CrNbTaTiV refractory high-entropy alloy as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of metal material preparation and forming, and relates to a CrNbTaTiV refractory high-entropy alloy and a preparation method and application thereof. The preparation method comprises the following steps: mixing Cr, Nb, Ta, Ti and V metals in an inert atmosphere, smelting into a master alloy ingot, heating, melting, atomizing and solidifying to prepare refractory high-entropy alloy powder; the refractory high-entropy alloy powder and a binder are mixed and extruded into wires, and a composite wire material is prepared; printing the composite wire material into a green body; and heating the green body in an inert atmosphere to remove the binder, sintering by utilizing hot isostatic pressing, and cooling to obtain the compact refractory high-entropy alloy. By means of the method of atomization quenching powder preparation, low-temperature bonding forming and solid-phase sintering densification, the preparation problem of the refractory high-entropy alloy single-phase BCC solid solution structure is fundamentally solved, the inherent element segregation problem of a traditional melting technology is effectively avoided, and the structure uniformity and the outstanding comprehensive mechanical property are ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal material preparation and forming, and particularly relates to a CrNbTaTiV refractory high-entropy alloy and a preparation method and application thereof. BACKGROUND

[0002] Refractory high-entropy alloys (RHEA), especially the system represented by Cr, Nb, Ta, Ti, V, etc., have great application potential in extreme environment fields such as aerospace, nuclear energy, and chemical industry due to their excellent strength, hardness, oxidation resistance, and creep resistance at high temperatures. These excellent properties are largely due to their unique single solid solution phase structure (usually BCC structure), which avoids the coarsening or phase transition of the strengthening phase in traditional high-temperature alloys at high temperatures, thereby obtaining excellent high-temperature stability.

[0003] At present, the mainstream methods for preparing refractory high-entropy alloys include traditional melting methods and emerging additive manufacturing technologies, but these methods have obvious technical bottlenecks when preparing alloys such as Cr, Nb, Ta, Ti, and V. For example, casting or arc melting melts, mixes, and casts ingots from high-purity metal raw materials under vacuum or inert atmosphere protection. Due to the significant differences in melting point, density, and atomic radius of Cr, Nb, Ta, Ti, and V, serious element segregation easily occurs during slow cooling, resulting in a non-equilibrium structure in which the single solid solution phase structure (usually BCC structure) coexists with brittle Laves phases and other intermetallic compounds, which seriously damages the plasticity and toughness of the material, making its actual performance much lower than the theoretical value. At the same time, due to the limitation of mold manufacturing, traditional casting cannot realize the integration of components with complex geometries such as internal flow channels, lightweight lattices, or biomimetic topologies, which greatly limits their application in high-performance parts.

[0004] While powder bed fusion technologies represented by selective laser melting (SLM) and electron beam melting (EBM) can directly form complex components, the huge thermal stress generated during local high-temperature melting and rapid solidification in the process of processing refractory high-entropy alloys easily causes macroscopic cracks in RHEA with high intrinsic brittleness. Under the action of high-energy beams, elements with lower boiling points (such as Cr) are prone to burnout, leading to deviation of the composition from the design value, affecting the uniformity of the structure and the stability of the performance. In addition, SLM / EBM equipment requires a high vacuum environment, with extremely high investment and maintenance costs, and the process parameter optimization for new material systems is difficult and time-consuming. In summary, the existing technologies are difficult to realize efficient and low-defect forming of complex components while ensuring the uniformity of the single-phase structure, which seriously restricts the engineering application of refractory high-entropy alloys. SUMMARY

[0005] The application aims to provide a CrNbTaTiV refractory high-entropy alloy and a preparation method and application thereof, so as to overcome the shortcomings of the prior art, avoid the solidification segregation problem in traditional casting and direct melting forming through a technical route of "atomization rapid cooling powder + solid phase sintering", and ensure that the initial powder is single-phase, the excellent organization is completely retained in the subsequent full solid phase processing flow, and the final product has a uniform single-phase BCC solid solution structure, so that the excellent performance of RHEA is exerted.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the application is as follows: In a first aspect, the application provides a preparation method of a CrNbTaTiV refractory high-entropy alloy, comprising the following steps: (1) mixing Cr, Nb, Ta, Ti and V metals, melting into a master alloy ingot under an inert atmosphere, heating and melting, atomizing and solidifying to prepare a refractory high-entropy alloy powder; (2) mixing the refractory high-entropy alloy powder with a binder, extruding into a wire to prepare a composite wire; (3) printing the composite wire according to a set printing model and printing parameters to prepare a green body; (4) removing the binder by heating under an inert atmosphere, and then sintering by hot isostatic pressing, and cooling to obtain the CrNbTaTiV refractory high-entropy alloy.

