High-strength cobalt-free hypoeutectic high-entropy alloy and preparation method thereof

Abstract

The application discloses a kind of high-strength cobalt-free hypoeutectic high-entropy alloys and preparation method thereof.The alloy includes the following atomic percentage elements: Al 10-25%, Cr 10-25%, Cu 15-30%, Fe 10-25%, Ni 10-25%;The alloy does not contain Co element, and the alloy is composed of FCC phase and BCC phase hypoeutectic;The alloy is based on the synergistic effect between each component, replaces Co with Cu element, realizes the formation of FCC phase and BCC phase hypoeutectic structure in the alloy, so as to greatly improve the comprehensive performance of alloy material.The alloy is prepared by laser melting deposition method, and the crystallization latent heat is consumed during the alloy eutectic growth process to eliminate the internal stress generated during high-speed cooling in the preparation process, so as to inhibit the generation of cracks.The alloy material effectively solves the contradiction between the mechanical strength and plasticity of high-entropy alloy, and the test shows that when the breaking strength is 1835MPa, the breaking plasticity can reach 28.8%, which greatly expands the application scene of the alloy.

Description

TECHNICAL FIELD

[0001] The application relates to a high-entropy alloy, in particular to a cobalt-free hypoeutectic high-entropy alloy with high strength and a preparation method thereof, and belongs to the technical field of high-entropy alloy preparation. TECHNICAL BACKGROUND

[0002] High-entropy alloys (HEAs) are a new multi-principal element alloy system, usually composed of 5 or more main elements, and the proportion is close to the equal atomic ratio. Although based on a completely new alloy design concept, high-entropy alloys still cannot escape the problem of the "strength-plasticity" contradiction of traditional structural materials, and how to realize the combination of high strength and high plasticity is the research focus of designing and preparing high-performance high-entropy alloys. Eutectic high-entropy alloys (EHEAs) are a new generation of high-entropy alloys based on the design of traditional eutectic alloys, which are composed of regularly alternating rod-shaped or sheet-shaped brittle and ductile phases, and can realize the synergistic effect of strength and plasticity. AlCoCrFeNi 2.1 Eutectic high-entropy alloys are a kind of eutectic high-entropy alloys that are widely studied at present, which have high strength and good plasticity. However, AlCoCrFeNi 2.1 contains Co element, and the production cost is high, which limits the application of the alloy in actual engineering field. Therefore, it is of important practical significance to develop Co-free eutectic high-entropy alloys with excellent mechanical properties.

[0003] At present, the method for preparing eutectic high-entropy alloys mainly is arc melting, which is prone to composition segregation, casting defects, and limited part shape, in addition, subsequent complex cutting processing will cause material waste and further increase the production cost.

[0004] Chinese patent (CN115433864A) discloses a hypoeutectic high-entropy alloy for friction materials and a preparation method thereof, which is composed of Al, Co, Cr, Fe, Ni and Hf elements, and the expression is (AlCoCrFeNi)100xHfx, 2≤x≤6, wherein Al, Co, Cr, Fe and Ni are in equal atomic ratio. The preparation is carried out by adopting arc melting method. The application utilizes the characteristics of large atomic radius of Hf, negative mixing enthalpy with other component elements and large difference in electronegativity, induces the hard Laves phase to precipitate at the grain boundary, and occurs second phase strengthening and fine grain strengthening, so that the hypoeutectic high-entropy alloy has the advantages of high hardness and good wear resistance. Although the alloy provided by the application has beneficial wear resistance and mechanical strength, the plasticity is poor, which is not conducive to subsequent processing, greatly limits the application field of the material, and the raw material still contains Co element.

[0005] Chinese patent (CN111534817B) discloses a laser deposition preparation Al xThe application discloses a method for preparing a TiCrMnCu high-entropy alloy, wherein five metal element powders of Al, Ti, Cr, Mn and Cu are configured according to an atomic ratio of 0-1.5:1:1:1:1, uniformly mixed by ball milling, dried, and then subjected to laser deposition, and the laser deposition is carried out under the following conditions: a powder feeding rate of 15 g / min, a laser power of 600 W, a scanning speed of 250 mm / min and a light spot diameter of 1.5 mm, and the laser deposition is carried out on a substrate by a coaxial powder feeding method; and the high-entropy alloy single phase and double phase can be changed during the laser deposition by adjusting the atomic ratio of the five metal element powders in the mixed powder.

