Preparation method and application of CoCrNi medium-entropy alloy material for additive manufacturing

Abstract

The application discloses a preparation method of a CoCrNi medium-entropy alloy material for additive manufacturing, and the CrCoNi medium-entropy alloy and the preparation method thereof comprise the following steps: a. adding 0%-1wt% of rare earth CeO2 into the CrCoNi medium-entropy alloy, and mixing powder according to ingredient design; b. inputting a workpiece scanning path file into a computer, and printing a single-variable medium-entropy alloy ingot at a set step scanning speed (600-900mm / s). The application optimizes the compactness of the CoCrNi medium-entropy alloy and reduces defects by adjusting process parameters of additive manufacturing, so that an additive manufacturing workpiece with high strength, good fracture toughness and good strength-plasticity matching is obtained. Compared with the prior art, the application optimizes the compactness of the CoCrNi medium-entropy alloy and reduces defects by adjusting process parameters of additive manufacturing, so that an additive manufacturing workpiece with high strength, good fracture toughness and good strength-plasticity matching is obtained.

Description

Technical Field

[0001] This invention relates to the field of CoCrNi medium-entropy alloy material preparation technology, and particularly to a method for preparing CoCrNi medium-entropy alloy material for additive manufacturing and its application. Background Technology

[0002] Multi-component alloys possess properties and characteristics distinct from traditional alloys, making them a popular and cutting-edge material in the field of metallic materials. Both medium-entropy and high-entropy alloys belong to the category of multi-component alloys, with medium-entropy alloys evolving from the design concepts of high-entropy alloys. Medium-entropy alloys are generally considered to be single-phase solid solution alloys composed of 3-4 main elements, defined as 1R≤ΔS≤1.5R, where ΔS is the mixing entropy and R is the molar gas constant. Due to their unique characteristics, including severe lattice distortion, slow diffusion, and the "cocktail" effect, medium-entropy alloy materials can achieve high strength and a good strength-ductility balance even at room temperature, without work hardening treatment. They have broad application prospects in advanced nuclear energy systems, hydrogen energy storage, and transportation.

[0003] Currently, the application of entropy alloys in additive manufacturing is a research hotspot both domestically and internationally in the exploration of materials with superior mechanical properties. Chinese patent CN109972019A discloses an additive manufacturing method for entropy alloys in the CrCoNi system; CN113414384A discloses an additive manufacturing method for entropy alloys in the CrCoNi system by adding a small amount of LaB6, thereby introducing La2O3 precipitates to form a second-phase strengthening mechanism; CN114734041A discloses an additive manufacturing method for lightweight, refractory, high-entropy materials in the WNbTiNi system. Existing technologies typically involve adding elements such as Mn and Si or using methods such as cold rolling to improve the tensile strength and elongation of entropy alloys. Therefore, developing a workpiece that improves the manufacturing defects and microstructure of entropy alloys in additive manufacturing, thereby significantly enhancing material properties, is of great significance for expanding the widespread application of entropy alloys in additive manufacturing.

[0004] Through in-depth research, the inventors of this application have obtained a method for preparing CoCrNi medium-entropy alloy materials for additive manufacturing and its application. This method can improve the workpieces with manufacturing defects and microstructure of medium-entropy alloys in additive manufacturing, thereby significantly improving the material properties. This is of great significance for expanding the wide application of medium-entropy alloys in additive manufacturing. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing CoCrNi medium-entropy alloy materials for additive manufacturing and their application, which can effectively improve material properties.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0007] A method for preparing CoCrNi medium-entropy alloy material for additive manufacturing includes the following steps:

[0008] Step 1: Take 99-99.9 wt.% of CrCoNi medium-entropy alloy matrix powder and 0.1-1 wt.% of CeO2 rare earth powder;

[0009] Step 2: The CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder are put into a ball mill for ball milling and mixing to obtain medium-entropy alloy composite powder;

[0010] Step 3: Place the medium-entropy alloy composite powder into the powder storage box of the selective laser melting equipment, design and save the pre-printed model, and send the scanning path file to the additive manufacturing equipment;

[0011] Step 4: Spread the medium-entropy alloy composite powder onto the stainless steel substrate, and use a laser to scan along the designed path at a scanning speed of 600-900 mm / s, a power of 150-250 W, a laser diameter of 0.1 mm, and a layer thickness of 0.03 mm. When the laser scans the upper and lower mixed powder planes, the scanning angle interval is 67°. The entire scanning process is carried out in a nitrogen atmosphere.

