Low temperature annealing + laser surface heat treatment method of bidirectional isomeric high-entropy alloy

Abstract

The application provides a bidirectional heterogeneous high-entropy alloy low-temperature annealing + laser surface heat treatment method, first, a high-entropy alloy ingot is prepared by adopting a vacuum arc melting technology, and is repeatedly melted for five times, then homogenization annealing treatment is carried out and hot forging is carried out into a slab; then, the high-entropy alloy slab is cold-rolled under high pressure, the microstructure is transformed into nanocrystalline / submicron crystalline, and a large number of deformation bands are formed; then low-temperature annealing treatment is carried out, and cooling is carried out in a water cooling mode, thereby forming a heterogeneous structure high-entropy alloy with a large grain size difference; finally, laser surface heat treatment is carried out on the high-entropy alloy after low-temperature annealing, thereby obtaining a gradient distribution of grain sizes along the depth direction, and each gradient layer is a bidirectional heterogeneous structure of coarse-grained-fine-grained mixed structure. Considering that the bidirectional heterogeneous structure is a coarse-grained-fine-grained composite structure in the depth and horizontal directions, so the bidirectional heterogeneous structure is more remarkable in improving the strength and plasticity of the high-entropy alloy.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous structure metal material preparation technology, and specifically relates to a low-temperature annealing + laser surface heat treatment method for bidirectional heterogeneous high-entropy alloys. Background Technology

[0002] High-entropy alloys are a new type of material based on the design concept of mixed entropy or configurational entropy. By mixing five or more main elements at equiatomic or near-equiatomic concentrations, they break with traditional alloy design principles. Currently, high-entropy alloys exhibit excellent performance in low-temperature toughness, corrosion resistance, and radiation resistance, showing broad application prospects. Among these, high ductility is a fundamental mechanical property of high-entropy alloys.

[0003] Patent application CN202110160745.4 proposes a layered heterogeneous metallic material and its preparation method. This method involves stacking, pre-heating, multiple cumulative rolling processes, and annealing to tightly bond magnesium-lithium alloys with significant differences in strength and plasticity, forming a layered heterogeneous structure. During deformation, the differences in strength and plasticity between different regions generate a heterogeneous deformation-induced strengthening effect, thereby simultaneously improving both the material's strength and plasticity. However, the process proposed in this patent requires multiple cumulative rolling processes, resulting in a complex flow and low production efficiency. Patent application CN202011185649.7 proposes a method for preparing heterogeneous high-entropy alloys. The principle involves stacking and fixing two high-entropy alloy plates of the same size, preheating them at high temperature, and then rolling them. The rolled plates are then cut in the middle, and the stacking, fixing, preheating, and rolling processes are repeated 5-6 times to obtain an ultrafine-grained high-entropy alloy plate containing dozens of interfaces. Subsequent annealing treatment causes some grains to grow, controlling the formation of a heterogeneous structure combining soft and hard phases, thus obtaining a high-strength, high-toughness heterogeneous high-entropy alloy with excellent performance. However, the process proposed in this patent requires multiple cumulative rolling processes and numerous repetitions, making the procedures quite complex.

[0004] It is worth noting that the two processes mentioned above can only prepare heterogeneous structures in a single direction. Considering that the main reason heterogeneous structures improve strength and ductility is the induction of geometrically necessary dislocation initiation and pile-up at the soft-phase-hard-phase interface, resulting in strong mutation-induced strengthening and work hardening, thus synergistically improving strength and ductility, this project will propose a bidirectional heterogeneous structure and its efficient and simple preparation method to further enhance the strength and ductility of high-entropy alloys. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a low-temperature annealing combined with laser surface heat treatment method for bidirectional heterogeneous high-entropy alloys. The bidirectional heterogeneous structure obtained by this method exhibits a coarse-fine grain mixed microstructure at each depth layer, with the average grain size decreasing gradually from the surface to the core along the depth direction.

[0006] The technical solution provided by this invention is as follows:

[0007] A low-temperature annealing + laser surface heat treatment method for a bidirectional heterogeneous high-entropy alloy includes the following steps:

[0008] (1) Smelting of ingots: Under a high-purity argon atmosphere, pure metal powders of Co, Cr, Fe, Mn and Ni with a purity of ≥99.7wt.% are selected as raw materials, and high-entropy alloy ingots are prepared by vacuum arc melting technology.

[0009] (2) Hot forging: The high entropy alloy ingot is hot forged into a forging blank with a thickness of 20-35mm at a temperature of 1050℃~1150℃;

[0010] (3) Homogenization annealing: The forged alloy block billet is subjected to high-temperature homogenization annealing. The holding temperature of homogenization annealing is 1000~1150℃, the holding time of homogenization annealing is 3~8h, and the cooling method is water cooling.

