Compact gamma-TiAl alloy sheet and preparation method thereof
Through the cyclic process of rolling and recrystallization annealing and pressureless reaction annealing treatment, the problems of temperature drop and holes in the preparation of γ-TiAl alloy sheets were solved, and efficient and low-cost production of γ-TiAl alloy sheets was achieved.
Patent Information
- Application Number
- CN202510983881.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-17
- Publication Date
- 2025-10-10
AI Technical Summary
The existing γ-TiAl alloy sheet preparation process has the problem that the temperature drops too quickly during rolling, resulting in a sharp drop in plasticity, making it difficult to achieve continuous rolling under isothermal conditions. In addition, the γ-TiAl sheets synthesized by the foil metallurgy method are prone to internal holes, resulting in high production costs and limited shape.
The Al-Ti-Al three-layer composite plate is prepared by a cyclic process of rolling and recrystallization annealing. Through pressureless low-temperature and high-temperature reaction annealing treatment, the formation of holes is avoided, and large-scale production and preparation of complex-shaped γ-TiAl alloy thin plates are achieved.
The appearance of pores in the TiAl3 phase is effectively avoided, production costs are reduced, and the preparation of large-area, pore-free γ-TiAl alloy sheets is achieved without shape restrictions, simplifying the process.
Smart Images
Figure CN120755209A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of preparation of gamma-TiAl alloy thin plates, in particular to a preparation method of a dense gamma-TiAl alloy thin plate and a gamma-TiAl alloy thin plate synthesized by the method. Background Art
[0002] With the rapid development of aviation and aerospace technology towards high thrust-to-weight ratio, long life, and low energy consumption, extreme service environments have placed almost stringent requirements on the performance of high-temperature structural materials. Compared with Ni-based high-temperature alloys and Ti-based alloys widely used in current aircraft engine hot end components and aerospace propulsion systems, TiAl-based alloys, with their unique intermetallic compound crystal structure, exhibit a more excellent comprehensive performance matrix. In terms of elastic modulus, oxidation resistance, and creep resistance, TiAl-based alloys are significantly superior to Ti-based alloys and are comparable to Ni-based alloys. However, the density of TiAl-based alloys is only 3.7~3.9g / cm 3 , less than half that of Ni-based alloys. TiAl-based alloys have an operating temperature of 600-900°C, bridging the gap between Ni-based and Ti-based alloys. Therefore, due to their excellent high-temperature mechanical properties and low density, TiAl-based alloys have been identified as high-temperature aerospace structural materials for temperatures between 600-900°C by the U.S. National Aeronautics and Space Program (NASP), Europe's Hermes and Sanger Program, and the European Air Transport Research Program (FESTIP).
[0003] γ-TiAl alloy plate (also known as γ-TiAl binary alloy plate) is an ideal material for making structures such as the skin of aviation and space shuttles, the heated end faces of hypersonic aircraft, and the heated areas near rocket engine nozzles. Currently, the commonly used methods for preparing γ-TiAl alloy plates are high-temperature rolling and foil metallurgy.
[0004] High-temperature rolling methods can be divided into ingot metallurgy (IM) and powder metallurgy (IM) routes, depending on the different routes used to obtain hot-rolled γ-TiAl alloy billets. Public information indicates that Plansee AG of Austria and the GKSS Research Center of Germany are world leaders in rolling large-scale TiAl-based alloy sheets, but the relevant processes are confidential. Domestic research on TiAl-based alloy sheet rolling processes is limited to the laboratory stage. The main problem is that traditional rolling equipment cannot achieve continuous rolling under isothermal conditions. The rapid temperature drop during rolling causes a sharp drop in plasticity, which increases the difficulty of rolling γ-TiAl alloy sheets. Consequently, the preparation process is complex, which in turn leads to the high price of γ-TiAl alloy sheets.
[0005] The foil metallurgy method involves alternately stacking raw materials, Ti foil and Al foil, into a layered structure. The γ-TiAl alloy sheet is then prepared through some or all of the following steps: hot pressing, sintering, rolling, and reaction annealing. This method avoids direct deformation of the brittle γ-TiAl alloy block and reduces production costs. Another advantage of the foil metallurgy method is that the Ti / Al layered composite sheet can be pre-processed into a complex-shaped plate product, which is then reaction-annealed to synthesize the γ-TiAl alloy sheet, achieving "deformation first, synthesis later." However, the main problem with the foil metallurgy method for preparing γ-TiAl alloy sheets is the presence of pores within the synthesized γ-TiAl sheet, which require pressure to be applied during the annealing process to reduce or eliminate them. However, applying pressure limits the production scale of the γ-TiAl binary alloy sheet and the shape of the γ-TiAl alloy sheet product. Furthermore, the thinner the foil, the more expensive it is, increasing the cost of surface treatment. Furthermore, the target composition of the resulting γ-TiAl alloy sheet is easily deviated and difficult to guarantee. Summary of the Invention
[0006] The present invention addresses shortcomings in γ-TiAl alloy plate preparation technology and provides a method for synthesizing a γ-TiAl alloy sheet by first thinning an Al-Ti-Al three-layer composite sheet to a target thickness through a rolling and recrystallization annealing cycle, followed by a high-temperature reaction annealing treatment without compression. This method first forms a thick Al-Ti-Al three-layer composite sheet with a flush composite interface, then produces a dense, hole-free γ-TiAl alloy sheet through reaction annealing. The alloy sheet area is not restricted, the preparation process is simple and convenient, and the production cost is significantly reduced compared to processes such as roll bonding and vacuum hot pressing.
