Method for regulating co depletion zone of hard metal brazed joint by surface plating co

Abstract

The present application is a method for regulating Co-depleted zone of hard alloy brazing joint by surface Co electroplating. The method comprises the following steps: placing hard alloy as cathode and cobalt plate as anode into an electroplating Co solution to carry out electroplating, so as to obtain a hard alloy sample with Co plating layer on the surface; then stacking the hard alloy coated with filler metal on steel in a vacuum brazing furnace to carry out brazing; the electroplated Co layer not only plays an isolation role, but also effectively supplements the Co concentration of the surface layer of the hard alloy, so as to realize reasonable regulation and control of the distribution of plastic and brittle phase in the intermediate layer of the joint. The present application has the advantages of simple method, small 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 method for adjusting the Co-depleted zone of cemented carbide brazed joints by surface electroplating with Co. Background Technology

[0002] Cemented carbide is a cermet material prepared by powder metallurgy using a high-melting-point metallic compound (WC) as the matrix phase and a transition metal (Co) as the binder phase. Due to its high strength, hardness, wear resistance, low coefficient of thermal expansion, and a series of excellent properties, it is known as the "teeth of industry." Cemented carbide can be machined into cutting and impact tools, high-temperature and high-pressure molds, and wear- and corrosion-resistant parts, and is widely used in aerospace, mechanical engineering, petroleum industry, geological exploration, and other fields. However, the difficulty in balancing the hardness and toughness of cemented carbide leads to a complex manufacturing process, making it difficult to obtain parts of large size or complex shapes, and also results in high costs. Therefore, brazing cemented carbide and steel can fully leverage their respective advantages to create engineering devices with excellent performance in industrial applications.

[0003] During brazing, the binder Co in the cemented carbide dissolves into the solder layer, similar to the cemented carbide being corroded by the solder alloy. This causes some of the solder alloy to leach into the cemented carbide matrix, forming a significant Co-depleted zone, which becomes the weakest point in the entire joint. The formation of the Co-depleted zone is mainly due to Co diffusing into the filler layer to form a reactive layer or dissolving in other phases.

[0004] To suppress excessive diffusion of elements from the substrate into the filler layer, researchers have designed multilayer composite solders to adjust the microstructure of the solder layer, thereby inhibiting excessive diffusion of elements from the matrix material into the solder layer. For example, Zhang et al. (Materials Science & Engineering A [J], 862 (2023) 144435.) used AgCuTi / Cu / AgCuTi sandwich composite filler to suppress excessive diffusion of Ni elements into the solder layer in Kovar alloy / AlN ceramic joints. However, cracks and voids are easily generated along the uninterrupted Cu layer in the solder layer, which is detrimental to the mechanical properties of the joint. Wang et al. (Journal of Materials Research and Technology [J], 23(2023) 4757-4765) used AgCuTi / Cu foam layer / AgCuTi composite filler to braze nickel alloy and SiC ceramic in a vacuum furnace to suppress excessive diffusion of Ni element in nickel-based alloy. The presence of Cu foam layer easily forms a large amount of Cu-Ti intermetallic compound in the brazing filler layer, which increases the joint stress and reduces the joint bonding strength.

[0005] Currently, my country lacks a suitable method to address the Co-depletion zone in WC-Co cemented carbide brazed joints. Therefore, designing multilayer composite brazing filler metals to improve the Co-depletion zone and shear strength in cemented carbide brazed joints has significant research value and importance. Summary of the Invention

[0006] The purpose of this invention is to solve the problem that during the brazing process of cemented carbide, Co dissolves into the brazing filler metal layer, forming a Co-depleted zone, which leads to easy fracture of the joint in the cemented carbide layer and ultimately results in low shear strength of the brazed joint with steel. This invention provides a method for adjusting the Co-depleted zone of cemented carbide brazed joints by surface electroplating Co. This method pre-plats a Co layer on the surface of the cemented carbide to replenish the Co in the cemented carbide; then, the microstructure of the joint is adjusted by metallurgically combining the Co layer with the brazing filler metal (i.e., designing a multi-layer composite brazing filler metal); due to the isolating effect of the electroplated Co layer, Co is prevented from dissolving from the cemented carbide into the brazing filler metal layer; at the same time, the Co layer effectively replenishes the Co concentration on the surface of the cemented carbide, achieving reasonable control over the distribution of plastic and brittle phases in the intermediate layer of the joint. This invention, when applied to the field of cemented carbide-steel joining, has advantages such as simple method, minimal damage to the base material, high production efficiency, and high shear strength.