[0007] The application proposes a new refractory high-entropy alloy component preparation strategy, aiming to simultaneously solve the preparation of single-phase body-centered cubic (BCC) solid solution organization, near-net forming of complex components and full densification sintering of the three traditionally mutually restrictive problems. The traditional metallurgical path based on "melting-solidification" is completely avoided, and a full-process solid phase technical route of "pre-alloyed powder preparation → low-temperature binder forming → solid-state diffusion densification" is adopted, so that a series of inherent defects caused by metal melting, such as element segregation, thermal cracks and composition out of control, are eliminated from the root.

[0008] In some other embodiments, in step (1), the purity of Cr, Nb, Ta, Ti and V metals is all > 99.9%, the mixed atomic ratio is 20:20:20:(20-30):(10-20), and the total mixed atomic ratio is 100; the number of melting is 3-6 times.

[0009] Specifically, the mixed atomic ratio of Cr, Nb, Ta, Ti and V metals is 20:20:20:20:20 or 20:20:20:30:10. The number of melting is 3, 4, 5 or 6 times, so as to ensure the uniformity of the melting of each metal component.

[0010] In some other embodiments, in step (1), the temperature for heating and melting is 1800-2000 ℃; The atomizing mode is to use inert gas jet impact and break into liquid droplets; The solidification mode is to use inert gas for heat exchange cooling, and the cooling rate is >10 5 K / s; the inert gas is one of argon and nitrogen; The refractory high-entropy alloy powder has a single body-centered cubic phase structure, and the particle size is 15-50 μm.

[0011] Specifically, the powder is prepared by gas atomization: the master alloy ingot is placed in the crucible of the gas atomization equipment, and is reheated to a completely molten state (for example, 1800-2000 ℃) under an inert atmosphere. The molten alloy liquid flows through the guide pipe and is broken into fine liquid droplets by high-speed inert gas (preferably argon) jet impact.

[0012] The fine alloy liquid droplets fly in the huge atomization tower and undergo >10 5 K / s of extremely high cooling speed, and are rapidly solidified into spherical or near-spherical powders. Due to the extremely fast cooling speed, atoms cannot diffuse and segregate in a long range, so they are "frozen" in the single BCC solid solution phase at high temperature.

[0013] The present application uses high cooling rate (10 5 K / s) technology such as gas atomization to prepare pre-alloy powder, which inhibits element diffusion and segregation in the powder preparation stage, and ensures that the single-phase BCC solid solution with uniform chemical composition is obtained from the raw materials.

[0014] In some other embodiments, in step (2), the volume content of the refractory high-entropy alloy powder in the mixture of the refractory high-entropy alloy powder and the binder is 55% to 70%; The binder includes a main binder and an auxiliary binder, wherein the main binder includes one or more of polylactic acid, ethylene-vinyl acetate copolymer, ABS resin, and polyformaldehyde, and the auxiliary binder includes one or more of polyethylene glycol, paraffin, and stearic acid.

[0015] In some other embodiments, in step (2), the binder is composed of the following components in mass percentage: 55-60% of the main binder, 30-40% of polyethylene glycol, and 5-15% of stearic acid; wherein the main binder is one or both of polyformaldehyde and ethylene-vinyl acetate copolymer; The temperature for extruding into a wire is 160-220 ℃; and the diameter of the composite wire is 1.75±0.05 mm or 2.85±0.05 mm.

[0016] In some other embodiments, in step (3), the printing parameters are as follows: the nozzle temperature is 190-240 ℃, the printing platform temperature is 50-80 ℃, the printing speed is 20-50 mm / s, and the filling rate is 100%.

[0017] The present application utilizes the maturity and cost advantage of the fused deposition modeling (such as 3D printing) technology itself in the manufacturing of complex geometries to realize the high-freedom, near-net-shape manufacturing of refractory high-entropy alloy components.

[0018] In some other embodiments, in step (4), the heating temperature for removing the binder is 200-500 ℃, the heating rate is 0.5-2 ℃ / min, and the holding time is 2-6 h. The temperature for hot isostatic pressing sintering is 1250-1450 ℃, the heating rate is 5-15 ℃ / min, the atmosphere is a mixed gas composed of high-pressure argon and 5% H2, the pressure is 100-200 MPa, and the holding time is 2-4 h.

[0019] The present application adopts the binder-based fused deposition modeling (FDM) technology to perform component molding. The molding temperature only needs to melt the binder (usually lower than 500 ℃), which is much lower than the melting point of the alloy, so that the thermal stress, cracking, element burning loss and secondary segregation caused by the high-temperature melting process are completely avoided. The hot isostatic pressing (HIP) technology is adopted to perform integrated debinding and solid-phase sintering on the green body. Under high temperature and high pressure, the powder particles realize densification through solid-state diffusion, and finally the full-density component with high density, small grain size and maintaining the initial single-phase structure is obtained. In particular, the present application adopts argon-hydrogen mixed gas diluted to below the lower limit of explosion as the sintering atmosphere, which fundamentally eliminates the risk of explosion, and at the same time, effectively removes the surface oxides of the particles by using a small amount of hydrogen gas with excellent reducing property, provides a clean metal interface for solid-state diffusion, and ensures the smooth progress of the densification process.