[0007] To achieve the above objectives, the present invention provides a method for preparing a dense γ-TiAl alloy sheet, which first obtains a thick Al-Ti-Al three-layer composite plate, then thins the Al-Ti-Al composite plate to a target thickness through a cyclic process of rolling and recrystallization annealing, while maintaining a flat interface, and finally performs a pressureless reaction annealing treatment to synthesize a dense γ-TiAl alloy sheet.
[0008] The present application utilizes the cyclic process of rolling and recrystallization annealing to prepare Al-Ti-Al composite sheet first, and then obtains the dense and pore-free gamma-TiAl alloy sheet through pressureless reaction annealing treatment. The preparation process is as follows: first, Ti plate and Al plate are compounded according to the layer arrangement structure of Al-Ti-Al to obtain thick Al-Ti-Al three-layer composite plate, and then the composite plate is thinned to the target thickness through the cyclic rolling and recrystallization annealing process, and then low-temperature and high-temperature pressureless reaction annealing is carried out. Since Al is on both sides of the Ti plate, the phenomenon of Al inclusion due to TiAl3 opposite growth during low-temperature annealing can be avoided, and the Kirkendall hole generated due to the difference in Al and Ti atomic diffusion coefficients can be discharged to the Al-TiAl3 interface. When Al is exhausted, the hole becomes part of the surface of TiAl3. The pore-free TiAl3-Ti-TiAl3 three-layer composite plate can synthesize the pore-free gamma-TiAl alloy sheet during the subsequent high-temperature pressureless reaction annealing process. Therefore, the present application can prepare the dense and pore-free gamma-TiAl alloy sheet through pressureless reaction annealing in an ordinary atmosphere furnace or a vacuum heat treatment furnace. In addition, since no pressure is applied during annealing, the Al-Ti-Al three-layer composite plate can be pre-formed into a complex-shaped part, and then pressureless reaction annealing is carried out to synthesize the dense gamma-TiAl alloy sheet product, truly realizing "deformation first and synthesis later".
[0009] As a limitation of the above technical solution, the Al-Ti-Al three-layer composite plate is prepared by explosion welding or rolling.
[0010] The Al-Ti-Al three-layer composite plate is prepared by explosion welding or rolling, and the rolling can be hot rolling or cold rolling to composite and thin the three-layer plate. The reduction rate of rolling is usually 20-40%, preferably 30-35%, which can ensure good combination of Al-Ti-Al plate; if the reduction is too small, Ti and Al plates are difficult to combine; if the reduction is too large, the Ti plate is prone to necking.
[0011] After the Al-Ti-Al three-layer composite plate is prepared, the cyclic process of rolling and recrystallization annealing can be used to prepare large-area Al-Ti-Al composite sheet, which greatly reduces the production cost.
[0012] As a limitation of the above technical solution, the thickness ratio of each plate in the Al-Ti-Al three-layer composite plate is adjusted according to the composition content of the gamma-TiAl alloy sheet.
[0013] As a limitation of the above technical solution, the Al-Ti-Al composite plate is thinned by rolling, and the reduction rate of each rolling is 20-40%, preferably 30-35%.
[0014] Cold rolling is usually used to thin the Al-Ti-Al composite plate. During the cyclic cold rolling and recrystallization annealing process, if the rolling reduction rate is too small, the production efficiency will be low, while if the rolling reduction rate is too large, the Ti plate will also easily produce necking.
[0015] As a limitation of the above technical solution, the rolled Al-Ti-Al composite plate is recrystallized and annealed at 550-650° C. for 0.5-2 h.
[0016] As a limitation of the above technical solution, the pressureless reaction annealing treatment is to first perform reaction annealing at a temperature of 630±20°C under pressureless conditions to generate a TiAl3-Ti-TiAl3 composite plate, and then perform reaction annealing at a temperature of 1300±50°C to promote the reaction of Ti and TiAl3 to synthesize a γ-TiAl alloy plate.
[0017] Pressureless reaction annealing treatment usually includes two-stage annealing, low temperature and high temperature. The Al in the Al-Ti-Al composite plate is depleted by low temperature annealing to generate a TiAl3-Ti-TiAl3 layered composite plate, and then high temperature annealing is further promoted to react with Ti and TiAl3 to synthesize a γ-TiAl alloy plate.
[0018] As a limitation of the above technical solution, the method for preparing a dense γ-TiAl alloy sheet includes the following steps: (1) Using a two-step explosive welding method to prepare an Al-Ti-Al three-layer composite plate, firstly, the first step is explosive welding to form a Ti-Al two-layer composite plate, and then the second step is explosive welding to form an Al-Ti-Al three-layer composite plate; or, The Al-Ti-Al three-layer composite plate is prepared by a rolling method. First, a surface-treated Ti plate and two Al plates are assembled and riveted according to an Al-Ti-Al three-layer stacking structure to obtain an Al-Ti-Al composite billet. The billet is then cold-rolled at room temperature or hot-rolled at 400°C on a rolling mill, and then recrystallized and annealed in a heat treatment furnace to produce an Al-Ti-Al three-layer composite plate. (2) Thinning the Al-Ti-Al three-layer composite plate to a thickness close to that of the final γ-TiAl alloy sheet through a rolling and recrystallization annealing cycle process to obtain an Al-Ti-Al composite sheet; wherein the rolling and recrystallization annealing before recrystallization annealing constitute one cycle, and the reduction rate of each cycle is 20-40%; (3) The Al-Ti-Al composite sheet is first subjected to low-temperature pressureless reaction annealing at a temperature of 630±20℃ until Al is consumed to form a TiAl3-Ti-TiAl3 composite sheet, and then subjected to high-temperature pressureless reaction annealing at a temperature of 1300±50℃ to promote the reaction between Ti and TiAl3 to form a γ-TiAl alloy sheet.