[0011] (4) Cold rolling: The forging billet after homogenization and annealing is rolled and deformed at room temperature, with a final rolling thickness of 0.8 to 4.5 mm and a reduction rate of 85% to 96.7%.

[0012] (5) Annealing heat treatment: The cold-rolled plate is placed in the furnace for annealing. The annealing temperature range is 470-650℃, the annealing holding time is 2-30min, and the cooling method is water cooling.

[0013] (6) Laser surface annealing heat treatment: The high-entropy alloy after low-temperature annealing is subjected to laser surface heat treatment using a temperature-controlled semiconductor laser. The laser spot size is flat-top rectangular, the laser power is 960-1200w, the scanning rate is 7-12mm / s, and the number of scans is 1-15.

[0014] Preferably, step (1) requires repeated melting five times.

[0015] Preferably, the oxide layer on the surface of the billet before hot forging in step (2) needs to be removed.

[0016] Preferably, no annealing is performed during the cold rolling process in step (4).

[0017] Preferably, the low-temperature annealing treatment in step (5) controls the spatial distribution and volume fraction of recrystallized and non-recrystallized structures in the heterogeneous structure by adjusting the annealing temperature and time.

[0018] Preferably, in step (6), if the thickness of the cold-rolled sheet is ≥2.5mm, laser surface heat treatment is performed on the upper and lower cold-rolled surfaces after low-temperature annealing, or laser surface heat treatment is performed on a single cold-rolled surface, and the depth of laser heat treatment is increased by increasing the number of scans.

[0019] Preferably, the laser surface heat treatment in step (6) uses a flat-top laser spot with a spot size of 6mm×8mm, 10mm×4mm, 14mm×3mm or 20mm×2mm.

[0020] The present invention also provides a bidirectional heterogeneous high-entropy alloy prepared by the above method.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The grain size of the bidirectional heterogeneous structure is gradient in the depth direction. Each gradient layer is a mixed coarse-fine grain heterogeneous structure. Therefore, the bidirectional heterogeneous structure provides more soft-hard phase interfaces. During plastic deformation, a large number of geometrically necessary dislocations will be generated near these interfaces, which will cause strong transformation-induced strengthening and work hardening. That is, the present invention greatly increases the content of soft-hard phase interfaces in the microstructure through the innovative design of the bidirectional heterogeneous structure, thereby greatly improving the strength and plasticity of high-entropy alloys.

[0023] (2) This invention can prepare bidirectional heterogeneous materials using only existing cold rolling mills, muffle furnaces and semiconductor lasers. It does not require repeated rolling and long-term annealing. Only by adjusting process parameters such as annealing temperature, annealing holding time, laser power and scanning speed, the volume ratio and spatial distribution of recrystallized and non-recrystallized structures in bidirectional heterogeneous high-entropy alloys can be controlled, thereby precisely controlling the strength and plasticity of the material. Therefore, the preparation and processing efficiency is higher and the performance is more controllable. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the annealing composite laser surface annealing heat treatment process in this invention;

[0025] Figure 2 This is a microhardness distribution diagram from the surface to the core of the bidirectional heterostructure CoCrFeMnNi high-entropy alloy in this invention.

[0026] Figure 3 This is a grain size distribution diagram of the surface region of the bidirectional heterostructure CoCrFeMnNi high-entropy alloy in this invention; Detailed Implementation

[0027] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0028] The composite heterogeneous high-entropy alloy of the present invention was subjected to room temperature tensile tests on an INSTRON 3369 universal testing machine in accordance with GB / T228-2010.

[0029] The low-temperature annealing combined with laser surface annealing process for bidirectional heterogeneous high-entropy alloys according to the present invention is illustrated in the following specific implementation examples:

[0030] Example 1

[0031] (1) Smelting of ingots: Under a high-purity argon atmosphere, pure metal powders of Co, Cr, Fe, Mn and Ni with a purity of ≥99.7wt.% were selected as raw materials. CoCrFeMnNi high-entropy alloy ingots were prepared by vacuum arc melting technology and repeatedly melted 5 times to ensure the uniformity of chemical composition.

[0032] (2) Hot forging: The oxide layer on the surface of the billet is removed by turning, and the billet is hot forged into a 20mm slab at 1050℃.

