Vacuum brazing method for chromium zirconium copper and stainless steel, brazing joint and application

Abstract

The invention belongs to the technical field of brazing, and particularly discloses a vacuum brazing method for chromium-zirconium-copper and stainless steel, a brazing joint and application, and the method comprises the following steps: cutting chromium-zirconium-copper and stainless steel base materials into round bars: preparing a Ni coating on the surface of the stainless steel after the stainless steel base material is pretreated; the Ag15CuP brazing filler metal is preset on a to-be-welded interface and placed in a vacuum brazing furnace, vacuumizing and heating are conducted, and then the Ag15CuP brazing filler metal is cooled to the room temperature; and low-temperature stress relief annealing is conducted on a brazed finished product, and furnace cooling is conducted to the room temperature. According to the vacuum brazing method for the chromium-zirconium-copper and the stainless steel, the brazing joint and the application, the novel silver-saving brazing filler metal Ag15CuP is selected as the brazing filler metal, efficient and reliable connection of the chromium-zirconium-copper and the stainless steel is achieved through the synergistic process scheme of stainless steel surface nickel plating modification, gradient temperature control vacuum brazing and low-temperature annealing, and the service life of the chromium-zirconium-copper and the stainless steel is prolonged. The obtained brazed joint is excellent in high-temperature and low-temperature cycle resistance, and can meet the service requirements of key components such as an airspace engine combustion chamber and a heat exchanger.

Description

Vacuum brazing method for chromium-zirconium-copper and stainless steel, brazed joints and applications Technical Field

[0001] This invention relates to the field of brazing technology, and in particular to a vacuum brazing method for chromium-zirconium-copper and stainless steel, as well as brazed joints and applications. Background Technology

[0002] Chromium-zirconium-copper alloys, due to their excellent thermal conductivity, electrical conductivity, and high-temperature strength, and stainless steel, due to its good corrosion resistance and structural stability, are widely used in high-end equipment such as aerospace engine combustion chambers and heat exchangers for dissimilar metal connections. Brazing is a key technology for achieving reliable connections between these dissimilar metals. Traditional processes often use high-silver brazing filler metals (such as Ag...). 72 Cu 28 Although it can achieve good joint performance, the scarcity and high cost of silver resources limit its large-scale application.

[0003] Ag15CuP brazing filler metal, a typical silver-saving filler metal, has a silver content of only 1 / 4 to 1 / 5 that of traditional high-silver filler metals, resulting in a significant cost advantage. However, its direct application to brazing chromium-zirconium copper and stainless steel faces three major technical bottlenecks: First, the filler metal has poor wettability on the stainless steel surface, easily leading to defects such as incomplete welding and inadequate filler seam filling. Second, the Fe and Cr elements in stainless steel readily react with the P elements in the filler metal, forming brittle intermetallic compounds such as Fe3P and Cr3P, which severely reduce the toughness and mechanical properties of the joint. Third, the thermal expansion coefficients of chromium-zirconium copper and stainless steel differ significantly (the thermal expansion coefficient of chromium-zirconium copper is approximately 18 × 10⁻⁶). -6 At / ℃, 304 stainless steel is approximately 11×10⁻⁶. -6 (°C) Residual stress concentration is easily generated during the brazing cooling process, which increases the risk of joint cracking.

[0004] Existing improvement solutions mainly focus on adjusting the solder composition, such as adding alloying elements like Ni and Sn to improve wettability, but they fail to address the fundamental problem of brittle phase formation from the perspective of interfacial compatibility. Some solutions use flux-assisted brazing, which can improve wettability, but flux residue can easily cause joint corrosion, affecting service reliability. Therefore, developing a process that leverages the synergistic effect of interfacial modification and process optimization to solve the bottleneck of dissimilar bonding with Ag15CuP solder, achieving a balance between low cost and high performance, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a vacuum brazing method, brazed joint, and application for chromium-zirconium-copper and stainless steel. By modifying the stainless steel surface with nickel plating, and combining process optimizations such as fine-tuning of the Ag15CuP brazing filler metal composition, gradient temperature control, and segmented cooling, the invention solves the problems of poor wettability, brittle phase formation at the interface, and insufficient mechanical properties when brazing chromium-zirconium-copper and stainless steel with Ag15CuP brazing filler metal. This achieves a balance between low cost and high performance in dissimilar metal joining, meeting the service requirements of high thermal conductivity components in aerospace.

