A kind of AlN reinforced lightweight heat-resistant high entropy alloy and preparation method thereof

Abstract

The present invention discloses an AlN reinforced lightweight heat-resistant high entropy alloy and a preparation method thereof. The atomic ratio of the alloy elements is expressed as follows: Al a CoCrFeNi b N c , wherein, 0.8≤a≤1.4, 1.8≤b≤2.4, 0.001≤c≤0.02. The preparation steps are: selecting a lightweight high entropy alloy system, calculating Gibbs free energy and interface energy, designing alloy composition, and preparing alloy ingots. The microstructural characteristics of the AlN reinforced lightweight heat-resistant high entropy alloy are composed of primary FCC phase dendrites and eutectic crystal layer organization, the eutectic crystal layer organization is composed of FCC phase and BCC phase, and submicron and micron AlN phases are dispersed in the primary FCC phase and the FCC phase in the eutectic crystal layer. The alloy material has excellent high-temperature tensile properties, which are higher than 300MPa and up to 500MPa, which is comparable to the existing AlCoCrFeNi 2.1 Compared with the alloy, the tensile strength at 900℃ is increased by 1 times. At the same time, the preparation process is simple and efficient.

Description

Technical Field

[0001] The present invention belongs to the field of lightweight high-entropy alloy materials, and in particular relates to an AlN-reinforced lightweight heat-resistant high-entropy alloy and a preparation method thereof. Background Art

[0002] Faced with increasingly severe energy and environmental challenges, research on lightweight structural materials is crucial. To date, lightweight materials have been widely developed and applied. For example, lightweight alloys such as magnesium, aluminum, and titanium alloys have partially replaced steel in applications such as automotive and aerospace. However, the high manufacturing costs and limited performance of existing lightweight alloys limit their wider application in practical engineering.

[0003] Compared with traditional lightweight alloys, lightweight high entropy alloys have excellent properties such as high hardness and strength, good high temperature resistance and corrosion resistance. 2.1 High entropy alloy is a typical lightweight eutectic high entropy alloy, composed of FCC soft phase and BCC hard phase. It shows excellent toughness at room temperature and its tensile strength can reach 1GPa. However, at high temperature, the FCC phase is prone to recrystallization and softening, resulting in a decrease in material strength. The tensile strength of the material at 700°C is 538MPa. Through high-temperature annealing process, researchers form a dispersed precipitate phase in the FCC phase dendrites to inhibit FCC phase recrystallization and pinning dislocations, thereby improving the high-temperature strength of the alloy. However, under higher temperature conditions, the precipitate phase will undergo coarsening, transformation, dissolution and other behaviors, and its strengthening effect will be reduced, resulting in no significant improvement in the high-temperature strength of the alloy. For example, Reference 1 "Deformation mechanism during high-temperature tensile test in an eutectic high-entropy alloy AlCoCrFeNi 2.1 " reported AlCoCrFeNi 2.1 B2 is precipitated in the FCC phase of the high entropy alloy IIphase, but the material still undergoes significant recrystallization softening at high temperatures, resulting in a tensile strength of only 200 MPa at 900°C. AlN ceramic phase has excellent properties such as high strength, high hardness, high temperature resistance, corrosion resistance, wear resistance and high thermal conductivity, but researchers often believe that AlN ceramics are inclusions in high-entropy alloys and will deteriorate the performance of the material. For example, document 2 "Oxidation behavior of arc melted AlCoCrFeNi multi-component high-entropy alloys" reported the presence of a small amount (<1 vol.%) of AlN particles in the cast AlCoCrFeNi high-entropy alloy, which was caused by impurity elements in the alloy raw materials. Therefore, the existing technology can no longer meet the high-temperature performance requirements, and there is an urgent need to develop new AlN-reinforced lightweight heat-resistant high-entropy alloy materials and technologies. Summary of the Invention

[0004] The present invention aims to provide an AlN-reinforced lightweight heat-resistant high-entropy alloy and a preparation method thereof. The lightweight high-entropy alloy has high high-temperature tensile strength, good heat resistance, simple preparation process, low cost, and is easy to promote and popularize.

