Preparation method of high-performance Ti2AlNb-based alloy plate

Abstract

The application discloses a preparation method of high-performance Ti2AlNb-based alloy plate and belongs to the technical field of titanium alloy plate preparation. The application discloses a preparation method of high-performance Ti2AlNb-based alloy plate, and the specific steps are as follows: firstly, the grain size is refined through multi-directional near-isothermal forging and hot rolling, and the comprehensive performance of the plate is improved, wherein the ingot is subjected to multi-directional near-isothermal forging in an alpha2+B2 phase zone (1020 DEG C-1040 DEG C) and an O+B2 phase zone (930 DEG C-960 DEG C), and the grain size of the forged alloy is refined through continuous temperature reduction phase transformation and recrystallization; then, only upper and lower cover plates are added to cover the plate, rivets are used to fix the blank, and hot rolling is carried out in an alpha2+O+B2 phase zone (980 DEG C-1010 DEG C), and the plate is air-cooled after rolling to obtain the Ti2AlNb-based alloy plate with relatively excellent performance. Then, through comparison and experiment, the process of 1000 DEG C / 20min / argon gas rapid cooling heat treatment is selected. Finally, the Ti2AlNb-based alloy plate with excellent performance at room temperature is obtained.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy sheet preparation technology, specifically relating to a method for preparing high-performance Ti2AlNb-based alloy sheets. Background Technology

[0002] In recent years, with the rapid development of the aerospace industry, there is an urgent need for high-performance new materials to meet the requirements of high-temperature components. Ti2AlNb-based alloys, developed from TiAl alloys, possess characteristics such as low density, high specific strength, high temperature resistance, oxidation resistance, and creep resistance. They can be used for extended periods at temperatures between 700 and 800°C and are expected to replace high-density Ni-based alloys and traditional titanium alloys, showing great potential for application in the aerospace field. However, as a metallic compound, Ti2AlNb-based alloys have coarse grains in their as-cast state, poor plasticity, and high deformation resistance, which limits their widespread use. Subsequent hot deformation treatments such as forging and rolling are necessary to refine the grains and improve alloy performance. Due to the limitations of forging for producing thin-walled parts, the preparation of high-performance plates is extremely important for broadening the development of Ti2AlNb-based alloys.

[0003] Currently, cladding rolling is commonly used to prepare Ti2AlNb-based alloy sheets. However, cladding rolling requires welding the cladding material and the sheet together, increasing the cost of billet preparation. Furthermore, machining is still required after cladding rolling to obtain the Ti2AlNb-based alloy sheet, making the process quite cumbersome. In addition, the overall mechanical properties of the rolled sheet are poor, necessitating high-temperature heat treatment to optimize its performance. However, prolonged high-temperature heat treatment can easily lead to grain growth, reducing the sheet's mechanical properties. Moreover, the cooling method during heat treatment affects the alloy's mechanical properties; furnace cooling easily precipitates a large amount of needle-like O phase, thus reducing the alloy's plasticity; and for large sheets, water-cooled heat treatment is difficult to implement. Therefore, it is necessary to control the microstructure and mechanical properties before and after rolling, and to rationally design the heat treatment process to obtain high-performance sheets. Summary of the Invention

[0004] To address the current practice of using cladding rolling to prepare Ti2AlNb-based alloy plates, which results in high billet preparation costs, complex and cumbersome process steps for obtaining the plates, poor overall mechanical properties of the hot-rolled plates, and failure to obtain plates with ideal properties after heat treatment, this invention provides a method for preparing high-performance Ti2AlNb-based alloy plates.

[0005] One objective of this invention is to provide a process for preparing high-performance Ti2AlNb-based alloy plates. This process refines the grain size of the forged alloy through cooling forging, simplifies the traditional hot rolling process of Ti2AlNb-based alloy plates, and finally performs appropriate heat treatment to obtain plates with excellent performance.

[0006] Another objective is to provide high-performance Ti2AlNb-based alloy sheets to meet their applications in aerospace equipment.

[0007] To achieve the above objectives, the present invention employs the following technical solutions:

[0008] A method for preparing a high-performance Ti2AlNb-based alloy plate includes the following steps:

[0009] Step 1, forging preparation: The ingot is subjected to multi-directional near isothermal forging in the α2+B2 phase region (1020℃~1040℃) and the O+B2 phase region (930℃~960℃), and then air-cooled to obtain the forging blank;

[0010] Step 2: Use two 2-5mm thick 304 stainless steel pieces to clamp the forging billet in the middle, and then use rivets to fix the four corners of the two 304 stainless steel pieces to form a billet for hot rolling; after rolling, air cool and remove the stainless steel. No machining is required to obtain a 0.8-1.2mm hot-rolled alloy plate.

