A preparation method of Ti2AlNb-based alloy foil

Abstract

The present invention discloses a method for preparing a Ti2AlNb-based alloy foil, which relates to the technical field of Ti2AlNb-based alloys. The method comprises the following steps: Step 1, performing multi-directional near-isothermal forging in the α2+B2 phase region on a Ti2AlNb-based alloy ingot to obtain a forging blank; Step 2, performing hot rolling in the α2+O+B2 phase region on the forging blank to obtain a Ti2AlNb-based alloy plate; Step 3, cold rolling the Ti2AlNb-based alloy plate to obtain a cold-rolled foil; and performing a short-time high-temperature annealing on the cold-rolled foil to obtain the Ti2AlNb-based alloy foil. The hot-rolled plate of the present invention can complete all cold rolling experiments without any intermediate annealing or plate lamination. The process is simple, efficient, and stable, with a yield rate of over 90%. The foil cold-rolled using the method of the present invention only needs a short-time annealing to obtain submicron-level grains and excellent mechanical properties.

Description

Technical Field

[0001] The invention relates to the technical field of Ti2AlNb-based alloys, in particular to a preparation method of a Ti2AlNb-based alloy foil. Background Art

[0002] With the rapid development of the aviation industry in recent years, there is an urgent need for new high-strength, high-temperature-resistant and lightweight foils to meet the needs of high-temperature components. Ti2AlNb-based alloys, developed from TiAl alloys, are expected to replace high-density Ni-based alloys and traditional titanium alloys due to their low density, high specific strength, high-temperature resistance, oxidation resistance and creep resistance, and have great application potential in the aerospace field. However, Ti2AlNb-based alloy foils are generally considered difficult to cold-work due to their high deformation resistance and low room-temperature plasticity, making foil preparation extremely difficult.

[0003] Currently, Ti2AlNb-based alloy foil is typically prepared by repeatedly annealing and cold rolling the hot-rolled sheet. This involves high-temperature annealing before each cold rolling pass, followed by final cold rolling to a specified thickness. Repeated annealing is essential for this preparation method, resulting in a complex process and low foil forming efficiency. Furthermore, the high-temperature oxidation that may occur during the pre-rolling high-temperature annealing process makes the sheet extremely susceptible to cracking during cold working. Furthermore, the roll-to-roll preparation process for Ti2AlNb-based alloy foil is extremely unstable, especially during the roll-to-roll of cold-deformed metals. Failure to meet the required dimensional consistency, surface flatness, and roller accuracy can lead to cracking and failure of the sheet during foil rolling.

[0004] Since the preparation technology of Ti2AlNb-based alloy foil is still immature, there is an urgent need to carry out research on high-efficiency and low-cost rolling of Ti2AlNb alloy foil. Summary of the Invention

[0005] Based on the above content, the present invention provides a method for preparing Ti2AlNb-based alloy foil, which solves the problems of unstable and complicated Ti2AlNb-based alloy foil process and low foil forming efficiency in the prior art by designing the microstructure of the Ti2AlNb-based alloy.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is a method for preparing a Ti2AlNb-based alloy foil, comprising the following steps:

[0008] Step 1, performing multi-directional near-isothermal forging in the α2+B2 phase region on the Ti2AlNb-based alloy ingot to obtain a forging blank;

[0009] Step 2, hot rolling the forging blank in the α2+O+B2 phase region to obtain a Ti2AlNb-based alloy plate;

[0010] Step 3: cold rolling the Ti2AlNb-based alloy sheet to obtain a cold-rolled foil; and short-time high-temperature annealing the cold-rolled foil to obtain the Ti2AlNb-based alloy foil.

[0011] In step 1, if the forging temperature is higher than the α2+B2 phase region, for example, the B2 single phase region temperature is used, the grain size will be coarse, affecting the subsequent yield and performance of the foil. If the forging temperature is lower than the α2+B2 phase region, for example, the α2+O+B2 phase region temperature is used, the alloy will be difficult to forge due to its large deformation resistance.

[0012] In step 2, the hot rolling temperature is lower than the α2+O+B2 phase region. For example, the temperature of the O+B2 phase region will generate strip-shaped O phase, which is not conducive to the room temperature plasticity of the alloy plate and affects the yield of the foil; higher than the α2+O+B2 phase region, for example, the temperature of the α2+B2 phase region is used, which is not conducive to initiating the dynamic recrystallization mechanism of the alloy, and the grain size is prone to unevenness, which is not conducive to the room temperature plasticity of the plate; the hot rolling temperature is selected in the α2+O+B2 phase region, which can introduce an appropriate amount of O phase, which can improve the problem of deformation inconsistency between the α2 phase and the B2 phase to a certain extent.