[0006] In summary, the market urgently needs a high-entropy alloy with low raw material cost and balanced mechanical strength and plasticity. SUMMARY

[0007] In view of the problems in the prior art, a first object of the application is to provide a high-strength cobalt-free hypoeutectic high-entropy alloy, and the synergistic effect between the component elements realizes the formation of a FCC phase and a BCC phase hypoeutectic structure in the alloy, thereby greatly improving the comprehensive performance of the alloy material; on one hand, by strictly controlling the addition amount of each component element, the alloy material has obvious high-entropy effect, and on the other hand, the combination relationship between the FCC phase and the BCC phase is controlled, the plasticity of the material is greatly improved on the premise of ensuring excellent mechanical strength of the material.

[0008] A second object of the application is to provide a preparation method of the high-strength cobalt-free hypoeutectic high-entropy alloy, and the laser melting deposition method is used to realize one-step forming preparation of the high-entropy alloy, and no pre-treatment and subsequent heat treatment process is needed, and further, the hypoeutectic high-entropy alloy can effectively eliminate internal stress generated during high-speed cooling in the preparation process, so as to inhibit crack generation.

[0009] To achieve the above technical purposes, the application provides a high-strength cobalt-free hypoeutectic high-entropy alloy, which comprises the following atomic percentage elements: Al 10-25%, Cr 10-25%, Cu 15-30%, Fe 10-25% and Ni 10-25%, and the alloy does not contain Co element and is composed of a FCC phase and a BCC phase hypoeutectic structure.

[0010] As a preferred scheme, the alloy is composed of the following atomic percentage elements: Al 10-20%, Cr 10-20%, Cu 15-30%, Fe 10-20%, and Ni 10-20%.

[0011] As a preferred scheme, the atomic ratio of Al, Cr, Fe and Ni is 1:1:1:1.

[0012] As a preferred scheme, the atomic ratio of Al and Cu is 1:1-1.6. Further preferably, the atomic ratio of Al and Cu is 1:1.2-1.6, and the atomic ratio of Al and Cu is most preferably 1:1.4-1.6.

[0013] The atomic ratio of Al and Cu should be strictly implemented according to the above requirements. If the addition amount of Cu is too low, the amount of FCC phase produced is too low, and the obtained alloy is too poor in plasticity. If the addition amount of Cu is too high, not only will it lead to too low content of BCC phase in the alloy, greatly reducing the fracture strength of the material, but also will lead to the generation of cracks in the material, causing the plasticity of the material to decrease. Therefore, only within the range required by the present application, the optimal value of the comprehensive performance of the alloy material can be achieved.

[0014] As a preferred scheme, the fracture strength of the alloy is 1500-2000 MPa, and the fracture plasticity is 20-32%.

[0015] The present application provides a preparation method of a high-strength cobalt-free hypoeutectic high-entropy alloy. The metal raw materials including Al, Cr, Fe, Cu and Ni are uniformly mixed and dried to obtain high-entropy alloy powder. The high-entropy alloy powder is placed in a powder feeding cylinder of a laser melting deposition device, and the alloy powder is deposited layer by layer on a stainless steel substrate under a protective atmosphere, and the high-strength cobalt-free hypoeutectic high-entropy alloy is obtained.

[0016] As a preferred scheme, the metal raw materials are high-purity Al powder, high-purity Cr powder, high-purity Fe powder, high-purity Cu powder and high-purity Ni powder; or, at least one of Cr, Fe, Cu and Ni is a high-purity alloy with Al; and the particle size of the metal raw materials is 50-100 μm.

[0017] As a preferred scheme, the raw materials are mixed in a powder mixer for 12-36 h.

[0018] As a preferred scheme, the protective atmosphere is high-purity nitrogen and / or high-purity argon.

[0019] As a preferred scheme, the drying method is one of vacuum drying, oven drying and freeze drying.

