the joint fails, thus negatively impacting the bonding performance of the joint. For example, Chen et al. (Int. Journal of Refractory Metals and Hard Materials[J], 2012, 33:70-74.) and Guo et al. (Int. Journal of Refractory Metals and Hard Materials[J], 2015, 51:250-257.) used CuZn solder and Ti / Ni / Ti multilayer solder, respectively, to braze cemented carbide and steel. In both cases, a significant Co-depleted region was formed in the cemented carbide near the solder layer, becoming the main area for joint fracture and resulting in low shear strengths of 154 MPa and 137 MPa, respectively.

[0004] Currently, the main approach to addressing the Co-depleted region in cemented carbide brazed joints, both domestically and internationally, is to modify the brazing filler metal composition to improve the joint's microstructure and properties. For example, Kengo Kaiwa et al. (Advanced Materials Research [J], 2014, 922: 322-327.) significantly reduced the area of ​​the Co-depleted region in the joint and improved the tensile strength of the joint by adding Co or Ni to AgCuZn brazing filler metal. However, the addition of alloying elements to the brazing filler metal layer often leads to unavoidable compositional segregation during the solidification process, affecting the local properties of the joint.

[0005] Currently, my country lacks a suitable method to address the Co-depleted region in WC-Co cemented carbide brazed joints. Therefore, designing novel processes to improve the Co-depleted region and bonding performance in cemented carbide brazed joints is of significant research value and importance. Summary of the Invention

[0006] The purpose of this invention is to solve the problem of poor bonding performance between WC-Co cemented carbide and steel during brazing, where Co dissolves into the brazing filler metal layer, forming a Co-depleted region. This invention provides a process for suppressing the Co-depleted region in WC-Co cemented carbide brazed joints and improving joint bonding performance through surface electroplating. The process involves pre-plating a Cu layer on the cemented carbide surface, followed by vacuum brazing to regulate Co diffusion behavior and the interfacial microstructure of the joint. Cu is chosen as the plating material due to its good bonding performance with WC and its status as a component of the brazing filler metal. In application, programmed temperature control ensures a good bond between the WC-Co cemented carbide and steel. This invention offers advantages such as simple process, minimal damage to the base material, high production efficiency, and high shear strength in the bonding of WC-Co cemented carbide and steel.

[0007] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0008] A method for suppressing Co-depleted regions in WC-Co cemented carbide brazed joints by surface electroplating, the method comprising the following steps:

[0009] Step 1: Pretreatment of cemented carbide and steel. First, polish with a 1500-3000# diamond disc, then perform ultrasonic cleaning in an ethanol solution for 15-30 minutes, and finally perform ultrasonic cleaning in acetone for 15-30 minutes.

[0010] Step 2: Immerse the cemented carbide obtained in Step 1 in a copper plating solution for electroplating. The anode and cathode are composed of a phosphorus-containing copper plate and the cemented carbide obtained in Step 1, respectively. The electroplating temperature is 15℃ to 40℃, the current mode is constant current, and the current density is 0.5~4A / dm³. 2 The electroplating time is 50 to 200 seconds, thus obtaining a hard alloy sample with a copper plating layer on the surface.

[0011] The copper plating solution comprises 160–180 g / L copper sulfate, 50–60 g / L sulfuric acid, 0.3–0.7 mg / L methyl violet, 0.3–0.7 g / L polyethylene glycol, 0.2–0.5 mg / L OP emulsifier, and 35–45 mg / L Cl... - ;

[0012] The cemented carbide is encapsulated with epoxy resin to ensure that the ratio of the exposed area of ​​the cemented carbide to the area of ​​the copper plate is 1:1.5 to 2.

[0013] Step 3: Apply a uniform thickness of brazing paste to the surfaces of both the steel treated in Step 1 and the cemented carbide treated in Step 3. Then, stack the cemented carbide on top of the steel to obtain the workpiece to be brazed and place it in a vacuum brazing furnace. Evacuate the vacuum brazing furnace to a vacuum level of 5 × 10⁻⁶. -4 ~5×10 -3 Heat is applied at Pa, and the vacuum brazing furnace is set to the temperature program and heated.