[0011] Step 3: The hot-rolled alloy sheet is subjected to rapid argon cooling heat treatment at 990-1010℃ for 15-25 minutes to obtain Ti2AlNb-based alloy sheet.

[0012] Furthermore, the atomic percentages in the ingot are as follows: Ti: 50-57%, Al: 20-25%, Nb: 22-27%.

[0013] Furthermore, the surface of the forging blank obtained in step 1 is coated with an anti-oxidation coating of 0.05mm to 0.1mm and covered with asbestos to prevent oxidation cracking during the forging process.

[0014] Furthermore, the forging blank obtained in step 1 has a microstructure consisting of a B2 phase matrix, a large number of acicular O phases and equiaxed α2 phases; the average grain size is 5 μm.

[0015] Furthermore, step 3 yields a Ti2AlNb-based alloy plate, the microstructure of which consists of equiaxed three-phase grains with a grain size of 1–5 μm.

[0016] Furthermore, in step 1, before each forging pass, the forging billet and the pad block that directly contacts the billet during forging are heated to a specified temperature and held at that temperature for 20-40 minutes before forging.

[0017] Furthermore, in step 1, the forging speed is 0.8–1.2 mm / s, and the forging passes for both forging phase zones are 3 times each, with each pass having a different direction and an included angle of approximately 90° to each other; the forging reduction in each pass is 30–50%; this makes the forging more uniform. Controlling the forging speed is crucial to avoid excessively fast reduction, which could lead to rapid fracture of the forging.

[0018] Furthermore, before rolling in step 2, the forged sheet is first chamfered with a chamfer size of R4mm; the billet is then placed in a heating furnace and heated to 980℃~1010℃, and held at that temperature for 5~25 minutes. This prevents stress concentration and cracking at the sharp corners of the sheet during hot rolling.

[0019] Furthermore, in step 2, the number of rolling passes is 5 to 9, and the rolling speed is 30 to 40% per pass, with the linear speed of the rolls being 0.12 to 0.18 m / s.

[0020] Furthermore, in step 3, the mixture is subjected to rapid argon cooling heat treatment at 1000℃ for 20 minutes.

[0021] The rolled sheet was subjected to rapid argon cooling heat treatment. After heat treatment, the microstructure consisted of equiaxed three-phase grains with a grain size of 2μm.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The preparation method of the present invention firstly refines the grains by inducing phase transformation through cooling forging in two phase regions with a large deformation, resulting in an average grain size of 5 μm; then, the alloy properties are further improved by hot rolling and heat treatment.

[0024] 2. The preparation method of the present invention reduces the cost of traditional hot-rolled Ti2AlNb-based alloy plates, eliminates the need for sealing welding, and reduces the cumbersome steps of encapsulated hot rolling.

[0025] 3. Through a series of experimental comparisons and appropriate heat treatment processes, this invention obtains high-performance Ti2AlNb-based alloy plates. Attached Figure Description

[0026] Figure 1 The microstructure of the forging billet in Example 1 is shown in (a) BSE; (b) BC image after EBSD treatment.

[0027] Figure 2 This is a macroscopic morphology diagram of the hot-rolled sheet material in Example 1;

[0028] Figure 3 The image shows the microstructure of the hot-rolled material after 1000℃ / 20min / argon rapid cooling heat treatment in Example 1. Detailed Implementation

[0029] Example 1

[0030] A method for preparing high-performance Ti2AlNb-based alloy plates includes the following steps:

