A cross-phase hot spinning method for heterogeneous titanium alloy thin-walled tubes

Abstract

This application discloses a cross-phase hot spinning method for forming a thin-walled titanium alloy tube with a heterogeneous structure, belonging to the technical field of titanium alloy thin-walled tube forming technology. The method comprises: heating a titanium alloy tube blank to a β single-phase region 20°C to 30°C above the β phase transformation point, and then performing a first spinning deformation process to obtain a titanium alloy copper blank with a fully lamellar structure. The fully lamellar structure has clear β grain boundaries and the lamellar α grains within the lamellar grains are arranged in a disordered and interwoven manner; the titanium alloy tube blank is then subjected to two to three hot spinning forming steps until the total thinning rate reaches 55% to 60%, resulting in a heterogeneous titanium alloy thin-walled tube. The hot spinning forming step comprises: air cooling the titanium alloy tube blank for a preset time to a stable temperature, then heating it to a two-phase region 50°C lower than the temperature reached by the previous spinning deformation process, and then performing spinning deformation. The titanium alloy thin-walled tube formed by this application can simultaneously achieve high strength and good plasticity.

Description

Technical Field

[0001] The present application relates to the technical field of titanium alloy thin-walled tube forming, and in particular to a cross-phase region hot spinning forming method for heterogeneous structure titanium alloy thin-walled tube. Background Art

[0002] Titanium alloy thin-walled cylindrical parts have become an important structural material in the aerospace industry due to their light weight, high strength, and lightweight characteristics. Spinning has become an effective process for manufacturing large titanium alloy thin-walled cylindrical parts due to its high process flexibility, simple molds, low forming loads, and high production efficiency. Because titanium alloys are inherently strong and difficult to deform, auxiliary heating during the spinning process can significantly reduce the material's deformation resistance during spinning, improve the material's plasticity, expand the size range of titanium alloy thin-walled cylindrical parts, and effectively improve the component structure and enhance its mechanical properties. Therefore, in recent years, the hot spinning process has been the most commonly used process for forming titanium alloy thin-walled cylindrical parts.

[0003] However, it is difficult for the existing hot spinning forming method of titanium alloy thin-walled cylindrical parts to simultaneously achieve high strength and good plasticity matching performance. Summary of the Invention

[0004] The embodiment of the present application provides a method for hot spinning forming a heterogeneous structure titanium alloy thin-walled tube across the phase region, which can solve the problem that the titanium alloy thin-walled cylindrical parts obtained by the existing hot spinning forming method of titanium alloy thin-walled cylindrical parts are difficult to achieve both high strength and good plasticity matching performance.

[0005] In order to achieve the above-mentioned purpose, the technical solution of the embodiment of the present invention is:

[0006] An embodiment of the present invention provides a method for hot spinning a heterogeneous titanium alloy thin-walled tube across phase regions, which is characterized by comprising:

[0007] The titanium alloy cylinder blank is heated to a β single phase region 20°C to 30°C above the β phase transformation point and then subjected to a first spinning deformation process to obtain a titanium alloy copper blank with a full lamellar structure having clear β grain boundaries and lamellar α grains arranged chaotically and interwoven within the lamellar grains;

[0008] The titanium alloy cylinder blank is subjected to two to three hot spinning steps until the total thinning rate reaches 55% to 60% to obtain a heterogeneous titanium alloy thin-wall cylinder;

[0009] Among them, the hot spinning forming step includes: air cooling the titanium alloy tube blank for a preset time to a stable temperature, and then heating it to a two-phase zone 50°C lower than the temperature of the previous spinning deformation before spinning deformation.

[0010] In a possible implementation, the thinning rate of each spinning deformation is 20% to 30%.

[0011] In a possible implementation, the preset time is 3 minutes to 5 minutes.

[0012] In a possible implementation, the stable temperature is 400°C to 450°C.

[0013] In a possible implementation, the heating method is induction heating.

