Method for assisting high-temperature alloy TLP connection by adding high-entropy alloy nanoparticles to middle layer

Abstract

The invention discloses a method for assisting high-temperature alloy TLP connection by adding high-entropy alloy nanoparticles to a middle layer, and relates to the technical field of welding. The method comprises the following steps: preparing high-entropy alloy nanoparticles; mixing the high-entropy alloy nanoparticles with the powder intermediate layer to obtain a composite intermediate layer; and under the vacuum condition, the high-temperature alloy to be welded is welded through the composite middle layer based on the TLP welding method, and a welded part is obtained. According to the method, the high chemical mixed entropy filling material is reasonably selected and introduced, so that elements of the middle layer and the high-alloying base metal are fully interacted, the variety and content of chemical components of a welding area are greatly increased, the chemical mixed entropy of each area is correspondingly increased at the same time, and each area of the joint is in a high entropy state; by adding the nanoparticles, growth of intermetallic compounds / eutectic phases can be inhibited and delayed, the crystal nucleus size is reduced, and the method has an effective effect on improving the mechanical properties, especially plasticity and toughness, of diffusion welding joints.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a method for TLP connection of a high-temperature alloy assisted by adding high-entropy alloy nanoparticles to an intermediate layer. Background Art

[0002] With the development of aviation technology, the service requirements for aircraft engines are also constantly increasing. The new generation of engines needs to develop in the direction of high thrust and high thrust-to-weight ratio. High-temperature alloys have become an indispensable key material in the manufacture of core parts of aircraft engines due to their excellent high-temperature strength, oxidation resistance and heat corrosion resistance. High-temperature alloys usually contain high-melting-point elements, and thermal cracks are prone to occur during welding, which leads to a decrease in joint performance. TLP diffusion welding has become one of the most promising welding methods for connecting high-temperature alloys due to its welding characteristics.

[0003] The TLP connection technology of high-temperature alloys usually uses a nickel-based alloy containing melting-reducing elements as the intermediate layer (melted at the welding temperature). As the melting-reducing elements diffuse into the base material, the liquidus temperature of the intermediate layer rises and isothermal solidification occurs to form a joint. However, the characteristics of the TLP connection technology make it very easy for brittle phases such as borides and low-melting-point eutectic structures to form inside the high-temperature alloy joints. Under harsh service conditions such as high temperature and dynamic loads, it is very easy to form a weak link for crack nucleation and expansion, resulting in insufficient comprehensive mechanical properties of the joint. How to regulate the precipitation of brittle phases, obtain a uniform structure with matching strength and toughness, and then improve the comprehensive mechanical properties of the joint has become a key technical bottleneck that needs to be broken through in TLP connection technology. Summary of the invention

[0004] The present invention aims at the deficiencies existing in the above-mentioned background technologies, and mainly solves the problem of insufficient comprehensive mechanical properties of joints caused by brittle phases such as borides and low-melting-point eutectic structures existing in TLP connections of high-temperature alloy materials. The present invention provides a method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to an intermediate layer. This method introduces high chemical mixing entropy filling materials by reasonable selection so that the elements of the intermediate layer and the high-alloyed base material fully interact with each other, thereby greatly improving the types and contents of the chemical components in the welding area. Correspondingly, the chemical mixing entropy of each region is also increased at the same time, and each region of the joint is in a high entropy state. At the same time, the nanoparticles will inhibit and delay the precipitation and growth of intermetallic compounds / eutectic phases, thereby improving the microstructure of the joint, thereby improving the mechanical properties of the diffusion welding joint, and especially having an effective effect on improving strength and toughness.

[0005] The first object of the present invention is to provide a method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to an intermediate layer, comprising the following steps:

[0006] Preparation of high entropy alloy nanoparticles;

[0007] Adding high entropy alloy nanoparticles to the powder middle layer and fully mixing them by a ball mill to obtain a composite middle layer;

[0008] Under vacuum conditions, the high-temperature alloy to be welded is welded using a composite intermediate layer based on a TLP connection method to obtain a welded part.

[0009] Preferably, the high entropy alloy nanoparticles are produced by arc discharge method or laser pulse method.

