NiCrTa high-temperature brazing filler metal and application of NiCrTa high-temperature brazing filler metal in brazing ultrahigh-temperature ceramic and refractory metal

Abstract

The invention discloses NiCrTa high-temperature brazing filler metal and application of the NiCrTa high-temperature brazing filler metal in brazing of ultrahigh-temperature ceramics and refractory metals, and the specific implementation steps are as follows: (1) preparing NiCrTa (Ni: Cr: Ta = (35-55): (30-40): (5-25) (at.%)) high-temperature brazing filler metal by adopting an electric arc melting method, then cutting into NiCrTa foils, and then polishing and cleaning the NiCrTa foils; (2) polishing the to-be-welded surfaces of the TaC-TaSi2 ceramic and the metal tantalum, and cleaning and drying the to-be-welded surfaces of the TaC-TaSi2 ceramic and the metal tantalum; (3) the NiCrTa foil is placed between the TaC-TaSi2 ceramic and the metal tantalum; and (4) the assembly part is put into a vacuum brazing furnace to be brazed. The stable connection of the TaC-TaSi2 ceramic and the metal tantalum is realized through the NiCrTa high-temperature brazing filler metal, and a compact joint structure is obtained. The joint shows excellent mechanical properties at room temperature and high temperature, and provides powerful support for engineering application of the material in the aerospace field.

Description

Technical Field

[0001] The present invention belongs to the technical field of vacuum brazing, and particularly relates to a NiCrTa high-temperature brazing filler metal and its application in brazing ultra-high temperature ceramics and refractory metals. Background Art

[0002] In recent years, hypersonic aircraft have become the research and development focus in the aerospace fields of many countries. With the rapid development of advanced aerospace aircraft technology, the flight speed and the thrust-to-weight ratio of engines have been continuously improved, and the working environment faced by the aircraft has become more severe. Against this background, ultra-high temperature ceramic materials are regarded as potential thermal protection materials in extreme aerodynamic environments due to their extremely high melting points and excellent high-temperature properties. Among them, tantalum carbide (TaC) ceramic is one of the substances with the highest known melting points at present, and has advantages such as high Young's modulus, high hardness, good chemical stability, and excellent high-temperature properties. In addition, TaSi 2 improves the density, strength, toughness, and oxidation resistance of TaC-based ceramics. TaC-TaSi 2 composite ceramics have excellent comprehensive properties and are expected to be used as thermal protection systems for hypersonic aircraft and components of scramjet engines. However, the intrinsic brittleness of ceramic materials has always restricted the engineering application of TaC-based ultra-high temperature ceramics.

[0003] Tantalum and its alloys have characteristics such as high-temperature stability, corrosion resistance, and biocompatibility, and can be used in professional fields such as aerospace and biomedicine. If TaC-based ultra-high temperature ceramics are combined with refractory metal Ta and its alloys, the performance advantages of ultra-high temperature ceramics and refractory metal base materials can be fully utilized to obtain a composite material with excellent comprehensive properties. Therefore, realizing the reliable connection of TaC-TaSi 2 ceramics and tantalum alloys is beneficial to the engineering application of such materials in the aerospace field, and has broad application prospects and important practical significance. Summary of the Invention

[0004] The purpose of the present invention is to provide a NiCrTa high-temperature brazing filler metal and its application in brazing ultra-high temperature ceramics and refractory metals. It can realize the reliable connection of TaC-TaSi 2 ceramics and tantalum alloys, and obtain a TaC-TaSi 2 ceramic and metal connection joint with good high-temperature performance.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions: A method for brazing ultra-high temperature ceramics and refractory metals, comprising the following steps: Step 1: Prepare a NiCrTa high-temperature brazing filler metal by an arc melting method, cut the NiCrTa high-temperature brazing filler metal into the form of NiCrTa foil and perform grinding and cleaning treatment; Step 2: TaC-TaSi 2 The surfaces to be welded of the TaC-TaSi ceramic and the tantalum alloy are polished with a diamond grinding wheel and water sandpaper respectively. After polishing, the workpieces to be welded are ultrasonically cleaned and dried; Step 3: Place the NiCrTa foil between the TaC-TaSi 2 ceramic and the tantalum alloy to complete the assembly; Step 4: Put the obtained assembled parts into a vacuum brazing furnace for brazing.

[0006] Furthermore, in step 1, the atomic percentage of metallic nickel in the NiCrTa high-temperature brazing filler metal is 35-55%, the atomic percentage of metallic chromium is 30-40%, and the atomic percentage of metallic tantalum is 5-25%.

