A high-strength and high-toughness high-entropy alloy at high temperature and its additive manufacturing method

Abstract

The present invention relates to a high-strength and toughness high-entropy alloy at high temperature and an additive manufacturing method thereof, and belongs to the technical field of alloy materials. In order to solve the problem that the existing manufacturing method cannot simultaneously improve the strength and plasticity of FeCoCrNi series high-entropy alloys at high temperature, the present invention provides a high-strength and toughness high-entropy alloy at high temperature and an additive manufacturing method thereof, and the atomic percentage of each element in the high-entropy alloy of the present invention is Fe: Co: Cr: Ni: Mo = 25-X: 25-X: 25-X: 25-X: 4X, wherein 2<X<4. The present invention introduces the Mo element on the basis of the FeCoCrNi high-entropy alloy and adopts the selective laser melting method to prepare the high-entropy alloy additive, precipitates the σ phase in the structure and reduces the stacking fault energy, transforms the deformation mechanism dominated by dislocation movement at high temperature into twin deformation, thereby simultaneously improving its strength and plasticity at high temperature, and expanding the application of FeCoCrNi series high-entropy alloys in high-temperature environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy materials, and in particular relates to a high-entropy alloy with high strength and toughness at high temperatures and an additive manufacturing method thereof. Background Art

[0002] High-entropy alloys (HEAs) represent a significant breakthrough in the field of alloys. They are material systems composed of five or more elements in equal or approximately equal atomic ratios. Due to the high-entropy effect, HEAs exhibit excellent mechanical properties and corrosion resistance, thus holding great promise for applications in aerospace and nuclear power. The primary strengthening mechanism of HEAs is the solid solution effect. While this mechanism does not result in a decrease in ductility, its strengthening effect at elevated temperatures is extremely poor. This high-temperature softening phenomenon, characterized by increased ductility and decreased strength at elevated temperatures, limits the application of HEAs in high-temperature environments. While significant efforts have been made to enhance the strength of HEAs, such as through precipitation strengthening of HEAs and dual-phase HEAs, these efforts have resulted in a significant decrease in the material's ductility. Therefore, developing feasible strategies to enhance the high-temperature strength of HEAs while minimizing the decrease in ductility is essential.

[0003] FeCoCrNi high-entropy alloy is one of the most widely studied high-entropy alloys. It is a face-centered cubic FCC single-phase alloy with good plasticity and good formability, but low strength. Previous studies have mostly improved the strength of FeCoCrNi high-entropy alloys through vacuum arc melting and composition design and element addition. These methods transform the lattice structure of FeCoCrNi high-entropy alloys from a single FCC structure to a mixed structure containing FCC structure and σ phase structure. Due to precipitation strengthening, the strength of FeCoCrNi high-entropy alloys is improved, but the plasticity is significantly reduced. Although the plasticity is improved at high temperatures, its strength decreases significantly. Dislocation movement remains the main mechanism of its deformation. How to change its high-temperature deformation mechanism to achieve a simultaneous improvement in high-temperature strength and plasticity is an urgent problem to be solved in this field. Summary of the Invention

[0004] In order to solve the problem that existing manufacturing methods cannot simultaneously improve the strength and plasticity of FeCoCrNi-based high-entropy alloys at high temperatures, the present invention provides a high-strength and high-toughness high-entropy alloy at high temperatures and an additive manufacturing method thereof.

[0005] The technical solution of the present invention:

[0006] A high-entropy alloy with high strength and toughness at high temperatures is composed of Fe, Co, Cr, Ni and Mo. The atomic percentage of each element in the high-entropy alloy is Fe:Co:Cr:Ni:Mo=25-X:25-X:25-X:25-X:4X, wherein 2<X<4.

[0007] A method for additively manufacturing a high-strength and high-toughness high-entropy alloy at high temperature, comprising the following steps:

[0008] Step 1, the atomic percentage of each element in the high entropy alloy is Fe:Co:Cr:Ni:Mo=25-X:25-X:25-X:25-X:4X, where 2<X<4, and FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder are weighed according to atomic percentage and fully mixed to obtain a mixed alloy powder;

[0009] Step 2: Using the mixed alloy powder obtained in step 1 as raw material, a high entropy alloy is printed by a selective laser melting method to obtain a printed high entropy alloy additive material.

