A method for multilayer diffusion bonding of refractory high-entropy alloy and superalloy

Abstract

This invention relates to the field of alloy materials technology and discloses a multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys. The invention involves setting a multilayer composite intermediate layer between the refractory high-entropy alloy and the high-temperature alloy, forming a stacked structure of refractory high-entropy alloy / Mo / Ni / high-temperature alloy. Under vacuum conditions, a stepped heating to 1300-1500℃ is employed with segmented holding. The compatibility of the BCC structure of the refractory high-entropy alloy is utilized to form a gradient diffusion layer, and a solid solution transition layer is formed at the Ni interface to suppress the formation of brittle phases. Simultaneously, the retarded diffusion effect of the refractory high-entropy alloy itself limits excessive diffusion of Ni atoms. After holding, gradient cooling and graded aging treatments are performed to obtain a compositional gradient metallurgical transition interface from the refractory high-entropy alloy to the high-temperature alloy. The joint of this invention exhibits a room temperature shear strength exceeding 500 MPa, with ductile fracture as the fracture mode, effectively solving the problem of reliable bonding between refractory high-entropy alloys and high-temperature alloys, and is suitable for the manufacture of ultra-high temperature hot-end components.

Description

Technical Field

[0001] This application relates to the field of alloy materials technology, and in particular to an interface strengthening method for the diffusion-restricted characteristics of refractory high-entropy alloys, specifically a diffusion bonding method between high-entropy alloys and metal matrices based on multilayer diffusion structures and phase diagram design. Background Technology

[0002] High-entropy alloys are a class of multi-component alloy systems composed of multiple main elements, exhibiting excellent high-temperature strength, oxidation resistance, and structural stability. In particular, refractory high-entropy alloys, represented by Mo, Nb, Ta, and W, have potential applications in extreme high-temperature environments.

[0003] However, refractory high-entropy alloys generally exhibit a significant hysteresis diffusion effect in material dynamics, with their atomic diffusion coefficients being significantly lower than those of traditional alloy systems. This characteristic manifests as difficulty in inter-diffusion of interfacial elements during diffusion bonding, making it difficult to form a continuous and stable metallurgical bonding layer. Consequently, insufficient interfacial bonding strength becomes a key issue restricting their engineering applications.

[0004] On the other hand, due to the high cost and processing difficulty of refractory high-entropy alloys, they are usually not used as integral structural materials in practical engineering. Instead, they are combined with traditional materials such as nickel-based superalloys to form composite structures to achieve a balance between performance and cost. In this process, the differences in composition, phase structure, and thermal expansion behavior between different materials make it easy for abrupt changes in composition and stress concentration to occur in the interface region, thereby further reducing the reliability of the connection.

[0005] Existing technologies typically employ methods such as single diffusion bonding, surface coating, or laser cladding to achieve the bonding of dissimilar materials. However, these methods do not fully consider the hysteretic diffusion characteristics of refractory high-entropy alloys and the phase diagram constraints of multi-element alloy systems, resulting in limited thickness of the interface diffusion layer, uncontrollable phase composition, and even the potential formation of brittle intermetallic compounds, making it difficult to obtain a stable and reliable bonding interface.

[0006] Therefore, there is an urgent need to propose an interface design method that can take into account both diffusion kinetics and phase stability in order to achieve high-strength bonding between refractory high-entropy alloys and other metallic materials. Summary of the Invention

[0007] Purpose of the invention: To address the problem of insufficient interfacial bonding caused by the hysteresis diffusion effect during the diffusion bonding process of refractory high-entropy alloys, this invention proposes an interfacial strengthening method based on multilayer diffusion structure and phase diagram design.

[0008] The core idea of ​​this invention is to construct a multilayer diffusion connection structure between a refractory high-entropy alloy and a metal matrix, introduce a diffusion transition layer and a nickel-based intermediate layer, and form a composition and microstructure gradient structure that gradually transitions from the high-entropy alloy side to the matrix side, thereby achieving continuous changes in interface properties.