[0031] Step 1: The ingot (atomic percentages of Ti: 53%, Al: 22%, Nb: 25%) is subjected to multi-directional near-isothermal forging in the α2+B2 phase region (1030℃), forging in 3 passes, each pass with a different direction and an included angle of approximately 90°; the forging speed is 1 mm / s, and the forging reduction in each pass is 45% to ensure more uniform forging; then, multi-directional near-isothermal forging is performed in the O+B2 phase region (950℃), forging in 3 passes, each pass... The forging directions are different, with included angles of approximately 90°; the forging speed is 1 mm / s, and the reduction per forging pass is 30%, making the forging more uniform; before each forging pass, the ingot and the pad block that directly contacts the ingot during forging are heated to a specified temperature and held for 30 minutes before forging to ensure the forging temperature and reduce the possibility of cracking in the forging; the deformation resistance is small and the reduction is high when forging in the α2+B2 phase region; while the deformation resistance is large and the reduction is low when forging in the low-temperature O+B2 phase region. During the forging process, cooling forging in the O+B2 phase region causes the microstructure to continuously undergo phase transformation and recrystallization, thereby reducing machining stress and homogenizing the microstructure and refining the grains. After forging, air cooling yields a forging blank with an average grain size of 5 μm (the microstructure morphology of the forging blank is shown in the figure). Figure 1 As shown, the microstructure consists of a B2 phase matrix, a large number of acicular O phases and equiaxed α2 phases; a 0.05 mm to 0.1 mm anti-oxidation coating is applied to the surface of the obtained forging billet, and asbestos is used for covering to prevent oxidation cracking during the forging process.

[0032] Step 2: Obtain a 9mm thick forged sheet from the forging billet through machining. Chamfer the sheet with a radius of 4mm (R4mm) to prevent stress concentration and cracking at sharp corners during hot rolling. Grind and polish the chamfered sheet, then spray it with a 0.05mm–0.1mm thick anti-oxidation coating to prevent excessive oxidation of the Ti2AlNb alloy surface.

[0033] Two 2mm thick 304 stainless steel plates, slightly larger than the forged plate, are selected. The forged plate is sandwiched in the middle, and the four corners of the two 304 stainless steel plates are fixed with rivets to form a billet. During rolling, this can prevent the Ti2AlNb alloy surface from directly contacting the rolls, which would cause the plate to cool down rapidly and thus increase the deformation resistance.

[0034] The billet is placed in a heating furnace and heated to the α2+O+B2 phase region (990℃) for hot rolling, and held at that temperature for 25 minutes to ensure the phase transformation, before the first rolling pass is performed.

[0035] With a reduction of 35% per pass and a roll linear speed of 0.15 m / s, sufficient dynamic recrystallization can be achieved under the conditions of large deformation and appropriate strain rate.

[0036] After the first rolling pass, the plate is held in the furnace for 10 minutes to ensure the rolling temperature and prevent cracking during rolling. After holding, the plate is rolled again with a reduction of 35%. This process is repeated, and the plate is then air-cooled.

[0037] After cooling to room temperature, the hot-rolled sheet can be directly removed without further machining.

[0038] Macroscopic morphology of the board as follows Figure 2 As shown, the total reduction of the plate was 88.8%, resulting in a high-quality Ti2AlNb-based alloy plate with a thickness of 1 mm and no surface cracks.

[0039] After hot rolling, the microstructure was subjected to rapid heat treatment at 1000℃ for 20 minutes using argon gas, as shown in the figure. Figure 3 As shown, the microstructure consists of equiaxed three-phase grains with a grain size of 2 μm.

[0040] Example 2

[0041] Step 1: The ingot (atomic percentages of Ti: 51%, Al: 22%, Nb: 27%) is subjected to multi-directional near-isothermal forging in the α2+B2 phase region (1040℃) in 3 passes, each pass having a different direction and an angle of approximately 90° between each other; the forging speed is 1.2 mm / s, and the forging reduction in each pass is 50% to make the forging more uniform; in the O+B2 phase region (960℃), multi-directional near-isothermal forging is performed in 3 passes, each pass having a different direction and an angle of approximately 90° between each other; the forging speed is 1.2 mm / s, and the forging reduction in each pass is 30%.

[0042] Step 2: Obtain a 9mm thick forged plate from the forging billet through machining, and then cut and chamfer it with a chamfer size of R4mm. Grind and polish the cut and chamfered plate, and spray it with an anti-oxidation coating with a thickness of 0.05mm to 0.1mm.

[0043] Select two pieces of 304 stainless steel with a thickness of 4mm and a size slightly larger than the forged plate. Clamp the forged plate in the middle and fix the four corners of the two pieces of 304 stainless steel with rivets to form a blank.

[0044] The billet is placed in a heating furnace and heated to the α2+O+B2 phase region (1010℃) for hot rolling, and held at that temperature for 25 minutes to ensure the phase transformation takes place before the first rolling pass is performed.