[0010] Furthermore, the particle size range of the FeCoCrNi aerosolized spherical powder and the FeCoCrNiMo aerosolized spherical powder in step 1 is 15 μm to 53 μm.

[0011] Furthermore, the thorough mixing in step 1 is to place the FeCoCrNi aerosolized spherical powder and the FeCoCrNiMo aerosolized spherical powder in a three-dimensional mixer and stir at a speed of 40 rpm / min for 5 hours under argon protection.

[0012] Furthermore, the printing process parameters of the selective laser melting method in step 2 are: the interlayer rotation angle is set to 65°~70°, the laser power is 160W~240W, the exposure time is 30μs~80μs, the line spacing is 50μm~150μm, and the dot spacing is 40μm~80μm.

[0013] Furthermore, the printing process parameters of the selective laser melting method in step 2 are: the interlayer rotation angle is set to 67°, the laser power is 200 W, the exposure time is 80 μs, the line spacing is 70 μm, the dot spacing is 60 μm, and the layer thickness is 40 μm.

[0014] Furthermore, before printing in the selective laser melting method described in step 2, the printing chamber is evacuated to reduce the oxygen content to less than 500 ppm, and printing is performed under the protection of an argon atmosphere.

[0015] Furthermore, the substrate used in the selective laser melting method in step 2 is 316L stainless steel. The surface of the substrate is polished until there is no oxide, and the impurities and dirt on the surface of the substrate are cleaned with acetone and alcohol respectively.

[0016] Furthermore, in the selective laser melting method in step 2, the preheating temperature of the substrate is 120°C.

[0017] Beneficial effects of the present invention:

[0018] The present invention introduces the Mo element on the basis of FeCoCrNi high entropy alloy and adopts the selective laser melting method to prepare high entropy alloy additive materials. The σ phase is precipitated in the obtained high entropy alloy additive materials and the stacking fault energy is reduced, so that the deformation mechanism of the high-entropy alloy additive materials at high temperatures is changed from a deformation mechanism dominated by dislocation movement to a deformation mechanism dominated by twinning. This change in deformation mechanism can effectively achieve a synergistic improvement in the strength and plasticity of high-entropy alloy additive materials at high temperatures. Compared with FeCoCrNi printed additive materials, the high-entropy alloy additive materials prepared by the present invention have an ultimate tensile strength and elongation of up to 145.8% and 149.1% at 800°C, respectively, which expands the application of FeCoCrNi-based high entropy alloys in high-temperature environments.

[0019] The selective laser melting method provided by the present invention enables in-situ alloying of alloy powder during the printing process, and can strengthen the alloy without subsequent treatment, and the operation process is convenient and fast. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 FeCoCrNiMo prepared in Example 1 0.5 Comparison of high-temperature tensile properties test results of printed high-entropy alloy additive and FeCoCrNi printed high-entropy alloy additive prepared in Comparative Example 1 at 600°C, 700°C, 800°C, and 900°C;

[0021] Figure 2 FeCoCrNiMo prepared in Example 1 0.5 Comparison of microscopic characterizations of printed high entropy alloy additives and FeCoCrNi printed high entropy alloy additives prepared in comparative example 1, wherein Figure a is the inverse pole figure of FeCoCrNi printed high entropy alloy additives, Figure b is the TEM image of FeCoCrNi printed high entropy alloy additives, and Figure c is the TEM image of FeCoCrNiMo 0.5 The inverse pole figure of the printed high entropy alloy additive, Figure d is FeCoCrNiMo 0.5 TEM image of printed high-entropy alloy additive;

[0022] Figure 3 TEM images of the high-temperature tensile uniform deformation structure of the FeCoCrNi printed high-entropy alloy additive prepared in Comparative Example 1, where Figure a is at 600°C, Figure b is an enlarged image at 600°C, Figure c is at 800°C, and Figure d is an enlarged image at 800°C;

[0023] Figure 4 FeCoCrNiMo prepared in Example 1 0.5 TEM images of the high-temperature tensile uniform deformation structure of the printed high-entropy alloy additive material, where Figure a is at 600℃, Figure b is an enlarged image at 600℃, Figure c is at 800℃, and Figure d is an enlarged image at 800℃;

[0024] Figure 5 Schematic diagram of the printed specimen processed according to ASTM E21 standard for tensile and impact property testing. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below with reference to the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be included in the scope of protection of the present invention. The process equipment or devices not specifically noted in the following examples are all conventional equipment or devices in the art. Unless otherwise specified, the raw materials used in the examples of the present invention can be obtained commercially; unless otherwise specified, the technical means used in the examples of the present invention are all conventional means well known to those skilled in the art.

