Titanium alloy grain refinement method

Abstract

The invention discloses a method for refining grains of a titanium alloy. According to the method, an original low-oxygen-content titanium alloy plate is subjected to cryogenic pretreatment, the temperature of the core of the original low-oxygen-content titanium alloy plate is reduced to a certain temperature, then the cryogenic low-oxygen-content titanium alloy plate is fed into a rolling mill, the single-pass reduction rate is controlled, cryogenic rolling is completed, high refinement and uniform distribution of crystal grains are achieved, and the low-oxygen-content titanium alloy plate is obtained. And the rolled titanium alloy plate is subjected to subzero treatment again, and the titanium alloy plate of the complex twin crystal structure formed by intersection of {11-22} and {10-11} twin crystals is obtained. The method has the beneficial effects that under the synergistic effect of low oxygen and deep cooling, even under the extremely small deformation amount, the cross effect of various twin crystal systems can be efficiently activated, a high-density and complex twin crystal structure is formed, high refinement and uniform distribution of crystal grains are achieved, then the mechanical strength and low-temperature toughness of the material are remarkably improved, and the service life of the material is prolonged. And the application requirements in a severe low-temperature service environment are met.

Description

Technical Field

[0001] This invention relates to the field of grain refinement technology, and more particularly to a method for grain refinement of titanium alloys. Background Technology

[0002] Currently, grain refinement methods for titanium alloys can be broadly categorized into three types: "extreme deformation-recrystallization," "deformation-phase transformation synergistic," and "rapid solidification / surface modification." Extreme deformation methods, represented by processes such as equal-diameter angular extrusion, high-pressure torsion, cumulative rolling, and multi-directional forging, can compress grains to submicron or even nanometer scales. However, these methods require high pressure and die life, and are often intermittent, making integration with conventional rolling lines difficult, resulting in insufficient scalability and cost advantages. Furthermore, high-density dislocations and residual stress narrow the subsequent shaping-heat treatment window, easily leading to microstructural recovery or abnormal grain growth. Deformation-phase transformation synergistic methods often involve rapid cooling after hot working in the β or α+β regions to induce martensite α′ refinement, or grain refinement through hydrogenation-dehydrogenation processes involving large deformation at low temperatures followed by dehydrogenation annealing. These methods are highly dependent on alloy composition and temperature control precision, have complex processes, and carry the risk of hydrogen embrittlement or microstructural overheating. Multiple thermal cycles also increase energy consumption. Rapid solidification / surface modification technologies such as selective laser melting, electron beam melting, powder metallurgy pressing-hot isostatic pressing, and friction stir processing can locally obtain ultrafine or even equiaxed nanocrystals, but the formed parts are often columnar crystals or only refined on the surface. Overall anisotropy and porosity defects are prominent, and secondary processes such as high-temperature hot isostatic pressing and thermomechanical treatment are still required to meet mechanical and dimensional requirements.

[0003] In summary, existing technologies are either limited by equipment investment and part size, or have lengthy processes, high energy consumption, and insufficient structural stability. They can only achieve localized refinement and are difficult to obtain uniform plate structures. Therefore, it is difficult to produce large-area, high-strength and high-toughness α-titanium alloy plates on industrial rolling production lines at low cost and high speed. There is an urgent need to develop new and efficient fine-grain deformation processes. Summary of the Invention

[0004] This invention discloses a method for refining the grains of titanium alloys to solve any of the above-mentioned and other potential problems in the prior art.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for refining the grains of titanium alloy plates. The method involves subjecting the original low-oxygen titanium alloy plate to cryogenic pretreatment to reduce the core temperature of the original low-oxygen titanium alloy plate to a certain temperature. The cryogenically pretreated low-oxygen titanium alloy plate is then fed into a rolling mill, and the single-pass reduction rate is controlled to complete the cryogenic rolling, thereby achieving highly refined and uniformly distributed grains. The rolled titanium alloy plate is then subjected to cryogenic treatment again to obtain a titanium alloy plate with a complex twin structure formed by the intersection of {11-22} and {10-11} twins.

[0006] Furthermore, the method specifically includes the following steps:

[0007] S1) Place the low oxygen content titanium alloy plate in a cryogenic chamber and immerse it completely in liquid nitrogen for no less than 20 minutes to allow the plate to cool uniformly from the surface to the core to -196°C, thus obtaining a cryogenic titanium alloy plate.

[0008] S2) The cryogenic titanium alloy plate obtained in S1) is fed into the rolling mill, and the arc thickness ratio l / d is set to 1.0–2.7, where d is the thickness of the titanium alloy plate. Single-pass pre-rolling is performed according to a certain reduction to complete the cryogenic rolling and obtain a titanium alloy plate with refined grains.

