Strengthening and toughening method for coherent precipitation strengthening type heterogeneous high-entropy alloy

Abstract

The invention relates to a strengthening and toughening method for coherent precipitation strengthening type heterogeneous high-entropy alloy. Comprising the following steps: cutting an as-cast CoCrNiAlTi high-entropy alloy plate into small blocks, and carrying out solution treatment; the roller speed of a rolling mill is set to be 85 + / -5 mm / s at the room temperature, an up-down synchronous mode is adopted, the thickness of each pass is reduced by 0.3 + / -0.02 mm, and the total rolling amount is 50 + / -1%; the rolled sample is subjected to annealing treatment at the temperature of 1250 + / -5 DEG C for 1 + / -0.1 min; removing a surface oxide layer, and continuously rolling for 80% to obtain a deformed structure; determining a recrystallization temperature; and high-temperature short-time annealing and low-temperature long-time aging treatment are conducted, and the coherent precipitation strengthening type heterogeneous high-entropy alloy is obtained. According to the method, a rolling deformation mode is utilized, deformed grains with certain orientation are formed in the structure in the rolling machining direction, the special structure is subjected to annealing and aging heat treatment, the internal dislocation density and the coordination effect of internal stress and grain boundaries are improved, and the high-entropy alloy with high plasticity is obtained.

Description

Technical Field

[0001] This invention belongs to the field of materials processing, and specifically relates to a method for strengthening and toughening coherent precipitation-strengthened heterogeneous high-entropy alloys. Background Technology

[0002] High-entropy alloys emerged in the early 21st century, but significant research has only begun in recent years. Precipitation strengthening has proven to be a highly effective mechanism for improving the yield strength of high-entropy alloys, and the coherent interface between the precipitate phase and the matrix is ​​crucial for achieving a good balance between strength and plasticity. A combination of room-temperature rolling and heat treatment processes yields metallic structural materials with excellent comprehensive performance, a good balance of strength and plasticity, and certain corrosion resistance, which can be widely used in high-tech fields such as aerospace. In recent years, significant progress has been made in the research of high-entropy alloys, achieving breakthroughs in material composition design, preparation processes, and performance optimization. Today, the design concepts of ultra-high strength, corrosion resistance, and high-temperature resistance have enabled the advantages of high-entropy alloys to be applied in various fields, making them a hot topic of close attention and research both domestically and internationally. Traditional CoCrNi-based high-entropy alloys have the following key drawbacks:

[0003] 1. The "high strength, low plasticity" trap: It is difficult to balance strength and plasticity.

[0004] II. Plasticity loss in precipitation-strengthened alloys: Introducing nano-precipitated phases (such as L12) can improve strength, but often leads to a sharp decrease in plasticity.

[0005] 3. Performance imbalance after simple mechanical treatment or heat treatment: either high strength but poor plasticity (such as CR state), or good plasticity but insufficient strength (such as recrystallization annealed state). Summary of the Invention

[0006] The purpose of this invention is to provide a method for strengthening and toughening high-entropy alloys by combining rolling with heat treatment. The method involves forming a long grain structure with certain orientation fibers through rolling deformation, and then combining high-temperature short-time annealing with low-temperature long-time aging to form a recrystallized structure with different grain sizes and generate a well-dispersed nano precipitate phase (L12 phase). This results in an industrial production method that achieves higher strength and plasticity than the original high-entropy alloy, thus meeting the needs of industrial production.

[0007] The technical solution to achieve the objective of this invention is: a method for strengthening and toughening coherent precipitation-reinforced heterogeneous high-entropy alloys, comprising the following steps:

[0008] Step (1): Cut the as-cast CoCrNiAlTi high-entropy alloy plate into small pieces and perform solid solution treatment to homogenize its composition;

[0009] Step (2): Set the rolling mill roll speed to 85±5 mm / s at room temperature, adopt the upper and lower synchronous mode, reduce the thickness by 0.3±0.02 mm per pass, and the total rolling amount is 50±1%; anneal the rolled sample at 1250±5℃ for 1±0.1 min to obtain a homogeneous structure with an average grain size of ~10 μm; remove the surface oxide layer and continue rolling for 80% to obtain a deformed structure;

[0010] Step (3): Determine the recrystallization temperature;

[0011] Step (4): Perform high-temperature short-time annealing and low-temperature long-time aging treatment to obtain a coherent precipitation-strengthened heterogeneous high-entropy alloy.

