A medium-temperature high-activity brazing filler metal for brazing ceramics and metals and its preparation method.

Abstract

This invention relates to the field of materials engineering technology, and discloses a medium-temperature high-activity brazing filler metal for brazing ceramics and metals and its preparation method. The composition includes: Sn 13-15 wt%, In 3-6 wt%, Ti-Zr low-melting-point master alloy 2-6 wt%, wherein the composition ratio of the Ti-Zr low-melting-point master alloy is between the eutectic point of the Ti-Zr binary phase diagram and the α-β minimum phase transformation temperature, the mass fraction of Zr is between 50.65% and 65.30%, and a small amount of Al or Si; the remaining component is Ag-Cu eutectic. The preparation method includes: 1) preparing raw materials; 2) electric arc furnace melting of the master alloy with high-melting-point elements; 3) smelting in a levitation furnace and casting the billet; 4) hot rolling, cleaning, and trimming; 5) Al powder or Al foil can be added during use. The advantages of this invention are: Sn and In work synergistically to reduce the solid and liquid phase lines of the brazing filler metal more effectively than when used alone; the brazing temperature of the filler metal is lower, and less brittle intermetallic compounds are generated compared to traditional Ag-Cu-Ti brazing filler metals; Al or Si elements have a strong affinity for specific ceramics, improving the mechanical properties of the brazed joint.

Description

Technical Field

[0001] This invention relates to the field of materials engineering technology, specifically to a medium-temperature high-activity brazing filler metal for brazing ceramics and metals and its preparation method. Background Technology

[0002] Ceramic materials possess excellent high-temperature resistance, heat dissipation, and insulation properties, leading to their widespread application in power facilities, electrical products, and aerospace structural and functional components. They also hold significant demand and promising applications in arc-extinguishing switches / relays and next-generation semiconductor circuit board substrates. Achieving reliable connections between ceramics and metals is crucial for advancing the application of ceramic materials. For example, in aerospace devices and vacuum interrupters in power transmission and distribution, a reliable connection between the ceramic shell and copper conductive components is essential. For joining dissimilar materials, brazing offers advantages such as connectivity, operability, process similarity, and high bonding strength. The primary condition for reliable brazing of ceramics and metals is the good wetting of the ceramic by the brazing filler metal. Most common metals exhibit poor wettability with ceramics; therefore, current ceramic-metal connections often utilize pre-plated metal or active metal brazing methods.

[0003] Currently, the most commonly used active metal brazing filler metal is AgCuTi-based filler metal. This type of filler metal has good wettability to ceramics and can be used for brazing ceramics and copper. However, on the one hand, Ag-Cu-Ti-based filler metals have limited activity and require a high vacuum; on the other hand, Ag-Cu-Ti-based filler metals require high brazing temperatures, which can easily lead to excessive thermal expansion and contraction after brazing, resulting in significant tensile stress on the ceramic side. Since the residual stress of the workpiece is positively correlated with its size and temperature, when the joint area is large or the temperature is high, the negative impact of excessive thermal expansion and contraction will be amplified many times over, leading to residual stress, deformation, or even cracking at the ceramic-metal joint.

[0004] Therefore, the current Ag-Cu-Ti brazing alloy's excessively high brazing temperature and limited activity severely restrict the brazable dimensions of workpieces and the service reliability of joints. It is necessary to optimize the design of the brazing alloy by lowering the solid-liquid phase line and increasing the activity of the brazing alloy to reduce the residual stress of the brazed joint and improve the reliability of the brazed joint. Summary of the Invention

[0005] This invention aims to provide a medium-temperature, high-activity brazing filler metal for brazing ceramics and metals, and its preparation process. The brazing filler metal of this invention is modified by adding specific elements to lower the brazing temperature and reduce ceramic cracking induced by excessive tensile stress due to thermal expansion and contraction.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A medium-temperature, high-activity brazing filler metal for brazing ceramics and metals comprises the following components by mass percentage: Sn 13-15wt%, In 3-6wt%, Ti-Zr low-melting-point master alloy 2-6wt%, wherein the composition ratio of the Ti-Zr low-melting-point master alloy is between the eutectic point of the Ti-Zr binary phase diagram and the α-β minimum phase transformation temperature, the mass fraction of Zr content is between 50.65% and 65.30%, and a small amount of Si or Al elements mentioned below, with the remaining components being Ag-Cu eutectic.