[0007] Furthermore, the arc melting method in step 1 is carried out under the protection of inert gas. Weigh Ni powder, Cr powder and Ta powder according to the mass percentage, put the materials into a vacuum melting and spinning ribbon furnace for melting. During the melting process, the maximum loading current of the arc does not exceed 500 A. After solidification, remelting is carried out, and the melting process is repeated at least ten times.

[0008] Furthermore, the thickness of the NiCrTa foil is 0.1 mm - 0.5 mm.

[0009] Furthermore, the polishing in step 1 uses water sandpaper for polishing. The steps include polishing successively with 400#, 800#, 1200# and 2000# water sandpaper. The time for ultrasonic cleaning is 5 - 20 min, and the cleaning agent used for ultrasonic cleaning is anhydrous ethanol or acetone.

[0010] Furthermore, the diamond grinding wheel and water sandpaper polishing steps in step 2 include using 400#, 1000# and 2000# diamond grinding wheels to polish the surface to be welded of the TaC-TaSi 2 ceramic, and using 400#, 600#, 800#, 1000#, 1500# and 2000# water sandpaper to polish the surface to be welded of the metallic tantalum. The time for ultrasonic cleaning is 5 - 20 min, and the cleaning agent used for ultrasonic cleaning is anhydrous ethanol or acetone.

[0011] Furthermore, the brazing process in step 4 is as follows: Heat up at a heating rate of 15 - 30 °C / min to 900 - 1100 °C and hold for 30 - 60 min, then heat up at a heating rate of 5 - 15 °C / min to 1300 - 1400 °C and hold for 20 - 40 min to form a reliable brazed joint. Cool down at a cooling rate of 3 - 10 °C / min to 400 - 500 °C, and finally cool down with the furnace to 20 - 25 °C. The vacuum degree during the holding process is less than or equal to 4×10 -2 Pa.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: The use of NiCrTa high-temperature filler metal in the present invention can achieve reliable connection between TaC-TaSi 2 ceramics and tantalum-based refractory alloys, and the joints have good high-temperature performance. The NiCrTa active filler metal designed in the present invention has good wettability to both TaC-based ceramics and tantalum alloys. The Ta element in the filler metal used in the present invention improves the compatibility between the filler metal and the base metal, and alleviates the residual stress caused by the difference in thermal expansion coefficient between ceramics and metals by reducing the melting point of the Ni-Cr alloy. The Cr element in the filler metal is an active element, which plays a key role in achieving good interfacial bonding between the filler metal and the ceramic base metal. During the brazing process, the Cr element can react with the ceramic main component TaC component to form (Ta,Cr)C, forming a metallurgical connection. The Cr element will also diffuse into the ceramic and react with the TaSi 2 component to form (Cr,Ta)Si 2 and distribute along the TaC grain boundaries, forming a ceramic-metal compound composite structure, further alleviating the problem of joint residual stress. The Ni element in the filler metal has a high affinity with Ta, and diffuses and reacts with metallic Ta during the brazing process to form Ni-Ta compounds, forming a metallurgical connection. The formed Ni-Ta compounds all have relatively high melting points and have good high-temperature application prospects. At the same time, the Cr-based solid solution and Ni-Ta compounds formed in the weld seam all have relatively high melting points, and the high-temperature resistance of the joint is improved. Therefore, the present invention realizes reliable connection between TaC-TaSi 2 ceramics and tantalum-based refractory alloys, and the joints have good high-temperature performance, with broad application prospects and important practical significance. In addition, the method of the present invention is simple to operate, and reliable connection between ceramics and metals can be achieved without any modification treatment on the specimens to be welded. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a flowchart of the brazing method for TaC-TaSi 2 ceramics and tantalum alloys.

[0014] Figure 2 is a scanning electron micrograph of the NiCrTa filler metal used in Example 1.

[0015] Figure 3 is a scanning electron micrograph of the brazed joint of TaC-TaSi 2 ceramics and metallic tantalum obtained in Example 1.

[0016] Figure 4 is a scanning electron micrograph of the joint obtained by using Ti-24Ni(at.%) to connect TaC-TaSi 2 ceramics and metallic Ta. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] To make the content of the present invention easier to understand, the technical solution of the present invention will be further described below in conjunction with specific embodiments, but it does not limit the scope of the present invention.