[0009] Specifically, this invention utilizes the high diffusion capacity of nickel to construct high diffusion channels in a multilayer structure to compensate for the hysteretic diffusion characteristics of refractory high-entropy alloys; simultaneously, it combines the phase diagram relationship of the multi-element alloy system to control the composition evolution path of the interface region, ensuring that the interface remains in a stable phase region during diffusion and avoiding the formation of brittle phases. During the multilayer diffusion connection process, the element diffusion behavior and phase composition evolution between the materials in each layer are controlled by the phase diagram relationship. Based on the phase diagram analysis of the refractory high-entropy alloy-Ni-high temperature alloy system, this invention designs the interface structure: (1) Refractory high-entropy alloy and Ni have good solid solution ability, which can form a stable FCC or FCC+BCC mixed phase region, which is conducive to diffusion transition; (2) Ni and nickel-based high temperature alloys are highly compatible in composition and phase structure, which can achieve metallurgical bonding without obvious interface abrupt changes; (3) By controlling the diffusion temperature and holding time, the interface region gradually evolves into a stable phase region, avoiding the formation of brittle intermetallic compounds. Based on the above phase diagram analysis, this invention achieves a continuous transition of interface composition and phase structure.

[0010] Based on this, through a heat treatment process of stepped heating and multi-stage heat preservation, the gradual diffusion of elements and the gradual evolution of interface structure are realized, ultimately forming a diffusion connection interface with gradient distribution characteristics.

[0011] Definition: The "refractory high-entropy alloy" mentioned in this invention refers to a BCC structure high-entropy alloy composed of four or more refractory metal elements such as Nb, Mo, Ta, W, and V in equimolar or near-equimolar proportions. Typical systems include, but are not limited to, NbMoTaW, NbMoTaWV, NbVMoCr, and NbMoVTa. The high-temperature alloy is a nickel-based high-temperature alloy, including powder metallurgy high-temperature alloys, wrought high-temperature alloys, and cast high-temperature alloys. Typical grades include, but are not limited to, GH4099, GH5188, GH3625, and GH4169.

[0012] To achieve the above objectives, the present invention provides a method for multilayer composite thermal diffusion bonding of a refractory high-entropy alloy and a high-temperature alloy, comprising the following steps:

[0013] Step 1: Pre-treat the refractory high-entropy alloy base material and the nickel-based high-temperature alloy base material;

[0014] Step 2: A multi-layer composite intermediate layer is set between the pretreated refractory high-entropy alloy base material and the nickel-based high-temperature alloy base material to form a stacked structure. An initial contact pressure of 0.5~5 MPa is applied to the stacked structure to make the layers fit tightly together. The multi-layer composite intermediate layer includes at least a molybdenum layer and a nickel layer.

[0015] Step 3: Evacuate the vacuum level to 5×10⁻⁶. -3 Below Pa;

[0016] Step four: Heating is carried out using a stepped heating program, and the temperature is maintained in sections. The stepped heating program includes maintaining the temperature for a certain period of time at 600~800℃, 900~1100℃, 1200~1400℃ and the highest connection temperature of 1300~1500℃ respectively.

[0017] Step 5: After the heat preservation is completed, gradient cooling combined with staged aging treatment is adopted, and then cooled to room temperature to obtain a refractory high-entropy alloy / high-temperature alloy composite component with a gradient transition interface.

[0018] Specifically, step one, pretreatment of the base material.

[0019] The refractory high-entropy alloy ingot and the nickel-based high-temperature alloy block to be joined are processed into a connecting block with a flat and polished surface. The surface roughness Ra of the connecting surface is Ra≤0.4μm by mechanical grinding and polishing. The connecting blocks are then ultrasonically cleaned in acetone and anhydrous ethanol for 10~15 minutes each, and dried for later use.

[0020] Specifically, step two involves the design and stacking of multi-layer composite intermediate layers.

[0021] The multilayer composite interlayer is either a two-layer composite interlayer of "molybdenum layer / nickel layer" or a three-layer composite interlayer of "nickel foil / molybdenum foil / nickel foil".

