Low-temperature superplastic TiAl alloy with double-phase fine grain structure and preparation method of low-temperature superplastic TiAl alloy
Through the high-energy ball milling and vacuum hot press sintering method of Ti-mAl-nX alloy, a low-temperature superplastic TiAl alloy was prepared, which solved the problem of hot processing of TiAl alloys, achieved fine crystal structure and high superplastic properties, simplified the process flow, and reduced energy consumption and pollution.
Patent Information
- Application Number
- CN202510473104.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-16
- Publication Date
- 2025-07-29
AI Technical Summary
The existing TiAl alloy has poor thermal processing deformation capability, narrow forming process window, high forming difficulty and high cost. The existing superplastic forming process is complicated and it is difficult to achieve fine crystal structure.
Using the chemical composition of Ti-mAl-nX alloy, a TiAl alloy with an equiaxed biphasic fine crystal structure was prepared by high-energy ball milling and vacuum hot pressing sintering, which simplifies the process flow, reduces the superplastic forming temperature, and increases the strain rate.
The superplastic deformation of TiAl alloy at low temperature is achieved, dense, poreless fine crystal structure is obtained, the preparation process is simplified, energy consumption and pollution are reduced, and superplastic properties are improved.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of TiAl alloy processing and preparation, and particularly relates to a low-temperature superplastic TiAl alloy with a duplex fine-grained structure and a preparation method thereof. Background Art
[0002] With the development of the new generation of aero-engines towards the direction of light weight and low fuel consumption, the demand for lightweight and high-performance high-temperature materials is increasing day by day. TiAl alloy is considered to be an ideal high-temperature structural material for aero-engines because of its advantages such as low density, high specific strength, good oxidation resistance and excellent creep resistance. Like most intermetallic compounds, TiAl alloy has intrinsic brittleness, is difficult to machine, and maintains a long-range ordered structure from room temperature to near the melting point. The grain boundary migration rate of the ordered phase is slow, and recrystallization is difficult. Therefore, the hot working deformation ability is poor, the forming process window is narrow, and the forming is difficult and costly.
[0003] The superplastic forming process (SPF) is a "new type of high-efficiency and low-cost process". Since the material is in a sticky state under superplastic conditions, there is no obvious necking and the forming pressure is small, so superplastic forming is especially suitable for forming materials with poor mechanical properties and difficult processing. Therefore, it is of great research value to develop superplastic TiAl alloys.
[0004] Generally speaking, a fine and uniform microstructure is a prerequisite for obtaining superplasticity. Therefore, fine grain preparation is the most critical step to achieve superplasticity. The general steps of the process for obtaining a fine-grained structure of TiAl alloy at present are: preparing the alloy → hot working / heat treatment operation → obtaining a fine-grained microstructure. For example, after Imayev et al. obtained a Ti-43.7Al-4.2Nb-0.5Mo-0.2B-0.2C ingot by vacuum arc remelting, the ingot was forged and heat-treated alternately for many times, and the microstructure of the γ-TiAl+α2-Ti3Al duplex alloy was effectively refined, realizing superplasticity (V.M. Imayev, A.A. Ganeev, R.M. Imayev, Principles of achieving superior superplastic properties in intermetallic alloys based on γ-TiAl+α2-Ti3Al, Intermetallics 101(2018)81-86); Sun et al. ball-milled Ti, Al, Nb elemental powders and 1wt% stearic acid for 20h and then obtained a Ti2AlC / TiAl composite material by hot pressing sintering. After isothermal forging and annealing, a fine and uniform microstructure was obtained, making it at 1000°C, 1×10 -5 s -1Superplastic behavior occurs under these conditions (H.Sun, X.Li, P.Zhang, et al., The microstructure and tensile properties of the Ti2AlC reinforced TiAl composites fabricated by powder metallurgy, Materials Science and Engineering: A 611(2014)257-262.). These processes for achieving superplasticity of TiAl alloys are relatively cumbersome and require multiple heat treatments and hot workings on the initially obtained alloy to obtain a fine-grained structure. The conditions for achieving superplasticity of the obtained TiAl alloys are relatively harsh and the superplasticity needs to be improved. Summary of the Invention
[0005] In view of the shortcomings of existing TiAl alloy preparation methods, such as poor hot working deformation ability, narrow forming process window, great forming difficulty and high cost, the purpose of the present invention is to provide a low-temperature superplastic TiAl alloy with a dual-phase fine-grained structure and a preparation method thereof. By optimizing the process and eliminating subsequent heat treatment and hot working, a fine-grained structure is also obtained, and the superplastic test temperature is reduced, the strain rate is increased, and the superplastic performance is improved.