[0010] Preferably, the high entropy alloy nanoparticles are prepared by an arc discharge method, comprising:

[0011] Design the composition of high entropy alloys;

[0012] Weigh the raw materials according to the composition of the high entropy alloy, mix them and press them into a target material;

[0013] The target material is used as an anode and a carbon rod is used as a cathode;

[0014] The anode and cathode are placed in a vacuum reaction chamber, filled with reaction gas, arc reaction parameters are set, arc discharge is performed, and high entropy alloy nanoparticles are obtained.

[0015] Preferably, the laser pulse method is used to prepare high entropy alloy nanoparticles, comprising:

[0016] Design the composition of high entropy alloys;

[0017] Weighing raw materials according to the composition of the high entropy alloy to prepare a solid high entropy alloy target;

[0018] Choose a liquid or gas phase environment;

[0019] Set pulse laser parameters;

[0020] Laser is used to hit the surface of the target material, triggering a high-temperature and high-pressure plasma plume. The various metal elements in the plume are condensed into high-entropy alloy nanoparticles through rapid cooling.

[0021] Preferably, in the liquid phase, the nanoparticles are dispersed in the liquid phase through an electrostatic stabilization mechanism, and the nanoparticles will adhere to the surface of the carrier.

[0022] Preferably, the composition design of the high entropy alloy is carried out according to the parent material to be welded, and the composition design is based on the Ω phase formation criterion, the δ phase stability criterion, and the VEC plasticity criterion;

[0023] The criterion for the formation of Ω phase is as follows:

[0024]

[0025] In the formula, c i 、c jare the atomic concentrations of elements i and j respectively; R is the gas constant; represents the mixing entropy of elements;

[0026] The δ phase stability criterion is as follows:

[0027]

[0028]

[0029] In the formula, r i is the atomic radius; δ is the average atomic radius difference;

[0030] The VEC plasticity criterion is as follows:

[0031]

[0032] Where, (VEC) i is the valence electron concentration of the ith element.

[0033] Preferably, the TLP connection is performed under high vacuum.

[0034] The second object of the present invention is to provide a welded part made by the above method.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention provides a method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to an intermediate layer. The method increases the mixed entropy value of the weld based on the high entropy effect and changes the thermodynamic conditions for the formation of eutectic structure. The present invention has a solid solubility that is superior to that of traditional alloys and helps to inhibit the diffusion of melting-reducing elements into the nickel-based high-temperature alloy parent material to form high-density borides. The joint prepared by the connection method provided by the present invention has high strength and toughness characteristics, and at the same time forms a strongly bonded coherent interface with the metal, which helps to activate the synergistic effect between various strengthening and toughening mechanisms including solid solution strengthening, fine grain strengthening (toughening) and dispersion strengthening.

[0037] Under the action of high entropy, delayed diffusion, lattice distortion and other effects, high-strength and high-toughness high-temperature alloy joints can be obtained. (1) The high entropy effect increases the mixed entropy value of the weld; (2) The solid solubility ability is superior to that of traditional alloys, which helps to inhibit the diffusion of melting-reducing elements into the nickel-based high-temperature alloy parent material to form high-density borides; (3) It has high strength and toughness characteristics, and at the same time forms a strong coherent interface with the metal, which helps to activate the synergistic effect of various strengthening and toughening mechanisms including solid solution strengthening, fine grain strengthening (toughening) and dispersion strengthening.

[0038] High entropy alloy nanoparticles have great potential as the doping phase of the intermediate layer to achieve the goal of regulating the joint structure and improving the comprehensive mechanical properties of the joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of TLP connection sample loading of high-temperature alloy / composite intermediate layer / high-temperature alloy. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0041] The purpose of the present invention is to solve the brittle phases such as boride and low melting point eutectic structure existing in TLP connection of high temperature alloy materials, thereby providing a welding method to improve the mechanical properties of the joint.

[0042] In order to achieve the above-mentioned object, the first aspect of the present invention provides a method for TLP connection of high-temperature alloys by adding high-entropy alloy nanoparticles to an intermediate layer, comprising the following steps:

[0043] Preparation of high entropy alloy nanoparticles;

[0044] Adding high entropy alloy nanoparticles to the powder middle layer, mixing them thoroughly by a ball mill to obtain a composite middle layer, adding pinene alcohol, and preparing the composite middle layer into a paste;

[0045] Under vacuum conditions, the high-temperature alloy to be welded is welded using a composite intermediate layer based on a TLP method to obtain a welded part.