[0005] The technical solution to achieve the purpose of the present invention is: an AlN reinforced lightweight heat-resistant high entropy alloy material, the atomic expression of the alloy element is: Al a CoCrFeNi b N c , among which, 0.8≤a≤1.4, 1.8≤b≤2.4, 0.001≤c≤0.02.

[0006] Furthermore, the microstructure characteristics of the AlN-reinforced lightweight heat-resistant high-entropy alloy material are as follows: it is composed of primary FCC phase dendrites and eutectic crystal layer structure, the eutectic crystal layer structure is composed of FCC phase and BCC phase, and submicron and micron AlN phases are dispersed in the primary FCC phase and the FCC phase in the eutectic crystal layer.

[0007] Furthermore, the lightweight, heat-resistant high-entropy alloy material has excellent high-temperature tensile properties, and its tensile strength at 900°C is higher than 300 MPa and reaches a maximum of 500 MPa.

[0008] A method for preparing the above-mentioned AlN reinforced lightweight heat-resistant high-entropy alloy material comprises the following steps:

[0009] Step 1: Select a lightweight high entropy alloy system, according to the equilibrium solidification phase diagram, Al a1 (CoCrFe) b1 Ni c1Five-element alloy, in which, in terms of atomic ratio, when a1=1, b1=1, c1=2.1, the eutectic point is reached, and FCC and BCC eutectic structures are precipitated. The FCC phase is prone to softening at high temperatures. In order to further strengthen the FCC phase, N element is introduced to react with Al to form AlN, which is dispersed in the FCC phase. The alloy composition for obtaining eutectic or near-eutectic structure under near-equilibrium solidification conditions is calculated using Thermal-Calc software to be Al. a CoCrFeNi b N c (atomic ratio), where 0.8≤a≤1.4, 1.8≤b≤2.4, 0.001≤c≤0.02;

[0010] Step 2: After mechanically grinding the surface of the metal raw material to remove the surface oxide scale, weigh the Al, Co, Cr, Fe, Ni metal raw materials and FeN particles according to the composition ratio of the first step;

[0011] Step 3: Place Al, Cu, Ni, Fe, FeN and Cr raw materials into a water-cooled copper crucible in the order of alloy composition ratio, cover the furnace and evacuate to 1×10 -2 Pa, fill the furnace with 0.04-0.06MPa argon gas, and use a water-cooled copper crucible suspension melting furnace to prepare alloy ingots;

[0012] Step 4: Smelt 3 to 4 times to obtain a uniformly mixed alloy ingot.

[0013] Furthermore, in the first step, the nitrogen element is added in the form of FeN particles.

[0014] Furthermore, in the first step, the Gibbs free energy of the reaction between each element in the alloy and FeN was calculated using first principles, and the temperature for generating dispersed nano-AlN particles was determined to be 700-2000°C.

[0015] Furthermore, in the first step, the element distribution during solidification was calculated using first principles, and the FCC and AlN phase interface with low interfacial energy was obtained through interfacial element enrichment.

[0016] Furthermore, in the second step, the purity (weight percentage) of the metal raw material is not less than 99.9%.

[0017] Furthermore, in the second step, the FeN particles have a size no greater than 5 μm and a purity greater than 99.9%.

[0018] Furthermore, in the third step, the purity (mol percentage) of the argon gas is not less than 99.99%.

[0019] Furthermore, in the fourth step, the smelting power is 20 to 30 kW.

[0020] Compared with the prior art, the present invention has the following advantages: (1) The microstructure consists of primary FCC phase dendrites and eutectic lamellae, and the eutectic lamellae consist of FCC phase and BCC phase, and the material has both strong plasticity; (2) Submicron and micron-sized AlN phases are dispersed in the primary FCC phase and the FCC phase in the eutectic lamellae, thereby enhancing the FCC phase; (3) The high-temperature strength of the lightweight high-entropy alloy is significantly improved; and (4) The preparation process is simple and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a preparation flow chart of the AlN reinforced lightweight heat-resistant high entropy alloy material of the present invention.