[0022] Option A (double intermediate layer): Molybdenum plate (or molybdenum foil) and nickel foil are stacked sequentially between the refractory high entropy alloy and the high temperature alloy to form a stacked structure of "refractory high entropy alloy / Mo / Ni / high temperature alloy", wherein the Mo layer is in direct contact with the refractory high entropy alloy side and the Ni layer is in direct contact with the high temperature alloy side.

[0023] Option B (three intermediate layers): Nickel foil, molybdenum foil, and nickel foil are stacked sequentially between the refractory high-entropy alloy and the high-temperature alloy to form a stacked structure of "refractory high-entropy alloy / Ni / Mo / Ni / high-temperature alloy".

[0024] The thickness of the Mo and Ni layers can be selected within the range of 50 to 500 μm, depending on the size of the connecting components.

[0025] The assembled laminated structure is placed in the uniform temperature zone of a vacuum hot press furnace or a vacuum diffusion welding furnace, and an initial contact pressure of 0.5~5MPa is applied to ensure that the layers are tightly bonded together.

[0026] Specifically, step three: vacuum extraction.

[0027] The furnace body was evacuated by sequentially starting the mechanical pump and diffusion pump, reducing the vacuum level inside the furnace to 5×10⁻⁶. -3 Below Pa.

[0028] Specifically, step four involves stepped heating and segmented heat preservation.

[0029] Considering the characteristics of refractory high-entropy alloys, such as high melting point (>2500℃) and extremely low diffusion coefficient, diffusion bonding treatment is carried out according to the following heating procedure:

[0030] a. Heat to 600-800℃ at a heating rate of 5-10℃ / min and hold for 30-60 minutes to eliminate the processing stress of the base material and the residual stress of the intermediate layer;

[0031] b. Heat to 900-1100℃ at a heating rate of 5-10℃ / min, hold for 30-60 minutes to promote element interdiffusion between the Ni layer and the high-temperature alloy side;

[0032] c. Heat to 1200~1400℃ at a heating rate of 3~8℃ / min, hold for 60~120 minutes, drive element diffusion between the Mo layer and the refractory high-entropy alloy side at high temperature, and form a gradient diffusion layer at the Ni / Mo interface.

[0033] d. Increase the temperature to the maximum connection temperature T at a heating rate of 2~5℃ / min. max T max = 1300~1500℃, heat preservation for 120~240 minutes to achieve full metallurgical bonding between layers.

[0034] In particular, the temperature range of steps c and d is 1200~1500℃. This temperature range is higher than the dissolution temperature of the γ′ phase of nickel-based superalloys but lower than its initial melting temperature (the melting point of nickel-based superalloys is usually 1260~1340℃). Within this temperature range, the Ni layer softens moderately but remains solid, which is conducive to element interdiffusion.

[0035] Specifically, step five involves gradient cooling and aging treatment.

[0036] After the heat preservation is completed, the temperature is slowly reduced to 800-1000℃ at a rate of 3-5℃ / min, followed by a graded aging treatment: first, the temperature is kept at 800-900℃ for 4-8 hours, then the temperature is reduced to 600-700℃ at a rate of 2-4℃ / min and kept for 8-16 hours, and finally the temperature is naturally cooled to below 100℃ with the furnace.

[0037] After the furnace temperature drops below 100℃, the furnace is opened, and the connected sample is taken out, thus obtaining a refractory high-entropy alloy / high-temperature alloy composite component with a gradient transition interface.

[0038] Furthermore, the initial contact pressure applied in step two is preferably 1~3 MPa, and the pressure direction is perpendicular to the connection interface.

[0039] Furthermore, in step four, when the highest connection temperature T... max At 1300~1450℃ and a holding time of 120~180 minutes, the interfacial diffusion layer structure of the obtained joint is as follows: Mo-rich (W, Ta) BCC diffusion layer (thickness 20~80μm) formed on the refractory high entropy alloy side / Ni-Mo solid solution transition layer (thickness 10~40μm) / Ni-based solid solution layer (thickness 50~150μm) / γ′-reinforcing layer (thickness 20~60μm) / high-temperature alloy matrix.