[0020] As a preferred scheme, when the drying method is vacuum drying, the conditions are: vacuum degree < 130 Pa, temperature is 100-120 DEG C, and drying time is 3-5 hours.

[0021] As a preferred scheme, the control parameters of the laser melting deposition equipment are: laser power is 800-1200 W, scanning speed is 400-500 mm / min, scanning interval is 0.7-1 mm, scanning layer thickness is 0.3-0.5 mm, and the rotating speed of the powder feeding tray is 0.6-1.0 r / min; and the scanning strategy is reciprocating scanning.

[0022] As a preferred scheme, the stainless steel substrate also needs to be pretreated before use, and the process is: after the 304 stainless steel substrate is placed in a sand blasting machine for sand blasting treatment, then acetone is used for cleaning until the surface of the substrate is clean and dust-free.

[0023] The application also provides a detailed preparation process of the high-strength cobalt-free hypoeutectic high-entropy alloy:

[0024] Step (1): according to the atomic ratio of Al, Cr, Cu, Fe and Ni as 1:1:x:1:1, the metal element powder is weighed, wherein 1<=x<=1.6, the particle size of the metal powder is 53-80 mu m, and the purity of each raw material is greater than or equal to 99.95 %;

[0025] Step (2): the metal powder weighed in step 1 is put into a powder mixer, and the powder is mixed for 24 hours at room temperature;

[0026] Step (3): the uniformly mixed metal powder in step 2 is put into a vacuum drying box, and dried at 100-120 DEG C for 3-5 hours to obtain dry AlCrCu x FeNi high-entropy alloy powder;

[0027] Step (4): 304 stainless steel is selected as a substrate, the surface of the substrate is treated by a sand blasting machine, then acetone is used for cleaning to remove surface stains, and finally the substrate is put into a forming bin of a laser melting deposition equipment;

[0028] Step (5): the dry AlCrCu x FeNi high-entropy alloy powder in step 3 is put into a powder feeding cylinder of a laser melting deposition equipment, the laser melting deposition equipment is started, the scanning strategy and process parameters are set, under the protection of high-purity argon, the AlCrCu x FeNi high-entropy alloy powder is deposited on the substrate layer by layer according to the preset parameters, and the high-strength cobalt-free hypoeutectic high-entropy alloy is obtained.

[0029] The scanning strategy is a reciprocating scanning strategy; and the process parameters are: a laser power of 800-1200W, a scanning speed of 400-500mm / min, a scanning interval of 1mm, and a scanning layer thickness of 0.5mm.

[0030] Compared with the prior art, the present application has the following beneficial technical effects:

[0031] 1) The high-entropy alloy provided by the present application realizes the formation of FCC phase and BCC phase hypoeutectic structures in the alloy based on the synergistic effect between the component elements, thereby greatly improving the comprehensive performance of the alloy material; on the one hand, by strictly controlling the addition amount of each component element, the alloy material is ensured to have a significant high-entropy effect; on the other hand, the combination relationship between the FCC phase and the BCC phase is controlled, the plasticity of the material is greatly improved on the premise of ensuring the excellent mechanical strength of the material, thereby expanding the application scenarios of the high-entropy alloy.

[0032] 2) The preparation method of the high-entropy alloy provided by the present application realizes one-step forming preparation of the high-entropy alloy by using a laser melting deposition method, without the need for a pretreatment and subsequent heat treatment process; further, the hypoeutectic high-entropy alloy provided by the present application can effectively eliminate the internal stress generated by high-speed cooling in the preparation process and inhibit the generation of cracks, because the crystallization latent heat needs to be consumed for atomic diffusion in the growth process.

