Silver-based brazing filler metal and method for brazing CVD diamond and kovar alloy

Abstract

The invention relates to the technical field of brazing, in particular to silver-based brazing filler metal for brazing CVD diamond and kovar alloy and a method. The silver-based brazing filler metal comprises Ag-Cu-In-Ti alloy powder and B powder; the Ag-Cu-In-Ti alloy powder is prepared from, by mass, 12%-15% of In, 1.5%-3.5% of Ti, 23%-30% of Cu and the balance Ag. And the B powder accounts for 0.2 wt%-2wt% of the Ag-Cu-In-Ti alloy powder. The content of a melting reduction element In in the brazing filler metal is low, and generation of brittle compounds containing In is reduced; and by adding the B powder, Ni3Ti and Fe2Ti in a brazed joint can be reduced, diffusion of the Ni element into the brazing filler metal is limited, high enrichment of the Ti element is promoted, a small amount of TiB and Cu-Ti strengthening phases can be generated, the strength of the joint is strengthened, and high-strength connection of the CVD diamond and the Kovar alloy can be achieved under the low-temperature brazing condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of brazing, in particular to a silver-based filler metal and method for brazing CVD diamond and Kovar alloy. BACKGROUND

[0002] With the development of new devices with high power, high efficiency and high frequency, the related supporting optical window materials are facing increasingly stringent performance requirements. Currently commonly used window materials such as sapphire, zinc sulfide, zinc selenide, germanium, gallium arsenide, silicon, etc. are a compromise between mechanical properties and optical transmittance, and it is difficult to simultaneously meet the comprehensive requirements of high temperature resistance, high power resistance, high frequency resistance, high mechanical strength, etc., and the application range is limited.

[0003] CVD diamond has excellent mechanical properties, high hardness, high thermal conductivity, large band gap, low dielectric constant, wide spectral transmittance range and low absorption coefficient, and is an ideal new generation of optical window material. In order to realize its application in optical window components, it needs to be reliably connected with a metal substrate, and currently mainly relies on brazing technology.

[0004] The existing brazing process mainly uses nickel-based, copper-based or silver-based active filler metal. Among them, the brazing temperature of nickel-based and copper-based filler metal is generally higher than 850℃, and high temperature easily leads to graphitization of diamond and causes high residual stress, increasing the risk of window cracking. In silver-based filler metal, although the Ag-Cu-Ti system can reduce the brazing temperature to a certain extent, it still needs to exceed 800℃. In order to further reduce the brazing temperature, the existing research attempts to add indium (In), tin (Sn) and other melting elements in Ag-Cu-Ti, and Ag-Cu-Sn-Ti, Ag-Cu-In-Ti can reduce the brazing temperature, but the low brazing temperature brings a major defect of low brazing joint strength, and Ag-Cu-Sn-Ti, Ag-Cu-In-Ti is easy to produce more brittle compounds CuSn3Ti5 / Ti3InC during brazing, especially when too much melting element Sn, In is added, which affects the strength and high temperature resistance of the joint.

[0005] At present, copper is widely studied because of its high thermal conductivity, but its thermal expansion coefficient is quite different from that of diamond, which easily causes diamond cracking; the thermal expansion coefficient of Kovar alloy is small, which is theoretically beneficial to relieve residual stress, but the research on low-temperature active brazing of CVD diamond and Kovar alloy is still limited.

[0006] Therefore, it is necessary to develop a low-temperature filler metal and brazing method suitable for CVD diamond and Kovar alloy, to realize high-strength connection of CVD diamond and Kovar alloy at a lower temperature, so as to meet the performance requirements of optical window components for high-power, high-efficiency and high-frequency devices.

[0007] In view of this, the present application is proposed. SUMMARY

[0008] The present application aims to provide a silver-based brazing filler metal and method for brazing CVD diamond and Kovar alloy, which realizes high-strength connection of CVD diamond and Kovar alloy at low temperature by optimizing the composition of the brazing filler metal.

[0009] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted: A silver-based brazing filler metal for brazing CVD diamond and Kovar alloy, comprising Ag-Cu-In-Ti alloy powder and B powder; the Ag-Cu-In-Ti alloy powder comprises, in terms of mass percentage, 12%-15% of In, 1.5%-3.5% of Ti, 23%-30% of Cu, and the balance of Ag; the B powder accounts for 0.2wt%-2wt% of the Ag-Cu-In-Ti alloy powder.