[0020] In the second aspect, the present application provides the CrNbTaTiV refractory high-entropy alloy prepared by the preparation method of the CrNbTaTiV refractory high-entropy alloy in the first aspect. The CrNbTaTiV refractory high-entropy alloy has a single body-centered cubic phase structure, a relative density of >99.7%, and an average grain size of 22 μm-38 μm.

[0021] In some other embodiments, at room temperature, the tensile strength is 1160-1265 MPa, the yield strength is 1070-1180 MPa, the elongation after fracture is 7.2-10.2%, and the Vickers hardness is 438-480 HV. The yield strength in 800 ℃ air is 650-700 MPa.

[0022] The CrNbTaTiV refractory high-entropy alloy component with uniform single-phase BCC solid solution structure, accurate chemical composition, complex shape, high density and excellent mechanical properties is stably prepared.

[0023] In a third aspect, the application provides the application of the CrNbTaTiV refractory high-entropy alloy in the aerospace, nuclear energy and chemical industry.

[0024] The CrNbTaTiV refractory high-entropy alloy prepared by the application can still maintain excellent strength, hardness, oxidation resistance and creep resistance at high temperatures, and has great application potential in the fields of aerospace, nuclear energy, chemical industry and other extreme environments.

[0025] The application has the following beneficial effects: (1) The application bypasses the solidification segregation problem in traditional casting and direct melting forming through the technical route of "atomization rapid cooling powder + solid phase sintering". The initial powder is single-phase, and the particle size of the powder, the formula of the binder, the powder loading rate of the wire material, the printing parameters and the process parameters of HIP can be independently adjusted, which provides a wide adjustment space for optimizing the microstructure and macroscopic performance of the material for different application requirements.

[0026] (2) The FDM 3D printing technology is used, and the low-temperature printing process (<500 °C) completely avoids the melting of the metal, and there is no thermal stress cracking problem caused by a large temperature gradient, and there is no problem of selective evaporation and burning loss of elements, which ensures the integrity and accuracy of the final component. At the same time, lightweight lattices, integrated complex flow channels, bionic structures and the like that cannot be realized by traditional methods can be manufactured, which greatly expands the application scenarios of the Cr-Nb-Ta-Ti-V high-entropy alloy, and realizes the integrated design and manufacturing of materials and structures. In addition, compared with SLM / EBM equipment, the FDM printer is low in price by several orders of magnitude, and has low operation environment requirements (no high vacuum is required), and is easy to maintain. This makes the research and development and small-batch production of high-performance refractory high-entropy alloy complex components more efficient and safe.

[0027] (3) The hot isostatic pressing (HIP) process ensures that the relative density of the final component can reach more than 99.8%, and almost completely eliminates internal pore defects. At the same time, the solid phase sintering process helps to obtain fine equiaxed crystal structure, combined with uniform single-phase structure, so that the final component performs excellently in strength, plasticity, hardness and high-temperature performance. BRIEF DESCRIPTION OF DRAWINGS

[0028] The drawings accompanying the specification of the application form a part of the application and serve to provide further understanding of the application, and the illustrative embodiments of the application and their description serve to explain the application without constituting an improper limitation of the application.

[0029] Figure 1 XRD pattern of the powder obtained in Example 1 of the present invention using atomization method; Figure 2 SEM image of the spherical powder obtained in Example 1 of the present invention using atomization method. DETAILED DESCRIPTION

[0030] Those skilled in the art will appreciate that the following examples are intended to be illustrative only and should not be viewed as limiting the scope of the present invention. Unless otherwise indicated, the specific conditions in the examples were carried out under conventional conditions or those recommended by the manufacturer. Where the components used are not specified, those conventionally available commercially were used.

[0031] Abbreviations and key terms used in the present invention are explained as follows: RHEA (Refractory High-Entropy Alloy): Refractory High-Entropy Alloy, refers to an alloy composed of multiple high-melting-point elements (typically with melting points higher than 1500°C) in equal or near-equal atomic ratios, and tends to form simple solid solution phases (such as BCC or FCC).

[0032] BCC (Body-Centered Cubic): Body-Centered Cubic, a common metallic crystal structure.

[0033] AM (Additive Manufacturing): Additive Manufacturing, commonly known as 3D printing, a manufacturing method that constructs objects by layering materials.

[0034] FDM (Fused Deposition Modeling): Fused Deposition Modeling, a common additive manufacturing technology that constructs parts layer by layer by heating and extruding thermoplastic filaments.