[0018] Example 1 As Figure 1 shown is the flow chart of the brazing method of TaC-TaSi 2 ceramics and tantalum metal, including the following steps: Step 1: Prepare NiCrTa active brazing filler metal foil. The two surfaces of the obtained NiCrTa foil are polished successively with 400#, 800#, 1200# and 2000# water sandpapers. The thickness of the brazing filler metal foil is 120μm, and the size is 6×6 mm 2 . The polished foil is put into absolute ethanol for ultrasonic cleaning treatment for 10 min; Prepare NiCrTa active brazing filler metal foil by arc melting method, in which the atomic percentages of each element are: Ni: 50%, Cr: 40%, Ta: 10%.

[0019] Convert according to the component ratio into the corresponding mass percentages, and weigh Ni powder, Cr powder and Ta powder according to the mass percentages. Put the materials into a vacuum melting and spinning ribbon furnace for melting. During the melting process, the maximum loading current of the arc does not exceed 500A. To ensure the uniformity of the brazing filler metal composition, remelt it after solidification, and the melting process is repeated ten times.

[0020] As Figure 2 shown is the scanning electron microscope image of the NiCrTa high-temperature brazing filler metal prepared in Example 1. From Figure 2 it can be seen that the 50Ni40Cr10Ta(at.%) alloy is composed of fcc-(Ni)+bcc-(Cr)+Ni 3 Ta phase and massive fcc-(Ni) phase.

[0021] Step 2: Use a wire electrical discharge machining machine to cut TaC-TaSi 2 ceramics and tantalum metal into cubes of 4mm×4mm×4mm and cuboids of 10mm×12mm×2mm respectively. The brazing surfaces of the cut TaC-TaSi 2 ceramics and tantalum metal are polished to 2000# respectively with diamond grinding wheels and water sandpapers. The brazing surface of TaC-TaSi 2 ceramics is polished with 400#, 1000# and 2000# diamond grinding wheels, and the brazing surface of tantalum metal is polished with 400#, 600#, 800#, 1000#, 1500# and 2000# water sandpapers. The polished workpieces to be welded are put into absolute ethanol for ultrasonic cleaning treatment for 10 min and dried; Step 3: Place the cleaned and dried TaC-TaSi 2 ceramics, NiCrTa foil and tantalum metal in sequence to complete the assembly.

[0022] Step 4: Put the assembled fitting into a vacuum brazing furnace, close the furnace door, evacuate the air, and start heating when the vacuum degree reaches 9×10 -3 Pa. The brazing process is as follows: heat at a heating rate of 20°C / min to 1000°C and hold for 30 min, then heat to 1350°C at a heating rate of 10°C / min and hold for 20 min, cool at a cooling rate of 5°C / min to 400°C, and finally cool in the furnace to room temperature to form a reliable brazed joint. The vacuum degree during the holding process is 3.5×10 -2 Pa.

[0023] After brazing, use a scanning electron microscope to observe the microscopic morphology of the joint interface. Figure 3 Figure for the scanning electron microscope of the brazed joint between TaC-TaSi 2 ceramics and tantalum metal obtained in Example 1. The left side is the ceramic base material, and the right side is the metal base material. It can be Figure 3 seen that the structure of the entire welded joint is dense, and a firm and defect-free metallurgical bond can be formed at the connection interface. Region I is the reaction layer of Ni element in the filler metal and tantalum metal to form Ni-Ta compound, forming a metallurgical connection and having a relatively high melting point. In region III, Cr element reacts with TaC component to form (Ta,Cr)C on the ceramic surface, forming a metallurgical connection; Cr element and TaSi 2 component form (Cr,Ta)Si 2 in the ceramic, forming a ceramic-metal compound composite structure to relieve the residual stress problem of the joint. Region II weld forms Cr-based solid solution and Ni-Ta compound, etc., and the reaction products have relatively high melting points. In summary, the formed joint structure is beneficial to the release of joint residual stress and the high-temperature resistance is also improved. Use an electronic universal testing machine to conduct a compression-shear test, and the given loading speed is 0.3 mm / min. After testing, the room-temperature shear strength of the joint reaches 132 MPa; when the test temperature is 600 o °C, the shear strength reaches 91 MPa.

[0024] Comparative Example 1 The difference between this comparative example and the example is that Ti-24Ni (at.%) high-temperature filler metal is used to connect TaC-TaSi 2 ceramics and metal Ta. The brazing process parameters are as follows: heat at a heating rate of 20°C / min to 800°C and hold for 30 min, then heat to 1040°C at a heating rate of 10°C / min and hold for 20 min, cool at a cooling rate of 5°C / min to 400°C, and finally cool in the furnace to room temperature. The vacuum degree during the holding process is 3.5×10 -2Pa, and the remaining steps are the same as those in Example 1. The scanning electron microscope image of the obtained joint is as shown in Figure 4 . On the left is the ceramic base material, and on the right is the metal base material. It can be seen that the reaction layer on the ceramic side is relatively thin, while a β-(Ti,Ta) reaction layer is formed on the metal side. The β-(Ti,Ta) phase will soften at high temperatures and will oxidize to form (Ti,Ta) 2 O, significantly reducing the high-temperature performance of the joint. A compression-shear test was carried out using an electronic universal testing machine. After testing, the room-temperature shear strength of the obtained joint was only 104 MPa.