[0040] Furthermore, the molybdenum layer is made of molybdenum foil or molybdenum plate with a purity of ≥99.95%, and the nickel layer is made of nickel foil with a purity of ≥99.9%. The thickness ratio of each layer is Mo layer: Ni layer = 1 : (1~3).

[0041] In addition, the method also includes the steps of characterizing the interface microstructure and testing the mechanical properties of the joined sample: using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to analyze the diffusion behavior and phase composition of interface elements, using a microhardness tester to test the interface gradient hardness distribution, and using shear strength test or tensile strength test to evaluate the mechanical properties of the joint.

[0042] Beneficial effects: Compared with the prior art, the present invention has the following technical effects:

[0043] (1) Overcome the limitations of hysteresis diffusion and improve the interfacial diffusion capability

[0044] By introducing a nickel-based intermediate layer to construct a high diffusion channel, the element diffusion rate in the interface region is effectively improved, enabling the originally limited diffusion connection process to be realized.

[0045] (2) Achieving gradient transition between interface components and tissue

[0046] Through multi-layer structural design and heat treatment control, the interface is transformed from an abrupt structure to a continuous gradient structure, significantly reducing interface stress concentration.

[0047] (3) Avoiding the formation of brittle phases based on phase diagram control

[0048] By constraining the evolution path of interface components through phase diagrams, the diffusion region can preferentially form a stable solid solution phase or a stable two-phase structure, thereby improving the toughness and reliability of the interface.

[0049] (4) Reduce the cost of using refractory high-entropy alloys

[0050] By using a composite structure design, high-entropy alloys are used only in key areas to achieve an optimal balance between performance and cost. Attached Figure Description

[0051] Figure 1 Scanning electron microscope (SEM) image of the diffusion region between the interface of the refractory high-entropy alloy and the Mo interface obtained in Example 1;

[0052] Figure 2 Microhardness photograph of the high-entropy alloy before interface reinforcement was prepared in Example 1;

[0053] Figure 3 Microhardness photograph of the high-entropy alloy without cracks after interface reinforcement, prepared in Example 1;

[0054] Figure 4 Micrograph of the Mo / Ni interface transition region prepared in Example 1;

[0055] Figure 5 Scanning electron microscope (SEM) image of the Ni / high-temperature alloy interface γ′ reinforcement layer prepared in Example 2;

[0056] Figure 6 This is an energy spectrum image of the interface element of the connector in Example 3. Detailed Implementation

[0057] In the specific implementation of this invention, the multilayer diffusion connection structure can be constructed by direct stacking, pre-placed intermediate layer or surface deposition, etc.; the diffusion transition layer can be formed by interface reaction or pre-set.

[0058] The following examples illustrate the invention using the diffusion bonding of high-entropy alloys and molybdenum-based materials as an example, but the invention is not limited to this specific material system.

[0059] Example 1

[0060] 1. Base material and intermediate layer material

[0061] In this embodiment, molybdenum is used as a transition diffusion element to simulate the role of a highly diffusive intermediate layer.

[0062] Refractory high-entropy alloy: NbMoTaW equimolar ratio refractory high-entropy alloy prepared by vacuum arc melting method, with dimensions of 40mm×30mm×10mm, and the connecting surfaces are polished to a surface roughness Ra≤0.4μm.

[0063] High-temperature alloy: GH4099 powder metallurgy nickel-based high-temperature alloy is used, with dimensions of 40mm×30mm×10mm. The connecting surfaces are polished to a surface roughness Ra≤0.4μm.

[0064] Intermediate layer: Molybdenum foil with a purity of ≥99.95% and a thickness of 200μm is selected; nickel foil with a purity of ≥99.9% and a thickness of 300μm is selected.