[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:
[0007] A low-temperature superplastic TiAl alloy with a dual-phase fine-grained structure. The chemical composition of the TiAl alloy (Ti-mAl-nX) in atomic percentage is as follows: Al is 35-55%, X is 1-10%, and the balance is Ti; X is Cr and / or Nb.
[0008] Furthermore, the TiAl alloy has an equiaxed two-phase fine-grained structure, which consists of a fine-grained γ-TiAl matrix phase and a fine-grained α2-Ti3Al second phase, and the α2-Ti3Al fine-grained structure is uniformly distributed in the γ-TiAl matrix.
[0009] Furthermore, the TiAl alloy exhibits good superplasticity in the temperature range of 800-900°C.
[0010] Furthermore, the method for preparing the low-temperature superplastic TiAl alloy having a dual-phase fine-grained structure comprises the following steps:
[0011] (1) Raw material preparation: The raw materials are aluminum powder, titanium powder and X powder (Cr powder and / or Nb powder);
[0012] (2) High-energy ball milling: Weigh each raw material according to the chemical composition of the TiAl alloy, mix them, and obtain mechanically alloyed powder after high-energy ball milling;
[0013] (3) Vacuum hot pressing and sintering: Carry out vacuum hot pressing and sintering on the mechanically alloyed powder obtained in step (2), with a sintering temperature of 1000 - 1350 °C, a sintering pressure of 30 - 60 MPa, a sintering time of 30 - 90 min, and a vacuum degree of above 6.67×10 -3 Pa. After sintering, the low-temperature superplastic TiAl alloy with a duplex fine-grained structure is obtained.
[0014] Furthermore, in step (1), the particle size of the raw material powder is 50 - 100 μm.
[0015] Furthermore, in step (2), the particle size range of the mechanically alloyed powder is 3 - 5 μm.
[0016] Furthermore, during the high-energy ball milling process in step (2), the ball milling time is 15 - 50 h (preferably 25 - 35 h), the ball-to-material mass ratio is (10 - 20):1, and the ball milling speed is (400 - 500) r / min; among which the grinding ball material is GCr15 steel balls, and the grinding balls are mixed with two sizes of steel balls. The size of the large steel balls is φ15 mm, the size of the small steel balls is φ10 mm, and the quantity ratio of the large steel balls to the small steel balls is 1:(2 - 4).
[0017] Furthermore, during the high-energy ball milling process in step (2), in order to prevent the ball milling tank from heating up, the machine is stopped for cooling for 2 h every 5 h, and 2 - 3 drops of alcohol are added as a process control agent to prevent excessive cold welding of the powder during the mechanical alloying process; in order to avoid or reduce air pollution as much as possible, all operations such as powder grinding, transportation, and storage are carried out under the protection of inert gas Ar.
[0018] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:
[0019] 1. By adjusting the composition and proportion of the TiAl alloy and using a simple one-step powder metallurgy method, the present invention can obtain a TiAl alloy with a duplex fine-grained equiaxed structure (fine-grained γ-TiAl phase + α2-Ti3Al phase structure), improve the strain rate of superplastic forming, reduce the temperature of superplastic forming, and also have high superplasticity.
[0020] 2. The present invention only prepares a fine and uniform structure through a single powder metallurgy method, that is: mechanical alloying + vacuum hot pressing and sintering. It is a near-net-shape forming method with uniform composition, no tissue defects such as porosity and segregation. The prepared alloy has no pores, high density, and stable structure. This process does not require additional hot working or heat treatment, simplifies the process, and is a low-energy-consuming and low-pollution TiAl superplastic forming method.
[0021] 3. The present invention provides a new reference for realizing the superplasticity of TiAl alloys by powder metallurgy, which is of great significance for promoting the wide application of TiAl alloys in aerospace. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 It is the SEM microstructural morphology of the TiAl alloy obtained after sintering with ball milling for 25 h in Example 1.
[0023] Figure 2 It is the SEM microstructural morphology of the TiAl alloy obtained after sintering with ball milling for 30 h in Example 2.
