Natural law selection for ceramic composite brazing high-entropy filler metal and preparation method

Abstract

The application discloses a preparation method of a high-entropy brazing filler metal for ceramic composite brazing, and comprises the following steps: (1) selecting elements, selecting high-purity materials, mixing and smelting; (2) performing metallographic test analysis, observing the structure and morphology, selecting a maximum single-phase region, and determining the elements in the region and the corresponding atomic percentage; (3) selecting high-purity materials, mixing and smelting; (4) performing metallographic test analysis, observing the structure; if the structure and component distribution are uniform, the preparation is completed; if the structure and component distribution are not uniform, the element composition of the maximum single-phase region is screened out, the elements in the region and the corresponding atomic percentage are determined, steps (2) and (3) are repeated until the structure and component distribution are uniform, and the preparation is completed. The high-entropy brazing filler metal obtained through the method is more suitable for homogenous or heterogeneous brazing of light-weight high-temperature-resistant ceramic matrix composites.

Description

Technical Field

[0001] This invention relates to the field of heterogeneous brazing technology for ceramic matrix composites, and more specifically to a natural method for selecting high-entropy brazing filler metals for brazing ceramic composites and a method for preparing them. Background Technology

[0002] With the increasing demands for lightweight, high operating temperature, and long service life in high-temperature environments, lightweight high-temperature resistant ceramic matrix composites have become an inevitable choice for the next generation of high-performance, high thrust-to-weight ratio aero engines.

[0003] Brazing is a key technology for achieving high-quality connections between lightweight, high-temperature resistant ceramic matrix composites and high-temperature alloys in hot-end components of aero-engines. However, due to the significant differences in the unique physical properties between ceramic matrix composites and metals, brazed joints of lightweight, high-temperature resistant ceramic matrix composites have long suffered from problems such as low success rate, complex interface structure, low joint strength, and high residual stress, making it difficult to meet the application requirements of lightweight, high-temperature resistant ceramic matrix composites in hot-end components such as exhaust nozzle seals. Therefore, the design and preparation of high-temperature brazing filler metals are prerequisites for effective connections.

[0004] High-entropy alloys are a new type of alloy system. As a brazing filler (a filler material used to form a weld), their unique thermodynamic and kinetic properties, as well as the cocktail effect, play an ideal and extremely important role in suppressing the excessive dissolution of base metal and brazing filler elements, reducing the unrestricted generation and growth of brittle phases at the interface, and improving the solid solution strengthening ability of the joint. They are one of the key brazing fillers for improving the high-temperature strength of brazed joints.

[0005] Extensive theoretical and experimental research has been conducted on high-entropy alloy brazing filler metals. However, the composition of these filler metals is primarily determined through empirical estimation and extensive trial-and-error experiments, as illustrated in invention patents CN 116043091 B, CN 116043091 B, and CN 116043091 B. Invention patent CN 114346346A discloses a method for brazing high-entropy carbide ceramics using a high-entropy alloy, but it does not mention the composition or design method of the high-entropy alloy. Invention patent CN 113182632 B describes the use of a high-entropy alloy AlCoCrFeNix for brazing C / C composite materials, with the high-entropy alloy ratio applied directly according to specifications, but it does not explain the composition design method or rationale.

[0006] Currently, the efficiency of high-entropy alloy design is relatively low, mainly due to the following reasons: First, the complex composition system makes accurate phase diagram calculations difficult; second, due to the low applicability of theoretical basis and empirical predictions to practical applications, most high-entropy alloys exhibit poor compatibility; finally, due to the complexity of element diffusion kinetics and thermodynamics, a huge amount of experimentation is required to achieve effective application, and high-entropy alloys as brazing fillers require high stability to benefit the high strength and high reliability of the entire brazed joint.