[0035] HIP (Hot Isostatic Pressing): Hot Isostatic Pressing, a process that processes materials under high temperature and high pressure, which can be used for densification and defect healing of powder metallurgy parts.

[0036] SLM (Selective Laser Melting): Selective Laser Melting, a powder bed fusion additive manufacturing technology.

[0037] Green Part: Refers to the preliminary shape of the body obtained by mixing metal or ceramic powder with binder and then through forming process (such as printing, injection), which has low strength and needs to be treated by subsequent debinding and sintering.

[0038] Debinding: The process of removing organic binder from green parts by heating or other means before sintering.

[0039] Sintering: The process of combining powder particles with each other through mechanisms such as diffusion at high temperatures below the melting point of the material, reducing porosity, increasing density and strength.

[0040] Dense Part: Refers to the final component with extremely low internal porosity (usually relative density > 99%) after densification processes such as sintering.

[0041] In view of the problems of CrNbTaTiV refractory high-entropy alloy preparation, such as difficulty in obtaining single-phase structure, easy cracking, uneven composition, and inability to form complex components, the present application provides a new, controllable and relatively low-cost additive manufacturing method, which can stably prepare CrNbTaTiV refractory high-entropy alloy components with uniform single-phase BCC solid solution structure, accurate chemical composition, complex shape, high density and excellent mechanical properties.

[0042] The CrNbTaTiV refractory high-entropy alloy additive manufacturing method provided by the present application comprises the following steps: Step 1: Preparation of single-phase CrNbTaTiV refractory high-entropy alloy powder (1) batching and smelting: according to equal atomic ratio or set near equal atomic ratio, take Cr, Nb, Ta, Ti and V metal blocks or particles with purity higher than 99.9%. In a vacuum induction suspension smelting furnace or a vacuum arc smelting furnace, smelt into a uniform master alloy ingot under inert gas (such as high-purity argon). In order to ensure uniform composition, multiple repeated smelting can be carried out.

[0043] (2) gas atomization powder making: place the master alloy ingot in the crucible of the gas atomization equipment (such as atomization tower), reheat to complete melting state (for example 1800-2000°C) under inert atmosphere, and the prepared molten alloy liquid flows through the guide pipe. The bottom of the guide pipe is impacted and broken into small alloy liquid droplets by high-speed inert gas (preferably argon) jet.

[0044] (3) rapid cooling and collection: when the small alloy liquid droplets fly in the huge atomization tower, they exchange heat with low-temperature inert gas, experience an extremely high cooling speed of >10 5 K / s, and quickly solidify into spherical or near-spherical powders. Due to the extremely high cooling speed, atoms cannot diffuse and segregate in long range, so they are "frozen" in the single BCC solid solution phase at high temperature.

[0045] (4) Sieving: The collected powder is sieved to select the particle size range (e.g. 15-50 pm) of the CrNbTaTiV single-phase alloy powder suitable for the subsequent process. The powder is confirmed to be a single BCC phase structure by X-ray diffraction (XRD) analysis.

[0046] Step 2: Preparation of 3D printable RHEA-polymer composite filament (1) Raw material preparation: Metal powder: CrNbTaTiV single-phase alloy powder (RHEA) prepared in step one.

[0047] Binder: A multi-component thermoplastic binder is used, which includes a main binder and an auxiliary binder. The main binder is used to provide the skeleton and strength of the filament and is selected from polylactic acid (PLA), ABS resin, or polyformaldehyde (POM). The auxiliary binder is used to reduce the viscosity of the system, improve the flowability, and facilitate subsequent low-temperature debinding, and is selected from polyethylene glycol (PEG), paraffin wax (PW), or stearic acid (SA).

[0048] (2) Mixing: The RHEA powder and the binder are uniformly mixed in a torque rheometer or a high-speed mixer according to the preset volume ratio (the volume content of the powder is preferably 55% to 70%). The mixing temperature needs to be higher than the softening point of the binder but lower than its decomposition temperature, so as to ensure that the binder can fully coat each particle of the RHEA powder and obtain a feedstock.

[0049] (3) Extrusion into filament: The uniformly mixed feedstock is fed into a twin-screw extruder, and extruded into a continuous filament at a set temperature (e.g. 160-220°C, depending on the binder) and screw speed. The filament passes through a cooling water tank, a traction device, and a laser diameter gauge for real-time monitoring and control of its diameter, and is finally wound into a disc. The diameter of the filament can be customized according to the requirements of the 3D printer, and is commonly 1.75 mm or 2.85 mm, with a diameter tolerance controlled within ±0.05 mm.

[0050] Step 3: Low-temperature additive manufacturing (3D printing) of green body (1) Equipment: A commercial or customized fused deposition modeling (FDM) 3D printer is used, preferably a printer with a heating chamber and a hardened steel nozzle to meet the printing requirements of high-filled powder filaments.