[0024] Figure 3 It is the SEM microstructural morphology of the TiAl alloy obtained after sintering with ball milling for 35 h in Example 3.
[0025] Figure 4 It is the tensile curve of the sintered TiAl alloy after ball milling for 25 h under different temperatures and 10 -3 s -1 conditions.
[0026] Figure 5 It is the tensile curve of the sintered TiAl alloy after ball milling for 30 h under different temperatures and 10 -3 s -1 conditions.
[0027] Figure 6 It is the tensile curve of the sintered TiAl alloy after ball milling for 35 h under different temperatures and 10 -3 s -1 conditions.
[0028] Figure 7 It is the tensile curve of the sintered TiAl alloy after ball milling for 35 h under different temperatures and 10 -4 s -1 conditions. DETAILED DESCRIPTION OF THE INVENTION
[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be described in detail below with reference to the drawings and embodiments.
[0030] The TiAl alloy with low-temperature superplasticity prepared by the present invention uses Ti powder, Al powder and X powder (Cr powder and / or Nb powder) as raw materials, and is subjected to mechanical alloying treatment by high-energy ball milling. The obtained powder after treatment is then vacuum hot-pressed and sintered to obtain an alloy with a fine-grained α2-Ti3Al + γ-TiAl structure based on γ-TiAl. The fine α2-Ti3Al is evenly distributed in the γ-TiAl matrix, and the sintered alloy is very dense and pore-free. Finally, the alloy achieves good superplasticity at a relatively low experimental temperature.
[0031] In the following examples, the particle size of the raw material powder is 50 - 100 μm.
[0032] In the following examples, when performing high - energy ball milling, two sizes of steel balls are used in a mixed ratio. The large steel balls have a size of φ15 mm, the small steel balls have a size of φ10 mm, and the quantity ratio of large steel balls to small steel balls is 1:(2 - 4).
[0033] Example 1:
[0034] This example provides a dual - phase fine - grained TiAl alloy with low - temperature superplasticity, and its preparation process is as follows:
[0035] 1. Prepare raw material powder and grinding balls:
[0036] Weigh the raw material powder, specifically: 49.728 g of Ti elemental powder, 27.972 g of Al elemental powder, 2.268 g of Cr elemental powder, 4.032 g of Nb elemental powder (total 84 g); weigh 840 g of GCr15 steel balls;
[0037] 2. High - energy ball milling: Load the weighed raw material powder and grinding balls into the ball - milling tank for high - energy ball - milling treatment. The ball milling is carried out under Ar gas protection. The ball - milling speed is 450 r / min, the ball - milling time is 25 h, stop and cool for 2 h every 5 h, and add 2 - 3 drops of alcohol as a process control agent to prevent excessive cold welding of the powder during mechanical alloying. Finally, a mechanically alloyed powder with a particle size of 3 - 5 μm is obtained.
[0038] 3. Load the obtained mechanically alloyed powder into a graphite mold for vacuum hot - pressing sintering. The heating is divided into three stages: heat up to 800 °C at a rate of 20 °C / min, then heat up to 1100 °C at a rate of 10 °C / min, and then heat up to 1200 °C at a rate of 5 °C / min. Keep it at 1200 °C for 60 min for sintering, the sintering pressure is 40 MPa, and the vacuum degree is 6.67×10 -3 Pa. After sintering, cool it to room temperature in the furnace, and an equiaxed dual - phase fine - grained TiAl alloy is obtained. This alloy has γ - TiAl as the matrix, and fine - grained α2 - Ti3Al is uniformly distributed in the γ - TiAl fine - grained structure, as Figure 1 shown.
[0039] Example 2:
[0040] This example provides a dual - phase fine - grained TiAl alloy with low - temperature superplasticity, and its preparation process is as follows:
[0041] 1. Prepare raw material powder and grinding balls:
[0042] Weigh the raw material powders, specifically: 49.728 g of Ti elemental powder, 27.972 g of Al elemental powder, 2.268 g of Cr elemental powder, 4.032 g of Nb elemental powder (84 g in total); weigh 840 g of GCr15 steel balls;
[0043] 2. High-energy ball milling: Load the weighed raw material powders and grinding balls into the ball mill for high-energy ball milling. The ball milling is carried out under the protection of Ar gas. The ball milling speed is 450 r / min, and the high-energy ball milling time is 30 h. Stop and cool for 2 h every 5 h, and add 2 - 3 drops of alcohol as a process control agent to prevent excessive cold welding of the powders during mechanical alloying. Finally, a mechanized alloy powder with a particle size of 3 - 5 μm is obtained.