[0022] Figure 2 This is a schematic diagram of the microstructure of AlN reinforced lightweight heat-resistant high entropy alloy material. DETAILED DESCRIPTION

[0023] In order to better understand the technical content of the present invention, specific embodiments are given and described below with reference to the accompanying drawings.

[0024] The preparation steps of the following examples are as follows Figure 1 The process diagram is shown in FIG.

[0025] The concept and principle of the present invention are: according to the equilibrium solidification phase diagram, Al a1 (CoCrFe) b1 Ni c1 A five-element alloy, in which, in terms of atomic percentage, when a1=1, b1=1, and c1=2.1, the eutectic point is reached and FCC and BCC eutectic structures are precipitated. However, the FCC phase is prone to softening at high temperatures, and the tensile strength of the material at 700°C is only 538MPa. In order to further strengthen the FCC phase, the N element is introduced to react with Al to form AlN, which is dispersed in the FCC phase, inhibiting recrystallization and pinning dislocations, thereby strengthening the FCC phase. The Gibbs free energy of the reaction of each element in the alloy with FeN was calculated using first principles, and the temperature for generating dispersed submicron and micron AlN phases was determined to be 700-2000°C. The element distribution during alloy solidification was calculated using first principles, and a low interface energy FCC and AlN phase interface was obtained by enriching the interface elements. The alloy composition for obtaining eutectic or near-eutectic structure under near-equilibrium solidification conditions was calculated using Thermal-Calc software to be Al a CoCrFeNi b N c (atomic ratio), where 0.8≤a≤1.4, 1.8≤b≤2.4, and 0.001≤c≤0.02.

[0026] Example 1

[0027] (1) Design alloy composition

[0028] Select the heat-resistant aluminum alloy system, according to the equilibrium solidification phase diagram, Al a1 (CoCrFe) b1 Ni c1 A five-element alloy, in which, in terms of atomic percentage, when a1=1, b1=1, and c1=2.1, the eutectic point is reached, FCC and BCC eutectic structures are precipitated, and the FCC phase is prone to softening at high temperatures. In order to further strengthen the FCC phase, the N element is introduced to react with Al to form AlN, which is dispersed in the FCC phase. The Gibbs free energy of the reaction of each element in the alloy with FeN was calculated using the first principles, and the temperature for generating dispersed submicron and micron AlN phases was determined to be 700-2000°C. The element distribution was calculated using the first principles, and a low interfacial energy FCC and AlN phase interface was obtained by enriching the interface elements. The alloy composition for obtaining a near-eutectic structure under near-equilibrium solidification conditions was calculated using Thermal-Calc software to be AlCoCrFeNi 2.1 N 0.01 (atomic ratio).

[0029] (2) Selection of raw materials

[0030] The purity of the metal components used in the alloy ingots prepared by the present invention is shown in Table 1. The alloy composition is AlCoCrFeNi 2.1 N 0.01 ;

[0031] Table 1 Purity of components used in preparing alloy ingots (wt.%)

[0032]

[0033] (3) Alloy ingot preparation

[0034] The alloy ingots were prepared using a water-cooled copper crucible suspension melting furnace. The specific procedure is as follows:

[0035] a. Prepare the materials according to the designed composition ratio; put the prepared materials into the water-cooled copper crucible in the melting furnace according to the weight of each ingot of about 200g, and add the materials in the order of Al, Cu, Ni, Fe, FeN, and Cr. Cover the furnace and evacuate to 1×10 -3 Pa; a certain amount of argon gas (99.999%) is filled into the furnace, and the argon pressure range is 0.04MPa;

[0036] b. Melt three times to obtain a uniformly mixed alloy ingot with a melting power of 30kW.

[0037] (4) Organization and performance testing

[0038] Schematic diagram of the microstructure of the prepared material Figure 2As shown, the material consists of primary FCC dendrites and eutectic lamellae. The eutectic lamellae are composed of FCC and BCC phases. Submicron and micron-sized AlN phases are dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical properties testing shows that the prepared material achieves a tensile strength of 450 MPa at 900°C, double that of the alloy reported in Reference 1.