[0013] Furthermore, in step 1, the atomic percentages of the Ti2AlNb-based alloy ingot are Ti: 52-56%, Al: 20-25%, and Nb: 23-27%.

[0014] Furthermore, in step 1, the temperature of the multi-directional near-isothermal forging in the α2+B2 phase region is 1040-1060°C.

[0015] Furthermore, in step 1, the multi-directional near-isothermal forging in the α2+B2 phase region is specifically as follows: there are 3 forging passes, each pass has a different direction, and the angles between the three directions are about 90° to each other; each forging pass is kept warm for 20-30 minutes, and the reduction for each forging pass is 40-50%; the cooling method is gas cooling, and the forging is cooled to room temperature.

[0016] Furthermore, in step 2, the temperature of the α2+O+B2 phase region hot rolling is 980-990°C.

[0017] Furthermore, in step 2, the α2+O+B2 phase region hot rolling is specifically as follows: jacket hot rolling, with a reduction of 20-30% per pass, a linear speed of the rolling roller of 0.12-0.18 m / s, and a total reduction greater than 85%; after each rolling pass, the steel is returned to the furnace and kept warm for 3-8 minutes before the next rolling pass; the cooling method is gas cooling, cooling to room temperature; the steel is returned to the furnace repeatedly for multiple rolling passes; and finally the jacket is removed to obtain a Ti2AlNb-based alloy plate.

[0018] Furthermore, in step 2, the thickness of the Ti2AlNb-based alloy plate is 1-1.4 mm; the Ti2AlNb-based alloy plate is composed of three phases: α2, O, and B2, with the α2 phase accounting for 5-10%, the O phase accounting for 40-50%, and the B2 phase accounting for 40-50%, and the average grain size is 3-10 μm.

[0019] Furthermore, in step 3, the cold rolling is performed with a reduction of 5-10% per pass, and each reduction is performed 4 times; the thickness of the cold rolled foil is 0.1-0.15 mm, the width is greater than 60 mm, and the length is greater than 250 mm.

[0020] Too low a reduction rate per cold rolling pass will affect rolling efficiency, while too high a reduction rate will affect the surface quality of the plate and cause edge cracks. Therefore, the preferred cold rolling reduction per pass in the present invention is 5-10%, more preferably 10%.

[0021] Furthermore, the short-time high-temperature annealing is specifically to keep the temperature at 950-1000°C for 8-15 minutes and then anneal with the furnace; the vacuum degree of the short-time high-temperature annealing is less than 10 -2 Pa.

[0022] The second technical solution of the present invention is to prepare the Ti2AlNb-based alloy foil using the above-mentioned preparation method.

[0023] Furthermore, the grain size of the Ti2AlNb-based alloy foil is 400-800 nm.

[0024] The third technical solution of the present invention is the application of the above-mentioned Ti2AlNb-based alloy foil in the field of aerospace.

[0025] Technical concept of the present invention:

[0026] The cold deformation ability of Ti2AlNb-based alloys is affected by phase ratio, grain size, and microstructural morphology. It is generally believed that the α2 phase in Ti2AlNb-based alloys is a brittle phase, while the B2 phase, with its numerous slip systems, is a ductile phase. The introduction of an appropriate amount of O phase can, to a certain extent, alleviate the incompatibility between the α2 and B2 phases. Current cold-rolling schemes for Ti2AlNb-based alloy foils focus on pre-rolling annealing to obtain more B2 phase, thereby promoting alloy deformation, while ignoring the O phase's ability to coordinate the deformation between the three phases at room temperature. Larger grain sizes are more susceptible to intergranular fracture, leading to crack propagation. Among different microstructural morphologies, equiaxed microstructures are more capable of coordinating deformation between grains.

[0027] In the early research and exploration, the present invention found that the B2 phase has more slip systems and is a tough phase, the α2 phase is a brittle phase, and when the α2+B2 phase structure is cold deformed, due to the incoordination of slip deformation, the α2 phase is prone to rupture, and the cracks are prone to extend from the ruptured α2 phase; and the O phase can also activate all slip systems at room temperature, that is, the O phase has a great influence on the cold deformation of the coordinated B2 phase and the α2 phase, and the microstructure with the equiaxed O phase can improve the cold rolling plasticity of the alloy, which is beneficial to the plastic deformation of the alloy; the present invention realizes a new method for successfully cold rolling Ti2AlNb-based alloy foil without intermediate annealing and plate stacking by designing a plate with a small and uniform grain size, a suitable phase ratio and a large area of ​​texture, thereby shortening the process steps and time and greatly improving work efficiency.

