A high yield strength fe-mn-co-cr-ti based metastable high-entropy alloy and a preparation method thereof

Abstract

This invention discloses a high-yield-strength Fe-Mn-Co-Cr-Ti metastable high-entropy alloy and its preparation method, belonging to the field of high-entropy alloys. The high-entropy alloy contains Fe, Mn, Co, Cr, Ti, and N elements, with the metal element ratio being Fe... a Mn b Co c Cr c Ti d The atomic percentages are a = 39.5–45, b = 30–40, c = 8–10, and d = 0.1–0.5, with a + b + 2c + d = 100. The high-entropy alloy contains an FCC matrix phase and a TiN reinforcing phase, and is prepared by direct energy deposition (DED). The matrix phase of the printed sample of this invention is the FCC phase, and the reinforcing phase TiN formed during gas atomization is dispersed in the matrix. After optimization, the tensile yield strength of the obtained workpiece is 505–515 MPa, the ultimate tensile strength is 725–755 MPa, and the elongation after fracture is 40–48%. This invention has a reasonable component design, a simple and controllable preparation process, and produces a product with superior performance, facilitating industrial application.

Description

Technical Field

[0001] This invention discloses a high yield strength Fe-Mn-Co-Cr-Ti metastable high-entropy alloy and its preparation method, belonging to the field of high-entropy alloys. Background Technology

[0002] In 2016, Professor Li Zhiming of Central South University introduced the concept of "metastability-engineering" into high-entropy alloys, preparing Fe-Mn-Co-Cr metastable high-entropy alloys. He designed a novel high-entropy alloy capable of martensitic phase transformation-induced plasticity. This metastable high-entropy alloy exhibits extremely excellent deformation capacity by distributing strain through different deformation mechanisms at different stages of deformation, making it a structural material with great future application potential. However, the extremely high strain capacity results in a relatively low yield strength.

[0003] The yield strength of as-cast Fe-Mn-Co-Cr metastable high-entropy alloys is only about 100-150 MPa. Even after complex processing techniques such as hot rolling, cold rolling, solution treatment and annealing, the yield strength can only reach about 300 MPa. Patent CN115572879A explicitly states that "a study reported that a FeCoMnCr high entropy alloy with a single-phase face-centered cubic structure [Z. He et al., Joint contribution of transformation and twinning to the high strength-ductility combination of a FeMnCoCr high entropy alloy at cryogenic temperatures, Mater. Sci. Eng. A, vol. 759, pp. 437-447, 2019] obtained excellent room temperature and low temperature mechanical properties. The room temperature yield strength and tensile strength of this alloy are 272 MPa and 481 MPa, respectively, and the uniform elongation is 47%. ... The FeCoMnCr high entropy alloys prepared in the prior art are mainly face-centered cubic structures, which also have the disadvantage of low yield strength of face-centered cubic metal materials. For example, the room temperature yield strength of the FeCoMnCr high entropy alloys prepared in the prior art is only about 300 MPa." Meanwhile, patent CN115354241A describes a low-temperature wear-resistant alloy with synergistic improvement in strength and plasticity. The alloy composition is as follows (atomic ratio): Fe: 45%–55%; Mn: 25%–35%; Co: 5%–15%; Cr: 5%–15%; C: 0.5%–1.5%; Ti: 0.5%–1.5%. The preparation method is as follows: First, according to the target composition of the alloy, determine the mass of Fe, Mn, Co, Cr, C, and Ti elements, clean them with anhydrous ethanol, weigh them for later use, and then use vacuum induction melting to melt Fe, Co, Cr, C, Ti, and Mn elements in sequence under inert gas protection and cast them at high temperature to obtain an alloy ingot. After holding the alloy ingot at a high temperature, roll it to obtain an alloy plate, then cold roll the alloy plate to obtain a rough alloy product. Finally, perform a final heat treatment in a heat treatment furnace at 650–900℃ for 1 hour, followed by water quenching to obtain a high-entropy alloy with the target composition. Example 2 of the patent states that "the alloy of Example 2 exhibits the best mechanical properties, maintaining a yield strength of approximately 560 MPa while achieving an elongation of approximately 45%." This indicates that in existing technologies, obtaining high-yield-strength FeCoMnCr high-entropy alloys generally requires hot working and heat treatment. Techniques for directly preparing high-yield-strength Fe-Mn-Co-Cr metastable high-entropy alloys using energy deposition technology without heat treatment are rarely reported. Summary of the Invention

