A high-plasticity Fe-Mn-Co-Cr-Si metastable high-entropy alloy and a preparation method thereof

Abstract

This invention discloses a highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy and its forming method using direct energy deposition technology, belonging to the field of high-entropy alloys. The metastable high-entropy alloy is an FCC single-phase alloy with the chemical formula Fe. a Mn b Co c Cr c Si d The atomic percentages are a = 35–45, b = 30–40, c = 8–10, and d = 0.5–6, where a + b + 2c + d = 100. The preparation method is as follows: using pre-alloyed powder as raw material, the product is obtained through additive manufacturing. During additive manufacturing, the laser spot diameter is controlled at 1–2.5 mm, the substrate preheating temperature at 100–150°C, the protective gas flow rate at 7–15 L / min, the laser power at 100–500 W, the laser scanning speed at 4–10 mm / s, the single-pass overlap at 25–50%, and the Z-axis lift at 0.4–0.55 mm. This invention has a simple process, requires no heat treatment or deformation treatment, and yields a product with excellent performance.

Description

Technical Field

[0001] This invention discloses a highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy and a direct energy deposition forming method, belonging to the field of high-entropy alloys. Background Technology

[0002] For traditional alloy steels, the addition of microalloying / substitution elements can significantly enhance their overall mechanical properties. Studies have shown that C has the highest (lowest) formation energy in Ni-rich (Cr-rich) alloys, while B and Si have the highest (lowest) formation energies in Cr-rich (Co-rich) alloys. Si's large atomic radius leads to severe lattice distortion, and its high formation energy reduces the stability of the fcc phase. Si substitution exhibits larger atomic mean square shifts, resulting in more severe local lattice mismatches. Lattice distortion caused by the substitution of low-atomic-radius nonmetallic elements is an effective means of improving the strength of high-entropy alloys. However, while increasing the strength of the metal, it inevitably reduces its plasticity. This strength-plasticity trade-off, leading to a lack of plasticity, has become a core problem limiting the expansion of the service applications of metallic materials.

[0003] Studies have reported that FeCoMnCr high-entropy alloys 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] have achieved 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, with a uniform elongation of 47%. The background art of patent CN115572879A states that "FeCoMnCr high-entropy alloys prepared in the prior art are mainly face-centered cubic structures, which also suffer from the disadvantage of low yield strength of face-centered cubic metal materials; for example, the room-temperature yield strength of FeCoMnCr high-entropy alloys prepared in the prior art is only about 300 MPa." Li Zhiming et al. developed a high-entropy iron-cobalt-manganese-chromium (FeCoMnCr) alloy containing a dual-phase structure of austenite and martensite [Z.Li et al., Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off, Nature, vol.534, pp.227-230, 2016]. Testing revealed that during deformation, the dense phase interfaces and martensitic phase transformation in the alloy simultaneously contributed to the plastic deformation, resulting in tensile strength and elongation at break that were significantly higher than those of single-phase austenitic high-entropy alloys and traditional low-entropy alloy systems (such as steel) with the best strength-ductility matching reported to date. This alloy exhibited a yield strength of 350 MPa, a tensile strength of 880 MPa, and a uniform elongation of 55% at room temperature.

[0004] Meanwhile, a search revealed that, to date, there are no reports on obtaining highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloys without hot deformation and heat treatment. Summary of the Invention

[0005] This invention is the first attempt to introduce an appropriate amount of Si into FeMnCrCo high-entropy alloys, while simultaneously solving problems such as uneven distribution of elements, especially Si, and poor batch-to-batch performance stability, resulting in products with superior strength and extremely high elongation. Furthermore, this invention is the first to develop a matching direct energy deposition (DED) forming method and optimize the process parameter range.

[0006] This invention discloses a metastable high-entropy Fe-Mn-Co-Cr-Si alloy that does not require hot forging, hot rolling, solution treatment, cold rolling, annealing, or quenching, resulting in a product with high strength, high elongation, and high batch stability.

[0007] This invention discloses a highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy, comprising Fe, Mn, Co, Cr, and Si, with the chemical formula Fe. a Mn b Co c Cr c Si d The high-entropy alloy has the following atomic percentages: a = 35–45, b = 30–40, c = 8–10, d = 0.5–6, and a + b + 2c + d = 100. The phase of the high-entropy alloy is an FCC single phase.

[0008] Preferably, the present invention provides a highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy, comprising Fe, Mn, Co, Cr and Si, with the chemical formula Fe. a Mn b Co c Cr c Si d The high-entropy alloy has the following atomic percentages: a = 40–45, b = 30–35, c = 9–10, d = 2–4, and a + b + 2c + d = 100. The phase of the high-entropy alloy is an FCC single phase.