[0010] Preferably, the B powder accounts for 0.6wt%-1wt% of the Ag-Cu-In-Ti alloy powder.

[0011] Preferably, the silver-based brazing filler metal further comprises Gd powder, and the Gd powder accounts for 0.1wt%-1wt% of the Ag-Cu-In-Ti alloy powder.

[0012] Preferably, the mass ratio of the Gd powder to the B powder is 1:2-10.

[0013] More preferably, the mass ratio of the Gd powder to the B powder is 1:2.7-8.

[0014] Preferably, the average particle size of the Ag-Cu-In-Ti alloy powder is 50-100μm.

[0015] Preferably, the average particle size of the Ag-Cu-In-Ti alloy powder is 5-10 times the average particle size of the B powder.

[0016] Preferably, the average particle size of the Ag-Cu-In-Ti alloy powder is 5-10 times the average particle size of the Gd powder.

[0017] A method for brazing CVD diamond and Kovar alloy, which adopts the silver-based brazing filler metal for brazing CVD diamond and Kovar alloy according to any one of the preceding embodiments.

[0018] Preferably, the brazing method comprises the following steps: S1. Cleaning and pretreating the CVD diamond and the Kovar alloy; S2. Mixing the silver-based brazing filler metal with an adhesive carrier to obtain a brazing filler metal paste; S3. Spread the brazing filler paste on the surface of the Kovar alloy to be welded, assemble with the CVD diamond, vacuum brazing, and cooling to obtain a brazing joint.

[0019] Preferably, the adhesive carrier comprises at least one of solid light welding brazing adhesive carrier ZT-D01, solid light welding brazing adhesive carrier ZT-D02, solid light welding brazing adhesive carrier ZT-D03, and hydroxyethyl cellulose.

[0020] Preferably, the vacuum degree of the vacuum brazing is ≤5×10 -3 Pa, the brazing temperature is 730-760℃, and the holding time is 8-15min.

[0021] Preferably, the cooling comprises: after the temperature is lowered to temperature T at a temperature lowering rate A, furnace cooling; the temperature lowering rate A is 2-4℃ / min, and the temperature T is 500-600℃.

[0022] Preferably, the shear strength of the brazing joint is ≥140MPa.

[0023] Compared with the prior art, the present application has the following beneficial effects: (1) The content of the melting reducing element In in the brazing filler is low, and the generation of In-containing brittle compounds is reduced; the addition of B powder can reduce Ni3Ti and Fe2Ti in the brazing joint, limit the diffusion of Ni element into the brazing filler, promote the enrichment of Ti element, greatly reduce the width of the Kovar dissolution area, generate a small amount of TiB and Cu-Ti strengthening phase, and strengthen the joint strength, and the joint fracture changes from brittle fracture when no B is added to ductile fracture when B is added.

[0024] (2) The present application adds Gd element in the brazing filler, the Gd element can adsorb oxygen atoms and impurities, and has the effect of refining grains, and a small amount of Gd element forms a certain range of encapsulation effect on B, effectively slowing down the aggregation of B element; Gd will react with B at the brazing temperature, and a small amount of Gd-B compounds (such as GdB2, GdB4, GdB6) will be generated in a short time, which has high hardness, stable chemical properties, and low thermal expansion coefficient, greatly improving the thermal expansion difference between the brazing filler layer and the diamond, and not easy to crack due to thermal stress; at the same time, the Gd element can combine with Ni element, reduce the diffusion of Ni, reduce the generation of brittle compounds, further improve the strength of the brazing joint, and the shear strength of the brazing joint can reach 238.25MPa, which is increased by 110% compared with the silver-based brazing filler without adding B and Gd.