[0007] To achieve the above objectives, the present invention is implemented according to the following technical solution: A method for adjusting the Co-depleted region of a cemented carbide brazed joint by surface electroplating Co, the method comprising the following steps: Step 1: Pretreatment of cemented carbide and steel. First, polish for 1-5 minutes to remove the surface oxide layer and ensure the surface is flat. Then, ultrasonically clean the sample with alcohol for 15-30 minutes. Finally, ultrasonically clean the sample with acetone for 15-30 minutes. Step 2: Place the cemented carbide sample obtained in Step 1 into a Co plating solution for electroplating. The anode and cathode are composed of a cobalt plate and the cemented carbide obtained in Step 1, respectively, to obtain a cemented carbide sample with a Co coating on the surface. The electroplating solution for Co consists of 20-30 g / L cobalt sulfate, 30-40 g / L boric acid, 1-4 mg / L saccharin, and 0.1-0.4 g / L sodium dodecyl sulfate; the ratio of the exposed area of ​​the cemented carbide to the area of ​​the cobalt plate is 1:1-1.5. The electroplating temperature is 10℃~30℃, and the current density is 1~3 A / dm³. 2 The electroplating time is 50~200 s; Step 3: Place the steel treated in Step 1 and the cemented carbide treated in Step 2 on a screen printing platform and coat both surfaces with a uniform thickness of brazing filler metal. 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 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 solder is any one of binary eutectic AgCuTi, AgCuSnTi, or ternary eutectic AgCuInTi solder; the solder layer thickness is 100~140 µm.

[0008] The steel used in step one is any one of the following grades: 45# steel, 55# steel, 60# steel, 42CrMoV, 40Cr, and AISI 1045 steel. The cemented carbide is any one of the following grades: YG6, YG8, YG15, YG18, and YG20 cemented carbide.

[0009] The dimensions of the cemented carbide and steel in step one are (2~20) mm × (2~20) mm × (2~10) mm and (5~30) mm × (5~30) mm × (2~20) mm, respectively.

[0010] The heating temperature program in step three is as follows: the temperature is increased from 20°C to 200-300°C at a rate of 15-30°C / min and held for 5-15 minutes; then the temperature is increased to 700-880°C at a rate of 5-15°C / min and held for 5-15 minutes; after heating, the temperature inside the furnace is decreased to 300-450°C at a rate of 5-20°C / min; and finally, the furnace is cooled.

[0011] The essential features of this invention are: This invention pre-plats a Co layer on the surface of a cemented carbide using a simple electroplating Co solution. The isolation effect of the Co layer prevents the Co element in the cemented carbide from dissolving into the brazing filler metal layer and effectively replenishes the Co concentration on the surface of the cemented carbide. In this way, the microstructure of the joint is adjusted by metallurgically combining the Co layer with the brazing filler metal (i.e., designing a multi-layer composite brazing filler metal). Furthermore, the pre-plated Co layer reacts in situ with the Ti element in the brazing filler metal during the brazing process, forming a rope-like Ti-Co reaction layer distributed in the brazing filler metal layer. Ultimately, this invention achieves reasonable control over the distribution of plastic and brittle phases in the intermediate layer of the joint.

[0012] The beneficial effects of this invention are as follows: 1. This invention pre-plats a Co layer on the surface of cemented carbide, and achieves the design of a multi-layer composite brazing filler metal in the brazed joint through metallurgical bonding between the Co layer and the brazing filler metal. The pre-plated Co layer on the surface of the cemented carbide effectively replenishes the Co concentration on the surface of the cemented carbide, and the area of ​​the Co-depleted zone in the final joint is about 1.5 µm, which is reduced by 75%.

[0013] 2. The pre-plated Co layer on the cemented carbide surface achieves effective metallurgical bonding with the brazing filler metal during the brazing process, forming a rope-like Ti-Co reaction layer distributed within the brazing filler metal layer. This ultimately achieves reasonable control over the phase distribution of the intermediate layer of the joint. The microstructure of the brazing filler metal layer consists of a silver-copper-indium eutectic ductile phase encapsulating brittle intermetallic compound phases such as Ti-Co and Cu2InTi. This alleviates joint stress to a certain extent, resulting in an average shear strength as high as 291 MPa and improving the cemented carbide / steel brazed joint by 49%.