[0007] Therefore, how to develop a high-entropy alloy brazing filler metal suitable for brazing lightweight, high-temperature resistant ceramic matrix composites is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] In view of this, the purpose of this invention is to provide a high-entropy brazing filler metal based on the natural selection of elements suitable for brazing lightweight high-temperature resistant ceramic matrix composites, as well as its preparation and application methods. It is mainly used to overcome the problems of low material connection success rate, complex interface structure, low joint strength, and large residual stress, and aims to improve the high-temperature strength and service life of brazed joints.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing a high-entropy brazing filler metal for brazing ceramic composites using a natural selection process, characterized by the following steps:

[0011] (1) Based on the target performance requirements of the brazed joint, select N elements that can meet the target performance or are related to the target performance, select high-purity materials of the corresponding elements, and adjust, mix, and smelt them in equal atomic ratios to obtain N-element high-entropy alloys.

[0012] (2) Metallographic analysis of N-element high-entropy alloy was performed, and the microstructure and morphology of N-element high-entropy alloy were observed by scanning electron microscopy. The largest single-phase region inherited from the natural mixing of elements was selected and measured by electron energy spectrometer to determine the element and its corresponding atomic percentage content in the region.

[0013] (3) Based on the X elements determined by the largest single-phase region, select high-purity materials of the corresponding elements and adjust, mix and smelt them in equal atomic ratios to obtain X-element high-entropy alloys.

[0014] (4) Metallographic analysis of the X-element high-entropy alloy was performed, and the microstructure of the X-element high-entropy alloy was observed using a scanning electron microscope;

[0015] If the structure and composition are uniformly distributed, then the high-entropy brazing filler metal for brazing ceramic composites can be selected using the natural method.

[0016] If the structure and composition are not uniform, the elemental composition of the largest single-phase region of the microstructure formed by smelting is selected and measured by an electron spectrometer to determine the element and its corresponding atomic percentage content in the region. At the same time, steps (2) and (3) are repeated until a Y-element high-entropy alloy with uniform structure and composition is selected, which is the high-entropy brazing filler metal selected by natural method for brazing ceramic composites.

[0017] Furthermore, in step (1) above, the brazed joint is a lightweight high-temperature resistant ceramic matrix composite brazed joint.

[0018] Furthermore, in step (1) above, the target performance includes temperature resistance, corrosion resistance, fatigue resistance, expansion, thermal conductivity, mechanical properties, thermal properties and electrical properties.

[0019] Furthermore, in step (1) above, N≥7.

[0020] Furthermore, in steps (1) and (3) above, the purity of the high-purity material is not less than 99.99%, and the shape is at least one of powder, block and filament; the mixing is mechanical stirring, vibration stirring or magnetic stirring; the melting is vacuum melting or induction melting in an air-isolated and oxygen-free environment, and the melting is repeated no less than 5 times.

[0021] Furthermore, in steps (2) and (4) above, the scanning electron microscope is a field emission electron microscope or a thermal field electron microscope with a resolution of not less than 50,000 times and is equipped with an electron energy spectrometer; the number of the largest single-phase regions is not less than 3, and the area is not less than 1 mm × 1 mm, and the component scanning rate is not less than 25 frames / s.

[0022] Furthermore, in step (3) above, X≤N.

[0023] Furthermore, in step (4) above, Y≤X.

[0024] A high-entropy solder prepared by the above-described method.

[0025] A method for using the high-entropy brazing filler metal prepared by the above method includes the following steps: first, the high-entropy brazing filler metal is made into a foil, then polished, cleaned and dried, and finally stacked in the order of lightweight high-temperature resistant ceramic matrix composite material-foil-high-temperature alloy and brazed.

[0026] Furthermore, the thickness of the aforementioned foil is 30-100 μm; the brazing equipment is a vacuum brazing furnace with an initial vacuum degree of 5 × 10⁻⁶. -3 Heat to 1000-1200℃ below Pa, hold for 5-20 minutes, and maintain a vacuum of 1×10⁻⁶ throughout the process. -2 Below Pa.

[0027] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. This invention utilizes the natural mixing characteristics between elements to minimize the design and guides the search for high-entropy alloy composition based on thermodynamic stability criteria, thereby achieving a stable combination; at the same time, quantitative elemental classification evaluation at the microscale is carried out by exploring the largest single-phase region inherited from the natural mixing between elements.