[0046] During welding, TLP connection is performed under high vacuum.

[0047] Wherein, the high entropy alloy nanoparticles are prepared by arc discharge method or laser pulse method.

[0048] Specifically, the high entropy alloy nanoparticles are prepared by an arc discharge method, comprising:

[0049] Design the composition of high entropy alloys;

[0050] Weigh the raw materials according to the composition of the high entropy alloy, mix them and press them into a target material;

[0051] The target material is used as an anode and a carbon rod is used as a cathode;

[0052] The anode and cathode are placed in a vacuum reaction chamber, filled with reaction gas, arc reaction parameters are set, arc discharge is performed, and high entropy alloy nanoparticles are obtained.

[0053] In one embodiment, the arc discharge method is a preparation method for converting metal into nanoparticles using high temperature plasma, and the specific steps are as follows:

[0054] (1) The target metal powder is mixed and pressed into a cylindrical target with a diameter of about 45 μm. The target is used as the anode, and a carbon rod is used as the cathode.

[0055] (2) Place the electrode in a vacuum reaction chamber, control the vacuum degree at about 10-3Pa, fill it with reaction gas (such as methane), and adjust the pressure to 0.2×10 5 Pa;

[0056] (3) The voltage of the arc reaction is set to 3 V and the current is 230 A. The arc discharge lasts for 5-10 minutes, generating a high plasma temperature (over 3000 K);

[0057] (4) Collect the cooled particles.

[0058] Specifically, the pulse laser method is used to prepare high entropy alloy nanoparticles, including:

[0059] Design the composition of high entropy alloys;

[0060] Weighing raw materials according to the composition of the high entropy alloy to prepare a solid high entropy alloy target;

[0061] Choose a liquid or gas phase environment;

[0062] Set pulse laser parameters;

[0063] Laser is used to hit the surface of the target material, triggering a high-temperature and high-pressure plasma plume. The various metal elements in the plume are condensed into high-entropy alloy nanoparticles through rapid cooling.

[0064] Among them, in the liquid phase, the nanoparticles are dispersed in the liquid phase through an electrostatic stabilization mechanism, and the nanoparticles will adhere to the surface of the carrier.

[0065] In one embodiment, the pulsed laser method uses a high-energy laser beam to evaporate metal in a liquid phase or a gas phase to form nanoparticles, and the specific steps are as follows:

[0066] (1) Preparing multiple metals into solid targets in a certain proportion;

[0067] (2) Select a liquid phase (such as ethanol, n-hexane) or gas phase (such as air or argon) according to the experimental requirements. If it is a liquid phase, the target needs to be immersed in a liquid (such as n-hexane or deionized water);

[0068] (3) Using nanosecond pulse laser, set the wavelength, pulse width, repetition rate and high power density; for example, Nd:YAG laser, set the wavelength to 1064nm, pulse width to 5ns, repetition rate to 2Hz and high power density to 2×109W / cm 2 .

[0069] (4) The laser strikes the target surface, triggering a high-temperature and high-pressure plasma plume. The various metal elements in the plume condense into alloy nanoparticles through rapid cooling (nanosecond level);

[0070] (5) In the liquid phase, nanoparticles are dispersed in the solution through an electrostatic stabilization mechanism; if carbon materials (such as graphene or CNFs) are used as carriers, the particles will adhere to their surface.

[0071] In one embodiment, the prepared nanoparticles are characterized by: scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and other methods to analyze the size, morphology and element distribution of the particles to ensure high uniformity and no phase separation. The melting point is verified by differential scanning calorimetry (DSC) based on JMatPro software estimation, and the high entropy alloy composition design is optimized based on the feedback of the results.

[0072] According to the present invention, the composition design of the high entropy alloy is carried out according to the parent material to be welded, and the composition design is based on the Ω phase formation criterion, the δ phase stability criterion, and the VEC plasticity criterion;

[0073] The criterion for the formation of Ω phase is as follows:

[0074]

[0075] In the formula, c i 、c j are the atomic concentrations of elements i and j respectively; R is the gas constant; represents the mixing entropy of elements;

[0076] The δ phase stability criterion is as follows:

[0077]

[0078]

[0079] In the formula, r i is the atomic radius; δ is the average atomic radius difference;

[0080] The VEC plasticity criterion is as follows:

[0081]

[0082] Where, (VEC) i is the valence electron concentration of the ith element.