[0014] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0015] The cross-phase hot spinning forming method for a heterogeneous titanium alloy thin-walled tube in the embodiment of the present application is a cross-phase hot spinning process. First, the titanium alloy tube blank is heated to a β single-phase region 20°C to 30°C above the β phase transformation point, and then the first spinning process is performed to obtain a titanium alloy copper blank with a fully lamellar structure. The fully lamellar structure has clear β grain boundaries and the lamellar α grains within the lamellar grains are arranged in a disordered and interwoven manner. The titanium alloy tube blank is then subjected to two to three more hot spinning steps until the total thinning rate reaches 55% to 60%, resulting in a heterogeneous titanium alloy thin-walled tube. The hot spinning forming step includes air cooling the titanium alloy tube blank for a preset time to a stable temperature, then heating it to a two-phase region 50°C lower than the temperature reached in the previous spinning process, and then spinning deformation is performed. In other words, heating it to a two-phase region close to the phase transformation point for spinning. The continuous dynamic recrystallization caused by local shear during the spinning process acts on the lath-shaped secondary α grains to achieve grain refinement and obtain spheroidized equiaxed α grains. Finally, the heterogeneous structure titanium alloy thin-walled tube obtained by hot spinning forming in a total of three to four passes includes a heterogeneous structure in which slender lath α grains and fine equiaxed α grains are interwoven. The lath α grains are 20μm to 60μm long and 2μm to 6μm wide. The distribution is no longer messy and is roughly distributed along the RD direction. There are a large number of subgrains inside the grains. The size of the fine equiaxed α grains is about 2μm to 6μm, thereby achieving the performance of high strength (over 1300MPa) and good plasticity matching of the titanium alloy thin-walled tube. It also achieves the thinning of the titanium alloy thin-walled tube under limited hot spinning forming (thinning rate is 55% to 60%). BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are 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.

[0017] Figure 1A physical picture of a thin-walled titanium alloy tube with heterogeneous structure formed in a specific embodiment of the present application;

[0018] Figure 2 Microstructure diagram of the RD-ND cross section of the TC4 titanium alloy cylinder blank provided in the embodiment of the present application: (a) low magnification; (b) high magnification;

[0019] Figure 3 Microstructure of the RD-ND cross section of a heterogeneous titanium alloy thin-walled tube formed in a specific embodiment of the present application: (a) low magnification; (b) high magnification;

[0020] Figure 4 The grain boundaries and subgrain boundaries of the TC4 titanium alloy cylinder blank provided in the embodiment of the present application (a) and the grain boundaries and subgrain boundaries of the heterogeneous structure titanium alloy thin-walled cylinder formed in the specific embodiment of the present application (b);

[0021] Figure 5 The tensile properties of the heterogeneous titanium alloy thin-walled tube formed in the specific embodiment of the present application;

[0022] Figure 6 Tensile strength and fracture morphology of a thin-walled titanium alloy tube with heterogeneous structure formed according to a specific embodiment of the present application: (a) low magnification; (b) high magnification. DETAILED DESCRIPTION

[0023] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0024] In the relevant description of this embodiment, the terms "including, containing, having" and the like are open terms, and are generally understood to include but not be limited to; the term "at least one" is generally understood to mean one or more, where "plurality" refers to two or more; the term "at least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items, for example, "at least one of a, b or c", or "at least one of a, b and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple respectively; the symbol "A / B" is used to describe the selection relationship of associated objects, generally indicating an "or" relationship before and after.

[0025] In the following description of the present embodiment, the terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0026] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0027] It will be understood by those skilled in the art that the numerical ranges in the examples of the present application are to be understood as also specifically disclosing each intermediate value between the upper and lower limits of the ranges. 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 independently be included or excluded within the range.

[0028] Unless otherwise indicated, the technical / scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which this application belongs. Although this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0029] An embodiment of the present invention provides a method for hot spinning forming a heterogeneous titanium alloy thin-walled tube across phase regions, comprising the following steps 1 and 2.

