A c-doped fe-mn-co-cr-c metastable high-entropy alloy and a direct energy deposition forming method

Abstract

The application discloses a kind of high-strength high-toughness Fe-Mn-Co-Cr-C metastable high-entropy alloy powder preparation and direct energy deposition technology forming method, belong to high-entropy alloy field.The metastable high-entropy alloy includes Fe, Mn, Co, Cr and C composition, and chemical formula is Fe a Mn b Co c Cr c C d Wherein atomic percentage a=35~45, b=30~40, c=8~10, d=0.5~3, and a+b+2c+d=100;The metastable high-entropy alloy phase is FCC single phase;The metastable high-entropy alloy is prepared by direct energy deposition technology.The application is optimized by component and preparation process, and the printing product with yield strength of 350~400MPa, ultimate tensile strength of 600~800MPa and elongation of 30~65% after breaking is obtained for the first time without heat treatment and / or deformation treatment.The application process is simple and controllable, and the obtained product has excellent performance and is convenient for industrial application.

Description

Technical Field

[0001] This invention discloses a method for preparing high-strength and high-toughness Fe-Mn-Co-Cr-C metastable high-entropy alloy powder and forming it using direct energy deposition technology, which belongs to the field of high-entropy alloys. Background Technology

[0002] High-entropy alloys (HEAs) contain five or more principal alloying elements and can stabilize solid solution phases by maximizing configurational entropy. Typically, HEAs can form single-phase solid solutions with face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP) structures. Among various HEAs, those with an FCC single-phase structure have lower stacking fault energy (SFE), good plasticity, and excellent fracture toughness. However, their lower strength limits their application as metallic structural materials. Similar to conventional alloys, current strengthening methods for FCC HEAs include alloying, phase transformation, nanocrystallization, and plastic deformation, which can improve strength but usually result in a loss of ductility. This phenomenon represents a long-standing strength-ductility trade-off in metallic materials.

[0003] Existing technologies have attempted to study FeMnCoCr high-entropy alloys, such as patent CN114855097A, which describes a method for improving the strength and low-temperature wear resistance of FeMnCoCr high-entropy alloys. This patent determines the mass of each element and the additional B element based on the molar ratio of the alloy elements, mixes them, melts and casts them to obtain an alloy ingot. The alloy ingot is then hot-rolled and air-cooled to obtain an alloy plate. After removing the surface oxide scale from the alloy plate, it is cold-rolled to obtain a rough alloy product. The rough alloy product is then heat-treated to obtain a high-entropy alloy with the target composition. The composition of the FeMnCoCr high-entropy alloy, calculated by molar ratio, is: Fe: 45%–55%, Mn: 25%–35%, Co: 5%–15%, Cr: 5%–15%, and the mass of the additional B element is 10 ppm–250 ppm. The high-entropy alloy obtained in this patent exhibits a dual-phase structure with coexisting FCC and HCP phases. Boolean atoms exist in the alloy as interstitial solid solutions. Under external force, the high-entropy alloy undergoes a martensitic phase transformation from the FCC phase to the HCP phase. Meanwhile, researchers have also studied FeCoMnCr high-entropy alloys with single-phase face-centered cubic structures. For example, Z. He et al. reported in "Joint contribution of transformation and twinning to the high temperatures" (Mater. Sci. Eng. A, vol. 759, pp. 437–447, 2019) a single-phase face-centered cubic FeCoMnCr high-entropy alloy with excellent room-temperature and low-temperature mechanical properties. This alloy has a room-temperature yield strength of 272 MPa and a tensile strength of 481 MPa, with a uniform elongation of 47%. Simultaneously, researchers in Zhenghong Fu's team at Central South University investigated the hydrogen embrittlement behavior of C-doped and CN-co-doped non-isoatomic FeMnCoCr high-entropy alloys under in-situ electrochemical hydrogen charging conditions.