[0006] To achieve the above objectives, this invention provides a vacuum brazing method for chromium zirconium copper and stainless steel, as well as the brazed joint and its application, comprising the following steps: Step 1: Cut the chromium zirconium copper and stainless steel base materials into round bars of the required size, and pre-treat them for later use; Step 2: After pre-treating the stainless steel base material, prepare a Ni coating with a thickness of 10µm on the stainless steel surface using a chemical nickel plating process; Step 3: Place Ag15CuP brazing filler metal on the interface between the nickel-plated stainless steel and the chromium zirconium copper to be brazed, place the assembly in a vacuum brazing furnace, evacuate and heat it to 800~900℃, hold it at that temperature for 10min, and then cool it to room temperature; Step 4: Perform low-temperature stress-relief annealing on the brazed finished product at a temperature of 280~320℃, hold it at that temperature for 1.5~2.5h, and then cool it to room temperature with the furnace.

[0007] Preferably, in step 1, the chromium zirconium copper is grade C18150, the stainless steel is 304, and it is mechanically polished to Ra=0.03~0.05μm; after ultrasonic cleaning with acetone for 15~20min and ultrasonic cleaning with dilute phosphoric acid solution for 10~15min, it is dried.

[0008] Preferably, in step 2, the stainless steel base material is mechanically polished to Ra=0.03~0.05μm, ultrasonically cleaned with acetone and dilute hydrochloric acid in sequence, and then dried; the surface roughness Ra of the Ni coating obtained by electroless nickel plating is ≤0.06μm.

[0009] Preferably, in step 3, the Ag15CuP solder is a foil-shaped solder, and the base material and solder are fixed using a tooling fixture after assembly; vacuum is then applied to 3×10⁻⁶. -4 ~8×10 -4 Pa; heating rate from room temperature to 300℃: 4℃ / min; heating rate from 300℃ to 600℃: 7℃ / min; heating rate from 600℃ to peak temperature: 2~3℃ / min; peak temperature: 800~900℃; vacuum level maintained ≤5×10 during heat preservation. -4 Pa; after reaching the peak temperature, cool to 500°C at a rate of 8~10°C / min, and then cool to room temperature at a rate of 12~15°C / min.

[0010] Preferably, the tooling fixture uses a niobium-tungsten alloy plate as the clamping plate and is fixed with a stainless steel 316 screw.

[0011] Preferably, the cooling process is as follows: heat up to 300°C, hold for 10 minutes, then heat up to the brazing temperature of 850°C, hold for 10 minutes, and finally air cool to 450°C and hold for 2 hours, followed by air cooling to room temperature.

[0012] Preferably, the composition of the Ag15CuP solder by mass percentage is: Ag 14.5%~15.5%, P 4.7%~5.3%, with Cu as the balance.

[0013] The present invention also provides a vacuum brazing joint for chromium zirconium copper and stainless steel, which is obtained by the above-described vacuum brazing method for chromium zirconium copper and stainless steel.

[0014] This invention also provides applications for vacuum brazing joints of chromium zirconium copper and stainless steel, which are used in the fabrication of aerospace engine combustion chambers and heat exchangers.

[0015] The advantages and beneficial effects of the above-mentioned vacuum brazing method for chromium zirconium copper and stainless steel, as well as the brazed joint and its application, are as follows: 1. The present invention uses a nickel plating process on the surface of stainless steel, which allows the brazing filler metal to be well spread on the surface of stainless steel, thus greatly improving the brazing effect.

[0016] 2. This invention reduces workpiece thermal deformation and ensures uniform wetting of the brazing filler metal and consistent joint quality by gradient control of the temperature of the vacuum brazing furnace. It is suitable for brazing precision parts such as stainless steel, high-temperature alloys, and dissimilar metals.

[0017] 3. The core purpose of this invention is to reduce deformation, prevent cracking, and stabilize dimensions by annealing the product. Vacuum brazing can reduce the residual stress of the joint by 30% to 80%.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 is a schematic diagram of the tooling fixture holding the base material; Figure 2 is a metallographic observation diagram of sample 1 in experimental group.

[0020] In the attached diagram, 1 represents the base material; 2 represents the screw; and 3 represents the clamping plate. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0023] The following examples are not intended to limit the invention, but are only for illustration. Unless otherwise specified, the experimental methods used in the following examples are generally performed under conventional conditions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0024] Example 1 describes a vacuum brazing method for chromium zirconium copper and stainless steel, as well as the brazed joint and its application, including the following steps: Step 1: Cut the chromium zirconium copper and stainless steel base material 1 into round bars of the required size and pre-treat them for later use: The chromium zirconium copper is grade C18150 and the stainless steel is 304; the stainless steel base material 1 is cut into round bars with a diameter of 16 mm and a length of 50 mm, and mechanically polished to Ra=0.03~0.05 μm; after ultrasonic cleaning with acetone for 15~20 min and ultrasonic cleaning with dilute phosphoric acid solution for 10~15 min, it is dried.