[0028] The present invention discloses the following technical effects:

[0029] 1. The method of the present invention first designs the microstructure of the cold-rolled initial material, and utilizes the static and dynamic recrystallization mechanisms generated under phase transformation theory and plastic deformation to refine the grain size of the Ti2AlNb-based alloy plate after hot rolling; introduces a large amount of equiaxed O phase to coordinate the cold rolling deformation of the B2 phase and α2 phase (wherein the α2 phase accounts for 5-10%, the O phase accounts for 40-50%, and the B2 phase accounts for 40-50%); at the same time, based on the orientation relationship theory, the O phase and the B2 phase adhere to a specific orientation relationship, generating a large area of ​​the same texture, which facilitates the propagation of slip and further cold rolling.

[0030] 2. In the preparation method of the present invention, the hot-rolled plate can complete all cold rolling experiments without any intermediate annealing and plate stacking. The process is simple, efficient and stable, and the yield rate is as high as over 90%.

[0031] 3. The foil after cold rolling by the method of the present invention only needs to be annealed for a short time to obtain submicron grains and excellent mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is the microstructure morphology of the forging blank prepared in step 1 of Example 1;

[0034] Figure 2 The microstructure morphology of the Ti2AlNb-based alloy plate prepared in step 2 of Example 1; (a) is the phase ratio distribution, and (b) is the angle grain boundary diagram;

[0035] Figure 3 This is a macroscopic morphology of the cold-rolled foil prepared in step 3 of Example 1;

[0036] Figure 4 These are the microstructural morphologies of the Ti2AlNb-based alloy foil prepared in step 3 of this embodiment; (a) is the BSE image, and (b) is the BC image in EBSD. DETAILED DESCRIPTION

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0039] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0040] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0041] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0042] The reagents and instruments used in the present invention without indicating the manufacturer are all conventional products that can be purchased from the market.

[0043] Unless otherwise specified, the "room temperature" in the present invention refers to 20-30°C.

[0044] Before heating, the ingot in the embodiment of the present invention is first ground and polished, and sprayed with an anti-oxidation coating with a thickness of 0.05mm-0.1mm to prevent oxidation cracking during the forging process.

[0045] The Ti2AlNb-based alloy ingot used in the embodiment of the present invention is a Ti-22Al-25Nb (atomic percentage) alloy.

[0046] Example 1

[0047] Step 1, forging of the alloy: the Ti2AlNb-based alloy ingot is subjected to multi-directional near-isothermal forging in the α2+B2 phase region (1040° C.), and air-cooled after forging to obtain a forging blank. During the multi-directional near-isothermal forging process, the ingot and forging device are heated to the specified temperature and then held at this temperature for 30 minutes before forging; after forging, they are returned to the furnace and held at this temperature for 30 minutes, and then forging is performed in the reverse direction (the forging temperature is held for 30 minutes before each forging pass to ensure the forging temperature in the α2+B2 phase region and reduce cracking of the forging; at the same time, the microstructure of the forging is ensured to be mainly composed of B2, which facilitates sufficient recrystallization of the microstructure during hot rolling); the number of forging passes is 3, with a reduction of 45% per forging pass, and each pass direction is different, with the angles between the three directions being approximately 90° to each other (during the forging process, the Ti2AlNb-based alloy ingot is subjected to large reduction thermal deformation from all directions to make the forging microstructure uniform and reduce the mechanical stress of the alloy); the forging speed is 1 mm / s (the forging speed is controlled to avoid excessive reduction speed, which may cause rapid cracking of the forging).

