A CrNbTaTiV Refractory High Entropy Alloy, Its Preparation Method and Application

Abstract

This invention belongs to the field of metal material preparation and forming technology, and relates to a CrNbTaTiV refractory high-entropy alloy, its preparation method, and its application. The preparation method includes the following steps: mixing Cr, Nb, Ta, Ti, and V metals in an inert atmosphere, melting them into a master alloy ingot, heating, melting, atomizing, and solidifying to produce refractory high-entropy alloy powder; mixing the refractory high-entropy alloy powder with a binder and extruding it into filaments to produce a composite filament; printing the composite filament into a green blank; heating the green blank in an inert atmosphere to remove the binder, then sintering it using hot isostatic pressing and cooling to obtain a dense refractory high-entropy alloy. This invention fundamentally solves the preparation problem of single-phase BCC solid solution microstructure of refractory high-entropy alloys through the method of "atomization rapid cooling powder preparation - low-temperature bonding and forming - solid-phase sintering for densification," effectively avoiding the elemental segregation problem inherent in traditional melting and solidification processes, and ensuring uniform microstructure and outstanding comprehensive mechanical properties.

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 methods melt, mix, and cast ingots by melting high-purity metal raw materials under vacuum or inert gas 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 coexisting with single solid solution phase structure (usually BCC structure) and brittle Laves phase 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, limited by mold manufacturing, traditional casting cannot realize integrated components with complex geometries such as internal flow channels, lightweight lattices, or biomimetic topologies, greatly limiting their application in high-performance components.

[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 process 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, existing technologies are difficult to achieve efficient and low-defect forming of complex components while ensuring uniformity of 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 procedure, 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:

[0007] In the first aspect, the application provides a preparation method of a CrNbTaTiV refractory high-entropy alloy, comprising the following steps:

[0008] (1) mixing Cr, Nb, Ta, Ti and V metals, melting into a master alloy ingot under an inert atmosphere, and preparing a refractory high-entropy alloy powder through heating, melting, atomization and solidification;

[0009] (2) mixing the refractory high-entropy alloy powder with a binder, and extruding into a composite wire to prepare a composite wire material;

[0010] (3) printing the composite wire material according to a set printing model and printing parameters to prepare a green body;

[0011] (4) removing the binder by heating under an inert atmosphere, and then sintering by hot isostatic pressing, so as to obtain the CrNbTaTiV refractory high-entropy alloy after cooling.

[0012] The application proposes a new refractory high-entropy alloy component preparation strategy, which aims 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.

[0013] 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.

[0014] 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 times is 3, 4, 5 or 6, which ensures the uniformity of the melting of each metal component.

[0015] In some other embodiments, in step (1), the temperature for heating and melting is 1800-2000 ℃;

[0016] The atomization method is to use inert gas jet impact and break into droplets.

[0017] The solidification method 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.

[0018] The refractory high-entropy alloy powder has a single body-centered cubic phase structure, and the particle size is 15-50 μm.

[0019] 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 melted state (for example, 1800-2000 ℃) under an inert atmosphere, and the molten alloy liquid flows through the guide pipe and is broken into fine droplets by high-speed inert gas (preferably argon) jet impact.

[0020] The fine alloy droplets fly in the huge atomization tower and undergo sufficient heat exchange with low-temperature inert gas, experience an extremely high cooling rate of >10 5 K / s, and rapidly solidify into spherical or near-spherical powder. Due to the extremely fast cooling rate, atoms cannot diffuse and segregate in a long range, so they are “frozen” in the single BCC solid solution phase at high temperature.

[0021] 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.

[0022] In some other embodiments, in step (2), in the mixture of refractory high-entropy alloy powder and binder, the volume content of refractory high-entropy alloy powder is 55% to 70%;

[0023] 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.

[0024] In some other embodiments, in step (2), the binder is composed of the following in percentage by mass: 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.

[0025] The temperature for extruding into a filament is 160-220 DEG C; and the diameter of the composite filament is 1.75+ / -0.05 mm or 2.85+ / -0.05 mm.