[0065] 2. Multi-layer intermediate layer stacking assembly

[0066] The NbMoTaW refractory high-entropy alloy / Mo foil (200μm) / Ni foil (300μm) / GH4099 high-temperature alloy were stacked and assembled in that order. The assembled stacked structure was placed in the homogenization zone of a vacuum hot press furnace and an initial contact pressure of 2 MPa was applied.

[0067] 3. Vacuum pumping

[0068] The furnace body was evacuated by sequentially starting the mechanical pump and diffusion pump, reducing the vacuum level inside the furnace to 5×10⁻⁶. -3 Below Pa.

[0069] 4. Stepped heating and segmented insulation

[0070] Perform diffusion ligation processing according to the following procedure:

[0071] a. Heat to 700℃ at a heating rate of 8℃ / min and hold for 45 minutes;

[0072] b. Heat to 1000℃ at a heating rate of 8℃ / min and hold for 45 minutes;

[0073] c. Increase the temperature to 1300℃ at a heating rate of 5℃ / min and hold for 90 minutes;

[0074] d. Heat to 1420℃ at a heating rate of 3℃ / min and hold for 180 minutes.

[0075] 5. Gradient cooling and aging treatment

[0076] After the heat preservation is completed, the temperature is reduced to 900℃ at a rate of 4℃ / min and held for 6 hours for the first stage of aging treatment; then the temperature is reduced to 650℃ at a rate of 3℃ / min and held for 12 hours for the second stage of aging treatment; then the furnace is naturally cooled to below 80℃.

[0077] 6. Characterization of interfacial microstructure

[0078] The joined samples were wire-cut longitudinally to prepare metallographic specimens. The microstructure of the interface region was observed using a scanning electron microscope (SEM), and the elemental distribution of the interface was determined using an energy dispersive spectroscopy (EDS) analyzer.

[0079] The results showed that a Mo-rich BCC solid solution diffusion layer with a thickness of approximately 50 μm was formed at the interface between the NbMoTaW refractory high-entropy alloy and the Mo foil. Mo atoms diffused gradient toward the HEA side, and the Mo content in the diffusion layer gradually decreased from approximately 80 at.% at the interface to approximately 25 at.% inside the HEA matrix. Figure 1 As shown, a Ni-Mo solid solution transition layer with a thickness of approximately 25 μm was formed at the interface between the Mo and Ni foils. Ni and Mo elements interdiffused, and no brittle intermetallic compounds were observed. Figure 4 As shown, where Figure 4 Image a is a magnified photograph of Mo and Ni foils under a magnifying objective lens. Figure 4 b is a magnified photograph of the Mo / Ni interface transition region under a magnifying objective lens. Figure 4 c and 4e are optical microscope images of the Mo / Ni transition region. Figure 4 Images d and 4f are optical microscope images of the Mo / Ni transition zone boundary. At the interface between the Ni foil and the GH4099 superalloy, a γ′ reinforcement layer with a thickness of approximately 40 μm is formed. The Ni3Al phase is dispersed in the FCC matrix, and the interface is dense, without pores or cracks.

[0080] 7. Mechanical property testing

[0081] A micro Vickers hardness tester was used, with a load of 500 gf. Hardness was tested sequentially from the refractory high-entropy alloy side to the high-temperature alloy side at lateral intervals of 0.2 mm. The test results are shown in Table 1.

[0082] Table 1. Gradient hardness test results of refractory high-entropy alloy / high-temperature alloy joints

[0083] Test location Hardness HV Remark NbMoTaW HEA matrix 405~420 HEA / Mo diffusion layer (0.1 mm from the interface) 480~545 Mo diffusion region Middle of Mo layer 220~240 Mo / Ni transition layer 280~310 Interdiffusion region Middle of Ni layer 120~150 Ni / High-Temperature Alloy Transition Layer 350~380 γ′ reinforcement region High-temperature alloy matrix 420~450

[0084] The results show that applying significant pressure before interfacial reinforcement in high-entropy alloys can cause surface cracks due to internal stress concentration. Figure 2 As shown, no cracks were generated when the same pressure was applied after interface reinforcement. Figure 3 As shown, the hardness of the interface region exhibits a gradient distribution from refractory high-entropy alloy → Mo diffusion region (high hardness) → pure Mo layer (low hardness) → Ni-Mo transition layer → Ni layer (even lower hardness) → γ′ strengthening layer → GH4099 matrix (high hardness). This "high-low-high" hardness distribution pattern effectively buffers the stress concentration at the interface.