[0019] As a limitation of the above technical solution, the raw materials used in step (1) are pure Ti plates and pure Al plates, and the surfaces of the Ti plates and Al plates are first mechanically polished to remove the oxide film, and then the polished surfaces are cleaned with ultrasound and alcohol; and / or, If the γ-TiAl alloy sheet obtained in step (3) has a compositional non-uniformity problem, the γ-TiAl alloy sheet is further subjected to pressureless homogenization annealing at 1300-1400° C. to promote uniform composition of Ti and Al atoms in the γ-TiAl alloy.
[0020] Improve the preparation operation and conditions of γ-TiAl alloy thin plates, optimize the production process and product structure performance, and save production costs.
[0021] At the same time, the present invention also provides a dense γ-TiAl alloy sheet synthesized by the above preparation method. Preferably, the thickness of the alloy sheet is 200-500 μm and the porosity is less than 0.5%. If the thickness of the alloy sheet is too large, the reaction annealing time will be very long and the cost will be high.
[0022] Furthermore, a dense γ-TiAl alloy plate product is synthesized by the above preparation method, that is, an Al-Ti-Al composite plate of target thickness is first prepared according to the above method, then formed into parts of complex shapes, and then subjected to pressureless reaction annealing to synthesize a dense γ-TiAl alloy plate product.
[0023] The preparation method of the present invention can be used to synthesize dense γ-TiAl alloy thin plates and various dense γ-TiAl alloy plate products.
[0024] In summary, the present invention first thins a thick Al-Ti-Al three-layer composite plate through a rolling and recrystallization annealing cycle to reduce its thickness to form a thin plate with a flat composite interface, wherein the initial interface of the Al-Ti-Al three-layer composite plate may be slightly uneven, and then flattens the composite interface through rolling and recrystallization annealing, and then performs pressureless reaction annealing. This method fundamentally and effectively avoids the appearance of pores in the TiAl3 phase, and can produce a dense, pore-free γ-TiAl alloy thin plate. Because the annealing treatment in the preparation process does not require the application of any pressure, the Al-Ti-Al three-layer composite plate can be pre-formed into parts with complex shapes, and then pressureless reaction annealing is performed to synthesize a dense γ-TiAl alloy plate product, truly achieving "deformation first, synthesis later". Moreover, large-area Al-Ti-Al composite thin plates can be produced at low cost and with a simplified process flow, which has a greatly promoting effect on the development of γ-TiAl alloy thin plate preparation technology. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1, backscattered scanning electron microscope photos and energy spectrum analysis results of the interface of Al-Ti-Al composite plate made by explosive welding, including (a) ×60 times; (b) ×300 times; (c) energy spectrum of point 1; (d) energy spectrum of point 2; (e) energy spectrum of point 3.
[0026] Figure 2 Metallographic photographs of a 6.7mm thick explosively welded Al-Ti-Al three-layer composite plate S-6.7mm thinned to different thicknesses through a cyclic rolling and recrystallization annealing process: (a) S1-3.4mm; (b) S1-1.2mm; (c) S1-0.54mm; (d) S2-0.54mm.
[0027] Figure 3 , uniaxial tensile curves of Al-Ti-Al composite plates S1-0.54mm and S2-0.54mm.
[0028] Figure 4 , Scanning electron microscope photos and energy spectrum analysis results of Al-Ti-Al composite plates at different annealing times: (a) S1-0.54mm@32h; (b) S1-0.54mm@64h; (c) S1-0.54mm@128h; (d) S2- 0.54mm@128h; (e) TiAl3 phase energy spectrum.
[0029] Figure 5 , Scanning electron microscope images of the TiAl3-Ti-TiAl3 composite plate (prepared by low-temperature annealing of the Al-Ti-Al composite plate S1-0.54mm) annealed at 1300℃ for 32h (a) and 128h (b) in an Ar gas protection environment, Ti-Al binary alloy phase diagram (c) and energy spectrum analysis results (d, e, f, g and h).
[0030] Figure 6 , explosive welding and cyclic cold rolling recrystallization annealing + pressureless reaction annealing to synthesize dense γ-TiAl alloy sheet.
[0031] Figure 7 , the hot-rolled Al-Ti-Al three-layer composite plate is thinned to plates of different thicknesses through a cyclic cold rolling and recrystallization annealing process; (a) 2.6mm; (b) 1.83mm; (c) 1.29mm; (d) 0.88mm; (e) 0.60mm.
[0032] Figure 8 Photos of Al-Ti-Al composite plate samples of different thicknesses prepared by hot rolling and cyclic cold rolling recrystallization annealing processes.
[0033] Figure 9 , Al-Ti-Al composite plates of different thicknesses and their samples after low temperature and high temperature annealing.
[0034] Figure 10 The preparation flowchart of the dense γ-TiAl alloy sheet of the present application.
[0035] Figure 11 The flowchart of the prior art scheme 1 of the foil metallurgy method for preparing the γ-TiAl alloy sheet.