[0026] In some other embodiments, in step (3), the printing parameters are as follows: the nozzle temperature is 190-240 DEG C, the printing platform temperature is 50-80 DEG C, the printing speed is 20-50 mm / s, and the filling rate is 100%.

[0027] The present application takes advantage of the maturity and cost advantage of the fused deposition modeling (such as 3D printing) technology in manufacturing complex geometries, and realizes high degree of freedom and near-net forming manufacturing of refractory high-entropy alloy components.

[0028] In some other embodiments, in step (4), the heating temperature for removing the binder is 200-500 DEG C, the heating rate is 0.5-2 DEG C / min, and the holding time is 2-6 h.

[0029] The temperature for hot isostatic pressing sintering is 1250-1450 DEG C, the heating rate is 5-15 DEG C / 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.

[0030] The present application adopts the binder-based fused deposition modeling (FDM) technology for component forming. The forming temperature only needs to melt the binder (usually below 500 DEG C), which is much lower than the melting point of the alloy, thereby completely avoiding thermal stress, cracking, element burning loss and secondary segregation caused by high-temperature melting process. The hot isostatic pressing (HIP) technology is adopted for integrated debinding and solid-phase sintering of the green body. Under high temperature and high pressure, the powder particles are densified through solid-state diffusion, and finally a fully dense component with high density, small grain size and original 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, utilizes the excellent reducing property of a small amount of hydrogen to effectively remove the surface oxides of the particles, providing a clean metal interface for solid-state diffusion, and ensuring the smooth progress of the densification process.

[0031] In a second aspect, the present application provides a preparation method of the CrNbTaTiV refractory high-entropy alloy in the first aspect, and 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 22-38 μm.

[0032] In some other embodiments, 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 at room temperature.

[0033] The yield strength in air at 800 DEG C is 650-700 MPa.

[0034] The CrNbTaTiV refractory high-entropy alloy component prepared by the present application has a uniform single-phase BCC solid solution structure, accurate chemical composition, complex shape, high density, and excellent mechanical properties.

[0035] In a third aspect, the present application provides the CrNbTaTiV refractory high-entropy alloy in the second aspect for use in the fields of aerospace, nuclear energy, and chemical industry.

[0036] The CrNbTaTiV refractory high-entropy alloy prepared by the present application still has 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.

[0037] The present application has the following beneficial effects:

[0038] (1) The present application bypasses the solidification segregation problem in traditional casting and direct melting forming through the technical route of "atomization and 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, the printing parameters, and the process parameters of HIP can all be independently adjusted, which provides a wide adjustment space for optimizing the microstructure and macroscopic properties of the material for different application requirements.

[0039] (2) By using FDM 3D printing technology, the low-temperature printing process (<500 °C) completely avoids the melting of the metal, and there is no problem of thermal stress cracking caused by a large temperature gradient, nor is there a problem of selective evaporation burning loss of elements, ensuring the integrity and accuracy of the final component. At the same time, it can manufacture lightweight lattices, integrated complex flow channels, bionic structures and other structures that cannot be achieved by traditional methods, greatly expanding the application scenarios of Cr-Nb-Ta-Ti-V high-entropy alloys, and realizing the integrated design and manufacturing of materials and structures. In addition, compared with SLM / EBM equipment, FDM printers are several orders of magnitude lower in price, have low operating environment requirements (no high vacuum required), and are 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.

[0040] (3) The hot isostatic pressing (HIP) process ensures that the relative density of the final component can reach more than 99.8%, almost completely eliminating internal porosity 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

[0041] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The embodiments of these drawings are set to explain the application, and do not constitute an improper limitation on the application.

