Method for simultaneously improving strength and plasticity of CrMnFeCoNi high-entropy alloy

Abstract

The invention discloses a method for simultaneously improving the strength and plasticity of a CrMnFeCoNi high-entropy alloy, and belongs to the technical field of material preparation. Pure CrMnFeCoNi high-entropy alloy powder and copper powder are subjected to ball milling, the mixed powder is subjected to discharge plasma sintering, an alloy block is obtained, the CrMnFeCoNi high-entropy alloy comprises 19.6% of Cr, 20.7% of Mn, 19.7% of Fe, 20.1% of Co and 19.9% of Ni, and the mass ratio of the CrMnFeCoNi high-entropy alloy powder to the copper powder ranges from 4: 1 to 9: 1. According to the CrMnFeCoNi high-entropy alloy prepared through the method, the strength is improved, meanwhile, the ductility is well improved, and the use requirements of some special occasions can be met.

Description

Technical Field

[0001] The invention relates to a method for simultaneously improving the strength and plasticity of a CrMnFeCoNi high entropy alloy, and belongs to the technical field of material preparation. Background Art

[0002] High-entropy alloys (HEAs) are a new type of alloy material. They were originally defined as new alloys composed of five or more main elements with similar contents and simple structures (close-packed hexagonal, face-centered cubic, body-centered cubic, etc.). The classic Cantor alloy (FeCrCoMnNi high-entropy alloy) is a single FCC phase structure. The preparation of high-entropy alloys usually involves high pressure, high temperature and inert gas environment, which increases manufacturing costs and energy consumption. For example, the casting process using the dealloying method requires high temperature and inert atmosphere. Although electrodeposition can be carried out at room temperature, the yield is low, only a few milligrams. Some high-entropy alloys exhibit brittleness at room temperature, but may exhibit better plasticity at low temperatures. The room-temperature brittleness of some high-entropy alloys may be due to impurity segregation at the grain boundaries. For example, the segregation of oxygen impurities will weaken the bonding force of the grain boundaries, causing the material to exhibit brittleness at room temperature. In high-entropy alloys, various elements are prone to produce precipitated phases during the sintering process, which directly affect the mechanical properties of the alloy. The appearance of σ phase and Laves phase will make the alloy's structure coarse, greatly increase the hardness of the area where the phase is located, and cause its plasticity to drop sharply.

[0003] Therefore, developing a high entropy alloy material with good strength and toughness is an urgent problem that technicians in this field need to solve. Summary of the invention

[0004] In order to solve the problems existing in the existing CrMnFeCoNi high entropy alloy materials, the present invention provides a method for simultaneously improving the strength and plasticity of the CrMnFeCoNi high entropy alloy, specifically: CrMnFeCoNi high entropy alloy powder and copper powder are ball-milled and mixed, and then pre-pressed and formed, and finally spark plasma sintering is performed to obtain the CrMnFeCoNi high entropy alloy with high strength and high plasticity.

[0005] Preferably, the CrMnFeCoNi high entropy alloy powder contains the following elements in percentage by mass: 19.6% Cr, 20.7% Mn, 19.7% Fe, 20.1% Co, and 19.9% ​​Ni, and the total percentage by mass of all elements is 100%.

[0006] Preferably, the mass ratio of the CrMnFeCoNi high entropy alloy powder to the copper powder is 4:1 to 9:1.

[0007] Preferably, the ball milling conditions are: the ball milling time is 5 to 60 minutes, the ball milling atmosphere is argon, the ball milling balls are steel balls, and the mass ratio of the total mass of the CrMnFeCoNi high entropy alloy powder and the copper powder to the mass of the steel balls is 3:1.

[0008] Preferably, the pre-pressing pressure is 10 to 20 MPa, and the pre-pressing time is 5 to 20 min.

[0009] Preferably, the spark plasma sintering conditions are: high vacuum to 5×10 -3 Pa~10×10 -3 Pa, set the heating current to 1000~3000A, and the heating voltage to 2~4V.

[0010] Preferably, the temperature conditions for spark plasma sintering are: heating from room temperature to 850°C~900°C at a heating rate of 100° / min, then heating to 900°C~950°C at a heating rate of 50° / min, keeping at 900°C~950°C for 10 minutes, and then furnace cooling to below 60°C. During this process, a constant axial pressure of 50MPa is always maintained.