[0045] The reduction per pass is 30%, and the linear speed of the rolls is 0.18 m / s.

[0046] After the first rolling pass is completed, the material is returned to the furnace and kept warm for 10 minutes before rolling again with a reduction of 30%. This process is repeated, and the material is then air-cooled after rolling.

[0047] After cooling to room temperature, the hot-rolled sheet can be directly removed without further machining.

[0048] Example 3

[0049] Step 1: The ingot (atomic percentages of Ti: 55%, Al: 20%, Nb: 23%) is subjected to multi-directional near-isothermal forging in the α2+B2 phase region (1020℃) for 3 passes, each pass having a different direction and an angle of approximately 90° between each other; the forging speed is 1 mm / s, and the forging reduction in each pass is 50% to make the forging more uniform; in the O+B2 phase region (930℃), multi-directional near-isothermal forging is performed for 3 passes, each pass having a different direction and an angle of approximately 90° between each other; the forging speed is 1 mm / s, and the forging reduction in each pass is 30%.

[0050] Step 2: Obtain a 9mm thick forged plate from the forging billet through machining, and then cut and chamfer it with a chamfer size of R4mm. Grind and polish the cut and chamfered plate, and spray it with an anti-oxidation coating with a thickness of 0.05mm to 0.1mm.

[0051] Select two pieces of 304 stainless steel with a thickness of 3mm and a size slightly larger than the forged plate. Clamp the forged plate in the middle and fix the four corners of the two pieces of 304 stainless steel with rivets to form a blank.

[0052] The billet is placed in a heating furnace and heated to the α2+O+B2 phase region (1000℃) for hot rolling, and held at that temperature for 25 minutes to ensure the phase transformation takes place before the first rolling pass is performed.

[0053] The reduction per pass is 40%, and the linear speed of the rolls is 0.12 m / s.

[0054] After the first rolling pass is completed, the material is returned to the furnace for 10 minutes to maintain its temperature before rolling again, with a reduction of 40%. This process is repeated, and the material is then air-cooled after rolling.

[0055] After cooling to room temperature, the hot-rolled sheet can be directly removed without further machining.

[0056] The room temperature mechanical properties of the embodiments are shown in Table 1.

[0057] Table 1. Room temperature mechanical properties of the alloys in different embodiments

[0058]

[0059] Therefore, it can be seen that hot-rolled plates with good mechanical properties can be obtained in different embodiments.

[0060] Comparative Example 1

[0061] The preparation method of the Ti2AlNb-based alloy sheet in this comparative example is the same as that in Example 1, except that the rolling temperature is adjusted to the O+B2 phase region (950℃), and a better Ti2AlNb-based alloy sheet is obtained under the same deformation.

[0062] The Ti2AlNb-based alloy forging used in this embodiment is the same as that in Example 1.

[0063] Comparative Example 2

[0064] The preparation method of the Ti2AlNb-based alloy sheet in this comparative example is the same as that in Example 1, except that the rolling temperature is adjusted to the α2+B2 phase region (1020℃), and a better Ti2AlNb-based alloy sheet is obtained under the same deformation.

[0065] The Ti2AlNb-based alloy plate used in this embodiment is the same as that in Example 1.

[0066] Comparative Analysis 1

[0067] The results of comparing Example 1 with Comparative Example 1 and Comparative Example 2 are shown in Table 2.

[0068] Table 2. Room temperature mechanical properties of alloys under different conditions

[0069]

[0070] Therefore, it can be seen that in Example 1, the strength and elongation of the hot-rolled plate in the α2+O+B2 phase region at room temperature are superior to those of the hot-rolled plates in the O+B2 and α2+B2 phase regions. Therefore, the plate from Example 1 was selected for heat treatment, and the heat treatment results were analyzed and compared to obtain a high-performance Ti2AlNb-based alloy plate.

[0071] Comparative Analysis 2

[0072] Then, using the same Ti2AlNb-based alloy sheet as in Example 1, the rolled sheet was subjected to rapid cooling at 950℃ / 20min / argon gas, 1000℃ / 20min / argon gas, 1020℃ / 20min / argon gas, 950℃ / 60min / argon gas, 1000℃ / 60min / argon gas, and 1020℃ / 60min / argon gas respectively.

[0073] The mechanical properties of the samples subjected to heat treatment at 950℃ / 20min / furnace cooling, 1000℃ / 20min / furnace cooling, 1020℃ / 20min / furnace cooling, 950℃ / 60min / furnace cooling, 1000℃ / 60min / furnace cooling, and 1020℃ / 60min / furnace cooling are compared in Table 3.