[0033] (3) Homogenization annealing: The forged alloy block is subjected to high-temperature homogenization annealing. The holding temperature of homogenization annealing is 1000℃, the holding time of homogenization annealing is 3h, the cooling method is water cooling, and the oxide layer on the surface is removed by grinding.

[0034] (4) Cold rolling: The alloy block is rolled and deformed at room temperature, and the original 20mm thick alloy block is cold rolled into a 0.8mm thick cold rolled plate with a reduction rate of about 96%.

[0035] (5) Annealing heat treatment: First, hold the temperature for at least 15 minutes and place a 304 stainless steel plate in advance to ensure the uniformity of the furnace temperature. Then, place the cold-rolled plate into the muffle furnace for annealing. The annealing temperature is 600℃, the annealing holding time is 5 minutes, and the cooling method is water cooling.

[0036] (6) Laser surface annealing heat treatment: A temperature-controlled semiconductor laser is used to perform laser surface heat treatment on the cold-rolled high-entropy alloy. The rectangular spot size is 6mm × 8mm, the laser power is 960W, the scanning rate is 7mm / s, and the number of scans is 1. A schematic diagram of the laser surface heat treatment process is shown below. Figure 1 As shown.

[0037] The bidirectional isomorphic CoCrFeMnNi high-entropy alloy prepared in this embodiment exhibits a gradient distribution of grain size that continuously decreases along the depth direction, and its hardness also shows a gradient distribution characteristic along the depth direction (e.g., Figure 2 As shown). Its surface layer is a fully recrystallized structure (as shown). Figure 3 As shown in the figure, the yield strength of this bidirectional heterostructure CoCrFeMnNi high-entropy alloy is 838 MPa and the uniform elongation is 15.2%.

[0038] Example 2

[0039] (1) Smelting of ingots: Under a high-purity argon atmosphere, pure metal powders of Co, Cr, Fe, Mn and Ni with a purity of ≥99.7wt.% were selected as raw materials. CoCrFeMnNi high-entropy alloy ingots were prepared by vacuum arc melting technology and repeatedly melted 5 times to ensure the uniformity of chemical composition.

[0040] (2) Hot forging: The oxide layer on the surface of the billet is removed by turning, and the billet is hot forged into a 30mm slab at 1100℃.

[0041] (3) Homogenization annealing: The forged alloy block is subjected to high-temperature homogenization annealing. The holding temperature of homogenization annealing is 1000℃, the holding time of homogenization annealing is 5h, the cooling method is water cooling, and the oxide layer on the surface is removed by grinding.

[0042] (4) Cold rolling: The alloy block is rolled and deformed at room temperature, and the original 30mm thick alloy block is cold rolled into a 1mm thick cold-rolled plate with a reduction rate of about 96.7%.

[0043] (5) Annealing heat treatment: First, hold the temperature for at least 15 minutes and place a 304 stainless steel plate in advance to ensure the uniformity of the furnace temperature. Then, place the cold-rolled plate into the muffle furnace for annealing. The annealing temperature is 470℃, the annealing holding time is 30 minutes, and the cooling method is water cooling.

[0044] (6) Laser surface annealing heat treatment: The high-entropy alloy after cold rolling is subjected to laser surface heat treatment using a temperature-controlled semiconductor laser. The rectangular spot size is 10mm×4mm, the laser power is 960w, the scanning rate is 8mm / s, and the number of scans is 1.

[0045] The biaxially oriented heterogeneous high-entropy alloy prepared in this embodiment exhibits a gradient grain size that decreases progressively along the depth direction. The surface consists of fully recrystallized grains, while the middle and bottom layers contain unrecrystallized grains embedded in layered deformation bands generated during cold rolling. This biaxially oriented heterogeneous CoCrFeMnNi high-entropy alloy has a yield strength of 877 MPa and a uniform elongation of 12.9%.

[0046] Example 3

[0047] (1) Smelting of ingots: Under a high-purity argon atmosphere, pure metal powders of Co, Cr, Fe, Mn and Ni with a purity of ≥99.7wt.% were selected as raw materials. CoCrFeMnNi high-entropy alloy ingots were prepared by vacuum arc melting technology and repeatedly melted 5 times to ensure the uniformity of chemical composition.

[0048] (2) Hot forging: The oxide layer on the surface of the billet is removed by turning, and the billet is hot forged into a 30mm slab at 1150℃.

[0049] (3) Homogenization annealing: The forged alloy block is subjected to high-temperature homogenization annealing. The holding temperature of homogenization annealing is 1150℃, the holding time of homogenization annealing is 3h, the cooling method is water cooling, and the oxide layer on the surface is removed by grinding.