[0039] Example 2

[0040] The alloy composition prepared in this embodiment is AlCoCrFeNi 2.1 N 0.02 (atomic ratio), and all other steps were the same as in Example 1. The alloy microstructure consisted of primary FCC dendrites and eutectic lamellae. The eutectic lamellae consisted of FCC and BCC phases. Submicron and micron-sized AlN phases were dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical property testing demonstrated that the prepared material achieved a tensile strength of 493 MPa at 900°C, double that of the alloy in Reference 1.

[0041] Example 3

[0042] The alloy composition prepared in this embodiment is AlCoCrFeNi 2.1 N 0.001 (atomic ratio), and all other steps were the same as in Example 1. The alloy microstructure consisted of primary FCC dendrites and eutectic lamellae. The eutectic lamellae consisted of FCC and BCC phases. Submicron and micron-sized AlN phases were dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical property testing demonstrated that the prepared material achieved a tensile strength of 365 MPa at 900°C.

[0043] Example 4

[0044] The alloy composition prepared in this embodiment is Al 1.4 CoCrFeNi 2.4 N 0.01 (atomic ratio), and all other steps were the same as in Example 1. The alloy microstructure consisted of primary FCC dendrites and eutectic lamellae. The eutectic lamellae consisted of FCC and BCC phases. Submicron and micron-sized AlN phases were dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical property testing demonstrated that the prepared material achieved a tensile strength of 473 MPa at 900°C.

[0045] Example 5

[0046] The alloy composition prepared in this embodiment is Al 1.4 CoCrFeNi 2.4 N 0.02(atomic ratio), and all other steps were the same as in Example 1. The alloy microstructure consisted of primary FCC dendrites and eutectic lamellae. The eutectic lamellae consisted of FCC and BCC phases. Submicron and micron-sized AlN phases were dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical property testing demonstrated that the prepared material achieved a tensile strength of 502 MPa at 900°C.

[0047] Example 6

[0048] The alloy composition prepared in this embodiment is Al 1.4 CoCrFeNi 2.4 N 0.001 (atomic ratio), and all other steps were the same as in Example 1. The alloy microstructure consisted of primary FCC dendrites and eutectic lamellae. The eutectic lamellae consisted of FCC and BCC phases. Submicron and micron-sized AlN phases were dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical property testing demonstrated that the prepared material achieved a tensile strength of 420 MPa at 900°C.

[0049] Example 7

[0050] The alloy composition prepared in this embodiment is Al 0.8 CoCrFeNi 1.8 N 0.01 (atomic ratio), and all other steps were the same as in Example 1. The alloy microstructure consisted of primary FCC dendrites and eutectic lamellae. The eutectic lamellae consisted of FCC and BCC phases. Submicron and micron-sized AlN phases were dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical property testing demonstrated that the prepared material achieved a tensile strength of 326 MPa at 900°C.

[0051] Example 8

[0052] The alloy composition prepared in this embodiment is Al 0.8 CoCrFeNi 1.8 N 0.02 (atomic ratio), and all other steps were the same as in Example 1. The alloy microstructure consisted of primary FCC dendrites and eutectic lamellae. The eutectic lamellae consisted of FCC and BCC phases. Submicron and micron-sized AlN phases were dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical property testing demonstrated that the prepared material achieved a tensile strength of 355 MPa at 900°C.

[0053] Example 9

[0054] The alloy composition prepared in this embodiment is Al 0.8 CoCrFeNi 1.8 N 0.001(atomic ratio), and all other steps were the same as in Example 1. The alloy microstructure consisted of primary FCC dendrites and eutectic lamellae. The eutectic lamellae consisted of FCC and BCC phases. Submicron and micron-sized AlN phases were dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical property testing demonstrated that the prepared material achieved a tensile strength of 301 MPa at 900°C.