[0004] A search revealed no reports to date of using direct energy deposition (DED) technology to prepare high-strength, high-toughness, C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloys. Summary of the Invention

[0005] To address the issues of low yield strength and significant loss of ductility associated with increasing strength in Fe-Mn-Co-Cr metastable high-entropy alloys, this invention designs the alloy composition. Spherical Fe-Mn-Co-Cr-C metastable high-entropy alloy powder is prepared through ball milling and mixing. Then, carbon atoms are doped into the FCC lattice of the Fe-Mn-Co-Cr metastable high-entropy alloy matrix using direct energy deposition (DED), inducing interstitial solid solution strengthening. Ultimately, the composition range designed in this invention yields a crack-free Fe-Mn-Co-Cr-C metastable high-entropy alloy with high yield strength and high ductility. This invention is the first attempt to use DED to prepare a high-strength, high-toughness, carbon-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy.

[0006] This invention discloses a carbon-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy, wherein the metastable high-entropy alloy comprises Fe, Mn, Co, Cr, and C, and its chemical formula is Fe. a Mn b Co c Cr c C d The molar ratio of a:b:c:d is 35-52:30-40:8-10:0.5-3; the metastable high-entropy alloy phase is an FCC single phase; the metastable high-entropy alloy is prepared by direct energy deposition technology.

[0007] Preferably, the present invention provides a C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy, comprising Fe, Mn, Co, Cr and C, with the chemical formula Fe. a Mn b Co c Cr c C d In molar percentage, a = 43.5–51.5, b = 30–35, c = 9–10, d = 0.5–1.5, and a + b + 2c + d = 100. The phase of the high-entropy alloy is an FCC single phase; the metastable high-entropy alloy is prepared by additive manufacturing process.

[0008] As a further preferred embodiment, the present invention provides a C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy, wherein the metastable high-entropy alloy sample FeMnCoCrC has, by molar percentage, 44.5-44.6% Fe, 34.6-34.7% Mn, 9.8-10% Co, 9.8-10% Cr, and 0.9-1.1% C.

[0009] As a further preferred embodiment, the present invention provides a C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy, wherein the metastable high-entropy alloy sample FeMnCoCrC, by molar percentage, comprises 44.55% Fe, 34.65% Mn, 9.9% Co, 9.9% Cr, and 1% C.

[0010] In this invention, carbon (C), as an interstitial atom, can be incorporated into FeMnCoCr metastable high-entropy alloys through appropriate dosage and processing. This increases stacking fault energy, thereby improving phase stability. It also maintains the transformation-induced plasticity (TRIP) effect while triggering twin-induced plasticity (TWIP), further enhancing the alloy's strain hardening capability. Secondly, carbon doping in FeMnCoCr metastable high-entropy alloys leads to severe lattice distortion, which strongly affects the interaction with dislocations. Through interstitial solid solution strengthening and the TWIP and TRIP effects, Fe-Mn-Co-Cr-C metastable high-entropy alloys can maintain good ductility while improving strength. Simultaneously, by controlling the parameters of 3D printing, an appropriate amount of C atoms can be added to the alloy system during rapid solidification, and by reducing residual stress, the alloy maintains the FCC phase structure, preserving its subsequent work hardening capability, thereby improving both plasticity and strength.

[0011] This invention discloses a direct energy deposition method for forming carbon-doped Fe-Mn-Co-Cr-C metastable high-entropy alloys, comprising the following steps:

[0012] S1: Weigh the raw materials Fe, Mn, Co, Cr, and C according to their atomic percentages. The raw materials can be either elemental metals or intermediate alloys. Use ethanol as the milling medium, with cemented carbide grinding balls at a ball-to-material mass ratio of 10:1 to 8:1. Set the mill speed to 200-400 r / min and the milling time to 48-96 h. Dry the resulting mixed powder under vacuum at 80-100℃ for 3-5 h; then sieve to select powder with a particle size of 53-120 μm to obtain the mixed powder.