[0048] Step 2, preparation of the plate: cut a 10mm thick forged plate from the forging blank prepared in step 1, grind and polish it, spray an anti-oxidation coating with a thickness of 0.05mm-0.1mm, and perform hot rolling in the α2+O+B2 phase region (the sheath material is 304 stainless steel, the upper cover thickness of the sheath is 4mm, and the lower cover thickness is 14mm; the lower cover is milled with a groove of the same size as the forged plate, and an 8mm sheath margin is left around the groove). Specifically, the forged plate is placed in the groove of the lower cover for sealing welding, and the vacuum degree inside the sheath is ensured to be less than 10 -1 Pa, forming a billet; placing the assembled billet in a heating furnace, heating it to a specified temperature of 990°C, and then holding it for 20 minutes (to ensure that phase transformation and recrystallization are fully carried out) for rolling; after each rolling pass, returning to the furnace and holding it for 5 minutes before rolling the next pass (the purpose of returning to the furnace and holding it is to ensure the rolling temperature of the plate and prevent the plate from cracking during rolling); repeatedly returning to the furnace and performing multiple rolling passes; the reduction amount of each pass is 25%, and the linear speed of the rolling roller is 0.15 m / s (appropriate reduction and strain rate are important conditions for obtaining excellent Ti2AlNb-based alloy plates); after the final rolling pass is completed, air cooling is performed; the sheath is removed, and the total reduction of the plate is 88%, obtaining a high-quality Ti2AlNb-based alloy plate with a thickness of 1.2 mm and no surface cracks (i.e., the cold-rolled initial material).

[0049] Step 3, preparation of foil: cold rolling the Ti2AlNb-based alloy sheet prepared in step 2, and performing multiple passes of rolling with small reduction; applying rolling oil on the Ti2AlNb alloy sheet and the surface of the roller, and using a special boss roller to perform asymmetric rolling to reduce the rolling force required for its deformation, and performing 4 passes of each reduction, each pass with a reduction of 10%, directly cold rolling to 0.1mm; the above cold rolled foil is placed in a vacuum of less than 10 -3 The Ti2AlNb-based alloy foil with excellent performance was obtained by keeping the temperature at 1000℃ for 10 minutes and then annealing in the furnace.

[0050] Based on the content of Example 1, in step 3, the rolling reduction per pass was determined by comparing the effects of different rolling reduction rates on the surface quality of the plate. Each rolling reduction was performed in four passes. The effects of different rolling reduction rates on the surface quality of the plate are shown in Table 1.

[0051] Based on the contents of Example 1, in step 3, when the reduction in each rolling pass is greater than 10%, the plate can be rolled to a reduced thickness and edge cracks are prone to occur; when the reduction in each rolling pass is less than or equal to 10%, the plate can be directly cold rolled to less than 0.15 mm without edge cracks; preferably, the reduction in each rolling pass is 10%.

[0052] Table 1 Effect of different reduction rates per pass on the surface quality of the plate

[0053]

[0054] Based on the content of Example 1, in step 3, the 0.1 mm cold-rolled foil is kept at 950°C or 1000°C for 10 minutes and then annealed in the furnace. The vacuum degree of the heating furnace is less than 10 -3 Pa; after annealing, the microstructure consists of grains of approximately 700 nm and exhibits excellent mechanical properties. The mechanical properties of the foils after different annealing processes are shown in Table 2.

[0055] Table 2 Mechanical properties of foil under different annealing processes

[0056]

[0057] The forging blank prepared in step 1 of this embodiment was subjected to backscattered electron scanning, and the results are shown in FIG. Figure 1 ;Depend on Figure 1 It can be seen that the microstructure of the forging blank is mainly composed of a large amount of B2 phase and some short rod-shaped α2 phase, and only a very small amount of needle-shaped O phase precipitates during the air cooling of the forging blank.

[0058] The microstructure morphology of the Ti2AlNb-based alloy plate prepared in step 2 of this embodiment is shown in FIG. Figure 2 As shown; Figure 2(a) is the phase ratio distribution, and (b) is the angle grain boundary diagram. Figure 2 It can be seen that the Ti2AlNb-based alloy plate finally obtained in step 2 is composed of α2, O, and B2 phases, with α2 phase accounting for 5%, O phase accounting for 47%, and B2 phase accounting for 48%. Since the hot rolling temperature is in the three-phase region and lower than the forging temperature, the temperature drop causes phase transformation, producing a large amount of equiaxed O phase. The dynamic recrystallization caused by phase transformation and plastic deformation refines the grains, with an average grain size of 8 μm. At the same time, since the O phase and B2 phase meet a specific orientation relationship after hot rolling, a large area of ​​the same texture {001} is generated. <110> The texture strength is 40.

[0059] Macroscopic morphology of the cold-rolled foil prepared in step 3 of this embodiment. Figure 3 It can be seen that the width of the cold-rolled foil is greater than 50 mm and the length is greater than 250 mm.

[0060] The microstructure morphology of the Ti2AlNb-based alloy foil prepared in step 3 of this embodiment is shown in FIG. Figure 4 As shown; (a) is the BSE map, and (b) is the BC map in EBSD.