[0026] Example 1

[0027] This embodiment provides a high-strength and high-toughness high-entropy alloy FeCoCrNiMo at high temperature 0.5 and additive manufacturing methods thereof.

[0028] The high-entropy alloy of this embodiment is composed of Fe, Co, Cr, Ni, and Mo. The atomic percentages of the elements in the high-entropy alloy are Fe:Co:Cr:Ni:Mo=25-X:25-X:25-X:25-X:4X, where X=2.78 in this embodiment. The atomic ratios of the elements in the high-entropy alloy of this embodiment are Fe:Co:Cr:Ni:Mo=1:1:1:1:0.5.

[0029] The additive manufacturing method for the high-entropy alloy in this example is selective laser melting. The printing powders used are FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder, both with a particle size range of 15 μm to 53 μm, purchased from Gierek Metal Materials (Shandong) Co., Ltd. The selective laser melting equipment is a Renishaw AM-400 laser 3D printing system. The substrate used is 316L stainless steel, measuring 250 mm × 250 mm × 15 mm. The substrate surface is polished with an angle grinder until it is free of oxides. Oil and dirt are then cleaned with acetone and alcohol, respectively.

[0030] The specific steps of the additive manufacturing method of high-strength and high-toughness high-entropy alloy at high temperature in this embodiment are as follows:

[0031] Step 1: FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder are placed in a three-dimensional mixer according to the atomic ratio, and stirred at 40 rpm / min for 5 hours under argon protection to obtain a mixed alloy powder;

[0032] Step 2: The mixed alloy powder obtained in step 1 is placed into the printer hopper. A predetermined printing size of 7 mm × 7 mm × 7 mm is constructed in the Renishaw-QuantAM software provided with the equipment. The interlayer rotation angle is set to 67° to release residual stress. The software automatically performs offline programming of the laser movement, setting the laser power to 200 W, the layer thickness to 40 μm, the line spacing to 70 μm, the dot spacing to 60 μm, the exposure time to 80 μs, and the substrate preheating temperature to 120°C.

[0033] Before printing, the printing chamber was evacuated to reduce the oxygen content to less than 500 ppm, and printing was performed under the protection of an argon atmosphere. The obtained additive material was cooled in the chamber for 2 hours to obtain a printed high-entropy alloy additive material.

[0034] Example 2

[0035] This embodiment provides a high-strength and high-toughness high-entropy alloy FeCoCrNiMo at high temperature 0.35 and additive manufacturing methods thereof.

[0036] The high-entropy alloy of this embodiment is composed of Fe, Co, Cr, Ni, and Mo. The atomic percentages of the elements in the high-entropy alloy are Fe:Co:Cr:Ni:Mo=25-X:25-X:25-X:25-X:4X, where X=2 in this embodiment. The atomic ratios of the elements in the high-entropy alloy of this embodiment are Fe:Co:Cr:Ni:Mo=1:1:1:1:0.35.

[0037] The additive manufacturing method for the high-entropy alloy in this example is selective laser melting. The printing powders used are FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder, both with a particle size range of 15 μm to 53 μm, purchased from Gierek Metal Materials (Shandong) Co., Ltd. The selective laser melting equipment is a Renishaw AM-400 laser 3D printing system. The substrate used is 316L stainless steel, measuring 250 mm × 250 mm × 15 mm. The substrate surface is polished with an angle grinder until it is free of oxides. Oil and dirt are then cleaned with acetone and alcohol, respectively.