[0011] Beneficial effects of the present invention

[0012] (1) The present invention prepares a heterogeneous structure material with uniform distribution of soft and hard phases by ball-milling CrMnFeCoNi high entropy alloy and copper powder and then sintering them through spark plasma, so that the strength and plasticity of the CrMnFeCoNi high entropy alloy are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Comparison of tensile curves of the pure high entropy alloy sintered at 900°C and the alloy with 20% copper powder added, which are heterostructures prepared in Example 1.

[0014] Figure 2 Comparison of tensile curves of pure high entropy alloy and 20% and 10% copper powder added heterostructures prepared in Example 2 and Example 3 at 950°C.

[0015] Figure 3 Phase distribution diagram of high entropy alloy and copper with 20% copper powder added to the heterostructure prepared in Example 2.

[0016] Figure 4 Phase distribution diagram of high entropy alloy and copper with 10% copper powder added to the heterostructure prepared in Example 3. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0018] The CrMnFeCoNi high entropy alloy powder used in the embodiment contains the following elements in percentage by mass: 19.6% Cr, 20.7% Mn, 19.7% Fe, 20.1% Co, and 19.9% ​​Ni, and the total percentage by mass of all elements is 100%.

[0019] The purity of the copper powder used is >99.9%.

[0020] Example 1

[0021] A method for simultaneously improving the strength and plasticity of a CrMnFeCoNi high entropy alloy comprises the following steps:

[0022] (1) CrMnFeCoNi high entropy alloy powder and copper powder were placed in a ball mill, wherein the mass ratio of CrMnFeCoNi high entropy alloy powder to copper powder was 4:1 (the amount of copper powder added was 20%), steel balls were added to the ball mill, and the mass ratio of the total mass of the powder (the total mass of the CrMnFeCoNi high entropy alloy powder and the copper powder) to the steel balls was 3:1, and the powders were ball milled for 5 minutes to obtain a uniformly mixed powder.

[0023] (2) The powder mixed evenly in step (1) is loaded into a graphite mold, a layer of carbon paper is placed between the powder and the graphite to prevent the sample from adhering to the surface of the mold, and the mold is placed in a discharge plasma sintering furnace. The sintering heating rate is 100° / min from room temperature to 850°C, and then the heating rate is increased to 900°C at a heating rate of 50° / min, and the temperature is kept at 900°C for 10 minutes, and then the furnace is cooled to below 60°C. From heating to furnace cooling to below 60 degrees Celsius, a constant axial pressure of 50MPa is always maintained. CrMnFeCoNi high entropy alloy is obtained, and the CrMnFeCoNi high entropy alloy is polished to a smooth surface with sandpaper of different roughness from coarse to fine, and the residual oxide layer on the surface is removed, polished, and set aside.

[0024] In order to verify the mechanical properties of the obtained CrMnFeCoNi high entropy alloy, the CrMnFeCoNi high entropy alloy obtained in step (2) was subjected to electric spark wire cutting, and without affecting the metal structure, a dog-bone-shaped tensile specimen was cut under a tensile testing machine to obtain a tensile curve. The mechanical properties of the heterostructured CrMnFeCoNi high entropy alloy material obtained by mechanical alloying and spark plasma sintering in this embodiment are as follows:

[0025] The samples prepared by mechanical alloying and spark plasma sintering have a yield strength of 445MPa, a tensile strength of 602MPa, and a uniform elongation of 9.2% ( Figure 1 S900-80 (adding 20% ​​pure copper) has a yield strength of 549MPa, a tensile strength of 685MPa, and a uniform elongation of 11.3% ( Figure 1 As shown by the “▲” curve in the figure, the yield strength, tensile strength and uniform elongation are increased by 104MPa, 83MPa and 2.1% respectively compared with the pure high entropy alloy (S900-HEA) sample.

[0026] By comparison, it can be seen that by adding 20% ​​copper powder by mass to the high entropy alloy powder, the heterogeneous structure high entropy alloy plate obtained after spark plasma sintering treatment has an increased yield strength and significantly improved plasticity compared with the pure high entropy alloy.