[0009] S3) The titanium alloy plate with refined grains obtained in S2) is placed in a cryogenic chamber and completely immersed in liquid nitrogen for 20-30 minutes to obtain a titanium alloy plate with a complex twin structure formed by the intersection of {11-22} and {10-11} twins.

[0010] Furthermore, the method also includes a uniform annealing step: before placing the low-oxygen titanium alloy plate in a cryogenic chamber, it is first homogenized and annealed at a temperature of 500-600℃ for 15-45 minutes, and then air-cooled to room temperature.

[0011] Furthermore, the low-oxygen titanium alloy plate in S1) is an α-titanium alloy plate (HCP crystal structure) with an oxygen content of <0.18wt%; and the upper limits of impurities are: Fe <0.05wt%, C <0.02wt%, N <0.02wt% and H <0.001wt%.

[0012] Furthermore, the single-pass reduction rate in S2) is 2% to 10%.

[0013] Furthermore, the yield strength of the titanium alloy plate treated by the method is increased by at least 15% compared with the original plate, and the impact toughness at -196°C is increased by at least 1.5 times.

[0014] A titanium alloy plate, which is prepared by the above-described method.

[0015] The principle of this invention is as follows:

[0016] By reducing the oxygen content in α-titanium (to less than 0.18 wt%) and cryogenic treatment (-196℃), {10-11} twinning in metal sheets was synergistically activated and efficiently. Since {10-11} twins are rare in hexagonal close-packed structures and difficult to activate under conventional conditions, the complex twins were utilized to achieve grain refinement of the sheet with small deformation, improving the overall mechanical properties of α-titanium. Highly efficient grain refinement was achieved by synergistically controlling the low oxygen content and cryogenic deformation conditions of the α-titanium alloy sheet. Controlling the oxygen content in the material to below 0.18 wt% significantly weakens the pinning effect of oxygen on twin boundaries, effectively promoting twin nucleation and propagation, especially beneficial for the formation of {10-11} twin systems that are difficult to activate under conventional conditions. At a cryogenic environment of -196℃, the critical shear stress for dislocation slip significantly increases, the slip mechanism is suppressed, and twinning becomes the dominant deformation mode. Meanwhile, cryogenic temperatures lower the thermodynamic barrier for twin nucleation, increasing the nucleation rate and growth rate of twins. Under the synergistic effect of low oxygen and cryogenic conditions, even with minimal deformation, the cross-interaction of multiple twin systems can be efficiently activated, forming a high-density, complex twin structure. This achieves highly refined and uniform grain distribution, thereby significantly improving the material's mechanical strength and low-temperature toughness, meeting the application requirements under harsh low-temperature service environments.

[0017] The beneficial effects of this invention are as follows: Due to the adoption of the above technical solution, the advantages of the deep cryogenic pre-rolling method for α-titanium alloy plates based on stimulating complex twinned fine grains proposed in this invention are:

[0018] (1) Small deformation: Only 2% to 10% reduction is required per pass, reducing energy consumption and equipment burden.

[0019] (2) No complex equipment required: It can be completed using a conventional cold rolling mill equipped with a simple liquid nitrogen cooling device, without the need for special equipment for severe plastic deformation, thus reducing equipment investment.

[0020] (3) Reduce subsequent processes: Because the board material deforms evenly and warps less during the process, the number of subsequent shaping, straightening and annealing is reduced, the production cycle is significantly shortened and the overall production cost is significantly reduced.

[0021] (4) Excellent low-temperature performance: The fine-grained structure significantly enhances toughness under low-temperature conditions, making it particularly suitable for low-temperature high-performance service environments. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for refining the grains of a titanium alloy plate according to the present invention.

[0023] Figure 2 The image shows the microstructure of a titanium alloy plate after being processed using the method described in Example 1 of this invention.

[0024] Figure 3 The image shows the microstructure of a titanium alloy plate after being processed using the method described in Example 2 of this invention.

[0025] Figure 4 The image shows the microstructure of a titanium alloy plate after being processed using the method described in Example 3 of this invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown, this invention discloses a method for grain refinement of titanium alloy plates. The method involves subjecting the original low-oxygen titanium alloy plate to cryogenic pretreatment, reducing the core temperature of the original low-oxygen titanium alloy plate to -196°C. The cryogenically pretreated low-oxygen titanium alloy plate is then fed into a rolling mill with controlled single-pass reduction rate to complete cryogenic rolling. The rolled titanium alloy plate is then subjected to cryogenic treatment again to obtain a titanium alloy plate with a complex twin structure formed by the intersection of {11-22} and {10-11} twins.