[0085] The mechanical properties of the joint were evaluated using shear strength testing at room temperature and 1000℃. The results showed that the room temperature shear strength reached 528 MPa, and the high-temperature shear strength at 1000℃ was 386 MPa. The joint exhibited typical ductile fracture characteristics in the shear test, with numerous dimples appearing on the fracture surface.

[0086] Example 2

[0087] To further verify the effect of the Mo interlayer on suppressing the formation of brittle intermetallic compounds, a control group was set up in this embodiment.

[0088] Control Group A: Following the process parameters of Example 1, but without placing a Mo foil between the refractory high-entropy alloy and the Ni foil; that is, using a two-layer intermediate structure of NbMoTaW / Ni / GH4099 for diffusion bonding, with the Ni / GH4099 interface strengthening layer as shown... Figure 5 As shown.

[0089] Control group B: Following the process parameters of Example 1, a Ta foil was placed between the refractory high-entropy alloy and the Ni foil to replace the Mo foil.

[0090] Experimental group: Same as Example 1.

[0091] The interfacial microstructure of each joint was characterized by scanning electron microscopy and energy dispersive spectroscopy, and the mechanical properties of the joints were evaluated by shear strength testing. The results are shown in Table 2.

[0092] Table 2 Comparison of interface microstructure and mechanical properties of joints with different intermediate layer schemes

[0093] plan Intermediate layer structure Interface features room temperature shear strength Fracture mode Control group A NbMoTaW / Ni / GH4099 <![CDATA[A Ni2Ti-type brittle intermetallic compound layer (with a thickness of about 15 μm) is formed at the interface, and microcracks exist in the compound layer]]> 342 MPa brittle fracture Control group B NbMoTaW / Ta / Ni / GH4099 <![CDATA[The Ta layer has a good interface bonding with the HEA, but a brittle Ni3Ta compound is formed at the Ta / Ni interface]]> 385 MPa Brittle fracture is the main type of fracture. experimental group NbMoTaW / Mo / Ni / GH4099 No brittle compounds were formed at any of the three interfaces, resulting in a gradient solid solution transition layer. 528 MPa ductile fracture

[0094] The results showed that when the refractory high-entropy alloy was in direct contact with the Ni layer, Ni atoms diffused violently towards the HEA side, reacting with elements such as Ti and Nb in the HEA to form Ni2Ti-type brittle intermetallic compounds, resulting in brittle fracture at the joint with a shear strength of only 342 MPa. When Ta was used as the interlayer, Ni3Ta brittle compounds formed at the Ta / Ni interface, and interface weakening still existed. However, when Mo was used as the interlayer, Mo had good metallurgical compatibility with both the HEA and Ni, and no brittle compounds formed at the three-layer interface, forming a gradient solid solution transition layer. The joint shear strength was significantly increased to 528 MPa, and the fracture mode changed to ductile fracture.

[0095] Example 3

[0096] This embodiment further optimizes the connection process parameters.

[0097] Based on Example 1, the maximum connection temperature T_max and the holding time were changed to study the influence of process parameters on joint performance.

[0098] The results showed that when the maximum connection temperature was between 1350 and 1420℃ and the holding time was between 120 and 180 minutes, the shear strength of the joint increased with increasing temperature and time. This is because the Mo atoms diffused sufficiently and the diffusion layer thickened, which is beneficial for interfacial stress buffering. The distribution of interfacial elements in the joint is as follows: Figure 6 As shown, the top black-and-white image is a backscattered electron microscope (SEM) image of the joint interface, and the four images below are energy dispersive X-ray spectroscopy (EDS) images of Ta, W, Mo, and Nb, respectively. However, when the temperature exceeds 1480℃ or the holding time is too long, trace amounts of Laves phase (Fe2Mo type) begin to aggregate at the interface, and the joint performance deteriorates. Therefore, the preferred process parameters are: maximum connection temperature 1350~1450℃, holding time 120~240 minutes; the optimal process parameters are: maximum connection temperature 1420℃, holding time 180 minutes.