[0025] (3) The silver-based brazing filler provided by the application can realize high-strength connection of CVD diamond and Kovar alloy at a lower brazing temperature; while ensuring high strength, the possibility of graphitization is significantly reduced, and the residual stress caused by high temperature is also alleviated. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed in the specific embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0027] Figure 1 The mixing, assembling and brazing schematic diagram provided for the embodiments of the present application; Figure 2 The weld microstructure diagram of the brazed joint in Example 1 of the present application; Figure 3 The weld microstructure diagram of the brazed joint in Example 2 of the present application; Figure 4 The weld microstructure diagram of the brazed joint in Example 3 of the present application; Figure 5 The weld microstructure diagram of the brazed joint in Example 4 of the present application; Figure 6 The weld microstructure diagram of the brazed joint in Example 5 of the present application; Figure 7 The weld microstructure diagram of the brazed joint in Example 6 of the present application; Figure 8 The weld microstructure diagram of the brazed joint in Comparative Example 1 of the present application; Figure 9 The weld microstructure diagram of the brazed joint in Comparative Example 2 of the present application; Figure 10 The weld microstructure diagram of the brazed joint in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described clearly and completely in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not mentioned by the manufacturer are conventional products that can be purchased on the market.

[0029] The silver-based brazing filler metal for brazing CVD diamond and Kovar alloy provided by the present application comprises Ag-Cu-In-Ti alloy powder and B powder; the Ag-Cu-In-Ti alloy powder comprises, in terms of mass percentage, 12%-15% of In, 1.5%-3.5% of Ti, 23%-30% of Cu, and the balance of Ag; and the B powder accounts for 0.2wt%-2wt% of the Ag-Cu-In-Ti alloy powder.

[0030] The In content in the traditional silver-copper-indium-titanium brazing filler metal is very high, generally 20wt%-24wt%, although the melting point can be reduced to a certain extent, the silver content in the brazing filler metal is low, the toughness and ductility of the brazed joint are low, and a large amount of brittle compounds are generated, resulting in very low joint strength. In view of the problem, the present application reduces the generation of In-containing brittle compounds by reducing the In content in the brazing filler metal; at the same time, the B powder is added to reduce Ni3Ti and Fe2Ti in the brazed joint, limit the diffusion of Ni element into the brazing filler metal, promote the high enrichment of Ti element, reduce the Kovar dissolution zone width, generate a small amount of TiB and Cu-Ti strengthening phase, strengthen the joint strength, and change the brittle fracture of the joint when no B is added to ductile fracture after adding B; the combination strength of CVD diamond and Kovar alloy can be significantly improved under low-temperature brazing conditions; while ensuring high strength, the graphitization possibility is significantly reduced, and the residual stress caused by high temperature is also relieved.

[0031] In some embodiments, typically but not limitedly, for example, in the Ag-Cu-In-Ti alloy powder, the mass percentage of In can be any one value or a range value composed of any two point values in 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, and 15%; the mass percentage of Ti can be any one value or a range value composed of any two point values in 1.5%, 2%, 2.5%, 3%, and 3.5%; the mass percentage of Cu can be any one value or a range value composed of any two point values in 23%, 25%, 28%, and 30%; and the addition amount of B powder can be any one value or a range value composed of any two point values in 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1wt%, 1.5wt%, and 2wt% of the Ag-Cu-In-Ti alloy powder.

[0032] In some preferred embodiments of the present application, the addition amount of B powder is 0.6wt%-1wt% of the Ag-Cu-In-Ti alloy powder.

[0033] If the B content is too low, the enhancement effect is not obvious; if the B content is too high, the aggregation of B element will be intensified, and at the same time, the Kovar dissolution zone will be too thin, and the joint strength will be reduced; by controlling the B content in the above range, a higher joint strength can be obtained.

[0034] In some embodiments of the present application, the silver-based filler metal further contains Gd powder, and the amount of Gd powder added is 0.1wt%-1wt% of the Ag-Cu-In-Ti alloy powder, for example, it can be any one value or a range value composed of any two point values of 0.1wt%, 0.2wt%, 0.3wt%, 0.5wt%, 0.8wt% and 1wt%.