[0008] Ti and Zr exist as low-melting intermediate alloys, while Ag and Cu exist as eutectic alloys.

[0009] As a preferred option, it also includes 0.3-0.6 wt% Si to facilitate brazing of Al2O3 ceramics.

[0010] As a preferred option, it also includes 2-2.5 wt% Al to facilitate brazing of AlN ceramics. Here, Al does not participate in the melting to form the brazing filler alloy, but is added directly to the brazing joint in foil or powder form. This pre-melts during the brazing process, providing initial wetting and improving the reliability of the brazed joint.

[0011] As a preferred option, it also includes 1.5-2.0 wt% Al to facilitate brazing of Si3N4 or SiC ceramics. The Al does not participate in the solder alloy melting process but is added directly to the brazing joint in foil or powder form, pre-melting and pre-wetting during the brazing process to improve the reliability of the brazed joint.

[0012] As a preferred option, it also includes 2-4 wt% Ni to facilitate brazing of ZrO2 ceramics. The introduction of Ni further improves the wettability of the brazing to ZrO2 ceramics, thereby enhancing the reliability of the connection.

[0013] As a preferred embodiment, in the Ti-Zr low-melting-point master alloy, the Zr content is adjusted according to the Ti content to maintain the low-melting-point master alloy state, and the solder undergoes a solid-state phase transformation at a temperature of 700°C, which is beneficial for the activation of the ceramic surface.

[0014] A method for preparing a medium-temperature, high-activity brazing filler metal for brazing ceramics and metals specifically includes the following steps:

[0015] 1) Prepare raw materials: Weigh the elemental metals or intermediate alloys according to the element mass percentages specified in the design documents, mix them, and store them separately for later use. The purity of the metals should not be less than 99.95%. Among them, Cu raw materials should be divided into two parts according to the following requirements.

[0016] 2) Ti metal blocks and Zr metal granules, with a combined mass equal to that of Cu, are pre-melted into an intermediate alloy in an electric arc furnace. During smelting, the metal blocks / granules are placed in the crucible of the electric arc furnace, and the vacuum level is evacuated to 10 using a vacuum pump. -2 Below Pa, Ar gas is then introduced into the electric arc melting system until the pressure difference meter reading is -0.05 MPa, and copper, Ti, and Zr are heated and melted using an arc current specification of 300-400 A.

[0017] 3) Repeated melting: Repeat melting 5-7 times until a homogenized CuTiZr intermediate alloy billet is obtained;

[0018] 4) Slicing and cleaning: Use wire cutting to cut the intermediate alloy billet into slices with a thickness of 0.2mm, and then use organic solvent to clean the slices to remove surface impurities and oil.

[0019] 5) Prepare each raw material separately and put it into a vacuum suspension melting furnace. If there is Ni or Si element, Ni is added in the form of thin sheets and Si is added in the form of powder. Melt under Ar gas protection.

[0020] 6) Cast into slabs and hot pickle to remove surface oxides and impurities.

[0021] 7) Hot rolling to form a thin strip with a thickness of 0.08 to 0.2 mm, trimming the rough edges, hot pickling, washing with water, vacuum drying, and packaging for later use.

[0022] The advantages of this invention compared with the prior art are: Sn and In are used to synergistically reduce the solidus and liquidus of the solder, which is more effective than Sn-dominant or In-dominant alone, and more effectively improves machinability. At the same time, the amount of Sn added is controlled within the limit of non-brittleness.