[0099] Results Analysis

[0100] 1. Mechanism of action of the Mo intermediate layer

[0101] This invention is the first to apply a Mo interlayer to the diffusion bonding of refractory high-entropy alloys and nickel-based superalloys. Its core mechanism of action is reflected in the following three aspects:

[0102] (1) Metallurgical compatibility between Mo and HEA: NbMoTaW refractory high entropy alloys and Mo both have BCC structures and have a wide range of mutual solubility regions. During high-temperature diffusion bonding, the diffusion activation energy of Mo atoms to the HEA side is low, which can form a continuous Mo-rich BCC solid solution transition layer, thus solving the problem of "diffusion difficulty" of refractory high entropy alloys.

[0103] (2) Moderate reaction between Mo and Ni: Mo and Ni can form Ni-Mo solid solution at high temperature without forming brittle intermetallic compounds (the solid solution region in the Ni-Mo binary phase diagram is wide, and the formation of intermetallic compounds such as Ni4Mo and Ni3Mo requires specific composition ratios and low-temperature aging conditions). Therefore, the Mo / Ni interface can form a solid solution transition layer with a composition gradient distribution, thus avoiding the formation of brittle phases.

[0104] (3) Using the hysteresis diffusion effect to suppress brittle phases: The lattice distortion effect of various main elements in refractory high-entropy alloys is significant, and the atomic diffusion rate is low, which effectively suppresses the excessive diffusion of Ni atoms to the HEA side. When Ni comes into direct contact with refractory high-entropy alloys, Ni will diffuse violently into the HEA and form Ni2Ti type brittle compounds with elements such as Ti and Nb; however, after introducing the Mo interlayer, the Mo layer acts as a diffusion barrier layer, and Ni atoms need to pass through the Mo layer to reach the HEA side, which lengthens the diffusion path. Moreover, the affinity between Mo and Ni is moderate, and the diffusion flux of Ni to the HEA side is significantly reduced, thus effectively suppressing the brittle phase.

[0105] 2. Enhancement Mechanism of Gradient Cooling and Aging Treatment

[0106] Prolonged high-temperature holding during the bonding process can lead to the dissolution of the γ′ strengthening phase on the high-temperature alloy side, resulting in strength degradation. This invention employs a slow, gradient cooling process after the holding period, followed by staged aging treatments at 900℃ and 650℃ to promote the re-precipitation of the γ′ phase (Ni3Al). Aging at 900℃ is beneficial for γ′ phase nucleation, while aging at 650℃ promotes γ′ phase growth and dispersed distribution, thus restoring the strength of the high-temperature alloy. Simultaneously, slow cooling helps release residual stress at the interface, preventing hot cracking caused by rapid cooling.

[0107] In summary, this invention provides a multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys. Through a multilayer intermediate layer structure design of "Mo / Ni layers," combined with a heat treatment process of stepped heating-segmented holding-gradient cooling-stage aging, the method utilizes the inherent hysteresis diffusion effect of the refractory high-entropy alloy to regulate interfacial reaction behavior. This forms a gradient metallurgical transition layer at the interface from the refractory high-entropy alloy to the high-temperature alloy, effectively suppressing the formation of brittle intermetallic compounds and achieving a high-strength metallurgical bond between the refractory high-entropy alloy and the high-temperature alloy. This method provides key technical support for the engineering application of NbMoTaW-based refractory high-entropy alloys and is suitable for manufacturing critical components in ultra-high temperature service environments such as hot-end components of aerospace engines and structural components of nuclear reactors.

[0108] The above description is merely a preferred embodiment of this application and is not intended to limit this application.