[0014] The steel plate used in step one is made of grade 35 steel, 40 steel, 45 steel, 50 steel and 40Cr steel, and the WC-Co cemented carbide is made of any one of grade YG6, YG8, YG15, YG18 and YG20 cemented carbide.

[0015] The dimensions of the cemented carbide and steel in step one are 2~20×2~20×2~10mm respectively. 3 5~30×5~30×2~20mm 3 .

[0016] The solder used in step four of step two is any one of AgCuTi, AgCuSnTi, or AgCuInTi solder.

[0017] The thickness of the solder layer in step four is 90–150 μm.

[0018] The heating temperature program in step four is to raise the temperature from 20°C to 700-900°C at a rate of 5-20°C / min, and hold it at 700-900°C for 5-15 minutes. After heating, the furnace temperature is lowered to 300-450°C at a rate of 5-20°C / min, and finally cooled with the furnace to obtain the WC-Co cemented carbide brazed joint.

[0019] The essential features of this invention are:

[0020] In this invention, a Cu plating layer is pre-plated on the surface of the cemented carbide, so that a Cu transition layer exists between the cemented carbide and the brazing filler metal. Then, the cemented carbide, Cu plating layer, brazing filler metal and steel are metallurgically bonded by vacuum brazing. The Cu plating layer can consume most of the Ti in the brazing filler metal, thereby reducing the Co depletion zone in the joint and improving the joint bonding performance.

[0021] Compared with existing brazing filler metals and brazing processes, the advantages of this invention are as follows:

[0022] 1. This invention achieves controllable fabrication of cemented carbide / steel joints through a composite process (electroplating + brazing). Examples 1 and 1 (Comparative Example) show that the presence or absence of a pre-applied Cu plating layer on the cemented carbide surface significantly affects the area of ​​the Co-depleted region in the joint. Specifically, the Co-depleted region in the brazed cemented carbide joint without a pre-applied Cu plating layer can reach 6 μm, while the Co-depleted region in the brazed cemented carbide joint with a pre-applied Cu plating layer is only about 1 μm. This indicates that pre-preparing an electroplated Cu layer on the cemented carbide surface effectively solves the problem of Co diffusion from the cemented carbide into the brazing filler metal layer during brazing, thus preventing the formation of a Co-depleted region.

[0023] 2. The electroplated Cu layer on the surface of cemented carbide is more likely to form a molten layer through metallurgical bonding with the brazing filler metal. This allows for reasonable control of the joint's microstructure and can alleviate joint stress to a certain extent. Compared with cemented carbide brazed joints without a pre-plated Cu layer, the joint bonding strength is increased by 49%.

[0024] 3. In particular, the joints obtained by this process can be used in wear-resistant devices with embedded cemented carbide sheets to ensure that the cemented carbide brazed joints will not fail due to the presence of Co-depleted regions. Meanwhile, this process is simple, low-cost, efficient, and widely applicable, showing promising application prospects. Attached Figure Description

[0025] Figure 1 This is a SEM image of the YG18 cemented carbide pre-plated Cu layer in Embodiment 1 of the present invention; wherein, Figure 1 (a) shows the surface morphology of the electroplated Cu layer; Figure 1 (b) shows the cross-sectional morphology of the electroplated Cu layer;

[0026] Figure 2 The images shown are SEM images and Co elemental surface scans of the YG18 cemented carbide / AgCuInTi brazing filler metal / 40Cr steel brazing joint in Embodiment 1 of this invention; wherein, Figure 2 (a) shows the overall microstructure of the joint; Figure 2 (b) shows the distribution of Co in cemented carbide;

[0027] Figure 3 This is a TEM image of the YG18 / Ag-Cu-In-Ti solder interface in Embodiment 1 of the present invention;

[0028] Figure 4 The diagram shows the shear strength test results in Example 1. Figure 4 (a) is a schematic diagram of the joint shear strength test in Example 1 of the present invention. Figure 4 (b) is a load-displacement curve of a cemented carbide brazed joint with and without a pre-coated layer. Detailed Implementation

[0029] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention and do not limit the scope of protection of the claims of this application.