[0036] Figure 12 The flowchart of the prior art scheme 2 of the foil metallurgy method for preparing the γ-TiAl alloy sheet.
[0037] Figure 13 The schematic diagram of the hole formation in the prior art of the foil metallurgy method for preparing the γ-TiAl alloy sheet. DETAILED DESCRIPTION
[0038] The technical schemes of the present application will be described clearly and completely in combination with the embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.
[0039] The experimental methods in the following examples and comparative examples are all the conventional methods, unless otherwise specified. The raw materials or test materials used are all the typical products purchased in the market, unless otherwise specified. The quantitative tests in the following examples and comparative examples are all set up with three repeated experiments, and the results are averaged.
[0040] Example 1
[0041] The Al-Ti-Al composite sheet is prepared by the cycle process of cold rolling-recrystallization annealing of the explosion-welded Al-Ti-Al three-layer composite sheet, and the γ-TiAl alloy sheet is synthesized by pressureless annealing reaction.
[0042] a, The experimental materials are pure Al (1060) plate (length x width x thickness is 500 mm x 500 mm x 2 mm) and pure Ti (TA1) plate (length x width x thickness is 500 mm x 500 mm x 3 mm). The thickness of Al is slightly larger than the required proportion because Al is more deformed than Ti after explosion welding and rolling. The initial state of the two plates is a uniform fully recrystallized structure. The Al-Ti-Al three-layer composite plate can be prepared by a two-step explosion welding method. Specifically, first, Al and Ti plates are used as the clad plate and the base plate respectively, and a Ti-Al two-layer composite plate is prepared by the first step of explosion welding. Then, the Ti-Al two-layer composite plate and the Al plate are used as the base plate and the clad plate respectively, and the Al-Ti-Al three-layer composite plate is prepared by the second step of explosion welding. Before each step of explosion welding, the oxide film and contaminants on the surface of the Ti and Al plates are removed by using a steel wire brush, and then the surface is cleaned with alcohol. After explosion welding, the composite plate is annealed at 380°C for 1 h and then flattened. The thickness of the flattened Al-Ti-Al composite plate is about 6.7 mm, which is denoted as S-6.7 mm. The Al-Ti-Al three-layer composite plate can also be obtained by rolling or purchased.
[0043] Figure 1 The backscattered scanning electron microscope image of the interface of the Al-Ti-Al composite plate prepared by explosion welding, wherein the black contrast region is Al and the gray-white contrast region is Ti. It can be seen from Figure 1 a that the interface of the explosion-welded Al-Ti-Al composite plate exhibits typical explosion-welded interface characteristics, i.e., a wavy interface, a vortex structure and a melting zone (the gray-black region in the figure), and the Al-Ti interface is well bonded without continuous unbonded zones, cracks or pores. Figure 1 b is Figure 1 a is the high-magnification scanning electron microscope image of the dashed box part in a. Energy spectrum analysis shows that the Ti content at points 1, 2 and 3 in the melting zone is 30 at.%, 31 at.% and 33 at.% respectively, and the Al content is 70 at.%, 69 at.% and 67 at.% respectively. The composition of the three points is close to that of the TiAl2 or Ti2Al5 phase. The reason for the wavy interface is that the Al plate and the Ti plate will collide violently under the driving of the explosive explosion, forming a high-temperature and high-pressure zone near the collision point. The sharp rise of temperature and pressure causes the interface metal to form a metal jet. During the entire cycle, the metal jet and the clad plate flow under the action of inertial force and the resistance of the base plate flow, and most of them move counterclockwise and accumulate, preliminarily forming a wavy interface. A small amount of jet moves clockwise on the surface of the base plate under the action of the resistance, forming a vortex pattern. In addition, under the action of plastic deformation heat, the temperature of the interface rises to the melting point of the base metal, causing the interface to melt and form a melting zone.
[0044] b. The explosive welded Al-Ti-Al three-layer composite plate was reduced to about 0.54 mm in thickness by a cyclic process of cold rolling (CR) - recrystallization annealing (RA). The cold rolling - recrystallization annealing cyclic process was as follows: S-6.7 mm→ CR→ 4.8 mm→ RA→ CR→ 3.4 mm→ RA→ CR→ 2.4 mm→ RA→ CR→ 1.7 mm→ RA→ CR→ 1.2 mm→ RA→ CR→ 0.8 mm→ RA→ CR→ 0.54 mm. The reduction of each cycle was in the range of 20-40%, and Al-Ti-Al composite plates with different thicknesses were obtained and denoted as S1-XX mm plates (XX was the corresponding thickness value).
[0045] As a comparison, the S1-3.4 mm composite plate was cold rolled to 0.54 mm in multiple passes without recrystallization annealing between passes, and the plate was denoted as S2-0.54 mm.