[0074] Table 3. Room temperature mechanical properties of the plates under different heat treatment processes

[0075]

[0076]

[0077] Argon rapid cooling heat treatment resulted in a significantly better room temperature elongation and superior overall performance compared to furnace cooling heat treatment. The elongation after 1000℃ / 20min / argon rapid cooling heat treatment was 13.8%, which is 3.7 times that after 1000℃ / 20min / furnace cooling. The shorter treatment time prevents grain growth, leading to better mechanical properties; therefore, 20min / argon rapid cooling heat treatment generally outperforms 60min / argon rapid cooling heat treatment. Furthermore, the elongation of argon rapid cooling heat treatment in the α2+O+B2 phase region (1000℃) was superior to that in the O+B2 phase region (950℃) and the α2+B2 phase region (1020℃).

[0078] Therefore, high-performance Ti2AlNb-based alloy plates can be obtained by hot-rolling the α2+O+B2 phase region plate and then subjecting it to rapid heat treatment at 1000℃ for 20 min with argon.

[0079] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A method for preparing high-performance Ti2AlNb-based alloy sheet material, characterized by: The method comprises the following steps: Step 1, multi-directional near isothermal forging is performed on the ingot in the α2+B2 phase region at 1020-1040℃ and the O+B2 phase region at 930-960℃, and the forged blank is obtained after air cooling; Step 2, before rolling, the forged blank is first chamfered, and the chamfer size is R4 mm; the forged blank is clamped in the middle by two pieces of 304 stainless steel, and the two pieces of 304 stainless steel are fixed at four corners by rivets to form a blank, and hot rolling is performed in the α2+O+B2 phase region at 980-1010℃; the hot-rolled alloy plate is obtained after air cooling and removal of the stainless steel without machining; Step 3, argon rapid cooling heat treatment is performed on the hot-rolled alloy plate at 990-1010℃, and the Ti2AlNb-based alloy plate is obtained after argon rapid cooling heat treatment for 15-25 min.

2. The method according to claim 1, wherein the method comprises the following steps: The atomic percentage in the ingot is as follows: Ti: 50-57%, Al: 20-25%, and Nb: 22-27%. ​ 3. The method of claim 1, wherein the method further comprises: The surface of the forged blank obtained in step 1 is coated with 0.05-0.1 mm of anti-oxidation paint, and is wrapped with asbestos. ​ 4. The method of claim 1, wherein the high-performance Ti2AlNb-based alloy sheet is prepared by the following steps: The microstructure of the forged blank obtained in step 1 is composed of a B2 phase matrix, a large number of needle-shaped O phases and equiaxed α2 phases. The average grain size is 5 μm. ​ 5. The method of claim 1, wherein the high-performance Ti2AlNb-based alloy sheet is prepared by the following steps: The Ti2AlNb-based alloy plate obtained in step 3 is composed of equiaxed three-phase grains, and the grain size is 1-5 μm. ​ 6. The method of claim 1, wherein the high-performance Ti2AlNb-based alloy sheet is prepared by the following steps: In step 1, the forged blank and the forging device are heated to the specified temperature and are kept for 20-40 min before each pass of forging. ​ 7. The method of claim 1, wherein the high-performance Ti2AlNb-based alloy sheet is prepared by the following steps: In step 1, the forging speed is 0.8-1.2 mm / s, the forging passes are 6, the directions of each pass are different and the included angles are 90°, and the reduction of each pass is 30-50%. ​ 8. The method of claim 1, wherein the high-performance Ti2AlNb-based alloy sheet is prepared by the following steps: In step 2, before rolling, the forged blank is first chamfered, and the chamfer size is R4 mm; the blank is placed in a heating furnace and is heated to 980-1010℃ and is kept for 5-25 min. ​ 9. The method of claim 1, wherein the high-performance Ti2AlNb-based alloy sheet is prepared by the following steps: In step 2, the rolling passes are 5-9, the reduction of each pass in step 2 is 30-40%, and the linear speed of the roller is 0.12-0.18 m / s. ​ 10. The method of claim 1, wherein the high-performance Ti2AlNb-based alloy sheet is prepared by the following steps: In step 3, argon rapid cooling heat treatment is performed at 1000℃ for 20 min. ​

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