[0030] Example 1

[0031] 1. A process for improving the microstructure and bonding properties of WC-Co cemented carbide brazed joints through surface electroplating, comprising the following steps:

[0032] Step 1: Pretreatment of cemented carbide and steel. First, polish with a 2000# diamond disc to ensure a smooth surface and remove the surface oxide layer. Then, place the sample in a beaker containing alcohol for 20 minutes of ultrasonic cleaning. Finally, place the sample in a beaker containing acetone for 20 minutes of ultrasonic cleaning to remove surface grease.

[0033] The steel plate and WC-Co cemented carbide are made of 40Cr steel (10×10×5mm). 3 YG18 cemented carbide (8×8×5mm) 3 ).

[0034] Step 2: The cemented carbide sample obtained in Step 1 is placed in a copper plating solution for electroplating. The anode and cathode are composed of a copper plate (containing 0.02% to 0.07 wt% phosphorus) and the cemented carbide obtained in Step 1, respectively. The cemented carbide is encapsulated with epoxy resin to ensure that the ratio of the exposed area of ​​the cemented carbide to the area of ​​the copper plate is 1:2.

[0035] The copper plating solution consists of 170 g / L copper sulfate, 56 g / L sulfuric acid (H2SO4), 0.5 mg / L methyl violet, 0.5 g / L polyethylene glycol, 0.3 mg / L OP emulsifier, and 40 mg / L Cl-.

[0036] Step 3: The electroplating temperature in Step 2 is 20℃, and the current density is 2A / dm³. 2 The current mode was constant current, and the electroplating time was 150s, thus obtaining a hard alloy sample with a copper plating layer on the surface.

[0037] Step 4: Apply a 60μm thick layer of AgCuInTi brazing paste to the surfaces of both the steel treated in Step 1 and the cemented carbide treated in Step 3. Then, stack the cemented carbide on top of the steel to obtain the workpiece to be brazed and place it in a vacuum brazing furnace. Evacuate the vacuum brazing furnace to a vacuum level of 5×10⁻⁶. -3 Heat is applied at Pa, and the vacuum brazing furnace is set to the temperature program and heated.

[0038] The heating temperature program is as follows: the temperature is increased from 20℃ to 250℃ at a rate of 20℃ / min and held for 10min; then the temperature is increased to 780℃ at a rate of 10℃ / min and held for 10min; after heating, the temperature inside the furnace is decreased to 400℃ at a rate of 15℃ / min, and finally cooled with the furnace.

[0039] 2. Sample testing

[0040] The morphology of the pre-coated Cu layer on the YG18 surface was observed using focused ion beam scanning electron microscopy (e.g., ...). Figure 1 (as shown) and the microstructure and Co element distribution of the joint (e.g.) Figure 2 As shown), the plating thickness is approximately 2.75 μm, the entire joint structure is dense and well-bonded, and the Co-depleted zone is only 1 μm; the microstructure of the YG18 / brazing filler interface was observed by transmission electron microscopy (as shown). Figure 3 As shown in the figure, a 100nm continuous titanium carbide reaction layer is formed at the interface, which ensures good bonding of the joint.

[0041] Shear strength was used to characterize the bonding quality of YG18 and 40Cr steel. The brazed specimen was installed in a pre-designed shearing die. The shearing diagram is shown below. Figure 4 As shown in (a), shear tests were conducted using an AGS-XD50kN universal testing machine at a speed of 0.5 mm / min. The shear strength of the joint was calculated according to GB / T 11363-2008, and the average shear strength of the YG18 cemented carbide / AgCuInTi brazing filler metal / 40Cr steel brazed joint was finally obtained as 295 MPa (as shown in (a)). Figure 4 (b) is shown.

[0042] Example 2

[0043] The other steps are the same as in Example 1, except that the steel plate is replaced with 35 steel and the cemented carbide is replaced with YG6.

[0044] The resulting brazed joint has a dense and good microstructure, with a Co depletion zone of 0.5 μm and an average shear strength of 291 MPa.

[0045] Example 3

[0046] The other steps are the same as in Example 1, except that the steel plate is replaced with 40 steel and the cemented carbide is replaced with YG8.

[0047] The resulting brazed joint has a dense and well-defined microstructure, with a Co-depleted zone of 0.7 μm and an average shear strength of 290 MPa.

[0048] Example 4

[0049] The other steps are the same as in Example 1, except that the solder is replaced with AgCuTi.