[0029] 2. This invention uses "natural selection" among metal elements as the core criterion for high-entropy brazing filler metal design. The high-entropy brazing filler metal obtained by this method is more suitable for homogeneous or heterogeneous brazing of lightweight high-temperature resistant ceramic matrix composites.

[0030] 3. This invention takes high-entropy brazing filler metals suitable for brazing lightweight high-temperature resistant ceramic matrix composites as the research object. Based on the periodic table of elements and the influencing factors in the development process of the base material, the composition design is completed, providing the basis and criteria for the selection of components for special high-entropy brazing filler metals.

[0031] 4. The purpose of this invention is to seek a high-entropy brazing filler metal with excellent performance and suitable for gold brazing of lightweight high-temperature resistant ceramic matrix composites within a nearly infinite composition space. Based on the element distribution characteristics of the periodic table and referring to the chemical reaction effects of the base material composition, a mixture of N elements was adopted. Through thermodynamic stability criteria, a high-entropy brazing filler metal with superior performance was "naturally selected", providing a new idea for the screening and design of related materials.

[0032] 5. The method of this invention relies on the original properties of elements to screen the composition of high-entropy alloys and design the proportions, which greatly improves the preparation efficiency and joint performance. At the same time, it avoids the drawbacks of high cost and low efficiency caused by a large number of experimental trials and errors, upgrades the irregularity of previous high-entropy alloy design, and provides a method and design idea for high-entropy alloy composition design. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the preparation method of high-entropy brazing filler metal for ceramic composite brazing using the natural method in Examples 1-2.

[0034] Figure 2 This is a schematic diagram of the "natural selection" of the high-entropy solder in Example 1;

[0035] Figure 3 This is a schematic diagram of the first round of "natural selection" for the high-entropy solder in Example 2;

[0036] Figure 4 This is a schematic diagram of the second round of "natural selection" for the high-entropy solder in Example 2;

[0037] Figure 5The microstructure morphology of joints 1-4 is shown.

[0038] Figure 6 The shear strength of joints 1-4. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] Natural methods are used to select high-entropy brazing filler metals for brazing ceramic composites, such as... Figure 1 As shown, the specific steps include:

[0042] (1) Based on the temperature resistance of the brazed joint of SiCf / SiC composite material and nickel-based high-temperature alloy GH536, according to the elements that can play a strengthening role in nickel-based high-temperature alloy GH536, nine elements "Al, Ti, Co, Nb, Mo, Hf, Ta, W and Re" are selected. The pure wires corresponding to the above nine elements with a purity of not less than 99.99% are selected, and they are mixed by equal atomic ratio, mechanically stirred, and vacuum induction melting is carried out in an oxygen-free environment isolated from air. The melting is repeated 5 times to obtain the nine-element high-entropy alloy.

[0043] (2) Metallographic analysis was performed on the smelted nine-element high-entropy alloy. The microstructure and morphology of the nine-element high-entropy alloy were observed using a field emission electron microscope with a resolution of not less than 50,000x and equipped with an electron spectrometer. The largest single-phase region with uniform microstructure distribution formed naturally during smelting was selected, and measurements were taken within a 1mm × 1mm area in the above region using an electron spectrometer at a composition scanning rate of 20 frames / s. It was found that the largest single-phase region was mainly composed of five elements: Ti, Nb, Mo, Ta, and Re. The compositions were Ti = 11.26 at.%, Nb = 15.01 at.%, Mo = 12.85 at.%, Ta = 12.51 at.%, and Re = 11.84 at.%, respectively. The schematic diagram is shown below. Figure 2 As shown;

[0044] (3) Based on the five elements determined by the largest single-phase region, select the elemental wire with a purity of not less than 99.99% corresponding to the five elements, and mix them with “18Ti24Nb20Mo19Ta19Re”. Mechanically stir and vacuum induction melting is carried out in an oxygen-free environment isolated from air. Repeat the melting 5 times to obtain a five-element high-entropy alloy.