[0042] Figure 1 XRD pattern of the powder obtained by using the atomization method in Example 1 of the present application;

[0043] Figure 2 SEM image of the spherical powder obtained by using the atomization method in Example 1 of the present application. DETAILED DESCRIPTION

[0044] Those skilled in the art will understand that the following examples are for illustration only and should not be taken as limiting the scope of the present application. If no specific conditions are specified in the examples, they are carried out under conventional conditions or according to the manufacturer's recommendations. If no manufacturer is specified for the components used, they are all conventional products that can be obtained commercially.

[0045] The abbreviations and key terms designed in the present application are explained as follows:

[0046] RHEA (Refractory High-Entropy Alloy): Refractory High-Entropy Alloy, refers to an alloy composed of multiple high-melting-point elements (usually with a melting point higher than 1500°C) in equal atomic ratio or near equal atomic ratio, and tends to form a simple solid solution phase (such as BCC or FCC).

[0047] BCC (Body-Centered Cubic): A common metallic crystal structure.

[0048] AM (Additive Manufacturing): Commonly known as 3D printing, it is a manufacturing method that constructs objects by depositing materials layer by layer.

[0049] FDM (Fused Deposition Modeling): Fused deposition modeling is a common additive manufacturing technology that builds parts layer by layer by heating and extruding thermoplastic filaments.

[0050] HIP (Hot Isostatic Pressing): A process for processing materials under high temperature and high pressure, which can be used for densification and defect healing of powder metallurgy parts.

[0051] SLM (Selective Laser Melting): Selective laser melting is an additive manufacturing technology that involves melting powder beds.

[0052] Green part: refers to a pre-formed blank obtained by mixing metal or ceramic powder with a binder and then forming it through a molding process (such as printing or injection). It has low strength and requires subsequent debinding and sintering treatment.

[0053] Debinding: The process of removing organic binders from green bodies by heating or other means before sintering.

[0054] Sintering: The process in which powder particles combine with each other through diffusion and other mechanisms at high temperatures below the melting point of the material, resulting in reduced porosity and increased density and strength.

[0055] Dense Part: Refers to the final part with extremely low internal porosity (usually relative density >99%) after densification processes such as sintering.

[0056] To address the problems of difficulty in obtaining single-phase microstructure, easy cracking, compositional inhomogeneity, and inability to form complex components in the current preparation of CrNbTaTiV refractory high-entropy alloys, this invention provides a novel additive manufacturing method with high controllability and relatively low cost. This method can stably prepare CrNbTaTiV refractory high-entropy alloy components with uniform single-phase BCC solid solution microstructure, accurate chemical composition, complex shape, high density, and excellent mechanical properties.

[0057] The additive manufacturing method for CrNbTaTiV refractory high-entropy alloys provided by this invention includes the following steps:

[0058] Step 1: Preparation of single-phase CrNbTaTiV refractory high-entropy alloy powder

[0059] (1) Ingredient preparation and melting: According to the equal atomic ratio or the set near equal atomic ratio, weigh the Cr, Nb, Ta, Ti and V metal blocks or particles with a purity higher than 99.9%. In a vacuum induction levitation melting furnace or a vacuum arc melting furnace, melt into a uniform master alloy ingot under an inert atmosphere (such as high-purity argon). To ensure uniform composition, multiple repeated melting can be performed.

[0060] (2) Gas atomization powder preparation: Place the master alloy ingot in the crucible of the gas atomization equipment (such as an atomization tower), reheat to a completely molten state (for example, 1800-2000°C) under an inert atmosphere, and the prepared molten alloy liquid flows through the guide pipe. The bottom of the guide pipe is impacted and broken into fine alloy droplets by a high-speed inert gas (preferably argon) jet.

[0061] (3) Rapid cooling and collection: The fine alloy droplets fly in the huge atomization tower and undergo sufficient heat exchange with the low-temperature inert gas, experiencing an extremely high cooling speed of >10 5 K / s, rapidly solidifying into spherical or near-spherical powder. Due to the extremely fast cooling speed, atoms cannot diffuse and segregate in a long range, so they are "frozen" in a single BCC solid solution phase at high temperature.