[0004] To address the low yield strength of Fe-Mn-Co-Cr metastable high-entropy alloys, this invention designs the alloy composition by adding a trace amount of Ti via vacuum atomization, using N2 as the gas source, to prepare spherical Fe-Mn-Co-Cr-Ti metastable high-entropy alloy powder. Direct energy deposition (DED) technology is then used to form TiN in situ within the matrix, with rapid solidification and second-phase precipitation synergistically enhancing the yield strength. Ultimately, the composition range designed in this invention yields a crack-free, high-yield-strength Fe-Mn-Co-Cr-Ti metastable high-entropy alloy.

[0005] This invention discloses a metastable high-entropy alloy with high yield strength based on the Fe-Mn-Co-Cr-Ti system, comprising Fe, Mn, Co, Cr, and Ti, with the metal element ratio being Fe. a Mn b Co c Cr c Ti d The molar ratio of a:b:c:d is 39.5–45:30–40:8–10:0.1–0.5. The high-entropy alloy consists of an FCC matrix phase and a TiN reinforcing phase. During preparation using direct energy deposition (DED) technology, the powder raw materials are prepared in an atomized gas containing nitrogen with a nitrogen content not exceeding 50%.

[0006] Preferably, the present invention provides a metastable high-entropy alloy of Fe-Mn-Co-Cr-Ti system with high yield strength, comprising Fe, Mn, Co, Cr and Ti, wherein the proportion of metallic elements is Fe a Mn b Co c Cr c Ti d In mole percentages, a = 40–45, b = 30–35, c = 8–10, d = 0.2–0.4, and a + b + 2c + d = 100.

[0007] As a further preferred embodiment, the present invention provides a metastable high-entropy alloy of Fe-Mn-Co-Cr-Ti system with high yield strength, wherein the high-entropy alloy comprises Fe, Mn, Co, Cr and Ti, and the expression for the metal elements in molar ratio is: (Fe 48 Mn 32 Co 10 Cr 10 ) 99.5 Ti 0.5 .

[0008] As a further preferred embodiment, the present invention provides a metastable high-entropy alloy of Fe-Mn-Co-Cr-Ti system with high yield strength, wherein the high-entropy alloy is composed of an FCC matrix phase and a TiN reinforcing phase, wherein nitrogen accounts for 0.7 to 0.9% of the total molar number of alloy elements.

[0009] As a further preferred embodiment, the present invention provides a metastable high-entropy alloy of Fe-Mn-Co-Cr-Ti system with high yield strength, wherein the high-entropy alloy comprises Fe, Mn, Co, Cr and Ti, and the expression for the metal elements in molar ratio is: (Fe 48 Mn 32 Co 10 Cr 10 ) 99.5 Ti 0.5 The high-entropy alloy is composed of an FCC matrix phase and a TiN reinforcing phase, wherein nitrogen accounts for 0.75 to 0.85% of the total molar number of alloying elements.

[0010] This invention discloses a direct energy deposition method for forming metastable high-entropy alloys based on the Fe-Mn-Co-Cr-Ti system with high yield strength, comprising the following steps:

[0011] S1: Weigh the raw materials Fe, Mn, Co, Cr and Ti according to the atomic percentage. The raw materials can be either elemental metals or intermediate alloys. Place the prepared raw materials into the copper crucible of the electromagnetic induction melting furnace in order of melting point, with the lowest melting point placed at the bottom and the highest melting point placed at the top. Melt and heat the material under an argon atmosphere. Melting is carried out under a positive pressure of 0.2 to 0.5 MPa. The melt begins to atomize when the temperature reaches above 1500°C.