[0045] (4) The smelted pentagonal high-entropy alloy was subjected to metallographic analysis, and the microstructure of the pentagonal high-entropy alloy was observed using a field emission electron microscope with a resolution of not less than 50,000 times and equipped with an electron energy spectrometer. It was found that the microstructure and composition were uniformly distributed, and the high-entropy brazing filler metal selected by natural method for brazing ceramic composites was obtained.

[0046] Example 2

[0047] Natural methods are used to select high-entropy brazing filler metals for brazing ceramic composites, such as... Figure 1 As shown, the specific steps include:

[0048] (1) Based on the brazing reaction and temperature resistance of the joint of nickel-based high-temperature alloy GH536, twelve elements "Ti, V, Fe, Co, Cu, Zr, Nb, Hf, Ta, Cr, Mo and W" were selected. Elemental wires with a purity of not less than 99.99% corresponding to the above twelve elements were selected, and they were mixed in equal atomic ratios, mechanically stirred, and vacuum induction melting was carried out in an oxygen-free environment isolated from air. The melting was repeated 5 times to obtain a twelve-element high-entropy alloy.

[0049] (2) Metallographic analysis was performed on the smelted twelve-element high-entropy alloy. The microstructure and morphology of the twelve-element high-entropy alloy were observed using a field emission electron microscope with a resolution of not less than 50,000x and equipped with an electron spectrometer. The largest single-phase region with uniform microstructure distribution formed naturally during smelting was selected, and measurements were taken within a 1mm × 1mm area in the above region using an electron spectrometer at a composition scanning rate of 20 frames / s. It was found that the largest single-phase region was mainly composed of nine elements: Ti, V, Fe, Co, Cu, Zr, Nb, Hf, and Ta. Their compositions were Ti = 5.22 at.%, V = 6.06 at.%, Fe = 10.60 at.%, Co = 10.27 at.%, Cu = 12.88 at.%, Zr = 10.84 at.%, Nb = 10.57 at.%, Hf = 10.28 at.%, and Ta = 10.33 at.%, respectively. The schematic diagram is shown below. Figure 3 As shown;

[0050] (3) Based on the nine elements determined by the largest single-phase region, select the single-element wires with a purity of not less than 99.99% corresponding to the nine elements, mix them by equal atomic ratio, mechanically stir them, and carry out vacuum induction melting in an oxygen-free environment isolated from air. Repeat the melting 5 times to obtain the nine-element high-entropy alloy.

[0051] (4) Metallographic analysis was performed on the smelted nine-element high-entropy alloy. The microstructure and morphology of the nine-element high-entropy alloy were observed using a field emission electron microscope with a resolution of not less than 50,000x and equipped with an electron spectrometer. The largest single-phase region with uniform microstructure distribution formed naturally during smelting was selected, and measurements were taken within a 1mm × 1mm area of ​​the above region using an electron spectrometer at a composition scanning rate of 20 frames / s. It was found that the largest single-phase region was mainly composed of five elements: Fe, Co, Cu, Zr, and Nb, with compositions of Fe = 12.60 at.%, Co = 13.27 at.%, Cu = 12.88 at.%, Zr = 10.84 at.%, and Nb = 10.57 at.%, respectively. The schematic diagram is shown below. Figure 4 As shown;

[0052] (5) Based on the five elements determined by the largest single-phase region, select the elemental wire with a purity of not less than 99.99% corresponding to the five elements, and mix them with “21Fe22Co21Cu18Zr18Nb”. Stir mechanically and perform vacuum induction melting in an oxygen-free environment isolated from air. Repeat the melting 5 times to obtain a five-element high-entropy alloy.

[0053] (6) The smelted pentagonal high-entropy alloy was subjected to metallographic analysis, and the microstructure of the pentagonal high-entropy alloy was observed using a field emission electron microscope with a resolution of not less than 50,000 times and equipped with an electron energy spectrometer. It was found that the microstructure and composition were uniformly distributed, and the high-entropy brazing filler metal selected by natural method for brazing ceramic composites was obtained.