[0046] Figure 2 a-c were backscattered scanning electron microscope images of Al-Ti-Al composite plates with different thicknesses prepared by a cyclic rolling-recrystallization annealing process from the explosive welded Al-Ti-Al three-layer composite plate S-6.7 mm, from Figure 2 a It can be seen that the explosive welded Al-Ti-Al three-layer composite plate S-6.7 mm was reduced to 3.4 mm by rolling and recrystallization annealing, and the interface became relatively flat, and the interface wave amplitude decreased from about 150 μm to about 90 μm. When the cyclic cold rolling-recrystallization annealing process was continued to reduce to 1.2 mm and 0.54 mm (b and 2c), the interfaces of S1-1.2 mm plate and S1-0.54 mm plate were more flat than that of S1-3.4 mm plate, and the interface wave amplitudes were 18 μm and 16 μm, respectively. Figure 2
[0047] Figure 2 d was a backscattered scanning electron microscope image of the Al-Ti-Al composite thin plate S2-0.54 mm prepared by multiple passes of continuous cold rolling from the Al-Ti-Al composite plate S1-3.4 mm, from Figure 2 d It can be seen that when the total reduction was large (d reached 84%) and there was no intermediate recrystallization annealing treatment, the Ti layer would neck and even break. Figure 2
[0048] The cause of necking can be explained as follows: During the rolling deformation process of the Al-Ti-Al three-layer composite plate, the outer Al layer of the composite plate elongates more in the rolling direction than the Ti layer, generating friction at the Ti-Al interface. The friction acting on the surface of the Ti layer causes the Ti layer to behave like a tensile specimen. For S1 plates of varying thickness, recrystallization annealing after each cold rolling cycle eliminates the work hardening of the Ti layer. The subsequent cold rolling cycle is equivalent to stretching the annealed Ti layer. When the reduction ratio per cycle is small, the strain of the cold-rolled Ti layer is less than the critical deformation for significant necking, so the interface remains flush. For S2 plates, multiple passes of cold rolling without annealing are equivalent to high-strain stretching of the recrystallized Ti layer. The total strain exceeds the critical deformation for necking or fracture in the Ti layer, resulting in necking or fracture.
[0049] Figure 3 The uniaxial tensile curves of two Al-Ti-Al composite plates with diameters of S1-0.54mm and S2-0.54mm are shown, with three samples taken from each type of composite plate. Figure 3 It can be seen that the tensile strength of the three specimens S1-1, S1-2 and S1-3 of the S1-0.54mm composite plate are 215.8, 212 and 243.9 MPa, respectively, and the elongation are 16.8%, 22.1% and 18.4%, respectively. The tensile strength of the three specimens S2-1, S2-2 and S2-3 of the S2-0.54mm composite plate are 125.9, 134.7 and 128.8 MPa, respectively, and the elongation are 13.5%, 7% and 2.2%, respectively. The tensile strength and elongation of the three specimens of S1-0.54mm composite plate are greater than those of the three specimens of S2-0.54mm composite plate. The reasons can be explained as follows: The Ti layer in the S2-0.54mm composite plate has a necking, which causes the cross-sectional area of the local Ti layer of the S2-0.54mm composite plate to be smaller than that of the local Ti layer of the S1-0.54mm composite plate. m =350~550Mpa) is much greater than the tensile strength of pure Al (R m =80Mpa). According to the superposition principle of the strength of layered composite materials, the reduction in the cross-sectional area of the Ti layer results in the tensile strength of the S2-0.54mm composite plate being lower than that of the S1-0.54mm composite plate. Furthermore, due to the lower tensile strength of the Al-Ti-Al composite plate at the necking point of the Ti layer, the plastic deformation of the S2-0.54mm composite plate during the tensile process is primarily concentrated at the necking point of the Ti layer, while other areas with thicker Ti layers experience almost no plastic deformation. In contrast, in the S1-0.54mm composite plate, due to the uniform thickness of the Ti and Al layers, the entire Ti layer undergoes significant plastic deformation along the rolling direction. Therefore, the elongation of the S2-0.54mm composite plate is lower than that of the S1-0.54mm composite plate.
[0050] c, the Al-Ti-Al composite sheet S1-0.54mm was slightly ground on both sides to make the thickness ratio of Al-Ti-Al close to 1:2:1 (total thickness about 0.48mm, although the thickness is reduced, it is still called S1-0.54mm), then annealed at 630℃ in air for different time until the Al is consumed. Similarly, the S2-0.54mm sheet was also annealed at 630℃ for 128h. The scanning electron microscope photos and energy spectrum analysis results of the interface of the Al-Ti-Al composite sheets annealed for different time are shown in Figure 4 Figure 4 a, b and c. As shown in Figure 4 a, for the S1-0.54mm sheet annealed for 32h, a gray intermetallic compound layer is formed between the black-gray Al layer and the gray-white Ti layer, the energy spectrum analysis result shows that it is TiAl3 phase Figure 4 e). With the annealing time prolonged to 64h, the thickness of TiAl3 phase is further increased, most of the Al is consumed, only a small amount of Al remains in the interface, see Figure 4 b; with the annealing time prolonged to 128h, all the Al is consumed, TiAl3-Ti-TiAl3 composite sheet is formed, see Figure 4 c, from Figure 4 c, it can be seen that only a small amount of holes are formed near the surface of TiAl3 phase. Figure 4 d is the scanning electron microscope photo of S2-0.54mm annealed for 128h, from Figure 4 d, it can be seen that at the original Ti necking or fracture position, there is still residual Al on the surface of the TiAl3-Ti-TiAl3 composite sheet formed, because the Al layer at the Ti necking or fracture position is thicker, in addition, holes will also appear in the TiAl3 phase at the Ti layer necking or fracture position, because the TiAl3 layer grows fastest in the direction perpendicular to the Ti layer, so the Al at the necking or fracture position is enclosed in the TiAl3 phase, with the annealing time prolonged, the enclosed Al diffuses outward to form TiAl3 phase, leaving holes at the original position.