[0028] The method of the present invention specifically includes the following steps:

[0029] S1) A low-oxygen titanium alloy plate is placed in a cryogenic chamber and completely immersed in liquid nitrogen for at least 20 minutes, allowing the plate to cool uniformly from the surface to the core to -196°C, thus obtaining a cryogenic titanium alloy plate. This process cools the titanium alloy and simultaneously activates the crystals.

[0030] S2) The cryogenic titanium alloy plate obtained in S1) is fed into a rolling mill for single-pass pre-rolling, while the arc-thickness ratio l / d is set to 1.0–2.7 (the arc-thickness ratio is the contact arc length between the titanium alloy plate and the roll when the plate is pressed down on the roll and the initial thickness d of the titanium alloy plate), to obtain the rolled titanium alloy plate; this is used to effectively stimulate multiple twins, including a large number of rare {10-11} twins, in the microstructure to refine the grains and avoid plate warping and cracking;

[0031] S3) The rolled titanium alloy plate obtained in S2) is placed in a cryogenic chamber and completely immersed in liquid nitrogen for 20-30 minutes to obtain a titanium alloy plate with a complex twin structure formed by the intersection of {11-22} and {10-11} twins. This is used to rapidly cool down the rolled titanium alloy plate and stabilize its microstructure.

[0032] The method further includes a uniform annealing step: before placing the low-oxygen titanium alloy plate in a cryogenic chamber, it is first homogenized and annealed at a temperature of 500-600℃ for 15-45 minutes, and then air-cooled, in order to homogenize the microstructure of the titanium alloy plate.

[0033] Furthermore, the low-oxygen titanium alloy plate in S1) is an α-titanium alloy plate with an oxygen content of <0.18wt%; the upper limits of impurities are: Fe <0.05wt%, C <0.02wt%, N <0.02wt% and H <0.001wt%.

[0034] Furthermore, the single-pass reduction rate in S2) is 2% to 10%.

[0035] Furthermore, the yield strength of the titanium alloy plate treated by the method is increased by more than 20% compared with the original plate, and the impact toughness at -196℃ is increased by more than 2 times.

[0036] Example 1:

[0037] S1) Place the low oxygen content titanium alloy plate in a cryogenic chamber and immerse it completely in liquid nitrogen for 20 minutes to allow the plate to cool uniformly from the surface to the core to -196°C, thus obtaining a cryogenic titanium alloy plate.

[0038] The low-oxygen titanium alloy plate is an α-titanium alloy plate with an oxygen content of 0.17 wt%. The upper limits of impurities are: Fe < 0.05 wt%, C < 0.02 wt%, N < 0.02 wt%, and H < 0.001 wt%.

[0039] S2) The cryogenic titanium alloy plate obtained in S1) is fed into the rolling mill for single-pass pre-rolling. The single-pass reduction rate is 4%, and the arc thickness ratio l / d is set to 1.0 to obtain the rolled titanium alloy plate.

[0040] S3) The rolled titanium alloy plate obtained in S2) is placed in a cryogenic chamber and completely immersed in liquid nitrogen for 25 minutes to obtain a titanium alloy plate with a complex twinned structure formed by {11-22} and {10-11} twin intersections. The microstructure of the titanium alloy plate is shown in the figure below. Figure 2 As shown, the yield strength is increased by 15%, and the impact toughness at -196℃ is increased by 1.5 times.

[0041] Example 2:

[0042] S1) Place the low oxygen content titanium alloy plate in a cryogenic chamber and immerse it completely in liquid nitrogen for 20 minutes to allow the plate to cool uniformly from the surface to the core to -196°C, thus obtaining a cryogenic titanium alloy plate.

[0043] The low-oxygen titanium alloy plate is an α-titanium alloy plate with an oxygen content of 0.15 wt%. The upper limits of impurities are: Fe < 0.05 wt%, C < 0.02 wt%, N < 0.02 wt%, and H < 0.001 wt%.

[0044] S2) The cryogenic titanium alloy plate obtained in S1) is fed into the rolling mill for single-pass pre-rolling. The single-pass reduction rate is 6%, and the arc thickness ratio l / d is set to 2.0 to obtain the rolled titanium alloy plate.