[0054] Comparative Example 1

[0055] The preparation method of high entropy solder with equal atomic ratio includes the following steps: Select elemental wires with a purity of not less than 99.99% corresponding to five elements: Ti, Nb, Mo, Ta and Re. Mix them with an equal atomic ratio of "20Ti20Nb20Mo20Ta20Re", mechanically stir, and perform vacuum induction melting in an oxygen-free environment isolated from air. Repeat the melting process 5 times to obtain high entropy solder with equal atomic ratio.

[0056] Comparative Example 2

[0057] The preparation method of high entropy solder with equal atomic ratio includes the following steps: Select five elemental wires with a purity of not less than 99.99% corresponding to the five elements "Fe, Co, Cu, Zr and Nb", mix them with equal atomic ratio "20Fe20Co20Cu20Zr20Nb", stir mechanically, and perform vacuum induction melting in an oxygen-free environment isolated from air. Repeat the melting process 5 times to obtain high entropy solder with equal atomic ratio.

[0058] Performance testing

[0059] The high-entropy brazing filler metals with equal atomic ratios prepared in Comparative Examples 1-2 and the naturally selected high-entropy brazing filler metals prepared in Examples 1-2 were respectively fabricated into foils with a thickness of 30 μm. These foils were then polished, ultrasonically cleaned, and dried. They were then stacked in a "hamburger" shape according to the order of SiCf / SiC composite material - foil - nickel-based superalloy GH536 to complete the assembly. Finally, the assembled samples were transferred to a vacuum brazing furnace, with an initial vacuum level of 5 × 10⁻⁶. -3 Below Pa, heat to 1200℃ and hold for 20 minutes for brazing. Maintain a vacuum level of 1×10⁻⁶ throughout the entire process. -2 Below Pa.

[0060] The brazed joints obtained by brazing according to the above method were named joint 1 (Comparative Example 1), joint 3 (Comparative Example 2), joint 2 (Example 1), and joint 4 (Example 2) respectively. Their microstructure morphology was observed, and the results are as follows: Figure 5 As shown. Its shear strength was tested, and the results are as follows. Figure 6 As shown.

[0061] The shear strength test method is as follows: The mechanical properties of the welded specimens (joints 1-4) are mainly characterized by their shear strength. The shear test is performed using a Gleeble-1500 thermal simulation testing machine. The brazed specimens are placed in the shear fixture, the testing machine is started, and the specimens are advanced at a speed of 0.5 mm / min at room temperature until they break. The maximum load F1 at the time of specimen breakage and the stable load F2 after breakage are recorded. The shear strength of the joint is calculated using formula (1). To improve the reliability and authenticity of the data, the average value of five shear tests of the brazed joints obtained under the same process parameters is taken as its effective shear strength:

[0062]

[0063] In equation (1), T is the shear strength of the joint (MPa); F is the kilogram force used to cut the specimen, F = F2 - F1 (kg); g is the gravitational acceleration, taken as g = 10 N / kg; S is the effective bearing area (mm²). 2 ).

[0064] Figure 5 The microstructures of joints (joint 1 and joint 3) obtained by two solders with equal atomic ratios and joints (joint 2 and joint 4) obtained by naturally selected solders are shown. Figure 5 It can be seen that the joints obtained with the same atomic ratio brazing filler metal (joint 1 and joint 3) exhibit cracking, indicating poor weld bonding; while the joints obtained with the naturally selected brazing filler metal (joint 2 and joint 4) show better interfacial bonding. This suggests that the naturally selected brazing filler metal is more suitable for brazing.

[0065] Figure 6A comparison of the shear strength of brazed joints 1-4 with different brazing filler metals. Figure 6 It can be seen that the strength of the brazed joints (joints 1 and 3) obtained by naturally selected brazing filler metal is significantly improved compared with that obtained by filler metal with equal atomic ratio.

[0066] The above experiments demonstrate that the method of this invention relies on the original properties of elements to screen the composition of high-entropy alloys for design and formulation, which greatly improves the preparation efficiency and joint performance. At the same time, it avoids the drawbacks of high cost and low efficiency caused by a large number of experimental trials and errors, upgrades the irregularity of previous high-entropy alloy design, and provides a method and design idea for high-entropy alloy composition design.