[0027] Example 2

[0028] A method for simultaneously improving the strength and plasticity of a CrMnFeCoNi high entropy alloy comprises the following steps:

[0029] (1) CrMnFeCoNi high entropy alloy powder and copper powder were placed in a ball mill, wherein the mass ratio of CrMnFeCoNi high entropy alloy powder to copper powder was 4:1 (the amount of copper powder added was 20%), steel balls were added to the ball mill, and the mass ratio of the total mass of the powder (the total mass of the CrMnFeCoNi high entropy alloy powder and the copper powder) to the steel balls was 3:1, and the powders were ball milled for 5 minutes to obtain a uniformly mixed powder.

[0030] (2) The powder mixed evenly in step (1) is loaded into a graphite mold, a layer of carbon paper is placed between the powder and the graphite to prevent the sample from adhering to the mold surface, and the mold is placed in a discharge plasma sintering furnace. The sintering heating rate is 100° / min from room temperature to 900°C, and then the temperature is increased to 950°C at a heating rate of 50° / min, and the temperature is kept at 950°C for 10 minutes, and then the furnace is cooled to below 60°C. From heating to furnace cooling to below 60 degrees Celsius, a constant axial pressure of 50MPa is always maintained. CrMnFeCoNi high entropy alloy is obtained, and the CrMnFeCoNi high entropy alloy is polished to a smooth surface with sandpaper of different roughness from coarse to fine, and the residual oxide layer on the surface is removed, polished, and set aside.

[0031] The phase distribution of high entropy alloy and copper in the CrMnFeCoNi high entropy alloy prepared in this embodiment is as follows: Figure 3 As shown, from Figure 3It can be seen that the ratio of copper powder to CrMnFeCoNi high entropy alloy powder is about 1:4. The Cu powder is evenly distributed in the high entropy alloy, forming a more uniformly distributed heterogeneous structure with soft and hard phases. The pure color area is the copper phase (FCC1), and the rest is the high entropy alloy phase (FCC2).

[0032] Example 3

[0033] A method for simultaneously improving the strength and plasticity of a CrMnFeCoNi high entropy alloy comprises the following steps:

[0034] (1) CrMnFeCoNi high entropy alloy powder and copper powder were placed in a ball mill, wherein the mass ratio of CrMnFeCoNi high entropy alloy powder to copper powder was 9:1 (the amount of copper powder added was 10%), steel balls were added to the ball mill, and the mass ratio of the total mass of the powder (the total mass of the CrMnFeCoNi high entropy alloy powder and the copper powder) to the steel balls was 3:1, and the powders were ball milled for 5 minutes to obtain a uniformly mixed powder.

[0035] (2) The powder mixed evenly in step (1) is loaded into a graphite mold, a layer of carbon paper is placed between the powder and the graphite to prevent the sample from adhering to the surface of the mold, and the mold is placed in a discharge plasma sintering furnace. The sintering heating rate is 100° / min from room temperature to 850°C, and then the heating rate is increased to 900°C at a heating rate of 50° / min, and the temperature is kept at 900°C for 10 minutes, and then the furnace is cooled to below 60°C. From heating to furnace cooling to below 60 degrees Celsius, a constant axial pressure of 50MPa is always maintained. CrMnFeCoNi high entropy alloy is obtained, and the CrMnFeCoNi high entropy alloy is polished to a smooth surface with sandpaper of different roughness from coarse to fine, and the residual oxide layer on the surface is removed, polished, and set aside.

[0036] The phase distribution of high entropy alloy and copper in the CrMnFeCoNi high entropy alloy prepared in this embodiment is as follows: Figure 4 As shown, from Figure 4 It can be seen that the ratio of copper powder to CrMnFeCoNi high entropy alloy powder is about 1:9. The Cu powder is evenly distributed in the high entropy alloy, and the relative content of copper powder is relatively small, forming a heterogeneous structure distribution of soft and hard distribution, but there are fewer soft and hard phase interfaces. The pure color area is the copper phase (FCC1), and the rest is the high entropy alloy phase (FCC2).