[0012] S2: Atomization is performed using vacuum atomization technology, and the atomizing gas is a mixture of argon and nitrogen; the atomization pressure is 4-5 MPa; direct energy deposition (DAD) powder is obtained; the nitrogen volume ratio in the mixture does not exceed 50%;

[0013] S3: Using the direct energy deposition (DAD) powder obtained in S2 as raw material, the particle size range of the powder is screened to be 53–120 μm, and the D50 is 80–100 μm, preferably 83 μm; the part model to be prepared is constructed using 3D software, and the movement path of the robotic arm is designed according to the shape of the model; the part is deposited on a 316L substrate using DAD technology, with a Gaussian distribution laser source, and Ar gas for both powder feeding and protective gas; the DAD process parameters are set as follows: laser spot diameter 1–2.5 mm, substrate preheating temperature 100–200 °C, protective gas flow rate 7–15 L / min, laser power 300–700 W, preferably 300–500 W, laser scanning speed 4–10 mm / s, single-pass overlap 40–50%, and Z-axis lift 0.35–0.55 mm; when the laser power is less than or equal to 500 W, the laser scanning speed should be less than or equal to 6.5 mm / s.

[0014] The preferred ratio of argon to nitrogen in the mixed gas is 2:1.

[0015] As a preferred embodiment, the present invention provides a direct energy deposition forming method for metastable high-entropy alloys based on the Fe-Mn-Co-Cr-Ti system with high yield strength. This method uses pre-alloyed powder prepared according to a designed composition as raw material and obtains the product through an additive manufacturing process. The additive manufacturing process includes 3D printing. During 3D printing, the laser spot diameter is controlled to be 1–1.75 mm, the substrate preheating temperature is 100–150 °C, the protective gas flow rate is 7–15 L / min, the laser power is 400–500 W, the laser scanning speed is 4–6 mm / s, more preferably 5–6 mm / s, the single-pass overlap is 25–50%, and the Z-axis lift is 0.4–0.55 mm.

[0016] Preferably, during 3D printing, the laser spot diameter is controlled at 1.25–1.75 mm, the substrate preheating temperature is 100–120 °C, the protective gas flow rate is 7–9 L / min, the laser power is 450–500 W, the laser scanning speed is 5–6 mm / s, the single-pass overlap is 48–52%, the Z-axis lift is 0.4–0.45 mm, and a laser serpentine reciprocating scan is performed with interlayer rotation of 90°.

[0017] This invention discloses a method for preparing metastable high-entropy alloy workpieces with high yield strength Fe-Mn-Co-Cr-Ti system using direct energy deposition (DED). The matrix phase of the printed sample is FCC phase, and the reinforcing phase TiN formed during gas atomization is dispersed in the matrix. The tensile yield strength of the obtained workpiece is 450-515 MPa, preferably 463-515 MPa, more preferably 505-515 MPa; the tensile strength is 590-755 MPa, preferably 725-755 MPa, more preferably 750-755 MPa; and the elongation after fracture is 26-50%, preferably 38-48%, more preferably 40-48%.

[0018] Principles and advantages

[0019] This invention prepares pre-alloyed powder of Fe-Mn-Co-Cr-Ti metastable high-entropy alloy powder by gas atomization. By adding N2 atmosphere, TiN reinforcing phase particles are formed. The yield strength is improved by rapid solidification through direct energy deposition technology and synergistic precipitation of the second phase. By controlling the printing parameters, a high-entropy alloy with a stable FCC phase can be directly formed. While maintaining high plasticity, the yield strength of the alloy is improved by precipitation strengthening.