[0014] 3. This method is simple, low-cost, efficient, and widely applicable, providing an effective example for brazing filler layer design in the entire brazing field, and has good application prospects. Attached Figure Description

[0015] Figure 1 This is a SEM image of the Co-plated YG18 cemented carbide layer in Embodiment 1 of the present invention, wherein... Figure 1 (a) shows the surface morphology of the Co coating. Figure 1 (b) shows the cross-sectional morphology of the Co coating; Figure 2 The images shown are SEM images and Co elemental surface scans of the YG18 cemented carbide (pre-formed Co layer) / AgCuInTi brazing filler metal / 40Cr steel brazing joint in Embodiment 1 of this invention; wherein, Figure 2 (a) is a microscopic morphology image of the brazed joint. Figure 2 (b) is a map showing the distribution of Co in the region marked in (a); Figure 3 This is a TEM image of the interface between YG18 cemented carbide (pre-placed Co layer) and Ag-Cu-In-Ti solder in Embodiment 1 of the present invention; 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 graph showing the relationship between the electroplating time and shear strength of the joint. Detailed Implementation

[0016] 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.

[0017] Example 1 A method for adjusting the Co-depleted region of a cemented carbide brazed joint by surface electroplating of Co, comprising the following steps: Step 1: Pretreatment of cemented carbide and steel. First, polish with a 2000# diamond disc for 2 minutes to remove the surface oxide layer and ensure the surface is flat. Then, ultrasonically clean the sample with alcohol for 15 minutes. Finally, ultrasonically clean the sample with acetone for 15 minutes. The steel plate is made of 40Cr steel and measures 10 mm × 10 mm × 5 mm. The cemented carbide is made of YG18 cemented carbide (tungsten-cobalt alloy, tungsten: 82%, cobalt: 18%) and measures 8 mm × 8 mm × 3 mm.

[0018] Step 2: The cemented carbide sample obtained in Step 1 is placed in a Co plating solution for electroplating. The anode and cathode are composed of a cobalt plate 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 cobalt plate is 1:1.5. The cobalt electroplating solution consists of 24 g / L cobalt sulfate, 35 g / L boric acid, 1.5 mg / L saccharin, and 0.2 g / L sodium dodecyl sulfate.

[0019] Step 3: The electroplating temperature in Step 2 is 20℃, and the current density is 2 A / dm³. 2 The electroplating time was 120 s, thus obtaining a cemented carbide sample with a Co coating on the surface; Step 4: Apply a 60 µm thick layer of ternary eutectic AgCuInTi solder paste to both the steel treated in Step 1 and the cemented carbide treated in Step 3 on a screen printing platform. 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. 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.

[0020] 1. Sample testing The morphology of the Co coating 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 (as shown) Figure 2As shown), the plating layer is dense and approximately 2.02 µm thick. The entire joint structure is dense and well-bonded. A rope-like Ti-Co layer of about 3 µm thickness exists in the solder layer and is encapsulated by a silver-copper-indium ternary eutectic. The Co-depleted region is only 1.5 µm. The microstructure of the YG18 / solder interface was observed using transmission electron microscopy (as shown). Figure 3 As shown in the figure, the WC at the interface is encapsulated by a Co-rich layer and undergoes an in-situ reaction to form a continuous titanium carbide reaction layer, ensuring good bonding at the joint interface.

[0021] Shear strength was used to characterize the connection quality between YG18 and 40Cr steels. The brazed specimens were installed into a designed shearing die. In the diagram, the cutting is shown as follows: 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, ultimately yielding the relationship between the pre-plating Co time and the shear strength of the YG18 cemented carbide / AgCuInTi brazing filler metal / 40Cr steel brazed joint (e.g., ...). Figure 4 (b) As shown, when the cemented carbide surface is not pre-plated with Co, the average shear strength of the joint is 195 MPa. After the cemented carbide surface is electroplated with Co for 120s, the average shear strength of the joint can reach 291 MPa.

[0022] Example 2 The other steps are the same as in Example 1, except that the Co electroplating time is changed to 150s. The resulting brazed joint has a dense and well-developed microstructure, with a Co-depleted zone of 1.3 µm and an average shear strength of 293 MPa.

[0023] Example 3 The other steps are the same as in Example 1, except that the solder is replaced with binary eutectic AgCuTi solder. The resulting brazed joint has a dense and well-defined microstructure, with a Co-depleted zone of 1.5 µm and an average shear strength of 263 MPa.