[0025] Step 2: After pretreatment of stainless steel base material 1, a Ni coating with a thickness of 10 μm is prepared on the stainless steel surface using chemical nickel plating process: Stainless steel base material 1 is mechanically polished to Ra=0.03~0.05μm, and then ultrasonically cleaned with acetone and dilute hydrochloric acid in sequence before drying; the surface roughness Ra of the Ni coating obtained by chemical nickel plating is ≤0.06μm.

[0026] Step 3: Pre-place Ag15CuP brazing filler metal on the interface between nickel-plated stainless steel and chromium-zirconium-copper alloy to be brazed. Place the assembly in a vacuum brazing furnace, evacuate and heat to 800~900℃, hold for 10 minutes, then cool to room temperature. The Ag15CuP brazing filler metal is in foil form, and its composition by mass percentage is: Ag 14.5%~15.5%, P 4.7%~5.3%, with Cu as the balance. After assembling the base material 1 and the brazing filler metal, fix them with a tooling fixture. The tooling fixture uses a niobium-tungsten alloy plate as the clamping plate 3 and is fixed with a stainless steel 316 screw 2. Evacuate to 3×10 -4 ~8×10 -4 Pa; heating rate from room temperature to 300℃: 4℃ / min; heating rate from 300 to 600℃: 7℃ / min; heating rate from 600℃ to peak temperature: 2~3℃ / min; peak temperature: 800~900℃; vacuum degree maintained at ≤5×10-4Pa during heat preservation; cooling to 500℃ at a rate of 8~10℃ / min after peak temperature, and then cooling to room temperature at a rate of 12~15℃ / min.

[0027] Step 4: Perform low-temperature stress-relief annealing on the brazed product at a temperature of 280~320℃ for 1.5~2.5h, and then cool it to room temperature in the furnace.

[0028] Example 2 I. Sample Pretreatment 1. Cleaning the outer circular surface: Use 1000#~1500# water-resistant sandpaper to evenly grind the outer circular surface along the axial direction of the stainless steel base rod to remove surface oxide scale, scratches, and machining burrs. After grinding, use compressed air (pressure 0.4~0.6MPa) to blow away residual grinding debris and prevent particulate impurities from entering the joint gap.

[0029] 2. Chemical Cleaning (thoroughly removes oil and oxide film): Prepare an alkaline degreasing solution: Sodium hydroxide (NaOH) 50-80 g / L + Sodium carbonate (Na2CO3) 30-50 g / L + Trisodium phosphate (Na3PO4•12H2O) 20-40 g / L + Nonionic surfactant (such as OP-10) 5-10 mL / L. Maintain the water temperature at 60-80℃. Completely immerse the round rod in the degreasing solution for 10-15 minutes, gently turning it every 3 minutes to ensure even degreasing of the end face and outer diameter (oil will severely affect solder wetting, leading to "cold solder joints"). After removal, rinse with running deionized water for 3-5 minutes to thoroughly remove any residual alkaline solution (to prevent subsequent corrosion).

[0030] 3. Oxide film removal: Oxide film removal from stainless steel round bars.

[0031] Prepare the pickling solution: 10-15 vol% nitric acid (HNO3, 68%) + 3-5 vol% hydrofluoric acid (HF, 40%) + 80-87 vol% deionized water. Immerse the bar at room temperature for 5-8 minutes. During the pickling process, gently shake the bar 2-3 times to ensure that the oxide film (such as Cr2O3) on the end face is completely removed. Remove the bar immediately after the surface turns a uniform silver-gray color.

[0032] Rinse quickly with deionized water for 5 minutes, then neutralize with 1-2 vol% sodium carbonate solution for 1-2 minutes, and finally rinse again with deionized water (residual hydrofluoric acid will corrode the substrate).

[0033] Removal of oxide film from chromium-zirconium-copper round bars.

[0034] Prepare a special pickling solution for copper: 20~30 vol% phosphoric acid (H3PO4, 85%) + 5~10 vol% sulfuric acid (H2SO4, 98%) + 60~75 vol% deionized water, water temperature 40~50℃, soak for 3~5 minutes.