[0050] (4) Cold rolling: The alloy block is rolled and deformed at room temperature, and the original 35mm thick alloy block is cold rolled into a 2mm thick cold-rolled plate with a reduction rate of about 94.3%.

[0051] (5) Annealing heat treatment: First, hold the temperature for at least 15 minutes and place a 304 stainless steel plate in advance to ensure the uniformity of the furnace temperature. Then, place the cold-rolled plate into the muffle furnace for annealing. The annealing temperature range is 550℃, the annealing holding time is 10 minutes, and the cooling method is water cooling.

[0052] (6) Laser surface annealing heat treatment: The high-entropy alloy after cold rolling is subjected to laser surface heat treatment using a temperature-controlled semiconductor laser. The rectangular spot size is 10mm×4mm, the laser power is 1200W, the scanning rate is 8mm / s, and the number of single-sided scans is 6.

[0053] The high-entropy alloy with a bidirectional heterostructure prepared in this embodiment exhibits a gradient distribution with grain size decreasing progressively along the depth direction. Simultaneously, the surface is observed to be in a fully recrystallized state, while the bottom is in a partially recrystallized state, with 23.1% of the grains remaining unrecrystallized. The yield strength of the bidirectional heterostructure CoCrFeMnNi high-entropy alloy is 744 MPa, and the uniform elongation is 22.5%.

[0054] Example 4

[0055] (1) Smelting of ingots: Under a high-purity argon atmosphere, pure metal powders of Co, Cr, Fe, Mn and Ni with a purity of ≥99.7wt.% were selected as raw materials. CoCrFeMnNi high-entropy alloy ingots were prepared by vacuum arc melting technology and repeatedly melted 5 times to ensure the uniformity of chemical composition.

[0056] (2) Hot forging: The oxide layer on the surface of the billet is removed by turning, and the billet is hot forged into a 25mm slab at 1125℃.

[0057] (3) Homogenization annealing: The forged alloy block is subjected to high-temperature homogenization annealing. The holding temperature of homogenization annealing is 1050℃, the holding time of homogenization annealing is 8h, the cooling method is water cooling, and the oxide layer on the surface is removed by grinding.

[0058] (4) Cold rolling: The alloy block is rolled and deformed at room temperature, and the original 25mm thick alloy block is cold rolled into a 2.5mm thick cold rolled plate with a reduction rate of about 90%.

[0059] (5) Annealing heat treatment: First, hold the temperature for at least 15 minutes and place a 304 stainless steel plate in advance to ensure the uniformity of the furnace temperature. Then, place the cold-rolled plate into the muffle furnace for annealing. The annealing temperature is 650℃, the annealing holding time is 2 minutes, and the cooling method is water cooling.

[0060] (6) Laser surface annealing heat treatment: The high-entropy alloy after cold rolling is subjected to laser surface heat treatment using a temperature-controlled semiconductor laser. The rectangular spot size is 14mm×3mm, the laser power is 1200w, the scanning rate is 8mm / s, and the number of single-sided scans is 15.

[0061] The high-entropy alloy with a bidirectional heterostructure prepared in this embodiment exhibits a gradient grain size distribution along the depth direction, with different proportions of coarse and fine grains in different gradient layers. The surface is observed to be in a fully recrystallized state, while the bottom is in a mixed state of partially recrystallized and unrecrystallized grains, with the unrecrystallized grains accounting for a smaller proportion. This bidirectional heterostructure CoCrFeMnNi high-entropy alloy has a yield strength of 684.7 MPa and a uniform elongation of 27.1%.

[0062] Example 5

[0063] (1) Smelting of ingots: Under a high-purity argon atmosphere, pure metal powders of Co, Cr, Fe, Mn and Ni with a purity of ≥99.7wt.% were selected as raw materials. CoCrFeMnNi high-entropy alloy ingots were prepared by vacuum arc melting technology and repeatedly melted 5 times to ensure the uniformity of chemical composition.

[0064] (2) Hot forging: The oxide layer on the surface of the billet is removed by turning, and the billet is hot forged into a 30mm slab at 1150℃.

[0065] (3) Homogenization annealing: The forged alloy block is subjected to high-temperature homogenization annealing. The holding temperature of homogenization annealing is 1150℃, the holding time of homogenization annealing is 3h, the cooling method is water cooling, and the oxide layer on the surface is removed by grinding.

[0066] (4) Cold rolling: The alloy block is rolled and deformed at room temperature, and the original 30mm thick alloy block is cold rolled into a 4.5mm thick cold rolled plate with a reduction rate of about 85%.