[0038] The specific steps of the additive manufacturing method of high-strength and high-toughness high-entropy alloy at high temperature in this embodiment are as follows:

[0039] Step 1: FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder are placed in a three-dimensional mixer according to the atomic ratio, and stirred at 40 rpm / min for 5 hours under argon protection to obtain a mixed alloy powder;

[0040] Step 2: The mixed alloy powder obtained in step 1 is placed into the printer hopper. A predetermined printing size of 7 mm × 7 mm × 7 mm is constructed in the Renishaw-QuantAM software provided with the Renishaw equipment. The interlayer rotation angle is set to 67° to release residual stress. The software automatically performs offline programming of the laser movement, setting the laser power to 160 W, the layer thickness to 40 μm, the line spacing to 70 μm, the dot spacing to 60 μm, the exposure time to 70 μs, and the substrate preheating temperature to 120°C.

[0041] Before printing, the printing chamber was evacuated to reduce the oxygen content to less than 500 ppm, and printing was performed under the protection of an argon atmosphere. The obtained additive material was cooled in the chamber for 2 hours to obtain a printed high-entropy alloy additive material.

[0042] Example 3

[0043] This embodiment provides a high-strength and high-toughness high-entropy alloy FeCoCrNiMo at high temperature 0.4 and additive manufacturing methods thereof.

[0044] The high-entropy alloy of this embodiment is composed of Fe, Co, Cr, Ni, and Mo. The atomic percentages of the elements in the high-entropy alloy are Fe:Co:Cr:Ni:Mo=25-X:25-X:25-X:25-X:4X, where X=2.27 in this embodiment. The atomic ratios of the elements in the high-entropy alloy of this embodiment are Fe:Co:Cr:Ni:Mo=1:1:1:1:0.4.

[0045] The additive manufacturing method for the high-entropy alloy in this example is selective laser melting. The printing powders used are FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder, both with a particle size range of 15 μm to 53 μm, purchased from Gierek Metal Materials (Shandong) Co., Ltd. The selective laser melting equipment is a Renishaw AM-400 laser 3D printing system. The substrate used is 316L stainless steel, measuring 250 mm × 250 mm × 15 mm. The substrate surface is polished with an angle grinder until free of oxides. Oil and dirt are then cleaned with acetone and alcohol, respectively.

[0046] The specific steps of the additive manufacturing method of high-strength and high-toughness high-entropy alloy at high temperature in this embodiment are as follows:

[0047] Step 1: FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder are placed in a three-dimensional mixer according to the atomic ratio, and stirred at 40 rpm / min for 5 hours under argon protection to obtain a mixed alloy powder;

[0048] Step 2: The mixed alloy powder obtained in step 1 is placed into the printer hopper. A predetermined printing size of 7 mm × 7 mm × 7 mm is constructed in the Renishaw-QuantAM software provided with the equipment. The interlayer rotation angle is set to 67° to release residual stress. The software automatically performs offline programming of the laser movement, setting the laser power to 240 W, the layer thickness to 40 μm, the line spacing to 60 μm, the dot spacing to 60 μm, the exposure time to 80 μs, and the substrate preheating temperature to 120°C.

[0049] Before printing, the printing chamber was evacuated to reduce the oxygen content to less than 500 ppm, and printing was performed under the protection of an argon atmosphere. The obtained additive material was cooled in the chamber for 2 hours to obtain a printed high-entropy alloy additive material.

[0050] Example 4

[0051] This embodiment provides a high-strength and high-toughness high-entropy alloy FeCoCrNiMo at high temperature 0.6 and additive manufacturing methods thereof.

[0052] The high-entropy alloy of this embodiment is composed of Fe, Co, Cr, Ni, and Mo. The atomic percentages of the elements in the high-entropy alloy are Fe:Co:Cr:Ni:Mo=25-X:25-X:25-X:25-X:4X, where X=3.26 in this embodiment. The atomic ratios of the elements in the high-entropy alloy of this embodiment are Fe:Co:Cr:Ni:Mo=1:1:1:1:0.6.

[0053] The additive manufacturing method for the high-entropy alloy in this example is selective laser melting. The printing powders used are FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder, both with a particle size range of 15 μm to 53 μm, purchased from Gierek Metal Materials (Shandong) Co., Ltd. The selective laser melting equipment is a Renishaw AM-400 laser 3D printing system. The substrate used is 316L stainless steel, measuring 250 mm × 250 mm × 15 mm. The substrate surface is polished with an angle grinder until free of oxides. Oil and dirt are then cleaned with acetone and alcohol, respectively.