[0023] The addition of active elements Ti and Zr in the form of low-melting-point master alloys results in a lower brazing temperature for the solder and less formation of brittle intermetallic compounds compared to traditional Ag-Cu-Ti solders, thus mitigating the adverse effects of brittle intermetallic compounds on the impact toughness of the brazed joint. In and Si have a strong affinity for Al, making them more suitable for brazing Al2O3 ceramics to metals. Al or Si have a strong affinity for Al2O3, Si3N4, SiC, or AlN ceramics, and the introduction of Al or Si further improves the mechanical properties of the brazed joint in specific ceramic-metal brazing processes. Attached Figure Description

[0024] Figure 1 This is a SEM microstructure diagram of the solder in Embodiment 1 of the present invention.

[0025] Figure 2 This is a DTA curve diagram of Embodiment 1 of the present invention.

[0026] Figure 3 This is a SEM microstructure diagram of the solder in Embodiment 2 of the present invention.

[0027] Figure 4 This is a DTA curve diagram of Embodiment 2 of the present invention.

[0028] Figure 5 This is a SEM microstructure diagram of the solder in Embodiment 3 of the present invention. Detailed Implementation

[0029] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0030] Example 1:

[0031] A medium-temperature, high-activity brazing filler metal for brazing ceramics and metals comprises the following components by mass percentage: Sn 15wt%, In 5wt%, Ti-Zr low-melting-point master alloy 3wt% (Ti and Zr mass fractions are 1.04wt% and 1.96wt%, respectively), and Ag-Cu eutectic 77wt% (where Ag and Cu mass fractions are 55.44wt% and 21.56wt%, respectively).

[0032] In this embodiment, by Figure 1 and Figure 2 The SEM microstructure and DTA curve of the solder show that there are no obvious defects in the solder. The solidus temperature of the solder is 675.68℃, which is nearly 105℃ lower than that of the most traditional inactive Ag-Cu eutectic solder.

[0033] Example 2:

[0034] A medium-temperature, high-activity brazing filler metal for brazing ceramics and metals comprises the following components by mass percentage: Sn 14wt%, In 3.6wt%, Ti-Zr low-melting-point master alloy 3.4wt% (Ti and Zr mass fractions are 1.6wt% and 1.8wt%, respectively), and Ag-Cu eutectic 79wt% (where Ag and Cu mass fractions are 56.88wt% and 22.12wt%, respectively).

[0035] In this embodiment, by Figure 3 and Figure 4 The SEM microstructure and DTA curve of the solder show that there are no obvious defects in the solder. The solidus temperature of the solder is 675.38℃, which is nearly 105℃ lower than that of the most traditional inactive Ag-Cu eutectic solder.

[0036] Example 3:

[0037] A medium-temperature, high-activity brazing filler metal for brazing ceramics and metals comprises the following components by mass percentage: Sn 14wt%, In 4wt%, Ti-Zr eutectic 3wt% (Ti and Zr mass fraction percentages are 1.04wt% and 1.96wt%, respectively), and Ag-Cu eutectic 79wt% (where Ag and Cu mass fractions are 56.88wt% and 22.12wt%, respectively).

[0038] Example 4:

[0039] A medium-temperature, high-activity brazing filler metal for brazing Al2O3 ceramics to metals comprises the following components by mass percentage: Sn 15wt%, In 4wt%, Si 0.3wt%, Ti-Zr eutectic 5wt% (Ti and Zr have mass fractions of 2.4wt% and 2.6wt%, respectively), and Ag-Cu eutectic 75.7wt% (Ag and Cu have mass fractions of 54.504wt% and 21.196wt%, respectively).

[0040] Example 5:

[0041] A medium-temperature, high-activity brazing filler metal for brazing ZrO2 ceramics to metals comprises the following components by mass percentage: Sn 14wt%, In 5wt%, Ni 3wt%, Si 0.6wt%, Ti-Zr low-melting-point master alloy 3wt% (Ti and Zr mass fractions are 1.4wt% and 1.6wt%, respectively), and Ag-Cu eutectic 74.4wt% (where Ag and Cu mass fractions are 53.568wt% and 20.832wt%, respectively).

[0042] In Examples 4 and 5, Si or Ni elements were added to make the brazing filler metal more suitable for brazing specialty ceramics.