[0013] S2: Using the mixed powder obtained in S1 as raw material; constructing the required part model using 3D software, and designing the robotic arm motion path according to the model shape; depositing the part on a 316L substrate using direct energy deposition technology, employing a Gaussian distributed laser light source, with Ar gas used for both powder feeding and protective gas; setting the direct energy deposition process parameters as follows: laser spot diameter 1-2 mm, substrate preheating temperature 100-200℃, protective gas flow rate 7-15 L / min, laser power 200-500 W, laser scanning speed 4-10 mm / s, single-pass overlap 40-50%, and Z-axis lift 0.35-0.55 mm.

[0014] Preferably, the particle size of the raw material powder is 50-200 micrometers.

[0015] Preferably, the particle size range of the mixed powder is 53-120 μm, and the D50 is 80-100 μm, preferably 83 μm.

[0016] As a preferred method, Fe, Mn, Co, Cr, and C elemental raw materials with a purity ≥99.9 wt.% were weighed according to the designed composition; the weights were accurately weighed according to the proportions, with an error within ±0.05 g; ethanol was used as the ball milling medium, the grinding balls were made of cemented carbide, the ball-to-material mass ratio was 10:1, the ball mill speed was 250 r / min, and the ball milling time was 72 h. The resulting mixed powder was dried at 70℃ under vacuum for 5 h. Then, the powder with a particle size of 53-120 μm was sieved and selected as the reserve powder for 3D printing.

[0017] As a preferred method, direct energy deposition technology is used for 3D printing. During 3D printing, the laser spot diameter is controlled at 1.25-1.75 mm, the substrate preheating temperature is 100-120℃, 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 48-52%, the Z-axis lift is 0.4-0.45 mm, and the laser performs a serpentine reciprocating scan with interlayer rotation of 90°.

[0018] As a further preferred option, direct energy deposition technology is used for 3D printing. During 3D printing, the laser spot diameter is controlled at 1.45-1.55 mm, the substrate preheating temperature is 100-105℃, the protective gas flow rate is 7.5-8.5 L / min, the laser power is 250-260 W, the laser scanning speed is 5.5-6 mm / s, the single-pass overlap is 49-51%, the Z-axis lift is 0.44-0.45 mm, and laser serpentine reciprocating scanning is performed with interlayer rotation of 90°.

[0019] The sample designed and printed by this invention has an FCC single phase, and the resulting workpiece has a tensile yield strength of 350-400 MPa, an ultimate tensile strength of 600-800 MPa, and an elongation after fracture of 30-65%.

[0020] After optimization, the sample designed and printed by this invention has an FCC single-phase phase, and the resulting workpiece has a tensile yield strength of 380–400 MPa, an ultimate tensile strength of 600–650 MPa, and an elongation after fracture of 50–65%. Specifically:

[0021] The tensile yield strength of the obtained product is 395.01 MPa, the ultimate tensile strength is 612.92 MPa, and the elongation after fracture is 63.04%.

[0022] The tensile yield strength of the obtained product is 385.89 MPa, the ultimate tensile strength is 620.03 MPa, and the elongation after fracture is 54.86%.

[0023] The tensile yield strength of the obtained product is 397.34 MPa, the ultimate tensile strength is 634.89 MPa, and the elongation after fracture is 50.62%.

[0024] Principles and advantages

[0025] In this invention, carbon (C), as an interstitial atom, can be incorporated into FeMnCoCr metastable high-entropy alloys through appropriate 3D printing with suitable parameters. This increases the stacking fault energy, thereby improving phase stability. It triggers twin-induced plasticity (TWIP) while maintaining transformation-induced plasticity (TRIP), further enhancing the alloy's strain hardening capability. Secondly, carbon doping in FeMnCoCr metastable high-entropy alloys leads to severe lattice distortion, which strongly affects the interaction with dislocations. Simultaneously, this invention uses ball milling to uniformly mix C with other main elements, ensuring effective C incorporation during subsequent printing. By controlling 3D printing parameters, C atoms are added to the alloy system during rapid solidification, and residual stress is reduced to maintain the FCC phase structure, preserving the ability to work harden and thus improving plasticity and strength. 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 of the product obtained in Example 1.