[0035] After observing the dissolution of the surface oxide film (CuO, ZrO2) and the appearance of a bright copper color, remove it and rinse it with running deionized water for 4-6 minutes (to avoid acid residue causing discoloration of the copper).

[0036] 4. Rinsing and Activation Treatment: Both types of round bars require a final rinsing: Immerse in ultrapure water (conductivity ≤10μS / cm) for 3 minutes, stirring gently during the process to remove residual ionic impurities. Optional Activation Treatment: For workpieces stored for more than 2 hours, immerse in 5 vol% dilute hydrochloric acid (HCl) at room temperature for 30 seconds before brazing to quickly remove the extremely thin oxide film formed after rinsing. Rinse thoroughly with ultrapure water immediately after removal.

[0037] 5. Drying Process: The cleaned round bars must be thoroughly dried to prevent moisture evaporation from causing bubbles during vacuum brazing, which could affect the vacuum level and joint quality. Drying process: Place in an oven and pre-dry at 80~100℃ for 15 minutes, then raise the temperature to 120~150℃ and hold for 30 minutes (for chromium zirconium copper, which has low water absorption, the time can be shortened to 20 minutes). After drying, allow to cool naturally to room temperature. During the cooling process, avoid contact with oil and dust (they can be placed in a clean, dry, sealed box or a special tray).

[0038] 6. Stainless steel nickel plating treatment: Electrochemical nickel plating treatment is performed on the stainless steel end face, with a plating thickness of 10um.

[0039] II. Sample Assembly 1. Place the sample on a clean workbench (with clean filter paper laid on it), align and fit the brazed ends of the two round rods together, ensuring that the coaxiality of the axis is ≤0.03mm, as shown in Figure 1.

[0040] 2. Placing the solder: Use foil-shaped silver-saving solder (Ag15CuP), cut into Φ16mm circular foil sheets (0.01mm thick), and place them between the two end faces (centered to avoid displacement).

[0041] Use a stainless steel positioning sleeve with an inner wall roughness Ra≤0.8μm (Φ16mm×5~8mm) to fit on the outside of the joint, or use high-temperature resistant molybdenum wire (0.2~0.3mm in diameter) to wrap around the joint 2~3 times to fix it, so as to prevent misalignment during brazing.

[0042] 3. The tooling fixture assembly is shown in Figure 1. Simple tooling is used for clamping to prevent misalignment during brazing.

[0043] III. Sample Brazing 1. Before loading the furnace, check the furnace body's sealing performance (e.g., whether the sealing rings are aged, whether the furnace door closes tightly), and replace any damaged sealing rings. Start the mechanical pump to pre-evacuate the furnace to ≤1×10 -2 mbar for 5 minutes to expel some air and moisture from the furnace, reducing subsequent vacuuming time.

[0044] 2. Place the sample and tooling together into the brazing furnace and close the furnace door.

[0045] IV. Gradient Temperature Controlled Vacuum Brazing Process: Optimizing vacuum brazing furnace parameters is crucial for ensuring joint quality. A process mode of "gradient heating - precise heat preservation - segmented cooling" is adopted: 1. Vacuum Control: Start the mechanical pump to pre-evacuate to ≤1×10⁻⁶. -2 mbar, continuously for 5 minutes to remove air and moisture from the furnace, then evacuate to 3×10 -4 ~8×10 -4 Pa, maintaining a vacuum degree ≤5×10 during insulation. -4 Pa, to avoid oxidation of the base material 1 and the brazing filler metal during the brazing process.

[0046] 2. Gradient heating: Heating rate from room temperature to 300℃ is 4℃ / min (slow heating to remove residual moisture); heating rate from 300 to 600℃ is 7℃ / min (rapid heating to shorten the process cycle); heating rate from 600℃ to the peak temperature (800~900℃) is 2~3℃ / min (slow heating to ensure uniform temperature between the base material 1 and the brazing filler metal, and to avoid thermal stress).

[0047] 3. Heat preservation and cooling: Hold the peak temperature for 10 minutes to ensure that the brazing filler metal is fully melted, wetted and metallurgically bonded to the base material 1; after the heat preservation is completed, cool to 500℃ at a rate of 8~10℃ / min (slow cooling reduces residual stress), and then cool to room temperature at a rate of 12~15℃ / min (rapid cooling inhibits the growth of brittle phases).

[0048] Example 3 Performance test.

[0049] 1. After the experimental products were produced, standard tensile test bars were prepared for each round bar. Four standard tensile tests were performed for each group of experiments, and the average value was taken as the final tensile result. The tensile properties of the obtained products are shown in Table 1.