[0030] Step 1: The titanium alloy cylinder blank is heated to a β single-phase region of 20°C to 30°C above the β phase transformation point (typical but non-restrictive temperatures such as 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C and 30°C) and then subjected to a first spinning deformation to obtain a titanium alloy copper blank with a full lamellar structure, in which the β grain boundaries of the full lamellar structure are clear and the lamellar α grains inside the lamellar grains are arranged in a chaotic manner and intertwined with each other.

[0031] Step 2: The titanium alloy tube blank is subjected to two to three hot spinning steps until the total thinning rate is 55% to 60% (typical but non-limiting thinning rates such as 55%, 56%, 57%, 58%, 59% and 60% can be obtained). The hot spinning step includes: air cooling the titanium alloy tube blank for a preset time to a stable temperature, and then heating it to a two-phase region 50°C lower than the temperature of the previous spinning deformation, and then spinning deformation (i.e., each heating is performed to a two-phase region close to the phase transition point for spinning). The preset time is 3 minutes to 5 minutes, and can be a typical but non-limiting time such as 3 minutes, 4 minutes and 5 minutes. The stable temperature is 400°C to 450°C, and can be a typical but non-limiting temperature such as 400°C, 410°C, 420°C, 430°C, 440°C and 450°C. The purpose of gradually lowering the temperature in the subsequent spinning passes in the two-phase region close to the phase transformation point is to utilize the continuous dynamic recrystallization caused by local shear during the hot spinning process to act on the lath-shaped secondary α grains. Under a large deformation, the grain boundaries can be generated along the local shear direction, thereby achieving grain refinement and obtaining spheroidized equiaxed α grains.

[0032] The thinning rate of each spinning deformation is 20% to 30%, which can be typical but non-limiting thinning rates such as 20%, 22%, 24%, 26%, 28% and 30%.

[0033] The heating method is induction heating, which has high efficiency and fast temperature rise. It can heat the titanium alloy thin-walled tube to 900℃~1000℃ in a relatively short time (5min~8min), which avoids the problem of severe oxidation of the titanium alloy thin-walled tube due to long-term exposure to air at high temperature.

[0034] Currently, the initial microstructure of titanium alloys during spinning is mostly equiaxed or bimodal, and the spinning temperature is mostly at a moderate temperature of 600-700°C. Temperatures that are too low to achieve significant microstructural transformations are difficult. Therefore, current hot spinning methods for thin-walled titanium alloy tubes cannot produce a heterogeneous microstructure with interwoven lamellar α grains and equiaxed α grains, and it is difficult to achieve effective thinning of components in a small number of passes.

[0035] The cross-phase hot spinning forming method for a heterogeneous titanium alloy thin-walled tube in the embodiment of the present application is a cross-phase hot spinning process. First, the titanium alloy tube blank is heated to a β single-phase region 20°C to 30°C above the β phase transformation point, and then the first spinning process is performed to obtain a titanium alloy copper blank with a fully lamellar structure. The fully lamellar structure has clear β grain boundaries and the lamellar α grains within the lamellar grains are arranged in a disordered and interwoven manner. The titanium alloy tube blank is then subjected to two to three more hot spinning steps until the total thinning rate reaches 55% to 60%, resulting in a heterogeneous titanium alloy thin-walled tube. The hot spinning forming step includes air cooling the titanium alloy tube blank for a preset time to a stable temperature, then heating it to a two-phase region 50°C lower than the temperature reached in the previous spinning process, and then spinning deformation is performed. In other words, heating it to a two-phase region close to the phase transformation point for spinning. The continuous dynamic recrystallization caused by local shear during the spinning process acts on the lath-shaped secondary α grains to achieve grain refinement and obtain spheroidized equiaxed α grains. Finally, the heterogeneous structure titanium alloy thin-walled tube obtained by hot spinning forming in a total of three to four passes includes a heterogeneous structure in which slender lath α grains and fine equiaxed α grains are interwoven. The lath α grains are 20μm to 60μm long and 2μm to 6μm wide. The distribution is no longer messy and is roughly distributed along the RD direction. There are a large number of subgrains inside the grains. The size of the fine equiaxed α grains is about 2μm to 6μm, thereby achieving the performance of high strength (over 1300MPa) and good plasticity matching of the titanium alloy thin-walled tube. It also achieves the thinning of the titanium alloy thin-walled tube under limited hot spinning forming (thinning rate is 55% to 60%).