[0029] Figure 4 The graph shows the quasi-static tensile properties of the product obtained in Example 2.

[0030] Figure 5 The graph shows the quasi-static tensile properties of the product obtained in Example 3.

[0031] Figure 6 The graph shows the quasi-static tensile properties of the product obtained in Example 4.

[0032] Figure 7 The image shows the quasi-static tensile properties of the product obtained in Comparative Example 1. Detailed Implementation

[0033] 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 ball milling and additive manufacturing technologies, etc.) can be made without departing from the principles of the present invention, and these should also be considered to fall within the protection scope of the present invention.

[0034] Example 1

[0035] A metastable high-entropy alloy based on the Fe-Mn-Co-Cr-C system with high yield strength was prepared by weighing elemental raw materials of Fe, Mn, Co, Cr, and C with a purity ≥99.9 wt.% (particle size of each raw material being 50-200 micrometers); the raw materials were accurately weighed according to the specified ratio, with an error within ±0.05 g; ethanol was used as the ball milling medium, the grinding balls were made of cemented carbide, the ball-to-material mass ratio was 10:1, the ball mill speed was 250 r / min, and the ball milling time was 72 h. The resulting mixed powder was dried at 70 °C under vacuum for 5 h. Then, the powder with a particle size of 53-120 μm was selected by sieving. The mixed alloy powder was dried in a vacuum drying 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 250W, 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° rotation between layers to form the original powder onto a 316L stainless steel substrate until the forming process was complete. A metastable high-entropy alloy sample, FeMnCoCrC, was obtained.

[0036] The obtained metastable high-entropy alloy sample (FeMnCoCrC) has the following molar percentages: Fe 44.55%, Mn 34.65%, Co 9.9%, Cr 9.9%, and C 1%.

[0037] The resulting printed product has a tensile strength of 612.92 MPa, a yield strength of 395.01 MPa, and an elongation of 63.04%.

[0038] Example 2

[0039] 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 620.03MPa, 385.89MPa, and 54.86%, respectively.

[0040] Example 3

[0041] 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 634.89MPa, 397.34MPa, and 50.62%, respectively.

[0042] Example 4

[0043] A metastable high-entropy alloy based on the Fe-Mn-Co-Cr-C system with high yield strength was prepared by weighing elemental raw materials of Fe, Mn, Co, Cr, and C with a purity ≥99.9 wt.% (particle size of each raw material being 50-200 micrometers); the raw materials were accurately weighed according to the specified ratio, with an error within ±0.05 g; ethanol was used as the ball milling medium, the grinding balls were made of cemented carbide, the ball-to-material mass ratio was 10:1, the ball mill speed was 250 r / min, and the ball milling time was 72 h. The resulting mixed powder was dried at 70 °C under vacuum for 5 h. Then, the powder with a particle size of 53-120 μm was selected by sieving. The mixed alloy powder was dried in a vacuum drying 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 250W, 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 deposit the original powder onto a 316L stainless steel substrate until the deposition was complete. A metastable high-entropy alloy sample, FeMnCoCrC (C2-250), was obtained.

[0044] The obtained metastable high-entropy alloy sample (FeMnCoCrC) has the following mole percentages: Fe 44.1%, Mn 34.3%, Co 9.8%, Cr 9.8%, and C 2%.

[0045] The resulting printed product has a tensile strength of 719.63 MPa, a yield strength of 528.97 MPa, and an elongation of 23.07%.

[0046] Comparative Example 1

[0047] In Example 1, the laser power was changed to 600W and the scanning speed was 6mm / 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 655.01MPa, the yield strength was 448.58MPa, and the elongation was 26.32%. It can be observed that when the printing process parameters are not within the scope of this invention, the plasticity of the sample is severely lost.