[0044] 3. Fill the obtained mechanical alloy into a graphite mold for vacuum hot pressing and sintering. The heating-up is divided into three stages: heat up to 800 °C at a rate of 20 °C / min, then heat up to 1100 °C at a rate of 10 °C / min, and finally heat up to 1200 °C at a rate of 5 °C / min. Keep it at 1200 °C for insulation sintering for 60 min. The sintering pressure is 40 MPa, and the vacuum degree is 6.67×10-3 Pa. After sintering, cool it in the furnace to room temperature, and an equiaxed duplex fine-grained TiAl alloy is obtained. This alloy is based on γ-TiAl, and fine-grained α2-Ti3Al is uniformly distributed in the γ-TiAl fine-grained structure, as Figure 2 shown.
[0045] Example 3:
[0046] This example provides a preparation method of a duplex fine-grained TiAl alloy with low-temperature superplasticity. The specific process is as follows:
[0047] 1. Prepare raw material powders and grinding balls:
[0048] Weigh the raw material powders, specifically: 49.728 g of Ti elemental powder, 27.972 g of Al elemental powder, 2.268 g of Cr elemental powder, 4.032 g of Nb elemental powder (84 g in total); weigh 840 g of GCr15 steel balls;
[0049] 2. High-energy ball milling: Load the weighed raw material powders and grinding balls into the ball mill for high-energy ball milling. The ball milling is carried out under the protection of Ar gas. The ball milling speed is 450 r / min, and the ball milling time is 35 h. Stop and cool for 2 h every 5 h, and add 2 - 3 drops of alcohol as a process control agent to prevent excessive cold welding of the powders during mechanical alloying. Finally, a mechanized alloy powder with a particle size of about 3 - 5 μm is obtained.
[0050] 3. The obtained mechanically alloyed powder was filled into a graphite mold for vacuum hot pressing and sintering. The heating process was divided into three stages: heating to 800 °C at a rate of 20 °C / min, then to 1100 °C at a rate of 10 °C / min, and finally to 1200 °C at a rate of 5 °C / min. It was held for sintering at 1200 °C for 60 min, with a sintering pressure of 40 MPa and a vacuum degree of 6.67×10-3 Pa. After sintering, it was cooled to room temperature in the furnace, and an equiaxed duplex fine-grained TiAl alloy was obtained. This alloy had a γ-TiAl matrix, and fine-grained α2-Ti3Al was uniformly distributed in the γ-TiAl fine-grained structure, as Figure 3 shown.
[0051] The performance of the TiAl alloy samples prepared in the above examples was tested, as follows:
[0052] Experimental test 1:
[0053] The TiAl alloy sample obtained in Example 1 was made into a tensile specimen and subjected to tensile tests at deformation temperatures of 800 °C, 850 °C, and 900 °C, and a strain rate of 10 -3 s -1 .
[0054] Experimental test 2:
[0055] The TiAl alloy sample obtained in Example 2 was made into a tensile specimen and subjected to tensile tests at deformation temperatures of 800 °C, 850 °C, and 900 °C, and a strain rate of 10 -3 s -1 .
[0056] Experimental test 3:
[0057] The TiAl alloy sample obtained in Example 3 was made into a tensile specimen and subjected to tensile tests at deformation temperatures of 800 °C, 850 °C, and 900 °C, and a strain rate of 10 -3 s -1 .
[0058] Experimental test 4:
[0059] The TiAl alloy sample obtained in Example 3 was made into a tensile specimen and subjected to tensile tests at deformation temperatures of 800 °C, 850 °C, and 900 °C, and a strain rate of 10 -4 s -1 .
[0060] A systematic study was conducted on the microstructure evolution law and high-temperature tensile properties of the TiAl alloy prepared by mechanical alloying + vacuum hot pressing sintering. The main results are as follows:
[0061] Figures 1 - 3SEM microstructures of Ti-Al-Cr-Nb mixed powders after ball milling and sintering for different ball milling times (25 h, 30 h, 35 h). Microscopic analysis shows that the alloy morphology is mainly composed of grayish-black γ-TiAl matrix phase and white α2-Ti3Al secondary phase. As the ball milling time extends from 25 h to 35 h, the secondary phase particle size shows a significant refinement trend, with the average particle size decreasing from about 1 μm to below 0.5 μm, and the distribution uniformity is significantly improved. At the same time, the matrix phase grain size is refined synchronously, forming a uniform fine-grained duplex microstructure, which provides favorable microscopic tissue conditions for subsequent superplastic deformation.