[0012] Step 5: After the selective laser melting equipment cools down, remove the stainless steel substrate and use wire cutting to separate the joint between the workpiece and the substrate.

[0013] In a preferred embodiment, the CrCoNi medium-entropy alloy matrix powder comprises 33.74-35.74 wt% Co, 29.66-31.66 wt% Cr, and 33.6-35.6 wt% Ni.

[0014] In a preferred embodiment, the particle size of the CrCoNi medium-entropy alloy matrix powder is 10-100 μm, and the particle size of the CeO2 rare earth powder is 1-10 μm.

[0015] In a preferred embodiment, in step two, during ball milling, the ball-to-material ratio is 1:1-1.5:1, the mixing time is 3-4 hours, the rotation speed of the ball mill is 400-700 r / min, and the speed is adjusted every hour.

[0016] In a preferred embodiment, before ball milling, the CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder are uniformly dispersed inside the ball mill.

[0017] In a preferred embodiment, CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder are uniformly dispersed inside a ball mill using a dispersing device. The dispersing device includes a first conveying pipe and a second conveying pipe. The first conveying pipe has multiple discharge nozzles, and the second conveying pipe includes an absorption section and a conveying section. The absorption section has multiple suction ports, and each suction port has a one-way valve that allows unidirectional flow from the outside to the inside. The absorption section is spirally wound around the first conveying pipe, and the conveying section is inserted into the first conveying pipe. The dispersing device is inserted into the ball mill, and CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder are conveyed into the first conveying pipe by airflow, while airflow is simultaneously introduced into the second conveying pipe.

[0018] In a preferred embodiment, the starting point of the absorption section corresponds to the starting point of the first conveying pipeline, the ending point of the absorption section corresponds to the ending point of the first conveying pipeline, the starting point of the conveying section corresponds to the ending point of the first conveying pipeline, and the ending point of the conveying section corresponds to the starting point of the first conveying pipeline.

[0019] In a preferred embodiment, the helical pitch of the absorption section gradually increases from its starting point to its ending point.

[0020] An application of a CoCrNi medium-entropy alloy material for additive manufacturing, the CoCrNi medium-entropy alloy material comprising 99-99.9 wt.% CrCoNi medium-entropy alloy matrix powder and 0.1-1 wt.% CeO2 rare earth powder, is used in nuclear energy manufacturing, hydrogen energy storage or transportation.

[0021] Compared with existing technologies, this invention utilizes the inherent strengthening mechanism of medium-entropy alloys: the combined effect of lattice frictional stress, grain boundary strengthening, and dislocation strengthening. Furthermore, by adding medium-entropy rare earth powder, the solid solution strengthening effect of the medium-entropy alloy is enhanced, resulting in a significant improvement in the mechanical properties of the resulting composite material. This yields high-strength, plastically balanced, high-performance workpieces that require no subsequent cold or hot machining. Simultaneously, the "diffusion retardation" effect prevents the formation of a brittle second phase, eliminating the need for material removal and resulting in high material utilization.