[0012] Furthermore, the specific composition of the CoCrNiAlTi high-entropy alloy in step (1), expressed as atomic percentage (at%), is as follows: Co%=34.5%, Cr%=33.8%, Ni%=25.6%, Al%=3%, Ti%=3.1%.

[0013] Further, the solution treatment in step (1) is as follows: cut into small pieces of 90~100 mm*45~55 mm*18~22 mm, and anneal at 1250±5℃ for 12±0.5 h for solution treatment.

[0014] Furthermore, the recrystallization temperature in step (3) is the temperature at which annealing for 1 hour forms a 100% recrystallized structure.

[0015] Furthermore, the specific parameters for the high-temperature short-time annealing in step (4) are: 950±5℃ for 1±0.1h, followed by water cooling.

[0016] Furthermore, the specific parameters for the low-temperature long-term aging in step (4) are: 700±2℃ for 2±0.2h, followed by water cooling.

[0017] A coherent precipitation-strengthened heterogeneous high-entropy alloy is prepared using the method described above.

[0018] Compared with the prior art, the significant advantages of this invention are:

[0019] (1) By increasing the Co content and moderately reducing the Ni content, this invention obtains an FCC matrix with a low and stable stacking fault energy. This is beneficial for the initiation of mechanical twinning to assist plastic deformation and provides an optimized matrix environment for subsequent precipitated phases. By controlling the total Al and Ti content within a few percent, this ratio is sufficient to precipitate a high-density nano-coherent L12 phase (mainly composed of (Ni, Co)3(Al, Ti)) after aging, achieving strong precipitation strengthening while effectively suppressing the formation of a large amount of brittle BCC / B2 phase. This achieves ultra-high strength while maximizing the preservation of the matrix's plastic potential.

[0020] (2) The core advantage of this invention lies in providing a clear, controllable, and efficient toughening technology path. By ensuring uniform deformation and controllable microstructure through "low-pressure, multi-pass rolling," and combined with the precise heat treatment window of "short-time high-temperature annealing + low-temperature long-time aging," heterogeneous high-entropy alloys with both high strength and good plasticity can be stably and repeatedly manufactured. This process parameter window is clear, and the process is stable, providing a reliable technical solution for high-performance high-entropy alloys to move from the laboratory to industrial applications.

[0021] (3) For the modified sample “CR”, its tensile strength is 1658 MPa, there is no yielding phenomenon, and the elongation at break is 2.4%. Although the tensile strength is high, its plastic deformation ability is very poor. By adjusting the heat treatment temperature and performing short-time high-temperature annealing treatment, after holding at 950℃ for 1 h, its tensile strength is 1237 MPa, its yield strength is 940 MPa, and its elongation at break is 26.5%, which improves its plasticity but reduces its tensile strength. Finally, it undergoes low-temperature aging treatment and holds at 700℃ for 2 h to achieve partial recrystallization. The recrystallization content is controlled to prevent too much plasticity loss. Finally, the tensile strength reaches 1747 MPa, which is about 5.4% higher than CR’s 1658 MPa. The yield strength reaches 1440 MPa, which is much higher than CR’s no obvious yielding phenomenon. The elongation at break is 14.4%, which is about 500% higher than CR’s 2.4%. This achieves material performance optimization and provides a treatment method for different industrial needs. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the rolling deformation technology in Example 1.

[0023] Figure 2 This is the engineering tensile curve diagram corresponding to the rolling and multi-stage heat treatment in Example 1.

[0024] Figure 3 The image shows the metallographic image of the CR sample in Example 1.

[0025] Figure 4The image shows the EBSD quality diagram of the microstructure after multi-stage heat treatment during rolling in Example 1.

[0026] Figure 5 This is a TEM image of the rolled multi-stage heat treatment process in Example 1.

[0027] Figure 6 This is a high-resolution transmission image of the microstructure after multi-stage heat treatment during rolling in Example 1.

[0028] Figure 7 The tensile curves are compared at different temperatures after rolling and multi-stage heat treatment in Comparative Example 1, showing the same deformation amount.