[0036] Heterogeneous structures are generally composed of coarse grains and fine grains, with the coarse grains surrounded by fine grains. This structure can effectively improve the material's strength and plasticity. The lamellar α phase in titanium alloys helps improve strength, while the equiaxed α phase contributes to good elongation. Furthermore, when the initial structure of the titanium alloy cylinder blank is lamellar, spheroidization occurs during deformation of the two-phase region, resulting in the final formed titanium alloy thin-walled cylinder having properties that match high strength and good plasticity.

[0037] The following provides a specific embodiment of the cross-phase hot spinning forming method of the heterogeneous structure titanium alloy thin-walled tube of the present application.

[0038] The measured composition (mass percentage) of the TC4 titanium alloy cylinder blank is as follows: 6.14Al, 4.13V, 0.16Fe, 0.016C, 0.014N, 0.09O, with the remainder being Ti. The initial wall thickness of the TC4 titanium alloy cylinder blank is 14 mm. Specific embodiments

[0040] The TC4 titanium alloy cylinder blank is heated to the β single phase region of 1000℃ (β phase transformation point temperature is 970℃~980℃, 20℃~30℃ above the β phase transformation point) and then subjected to the first spinning deformation. The spinning thinning amount is 3mm and the thinning rate is 21.7%. A titanium alloy copper blank with a full lamellar structure is obtained. The β grain boundaries of the full lamellar structure are clear and the lamellar α grains inside the lamellar grains are arranged chaotically and intertwined.

[0041] The titanium alloy tube blank obtained by the first spinning deformation was air-cooled to 400°C for 3 minutes, and then heated to a two-phase region of 950°C (50°C lower than the temperature during the first spinning deformation) before the second spinning deformation was performed. The thinning amount was 3mm and the thinning rate was 27.3%.

[0042] The titanium alloy tube blank obtained after the second spinning deformation was air-cooled for 3 minutes to 400°C, and then heated to 900°C (50°C lower than the temperature heated during the second spinning deformation) in the two-phase region for the third spinning deformation, with a thinning amount of 2mm and a thinning rate of 25%.

[0043] The above embodiment obtains the desired heterogeneous structure through a total of three hot spinning passes, with a total thinning rate of 57.1%.

[0044] Figure 1 A physical picture of a heterogeneous titanium alloy thin-walled tube formed according to a specific embodiment of the present application. Figure 2 The microstructure diagram of the RD-ND section of the TC4 titanium alloy cylinder blank provided in the embodiment of this application: (a) low magnification; (b) high magnification. Figure 2 It can be seen that the equiaxed grains in the TC4 titanium alloy cylinder blank are relatively large and are not distributed between the lath grains. Figure 3 The microstructure of the RD-ND cross section of the heterogeneous titanium alloy thin-walled tube formed in the specific embodiment of this application: (a) low magnification; (b) high magnification. Figure 3 It can be seen that after a total of three spinning forming processes, the organizational morphology of the formed heterogeneous structure titanium alloy thin-walled tube changes. At this time, lamellar grains can no longer be observed in the organization, but it has transformed into an interwoven distribution of slender lamellar α grains and spheroidized equiaxed α grains, and the size of the equiaxed grains is very small.

[0045] Figure 4 The grain boundaries and subgrain boundaries (a) of the TC4 titanium alloy cylinder blank provided in the embodiment of the present application and the grain boundaries and subgrain boundaries (b) of the heterogeneous structure titanium alloy thin-walled cylinder formed in the specific embodiment of the present application. Figure 4In (a) and (b), the grain boundary is defined by the orientation difference between two adjacent regions. When the orientation difference between adjacent regions is greater than 15°, it is defined as a large-angle grain boundary, represented by a thick black line; when the orientation difference is between 3° and 15°, it is a medium-angle grain boundary, represented by a thin green line; when the orientation difference is less than 3°, it is a small-angle grain boundary, represented by a thin red line.