[0051] The TiAl3-Ti-TiAl3 composite sheet synthesized by low temperature annealing of the Al-Ti-Al composite sheet S1-0.54mm was annealed at 1300℃ for 32h and 128h respectively under argon protection, the argon pressure is less than 0.01Mpa, which is so small that it can be ignored. The backscattered scanning electron microscope photos and energy spectrum analysis results of the two annealed samples are shown in Figure 5 Figure 5 a, b and c. As shown in Figure 5 a, the TiAl3-Ti-TiAl3 composite sheet annealed for 32h is divided into three layers from the side to the center, the energy spectrum analysis results of points 1, 2 and 3 Figure 5 d, e and f are listed in Figure 5a In the upper right table, combined with the Ti-Al binary alloy phase diagram, see Figure 5 c, it can be determined that points 1, 2 and 3 are TiAl2 phase, γ-TiAl phase and Ti3Al phase respectively, which means that the original Ti and TiAl3 phases disappear. Figure 5 b It can be seen that after annealing for 128h, only two phases remain in the sample. The energy spectrum analysis results of points 1 and 2 ( Figure 5 g and h) are listed in Figure 5 The table in the upper right corner of Figure b, combined with the Ti-Al binary alloy phase diagram, confirms that the two phases are γ-TiAl and Ti3Al. Furthermore, in the sample annealed for 128 hours, except for a small number of pores near the surface, no pores exist within the γ-TiAl or Ti3Al phases.
[0052] The above process flow diagram is as follows Figure 6 shown.
[0053] Example 2
[0054] Hot-rolled Al-Ti-Al three-layer composite plate is prepared by a cold rolling-recrystallization annealing cycle process to prepare Al-Ti-Al composite thin plate, and γ-TiAl alloy thin plate is synthesized by pressureless annealing reaction.
[0055] a. The experimental materials used were TA1 pure titanium plates (100mm×60mm×2.5mm) and 1060 pure aluminum plates (100mm×60mm×1.5mm). Before rolling, both the Ti and Al plates were recrystallized and annealed at 600℃ in a heat treatment furnace for 1h. The surface oxide film of the annealed Ti and Al plates was then removed with a wire brush. The plates were then cleaned in an ultrasonic cleaner and dried. After stacking in the Al-Ti-Al sequence, one end was riveted with a rivet and the other end was tied with wire. The riveted samples were placed in a 400℃ muffle furnace for 12 minutes, then hot-rolled and laminated in a two-roll mill. After recrystallization annealing at 600℃ for 1h, a well-bonded Al-Ti-Al three-layer composite plate was obtained. The rolling reduction was approximately 33%, and the resulting composite plate had a thickness of 3.75mm, denoted as S-3.75mm.
[0056] b. The hot-rolled Al-Ti-Al three-layer composite sheet was thinned to a final thickness of approximately 0.40 mm through a cold rolling (CR)-recrystallization annealing (RA) cycle. The CR-RA cycle was as follows: S-3.75 mm → CR → 2.6 mm → RA → CR → 1.83 mm → RA → CR → 1.29 mm → RA → CR → 0.88 mm → RA → CR → 0.60 mm → RA → CR → 0.40 mm.
[0057] Figure 7 are photos of Al-Ti-Al composite sheets of different thicknesses prepared by hot rolling and cyclic cold rolling and recrystallization annealing process, wherein the 3.75mm-thick Al-Ti-Al three-layer composite sheet is the initial hot-rolled composite sheet, and the 2.6mm-, 0.88mm- and 0.40mm-thick Al-Ti-Al composite sheets are prepared by subsequent cyclic cold rolling and recrystallization annealing thinning process.
[0058] Figure 8 are interface metallographic photos of hot-rolled Al-Ti-Al composite sheets of different thicknesses, from Figure 8 It can be seen that, by the cyclic rolling and recrystallization annealing process, the interfaces of Al-Ti-Al composite sheets of different thicknesses are relatively flat. The Al-Ti-Al composite sheets prepared by the process can also be subjected to pressureless reaction annealing to synthesize dense γ-TiAl alloy sheets, and the operation and mechanism are the same as those of Example 1, therefore, the scanning electron microscope photos of the samples after pressureless reaction annealing at low and high temperatures are not provided, Figure 9 are metallographic inlay photos of Al-Ti-Al composite sheets of different thicknesses prepared by the cyclic rolling and recrystallization annealing process and the 0.4mm-thick Al-Ti-Al composite sheet after pressureless reaction annealing.
[0059] The preparation flowchart of the dense γ-TiAl alloy sheet of the present application is shown in Figure 10 .
[0060] Comparative Example
[0061] Currently, there are mainly two technical solutions for preparing γ-TiAl binary alloy sheets by foil metallurgy method.
[0062] Technical solution 1 is shown in Figure 11 , and the specific process steps are as follows: first, a plurality of Ti plates and Al plates (which have been surface treated) are combined by vacuum hot diffusion welding or hot diffusion welding + hot rolling (a) and (b) and (11c); then, the Ti-Al layered composite sheet is subjected to low-temperature annealing in a vacuum hot-pressing sintering furnace, and the low-temperature annealing temperature is above and below the melting point of Al, so as to generate a Ti-TiAl3 layered composite sheet (d) by Ti-Al solid-phase reaction or solid-liquid reaction, and pressure needs to be applied during the low-temperature annealing process to reduce the pores in the TiAl3 phase; then, the Ti-TiAl3 layered composite sheet is subjected to high-temperature annealing at a temperature ranging from 1000 to 1300℃ to synthesize a γ-TiAl alloy sheet, and pressure needs to be applied during the annealing process to eliminate the Kirkendall pores (e); finally, the γ-TiAl alloy sheet is subjected to homogenization annealing at a temperature ranging from 1300 to 1400℃ (f). Figure 11 Figure 11 Figure 11 Figure 11 Figure 11 f) No pressure is applied during the homogenization annealing stage.