[0048] Comparative Example 2

[0049] 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.

[0050] The tensile strength of the obtained printed sample was 611.17 MPa, the yield strength was 300.21 MPa, the elongation was 44.51%, and the density was 99.73%.

[0051] As can be seen from Comparative Examples 1 and 2 and the embodiments of the present invention, the present invention can obtain high-quality printed products with high tensile strength, high yield strength and high elongation through the synergistic effect of components and printing process parameters.

Claims

1. A C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy, characterized in that: The metastable high-entropy alloy comprises Fe, Mn, Co, Cr, and C. In the metastable high-entropy alloy sample FeMnCoCrC, the molar percentages are: Fe 44.5-44.6%, Mn 34.6-34.7%, Co 9.8-10%, Cr 9.8-10%, and C 0.9-1.1%. The metastable high-entropy alloy phase is an FCC single phase. The metastable high-entropy alloy is prepared using direct energy deposition (DAD) technology. The DAD preparation process includes the following steps: S1: Weigh the raw materials Fe, Mn, Co, Cr, and C according to the atomic percentage ratio. The raw materials are elemental metals and / or intermediate alloys. Use ethanol as the ball milling medium, and the grinding balls are made of cemented carbide. The ball-to-material mass ratio is 10:1 to 8:

1. The ball mill speed is 200-400 r / min, and the ball milling time is 48-96 h. Dry the resulting mixed powder under vacuum at 80-100℃ for 3-5 h. Then, sieve and select powder with a particle size of 53-120 μm to obtain the mixed powder. S2: Using the mixed powder obtained in S1 as raw material; constructing the required part model using 3D software, and designing the robotic arm motion path according to the model shape; depositing the part on a 316L substrate using direct energy deposition technology, employing a Gaussian distributed laser light source, with Ar gas used for powder feeding and protective gas; the direct energy deposition technology is a 3D printing technology, during which 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 48~52%, the Z-axis lift is 0.4~0.45mm, and laser serpentine reciprocating scanning is performed with interlayer rotation of 90°.

2. The C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy according to claim 1, characterized in that: The metastable high-entropy alloy sample FeMnCoCrC, by molar percentage, has Fe of 44.55%, Mn of 34.65%, Co of 9.9%, Cr of 9.9%, and C of 1%.

3. The C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy according to claim 1, characterized in that: The particle size range of the raw material powder is 50-200 micrometers; The particle size range of the mixed powder is 53~120 μm, and the D50 is 80~100 μm.

4. The C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy according to claim 1, characterized in that: According to the design composition, Fe, Mn, Co, Cr and C elemental raw materials with a purity ≥99.9wt.% were weighed; the weights were accurately weighed according to the ratio, with an error of ±0.05g; ethanol was used as the ball milling medium, the grinding balls were made of cemented carbide, the ball-to-material mass ratio was 10:1, the ball mill speed was 250 r / min, and the ball milling time was 72 h; the resulting mixed powder was dried at 70 ℃ under vacuum for 5 h; then the powder with a particle size of 53-120μm was sieved and selected as the spare powder for 3D printing.

5. The C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy according to claim 1, characterized in that: During 3D printing, the laser spot diameter is controlled at 1.45~1.55mm, the substrate preheating temperature is 100~105℃, the protective gas flow rate is 7.5~8.5L / min, the laser power is 250~260W, the laser scanning speed is 5.5~6mm / s, the single-pass overlap is 49~51%, the Z-axis lift is 0.44~0.45mm, and a laser serpentine reciprocating scan is performed with 90° rotation between layers.

6. The C-doped Fe-Mn-Co-Cr-C metastable high-entropy alloy according to claim 1, characterized in that: The printed sample has an FCC single phase, and the tensile yield strength of the resulting workpiece is 350~400MPa, the ultimate tensile strength is 600~800MPa, and the elongation after fracture is 30~65%.

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