[0067] (5) Annealing heat treatment: First, hold the temperature for at least 15 minutes and place a 304 stainless steel plate in advance to ensure the uniformity of the furnace temperature. Then, place the cold-rolled plate into the muffle furnace for annealing. The annealing temperature range is 650℃, the annealing holding time is 2 minutes, and the cooling method is water cooling.

[0068] (6) Laser surface annealing heat treatment: The high-entropy alloy after cold rolling is subjected to laser surface heat treatment using a temperature-controlled semiconductor laser. The rectangular spot size is 20mm×2mm, the laser power is 1700W, the scanning rate is 12mm / s, and the number of scans on the front and back sides is 15 times each.

[0069] The grain size of the biaxial heterostructure high-entropy alloy prepared in this embodiment is gradient distributed along the depth direction. The surface layer consists of coarse, fully recrystallized grains, while recrystallized grains and non-recrystallized grains can be observed simultaneously in the middle and bottom. However, the proportion of non-recrystallized grains is relatively low, and the strength difference between the soft and hard regions is small. The yield strength of the biaxial heterostructure CoCrFeMnNi high-entropy alloy is 660 MPa, and the uniform elongation is 30.5%.

[0070] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A low temperature annealing + laser surface heat treatment method of a bidirectional isomeric high-entropy alloy, characterized in that, The method comprises the following steps: (1) Smelting of ingot: under a high-purity argon atmosphere, pure metal powders of Co, Cr, Fe, Mn and Ni with a purity of ≥99.7wt.% are selected as raw materials, and vacuum arc melting technology is used to prepare a high-entropy alloy ingot; (2) Hot forging: the high-entropy alloy ingot is hot forged into a forged blank with a thickness of 20-35 mm at a temperature of 1050-1150°C; (3) Homogenization annealing: the alloy block forged blank is subjected to high-temperature homogenization annealing, the homogenization annealing temperature is 1000-1150°C, the homogenization annealing time is 3-8h, and the cooling mode is water cooling; (4) Cold rolling: the forged blank after homogenization annealing is deformed by rolling at room temperature, the final rolling thickness is 0.8-4.5mm, and the reduction rate is 85%-96.7%; (5) Annealing heat treatment: the cold-rolled plate is placed in a furnace for annealing, the annealing temperature range is 470-650°C, the annealing holding time is 2-30min, and the cooling mode is water cooling; (6) Laser surface annealing heat treatment: a temperature-controlled semiconductor laser is used to perform laser surface heat treatment on the low-temperature annealed high-entropy alloy, a flat-top rectangular light spot is used, the laser power is 960-1200w, the scanning speed is 7-12mm / s, and the scanning times are 1-15 times; The bidirectional heterogeneous structure of the high-entropy alloy has a gradient distribution of grain size in the depth direction, and each gradient layer has a heterogeneous structure of coarse-grained and fine-grained mixed structure.

2. The method of claim 1, wherein the low temperature annealing + laser surface heat treatment of the bi-directional heterogeneous high-entropy alloy is characterized by, In step (1), the melting needs to be repeated five times.

3. The method of claim 1, wherein the low temperature annealing + laser surface heat treatment of the bi-directional heterogeneous high-entropy alloy is characterized by, In step (2), the surface oxide layer of the cast blank before hot forging needs to be removed.

4. The method of claim 1, wherein the low temperature annealing + laser surface heat treatment of the bi-directional heterogeneous high-entropy alloy is characterized by, In step (4), no annealing treatment is performed during cold rolling.

5. The method of claim 1, wherein the low temperature annealing + laser surface heat treatment of the bi-directional heterogeneous high-entropy alloy is characterized by, In step (5), the low-temperature annealing treatment realizes the regulation of the spatial distribution and volume fraction of the recrystallized structure and the unrecrystallized structure in the heterogeneous structure by regulating the annealing holding temperature and time.

6. The method of claim 1, wherein the low temperature annealing + laser surface heat treatment of the bi-directional heterogeneous high-entropy alloy is characterized by, In step (6), if the thickness specification of the cold-rolled plate is ≥2.5mm, the upper and lower cold-rolled surfaces after low-temperature annealing treatment are subjected to laser surface heat treatment.

7. The method of claim 1, wherein the low temperature annealing + laser surface heat treatment of the bi-directional heterogeneous high-entropy alloy is characterized by, In step (6), the laser surface heat treatment selects a flat-top light spot, and the light spot size is 6mm×8mm, 10mm×4mm, 14mm×3mm or 20mm×2mm.

8. The bidirectional heterogeneous structure high-entropy alloy prepared by the method of any one of claims 1-7.

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