[0051] (2) Printing process: The filament prepared in step two is installed on the FDM printer, and the printing parameters and programs (G code) are generated according to the pre-designed three-dimensional model (CAD file) and slicing software.

[0052] The printing parameters include nozzle temperature, platform temperature, printing speed, and filling rate, and the specific parameter ranges are as follows: nozzle temperature: 190-240°C (sufficient to melt the binder but not to decompose it). Platform temperature: 50-80°C (to reduce warping). Printing speed: 20-50 mm / s. Filling rate: 100% (to obtain a dense green body).

[0053] (3) Obtain a green body: the printer prints the accumulated composite material layer by layer according to the printing program, and finally forms a three-dimensional green body (Green Part) composed of RHEA powder and binder consistent with the digital model. The green body has a certain geometric shape, but is low in strength and not dense.

[0054] Step 4: debinding and hot isostatic pressing (HIP) sintering (1) Furnace loading: place the printed green body on the tooling of the hot isostatic pressing furnace.

[0055] (2) Debinding stage: seal the furnace body, vacuumize and then fill high-purity argon. Heat the furnace temperature to one or more platform temperatures (for example, 200°C and 450°C) at a slow heating rate (for example, 0.5-2°C / min) to sequentially decompose and evaporate the binder in the green body. Slow heating is to avoid cracking or deformation of the green body due to high pressure caused by rapid gasification of the binder. After this stage is completed, a porous "brown body" composed of weakly connected metal powder particles is obtained.

[0056] (3) HIP sintering stage: in the same furnace cycle, after debinding is completed, continue to increase the temperature to the sintering temperature (for example, 1250°C - 1450°C, which is lower than the solidus temperature of the alloy). At the same time, high-pressure argon + 5% H2 mixed gas is introduced into the furnace, so that the pressure is increased to 100-200 MPa, and the temperature is kept for 2-4 h. The high temperature provides the driving force for atomic diffusion, causing the contact interface between adjacent powder particles to shrink, grow, and fuse. The high pressure provides an external mechanical driving force to promote creep and plastic flow of the material, thereby crushing and eliminating internal residual pores.

[0057] (4) Cooling and furnace discharge: after the holding is completed, the furnace is cooled to room temperature. After the pressure is released, the CrNbTaTiV refractory high-entropy alloy component with high density (relative density > 99.8%), uniform structure, and excellent performance is obtained.

[0058] The scheme of the present application is further illustrated below in combination with specific embodiments: Example 1 The present embodiment provides a CrNbTaTiV refractory high-entropy alloy and a preparation method, which specifically comprises the following steps: (1) Cr20 Nb 20 Ta 20 Ti 20 V 20 The Cr, Nb, Ta, Ti and V metal particles with purity > 99.9% were weighed and placed in a vacuum arc melting furnace to be melted 5 times under high-purity argon to produce a uniform master alloy ingot. The master alloy ingot was placed in a crucible of a gas atomization tower and atomized under high-pressure argon to produce spherical powder (RHEA powder). XRD analysis showed that the powder was a single BCC solid solution phase.

[0059] (2) The RHEA powder was mixed with a binder at high speed, and a composite wire with a diameter of 1.75 ± 0.03 mm was prepared by a double-screw extruder at 190°C. The volume content of the RHEA powder was 60%, and the binder was composed of the following components by mass percentage: polyformaldehyde (POM) 60%, polyethylene glycol (PEG) 35%, and stearic acid (SA) 5%.

[0060] (3) The printing model used for 3D printing was an ASTM E8 standard tensile specimen. The printing parameters were: nozzle temperature 215°C, platform temperature 60°C, printing speed 30 mm / s, layer height 0.2 mm, 100% filling, and a green body was obtained by printing.

[0061] (4) The green body was heated to 220°C at a rate of 1°C / min under a flowing argon atmosphere and held for 2 h (to remove PEG), and then heated to 480°C at a rate of 1°C / min and held for 3 h (to remove POM) for debinding treatment. After debinding, the same furnace was continued to be heated to 1350°C at a rate of 10°C / min, and the pressure was increased to 150 MPa, and held for 3 h, and then cooled in the furnace to obtain a CrNbTaTiV refractory high-entropy alloy.

[0062] The properties of the prepared CrNbTaTiV refractory high-entropy alloy were tested, and the results were as follows: Relative density: The relative density was 99.85% measured by the Archimedes method.

[0063] Microstructure: Metallographic analysis showed a uniform single-phase BCC structure without Laves phase or other second phases, and the average grain size was about 22 μm.

[0064] Mechanical properties (room temperature): tensile strength 1210 MPa, yield strength 1125 MPa, elongation after fracture 8.5%, and Vickers hardness 455 HV.

[0065] From Figure 1 It can be seen that the powder obtained by atomization method is basically single-phase without other second phases. From Figure 2It can be seen that the average grain size of the spherical powder obtained by atomization is about 22 μm.