[0035] Since B is a light element, it will have a more obvious aggregation effect, and too much aggregation of B will cause the joint to be too hard and brittle and fail, so a certain method is needed to make it uniformly dispersed in the brazed joint; the present application adds Gd in the filler metal, Gd element has great advantage in adsorbing oxygen atoms and impurity elements, and has the effect of refining grains, trace Gd element forms a certain range of encapsulation effect on B, effectively slows down the aggregation of B element, and makes B uniformly distributed in the weld; Gd may promote the element diffusion between diamond and filler metal, filler metal and Kovar alloy, forming a more stable interface transition layer; in addition, Gd element can also combine with Ni element, reduce the diffusion of Ni, and reduce the generation of brittle compounds; Gd and B will react at brazing temperature, a small amount of Gd-B compound will be generated in a short time, which has high hardness, stable chemical properties and low thermal expansion coefficient, greatly improving the thermal expansion difference between the filler metal layer and the diamond, and is not easy to crack due to thermal stress; further improve the strength of the brazed joint. When the amount of Gd element added is too small, the joint strength improves less; when the amount of Gd element added is too much, it will cause the wettability of the Kovar alloy surface to decrease, the joint formed by the filler metal on the Kovar alloy surface is uneven, and less related solid solution compounds are generated in the filler metal, resulting in a decrease in strength.

[0036] In some embodiments of the present application, the mass ratio of Gd powder and B powder in the filler metal is 1:2-10, for example, it can be any one value or a range value composed of any two point values of 1:2, 1:3, 1:4, 1:5, 1:6, 1:8 and 1:10.

[0037] In some preferred embodiments of the present application, the mass ratio of Gd powder and B powder in the filler metal is 1:2.7-8.

[0038] The synergistic strengthening effect of Gd and B is not simply dependent on the individual content of the two, but closely related to their relative ratio. Only when the two are in a specific ratio, can an effective Gd-B compound state be formed during brazing, thus realizing the synchronous optimization of the microstructure and performance of the brazed joint. When the mass ratio of Gd to B is low, the Gd element is insufficient to fully combine with the B element in the system, and only a small amount of Gd-B compound or enrichment phase can be formed during brazing, which is difficult to effectively constrain the aggregation behavior of B. Under this condition, part of B still exists in a free or agglomerated state, which is easy to form a local hard and brittle zone in the brazing seam, and the inhibition effect on the diffusion of Ni and other Kovar alloy elements is limited, resulting in an unobvious overall strengthening effect of the joint and a low shear strength. When the mass ratio of Gd to B is high, the Gd element that can combine with B in the system is excessive, in addition to forming Gd-B compounds, the excess Gd is easy to segregate or participate in other reaction processes, thus adversely affecting the wetting behavior of the brazing filler metal and the continuity of the brazing seam. In addition, the formation of excessive Gd-B type high-hardness phase will increase the brittleness of the brazing seam, making the joint more prone to brittle fracture under external load, which will in turn lead to a decrease in shear strength.

[0039] With the change of the addition ratio of Gd to B, the Gd-B product formed during brazing can evolve from low boronization degree to high boronization degree, and the quantity and distribution state of the product change accordingly. In comparison, when the mass ratio of Gd to B is 1:4, the ratio relationship of the two is the most matched, the quantity of the Gd-B compound formed during brazing is moderate and the distribution is uniform, which can effectively disperse and passivate the B element, and will not weaken the wettability of the brazing filler metal due to excessive generation. Under this ratio condition, the synergistic effect of Gd-B compound and Cu-Ti strengthening phase significantly inhibits the diffusion of Ni element, making the brazing seam structure uniform and dense, thus obtaining the highest brazed joint shear strength. For example, when the content of B in the brazing filler metal is about 0.8wt%, the addition amount of Gd increases from 0.1wt% to 0.3wt%, the strength of the brazed joint first increases and then decreases, and the strengthening effect is best when the addition amount of Gd is about 0.2wt%; when the content of Gd is about 0.1wt%, the Gd element is insufficient to fully combine with the B element in the system, and the joint strength shows a downward trend; when the content of Gd is about 0.3wt%, the Gd element that can combine with B in the system is excessive, and the joint strength also shows a downward trend; but both are higher than the best joint strength without adding B and Gd.

[0040] In some specific embodiments of the present application, the average particle size of the Ag-Cu-In-Ti alloy powder is 50-100 μm, for example, it can be any point value or a range value composed of any two point values among 50 μm, 60 μm, 70 μm, 80 μm, 90 μm and 100 μm.