[0029] Figure 8 The tensile curves are for comparing low-temperature and room-temperature tensile tests after multi-stage heat treatment in Comparative Example 1. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings.

[0031] Example 1

[0032] A method for strengthening and toughening coherent precipitation-reinforced heterostructure high-entropy alloys through microstructure design includes the following steps:

[0033] The experimental raw material was a 20 mm thick cast Co35Cr32Ni27A13Ti3 high-entropy alloy plate purchased from Yanbang New Materials Technology Co., Ltd. The sample was cut into 100 mm * 50 mm pieces using wire cutting and annealed at 1250℃ for 12 h for solution treatment. The grain size after solution treatment was relatively large, approximately 300 μm, thus requiring some grain refinement. The sample was then rolled, with rotating rolls applying pressure to the billet to induce continuous plastic deformation. Under the compressive force of the rolls, the billet's thickness decreased and its length increased, following the law of constant volume.

[0034] A 130X250 experimental rolling mill was used to perform low-pressure, multi-pass rolling of the Co35Cr32Ni27A13Ti3 high-entropy alloy sample at room temperature. The mill was set to synchronous mode, with the speed of the upper and lower rolling rollers controlled at 85 mm / s and the rolling amount at 50%. The rolled sample was then annealed at 1250℃ for 1 min to obtain a uniform structure with a grain size of ~10 μm. The surface oxide layer was removed using a metallographic polishing machine, and rolling continued for another 80% until the billet thickness reached 2.02 mm.

[0035] The recrystallization temperature was determined to be the temperature at which 100% recrystallized structure is formed after annealing for 1 hour. The heat treatment temperature was set, and first, a high-temperature short-time annealing treatment was performed at 950℃ for 1 hour, followed by water cooling. Then, a low-temperature long-time aging treatment was performed at 700℃ for 2 hours, followed by water cooling.

[0036] The specific composition of the CoCrNiAlTi high-entropy alloy is Co%=34.5%, Cr%=33.8%, Ni%=25.6%, Al%=3%, and Ti%=3.1%. It is formed into long, fibrous grains through rolling deformation.

[0037] The rolling deformation process consists of two parts. First, the original 20mm thick billet is cold-rolled to 10.06mm at room temperature. Rolling is divided into longitudinal rolling, transverse rolling, and skew rolling. This invention uses longitudinal rolling, where the billet passes between two rollers rotating in opposite directions, undergoing plastic deformation. After multiple passes with low reduction in pressure, each pass reducing the thickness by 0.3mm, the block billet is uniformly thinned, completing the deformation. Then, to avoid excessively fine grains, the block material after R50% is heat-treated. After holding at 1250℃ for 1 minute, the average grain size is 10 μm. It is then cold-rolled by 80%, and named "CR".

[0038] pass Figure 1 The CoCrNiAlTi high-entropy alloy was subjected to rolling deformation to obtain the required thickness. The speed of the upper and lower rolling rolls was set to 85 mm / s, and the diameter decreased by 0.3 mm per pass. Figure 3 Metallographic image of the CR sample;

[0039] pass Figure 2 The specific heat treatment parameters were determined. The tensile strength of CR was 1658 MPa, with almost no yielding phenomenon and a fracture elongation of 2.4%. After high-temperature short-time heat treatment, its tensile strength was 1237 MPa after holding at 950℃ for 1 hour, which was slightly reduced, but its yield strength was 940 MPa, which was much improved. The fracture elongation was 26.5%, which was 1004% improved. After holding at 700℃ for 2 hours, its tensile strength was 1747 MPa, which was 5.4% higher than that of CR. Its yield strength was 1440 MPa, which was much improved compared to the lack of obvious yielding phenomenon of CR. The fracture elongation was 14.4%, which was 500% higher than that of CR. This is a method to improve the strength and plasticity of the material at the same time. Figure (4) is a schematic diagram of the internal changes of CoCrNiAlTi high-entropy alloy after rolling deformation and heat treatment. Figure (5) is a schematic diagram of its microstructure, which shows the microstructure after deformation heat treatment. Figure (6) is a high-resolution schematic diagram of its microstructure. The L12 precipitate phase can be seen to be uniformly distributed within the microstructure after deformation heat treatment.