[0025] In summary, the present invention uses a NiCrTa filler metal for vacuum brazing of TaC-TaSi 2 ceramics and tantalum-based refractory alloys. The obtained joint has a dense structure and good room-temperature and high-temperature mechanical properties. A metallurgical connection is formed between the filler metal and the base material, and the interface bonding is good. Among them, a ceramic-metal compound composite structure is formed by reaction on the ceramic side, relieving the stress concentration problem and improving the welding quality. In addition, high-melting-point compounds are formed in the joint, enabling the joint to meet the requirements of high-temperature service. Finally, a TaC-TaSi 2 ceramic and metal joint with good high-temperature performance is obtained, which has broad application prospects and important practical significance.

[0026] The above embodiments are the preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious substitution without departing from the concept of the technical solution of the present invention is within the protection scope of the present invention.

Claims

1. A method for brazing ultrahigh temperature ceramics and refractory metals, characterized in that: The steps include: Step 1: Prepare NiCrTa high temperature solder by arc melting method, cut NiCrTa high temperature solder into NiCrTa foil and grind and clean it; Step 2: The surfaces to be welded of TaC-TaSi2 ceramic and tantalum alloy are polished with diamond grinding disc and water sandpaper respectively, and the polished parts to be welded are ultrasonically cleaned and dried; Step 3: Place the NiCrTa foil between the TaC-TaSi2 ceramic and the tantalum alloy to complete the assembly; Step 4: Place the obtained assembly into a vacuum brazing furnace for brazing.

2. The method for brazing ultrahigh temperature ceramics and refractory metals according to claim 1, characterized in that: In the NiCrTa high temperature solder in step 1, the atomic percentage of metal nickel is 35-55%, the atomic percentage of metal chromium is 30-40%, and the atomic percentage of metal tantalum is 5-25%.

3. The method for brazing ultrahigh temperature ceramics and refractory metals according to claim 1, characterized in that: The arc melting method described in step 1 is carried out under the protection of inert gas. Ni powder, Cr powder and Ta powder are weighed according to mass percentage, and the materials are placed in a vacuum melting belt furnace for melting. During the melting process, the maximum loading current of the arc does not exceed 500A. After solidification, it is remelted, and the melting process is repeated at least ten times.

4. The method for brazing ultrahigh temperature ceramics and refractory metals according to claim 1, characterized in that: The thickness of the NiCrTa foil is 0.1 mm-0.5 mm.

5. The method for brazing ultrahigh temperature ceramics and refractory metals according to claim 1, characterized in that: The polishing described in step 1 is performed using water sandpaper, and the steps include using 400#, 800#, 1200# and 2000# water sandpaper for polishing in sequence. The ultrasonic cleaning time is 5-20min, and the cleaning agent used for ultrasonic cleaning is anhydrous ethanol or acetone.

6. The method for brazing ultrahigh temperature ceramics and refractory metals according to claim 1, characterized in that: The diamond grinding wheel and water sandpaper polishing step described in step 2 includes polishing the surface to be welded of TaC-TaSi2 ceramics with 400#, 1000# and 2000# diamond grinding wheels, and polishing the surface to be welded of metal tantalum with 400#, 600#, 800#, 1000#, 1500# and 2000# water sandpaper. The ultrasonic cleaning time is 5-20min, and the cleaning agent used for ultrasonic cleaning is anhydrous ethanol or acetone.

7. The method for brazing ultrahigh temperature ceramics and refractory metals according to claim 1, characterized in that: The brazing process in step 4 is as follows: heating to 900-1100°C at a heating rate of 15-30°C / min and keeping warm for 30-60min, then heating to 1300-1400°C at a heating rate of 5-15°C / min and keeping warm for 20-40min to form a reliable brazing joint, cooling to 400-500°C at a cooling rate of 3-10°C / min, and finally cooling to 20-25°C with the furnace.

8. The method for brazing ultrahigh temperature ceramics and refractory metals according to claim 7, characterized in that: The vacuum degree of the heat preservation process is less than or equal to 4×10 -2 Pa.

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