Claims

1. A method for multilayer composite thermal diffusion bonding of a refractory high-entropy alloy and a high-temperature alloy, characterized in that, Includes the following steps: Step 1: Pre-treat the refractory high-entropy alloy base material and the nickel-based high-temperature alloy base material; Step 2: A multi-layer composite intermediate layer is set between the pretreated refractory high-entropy alloy base material and the nickel-based high-temperature alloy base material to form a stacked structure. An initial contact pressure of 0.5~5 MPa is applied to the stacked structure to make the layers fit tightly together. The multi-layer composite intermediate layer includes at least a molybdenum layer and a nickel layer. Step 3: Evacuate the vacuum level to 5×10⁻⁶. -3 Below Pa; Step four: Heating is carried out using a stepped heating program, and the temperature is maintained in sections. The stepped heating program includes maintaining the temperature for a certain period of time at 600~800℃, 900~1100℃, 1200~1400℃ and the highest connection temperature of 1300~1500℃ respectively. Step 5: After the heat preservation is completed, gradient cooling combined with staged aging treatment is adopted, and then cooled to room temperature to obtain a refractory high-entropy alloy / high-temperature alloy composite component with a gradient transition interface.

2. The multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys according to claim 1, characterized in that, In step one, the pretreatment is as follows: the refractory high-entropy alloy ingot and the nickel-based high-temperature alloy block to be joined are processed into a connecting block with a flat and polished surface. The surface roughness Ra of the connecting surface is Ra≤0.4μm by mechanical grinding and polishing. The connecting surface is then ultrasonically cleaned in acetone and anhydrous ethanol for 10~15 minutes each, and then dried for later use.

3. The multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys according to claim 1, characterized in that, In step two, the composite intermediate layer is either a "molybdenum layer / nickel layer" double-layer composite intermediate layer or a "nickel foil / molybdenum foil / nickel foil" triple-layer composite intermediate layer.

4. The multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys according to claim 1, characterized in that, In step two, the thickness of the molybdenum layer and the nickel layer are each independently 50~500μm, and the thickness ratio of the molybdenum layer to the nickel layer is 1:(1~3).

5. The multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys according to claim 3, characterized in that, When the composite intermediate layer is a double-layer composite intermediate layer, a stacked structure of "refractory high-entropy alloy / Mo / Ni / high-temperature alloy" is formed.

6. The multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys according to claim 3, characterized in that, When the composite intermediate layer is a three-layer composite intermediate layer, a stacked structure of "refractory high entropy alloy / Ni / Mo / Ni / high temperature alloy" is formed.

7. The multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys according to claim 1, characterized in that, In step two, the initial contact pressure applied is 1~3 MPa, and the pressure direction is perpendicular to the connection interface.

8. The multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys according to claim 1, characterized in that, In step four, the stepped heating process specifically includes: a. Heat to 600-800℃ at a heating rate of 5-10℃ / min, and hold for 30-60 minutes; b. Increase the temperature to 900-1100℃ at a heating rate of 5-10℃ / min, and hold for 30-60 minutes; c. Increase the temperature to 1200-1400℃ at a heating rate of 3-8℃ / min, and hold for 60-120 minutes; d. Heat to the maximum connection temperature T_max at a heating rate of 2~5℃ / min, T_max = 1300~1500℃, and hold for 120~240 minutes.

9. The multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys according to claim 8, characterized in that, In step four, the highest connection temperature T max At 1300~1450℃, the heat preservation time is 120~180 minutes.

10. The multilayer composite thermal diffusion bonding method for refractory high-entropy alloys and high-temperature alloys according to claim 1, characterized in that, The gradient cooling and graded aging treatment described in step five is as follows: the temperature is slowly reduced to 800-1000℃ at a rate of 3-5℃ / min, followed by holding at 800-900℃ for 4-8 hours for the first stage of aging treatment, then the temperature is reduced to 600-700℃ at a rate of 2-4℃ / min for 8-16 hours for the second stage of aging treatment, and finally the furnace is naturally cooled to below 100℃.

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