[0040] Comparative Example 1

[0041] like Figure 7 As shown, using the same CoCrNiAlTi high-entropy alloy as in Example 1, and after obtaining CoCrNiAlTi high-entropy alloy blocks of the same thickness through the same rolling deformation method, different short-time high-temperature annealing and long-time low-temperature aging treatments were performed, controlling the same variables as in Example 1. The resulting tensile curve comparison chart is as follows:

[0042] Therefore, when the low-temperature long-time aging treatment parameters remain unchanged, adjusting the high-temperature short-time annealing parameters to 1000℃ for 5min can yield a comprehensive performance with lower strength but stronger plasticity, with a yield strength of 1200MPa and a fracture elongation of 25.0%. Although the plasticity is improved compared to CR, the strength will be reduced, which is not as good as the result obtained by the method in Example 1.

[0043] pass Figure 8 It can be seen that for the same CoCrNiAlTi high-entropy alloy, after undergoing the same rolling deformation, high-temperature short-time annealing and low-temperature long-time aging treatment with the same parameters, tensile tests were conducted in a low-temperature environment of -196°C, and the tensile curves were compared as follows:

[0044] The black dashed line represents the tensile curve at 950℃ for 1 hour, with a tensile strength of 2000MPa, a yield strength of 1600MPa, and a fracture elongation of 22%. Compared with the same parameters at room temperature, both the strength and plasticity are improved. Therefore, the CoCrNiAlTi high-entropy alloy that has undergone high-temperature short-time annealing treatment with these parameters has stronger performance in extremely cold environments.

[0045] Based on Comparative Example 1, the deformation method and heat treatment parameters of Example 1 are superior and feasible.

[0046] The equipment and heat treatment parameters obtained in this embodiment of the invention for strengthening and toughening CoCrNiAlTi high-entropy alloys have achieved optimization and breakthroughs in the performance of martensitic stainless steel, and can be applied in aerospace, automotive and other fields.

[0047] The equipment, operating steps, and operating methods not covered in this invention are the same as or can be implemented using existing technologies. They are not described in detail in this application.

[0048] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for strengthening and toughening coherent precipitation-reinforced heterogeneous high-entropy alloys, characterized in that, Includes the following steps: Step (1): Cut the as-cast CoCrNiAlTi high-entropy alloy plate into small pieces and perform solid solution treatment to homogenize its composition; Step (2): Set the rolling mill roll speed to 85±5 mm / s at room temperature, adopt the upper and lower synchronous mode, reduce the thickness by 0.3±0.02 mm per pass, and the total rolling amount is 50±1%; anneal the rolled sample at 1250±5℃ for 1±0.1 min to obtain a homogeneous structure with an average grain size of ~10 μm; remove the surface oxide layer and continue rolling for 80% to obtain a deformed structure; Step (3): Determine the recrystallization temperature; Step (4): Perform high-temperature short-time annealing and low-temperature long-time aging treatment to obtain a coherent precipitation-strengthened heterogeneous high-entropy alloy.

2. The method according to claim 1, characterized in that, The specific composition of the CoCrNiAlTi high-entropy alloy in step (1), expressed as atomic percentage (at%), is as follows: Co%=34.5%, Cr%=33.8%, Ni%=25.6%, Al%=3%, Ti%=3.1%.

3. The method according to claim 2, characterized in that, The solution treatment in step (1) is as follows: cut into small pieces of 90~100mm*45~55mm*18~22mm and anneal at 1250±5℃ for 12±0.5h for solution treatment.

4. The method according to claim 3, characterized in that, The recrystallization temperature in step (3) is the temperature at which annealing for 1 hour forms a 100% recrystallized structure.

5. The method according to claim 4, characterized in that, The specific parameters for the high-temperature short-time annealing in step (4) are: 950±5℃ for 1±0.1h, followed by water cooling.

6. The method according to claim 5, characterized in that, The specific parameters for the low-temperature long-term aging in step (4) are: 700±2℃ for 2±0.2h, followed by water cooling.

7. A coherent precipitation-strengthened heterostructure high-entropy alloy, characterized in that, Prepared using the method described in any one of claims 1-6.

Images