[0067] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high-entropy brazing filler metal for brazing ceramic composites using a natural selection process, characterized in that, Specifically, the following steps are included: (1) Based on the target performance requirements of the brazed joint, select N elements that can meet the target performance or are related to the target performance, select high-purity materials of the corresponding elements, and adjust, mix, and smelt them in equal atomic ratios to obtain N-element high-entropy alloys. (2) Metallographic analysis of N-element high-entropy alloy was performed, and the microstructure and morphology of N-element high-entropy alloy were observed by scanning electron microscopy. The largest single-phase region inherited from the natural mixing of elements was selected and measured by electron energy spectrometer to determine the element and its corresponding atomic percentage content in the region. (3) Based on the X elements determined by the largest single-phase region, select high-purity materials of the corresponding elements and adjust, mix and smelt them in equal atomic ratios to obtain X-element high-entropy alloys. (4) Metallographic analysis of the X-element high-entropy alloy was performed, and the microstructure of the X-element high-entropy alloy was observed using a scanning electron microscope; If the structure and composition are uniformly distributed, then the high-entropy brazing filler metal selected by the natural method for brazing ceramic composites is obtained. If the structure and composition are not uniform, the elemental composition of the largest single-phase region of the microstructure formed by smelting is selected and measured by an electron spectrometer to determine the element and its corresponding atomic percentage content in the region. At the same time, steps (2) and (3) are repeated until a Y-element high-entropy alloy with uniform structure and composition is selected, which is the high-entropy brazing filler metal selected by the natural method for brazing ceramic composites.

2. The method for preparing a high-entropy brazing filler metal for ceramic composite brazing using a natural selection process according to claim 1, characterized in that, In step (1), the brazing joint is a lightweight high-temperature resistant ceramic matrix composite brazing joint.

3. The method for preparing a high-entropy brazing filler metal for ceramic composite brazing using a natural selection process according to claim 1, characterized in that, In step (1), the target properties include temperature resistance, corrosion resistance, fatigue resistance, expansion, thermal conductivity, mechanical properties, thermal properties and electrical properties.

4. The method for preparing a high-entropy brazing filler metal for ceramic composite brazing using a natural selection process according to claim 1, characterized in that, In step (1), N ≥ 7.

5. The method for preparing a high-entropy brazing filler metal for ceramic composite brazing using a natural selection process according to claim 1, characterized in that, In steps (1) and (3), the purity of the high-purity material is not less than 99.99%, and the shape is at least one of powder, block and filament; the mixing is mechanical stirring, vibration stirring or magnetic field stirring; the melting is vacuum melting or induction melting in an air-isolated and oxygen-free environment, and the melting is repeated no less than 5 times.

6. The method for preparing a high-entropy brazing filler metal for ceramic composite brazing using a natural selection process according to claim 1, characterized in that, In steps (2) and (4), the scanning electron microscope is a field emission electron microscope or a thermal field electron microscope with a resolution of not less than 50,000 times and is equipped with an electron energy spectrometer; the number of the largest single-phase regions is not less than 3, and the area is not less than 1 mm × 1 mm, and the component scanning rate is not less than 25 frames / s.

7. The method for preparing a high-entropy brazing filler metal for ceramic composite brazing using a natural selection process according to claim 1, characterized in that, In step (3), X ≤ N; in step (4), Y ≤ X.

8. A high-entropy solder prepared by the preparation method according to any one of claims 1-7.

9. A method of using a high-entropy solder prepared by the preparation method according to any one of claims 1-7, characterized in that, Specifically, the following steps are included: First, the high-entropy brazing filler metal is made into foil, then polished, cleaned and dried, and finally stacked in the order of lightweight high-temperature resistant ceramic matrix composite material - foil - high-temperature alloy and brazed.

10. A method for using a high-entropy solder according to claim 9, characterized in that, The foil has a thickness of 30-100 μm; the brazing equipment is a vacuum brazing furnace with an initial vacuum degree of 5 × 10⁻⁶. -3 Heat to 1000-1200℃ below Pa, hold for 5-20 minutes, and maintain a vacuum of 1×10⁻⁶ throughout the process. -2 Below Pa.

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