[0043] Example 6:

[0044] A medium-temperature, high-activity brazing filler metal for brazing Si3N4 or SiC ceramics to metals comprises the following components by mass percentage: Sn 14wt%, In 5wt%, Si 0.4wt%, Ti-Zr low-melting-point master alloy 5wt% (Ti and Zr mass fractions are 2.4wt% and 2.6wt%, respectively), and Ag-Cu eutectic 75.6wt% (where Ag and Cu mass fractions are 54.432wt% and 21.168wt%, respectively). During brazing of Si3N4 or SiC ceramics, an aluminum foil weighing 2% of the filler metal is pre-placed on the ceramic side to induce wetting of the ceramic by the filler metal.

[0045] Example 7:

[0046] A medium-temperature, high-activity brazing filler metal for brazing ceramics and metals comprises the following components by mass percentage: Sn 13wt%, In 6wt%, Si 0.5wt%, Ti-Zr low-melting-point master alloy 3wt% (Ti and Zr mass fractions are 1.4wt% and 1.6wt%, respectively), and Ag-Cu eutectic 77.5wt% (Ag and Cu mass fractions are 55.8wt% and 21.7wt%, respectively). During brazing of AlN ceramics to Mo, 2.4% of the filler metal mass of 200-mesh fine aluminum powder is pre-powdered on the ceramic side (directly added to the brazing seam).

[0047] In this invention, the elements Sn and In are used synergistically to reduce the solidus and liquidus lines of the solder, which is more effective than In-dominant methods. At the same time, the amounts of Sn and In added do not exceed the limits for embrittlement.

[0048] The active elements Ti and Zr are added in eutectic form, which results in a lower brazing temperature for this solder. Due to the combination of Ti and Zr, the solder contains less brittle Cu-Ti intermetallic compound compared to traditional AgCuTi solders, thus mitigating the damage of brittle intermetallic compounds to the brazed joint (during the reaction at the brazing interface, free Ti will correspondingly release Zr, and the presence of free dispersed particles helps to disrupt the formation of continuous large-sized intermetallic compounds).

[0049] This solution contains In and Si elements, both of which have a strong affinity for Al, making this brazing filler metal particularly suitable for brazing Al2O3 ceramics to metals.

[0050] This invention is used for brazing connections between ceramics and metals, especially Al2O3 ceramics and metals. For AlN, Si3N4 or SiC ceramics, aluminum foil or aluminum powder can be pre-prepared during brazing.

[0051] The brazing of ceramics and metals is prone to cracking, mainly due to two reasons. First, most common metals have poor wettability with ceramics, and only a few active elements can produce good wetting. Second, the thermal expansion coefficients of metals and ceramics differ significantly. During cooling, excessive differential thermal expansion and contraction leads to large tensile stress inside the ceramic, causing cracks at the ceramic ends. There are two main theoretical and technical approaches to solving this problem: one is to use an intermediate layer with a thermal expansion coefficient between the two to alleviate stress; the other is to use a low-melting-point brazing filler metal to lower the brazing temperature. This invention modifies traditional Ag-Cu-Ti brazing filler metals with high soldering temperatures by adding elements. Sn is used as the main element to lower the melting point, while In is used as a secondary element to lower the melting point and as an active element. Ti, which often produces brittle phases, is added to the filler metal along with Zr to form a low-melting-point intermediate alloy. Si is also added to enhance the wettability of the filler metal to ceramics. In other words, by developing Ag-Cu-Sn-In-Si-Ti-Zr brazing filler metals, this invention reduces the soldering temperature of brazing filler metals for ceramics, thereby reducing ceramic cracking caused by excessive thermal expansion and contraction due to excessively high soldering temperatures.

[0052] The present invention and its embodiments have been described above. This description is not restrictive; the embodiments given and the accompanying drawings are merely one example of the present invention, and the actual components are not limited thereto. In conclusion, if those skilled in the art are inspired by this description and, without departing from the spirit of the invention, design similar combinations of components and embodiments to this technical solution, all such designs should fall within the protection scope of the present invention.