[0020] This invention utilizes Ti and N-doped Fe-Mn-Co-Cr-Ti metastable high-entropy alloy powder, which has a second-phase precipitation strengthening structure with a TiN-reinforced FCC matrix. The plasticity of the direct energy deposition printed sample reaches more than 25% (after optimization, the elongation can reach 40-48%, and the tensile strength is 700-755 MPa, and the yield strength is 405-515 MPa). In the field of additive manufacturing of metal materials, the yield strength of the product obtained by this invention is excellent. Attached Figure Description

[0021] Figure 1 The image shows an optical microscope characterization of the product obtained in Example 1.

[0022] Figure 2 X-ray diffraction patterns of the powder and printed sample used in Example 1;

[0023] Figure 3 The graph shows the quasi-static tensile properties of the product obtained in Example 1.

[0024] Figure 4 The graph shows the quasi-static tensile properties of the product obtained in Example 2.

[0025] Figure 5 The graph shows the quasi-static tensile properties of the product obtained in Example 3.

[0026] Figure 6 The image shows the quasi-static tensile properties of the product obtained in Comparative Example 1. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that for those skilled in the art, various modifications and improvements (including smelting, vacuum atomization, and additive manufacturing technologies, etc.) can be made without departing from the principle of the present invention, and these should also be considered to fall within the protection scope of the present invention.

[0028] Example 1

[0029] A metastable high-entropy alloy based on the Fe-Mn-Co-Cr-Ti system with high yield strength was prepared by weighing Fe, Mn, Co, Cr, and Ti elemental raw materials with a purity ≥99.9 wt.%; weighing them precisely according to the specified ratio with an error within ±0.05 g; placing the weighed metal raw materials into an electromagnetic induction melting crucible in order of increasing melting point, with the lowest melting point element placed at the bottom and the highest melting point element placed at the top; and evacuating the crucible to a vacuum of 2 × 10⁻⁶. -1Pa, then pure argon gas is introduced to 0.4 MPa; after the melting temperature reaches 1550℃, nitrogen-containing (Fe) gas is prepared by vacuum atomization technology using a high-pressure, high-speed argon-nitrogen mixture (the molar ratio of argon to nitrogen in the mixture is 2:1) at 4.0 MPa. 48 Mn 32 Co 10 Cr 10 ) 99.5 Ti 0.5 Spherical pre-alloyed powder was prepared and dried in a vacuum oven at 100℃ for 3 hours. After furnace cooling, the powder with a particle size of 53-120μm was sieved and added to the powder feed tank of a direct energy deposition (DED) system. The DED system parameters were set as follows: laser spot diameter 1.5mm, substrate preheating temperature 150℃, laser power 500W, scanning speed 6mm / s, Z-axis lift 0.45mm, single-pass overlap 50%, and Ar protective gas flow rate 8L / min. The DED system was then started, and a serpentine laser scanning motion was performed with 90° interlayer rotation to solidify the original powder onto a 316L stainless steel substrate until the solidification process was complete. A nitrogen-containing metastable high-entropy alloy sample, FeMnCoCrTi, was obtained (where nitrogen content was 0.8% by molar percentage). The resulting printed product has a tensile strength of 752.74 MPa, a yield strength of 514.11 MPa, and an elongation of 40.21%.

[0030] Example 2

[0031] In Example 1, the laser power was changed to 700W and the scanning speed was changed to 8mm / s in the direct energy deposition equipment parameters, while other parameters remained the same as in Example 1, resulting in a high-entropy alloy sample. The obtained printed product had a tensile strength of 598.01MPa, a yield strength of 463.57MPa, and an elongation of 26.46%.

[0032] Example 3

[0033] In Example 1, the laser power was changed to 300W and the scanning speed was changed to 4mm / s in the direct energy deposition equipment parameters, while other parameters remained the same as in Example 1, resulting in a high-entropy alloy sample. The obtained printed product had a tensile strength of 730.23MPa, a yield strength of 506.97MPa, and an elongation of 47.24%.