[0033] 3) In the technical scheme provided by the present application, inexpensive Cu is used to replace Co to prepare the high-entropy alloy, which can save costs and facilitate large-scale production on the one hand, and can utilize the repulsion between Cu and Fe and Cr to form a more obvious FCC phase, thereby adjusting the plasticity of the material; through testing, the high-entropy alloy prepared by using the technical scheme provided by the present application has excellent mechanical strength and plasticity, the fracture plasticity can reach 28.8% when the fracture strength is 1835MPa, the balance between the mechanical strength and the plasticity is realized, and the comprehensive performance of the material is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 XRD patterns of Example 1, Example 2, Example 3, and Comparative Example 1 of the present application;

[0035] Figure 2 Microstructure image of Example 1 of the present application;

[0036] Figure 3 Microstructure image of Example 2 of the present application;

[0037] Figure 4 Microstructure image of Example 3 of the present application;

[0038] Figure 5Microstructure image of the present application comparative example 1

[0039] Figure 6 Room temperature compressive stress-strain curve of the present application example 1, example 2, example 3, comparative example 1. DETAILED DESCRIPTION

[0040] The present application will be further described below in conjunction with the drawings and specific embodiments, and the specific embodiments described herein include but are not limited to the following examples.

[0041] Example 1

[0042] The present embodiment provides an AlCrCu x The preparation method of the FeNi high-entropy alloy, wherein x = 1, the specific steps are as follows:

[0043] Step (1): weigh Al, Cr, Cu, Fe and Ni powders according to the atomic ratio of 1:1:1:1:1, the raw materials are all spherical powders with a particle size of 53-80 μm, the purity of each raw material is ≥99.95wt.%, and the alloy configuration entropy ΔS conf = 1.61R, which meets the requirement of high-entropy alloy ΔS conf ≥ 1.5R;

[0044] Step (2): put the weighed metal powders in step 1 into a powder mixer and mix for 24 hours;

[0045] Step (3): put the uniformly mixed metal powders in step 2 into a vacuum drying oven and dry at 120℃ for 3 hours to obtain dry AlCrCuFeNi high-entropy alloy powders;

[0046] Step (4): select 304 stainless steel as the substrate, sandblast the surface of the substrate with a sandblasting machine, then clean it with acetone to remove surface stains, and finally put the substrate into the forming bin of the laser melting and deposition equipment;

[0047] Step (5) put the dry AlCrCuFeNi high-entropy alloy powders in step 3 into the powder feeding cylinder of the laser melting and deposition equipment, start the laser melting and deposition equipment, set the laser power to 1000W, the scanning speed to 500mm / min, the scanning interval to 1mm, the scanning layer thickness to 0.5mm, the powder feeding disc rotation speed to 0.6r / min, and the scanning strategy to reciprocating scanning, and the protective atmosphere to argon; according to the preset parameters, the AlCrCuxFeNi high-entropy alloy powders are deposited layer by layer on the 304 stainless steel substrate to obtain the as-deposited bulk AlCrCuFeNi high-entropy alloy.

[0048] Example 2

[0049] The present embodiment provides an AlCrCu xA preparation method of FeNi high-entropy alloy, wherein x=1.4, and the specific steps are as follows:

[0050] Step (1): Al, Cr, Cu, Fe and Ni powders are weighed according to an atomic ratio of 1:1:1.4:1:1, the raw materials are all spherical powders with a particle size of 53-80 μm, the purity of each raw material is greater than or equal to 99.95 wt.%, and the alloy configuration entropy ΔS conf =1.60R, which meets the requirement of high-entropy alloy ΔS conf ≥1.5R;

[0051] Step (2): the metal powders weighed in step 1 are put into a powder mixer and mixed for 24 hours;

[0052] Step (3): the uniformly mixed metal powders in step 2 are put into a vacuum drying box and dried at 120℃ for 3 hours to obtain dry AlCrCu 1.4 FeNi high-entropy alloy powders;

[0053] Step (4): 304 stainless steel is selected as a substrate, the surface of the substrate is sandblasted by a sandblasting machine, then the substrate is cleaned with acetone to remove surface stains, and finally the substrate is put into a forming bin of a laser melting and depositing device;

[0054] Step (5): the dry AlCrCu 1.4 FeNi high-entropy alloy powders in step 3 are put into a powder feeding cylinder of the laser melting and depositing device, the laser melting and depositing device is started, the laser power is set to 1000 W, the scanning speed is set to 500 mm / min, the scanning interval is set to 1 mm, the scanning layer thickness is set to 0.5 mm, the rotating speed of the powder feeding disc is set to 0.6 r / min, the scanning strategy is set to reciprocating scanning, and the protective atmosphere is set to argon; the AlCrCu 1.4 FeNi high-entropy alloy powders are deposited layer by layer on the 304 stainless steel substrate according to the preset parameters to obtain a deposited bulk AlCrCu 1.4 FeNi high-entropy alloy.