[0066] Example 2 The embodiment provides a CrNbTaTiV refractory high-entropy alloy and a preparation method. Different from the embodiment 1, the preparation process of the steps (2)-step (4) is as follows: (2) The RHEA powder and a binder are mixed at high speed, and a composite wire with a diameter of 1.75±0.04 mm is prepared by a double-screw extruder at 150°C. The volume content of the RHEA powder is 62%, and the binder is composed of the following components in percentage by mass: ethylene-vinyl acetate copolymer (EVA) 55%, paraffin wax (PW) 40%, and stearic acid (SA) 5%.

[0067] (3) The printing model used for 3D printing is an ASTM E8 standard tensile specimen. The printing parameters are as follows: nozzle temperature 195°C, platform temperature 50°C, printing speed 40 mm / s, layer height 0.2 mm, 100% filling, and a green body is obtained by printing.

[0068] (4) The green body is heated to 500 °C at 0.8 °C / min under the atmosphere of flowing argon, and is kept for 4 h (the paraffin wax and EVA are removed slowly in the process). After debinding, the temperature is increased to 1400 °C at 10 °C / min, and the pressure is increased to 120 MPa, and the alloy is kept for 2 h, and then is cooled in the furnace to obtain the CrNbTaTiV refractory high-entropy alloy.

[0069] The other preparation steps are consistent with those in the embodiment 1.

[0070] The CrNbTaTiV refractory high-entropy alloy is subjected to performance testing, and the results are as follows: Relative density: The relative density measured by the Archimedes method is 99.91%.

[0071] Microstructure: Due to the high sintering temperature, the grains grow, and the average grain size is about 38 μm. The structure is still a uniform single-phase BCC structure.

[0072] Mechanical properties (room temperature): the tensile strength is 1160 MPa, the yield strength is 1070 MPa, and the elongation after fracture is 10.2% (the grain coarsening leads to a slight decrease in strength and an increase in plasticity). The Vickers hardness is 438 HV.

[0073] Example 3 The embodiment provides a CrNbTaTiV refractory high-entropy alloy and a preparation method. Different from the embodiment 1, the preparation process of the steps (2)-step (4) is as follows: (1) non-equivalent atomic ratio Cr 20 Nb 20 Ta 20 Ti 30 V 10 Cr, Nb, Ta, Ti and V metal particles with purity > 99.9% were weighed and placed in a vacuum arc melting furnace, and melted 5 times under high-purity argon to produce a uniform master alloy ingot. The master alloy ingot was placed in a crucible of a gas atomization tower and atomized under high pressure argon to produce spherical powder (RHEA powder). XRD analysis showed that the powder was a single BCC solid solution phase.

[0074] (2) The RHEA powder was mixed with a binder at high speed, and a composite wire with a diameter of 1.75±0.03 mm was prepared by a double screw extruder at 195 °C. The volume content of the RHEA powder was 65%, and the binder was composed of the following components by mass percentage: polyformaldehyde (POM) 60%, polyethylene glycol (PEG) 35%, and stearic acid (SA) 5%.

[0075] (3) The printing model used for 3D printing was a BCC lattice structure with a size of 20 mm×20 mm×20 mm, and the rod diameter was 1.5 mm. The printing parameters were: nozzle temperature 215 °C, platform temperature 60 °C, printing speed 30 mm / s, layer height 0.2 mm, 100% filling, and a green body was obtained by printing.

[0076] (4) The green body was heated to 220 °C at a rate of 1 °C / min under a flowing argon atmosphere and held for 2 h (to remove PEG), and then heated to 480 °C at a rate of 1 °C / min and held for 3 h (to remove POM) for debinding treatment. After debinding, the same furnace was continued to be heated to 1300 °C at a rate of 10 °C / min, and the pressure was increased to 180 MPa, and held for 4 h, and then cooled in the furnace to obtain a CrNbTaTiV refractory high-entropy alloy.

[0077] The properties of the prepared CrNbTaTiV refractory high-entropy alloy were tested, and the results were as follows: Product morphology: a complex BCC lattice array structure dense part with complete shape, no fracture and no obvious deformation was successfully prepared.

[0078] Relative density: the rod part of the lattice structure was cut and sampled, and the relative density was measured by the Archimedes method to be > 99.7%.

[0079] Microstructure: the metallographic structure was uniform and fine single-phase BCC equiaxed crystal, and the average grain size was about 28 μm.

[0080] Hardness: the Vickers hardness on the cross section of the rod was 480 HV. This example proves the ability of the present application to manufacture complex structural parts.