[0022] This invention boasts advantages such as short manufacturing time, low cost of added rare earth oxides, significantly improved mechanical properties, and a balance between strength and plasticity. Specifically, its innovations include: the addition of rare earth CeO2 to the medium-entropy alloy CrCoNi is low-cost, and high-purity CeO2 is readily available on the mainstream market. Therefore, by adding only trace amounts of CeO2 to the medium-entropy alloy CrCoNi, the yield strength, ultimate tensile strength, and other mechanical properties can be significantly improved with almost no increase in cost. The manufacturing method of this invention utilizes laser additive manufacturing, which offers the advantage of a direct and convenient process, eliminating cumbersome processing steps and thus greatly improving material utilization. However, during laser additive manufacturing, different scanning speeds and laser powers can lead to variations in the porosity of the finished product. Generally, increased porosity in components results in decreased mechanical properties. Through numerous experiments using specific stepped scanning rates and laser powers, this invention has discovered additive-manufactured workpieces with low porosity, high strength, and a balanced strength and plasticity. Attached Figure Description

[0023] Figure 1 The XRD diffraction pattern is shown in the diagram of the medium-entropy alloy composite material prepared according to the present invention.

[0024] Figure 2 This is a comparison chart of the tensile properties of the medium-entropy composite gold material prepared according to the present invention under the conditions of laser power of 200W and scanning speed of 700mm / s.

[0025] Figure 3 This is an EBSD (electron backscattering diffraction) orientation distribution diagram of adjacent vertical planes of the medium-entropy alloy composite material prepared according to the present invention.

[0026] Figure 4 This is a work hardening rate curve of the medium-entropy alloy composite material prepared according to the present invention under the parameter conditions of 200W power and 700mm / s speed.

[0027] Figure 5 This invention relates to a comparison of the true stress and true strain properties of a medium-entropy alloy composite material prepared according to the invention under the parameters of laser power 200W and scanning speed 700mm / s.

[0028] Figure 6 This is a schematic diagram of the dispersion device used in this invention.

[0029] Figure 7 This is a schematic diagram of the cooperative structure of the first conveying pipe and the conveying section of the dispersing device used in this invention.

[0030] In the picture

[0031] First conveying pipe 1; discharge nozzle 2; second conveying pipe 3; absorption section 4; suction inlet 5; conveying section 6. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings.

[0033] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention. Example 1

[0034] A method for preparing CoCrNi medium-entropy alloy material for additive manufacturing includes the following steps:

[0035] Step 1: Take 99.5 wt.% of CrCoNi medium-entropy alloy matrix powder and 0.5 wt.% of CeO2 rare earth powder. The CrCoNi medium-entropy alloy matrix powder has three specific component ratios: 34.7 wt% Co, 30.55 wt% Cr, and 34.54 wt% Ni. The particle size of the CrCoNi medium-entropy alloy matrix powder is 10-100 μm, and the particle size of the CeO2 rare earth powder is 1-10 μm. This particle size can be dispersed in the medium-entropy alloy matrix powder to improve the solid solution strengthening effect of the fcc solid solution.

[0036] There is no positive correlation between the rare earth content in medium-entropy alloy composite powder and its mechanical properties. When the rare earth content is too high, its mechanical properties, such as yield strength, will be significantly reduced. It is necessary to reasonably add rare earth content to change the mechanical properties and plastic deformation capacity of the composite material. In this embodiment, the proportion of rare earth powder is selected as 0.5 wt.%, which meets this requirement.

[0037] The 99.5wt% CrCoNi medium-entropy alloy matrix powder provided in this embodiment utilizes the inherent strengthening mechanism of medium-entropy alloys: the combined effect of lattice friction stress, grain boundary strengthening, and dislocation strengthening. During workpiece deformation, dislocation accumulation and entanglement occur, hindering subsequent dislocation movement and thus improving mechanical properties. Furthermore, the addition of rare earth powder enhances the solid solution strengthening effect of the medium-entropy alloy, resulting in a significant improvement in the mechanical properties of the resulting composite material. Moreover, the mixing of CrCoNi medium-entropy alloy matrix powder and CeO2 powder in the aforementioned proportions allows for optimal control of the average grain size of the printed workpiece's microstructure.