[0037] In order to verify the mechanical properties of the obtained CrMnFeCoNi high entropy alloy, the CrMnFeCoNi high entropy alloy obtained in Example 2 and Example 3 was subjected to electric spark wire cutting, and without affecting the metal structure, a dog-bone-shaped tensile specimen was cut under a tensile testing machine to obtain a tensile curve. The mechanical properties of the heterostructured CrMnFeCoNi high entropy alloy material obtained by mechanical alloying and spark plasma sintering in this embodiment are as follows:

[0038] After mechanical alloying and spark plasma sintering, the pure high entropy alloy (S950-HEA) has a yield strength of 415 MPa, a tensile strength of 561 MPa, and a uniform elongation of 7.0% ( Figure 2 S950-90 (with 10% pure copper added) has a yield strength of 510MPa, a tensile strength of 680MPa, and a uniform elongation of 9.9% ( Figure 2 S950-80 (with 20% pure copper added) has a yield strength of 475MPa, a tensile strength of 700MPa, and a uniform elongation of 23.1% ( Figure 2 ). From the engineering stress-strain curves of the three samples, it can be seen that the yield strength and tensile strength of sample S950-90 are almost the same as those of sample S950-80, but the uniform elongation of sample S950-80 is 13.2% higher than that of sample S950-90. Compared with the pure high entropy alloy (S950-HEA) sample, the yield strength, tensile strength and uniform elongation of sample S950-80 are increased by 60MPa, 139MPa and 16.1.1% respectively.

[0039] By comparison, it can be seen that the heterogeneous structure CrMnFeCoNi high entropy alloy obtained by adding 20% ​​copper powder by mass to the high entropy alloy powder after spark plasma sintering has increased yield strength and significantly improved plasticity compared with the pure CrMnFeCoNi high entropy alloy.

Claims

1. A method for simultaneously improving the strength and plasticity of a CrMnFeCoNi high entropy alloy, characterized in that: The CrMnFeCoNi high entropy alloy powder and the copper powder are ball-milled and mixed, and then pre-pressed and finally sintered by spark plasma to obtain the CrMnFeCoNi high entropy alloy with high strength and high plasticity.

2. The method for simultaneously improving the strength and plasticity of CrMnFeCoNi high entropy alloy according to claim 1, characterized in that: The CrMnFeCoNi high entropy alloy powder contains the following elements in percentage by mass: 19.6% Cr, 20.7% Mn, 19.7% Fe, 20.1% Co, and 19.9% ​​Ni, and the total percentage by mass of all elements is 100%.

3. The method for simultaneously improving the strength and plasticity of CrMnFeCoNi high entropy alloy according to claim 1, characterized in that: The mass ratio of the CrMnFeCoNi high entropy alloy powder to the copper powder is 4:1 to 9:

1.

4. The method for simultaneously improving the strength and plasticity of CrMnFeCoNi high entropy alloy according to claim 1, characterized in that: The ball milling conditions are as follows: the ball milling time is 5 to 60 minutes, the ball milling atmosphere is argon, the ball milling balls are steel balls, and the mass ratio of the total mass of the CrMnFeCoNi high entropy alloy powder and the copper powder to the mass of the steel balls is 3:

1.

5. The method for simultaneously improving the strength and plasticity of CrMnFeCoNi high entropy alloy according to claim 1, characterized in that: The pre-pressing pressure is 10-20 MPa, and the pre-pressing time is 5-20 min.

6. The method for simultaneously improving the strength and plasticity of CrMnFeCoNi high entropy alloy according to claim 1, characterized in that: The conditions for spark plasma sintering are: high vacuum to 5×10 -3 Pa~10×10 -3 Pa, set the heating current to 1000~3000A, and the heating voltage to 2~4V.

7. The method for simultaneously improving the strength and plasticity of CrMnFeCoNi high entropy alloy according to claim 1, characterized in that: The temperature conditions of spark plasma sintering are as follows: heating from room temperature to 850°C~900°C at a heating rate of 100° / min, then heating to 900°C~950°C at a heating rate of 50° / min, keeping at 900°C~950°C for 10 minutes, and then cooling the furnace to below 60°C. During this process, a constant axial pressure of 50MPa is maintained.

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