[0054] The specific steps of the additive manufacturing method of high-strength and high-toughness high-entropy alloy at high temperature in this embodiment are as follows:

[0055] Step 1: FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder are placed in a three-dimensional mixer according to the atomic ratio, and stirred at 40 rpm / min for 5 hours under argon protection to obtain a mixed alloy powder;

[0056] Step 2: The mixed alloy powder obtained in step 1 is placed into the printer hopper. A predetermined printing size of 7 mm × 7 mm × 7 mm is constructed in the Renishaw-QuantAM software provided with the equipment. The interlayer rotation angle is set to 67° to release residual stress. The software automatically performs offline programming of the laser movement, setting the laser power to 200 W, the layer thickness to 40 μm, the line spacing to 70 μm, the dot spacing to 60 μm, the exposure time to 80 μs, and the substrate preheating temperature to 120°C.

[0057] Before printing, the printing chamber was evacuated to reduce the oxygen content to less than 500 ppm, and printing was performed under the protection of an argon atmosphere. The obtained additive material was cooled in the chamber for 2 hours to obtain a printed high-entropy alloy additive material.

[0058] Comparative Example 1

[0059] This comparative example provides a high entropy alloy FeCoCrNi and an additive manufacturing method thereof.

[0060] The additive manufacturing method for the high-entropy alloy in this comparative example was selective laser melting. The printing powder used was FeCoCrNi aerosolized spherical powder with a particle size range of 15 μm to 53 μm, purchased from Gierek Metal Materials (Shandong) Co., Ltd. The selective laser melting equipment was a Renishaw AM-400 laser 3D printing system. The substrate used was a 316L stainless steel substrate measuring 250 mm × 250 mm × 15 mm. The substrate surface was polished with an angle grinder until free of oxides. Oil and dirt were cleaned from the substrate surface with acetone and alcohol, respectively.

[0061] The specific steps of the additive manufacturing method of high-strength and high-toughness high-entropy alloy at high temperature in this comparative example are as follows:

[0062] FeCoCrNi aerosolized spherical powder was placed into the printer hopper. A predetermined print size of 7mm×7mm×7mm was constructed in Renishaw's built-in software Renishaw-QuantAM. The interlayer rotation angle was set to 67° to release residual stress. The software automatically performed offline programming of the laser movement, with settings for laser power of 200W, layer thickness of 40μm, line spacing of 70μm, dot spacing of 60μm, exposure time of 80μs, and substrate preheating temperature of 120°C.

[0063] Before printing, the printing chamber was evacuated to reduce the oxygen content to less than 500 ppm, and printing was performed under the protection of an argon atmosphere. The obtained additive material was cooled in the chamber for 2 hours to obtain a printed high-entropy alloy additive material.

[0064] Comparative Example 2

[0065] This comparative example provides a high entropy alloy FeCoCrNiMo 0.1 and additive manufacturing methods thereof.

[0066] The high-entropy alloy of this comparative example is composed of Fe, Co, Cr, Ni, and Mo. The atomic percentages of the elements in the high-entropy alloy are Fe:Co:Cr:Ni:Mo=25-X:25-X:25-X:25-X:4X, where X=0.61. The atomic ratios of the elements in the high-entropy alloy of this comparative example are Fe:Co:Cr:Ni:Mo=1:1:1:1:0.1.

[0067] The additive manufacturing method for the high-entropy alloy in this comparative example was selective laser melting. The printing powders used were FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder, both with particle sizes ranging from 15 μm to 53 mm, purchased from Gierek Metal Materials (Shandong) Co., Ltd. The selective laser melting equipment was a Renishaw AM-400 laser 3D printing system. The substrate used was 316L stainless steel, measuring 250 mm × 250 mm × 15 mm. The substrate surface was polished with an angle grinder until free of oxides. Oil and dirt were cleaned from the substrate surface with acetone and alcohol, respectively.