[0041] In some specific embodiments of the present invention, the average particle size of the Ag-Cu-In-Ti alloy powder is 5-10 times the average particle size of the B powder. For example, it can be any one value or a range of any two values ​​from 5, 6, 7, 8, 9, and 10 times. The purpose is to ensure that the "skeleton gaps" formed by the alloy powder particles are sufficient to accommodate the B powder, and that the gap size is uniform, so that the B powder is evenly distributed. At the same time, it allows the smaller B powder particles to flow flexibly inside the larger alloy powder particles, avoiding the obstruction of flow due to excessively small local gaps.

[0042] In some specific embodiments of the present invention, the average particle size of Ag-Cu-In-Ti alloy powder is 5-10 times the average particle size of Gd powder. For example, it can be any one value or a range of any two values ​​among 5, 6, 7, 8, 9, and 10 times.

[0043] A second aspect of the present invention provides a method for brazing CVD diamond to Kovar alloy, wherein the brazing is performed using a silver-based brazing filler metal for brazing CVD diamond to Kovar alloy as described in any of the foregoing embodiments.

[0044] like Figure 1 As shown, in some specific embodiments of the present invention, the brazing method includes the following steps: S1. Cleaning and pretreatment of CVD diamond and Kovar alloy; S2. Mix the silver-based solder with the adhesive carrier to obtain solder paste; S3. Spread the brazing paste on the Kovar alloy surface to be brazed, assemble it with CVD diamond, perform vacuum brazing, cool it, and obtain the brazed joint.

[0045] The brazing process of this invention is simple and easy to operate, and can achieve a reliable connection between CVD diamond and Kovar alloy at low temperatures, resulting in a high bonding strength of the brazed joint.

[0046] In some specific embodiments of the present invention, in step S1, the cleaning pretreatment includes: placing CVD diamond and Kovar alloy in acetone for ultrasonic cleaning to remove impurities from the substrate surface.

[0047] In some specific embodiments of the present invention, step S1 includes the following steps before cleaning pretreatment: laser cutting CVD diamond and Kovar alloy, and sanding the surface of Kovar alloy to be welded with sandpaper to make its surface smooth and free of impurities.

[0048] In some specific embodiments of the present invention, in step S2, the adhesive carrier used includes at least one of the following: Guguang welding brazing adhesive carrier ZT-D01, Guguang welding brazing adhesive carrier ZT-D02, Guguang welding brazing adhesive carrier ZT-D03, and hydroxyethyl cellulose.

[0049] In some embodiments of the present application, in step S2, the step of preparing the brazing filler paste comprises: ball-milling mixing the Ag-Cu-In-Ti alloy powder with the B powder, and then adding the adhesive carrier to stir uniformly to form a paste state.

[0050] In some embodiments of the present application, in step S2, the step of preparing the brazing filler paste comprises: ball-milling mixing the Ag-Cu-In-Ti alloy powder with the B powder and the Gd powder, and then adding the adhesive carrier to stir uniformly to form a paste state; wherein the B powder and the Gd powder can be added simultaneously for ball-milling mixing, or can be added separately for ball-milling mixing, and finally the adhesive carrier is added.

[0051] In some embodiments of the present application, in step S3, the brazing filler paste is spread on the Kovar alloy by screen printing; the advantage of screen printing for spreading the brazing filler paste is that it can realize "precise, uniform and efficient" material distribution, and is especially suitable for thin and large-area spreading requirements; the squeegee pressure and speed of screen printing can be adjusted and controlled, so that the brazing filler paste can be uniformly extruded through the mesh to the surface of the substrate, and the B powder agglomeration can be further broken to realize uniform distribution at the micro level.

[0052] In some embodiments of the present application, in step S3, the coating thickness of the brazing filler paste is 50-100 μm, for example, it can be any point value or a range value composed of any two point values in 50 μm, 60 μm, 80 μm and 100 μm.

[0053] In some embodiments of the present application, in step S3, the vacuum degree of vacuum brazing is ≤5×10 -3 Pa, the brazing temperature is 730-760℃, for example, it can be any point value or a range value composed of any two point values in 730℃, 740℃, 750℃ and 760℃; the holding time is 8-15 min, for example, it can be any point value or a range value composed of any two point values in 8 min, 10 min, 12 min and 15 min. The brazing temperature of the method of the present application is low, which can significantly reduce the possibility of graphitization and relieve residual stress caused by high temperature; at the same time, it can also ensure high joint strength.