[0062] (4) Screening: The collected powder is screened to select the particle size range (for example, 15-50 μm) of the CrNbTaTiV single-phase alloy powder suitable for subsequent processes. X-ray diffraction (XRD) analysis confirms that the powder is a single BCC phase structure.

[0063] Step 2: Preparation of 3D printable RHEA-polymer composite wire

[0064] (1) Raw material preparation: Metal powder: CrNbTaTiV single-phase alloy powder (RHEA) prepared in step one.

[0065] 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 wire 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).

[0066] (2) Mixing: The RHEA powder and the binder are mixed uniformly in a torque rheometer or a high-speed mixer at a predetermined volume ratio (the volume content of the powder is preferably 55% to 70%). The mixing temperature is higher than the softening point of the binder but lower than the decomposition temperature of the binder, so as to ensure that the binder can fully coat each RHEA powder to obtain a feedstock.

[0067] (3) Extruding into a filament: The uniformly mixed feedstock is sent into a twin-screw extruder to be extruded into a continuous filament at a set temperature (for example, 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 to monitor and control its diameter in real time, 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.

[0068] Step 3: Low-temperature additive manufacturing (3D printing) of a green part

[0069] (1) Equipment: A commercial or customized fused deposition modeling (FDM) 3D printer is used, and a printer with a heating chamber and a hardened steel nozzle is preferably used to meet the printing requirements of the high-filled powder filament.

[0070] (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.

[0071] 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 part).

[0072] (3) Obtaining a green part: The printer prints the composite material layer by layer according to the printing program, and finally forms a three-dimensional green part (Green Part) composed of RHEA powder and binder, which is consistent with the digital model. The green part has a certain geometric shape, but has low strength and is not dense.

[0073] Step 4: Debinding and hot isostatic pressing (HIP) sintering

[0074] (1) Furnace loading: The printed green part is placed on the tooling of the hot isostatic pressing furnace.

[0075] (2) Degreasing stage: seal the furnace body, after vacuumizing, fill in 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 the green body cracking or deforming due to high pressure caused by rapid gasification of the binder. After this stage is completed, a porous "brown body" formed by weakly connected metal powder particles is obtained.

[0076] (3) HIP sintering stage: in the same furnace cycle, after degreasing is completed, continue to increase the temperature to a 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 effect of high temperature is to provide a driving force for atomic diffusion, so that the contact interface of adjacent powder particles shrinks, grows and fuses. The effect of high pressure is to provide an external mechanical driving force to promote the creep and plastic flow of the material, so as to crush and eliminate the internal residual pores.

[0077] (4) Cooling and discharging: after the holding is completed, the furnace is cooled to room temperature. After the pressure is released, a CrNbTaTiV refractory high-entropy alloy component with high density (relative density > 99.8%), uniform structure and excellent performance is obtained.

[0078] The scheme of the present application is further illustrated as follows in combination with specific examples:

[0079] Example 1

[0080] The present embodiment provides a CrNbTaTiV refractory high-entropy alloy and a preparation method, which specifically comprises the following steps:

[0081] (1) According to the equal atomic ratio Cr 20 Nb 20 Ta 20 Ti 20 V 20 , take Cr, Nb, Ta, Ti and V metal particles with a purity of > 99.9%, and place them in a vacuum arc melting furnace to melt 5 times under high-purity argon to prepare a uniform master alloy ingot. The master alloy ingot is placed in a crucible of a gas atomization tower and atomized under high-pressure argon to prepare spherical powder (RHEA powder). XRD analysis shows that the powder is a single BCC solid solution phase.

[0082] (2) The RHEA powder is mixed with a binder at high speed, and a composite wire with a diameter of 1.75±0.03 mm is prepared by a double-screw extruder at 190°C. The volume content of the RHEA powder is 60%, and the binder is composed of the following components in mass percentage: polyformaldehyde (POM) 60%, polyethylene glycol (PEG) 35%, and stearic acid (SA) 5%.