[0050] Table 1 Tensile property test results

[0051] Experimental group 1 was brazed according to the brazing process method of Example 2. Metallographic observation of the resulting product (as shown in Figure 2) revealed that the brazed joint structure was a typical solidified structure of silver-copper eutectic brazing filler metal, with no obvious defects such as porosity or cracks. This indicates that the wetting and filling effect of the brazing filler metal was good during the brazing process, resulting in a high-quality joint. Subsequent tensile testing using standard tensile test bars yielded a tensile strength of 242 MPa, further demonstrating that the brazing process fully meets the requirements for joining these two materials.

[0052] Experimental Group 1: Heating to 300℃ and holding for 10 min → Heating to 850℃ and holding for 10 min → Direct furnace cooling to room temperature; The resulting brazed joint had no obvious pores or cracks, and the shear strength reached 242 MPa, indicating good brazing effect.

[0053] Control group 2: Heating to 300℃ and holding for 10 min → Heating to 850℃ and holding for 10 min → Air cooling to 450℃ and holding for 2 h → Air cooling to room temperature; The tensile strength of the resulting joint was significantly improved, which is the optimal cooling regime and can be applied to actual production.

[0054] Control group 3: Heating to 300℃ and holding for 10 min → heating to 850℃ and holding for 10 min → furnace cooling to 450℃ and holding for 2 h → furnace cooling to room temperature; The tensile strength and yield strength of the resulting joints were not significantly improved, and the effect on performance optimization was small.

[0055] 2. Equipment and methods for testing the weld tightness of the product: A helium mass spectrometer leak detector (accuracy up to 1×10⁻⁶) from Beijing Zhongke Keyi Co., Ltd. was used. -11 (meeting ultra-high vacuum leak detection requirements, mbar•L / s), the brazed joint was subjected to negative pressure helium mass spectrometry leak detection. The brazed joint was sealed as a test chamber and evacuated to 1×10 mbar•L / s. -5 After Pa, high-purity helium (99.999%) is introduced, and external helium leakage signals are detected. The detection is carried out continuously for 30 minutes, and the leakage rate value is recorded. Each group of samples is tested 5 times and the average value is taken.

[0056] Test Results and Judgment: The helium mass spectrometry leakage rate of the brazed joints of this invention was found to be within the range of 1.2 × 10⁻⁶. -10 ~3.5×10 -10 Within the mbar•L / s range, no samples exceeded the upper limit. This indicator meets the aerospace high-sealing component leak detection standards (the aerospace industry requires ≤1×10⁻⁶ airtightness for engine combustion chambers and heat exchangers). -9 The test result (mbar·L / s) proves that the metallurgical bond of the joint is dense, with no micropores, microcracks or other leakage channels, and the sealing performance meets the service requirements of key aerospace components.

[0057] 3. High-temperature cycling experiments were conducted using a high-temperature box-type resistance furnace (temperature control accuracy ±1℃, meeting the precise temperature control requirements for 600℃ high-temperature cycling) paired with an electronic universal testing machine (accuracy class 0.5, conforming to the mechanical property testing standards for brazed joints). High-temperature cycling and subsequent strength testing experiments were performed on the brazed joints. The brazed joints were processed into standard tensile specimens and placed in the high-temperature box-type resistance furnace for 600℃ × 50 cycles. After cycling, the specimens were cooled to room temperature and tensile strength was tested on the electronic universal testing machine. The retention rate was calculated by the ratio of the tensile strength after cycling to the original tensile strength. Each group of specimens was tested in parallel for 5 times, and the average value was taken as the final test result, as shown in Table 2.

[0058] Table 2 Test Results

[0059] The cycle parameters were set strictly in accordance with the thermal fatigue test specifications for high-temperature components in aerospace. The single cycle process was as follows: the temperature was increased from room temperature to 600℃ at a rate of 10℃ / min, held for 30 minutes to ensure uniform temperature of the joint, and then cooled to room temperature at a rate of 8℃ / min. The temperature was held at room temperature for 20 minutes to release instantaneous stress. This is one complete high-temperature cycle. A total of 50 cycles were completed. The temperature inside the furnace was monitored in real time throughout the process to avoid temperature drift affecting the experimental results.

[0060] Testing revealed that the chromium-zirconium copper and stainless steel brazed joints prepared by the process of this invention retained a tensile strength of 90.6% to 94.8% after 50 cycles at 600℃. All test results were ≥90%, and the joints showed no macroscopic cracking, interface peeling, or brazing seam detachment after the cycles. Therefore, this indicator was determined to meet the requirements set by the invention.