[0055] Example 3

[0056] This example provides a preparation method of AlCrCu x FeNi high-entropy alloy, wherein x=1.6, and the specific steps are as follows:

[0057] Step (1): Al, Cr, Cu, Fe and Ni powders are weighed according to an atomic ratio of 1:1:1.6:1:1, the raw materials are all spherical powders with a particle size of 53-80 μm, the purity of each raw material is greater than or equal to 99.95 wt.%, and the alloy configuration entropy ΔS conf =1.59R, which meets the requirement of high-entropy alloy ΔS conf ≥1.5R;

[0058] Step (2): Put the weighed metal powder in step 1 into a powder mixer and mix for 24 hours;

[0059] Step (3): Put the uniformly mixed metal powder in step 2 into a vacuum drying oven and dry at 120°C for 3 hours to obtain dry AlCrCu 1.6 FeNi high-entropy alloy powder;

[0060] Step (4): Select 304 stainless steel as the substrate, use a sandblasting machine to sandblast the surface, then clean it with acetone to remove surface stains, and finally put the substrate into the forming bin of the laser melting and deposition equipment;

[0061] Step (5): Put the dry AlCrCu 1.6 FeNi high-entropy alloy powder in step 3 into the powder feeding cylinder of the laser melting and deposition equipment, start the laser melting and deposition equipment, set the laser power to 1000W, the scanning speed to 500mm / min, the scanning interval to 1mm, the scanning layer thickness to 0.5mm, the rotation speed of the powder feeding disc to 0.6r / min, and the scanning strategy to reciprocating scanning, and the protective atmosphere to argon; according to the preset parameters, deposit the AlCrCu 1.6 FeNi high-entropy alloy powder layer by layer on the 304 stainless steel substrate to obtain the as-deposited bulk AlCrCu 1.6 FeNi high-entropy alloy.

[0062] Comparative Example 1

[0063] This comparative example has the same specific preparation process as Example 2, except that the AlCrCu x FeNi high-entropy alloy has an atomic ratio of each element of 1:1:1.8:1:1, and the configurational entropy ΔS conf = 1.58R.

[0064] Analysis of experimental results:

[0065] Figure 1 is the XRD pattern of the laser additive manufactured AlCrCu x FeNi high-entropy alloy. From the figure, when x = 1, the alloy is composed of FCC + BCC dual phases, with the increase of Cu element content, the content of FCC phase increases and the content of BCC phase decreases, when x = 1.8, the alloy is mainly composed of FCC phase, and the diffraction peak of BCC phase basically disappears. Figure 2 is the microstructure diagram of the high-entropy alloy of Example 1. From the figure, the alloy is mainly composed of BCC phase, and a small amount of FCC phase is distributed around the BCC. Figure 3 is the microstructure diagram of the high-entropy alloy of Example 2, which is mainly composed of primary BCC phase and eutectic structure. Figure 4The image shows the microstructure of the high-entropy alloy in Example 3. The alloy exhibits a typical dendritic structure, consisting of FCC and BCC phases. Figure 5 As shown in Comparative Example 1, the alloy exhibits a typical dendritic structure, mainly composed of the FCC phase, with a small amount of BCC phase distributed around the FCC, and numerous cracks appearing in the interdendritic region.

[0066] To further verify the mechanical properties and strain relationship of the obtained materials, the present invention also conducted stress-strain tests on the materials obtained in Examples 1-3 and Comparative Example 1, and the results are as follows: Figure 6 As shown in Table 1.