[0083] (3) The printing model for 3D printing is an ASTM E8 standard tensile specimen. The printing parameters are as follows: nozzle temperature 215°C, platform temperature 60°C, printing speed 30 mm / s, layer height 0.2 mm, 100% filling, and a green body is obtained by printing.

[0084] (4) The green body is subjected to debinding treatment by being heated to 220°C at a rate of 1°C / min under a flowing argon atmosphere and then being kept at 220°C for 2 h (to remove PEG), and then being heated to 480°C at a rate of 1°C / min and kept at 480°C for 3 h (to remove POM). After debinding, the same furnace is used to heat the sample to 1350°C at a rate of 10°C / min while applying a pressure of 150 MPa, and the sample is kept at 1350°C for 3 h, and then the sample is cooled in the furnace to obtain a CrNbTaTiV refractory high-entropy alloy.

[0085] The CrNbTaTiV refractory high-entropy alloy obtained is subjected to performance testing, and the results are as follows:

[0086] Relative density: The relative density is 99.85% as measured by the Archimedes method.

[0087] Microstructure: Metallographic analysis shows that the microstructure is a uniform single-phase BCC structure without Laves phase or other second phases, and the average grain size is about 22 μm.

[0088] Mechanical properties (room temperature): the tensile strength is 1210 MPa, the yield strength is 1125 MPa, the elongation after fracture is 8.5%, and the Vickers hardness is 455 HV.

[0089] It can be seen from Figure 1 that the powder obtained by atomization is basically single-phase without other second phases. It can be seen from Figure 2 that the average grain size of the spherical powder obtained by atomization is about 22 μm.

[0090] Example 2

[0091] This example provides a CrNbTaTiV refractory high-entropy alloy and a preparation method. The difference from Example 1 is that the preparation process of steps (2)-(4) is as follows:

[0092] (2) The RHEA powder is mixed with a binder 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 mass percentage: ethylene-vinyl acetate copolymer (EVA) 55%, paraffin wax (PW) 40%, and stearic acid (SA) 5%.

[0093] (3) The printing model for 3D printing is an ASTM E8 standard tensile specimen. The printing parameters are: 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.

[0094] (4) The green body is heated to 500°C at a rate of 0.8°C / min under a flowing argon atmosphere, and is kept at this temperature for 4 h (paraffin wax and EVA are removed slowly during this process). After debinding, the temperature is increased to 1400°C at a rate of 10°C / min, and the pressure is increased to 120 MPa. The alloy is kept at this temperature for 2 h, and is then cooled in the furnace to obtain a CrNbTaTiV refractory high-entropy alloy.

[0095] The other preparation steps are the same as those in Example 1.

[0096] The CrNbTaTiV refractory high-entropy alloy prepared is subjected to performance testing, and the results are as follows:

[0097] Relative density: The relative density measured by the Archimedes method is 99.91%.

[0098] 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.

[0099] Mechanical properties (room temperature): The tensile strength is 1160 MPa, the yield strength is 1070 MPa, and the elongation after fracture is 10.2% (grain coarsening causes a slight decrease in strength and an increase in plasticity). The Vickers hardness is 438 HV.

[0100] Example 3

[0101] This example provides a CrNbTaTiV refractory high-entropy alloy and a preparation method, which specifically comprises the following steps: different from Example 1, the preparation process of steps (2)-(4) is as follows:

[0102] (1) The non-equivalent atomic ratio of CrNbTaTiV is non-equivalent atomic ratio Cr 20 Nb 20 Ta 20 Ti 30 V 10Cr, 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 form 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 form spherical powder (RHEA powder). XRD analysis showed that the powder was a single BCC solid solution phase.

[0103] (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%.

[0104] (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 as follows: 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.

[0105] (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 the temperature was held for 4 h, and then the furnace was cooled to obtain a CrNbTaTiV refractory high-entropy alloy.

[0106] The performance of the prepared CrNbTaTiV refractory high-entropy alloy was tested, and the results were as follows:

[0107] Product morphology: A complex BCC lattice structure dense part with complete appearance, no fracture, and no obvious deformation was successfully prepared.