[0054] In some embodiments of the present application, the cooling comprises: after the temperature is lowered to temperature T at a cooling rate A, furnace cooling is performed; the cooling rate A is 2-4℃ / min, for example, it can be any point value or a range value composed of any two point values in 2℃, 2.5℃, 3℃, 3.5℃ and 4℃; the temperature T is 500-600℃, for example, it can be any point value or a range value composed of any two point values in 500℃, 520℃, 550℃, 580℃ and 600℃. It can avoid large residual stress caused by rapid cooling.

[0055] In some specific embodiments of the present invention, the shear strength of the brazed joint is ≥140MPa. For example, it can be any one value or a range of any two values ​​among 140MPa, 160MPa, 187MPa, 200MPa, and 240MPa.

[0056] In some preferred embodiments of the present invention, the shear strength of the brazed joint is ≥200MPa; the present invention can achieve a high-strength connection with a shear strength ≥200MPa under low-temperature brazing conditions not exceeding 760℃.

[0057] The following detailed description of some embodiments of the present invention is provided in conjunction with specific application examples. Unless otherwise specified, all raw materials used in the embodiments can be obtained commercially available.

[0058] Example 1 This embodiment provides a silver-based brazing filler metal for brazing CVD diamond and Kovar alloy, including Ag. 60 Cu 24 In 13 Ti3 alloy powder (wt%), B powder and Gd powder; B powder accounts for a certain percentage of Ag. 60 Cu 24 In 13 0.8 wt% Ti3 alloy powder, Gd powder accounting for Ag 60 Cu 24 In 13 0.2wt% of Ti3 alloy powder; Ag 60 Cu 24 In 13 The average particle size of Ti3 alloy powder is 50 μm, while the average particle size of B powder and Gd powder is 10 μm.

[0059] The method for brazing CVD diamond to Kovar alloy includes the following steps: S1. Laser cutting of CVD diamond and Kovar alloy (Kovar4J33), sanding the Kovar alloy surface to be welded with sandpaper to make it smooth and free of impurities, ultrasonic cleaning of CVD diamond and Kovar alloy in acetone to remove impurities from the substrate surface; S2. Add Ag 60 Cu 24 In 13 Ti3 alloy powder, B powder, and Gd powder were ball-milled at 250 rpm for 2 hours. Then, ZT-D01 brazing adhesive carrier was added and stirred evenly to obtain brazing paste. S3. Apply solder paste to the Kovar alloy surface to be soldered using screen printing, with a coating thickness of 80 μm. Then, assemble it with CVD diamond bonding material and place it in a vacuum brazing furnace, evacuating to a vacuum level of 5 × 10⁻⁶. -3Pa was held at 760℃ for 10 minutes, then cooled to 600℃ at a rate of 3℃ / min, and then cooled in the furnace to obtain the brazed joint.

[0060] The weld microstructure of the brazed joint in Example 1 is shown in the figure below. Figure 2 As shown, the NiTi compound basically disappeared, the Kovar dissolution zone width was about 8 μm, and B showed a large dispersion.

[0061] Example 2 Example 2 is similar to Example 1, except that: the proportion of Gd powder to Ag is [missing information]. 60 Cu 24 In 13 The Ti3 alloy powder was 0.1 wt%, and all other conditions were the same as in Example 1.

[0062] The weld microstructure of the brazed joint in Example 2 is shown in the figure below. Figure 3 As shown, the NiTi compound basically disappeared, the Kovar dissolution zone was about 10 μm wide, and B was highly dispersed.

[0063] Example 3 Example 3 is similar to Example 1, except that: the proportion of Gd powder to Ag is [missing information]. 60 Cu 24 In 13 The Ti3 alloy powder was 0.3 wt%, and all other conditions were the same as in Example 1.

[0064] The weld microstructure of the brazed joint in Example 3 is shown in the figure below. Figure 4 As shown, the NiTi compound basically disappeared, the Kovar dissolution zone was about 5 μm wide, and B was highly dispersed.