Claims

1. A medium-temperature, high-activity brazing filler metal for brazing ceramics and metals, characterized in that, The composition by mass percentage includes: Sn 13-15wt%, In 3-6wt%, Ti-Zr low-melting-point master alloy 2-6wt%, wherein the composition of the Ti-Zr low-melting-point master alloy is between the eutectic point of the Ti-Zr binary phase diagram and the α-β minimum phase transformation temperature, the mass fraction of Zr content is between 50.65% and 65.30%, and the trace elements mentioned below, with the remainder being Ag-Cu eutectic. Ti and Zr are added in the form of low-melting-point intermediate alloys, while Ag and Cu exist in eutectic form.

2. The medium-temperature high-activity brazing filler metal for brazing ceramics and metals according to claim 1, characterized in that, To prevent Zr powder from spontaneously combusting during smelting, Zr should be added as Zr rods or Zr particles when smelting Ti-Zr master alloys.

3. The medium-temperature high-activity brazing filler metal for brazing ceramics and metals according to claim 1, characterized in that: It also includes 0.3-0.6 wt% Si for brazing Al2O3 ceramics.

4. The medium-temperature high-activity brazing filler metal for brazing ceramics and metals according to claim 1, characterized in that: It also includes 2-2.5 wt% Al for brazing AlN ceramics; Al does not participate in the solder alloy melting process, but is added directly to the solder joint in the form of foil or powder.

5. The medium-temperature high-activity brazing filler metal for brazing ceramics and metals according to claim 1, characterized in that: It also includes 1.5-2.0 wt% Al to facilitate brazing of Si3N4 or SiC ceramics; Al does not participate in the solder alloy melting process, but is added directly to the solder joint in the form of foil or powder.

6. The medium-temperature high-activity brazing filler metal for brazing ceramics and metals according to claim 1, characterized in that: It also includes 2-4 wt% Ni for brazing ZrO2 ceramics.

7. The medium-temperature high-activity brazing filler metal for brazing ceramics and metals according to claim 1, characterized in that: In the Ti-Zr low-melting-point master alloy, the Zr content is adjusted according to the Ti content to maintain the low-melting-point master alloy state, and the solder will undergo a solid phase transformation at a temperature of 700℃, which is beneficial to the activation of the ceramic surface.

8. The medium-temperature high-activity brazing filler metal for brazing ceramics and metals according to claim 1, characterized in that: In the Ag-Cu eutectic, the Cu content is adjusted according to the Ag content to maintain the eutectic ratio, which is beneficial for the flow and spreading of the solder.

9. A method for preparing a medium-temperature, high-activity brazing filler metal for brazing ceramics and metals, characterized in that, Specifically, the following steps are included: 1) Prepare raw materials: According to the mass percentage ratio, the Cu raw material shall be divided into two parts as follows; 2) Ti and Zr, along with an equal mass of Cu, are pre-melted into an intermediate alloy in an electric arc furnace; the vacuum level is then evacuated to 10 using a vacuum pump. -2 Below Pa, Ar gas is then introduced into the electric arc melting system until the differential pressure gauge reading is -0.05 MPa, and the raw materials are melted using a current specification of 300-400 A; 3) Repeated melting: Repeat 5-7 times until a homogenized CuTiZr intermediate alloy billet is obtained; Prepare each raw material separately and place them into the vacuum melting furnace; 4) Slicing and polishing: Use wire cutting to cut the intermediate alloy billet into thin slices with a thickness of 0.2mm, and then use organic solvent to clean the slices to remove surface impurities and oil stains; 5) Place all metals into the suspension furnace. If Ni or Si is present, Ni is added in flake form and Si is added in powder form. Smelting under Ar gas protection; 6) Cast into slabs and use hot acid washing to remove surface oxides and impurities; 7) Hot rolling to form a thin strip with a thickness of 0.08 to 0.2 mm, trimming the rough edges, hot pickling, washing with water, vacuum drying, and packaging for later use.

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