[0038] Step 2: Add CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder to a ball mill for ball milling and mixing. The ball-to-powder ratio is 1:1-1.5:1, the mixing time is 3-4 hours, the rotation speed of the ball mill is 400-700 r / min, and the speed is adjusted every 1 hour to obtain medium-entropy alloy composite powder. The medium-entropy alloy composite powder after mixing needs to meet the following standards: the mixed powder has no obvious color deviation, the particle size is roughly uniform, and there should be no irregular small spherical agglomerates.

[0039] Furthermore, before ball milling, the CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder are evenly distributed inside the ball mill to prevent the powder from accumulating in a certain area inside the ball mill, which is conducive to achieving uniform ball milling and dispersion of the powder.

[0040] To achieve uniform distribution, a distribution device is installed to uniformly distribute the CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder inside the ball mill. Figure 6 and Figure 7 As shown, the dispersing device includes a first conveying pipe 1 and a second conveying pipe 3. The first conveying pipe 1 is provided with multiple discharge nozzles 2. The second conveying pipe 3 includes an absorption section 4 and a conveying section 6. The absorption section 4 is provided with multiple suction ports 5. Each suction port 5 is provided with a one-way valve that allows unidirectional flow from the outside to the inside. The absorption section 4 is spirally wound around the first conveying pipe 1. The conveying section 6 is inserted into the first conveying pipe 1. The dispersing steps include: inserting the dispersing device into the ball mill, conveying CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder into the first conveying pipe 1 through airflow, and simultaneously introducing airflow into the second conveying pipe 3.

[0041] With the above structural configuration, the mixed powder of CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder is input through the first conveying pipe 1 and ejected from the discharge nozzle 2 of the first pipe. Since the first conveying pipe 1 has a certain length, it covers the axial area of ​​the ball mill, thus enabling the mixed powder to fully cover the axial area of ​​the ball mill. At the same time, the suction port 5 on the absorption section 4 performs secondary absorption on the powder ejected from the discharge nozzle 2, changing the direction of the powder and causing collisions between the powder particles, resulting in a good mixing effect. The powder entering the absorption section 4 is then transported into the conveying section 6 by the airflow and conveyed back into the first conveying pipe 1, where it is ejected again. In this reciprocating ejection and absorption process, a good mixing effect is achieved.

[0042] To further improve technical efficiency, the starting point of the absorption section 4 corresponds to the starting point of the first conveying pipe 1, and the ending point of the absorption section 4 corresponds to the ending point of the first conveying pipe 1. Similarly, the starting point of the conveying section 6 corresponds to the ending point of the first conveying pipe 1, and the ending point of the conveying section 6 corresponds to the starting point of the first conveying pipe 1. With this structural arrangement, since the tubular structure typically discharges more material at its end, the powder is replenished to the starting point of the first conveying pipe 1 via the conveying section 6. This increases the amount of powder at the starting point of the first conveying pipe 1, thereby replenishing the material at the starting and ending points of the first conveying pipe 1 and ensuring that the material is as uniform as possible between the beginning and end points, thus achieving uniform material distribution.

[0043] To further improve the uniform distribution effect, the spiral pitch of the absorption section 4 gradually increases from its starting point to its ending point. Because the spiral pitch at the starting point of the absorption section 4 is small, the pipe density is high, and there are more suction ports 5, it can generate more suction at the starting point of the first conveying pipe 1, so that the powder at the starting point of the first conveying pipe 1 can be ejected by force, thus achieving uniform distribution of powder from the starting point to the ending point of the first and second pipes.

[0044] Step 3: Dry the medium-entropy alloy composite powder, filter it through a 235-mesh sieve, and fill it into the powder storage box of the selective laser melting equipment. Design and save the pre-printed model in the computer, and transfer the scanning path file to the additive manufacturing equipment via USB flash drive.