[0055] Example 10

[0056] The alloy composition prepared in this embodiment is Al 1.1 CoCrFeNi 2.2 N 0.02 (atomic ratio), and all other steps were the same as in Example 1. The alloy microstructure consisted of primary FCC dendrites and eutectic lamellae. The eutectic lamellae consisted of FCC and BCC phases. Submicron and micron-sized AlN phases were dispersed within the primary FCC phase and the FCC phase within the eutectic lamellae. Mechanical property testing demonstrated that the prepared material achieved a tensile strength of 508 MPa at 900°C.

[0057] Comparative Example 1

[0058] Document 1 "Deformation mechanism during high-temperature tensile test inan eutectic high-entropy alloy AlCoCrFeNi 2.1 " reported AlCoCrFeNi 2.1 B2 is precipitated in the L12-Ni3Al(FCC) phase in the high entropy alloy II Phase, B2-NiAl (BCC) phase precipitated L1 2,II phase, but the material still undergoes significant recrystallization softening at high temperatures, and its tensile strength at 900℃ is only 200MPa.

[0059] The alloy compositions and properties of the examples and comparative examples are compared, as shown in Table 2.

[0060] Table 2

[0061] While the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. An AlN reinforced lightweight heat-resistant high entropy alloy material, characterized in that: The atomic expression of its alloying elements is: Al a CoCrFeNi b N c , where 0.8≤a≤1.4, 1.8≤b≤2.4, 0.001≤c≤0.02; Among them, the organizational characteristics of the high-entropy alloy material are: composed of primary FCC phase dendrites and eutectic crystal layer organization, the eutectic crystal layer organization is composed of FCC phase and BCC phase, and submicron and micron AlN phases are dispersed in the primary FCC phase and the FCC phase in the eutectic crystal layer.

2. The high entropy alloy material according to claim 1, wherein The high entropy alloy material has excellent high-temperature tensile properties, and its tensile strength at 900°C is higher than 300 MPa.

3. A method for preparing a high entropy alloy material according to any one of claims 1-2, characterized in that: The following steps are involved: Step 1: Select a lightweight high entropy alloy system, according to the equilibrium solidification phase diagram, Al a1 (CoCrFe) b1 Ni c1 Five-element alloy, in which, in terms of atomic ratio, when a1=1, b1=1, c1=2.1, the eutectic point is reached, and FCC and BCC eutectic structures are precipitated. The FCC phase is prone to softening at high temperatures. In order to strengthen the FCC phase, N element is introduced to react with Al to form AlN, which is dispersed in the FCC phase. The element distribution during solidification is calculated using first principles. The interface between FCC and AlN with low interface energy is obtained by enriching the interface elements. The alloy composition for obtaining eutectic or near-eutectic structure under near-equilibrium solidification conditions is calculated using Thermal-Calc software to be Al. a CoCrFeNi b N c , where 0.8≤a≤1.4, 1.8≤b≤2.4, 0.001≤c≤0.02; Step 2: After mechanically grinding the surface of the metal raw material to remove the surface oxide scale, weigh the Al, Co, Cr, Fe, Ni metal raw materials and FeN particles according to the composition ratio of the first step; Step 3: Al, Cu, Ni, Fe, FeN, and Cr raw materials are placed in a water-cooled copper crucible in sequence, vacuumed, and filled with argon gas to prepare alloy ingots using a water-cooled copper crucible suspension melting furnace; Step 4: Smelt 3 to 4 times to obtain a uniformly mixed alloy ingot.

4. The method according to claim 3, wherein In the first step, the Gibbs free energy of the reaction between each element in the alloy and FeN was calculated using first principles, and the temperature for generating dispersed nano-AlN particles was determined to be 700-2000°C.

5. The method according to claim 3, wherein In the second step, the purity of the metal raw material is not less than 99.9%.

6. The method according to claim 3, wherein In the second step, the FeN particles have a size no greater than 5 μm and a purity greater than 99.9%.

7. The method according to claim 3, wherein In the third step, vacuum is applied to 1×10 -2 Pa below, fill the furnace with 0.04 ~ 0.06MPa argon gas.

8. The method according to claim 3, wherein In the fourth step, the smelting power is 20 to 30 kW.

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