[0081] Example 4 This example provides a CrNbTaTiV refractory high-entropy alloy and a preparation method, which is different from Example 1 in that the preparation process in step (4) is as follows: (4) The green body is heated to 220 °C at a rate of 1 °C / min under a flowing argon atmosphere for 2 h (to remove PEG), and then heated to 480 °C at a rate of 1 °C / min for 3 h (to remove POM) for debinding treatment. To obtain finer grains to improve high-temperature performance, a lower sintering temperature and a higher pressure are used. After debinding, the same furnace is used to continue heating to 1280 °C at a rate of 10 °C / min while pressurizing to 200 MPa, and then holding for 4 h, and then cooling in the furnace to obtain the CrNbTaTiV refractory high-entropy alloy.

[0082] Other preparation steps are consistent with Example 1.

[0083] The CrNbTaTiV refractory high-entropy alloy prepared is subjected to performance testing, and the results are as follows: Relative density: The relative density measured by the Archimedes method is 99.95% (higher pressure helps densification).

[0084] Microstructure: Due to the lower sintering temperature, grain growth is effectively inhibited, and the average grain size is only 24 μm. The structure is a uniform single-phase BCC structure.

[0085] Mechanical properties (room temperature): The tensile strength is 1265 MPa, the yield strength is 1180 MPa, and the elongation after fracture is 7.2%. The Vickers hardness is 470 HV.

[0086] High-temperature performance: The sample is subjected to tensile testing at 800 °C in air, and the yield strength is measured to be as high as 680 MPa, showing excellent high-temperature mechanical properties, which proves that the components prepared by the method are suitable for high-temperature load-bearing environments.

[0087] Comparative Example 1 This comparative example provides a CrNbTaTiV refractory high-entropy alloy and a preparation method, which is different from Example 1 in that the preparation process in step (4) is as follows: ordinary pressureless high-temperature sintering is used, and after debinding, the above product is heated to 1350 °C at a rate of 10 °C / min under a flowing high-purity argon (99.999%) atmosphere, but maintained at atmospheric pressure (without pressurization), and then held for 3 h, and then cooled in the furnace. No pressure is applied during the sintering process.

[0088] The relative density of the final product is only 95.2% measured by Archimedes method, mainly due to the lack of sintering pressure, and the internal pores are difficult to close. Metallography shows that the main phase is BCC, and a large number of residual pores and a small amount of pore aggregation are observed. The average grain size is about 25 μm, indicating that the porosity significantly reduces the continuity of the material. The tensile strength at room temperature is 865 MPa, the yield strength is 780 MPa, the elongation after fracture is 1.2%, and the Vickers hardness is 375 HV. Analysis shows that the strength, plasticity and hardness are significantly reduced, especially the plasticity deterioration is obvious, which is directly related to the high porosity.

[0089] Although the atomic diffusion is enhanced at high temperature, the lack of strong driving force provided by pressure is not enough to effectively eliminate the pores and cavities between the powder contact points and the layers inside the 3D printing green body, resulting in low density of the final product. Residual porosity becomes a stress concentration point and a crack initiation site, which seriously damages the strength and plasticity of the material.

[0090] It should be noted here that general pressure sintering can only be pressed in the axial direction, and cannot be uniformly pressed in all directions, which means that for 3D printed products with complex shapes, especially products with hollow structures, general hot-pressing sintering equipment cannot apply pressure during the sintering process.

[0091] Comparative Example 2 This comparative example provides a CrNbTaTiV refractory high-entropy alloy and a preparation method, which is different from Example 1 in that the preparation process of step (4) is as follows: hot isostatic pressing sintering is used, but the atmosphere during sintering is high-purity argon, and no reducing atmosphere hydrogen is added. Under the pure high-purity argon (99.999%, without hydrogen) atmosphere, the temperature is raised to 1350°C at 10°C / min, and the pressure is increased to 150 MPa, and then the temperature is kept for 3h, and then the furnace is cooled.

[0092] The relative density of the final product is 99.2% measured by Archimedes method. Metallography shows that the overall phase is BCC, and local discontinuous point or micro-film oxides (mainly from the trace surface oxide layer remaining after debinding) can be observed at the grain boundary. The tensile strength at room temperature is 995 MPa, the yield strength is 820 MPa, the elongation after fracture is 2.8%, and the Vickers hardness is 410 HV. The overall performance is lower than that of Example 1.

[0093] The scanning electron microscope observation of the tensile fracture shows that there is a characteristic of intergranular fracture, and the oxide inclusions are detected at the grain boundary. It is considered that the high pressure and high temperature of HIP significantly improves the density, but the pure argon atmosphere is inert and lacks reducing property. The very thin oxide layer formed on the surface of the powder (especially high active elements such as Ti, Nb, etc.) during storage, processing and debinding is not reduced at high temperature of HIP. These oxides are enriched at the grain boundary, which destroys the chemical uniformity of the matrix and forms brittle inclusions at the grain boundary, seriously damaging the grain boundary bonding strength, resulting in the material showing brittle fracture characteristics, especially the plasticity and strength decrease significantly. The addition of a small amount of hydrogen can effectively reduce these trace surface oxides, restore the clean metal surface to facilitate atomic diffusion and interface healing, which is crucial to obtain high strength and high plasticity.