[0108] 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%.

[0109] Microstructure: The metallographic structure was a uniform and fine single-phase BCC equiaxed crystal, and the average grain size was about 28 μm.

[0110] Hardness: The Vickers hardness on the rod section was 480 HV. This example proves the ability of the application to manufacture complex structural parts.

[0111] Example 4

[0112] The embodiment provides a CrNbTaTiV refractory high-entropy alloy and a preparation method. Different from the embodiment 1, the preparation process in step (4) is as follows:

[0113] (4) The green body is subjected to debinding treatment under the atmosphere of flowing argon, is heated to 220°C at a rate of 1°C / min and is kept for 2h (PEG is removed), and is heated to 480°C at a rate of 1°C / min and is kept for 3h (POM is removed). In order to obtain finer grains and improve high-temperature performance, a lower sintering temperature and a higher pressure are used. After debinding, the same furnace is used to heat to 1280°C at a rate of 10°C / min, and is pressurized to 200 MPa, and is kept for 4h, and then is cooled in the furnace to obtain the CrNbTaTiV refractory high-entropy alloy.

[0114] Other preparation steps are consistent with the embodiment 1.

[0115] The prepared CrNbTaTiV refractory high-entropy alloy is subjected to performance testing, and the results are as follows:

[0116] Relative density: The relative density measured by the Archimedes method is 99.95% (higher pressure helps densification).

[0117] Microstructure: Due to the lower sintering temperature, the grain growth is effectively inhibited, and the average grain size is only 24μm. The structure is a uniform single-phase BCC structure.

[0118] 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.

[0119] High-temperature performance: The sample is subjected to tensile testing at 800°C in air, and the yield strength is as high as 680 MPa, which shows excellent high-temperature mechanical properties, and proves that the components prepared by the method are suitable for high-temperature load-bearing environments.

[0120] Comparative example 1

[0121] The comparative example provides a CrNbTaTiV refractory high-entropy alloy and a preparation method. Different from the embodiment 1, the preparation process in step (4) is as follows: ordinary pressureless high-temperature sintering is used, the product is heated to 1350°C at a rate of 10°C / min under the atmosphere of flowing high-purity argon (99.999%) after debinding, but maintains normal pressure (without pressurization), is kept for 3h, and then is cooled in the furnace, and no pressure is applied during the sintering process.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] Comparative Example 2

[0126] 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 hydrogen is not 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.

[0127] 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.

[0128] 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 exhibiting brittle fracture characteristics, especially the significant decrease of plasticity and strength. 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 for obtaining high strength and high plasticity.

[0129] In conclusion, 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.

[0130] The above is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles 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; The temperature of the heating and melting is 1800-2000 ℃; The atomizing mode 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 refractory high-entropy alloy powder has a single body-centered cubic phase structure; (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) using a hot isostatic pressing technology to integrally debind and solid-phase sinter the green body; In the debinding stage, the green body is heated to remove the binder under an inert atmosphere to obtain a porous brown body formed by weakly connecting metal powder particles; then, in the same furnace, sintering is performed by hot isostatic pressing, and after cooling, the CrNbTaTiV refractory high-entropy alloy is obtained; The temperature of the 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; The CrNbTaTiV refractory high-entropy alloy has a single body-centered cubic phase structure; The mixed atomic ratio of the Cr, Nb, Ta, Ti and V metals is 20:20:20:(20-30):(10-20), and the total mixed atomic ratio is 100.

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 all >99.9%; 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: melting the CrNbTaTiV refractory high-entropy alloy in a vacuum arc melting furnace; and casting the CrNbTaTiV refractory high-entropy alloy. In step (1), the inert atmosphere is one of argon and nitrogen; The refractory high-entropy alloy powder has a particle size of 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 temperature of the extrusion 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.

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.

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 relative density of more than 99.7%, and an average grain size of 22-38 mu m.

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 DEG C is 650-700 MPa.

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

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