[0068] The specific steps of the additive manufacturing method of high-strength and high-toughness high-entropy alloy at high temperature in this comparative example are as follows:

[0069] Step 1: FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder are placed in a three-dimensional mixer according to the atomic ratio, and stirred at 40 rpm / min for 5 hours under argon protection to obtain a mixed alloy powder;

[0070] Step 2: The mixed powder was placed into the printer hopper. A predetermined print size of 7mm×7mm×7mm was created in Renishaw-QuantAM, the software that comes with the equipment. The interlayer rotation angle was set to 67° to release residual stress. The software automatically performed offline programming of the laser movement, with the laser power set to 200W, the layer thickness to 40μm, the line spacing to 70μm, the dot spacing to 60μm, the exposure time to 80μs, and the substrate preheat temperature to 120°C.

[0071] Before printing, the printing chamber was evacuated to reduce the oxygen content to less than 500 ppm, and printing was performed under the protection of an argon atmosphere. The obtained additive material was cooled in the chamber for 2 hours to obtain a printed high-entropy alloy additive material.

[0072] In order to conduct tensile and impact performance tests, the printed samples were processed according to ASTM E21 standards. Figure 5 The tensile tests were carried out using a universal testing machine at 600°C, 700°C, 800°C, and 900°C, with a tensile rate of 5×10 -4Table 1 shows the mechanical property test results of FeCoCrNiMox high entropy alloys prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 at different temperatures.

[0073] Table 1

[0074]

[0075] From the data in Table 1, it can be seen that the yield strength and tensile strength of the high entropy alloy prepared by the preparation method of the present invention are better than those of the comparative example. 0.5 Has better strength and plasticity.

[0076] Elongation after fracture is often used as an important indicator of a material's plasticity. This is determined by measuring the gauge length before the tensile test. After the specimen breaks, the fracture is realigned and the gauge length is measured again. The ratio of the extended gauge length to the original gauge length is the elongation after fracture.

[0077] For FeCoCrNi high entropy alloy and FeCoCrNiMo after adding Mo to optimize performance 0.5 The tensile properties of high entropy alloys were tested at different temperatures. The test results are as follows: Figure 1 The results show that FeCoCrNiMo 0.5 The high temperature tensile properties of FeCoCrNi are quite different from those of FeCoCrNi. 0.5 The strength of FeCoCrNi shows a significant downward trend with increasing temperature, and there is a large gap between the yield strength and tensile strength of the samples at the same temperature. As for the plasticity of the material, the plasticity of FeCoCrNi generally increases with increasing temperature, but FeCoCrNiMo 0.5 The plasticity law of FeCoCrNiMo has changed significantly, and the plasticity has decreased significantly from 600℃ to 700℃, but at 800℃ 0.5 The high temperature plasticity of FeCoCrNiMo is greatly improved, and the elongation reaches 14.1%. 0.5 Both have better strength and plasticity than FeCoCrNi.

[0078] In order to explore the mechanism of high temperature performance change, the microstructure of the two samples was studied. Figure 2 As shown, the FeCoCrNi HEA printed sample is different from the FeCoCrNiMo 0.5 The HEA printed samples generally showed columnar crystals and vertical growth trends, but the FeCoCrNiMo 0.5 The grain size of the microstructure is obviously refined. Figure 2 Figure b of FeCoCrNi and Figure d of FeCoCrNiMo0.5 From the TEM image of the sample, it can be seen that there is no precipitate phase in the dislocation network of FeCoCrNi, while FeCoCrNiMo 0.5 Long strips of precipitated σ phase appeared in the dislocation network. According to the selected area electron diffraction pattern, the σ phase has a different crystal structure from the matrix.

[0079] exist Figure 3 FeCoCrNi and Figure 4 FeCoCrNiMo 0.5 It is observed in the tensile uniform deformation microstructure that FeCoCrNi and FeCoCrNiMo 0.5 The number of dislocation networks is reduced and the number of dislocation entanglements is reduced, but unlike FeCoCrNi, FeCoCrNiMo 0.5 The twin structure appears in the stacking fault energy of the two alloys. The stacking fault energy of the two alloys is calculated by formula (1) and (2), where K 111ω0 is the proportional constant, which is 6.6; G (111) is the shear modulus on the (111) plane. The macroscopic shear modulus of HEAs calculated by JMatPro software is 90.34 GPa; α0 is the lattice constant; A is a constant related to anisotropy, with a value of 3.43; ε is the microstrain determined by the Williamson–Hallplot diagram; α is the stacking fault probability; θ (hkl) It is the hkl plane of FCC phase in XRD.