[0094] In summary, the CrNbTaTiV refractory high-entropy alloy and the preparation method provided by the present application avoid the melting-solidification process in the traditional process innovatively, fundamentally inhibit element segregation and residual thermal stress, and successfully realize a component with uniform single-phase BCC solid solution structure, high density, complex geometric shape and excellent mechanical properties. The method has the advantages of high controllability and low cost, and provides a breakthrough solution for the preparation of high-performance refractory high-entropy alloy components.

[0095] The above is only the preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of preparing a CrNbTaTiV refractory high-entropy alloy, characterized by, The method comprises the following steps: (1) mixing Cr, Nb, Ta, Ti and V metals, smelting into a master alloy ingot under an inert atmosphere, heating and melting, atomizing and solidifying to prepare a refractory high-entropy alloy powder; (2) mixing the refractory high-entropy alloy powder with a binder, extruding into a wire to prepare a composite wire; (3) printing the composite wire according to a set printing model and printing parameters to prepare a green body; (4) removing the binder by heating under an inert atmosphere, and then sintering by hot isostatic pressing, and then cooling to obtain the CrNbTaTiV refractory high-entropy alloy.

2. The method of claim 1, wherein the CrNbTaTiV refractory high-entropy alloy is prepared by the steps of: In step (1), the purity of the Cr, Nb, Ta, Ti and V metals is greater than 99.9%, the mixed atomic ratio is 20:20:20:(20-30):(10-20), and the total mixed atomic ratio is 100; the smelting frequency is 3-6 times.

3. The method of claim 1, wherein the CrNbTaTiV refractory high-entropy alloy is prepared by the steps of: In step (1), the heating and melting temperature is 1800-2000 ℃; The atomization method is to use inert gas jet impact to break into droplets; The solidification is performed by heat exchange cooling with an inert gas at a rate > 10 5 K / s; The inert atmosphere is one of argon and nitrogen; The refractory high-entropy alloy powder has a single body-centered cubic phase structure, and the particle size is 15-50 μm.

4. The method of claim 1, wherein the CrNbTaTiV refractory high-entropy alloy is prepared by the steps of: In step (2), the volume content of the refractory high-entropy alloy powder in the mixture of the refractory high-entropy alloy powder and the binder is 55%-70%; The binder comprises a main binder and an auxiliary binder, wherein the main binder comprises one or more of polylactic acid, ethylene-vinyl acetate copolymer, ABS resin and polyformaldehyde, and the auxiliary binder comprises one or more of polyethylene glycol, paraffin and stearic acid.

5. The method of claim 1, wherein the CrNbTaTiV refractory high-entropy alloy is prepared by the steps of: In step (2), the binder comprises the following components by mass percentage: 55%-60% of the main binder, 30%-40% of polyethylene glycol, and 5%-15% of stearic acid; wherein the main binder is one or both of polyformaldehyde and ethylene-vinyl acetate copolymer; The extrusion temperature is 160-220 ℃; and the diameter of the composite wire is 1.75±0.05 mm or 2.85±0.05 mm.

6. The method of claim 1, wherein the CrNbTaTiV refractory high-entropy alloy is prepared by the steps of: In step (3), the printing parameters are as follows: the nozzle temperature is 190-240 ℃, the printing platform temperature is 50-80 ℃, the printing speed is 20-50 mm / s, and the filling rate is 100%.

7. The method of claim 1, wherein the CrNbTaTiV refractory high-entropy alloy is prepared by the steps of: In step (4), the heating temperature for removing the binder is 200-500 ℃, the heating rate is 0.5-2 ℃ / min, and the holding time is 2-6 h; The hot isostatic pressing sintering temperature is 1250-1450 ℃, the heating rate is 5-15 ℃ / min, the atmosphere is a mixed gas composed of high-pressure argon and 5% H2, the pressure is 100-200 MPa, and the holding time is 2-4 h.

8. A method of producing the CrNbTaTiV refractory high-entropy alloy according to any one of claims 1 to 7, characterized in that, The CrNbTaTiV refractory high-entropy alloy has a single body-centered cubic phase structure, the relative density is greater than 99.7%, and the average grain size is 22 μm-38 μm.

9. The CrNbTaTiV refractory high-entropy alloy of claim 8, wherein, At room temperature, the tensile strength is 1160-1265 MPa, the yield strength is 1070-1180 MPa, the elongation after fracture is 7.2-10.2%, and the Vickers hardness is 438-480 HV. The yield strength in air at 800°C is 650-700 MPa.

10. Use of the CrNbTaTiV refractory high-entropy alloy according to claim 8 or 9, characterized in that The applications are applications in the fields of aerospace, nuclear energy, chemical industry.

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