[0065] Example 4 Example 4 is similar to Example 1, except that the silver-based brazing filler metal for brazing CVD diamond and Kovar alloy does not contain Gd powder, and all other conditions are the same as in Example 1.

[0066] The weld microstructure of the brazed joint in Example 4 is shown in the figure below. Figure 5 As shown, NiTi compounds are scarce, the Kovar dissolution zone is about 12 μm wide, and B is relatively concentrated.

[0067] Example 5 Example 5 is similar to Example 4, except that: B powder accounts for a certain percentage of Ag. 60 Cu 24 In 13 The Ti3 alloy powder was 0.6 wt%, and all other conditions were the same as in Example 4.

[0068] The weld microstructure of the brazed joint in Example 5 is shown in the figure below. Figure 6As shown, there are fewer NiTi compounds, the Kovar dissolution zone is about 15 μm wide, and the B distribution is relatively aggregated, but the degree of aggregation is lower than that in Example 4.

[0069] Example 6 Example 6 is similar to Example 4, except that B powder accounts for a certain percentage of Ag. 60 Cu 24 In 13 The Ti3 alloy powder was 1 wt%, and all other conditions were the same as in Example 4.

[0070] The weld microstructure of the brazed joint in Example 6 is shown in the figure below. Figure 7 As shown, NiTi compounds are very scarce, the Kovar dissolution zone is about 10 μm wide, and the B distribution is very concentrated, with a large amount distributed inside the joint.

[0071] Comparative Example 1 Comparative Example 1 is similar to Example 1, except that the silver-based brazing filler metal used for brazing CVD diamond and Kovar alloy does not contain boron powder or cadmium powder, but directly uses Ag powder. 60 Cu 24 In 13 Ti3 alloy powder (wt%) was used as the brazing filler metal for brazing, and all other conditions were the same as in Example 1.

[0072] The weld microstructure of the brazed joint in Comparative Example 1 is shown in the figure below. Figure 8 As shown, a large amount of NiTi compounds are generated, the Kovar dissolution zone is about 30 μm wide, the TiC layer on the diamond side is relatively thick, and there is an excessive accumulation of brittle compounds.

[0073] Comparative Example 2 Comparative Example 2 is similar to Comparative Example 1, except that the brazing temperature is 730℃, and all other conditions are the same as those in Comparative Example 1.

[0074] The weld microstructure of the brazed joint in Comparative Example 2 is shown in the figure below. Figure 9 As shown, a large amount of NiTi compounds are distributed in the lower part of the joint, the Kovar dissolution zone is about 20 μm wide, and the thickness of TiC generated on the diamond side is moderate.

[0075] Comparative Example 3 Comparative Example 3 is similar to Comparative Example 1, except that the brazing temperature is 700℃, and all other conditions are the same as those in Comparative Example 1.

[0076] The weld microstructure of the brazed joint in Comparative Example 3 is shown in the figure below. Figure 10 As shown, less NiTi compound was formed, the Kovar dissolution zone width was about 15 μm, and the TiC thickness at the diamond interface was relatively small.

[0077] Test case The shear strength of the brazed joints in each embodiment and comparative example was tested respectively. The test method was in accordance with GB / T-11363-2008. The test results are shown in Table 1.

[0078] Table 1

[0079] From Table 1 and Figures 2-7 The results show that the overall strength of the brazed joints after adding boron (B) is higher than that without B. Furthermore, the shear strength initially increases and then decreases with increasing B content, reaching its highest point when B powder accounts for 0.8 wt% of the alloy powder. The presence of B helps reduce the dissolution and diffusion of Kovar alloying elements, significantly reducing the formation of Ni3Ti brittle compounds. By hindering element diffusion, it forms titanium-rich and iron-rich regions within the brazing filler metal, altering the phase composition of the brazed joint seam to some extent and forming a Cu-Ti reinforcing phase. With increasing B content, the width of the diffusion zone in the metal matrix gradually decreases. Since B is a lightweight element, it exhibits a significant aggregation effect. Adding Gd reduces the aggregation effect of the lightweight element B, making B more dispersed and further improving the shear strength of the brazed joint.