[0080] The calculated stacking fault energy of FeCoCrNi is 32.5mJ / m 2 ,FeCoCrNiMo 0.5 The stacking fault energy is 17.9mJ / m 2 .

[0081]

[0082]

[0083] The addition of Mo makes FeCoCrNiMo 0.5 The stacking fault energy is reduced, which leads to a change in its deformation mechanism. Twins can act as slip sources, guiding dislocation slip, effectively reducing crystal damage inside the grains, and promoting plastic deformation of the alloy. At the same time, twins can block the movement of dislocations during deformation and enhance the strength of the alloy. This is the reason why FeCoCrNiMo 0.5 This is an important reason for achieving simultaneous improvement in strength and plasticity.

[0084] In addition, if Figure 4 FeCoCrNiMo shown 0.5The long strips of σ phase precipitated in the matrix are dispersed in the matrix. During the deformation process, the σ phase interacts with the dislocations, and the dislocation movement is hindered. The σ phase strengthens the alloy through the Orowan mechanism. Due to the different structures of the σ phase and the matrix, the twins cannot pass through the σ phase during movement, and the tetragonal σ phase and the FCC structure matrix cannot undergo cooperative deformation, which improves the high temperature strength of the alloy. FeCoCrNiMo is clearly observed at 800℃. 0.5 The σ phase changes from long strips to granules, the number of twins is reduced, the number of dislocations is greatly reduced, and its high temperature plasticity is greatly improved. 0.5 The precipitation of σ phase and the transformation of deformation mechanism caused by the reduction of stacking fault energy together achieve its high strength and toughness at high temperature.

Claims

1. A method for additive manufacturing of high-strength and high-toughness high-entropy alloys at high temperatures, characterized in that: The following steps are involved: Step 1, the atomic percentage of each element in the high entropy alloy is Fe: Co: Cr: Ni: Mo = 25-X: 25-X: 25-X: 25-X: 4X, where 2 < X < 4, weighing FeCoCrNi aerosolized spherical powder and FeCoCrNiMo aerosolized spherical powder according to atomic percentage and fully mixing them to obtain a mixed alloy powder, wherein the particle size range of the FeCoCrNi aerosolized spherical powder and the FeCoCrNiMo aerosolized spherical powder are both 15 μm to 53 μm, and the fully mixing is to place the FeCoCrNi aerosolized spherical powder and the FeCoCrNiMo aerosolized spherical powder in a three-dimensional mixer and stir them at a speed of 40 rpm / min for 5 hours under argon protection; Step 2: Using the mixed alloy powder obtained in step 1 as raw material, a high-entropy alloy is printed by a selective laser melting method. The printing process parameters of the selective laser melting method are as follows: the interlayer rotation angle is set to 67°, the laser power is 160W~240W, the exposure time is 70μs~80μs, the line spacing is 60μm~70μm, the dot spacing is 60μm, and the layer thickness is 40μm to obtain a printed high-entropy alloy additive.

2. The additive manufacturing method of a high-strength and high-toughness high-entropy alloy at high temperature according to claim 1, characterized in that: In the selective laser melting method of step 2, the laser power is 200 W, the exposure time is 80 μs, and the line spacing is 70 μm.

3. The additive manufacturing method of a high-strength and high-toughness high-entropy alloy at high temperature according to claim 2, characterized in that: In step 2, the printing chamber is evacuated before printing by the selective laser melting method to reduce the oxygen content to less than 500 ppm, and printing is performed under the protection of an argon atmosphere.

4. The additive manufacturing method of a high-strength and high-toughness high-entropy alloy at high temperature according to claim 3, characterized in that: The substrate used in the selective laser melting method in step 2 is 316L stainless steel. The surface of the substrate is polished until there is no oxide, and the oil and dirt on the surface of the substrate are cleaned with acetone and alcohol respectively.

5. The additive manufacturing method of a high-strength and high-toughness high-entropy alloy at high temperature according to claim 4, characterized in that: In the selective laser melting method in step 2, the preheating temperature of the substrate is 120°C.

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