[0045] Step 4: The medium-entropy alloy composite powder is spread evenly onto a stainless steel substrate using a scraper. The stainless steel substrate is cleaned to remove oil stains, impurities, and other foreign matter. A laser is then used to scan along a designed path at a scanning speed of 700 mm / s, a power of 200 W, a laser diameter of 0.1 mm, and a layer thickness of 0.03 mm. After each layer is scanned, the computer controls the substrate to descend by one layer's thickness, while the powder spreading system simultaneously lays in the new layer of powder. When scanning adjacent layers of mixed powder, the laser scanning angle is spaced at 67° intervals to reduce the formation of cracks or gaps during the melting of the medium-entropy alloy composite material. The entire scanning process is conducted in a nitrogen atmosphere to prevent oxidation of the powder during melting and the formation of an unstable second phase.

[0046] Step 5: After the selective laser melting equipment cools down, remove the stainless steel substrate and use wire cutting to separate the joint between the workpiece and the substrate.

[0047] The method for preparing CoCrNi medium-entropy alloy material for additive manufacturing in this embodiment has the advantages of short manufacturing time, low cost of added rare earth oxides, significantly improved mechanical properties, and a good balance of strength and plasticity. Specifically, it is reflected in the following innovations:

[0048] The rare earth element CeO2 added to the medium-entropy alloy CrCoNi is low in cost and high-purity products are readily available on the mainstream market. Therefore, adding only trace amounts of CeO2 to the medium-entropy alloy CrCoNi can significantly improve its mechanical properties, such as yield strength and ultimate tensile strength, with almost no increase in cost. This embodiment uses laser additive manufacturing, which has the advantage of a direct and convenient manufacturing process without cumbersome processing steps, thus greatly improving material utilization. However, during laser additive manufacturing, different scanning speeds and laser powers can lead to changes in the porosity of the finished product. Generally speaking, increased porosity in a component leads to a decrease in its mechanical properties. This embodiment uses a specific stepped scanning rate and laser power to discover additively manufactured workpieces with low porosity, high strength, and a good balance of strength and plasticity.

[0049] After the medium-entropy alloy composite material was mixed in a ball mill, XRD experiments were performed, and the results showed a single-phase FCC structure, such as... Figure 1 .

[0050] Depend on Figure 2 It can be seen that, under the parameters of laser speed of 700 mm / s and laser energy of 200 W, the medium-entropy alloy composite material with 0.5 wt.% CeO2 rare earth added has a yield strength of nearly 100 MPa, an ultimate tensile strength of nearly 200 MPa, and an elongation of nearly 10% compared with the CrCoNi medium-entropy alloy without rare earth added.

[0051] In this embodiment, EBSD (electron backscattering diffraction) experiments were conducted on the medium-entropy alloy composite material with 0.5% CeO2. Figure 3 As shown in the figure, the workpiece has random and uniform grain orientation, ensuring its mechanical properties.

[0052] Depend on Figure 4 It is known that the workpiece formed from a medium-entropy alloy composite material with 0.5 wt.% CeO2 rare earth elements, under laser speed of 700 mm / s and laser energy of 200 W, exhibits a very high work hardening rate of 5000 MPa after a small amount of true strain change, far exceeding the work hardening rate of 2000 MPa for workpieces without rare earth elements. Figure 5 It can be seen that the true stress of the medium-entropy alloy composite material with 0.5wt.% CeO2 rare earth added reaches nearly 1400 MPa under the parameters of laser speed 700 mm / s and laser energy 200 W.

[0053] As can be seen, the medium-entropy alloy composite material prepared by additive manufacturing using a mixture of medium-entropy alloy and rare earth CeO2 in this application significantly improves both tensile strength and yield strength compared to medium-entropy alloy without rare earth. Example 2

[0054] An application of a CoCrNi medium-entropy alloy material for additive manufacturing, the CoCrNi medium-entropy alloy material comprising 99-99.9 wt.% CrCoNi medium-entropy alloy matrix powder and 0.1-1 wt.% CeO2 rare earth powder, wherein the amount of CeO2 rare earth powder is preferably set to 0.5 wt.%, and it is used in nuclear energy manufacturing, hydrogen energy storage or transportation.