[0050] The resulting brazed joint has a dense and well-developed microstructure, with a Co-depleted zone of 2 μm and an average shear strength of 240 MPa.

[0051] Example 5

[0052] The other steps are the same as in Example 1, except that the solder is replaced with AgCuSnTi.

[0053] The resulting brazed joint has a dense microstructure, a Co-depleted zone of 1.2 μm, and an average shear strength of 265 MPa.

[0054] Comparative Example 1

[0055] The other steps are the same as in Example 1, except that steps one, two and three are removed, that is, the surface of the cemented carbide is not pre-plated with a Cu layer.

[0056] The resulting brazed joint has a dense and well-developed microstructure, with a Co-depleted zone of 6 μm and an average shear strength of 198 MPa.

[0057] Comparative Example 2

[0058] The other steps are the same as in Example 1, except that the brazing filler metal is replaced with AgCuSnTi and steps one, two and three are removed, that is, the surface of the cemented carbide is not pre-plated with a Cu layer.

[0059] The resulting brazed joint has a dense and well-developed microstructure, with a Co-depleted zone of 10 μm and an average shear strength of 195 MPa.

[0060] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

[0061] Matters not covered in this invention are common knowledge.

Claims

1. A method for suppressing Co-depleted regions in WC-Co cemented carbide brazed joints by surface electroplating, characterized in that the method comprises the following steps: Step 1: Pretreatment of cemented carbide and steel. First, polish with a 1500~3000# diamond disc, then perform ultrasonic cleaning in an ethanol solution for 15~30 minutes, and finally perform ultrasonic cleaning in acetone for 15~30 minutes. Step 2: Immerse the cemented carbide obtained in Step 1 in a copper plating solution for electroplating. The anode and cathode are composed of a phosphorus-containing copper plate and the cemented carbide obtained in Step 1, respectively. The electroplating temperature is 15℃ to 40℃, the current mode is constant current, and the current density is 0.5~4 A / dm³. 2 The electroplating time is 50~200 s, thus obtaining a hard alloy sample with a copper plating layer on the surface; in, The copper plating solution consists of 160-180 g / L copper sulfate, 50-60 g / L sulfuric acid, 0.3-0.7 mg / L methyl violet, 0.3-0.7 g / L polyethylene glycol, 0.2-0.5 mg / L OP emulsifier, and 35-45 mg / L Cl. - ; Step 3: Apply a uniform thickness of brazing paste to the surfaces of both the steel treated in Step 1 and the cemented carbide treated in Step 3. Then, stack the cemented carbide on top of the steel to obtain the workpiece to be brazed and place it in a vacuum brazing furnace. Evacuate the vacuum brazing furnace to a vacuum level of 5 × 10⁻⁶. -4 ~5×10 -3 Heat is applied at Pa, and the vacuum brazing furnace is set to the temperature program and heated. The heating temperature program is to raise the temperature from 20℃ to 700-900℃ at a rate of 5-20℃ / min, and hold it at 700-900℃ for 5-15 minutes. After heating, the furnace temperature is lowered to 300-450℃ at a rate of 5-20℃ / min, and finally cooled with the furnace to obtain the WC-Co cemented carbide brazed joint. The steel plate in step one is made of grade 35 steel, 40 steel, 45 steel, 50 steel or 40Cr steel, and the WC-Co cemented carbide is made of any one of grade YG6, YG8, YG15, YG18 and YG20 cemented carbide. The solder used in step three is any one of AgCuTi, AgCuSnTi, or AgCuInTi solder.

2. The method for suppressing the Co-depletion region in a WC-Co cemented carbide brazed joint by surface electroplating as described in claim 1, characterized in that, The dimensions of the cemented carbide and steel are 2~20 × 2~20 × 2~10 mm, respectively. 3 5~30 × 5~30 × 2~20 mm 3 .

3. The method for suppressing the Co-depletion region in a WC-Co cemented carbide brazed joint by surface electroplating as described in claim 1, characterized in that, The thickness of the solder layer in step three is 100~140 µm.

4. The method for suppressing the Co-depleted region in a WC-Co cemented carbide brazed joint by surface electroplating as described in claim 1, characterized in that, During electroplating, the ratio of the exposed area of ​​the cemented carbide to the area of ​​the copper plate is 1:1.5~2.

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