[0024] Example 4 The other steps are the same as in Example 1, except that the solder is replaced with AgCuSnTi. The resulting brazed joint has a dense microstructure, a Co-depleted zone of 1.8 µm, and an average shear strength of 271 MPa.

[0025] Example 5 The other steps are the same as in Example 1, except that the steel plate is replaced with 45# steel and the cemented carbide is replaced with YG20. The resulting brazed joint has a dense and well-developed microstructure, with a Co-depleted zone of 1.2 µm and an average shear strength of 295 MPa.

[0026] Example 6 The other steps are the same as in Example 1, except that the steel plate is replaced with 42CrMoV steel and the cemented carbide is replaced with YG8. The resulting brazed joint has a dense and well-developed microstructure, with a Co-depleted zone of 2.2 µm and an average shear strength of 285 MPa.

[0027] Comparative Example 1 The other steps are the same as in Example 1, except that steps one, two and three are omitted, that is, cobalt is not electroplated on the surface of the cemented carbide. 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 195 MPa.

[0028] Comparative Example 2 The other steps are the same as in Example 1, except that the solder is replaced with binary eutectic AgCuTi solder and steps one, two and three are removed, that is, the surface of the cemented carbide is not electroplated with cobalt. The resulting brazed joint has a dense and well-defined microstructure, with a Co-depleted zone of 5.5 µm and an average shear strength of 193 MPa.

[0029] This is because the Co-depleted zone is significantly larger than 5µm. This region consists of WC particles with large hardness differences, Ag-based solid solutions, and Cu-based solid solutions, resulting in high stress. Therefore, the joint is prone to crack propagation from this region during shearing, leading to premature joint failure.

[0030] 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.

[0031] Matters not covered in this invention are common knowledge.

Claims

1. A method for adjusting the Co-depleted region of a cemented carbide brazed joint by surface electroplating Co, characterized in that the method includes the following steps: Step 1: Pretreatment of cemented carbide and steel. First, polish for 1-5 minutes to remove the surface oxide layer and ensure the surface is flat. Then, ultrasonically clean the sample with alcohol for 15-30 minutes. Finally, ultrasonically clean the sample with acetone for 15-30 minutes. Step 2: Place the cemented carbide sample obtained in Step 1 into a Co plating solution for electroplating. The anode and cathode are composed of a cobalt plate and the cemented carbide obtained in Step 1, respectively, to obtain a cemented carbide with a Co coating on the surface. in, The composition of the Co electroplating solution is 20~30 g / L cobalt sulfate, 30~40 g / L boric acid, 1~4 mg / L saccharin, and 0.1~0.4 g / L sodium dodecyl sulfate; the ratio of the exposed area of ​​the cemented carbide to the area of ​​the cobalt plate is 1:1~1.

5. The electroplating temperature is 10℃~30℃, and the current density is 1~3 A / dm³. 2 The electroplating time is 50~200 s; Step 3: Place the steel treated in Step 1 and the cemented carbide treated in Step 2 on a screen printing platform and coat both surfaces with brazing filler metal. 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 5×10⁻⁶. -4 ~5×10 -3 Heating is performed at Pa, and the vacuum brazing furnace is heated to a programmed temperature rise to obtain a brazed joint with a Co coating in the intermediate layer; The solder is any one of AgCuTi, AgCuSnTi, or AgCuInTi; the solder layer thickness is 100~140 µm. The steel used in step one is any one of the following grades: 45# steel, 55# steel, 60# steel, 42CrMoV, 40Cr, and AISI 1045 steel. The cemented carbide is any one of the following grades: YG6, YG8, YG15, YG18, and YG20 cemented carbide.

2. The method for adjusting the Co-depleted region of a cemented carbide brazed joint by surface electroplating Co as described in claim 1, characterized in that: The dimensions of the cemented carbide and steel in step one are (2~20) mm × (2~20) mm × (2~10) mm and (5~30) mm × (5~30) mm × (2~20) mm, respectively.

3. The method for adjusting the Co-depleted region of a cemented carbide brazed joint by surface electroplating Co as described in claim 1, characterized in that: The programmed heating in step three involves raising the temperature from 20°C to 200-300°C at a rate of 15-30°C / min and holding it for 5-15 minutes, then raising it to 700-880°C at a rate of 5-15°C / min and holding it 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.

Images