[0009] As a further preferred embodiment, the present invention provides a highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy, comprising Fe, Mn, Co, Cr and Si, with the chemical formula Fe. a Mn b Co c Cr c Si d The atomic percentages are a = 43–44, b = 33–34, c = 9.5–10, and d = 2.9–3.1, and a + b + 2c + d = 100. The phase of the high-entropy alloy is an FCC single phase.

[0010] As a further preferred embodiment, the present invention provides a highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy, wherein, by atomic percentage, Fe is 43.65%, Mn is 33.95%, Co is 9.7%, Cr is 9.7%, and Si is 3%.

[0011] This invention introduces Si into Fe-Mn-Co-Cr alloys. As a metalloid element, Si directly alters the work hardening behavior of the alloy during strain. Therefore, the amount of Si added needs precise control; otherwise, the plasticity of this alloy system will be significantly reduced. The thermophysical properties of Si differ considerably from those of Fe, Mn, Co, and Cr. Alloys heavily doped with Si often exhibit severe segregation during solidification, leading to uneven element distribution and poor batch-to-batch performance stability. Therefore, in this invention, the amount of Si introduced must be strictly controlled between 0.5% and 6%, preferably 2% to 4%, and more preferably 2.9% to 3.1%.

[0012] This invention discloses a method for preparing a highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy. Using pre-alloyed powder prepared according to a designed composition as raw material, the product is obtained through an additive manufacturing process. The additive manufacturing process includes 3D printing. During 3D printing, the laser spot diameter is controlled at 1–2.5 mm, the substrate preheating temperature at 100–150 °C, the protective gas flow rate at 7–15 L / min, the laser power at 100–500 W, the laser scanning speed at 4–10 mm / s, the single-pass overlap at 25–50%, and the Z-axis lift at 0.4–0.55 mm. In this invention, the laser scanning speed cannot be too fast, otherwise the overall performance of the product will rapidly decline.

[0013] 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 250–350 W, the laser scanning speed is 4–6 mm / s, the single-pass overlap is 35–45%, the Z-axis lift is 0.4–0.45 mm, and a laser serpentine reciprocating scan is performed with interlayer rotation of 90°.

[0014] As a further preferred option, during 3D printing, the laser spot diameter is 1.5mm, the substrate preheating temperature is 100℃, the laser power is 300W, the scanning speed is 4mm / s, the Z-axis lift is 0.40mm, the single-pass overlap is 40%, the Ar protective gas flow rate is 8L / min, the direct energy deposition equipment is turned on, and a laser serpentine reciprocating scan is performed with 90° rotation between layers.

[0015] This invention discloses a method for preparing a highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy; the pre-alloyed powder prepared according to the designed composition is prepared through the following steps:

[0016] The raw materials Fe, Mn, Co, Cr, and Si are weighed according to atomic percentage. Both elemental metals and intermediate alloys can be used. The prepared raw materials are placed in the crucible of the electromagnetic induction melting furnace in descending order of melting point, with the lowest melting point at the bottom and the highest at the top. Melting and heating are carried out under an argon atmosphere at a positive pressure of 0.2–0.5 MPa. The melt begins to atomize when the temperature reaches above 1400°C (preferably 1480–1520°C). The atomizing gas is argon, nitrogen, helium, or a mixture of these gases. The atomization pressure is 3.5–4.5 MPa.

[0017] To further improve the performance of 3D printed products, the powder obtained from atomization is screened to obtain spare powder for printing. The particle size range of the spare powder for 3D printing is 53-120μm, and the D50 is 80-100μm, preferably 83μm.

[0018] The printed sample designed and prepared by this invention is a stable FCC single phase. The tensile yield strength of the obtained workpiece is 300-355 MPa, the tensile strength is 640-755 MPa, and the elongation after fracture is 29-40%.

[0019] After optimization, the tensile yield strength of the resulting workpiece is 335–355 MPa, the tensile strength is 730–755 MPa, and the elongation after fracture is 29–38.5%.

[0020] After further optimization, the tensile yield strength of the obtained workpiece is 350-355 MPa, the tensile strength is 750-755 MPa, and the elongation after fracture is 29-30%.

[0021] This invention eliminates the need for a series of extremely long and complex processing steps, such as hot rolling, cold rolling, solution annealing, quenching, and homogenization. Not only does it avoid serious waste of raw materials, but it also solves the problem of "constraining the degree of freedom of workpiece structure" in the prior art.

[0022] The density of the 3D printed parts obtained by this invention is 97%-99%. Furthermore, the 3D printed parts do not exhibit cracking.