[0063] Technical solution 2, such as Figure 12 As shown, the specific process steps are as follows: First, a multi-layer Ti / Al composite plate is prepared by a rolling process. The rolling process is to alternately stack and rivet multiple surface-treated Ti and Al plates ( Figure 12 a and 12b), and then the riveted Ti-Al multilayer plate is composited by a rolling mill, and then the Ti-Al layered composite plate is cut from the middle, and the Ti-Al composite plate is surface treated and riveted again, and then thinned by a rolling mill, and this cycle is repeated many times ( Figure 12 c); the multilayer Ti-Al composite plate after lamination is annealed at low temperature in a vacuum hot pressing furnace to generate a Ti-TiAl3 layered composite plate ( Figure 12 d), and then the Ti-TiAl3 layered composite plate is annealed at high temperature in a vacuum hot pressing sintering furnace to generate a γ-TiAl alloy plate and subsequently homogenized annealed to generate a lamellar γ-TiAl alloy plate ( Figure 12 e and Figure 12 f). During the entire reaction annealing process, pressure needs to be applied to eliminate the pores. Alternatively, the Ti-TiAl3 layered composite plate generated by low-temperature annealing of the rolled Ti-Al composite plate can be cold-rolled to reduce the pores in the TiAl3 phase. The Ti-TiAl3 layered composite plate is then annealed at high temperature to form a γ-TiAl alloy plate, which is then hot-rolled to eliminate the pores. This preparation process is cumbersome.
[0064] The foil metallurgy method for preparing γ-TiAl alloy plates is to first use diffusion welding, rolling or explosion welding to composite multiple layers of Ti and Al foils to prepare Ti-Al layered composite plates, and then subject the Ti-Al layered composite plates to reaction annealing, which usually includes two-stage annealing at low temperature and high temperature. The low-temperature annealing is performed at temperatures above and below the melting point of Al (660°C). The Al in the Ti-Al composite plate is depleted through low-temperature annealing to form a Ti-TiAl3 layered composite plate, and then high-temperature annealing is performed at a temperature above 1000°C to further promote the reaction between Ti and TiAl3 to synthesize γ-TiAl alloy plates.
[0065] γ-TiAl alloy sheets prepared by foil metallurgy are prone to internal voids. These voids are primarily formed during the reaction and diffusion process between the alternating Al and Ti sheets to form the Ti-TiAl3 layered composite sheet. If the annealing temperature is below the melting point of Al, the Kirkendall effect and the non-straight opposing growth of the TiAl3 phase lead to the formation of numerous voids within the TiAl3 phase, especially in its central region. If the annealing temperature is above the melting point of Al, the Ti-Al solid-liquid reaction forms a granular TiAl3 phase. Upon contact between the granular TiAl3 particles, Al is intercalated between the particles, ultimately leading to voids within the TiAl3 phase. During the subsequent high-temperature annealing process, if no pressure is applied, the voids in the TiAl3 phase remain within the resulting γ-TiAl alloy sheet. Therefore, to achieve void-free γ-TiAl alloy sheets, a certain amount of pressure must be applied to the sheet during both low- and high-temperature annealing processes.
[0066] The existing technical solutions for preparing γ-TiAl alloy plates by foil metallurgy currently have the following disadvantages: 1) Previous generations have used thinner Al and Ti foils to alternately stack multiple layers to prepare Ti-Al layered composite plates, that is, almost every Al foil is sandwiched between two adjacent Ti foils. During low-temperature annealing below the melting point of Al, due to the Kirkendall effect and the non-straight growth of the TiAl3 phase, a large number of pores are formed in the middle of the TiAl3 phase (the middle of the Al before the reaction). The pore formation process is as follows: Figure 13 As shown, first, Al and Ti react with each other to form a counter-growing wavy TiAl3 phase ( Figure 13 a) As the reaction time increases, the faster growing TiAl3 layers begin to connect with each other, and Al is distributed discontinuously in the TiAl3 phase ( Figure 13 b) After the reaction is completed, a small amount of Al still remains in the TiAl3 phase. At the same time, due to the difference in the diffusion rates of Al and Ti atoms, Kirkendall holes are formed in the Al at the front of the TiAl3-Al interface until the Al is exhausted to form larger holes ( Figure 13c). During low-temperature annealing at a temperature above the melting point of Al, Al will be mixed between the granular TiAl3 phases, and holes will also be formed in the TiAl3 phase. If pressure is not applied to the Ti-TiAl3 layered composite plate containing holes during the subsequent high-temperature annealing process, these holes will remain in the γ-TiAl alloy plate synthesized by high-temperature annealing and reduce the mechanical properties of the alloy plate. If pressure is applied during the synthesis of the γ-TiAl alloy plate, it will be difficult to prepare plate products with complex shapes, and it will be difficult to produce plate products on a large scale. In addition, the thinner the foil, the more expensive it is, which increases the cost of surface treatment, and the target composition of the prepared γ-TiAl alloy plate is also easy to deviate. 2) The cumulative rolling process can reduce the layer thickness of the Ti plate and the Al plate, thereby shortening the annealing time, but the process cycle is long, the efficiency is low, and the production cost is high. It is difficult to prepare large-sized γ-TiAl alloy plates using vacuum hot pressing, and the production cost is high.