[0034] Comparative Example 1

[0035] In Example 1, the laser power was changed to 800W and the scanning speed to 8mm / s in the direct energy deposition equipment parameters, while other parameters remained the same as in Example 1, resulting in a high-entropy alloy sample. The resulting printed product exhibited a tensile strength of 599.04MPa, a yield strength of 457.69MPa, and an elongation of 22.16%. This comparative example demonstrates that when the direct energy deposition process parameters are outside this range, the sample's performance significantly deteriorates.

[0036] Comparative Example 2

[0037] A metastable high-entropy alloy based on the Fe-Mn-Co-Cr system without elemental dopant was prepared by weighing elemental raw materials of Fe, Mn, Co, and Cr with a purity ≥ 99.9 wt.% and using vacuum atomization technology to prepare an alloy with the composition Fe... 48 Mn 32 Co 10 Cr 10 After spherical pre-alloying powder is formed, it is dried in a vacuum drying oven at 100℃ for 3 hours. After furnace cooling, the powder with a particle size of 53-120μm is sieved and added to the powder feeding cylinder of a direct energy deposition (DED) system. The DED system parameters are set as follows: laser spot diameter 1.5mm, substrate preheating temperature 100℃, laser power 300W, scanning speed 6mm / s, Z-axis lift 0.45mm, single-pass overlap 40%, Ar protective gas flow rate 8L / min. The DED system is then started, and a serpentine laser scanning motion is performed with 90° interlayer rotation to form the original powder onto a 316L stainless steel substrate until the forming process is complete. A metastable high-entropy alloy with no doped Fe-Mn-Co-Cr is obtained.

[0038] The obtained printed sample had a tensile strength of 611.17 MPa, a yield strength of 300.21 MPa, an elongation of 44.51%, and a density of 99.73%. A comparison reveals that doping with Ti in the Fe-Mn-Co-Cr metastable high-entropy alloy can significantly improve strength, with the yield strength increasing by 100-200 MPa.

[0039] Comparative Example 3

[0040] All other conditions are the same as in Example 1, except that the laser power and scanning speed in the direct energy deposition equipment parameters of Example 1 are changed to 300W and 7mm / s.

[0041] A metastable high-entropy alloy based on the Fe-Mn-Co-Cr-Ti system with high yield strength was prepared by weighing Fe, Mn, Co, Cr, and Ti elemental raw materials with a purity ≥99.9 wt.%; weighing them precisely according to the specified ratio with an error within ±0.05 g; placing the weighed metal raw materials into an electromagnetic induction melting crucible in order of increasing melting point, with the lowest melting point element placed at the bottom and the highest melting point element placed at the top; and evacuating the crucible to a vacuum of 2 × 10⁻⁶. -1 Pa, then pure argon gas is introduced to 0.4 MPa; after the melting temperature reaches 1550℃, argon gas at 4.0 MPa high pressure and high speed is used to prepare (Fe) through vacuum atomization technology. 48 Mn 32 Co 10 Cr 10 ) 99.5 Ti 0.5 Spherical pre-alloyed powder,

[0042] The tensile strength of the obtained printed sample was 582.58 MPa, the yield strength was 431.89 MPa, and the elongation was 24.45%.

[0043] Comparative Example 4

[0044] All other conditions are the same as in Example 1, except that the laser power and scanning speed in the direct energy deposition equipment parameters of Example 1 are changed to 700W and 4mm / s.