[0067] Table 1

[0068] Sample No. Breaking strength (MPa) Breaking plasticity (%) Example 1 1934 20.6 Example 2 1835 28.8 Example 3 1560 32.3 Comparative Example 1 1416.2 30.15

[0069] pass Figure 6 As shown in Table 1, within the scope defined by this invention, the fracture strength of the material gradually decreases and the plasticity gradually increases with the increase of Cu content. However, once the amount of Cu added exceeds the scope defined by this invention, cracks will form, causing a simultaneous decrease in both the strength and plasticity of the material. Therefore, only by preparing the material within the scope required by this invention can a high-entropy alloy with excellent performance be obtained. Furthermore, as shown in Examples 1 and 2, the fracture strength decreased by 5.1%, while the fracture plasticity increased by 40%. As shown in Examples 2 and 3, the fracture strength decreased by 15%, but the fracture plasticity only increased by 12%. This indicates that by further increasing the Cu content based on Example 2, the rate of decrease in the fracture strength will gradually catch up with and exceed the rate of increase in plasticity. Therefore, the amount of Cu added in Example 2 represents the optimal balance between fracture strength and plasticity.

[0070] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Those skilled in the art can make various adjustments within their knowledge without departing from the principles of the present invention, and such adjustments are still considered to be within the scope of protection of the present invention.

Claims

1. A high-strength cobalt-free hypoeutectic high-entropy alloy, characterized in that: The alloy is composed of the following atomic percentage elements: Al 10~25%, Cr 10~25%, Cu 15~30%, Fe 10~25%, Ni 10~25%; the alloy does not contain Co element, and the alloy is composed of FCC phase and BCC phase hypoeutectic; The atomic ratio of Al to Cu is 1:1.2~1.6; the fracture strength of the alloy is 1500~2000MPa, and the fracture plasticity is 20~32%.

2. The high-strength cobalt-free hypoeutectic high-entropy alloy according to claim 1, characterized in that: The alloy is composed of the following atomic percentage elements : Al 10~20%, Cr 10~20%, Cu 15~30%, Fe 10~20%, Ni 10~20%; the atomic ratio of Al, Cr, Fe and Ni is 1:1:1:

1.

3. The preparation method of the high-strength cobalt-free hypoeutectic high-entropy alloy according to claim 1 or 2, characterized in that: After the metal raw materials including Al, Cr, Fe, Cu and Ni are uniformly mixed, the high-entropy alloy powder is obtained by drying; the high-entropy alloy powder is placed in the powder feeding cylinder of the laser melting deposition equipment, and the alloy powder is deposited on the stainless steel substrate layer by layer in a protective atmosphere, thereby obtaining the alloy. The control parameters of the laser melting deposition equipment are: the laser power is 800 W~1200 W, the scanning speed is 400mm / min~500 mm / min, the scanning interval is 0.7mm~1 mm, the scanning layer thickness is 0.3 mm~0.5 mm, and the rotation speed of the powder feeding disc is 0.6r / min~1.0 r / min; the scanning strategy is reciprocating scanning.

4. The method according to claim 3, wherein the high-strength cobalt-free hypoeutectic high-entropy alloy is prepared by the following steps of: The metal raw materials are high-purity Al powder, high-purity Cr powder, high-purity Fe powder, high-purity Cu powder and high-purity Ni powder; or, at least one of Cr, Fe, Cu and Ni is a high-purity alloy with Al; the particle size of the metal raw materials is 50~100μm. ​ 5. The method for preparing a high-strength cobalt-free hypoeutectic high-entropy alloy according to claim 3, characterized in that: The raw materials are mixed in a powder mixer for 12~36h; the protective atmosphere is high-purity nitrogen and / or high-purity argon.

6. The method according to claim 3, wherein the high-strength cobalt-free hypoeutectic high-entropy alloy is prepared by the following steps of: The drying method is one of vacuum drying, oven drying and freeze drying; when the drying method is vacuum drying, the conditions are: vacuum degree <130 Pa, temperature is 100~120℃, and drying time is 3~5 hours. ​ 7. The method according to claim 3, wherein the high-strength cobalt-free hypoeutectic high-entropy alloy is prepared by the following steps of: The stainless steel substrate also needs to be pretreated before use, and the process is: the 304 stainless steel substrate is placed in a sand blasting machine for sand blasting treatment, and then cleaned with acetone until the surface of the substrate is clean and dust-free. ​

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