[0055] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Unless otherwise specified, an element defined by the phrase "comprising..." or "including..." does not exclude the presence of additional elements in the process, method, article, or terminal device that includes said element. Additionally, in this document, "greater than," "less than," "exceeding," etc., are understood to exclude the stated number; "above," "below," "within," etc., are understood to include the stated number.

[0056] The above description of the embodiments is provided to facilitate understanding and use of the present invention by those skilled in the art. It is obvious to those skilled in the art that various modifications can be easily made to the embodiments, and the general principles described herein can be applied to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing CoCrNi medium-entropy alloy material for additive manufacturing, characterized in that, Includes the following steps: Step 1: Take 99.5 wt.% of CrCoNi medium-entropy alloy matrix powder and 0.5 wt.% of CeO2 rare earth powder; Step 2: CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder are fed into a ball mill for ball milling and mixing to obtain medium-entropy alloy composite powder. The CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder are uniformly dispersed inside the ball mill using a dispersing device. The dispersing device includes a first conveying pipe and a second conveying pipe. The first conveying pipe has multiple discharge nozzles, and the second conveying pipe includes an absorption section and a conveying section. The absorption section has multiple suction ports, each equipped with a one-way valve that allows unidirectional flow from the outside in. The absorption section is spirally wound around the first conveying pipe, and the conveying section is inserted into the first conveying pipe. The dispersing device is inserted into the ball mill, and the CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder are conveyed into the first conveying pipe via airflow. Simultaneously, airflow is introduced into the second conveying pipe. The spiral pitch of the absorption section gradually increases from its starting point to its ending point. Step 3: Place the medium-entropy alloy composite powder into the powder storage box of the selective laser melting equipment, design and save the pre-printed model, and send the scanning path file to the additive manufacturing equipment; Step 4: Spread the medium-entropy alloy composite powder onto the stainless steel substrate, and use a laser to scan along the designed path at a scanning speed of 600-900 mm / s, a power of 150-250 W, a laser diameter of 0.1 mm, and a layer thickness of 0.03 mm. When the laser scans the upper and lower mixed powder planes, the scanning angle interval is 67°. The entire scanning process is carried out in a nitrogen atmosphere. Step 5: After the selective laser melting equipment cools down, remove the stainless steel substrate and use wire cutting to separate the joint between the workpiece and the substrate.

2. The method for preparing a CoCrNi medium-entropy alloy material for additive manufacturing according to claim 1, characterized in that, The CrCoNi medium-entropy alloy matrix powder comprises 33.74-35.74 wt% Co, 29.66-31.66 wt% Cr, and 33.6-35.6 wt% Ni.

3. The method for preparing a CoCrNi medium-entropy alloy material for additive manufacturing according to claim 1, characterized in that, The particle size of the CrCoNi medium-entropy alloy matrix powder is 10-100 μm, and the particle size of the CeO2 rare earth powder is 1-10 μm.

4. The method for preparing a CoCrNi medium-entropy alloy material for additive manufacturing according to claim 1, characterized in that, In step two, during ball milling, the ball-to-material ratio is 1:1-1.5:1, the mixing time is 3-4 hours, the rotation speed of the ball mill is 400-700 r / min, and the speed is adjusted every hour.

5. The method for preparing a CoCrNi medium-entropy alloy material for additive manufacturing according to claim 1, characterized in that, Before ball milling, the CrCoNi medium-entropy alloy matrix powder and CeO2 rare earth powder are evenly distributed inside the ball mill.

6. The method for preparing a CoCrNi medium-entropy alloy material for additive manufacturing according to claim 1, characterized in that, The starting point of the absorption section corresponds to the starting point of the first conveying pipeline, the ending point of the absorption section corresponds to the ending point of the first conveying pipeline, the starting point of the conveying section corresponds to the ending point of the first conveying pipeline, and the ending point of the conveying section corresponds to the starting point of the first conveying pipeline.

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