[0061] The inventors also conducted the following experiments:

[0062] 1. When the average grain size of the cold-rolled original plate is greater than 200 μm, under the same cold rolling process as step 3 of Example 1, when the reduction per rolling pass is 10%, severe edge cracking occurs when the total reduction is 20-30%, making further rolling difficult.

[0063] 2. When the proportion of α2 phase in the cold-rolled original plate phase is greater than 20% and the average grain size is 0-30 μm, under the same cold rolling process as step 3 of Example 1, when the reduction per rolling pass is 10%, severe edge cracks occur when the total reduction is 20-25%, making further rolling difficult.

[0064] 3. When the O phase accounts for more than 60% of the cold-rolled original plate phase ratio and the average grain size is 0-30 μm, under the same cold rolling process as step 3 of Example 1, when the reduction per rolling pass is 10%, severe edge cracks occur when the total reduction is 55-60%, making further rolling difficult.

[0065] 4. When the B2 phase accounts for more than 80% of the cold-rolled original plate phase and the average grain size is 0-30 μm, under the same cold rolling process as step 3 of Example 1, when the reduction per rolling pass is 10%, edge cracking occurs at a total reduction of 60-65%, and the yield rate is low.

[0066] The present invention first designs the microstructure of the cold-rolled starting material through multi-directional near-isothermal forging and canned hot rolling. Static and dynamic recrystallization mechanisms are utilized to refine the grain size of the hot-rolled Ti2AlNb-based alloy sheet. A large amount of equiaxed O phase is introduced to coordinate the cold-rolling deformation of the B2 and α2 phases, with the α2 phase accounting for 5-10%, the O phase accounting for 40-50%, and the B2 phase accounting for 40-50%. Furthermore, based on the theory of orientation relationships, the O and B2 phases adhere to a specific orientation relationship, resulting in a large-area uniform texture during hot-rolling, facilitating slip transfer and cold rolling. The hot-rolled sheet is then subjected to multiple passes of cold rolling at low reduction, eliminating the need for intermediate annealing and sheet-to-sheet rolling, to successfully produce Ti2AlNb-based alloy foil. This process is simple and stable, with a yield exceeding 90%. After cold rolling, foil with excellent performance is obtained after a short processing time. This provides a new solution and process for the preparation of Ti2AlNb-based alloy foil.

[0067] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a Ti2AlNb-based alloy foil, characterized in that: The following steps are involved: Step 1, performing multi-directional near-isothermal forging in the α2+B2 phase region on the Ti2AlNb-based alloy ingot to obtain a forging blank; Step 2, hot rolling the forging blank in the α2+O+B2 phase region to obtain a Ti2AlNb-based alloy plate; Step 3, cold rolling the Ti2AlNb-based alloy sheet to obtain a cold-rolled foil; and short-time high-temperature annealing the cold-rolled foil to obtain the Ti2AlNb-based alloy foil; The temperature of the multi-directional near-isothermal forging in the α2+B2 phase region is 1040-1060°C; The temperature of the α2+O+B2 phase region hot rolling is 980-990°C; The short-time high-temperature annealing is specifically to keep the temperature at 950-1000°C for 8-15 minutes and then anneal with the furnace; the vacuum degree of the short-time high-temperature annealing is less than 10 -2 Pa.

2. The preparation method according to claim 1, characterized in that In step 1, the atomic percentages of the Ti2AlNb-based alloy ingot are Ti: 52-56%, Al: 20-25%, and Nb: 23-27%.

3. The preparation method according to claim 1, characterized in that In step 2, the α2+O+B2 phase region hot rolling is specifically as follows: jacket hot rolling, with a reduction of 20-30% per pass, a linear speed of the rollers of 0.12-0.18 m / s, and a total reduction greater than 85%.

4. The preparation method according to claim 1, characterized in that In step 2, the thickness of the Ti2AlNb-based alloy plate is 1-1.4 mm; the Ti2AlNb-based alloy plate is composed of three phases: α2, O, and B2, with the α2 phase accounting for 5-10%, the O phase accounting for 40-50%, the B2 phase accounting for 40-50%, and the average grain size being 3-10 μm.

5. The preparation method according to claim 1, characterized in that In step 3, the cold rolling is performed with a reduction of 5-10% per pass, and each reduction is performed 4 times; the thickness of the cold rolled foil is 0.1-0.15 mm.

6. The Ti2AlNb-based alloy foil prepared according to the preparation method according to any one of claims 1 to 5.

7. Use of the Ti2AlNb-based alloy foil according to claim 6 in the field of aerospace.

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