[0080] Depend on Figures 8-10 It can be seen that without the addition of B and Gd, as the brazing temperature increases, the amount of brittle Ni3Ti compounds inside the interface gradually increases, the microstructure gradually becomes coarser, and extends to the near-diamond side; the erosion of the Kovar alloy base material gradually intensifies, reaching a maximum erosion width of 30 μm at 760℃; and the TiC thickness gradually increases. Data from Comparative Examples 1-3 show that 730℃ is the optimal welding temperature without the addition of B and Gd, but the joint strength is still relatively low at this temperature. This indicates that simply optimizing the brazing process is insufficient to significantly improve the joint strength; therefore, optimizing the brazing alloy composition is necessary to further improve the joint condition. This invention achieves a significant improvement in joint strength by adding appropriate amounts of B powder and Gd powder. The optimal brazing temperature also changes due to the altered brazing alloy composition after adding B and Gd. The embodiment of this invention shows good overall brazing performance at 760℃; the joint strength can be increased to over 200 MPa, reaching a maximum of 238.25 MPa, which is approximately 110% higher than the joint strength under the optimal brazing conditions without the addition of B and Gd.

[0081] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A silver-based brazing filler metal for brazing CVD diamond and Kovar alloy, characterized in that, It includes Ag-Cu-In-Ti alloy powder and B powder; by mass percentage, the Ag-Cu-In-Ti alloy powder comprises: 12%-15% In, 1.5%-3.5% Ti, 23%-30% Cu and the balance Ag; the B powder accounts for 0.2wt%-2wt% of the Ag-Cu-In-Ti alloy powder.

2. The silver-based brazing filler metal for brazing CVD diamond and Kovar alloy according to claim 1, characterized in that, The B powder accounts for 0.6wt%-1wt% of the Ag-Cu-In-Ti alloy powder.

3. The silver-based brazing filler metal for brazing CVD diamond and Kovar alloy according to claim 1 or 2, characterized in that, The silver-based solder also contains Gd powder, which accounts for 0.1 wt% to 1 wt% of the Ag-Cu-In-Ti alloy powder. Preferably, the mass ratio of the Gd powder to the B powder is 1:2-10; More preferably, the mass ratio of the Gd powder to the B powder is 1:2.7-8.

4. The silver-based brazing filler metal for brazing CVD diamond and Kovar alloy according to claim 1, characterized in that, The average particle size of the Ag-Cu-In-Ti alloy powder is 50-100 μm.

5. The silver-based brazing filler metal for brazing CVD diamond and Kovar alloy according to claim 1, characterized in that, The average particle size of the Ag-Cu-In-Ti alloy powder is 5-10 times that of the average particle size of the B powder.

6. The silver-based brazing filler metal for brazing CVD diamond and Kovar alloy according to claim 3, characterized in that, The average particle size of the Ag-Cu-In-Ti alloy powder is 5-10 times that of the average particle size of the Gd powder.

7. A method for brazing CVD diamond to Kovar alloy, characterized in that, The silver-based brazing filler metal of CVD diamond and Kovar alloy as described in any one of claims 1-6 is used for brazing.

8. The method for brazing CVD diamond and Kovar alloy according to claim 7, characterized in that, Includes the following steps: S1. Cleaning and pretreatment of CVD diamond and Kovar alloy; S2. Mix the silver-based solder with an adhesive carrier to obtain solder paste; S3. Spread the brazing paste on the Kovar alloy surface to be brazed, assemble it with the CVD diamond, perform vacuum brazing, cool, and obtain a brazed joint.

9. The method for brazing CVD diamond and Kovar alloy according to claim 8, characterized in that, It meets at least one of the following characteristics: (1) The adhesive carrier includes at least one of the following: ZT-D01, ZT-D02, ZT-D03, and hydroxyethyl cellulose; (2) The vacuum degree of the vacuum brazing is ≤5×10 -3 Pa, brazing temperature is 730-760℃, holding time is 8-15min; (3) The cooling includes: cooling the furnace at a cooling rate A to a temperature T; the cooling rate A is 2-4℃ / min and the temperature T is 500-600℃.

10. The method for brazing CVD diamond and Kovar alloy according to claim 8 or 9, characterized in that, The shear strength of the brazed joint is ≥140MPa.

Images