[0023] This invention uses a Si-doped Fe-Mn-Co-Cr-Si metastable high-entropy alloy with a single-phase FCC structure. The addition of Si reduces the cost of alloy raw materials to a certain extent. The plasticity of the direct energy deposition printed sample reaches more than 25%. In the field of additive manufacturing of metal materials, the plasticity of this patented composition is relatively excellent.

[0024] Principles and advantages

[0025] This invention introduces Si into Fe-Mn-Co-Cr alloys. Si, as a metalloid element, directly alters the work hardening behavior of the alloy during strain. Simultaneously, the incorporation of Si can reduce the cost of the alloy to some extent. However, because the thermophysical properties of Si differ significantly from those of Fe, Mn, Co, and Cr, alloys heavily doped with Si often exhibit severe segregation during solidification, leading to uneven element distribution and poor batch-to-batch performance stability. This invention utilizes appropriate printing parameters to effectively avoid Si segregation. By controlling the process parameters of direct energy deposition, the prepared samples possess a stable FCC phase. In the field of additive manufacturing of metallic materials, the composition of this patent exhibits superior plasticity. Attached Figure Description

[0026] Figure 1 The image shows an optical microscope characterization of the product obtained in Example 1.

[0027] Figure 2 X-ray diffraction patterns of the powder and printed sample used in Example 1;

[0028] Figure 3 The graph shows the quasi-static tensile properties test results of the printed sample obtained in Example 1;

[0029] Figure 4 This is a graph showing the quasi-static tensile properties test results of the printed sample obtained in Example 2;

[0030] Figure 5 The graph shows the quasi-static tensile properties test results of the printed sample obtained in Example 3;

[0031] Figure 6 The figure shows the quasi-static tensile properties test results of the printed sample obtained in Comparative Example 1.

[0032] Figure 7 This is a graph showing the quasi-static tensile properties test results of the printed sample obtained in Example 4; Detailed Implementation

[0033] Example 1

[0034] A highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy was prepared by weighing elemental Fe, Mn, Co, and Cr with a purity ≥ 99.9 wt.% and accurately weighing them according to the specified ratio, with an error within ±0.05 g. The weighed elemental materials were then placed in 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 at the top. Pure titanium ingots were then placed in another water-cooled copper crucible and evacuated to a vacuum of 2 × 10⁻⁶. -1Pa, then pure argon gas was introduced to 0.5 MPa; after the melting temperature reached 1500℃, spherical pre-alloyed powder was prepared by vacuum atomization using 4.0 MPa high-pressure, high-speed argon gas as the atomizing gas; the pre-alloyed powder was dried in a vacuum drying oven at 100℃ for 3 hours, and after furnace cooling, the powder with a particle size of 53-120 μm was sieved and added to the powder feeding cylinder of the direct energy deposition equipment; the direct energy deposition equipment parameters were set as follows: laser spot diameter 1.5 mm, substrate preheating temperature 100℃, laser power: 300 W; scanning speed: 4 mm / s; Z-axis lift: 0.40 mm, single-pass overlap: 40%, Ar protective gas flow rate 8 L / min, and the direct energy deposition equipment was turned on; laser serpentine reciprocating scanning was performed, with interlayer rotation of 90°, so that the original powder was formed on the 316L stainless steel substrate until the forming was completed. Metastable high-entropy alloy sample FeMnCoCrSi was obtained.

[0035] The obtained metastable high-entropy alloy sample FeMnCoCrSi, by mole percentage, is 43.65% Fe, 33.95% Mn, 9.7% Co, 9.7% Cr, and 3% Si.

[0036] The resulting printed product has a tensile strength of 735.48 MPa, a yield strength of 338.06 MPa, and an elongation of 38.14%.

[0037] Example 2

[0038] In Example 1, the laser power was changed to 500W and the scanning speed to 6mm / s; all other parameters remained the same as in Example 1, resulting in a high-entropy alloy sample. The tensile strength, yield strength, and elongation of the printed sample were 711.88MPa, 345.92MPa, and 26.37%, respectively.

[0039] Example 3

[0040] In Example 1, the laser power was changed to 200W and the scanning speed was set to 4mm / s; all other parameters remained the same as in Example 1, resulting in a high-entropy alloy sample. The tensile strength, yield strength, and elongation of the printed sample were 640.06MPa, 310.59MPa, and 28.11%, respectively.

[0041] Example 4

[0042] The composition ratio in Example 1 was adjusted to: FeMnCoCrSi, with Fe at 42.75%, Mn at 33.25%, Co at 9.5%, Cr at 9.5%, and Si at 5% (molar percentage). All other parameters remained the same as in Example 1, resulting in a high-entropy alloy sample. The obtained printed sample exhibited a tensile strength of 750.23 MPa, a yield strength of 353.61 MPa, and an elongation of 29.63%.