[0067] In summary, the present invention utilizes cold rolling, hot rolling, or explosive welding to first produce a thick Al-Ti-Al three-layer composite plate, then employs a rolling and recrystallization annealing cycle to produce an Al-Ti-Al composite sheet with a flush interface, and then performs pressureless reaction annealing to synthesize a dense γ-TiAl alloy sheet. This fundamentally avoids the appearance of pores within the TiAl3 phase, and allows the production of a dense, void-free γ-TiAl alloy sheet by simply performing pressureless reaction annealing in a normal atmosphere or a vacuum heat treatment furnace. In addition, since no pressure is required during the annealing process, the Al-Ti-Al composite plate can be pre-processed into parts with complex shapes, and then annealed to synthesize a dense γ-TiAl alloy sheet product, truly achieving "forming first, then synthesis."
[0068] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of this application, several variations and improvements can be made, which all fall within the scope of protection of this application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.
Claims
1. A method for preparing a dense γ-TiAl alloy sheet, characterized in that: An Al-Ti-Al three-layer composite plate is obtained, and then the Al-Ti-Al composite plate is thinned to the target thickness through a cyclic process of rolling and recrystallization annealing. Finally, a pressureless reaction annealing treatment is performed to synthesize a dense γ-TiAl alloy sheet.
2. The method for preparing a dense γ-TiAl alloy sheet according to claim 1, characterized in that: The Al-Ti-Al three-layer composite plate is prepared by explosive welding or rolling.
3. The method for preparing a dense γ-TiAl alloy sheet according to claim 1, wherein: The thickness ratio of each plate in the Al-Ti-Al three-layer composite plate is adjusted according to the component content of the γ-TiAl alloy thin plate.
4. The method for preparing a dense γ-TiAl alloy sheet according to claim 1, wherein: The Al-Ti-Al composite plate is thinned by rolling, with a reduction ratio of 20-40% per rolling, preferably 30-35%.
5. The method for preparing a dense γ-TiAl alloy sheet according to claim 1, wherein: The rolled Al-Ti-Al composite plate is recrystallized and annealed at 550-650°C for 0.5-2h.
6. The method for preparing a dense γ-TiAl alloy sheet according to claim 1, characterized in that: The pressureless reaction annealing treatment is to first perform reaction annealing at a temperature of 630±20°C under pressureless conditions to generate a TiAl3-Ti-TiAl3 composite plate, and then perform reaction annealing at a temperature of 1300±50°C to promote the reaction of Ti and TiAl3 to synthesize a γ-TiAl alloy plate.
7. The method for preparing a dense γ-TiAl alloy sheet according to any one of claims 1 to 6, characterized in that: The following steps are included: (1) using a two-step explosive welding method to prepare an Al-Ti-Al three-layer composite plate, firstly by explosive welding to form a Ti-Al two-layer composite plate, and then by explosive welding to form an Al-Ti-Al three-layer composite plate in a second step; or The Al-Ti-Al three-layer composite plate is prepared by a rolling method. First, one Ti plate and two Al plates are assembled and riveted according to the Al-Ti-Al three-layer stacking structure to obtain an Al-Ti-Al composite billet. The Al-Ti-Al composite billet is then cold-rolled at room temperature or hot-rolled at 400°C on a rolling mill. The Al-Ti-Al three-layer composite plate is then recrystallized and annealed in a heat treatment furnace. (2) Thinning the Al-Ti-Al three-layer composite plate through a rolling and recrystallization annealing cycle process to obtain an Al-Ti-Al composite thin plate; wherein the rolling before recrystallization annealing and the recrystallization annealing constitute one cycle, and the rolling reduction rate of each cycle is 20-40%; (3) The Al-Ti-Al composite sheet is first subjected to low-temperature pressureless reaction annealing treatment at a temperature of 630±20℃ until Al is exhausted to form a TiAl3-Ti-TiAl3 composite sheet, and then subjected to high-temperature pressureless reaction annealing treatment at a temperature of 1300±50℃ to promote the reaction between Ti and TiAl3 to form a γ-TiAl alloy sheet.
8. The method for preparing a dense γ-TiAl alloy sheet according to claim 7, characterized in that : The raw materials used in step (1) are pure Ti plate and pure Al plate. First, the surfaces of the Ti plate and Al plate are mechanically polished to remove the oxide film, and then the polished surfaces are cleaned with ultrasound and alcohol; and / or, If the γ-TiAl alloy sheet obtained in step (3) has a compositional non-uniformity problem, the γ-TiAl alloy sheet is further subjected to pressureless homogenization annealing at 1300-1400° C. to promote uniform composition of Ti and Al atoms in the γ-TiAl alloy.
9. A dense γ-TiAl alloy sheet, characterized by: Prepared by the preparation method according to any one of claims 1 to 8, preferably, the alloy sheet has a thickness of 200 to 500 μm and a porosity of less than 0.5%.
10. A dense γ-TiAl alloy plate product, characterized in that: According to the preparation method according to any one of claims 1 to 8, an Al-Ti-Al composite plate of target thickness is first prepared, then formed into parts of complex shapes, and then subjected to pressureless reaction annealing to synthesize a dense γ-TiAl alloy plate product.