[0045] S3) The rolled titanium alloy plate obtained in S2) is placed in a cryogenic chamber and completely immersed in liquid nitrogen for 28 minutes, resulting in a titanium alloy plate with a complex twinned structure formed by {11-22} and {10-11} twin intersections. The microstructure of the titanium alloy plate is shown in the image. Figure 3 As shown, the yield strength is increased by about 20%, and the impact toughness at -196℃ is increased by about 1.8 times.

[0046] Example 3:

[0047] S1) Place the low oxygen content titanium alloy plate in a cryogenic chamber and immerse it completely in liquid nitrogen for 22 minutes to allow the plate to cool uniformly from the surface to the core to -196°C, thus obtaining a cryogenic titanium alloy plate.

[0048] The low-oxygen titanium alloy plate is an α-titanium alloy plate with an oxygen content of 0.13 wt%. The upper limits of impurities are: Fe < 0.05 wt%, C < 0.02 wt%, N < 0.02 wt%, and H < 0.001 wt%.

[0049] S2) The cryogenic titanium alloy plate obtained in S1) is fed into the rolling mill for single-pass pre-rolling with a single-pass reduction rate of 10% and the arc thickness ratio l / d is set to 2.7 to obtain the rolled titanium alloy plate.

[0050] S3) The rolled titanium alloy plate obtained in S2) is placed in a cryogenic chamber and completely immersed in liquid nitrogen for 30 minutes, resulting in a titanium alloy plate with a complex twinned structure formed by the intersection of {11-22} and {10-11} twins. The microstructure of the titanium alloy plate is shown in the image. Figure 4 As shown, the yield strength is increased by ≥20%, and the impact toughness at -196℃ is increased by ≈2 times. The above examples fully verify the significant effect of this method in promoting the formation of complex twin structures and grain refinement.

[0051] The above provides a detailed description of a method for grain refinement of titanium alloys according to embodiments of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and its core ideas; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0052] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0053] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0054] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0055] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method of grain refinement of a titanium alloy sheet, characterized by, The method comprises the following steps: S1) placing the low-oxygen titanium alloy plate in a deep-freezing box, completely immersing the plate in liquid nitrogen for not less than 20 min, and uniformly lowering the temperature of the plate from the surface to the core to-196 DEG C to obtain a deep-freezing titanium alloy plate; S2) sending the deep-freezing titanium alloy plate obtained in S1) into a rolling mill, setting the arc thickness ratio l / d to 1.0-2.7, and performing single-pass pre-rolling according to a certain reduction to complete deep-freezing rolling and obtain a grain-refined titanium alloy plate; and S3) placing the grain-refined titanium alloy plate obtained in S2) in a deep-freezing box again, completely immersing the plate in liquid nitrogen for 20-30 min to obtain a titanium alloy plate with a complex twin crystal structure formed by the intersection of {11-22} and {10-11} twin crystals.

2. The method of claim 1, wherein, The method specifically comprises the following steps: S1) placing the low-oxygen titanium alloy plate in a deep-freezing box, completely immersing the plate in liquid nitrogen for not less than 20 min, and uniformly lowering the temperature of the plate from the surface to the core to-196 DEG C to obtain a deep-freezing titanium alloy plate; S2) sending the deep-freezing titanium alloy plate obtained in S1) into a rolling mill, setting the arc thickness ratio l / d to 1.0-2.7, and performing single-pass pre-rolling according to a certain reduction to complete deep-freezing rolling and obtain a grain-refined titanium alloy plate; S3) placing the grain-refined titanium alloy plate obtained in S2) in a deep-freezing box again, completely immersing the plate in liquid nitrogen for 20-30 min to obtain a titanium alloy plate with a complex twin crystal structure formed by the intersection of {11-22} and {10-11} twin crystals.

3. The method of claim 2, wherein, The method further comprises a homogenizing annealing step: before being placed in the deep-freezing box, the low-oxygen titanium alloy plate is first homogenized annealed at a temperature of 500-600 DEG C for 15-45 min, and then air-cooled to room temperature.

4. The method according to claim 2 or 3, characterized in that, The low-oxygen titanium alloy plate in S1) is an α-titanium alloy plate, and the oxygen content is <0.18 wt%, and the upper limits of impurities are as follows: Fe <0.05 wt%, C <0.02 wt%, N <0.02 wt% and H <0.001 wt%.

5. The method of claim 2, wherein, The single-pass reduction rate in S2) is 2%-10%.

6. The method of claim 2, wherein, The yield strength of the titanium alloy plate processed by the method is increased by at least 15% compared with that of the original plate, and the impact toughness at-196 DEG C is increased by at least 1.5 times.

7. A titanium alloy sheet, characterized by, The titanium alloy plate is prepared by the method according to any one of claims 1-6.

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