[0045] A metastable high-entropy alloy based on the Fe-Mn-Co-Cr-Ti system with high yield strength was prepared by weighing Fe, Mn, Co, Cr, and Ti elemental raw materials with a purity ≥99.9 wt.%; weighing them precisely according to the specified ratio with an error within ±0.05 g; placing the weighed metal raw materials into an electromagnetic induction melting crucible in order of increasing melting point, with the lowest melting point element placed at the bottom and the highest melting point element placed at the top; and evacuating the crucible to a vacuum of 2 × 10⁻⁶. -1 Pa, then pure argon gas is introduced to 0.4 MPa; after the melting temperature reaches 1550℃, nitrogen-containing (Fe) gas is prepared by vacuum atomization technology using a high-pressure, high-speed argon-nitrogen mixture (the molar ratio of argon to nitrogen in the mixture is 1:2) at 4.0 MPa. 48 Mn 32 Co 10 Cr 10 ) 99.5 Ti 0.5 Spherical pre-alloyed powder,

[0046] The tensile strength of the obtained printed sample was 705.64 MPa, the yield strength was 542.76 MPa, and the elongation was 16.75%.

Claims

1. A high yield strength Fe-Mn-Co-Cr-Ti based meta-stable high-entropy alloy, characterized by: Including Fe, Mn, Co, Cr, Ti, and N elements, the molar ratio of the metallic elements is expressed as: (Fe 48 Mn 32 Co 10 Cr 10 ) 99.5 Ti 0.5 The high-entropy alloy contains an FCC matrix phase and a TiN reinforcing phase. The metastable high-entropy alloy with high yield strength Fe-Mn-Co-Cr-Ti system is prepared by direct energy deposition technology. During the preparation by direct energy deposition technology, the powder raw materials used are prepared in an atomized gas containing nitrogen with a nitrogen content not exceeding 50%. The high-yield-strength Fe-Mn-Co-Cr-Ti metastable high-entropy alloy is prepared by the following steps: S1: Weigh the raw materials Fe, Mn, Co, Cr and Ti according to the atomic percentage. The raw materials are selected as elemental metals and / or intermediate alloys. Place the prepared raw materials into the copper crucible of the electromagnetic induction melting furnace in order of melting point, with the lowest melting point placed at the bottom and the highest melting point placed at the top. Melt and heat under argon atmosphere protection. Melting is carried out under positive pressure of 0.2 to 0.5 MPa. The melt begins to atomize when the temperature reaches above 1500℃. S2: Atomization is performed using vacuum atomization technology, with the atomizing gas being a mixture of argon and nitrogen; the atomization pressure is 4~5 MPa; direct energy deposition (DAD) powder is obtained; the nitrogen volume percentage in the mixture does not exceed 50%. S3: Using the direct energy deposition powder obtained in S2 as raw material, the particle size range of the powder is 53~120 μm and the D50 is 80~100 μm; The required part model was constructed using 3D software, and the robotic arm's motion path was designed based on the model's shape. Direct energy deposition (DED) was used to deposit the part onto a 316L substrate, employing a Gaussian-distributed laser source. Ar gas was used for both powder feeding and protective gas. The DED process parameters were set as follows: The laser spot diameter is controlled at 1.25~1.75mm, the substrate preheating temperature is 100~120℃, the protective gas flow rate is 7~9 L / min, the laser power is 450~500W, the laser scanning speed is 5~6mm / s, the single-pass overlap is 48~52%, the Z-axis lift is 0.4~0.45mm, and a laser serpentine reciprocating scan is performed with interlayer rotation of 90°. In the high-entropy alloy, nitrogen accounts for 0.7 to 0.9% of the total molar number of alloying elements. 2.The high yield strength Fe-Mn-Co-Cr-Ti based metastable high-entropy alloy according to claim 1, characterized in that: In the high-entropy alloy, nitrogen accounts for 0.75 to 0.85% of the total molar number of alloying elements.

3. The method for preparing a metastable high-entropy alloy of Fe-Mn-Co-Cr-Ti system with high yield strength according to claim 1, characterized in that: The resulting workpiece has a tensile yield strength of 505~515MPa, a tensile strength of 725~755MPa, and an elongation after fracture of 40~48%.

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