[0083] The method provided by the invention performs TLP connection under high vacuum degree.

[0084] A second aspect of the present invention provides a welded part.

[0085] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0086] Example

[0087] A high-strength and toughness diffusion welding method for powder high-temperature alloy FGH99 based on adding high-entropy alloy nanoparticles to the intermediate layer, comprising the following steps:

[0088] 1. Use FGH99 as the base material. Use wire cutting machine to cut the base material into 10×5×2mm before welding. 3 and 5×5×5mm 3 Before welding, the base material needs to be gradually ground to 2000# SIC sandpaper, and then polished to ensure the flatness and smoothness of the welding surface;

[0089] Second, BNi-2 is the most studied and widely used nickel-based alloy in the current standard commercial intermediate layer. At the same time, it has the main elements of FGH99 high-temperature alloy, and the operating temperature range (1010-1177°C) is within the process window of the parent material weldability. It has excellent wettability to nickel-based high-temperature alloys, and the formed joints have good high-temperature strength and oxidation resistance. In order to avoid the problem of insufficient toughness caused by conventional welding methods, the CoCrFeNiMo system is selected, which covers the main elements of BNi-2 and FGH99 high-temperature alloy parent materials, and the alloying elements are ≥5, which meets the basic requirements for the formation of high-entropy alloys;

[0090] The reason for choosing this alloy system as the filler metal is mainly based on the Ω phase formation criterion, δ phase stability criterion, and VEC plasticity criterion in the above formula; the high entropy alloy nanoparticles are prepared according to the arc discharge method; the prepared high entropy alloy nanoparticles and the BNi-2 powder matrix to be mixed need to be mixed by a QM-3SP4 planetary high-energy ball mill (1.5kW, maximum speed 530rpm), and then configured into a paste-like intermediate layer by adding pine oil;

[0091] 3. When the vacuum degree is 3.3×10 -3 Pa and a temperature of 1100 °C, TLP connections were performed for 30 min, 60 min, 90 min, and 120 min, and then the samples were cooled in a furnace to room temperature to complete the welding process;

[0092] Fourth, after TLP connection, the cross section of the joint was polished and chemically etched in a reagent (10mL HNO3+10mL C2H4O2+15mL HCl) for 5s to 6s. The microstructure and crystallographic features of the joint were characterized by field emission scanning electron microscopy (ZEISS Gemini 500), energy dispersive spectrometer (EDS) and electron backscatter diffractometer (EBSD). The details of the reaction phase in the TLP joint were identified by field emission transmission electron microscopy (FEI-TEM, Talos F200 X).

[0093] In the TLP connection method of FGH99 in this embodiment, CoCrFeNiMo high entropy alloy nanoparticles are introduced into BNi-2. When the temperature is 1100°C and the holding time is 30 minutes, the eutectic phase of the joint disappears, indicating that the high entropy alloy can effectively inhibit the formation of the eutectic structure of the joint. At the same time, as the content of high entropy alloy nanoparticles increases within a certain range, the volume fraction and size of the boride in the joint area are reduced. It can be seen that the addition of high entropy alloy nanoparticles can effectively inhibit the formation of boride and eutectic structure in the joint.

[0094] See also Figure 1 As shown in the figure, it is a schematic diagram of high temperature alloy loading.

[0095] Figure 1 Schematic diagram of sample loading for adding high-entropy alloy nanoparticles to assist in TLP connection of high-temperature alloys. Before loading, the surface to be welded needs to undergo a series of grinding and polishing work to ensure its flatness. For the composite intermediate layer, the prepared high-entropy alloy nanoparticles and the intermediate layer matrix need to be fully mixed using a ball mill, and then pine oil is used to prepare them into a corresponding paste-like composite intermediate layer to facilitate the clamping of the welded parts.