[0046] like Figure 4 (a) shows that the lath grains and equiaxed grains of the dual-state structure of the TC4 titanium alloy tube blank are not interwoven (equiaxed grains are not distributed between the lath grains), and the equiaxed grains are large in size. The overall density of small-angle grain boundaries and medium-angle grain boundaries in the TC4 titanium alloy tube blank is relatively low and unevenly distributed. They are basically not observed in the primary α phase grains, and only a small amount of subgrain boundaries are inside the lath grains. Figure 4 (b) First, it can be seen that the grain shape and orientation have changed significantly. The lamellar α grains are distributed roughly along the RD direction, and a large number of subgrains appear inside the lamellar α grains. In addition, due to the spheroidization of the lamellar layers, the number of high-angle grain boundaries has also increased significantly, generating many small equiaxed α grains distributed between the lamellar α grains.

[0047] Figure 5 The tensile properties of the heterogeneous titanium alloy thin-walled tube formed in the specific embodiment of the present application. As can be seen from the figure, the heterogeneous titanium alloy thin-walled tube in the specific embodiment has high strength.

[0048] Figure 6 The tensile and fracture morphology of the heterogeneous titanium alloy thin-walled tube formed in the specific embodiment of this application: (a) low magnification; (b) high magnification. Figure 6 It can be seen that the fracture presents an obvious ductile fracture. Under high magnification, dense dimples can be observed, with sizes ranging from 2μm to 10μm, indicating that the heterogeneous structure titanium alloy thin-walled tube formed in the specific embodiment has good plasticity.

[0049] As can be seen from the above, the heterogeneous structure of the titanium alloy thin-walled tube obtained in the specific embodiment includes a heterogeneous structure composed of an interweaving distribution of elongated lamellar α grains and fine equiaxed α grains. The lamellar α grains are 20μm to 50μm long and 3μm to 5μm wide, and are no longer randomly distributed, generally distributed along the RD direction. Numerous subgrains are present within the grains, and the fine equiaxed α grains are approximately 3μm to 5μm in size. The resulting heterogeneous structure TC4 titanium alloy thin-walled tube has a tensile strength of 1350MPa, an elongation of 6.8%, and a ductile fracture mode.

[0050] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other. Each embodiment focuses on the differences from other embodiments.

[0051] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for hot spinning forming a heterogeneous titanium alloy thin-walled tube across phase regions, characterized in that: include: The titanium alloy cylinder blank is heated to a β single phase region 20°C to 30°C above the β phase transformation point and then subjected to a first spinning deformation process to obtain a titanium alloy cylinder blank with a full lamellar structure having clear β grain boundaries and lamellar α grains arranged in a disordered and interwoven manner within the lamellar grains; The titanium alloy cylinder blank is subjected to two to three hot spinning steps until the total thinning rate is 55% to 60% to obtain a heterogeneous titanium alloy thin-walled cylinder; Among them, the hot spinning forming step includes: air cooling the titanium alloy tube blank for a preset time to a stable temperature, and then heating it to a two-phase zone 50°C lower than the temperature of the previous spinning deformation before spinning deformation.

2. The cross-phase hot spinning forming method of heterogeneous structure titanium alloy thin-walled tube according to claim 1 is characterized in that: The thinning rate of each spinning deformation is 20%~30%.

3. The cross-phase hot spinning forming method of heterogeneous structure titanium alloy thin-walled tube according to claim 1 is characterized in that: The preset time is 3 minutes to 5 minutes.

4. The cross-phase hot spinning forming method of heterogeneous structure titanium alloy thin-walled tube according to claim 1 is characterized in that: The stable temperature is 400°C to 450°C.

5. The cross-phase hot spinning forming method of heterogeneous structure titanium alloy thin-walled tube according to claim 1 is characterized in that: The heating method is induction heating.

Images