[0043] Comparative Example 1

[0044] In Example 1, the laser power was changed to 600W and the scanning speed was 8mm / s; all other parameters remained the same as in Example 1, resulting in a high-entropy alloy sample. The tensile strength of the printed sample was 568.63MPa, the yield strength was 287.84MPa, and the elongation was 17.41%. It can be seen that when the printing process parameters are not within the scope of this invention, the performance of the sample suffers a severe loss.

[0045] Comparative Example 2

[0046] 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.%. Spherical pre-alloyed powder with the composition Fe48Mn32Co10Cr10 was prepared using vacuum atomization technology. The pre-alloyed powder was then dried in a vacuum drying oven at 100℃ for 3 hours. After furnace cooling, the powder was sieved to a particle size of 53-120 μm and added to the powder feeding cylinder of a direct energy deposition (DED) device. The DED device parameters were set as follows: laser spot diameter 1.5 mm, substrate preheating temperature 100℃, laser power 300 W, scanning speed 6 mm / s, Z-axis lift 0.45 mm, single-pass overlap 40%, and Ar protective gas flow rate 8 L / min. The DED device was then turned on, and a serpentine laser scanning process was performed with 90° interlayer rotation to form the original powder onto a 316L stainless steel substrate until the forming process was complete. Metastable high-entropy alloys based on the Fe-Mn-Co-Cr system without doping elements were obtained.

[0047] The obtained printed sample has 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%. Comparatively, it can be seen that this invention can effectively dope Si into Fe-Mn-Co-Cr metastable high-entropy alloys, improving strength while maintaining good plasticity. Furthermore, the addition of a large amount of Si can effectively reduce the cost of this high-entropy alloy system.

[0048] Comparative Example 3

[0049] The other conditions are the same as in Example 4, except that the scanning speed is increased to 16 mm / s.

[0050] The resulting printed product has a tensile strength of 612.91 MPa, a yield strength of 304.38 MPa, and an elongation of 19.18%.

Claims

1. A highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy, characterized in that: The highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy is composed of Fe, Mn, Co, Cr, and Si, with the chemical formula Fe. a Mn b Co c Cr c Si d The high-entropy alloy has the following atomic percentages: a = 43~44, b = 33~34, c = 9.5~10, d = 2.9~3.1, and a + b + 2c + d = 100; the phase of the high-entropy alloy is an FCC single phase. The highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy is prepared by the following process: Using pre-alloyed powder prepared according to the designed composition as raw material, the product is obtained through additive manufacturing process. The additive manufacturing process includes 3D printing. During 3D printing, 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 250~350W, the laser scanning speed is 4~6mm / s, the single-pass overlap is 35~45%, the Z-axis lifting amount is 0.4~0.45mm, and laser serpentine reciprocating scanning is performed with interlayer rotation of 90°. The pre-alloy powder is prepared by the following steps: The raw materials Fe, Mn, Co, Cr, and Si are weighed according to atomic percentage. Both elemental metals and intermediate alloys can be used. The prepared raw materials are placed in the crucible of the electromagnetic induction melting furnace in descending order of melting point, with the lowest melting point at the bottom and the highest melting point at the top. Melting is carried out under an argon atmosphere at a positive pressure of 0.2–0.5 MPa. The melt begins to atomize when the temperature reaches 1480–1520 °C. The atomizing gas is at least one of argon, nitrogen, and helium; the atomization pressure is 3.5–4.5 MPa. The powder obtained by atomization is screened to obtain printing spare powder; the particle size range of the 3D printing spare powder is 53~120μm, and the D50 is 80~100μm.

2. The highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy according to claim 1, characterized in that: In the metastable high-entropy Fe-Mn-Co-Cr-Si system of highly ductile alloys, the atomic percentages are 43.65% Fe, 33.95% Mn, 9.7% Co, 9.7% Cr, and 3% Si.

3. The highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy according to claim 1, characterized in that: The particle size range of the 3D printing spare powder is 53~120μm, and the D50 is 83μm.

4. The highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy according to claim 1, characterized in that: The printed sample is a stable FCC single phase. The tensile yield strength of the obtained workpiece is 300~355 MPa, the tensile strength is 640~755 MPa, and the elongation after fracture is 29~40%.

5. The highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy according to claim 4, characterized in that: The tensile yield strength of the obtained workpiece is 335~355 MPa, the tensile strength is 730~755 MPa, and the elongation after fracture is 29~38.5%.

6. The highly ductile Fe-Mn-Co-Cr-Si metastable high-entropy alloy according to claim 5, characterized in that: The tensile yield strength of the obtained workpiece is 350~355 MPa, the tensile strength is 750~755 MPa, and the elongation after fracture is 29~30%.

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