[0096] In summary, the present invention provides a method for transient liquid phase diffusion (TLP) connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to an intermediate layer, the method comprising preparing high-entropy alloy nanoparticles; fully mixing the high-entropy alloy nanoparticles with the powder intermediate layer through a ball mill to obtain a composite intermediate layer; under vacuum conditions, the composite intermediate layer composed of high-entropy alloy nanoparticles introduced into the intermediate layer is used to weld the high-temperature alloy to be welded based on the TLP connection method to obtain a welded connection. The present invention introduces high chemical mixing entropy filling materials by reasonable selection so that the elements of the intermediate layer and the high-alloyed parent material fully interact, greatly improving the types and contents of the chemical components of the welding area, and correspondingly, the chemical mixing entropy of each region is also increased at the same time, and each region of the joint is in a high entropy state; not only that, the addition of nanoparticles can inhibit and delay the growth of intermetallic compounds / eutectic phases. Its mechanism of action is the adsorption effect of nanoparticles: nanoparticles are adsorbed onto the intermetallic compounds or eutectic phase nuclei appearing in the metal liquid phase, acting as a barrier medium to hinder element diffusion or interfacial reaction, thereby reducing the nucleation rate and the size of the nucleus, which is effective in improving the mechanical properties of diffusion welding joints, especially plasticity and toughness.

[0097] The above embodiments are only some embodiments listed for facilitating understanding of the synthesis and application methods of the materials of the present invention, and are not intended to limit the present invention. It is understood that relevant practitioners can easily make appropriate modifications to this structure, so any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to the intermediate layer, characterized in that: The following steps are involved: Preparation of high entropy alloy nanoparticles; The high entropy alloy nanoparticles and the powder intermediate layer are fully mixed by a ball mill to obtain a composite intermediate layer, and then the composite intermediate layer is prepared into a paste intermediate layer by pine alcohol; Under vacuum conditions, the high-temperature alloy to be welded is welded using a composite intermediate layer based on a transient liquid phase diffusion welding method (TLP) to obtain a welded connection.

2. The method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to the intermediate layer according to claim 1, characterized in that: The high entropy alloy nanoparticles are prepared by an arc discharge method or a laser pulse method.

3. The method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to the intermediate layer according to claim 2, characterized in that: The high entropy alloy nanoparticles are prepared by arc discharge method, including: Design the composition of high entropy alloys; Weigh the raw materials according to the composition of the high entropy alloy, mix them and press them into a target material; The target material is used as an anode and a carbon rod is used as a cathode; The anode and cathode are placed in a vacuum reaction chamber, filled with reaction gas, arc reaction parameters are set, arc discharge is performed, and high entropy alloy nanoparticles are obtained.

4. The method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to the intermediate layer according to claim 2, characterized in that: The laser pulse method is used to prepare high entropy alloy nanoparticles, including: Design the composition of high entropy alloys; Weighing raw materials according to the composition of the high entropy alloy to prepare a solid high entropy alloy target; Choose a liquid or gas phase environment; Set pulse laser parameters; Laser is used to hit the surface of the target material, triggering a high-temperature and high-pressure plasma plume. The various metal elements in the plume are condensed into high-entropy alloy nanoparticles through rapid cooling.

5. The method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to the intermediate layer according to claim 4, characterized in that: In the liquid phase, the nanoparticles are dispersed in the liquid phase through an electrostatic stabilization mechanism, and the nanoparticles will adhere to the surface of the carrier.

6. The method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to the intermediate layer according to claim 3 or 4, characterized in that: The composition design of the high entropy alloy is carried out according to the parent material to be welded, and the composition design is based on the Ω phase formation criterion, the δ phase stability criterion, and the VEC plasticity criterion; The criterion for the formation of Ω phase is as follows: In the formula, c i 、c j are the atomic concentrations of elements i and j respectively; R is the gas constant; represents the mixing entropy of elements; The δ phase stability criterion is as follows: In the formula, r i is the atomic radius; δ is the average atomic radius difference; The VEC plasticity criterion is as follows: Where, (VEC) i is the valence electron concentration of the ith element.

7. The method for TLP connection of high-temperature alloys assisted by adding high-entropy alloy nanoparticles to the intermediate layer according to claim 1, characterized in that: The TLP connection was performed under high vacuum.

8. A connecting piece obtained by the method according to claims 1 to 7.

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