[0061] The 5-10μm Ni coating on the stainless steel surface eliminates the obstacle of the oxide film on the stainless steel surface to the wetting of the brazing filler metal. The Ag15CuP brazing filler metal achieves full filling of the brazing seam under gradient temperature control. Low-temperature stress-relief annealing eliminates the micro gaps in the brazing seam. The synergistic effect of the three factors makes the brazing seam density reach more than 99.9%, which supports the realization of ultra-high airtightness from the perspective of process principle.

[0062] Therefore, the present invention adopts the above-mentioned vacuum brazing method and brazed joint for chromium zirconium copper and stainless steel, and achieves efficient and reliable connection between the two through the synergistic process of "stainless steel surface nickel plating modification - gradient temperature controlled vacuum brazing - low temperature annealing".

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A vacuum brazing method for chromium-zirconium-copper and stainless steel, characterized in that, The process includes the following steps: Step 1: Cut the chromium zirconium copper and stainless steel base materials into round bars of the required size, and pre-treat them for later use; Step 2: After pre-treating the stainless steel base material, prepare a 10μm thick Ni coating on the stainless steel surface using a chemical nickel plating process; Step 3: Place Ag15CuP brazing filler metal on the interface between the nickel-plated stainless steel and the chromium zirconium copper to be brazed, place the assembly in a vacuum brazing furnace, evacuate and heat it to 800~900℃, hold it for 10min, and then cool it to room temperature; Step 4: Perform low-temperature stress-relief annealing on the brazed finished product at a temperature of 450℃, hold it for 1.5~2.5h, and then cool it to room temperature with the furnace.

2. The vacuum brazing method for chromium-zirconium copper and stainless steel according to claim 1, characterized in that: In step 1, the chromium zirconium copper is grade C18150, the stainless steel is 304, and it is mechanically polished to Ra=0.03~0.05μm; After ultrasonic cleaning with acetone for 15-20 minutes and ultrasonic cleaning with dilute phosphoric acid solution for 10-15 minutes, the product is dried.

3. The vacuum brazing method for chromium-zirconium copper and stainless steel according to claim 1, characterized in that: In step 2, the stainless steel base material is mechanically polished to Ra=0.03~0.05μm, then ultrasonically cleaned with acetone and dilute hydrochloric acid in sequence, and then dried; the surface roughness Ra of the Ni coating obtained by electroless nickel plating is ≤0.06μm.

4. The vacuum brazing method for chromium-zirconium copper and stainless steel according to claim 1, characterized in that: In step 3, the Ag15CuP solder is in foil form. After the base material and the solder are assembled, they are fixed with tooling fixtures; vacuum is then applied to 3×10⁻⁶. -4 ~8×10 - 4 Pa; heating rate from room temperature to 300℃: 4℃ / min; heating rate from 300℃ to 600℃: 7℃ / min; heating rate from 600℃ to peak temperature: 2~3℃ / min; peak temperature: 800~900℃; vacuum level maintained ≤5×10 during heat preservation. -4 Pa; after reaching the peak temperature, cool to 500°C at a rate of 8~10°C / min, and then cool to room temperature at a rate of 12~15°C / min.

5. The vacuum brazing method for chromium-zirconium copper and stainless steel according to claim 4, characterized in that: The tooling fixture uses a niobium-tungsten alloy plate as the clamping plate and is fixed with a stainless steel 316 screw.

6. The vacuum brazing method for chromium-zirconium copper and stainless steel according to claim 4, characterized in that: The cooling process is as follows: heat up to 300℃, hold for 10 minutes, then heat up to the brazing temperature of 850℃, hold for 10 minutes, and finally air cool to 450℃ and hold for 2 hours, followed by air cooling to room temperature.

7. The vacuum brazing method for chromium-zirconium copper and stainless steel according to claim 1, characterized in that: The composition of the Ag15CuP solder, by mass percentage, is: Ag 14.5%~15.5%, P 4.7%~5.3%, with Cu as the balance.

8. A vacuum brazing joint for chromium-zirconium-copper and stainless steel, characterized in that: It is obtained by the vacuum brazing method for chromium zirconium copper and stainless steel as described in any one of claims 1-7.

9. The application of the vacuum brazing joint for chromium-zirconium-copper and stainless steel according to claim 8, characterized in that: Welded joints are used in the fabrication of aerospace engine combustion chambers and heat exchangers.

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