[0062] Figures 4 - 6 The high-temperature tensile properties of alloy specimens with different ball milling times were compared in the temperature range of 800 - 900 °C and at a strain rate of 1×10 -3 s -1 . When the ball milling time was 25 h, the material did not show obvious plastic deformation at 800 °C, and the elongation after fracture at 850 °C and 900 °C was 25% and 47% respectively. After extending the ball milling time to 30 h, the material showed plastic deformation ability in the range of 800 - 900 °C, and the elongation at 900 °C reached 118%, showing typical superplastic characteristics. When the ball milling time was further increased to 35 h, the superplastic temperature window expanded to 850 - 900 °C, and the corresponding elongation increased to 119% and 210% respectively. It should be noted that when the strain rate was reduced to 1×10 -4 s -1 under the ball milling condition of 35 h (see Figure 7 ), the material showed significant superplasticity in the range of 800 - 900 °C, and the elongation reached 165%, 280% and 320% respectively, showing excellent strain rate sensitivity.
[0063] This invention proves that significant superplastic deformation of TiAl alloy can be achieved by optimizing the mechanical alloying process parameters and cooperating with appropriate tensile conditions. This performance improvement is mainly attributed to the synergistic effect of fine grain strengthening effect and dynamic recrystallization mechanism. The research results provide an important theoretical basis for the superplastic forming technology of TiAl-based alloys.
[0064] The above embodiments only represent several implementation modes of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.
Claims
1. A low-temperature superplastic TiAl alloy with a duplex fine-grained structure, characterized in that: In atomic percentage, the chemical composition of the TiAl alloy is as follows: Al is 35 - 55%, X is 1 - 10%, and the balance is Ti; X is Cr and / or Nb.
2. The low-temperature superplastic TiAl alloy with a duplex fine-grained structure according to claim 1, characterized in that: The TiAl alloy has an equiaxed duplex fine-grained structure, which consists of a fine-grained γ-TiAl matrix phase and a fine-grained α2-Ti3Al second phase, and the α2-Ti3Al fine-grained structure is uniformly distributed in the γ-TiAl matrix.
3. The low-temperature superplastic TiAl alloy with a duplex fine-grained structure according to claim 1, characterized in that: The TiAl alloy exhibits good superplasticity in the temperature range of 800 - 900 °C.
4. The preparation method of the low-temperature superplastic TiAl alloy with a duplex fine-grained structure according to claim 1, characterized in that: The method comprises the following steps: (1) Raw material preparation: The raw materials are aluminum powder, titanium powder, and X powder (Cr powder and / or Nb powder); (2) High-energy ball milling: Weigh each raw material according to the chemical composition of the TiAl alloy, mix them, and obtain mechanically alloyed powder after high-energy ball milling; (3) Vacuum hot pressing sintering: The mechanically alloyed powder obtained in step (2) is subjected to vacuum hot pressing sintering at a sintering temperature of 1000 - 1350 °C, a sintering pressure of 30 - 60 MPa, a sintering time of 30 - 90 min, and a vacuum degree of 6.67×10 -3 Pa or more. After sintering, the low-temperature superplastic TiAl alloy with a duplex fine-grained structure is obtained.
5. The preparation method of the low-temperature superplastic TiAl alloy with a duplex fine-grained structure according to claim 4, characterized in that: In step (1), the particle size of the raw material powders is all 50 - 100 μm.
6. The preparation method of the low-temperature superplastic TiAl alloy with a duplex fine-grained structure according to claim 4, characterized in that: In step (2), the particle size range of the mechanically alloyed powder is 3 - 5 μm.
7. The preparation method of the low-temperature superplastic TiAl alloy with a duplex fine-grained structure according to claim 4, characterized in that: During the high-energy ball milling process in step (2), the ball milling time is 15 - 50 h (preferably 25 - 35 h), the ball-to-material mass ratio is (10 - 20):1, and the ball milling speed is (400 - 500) r / min; among which the grinding ball material is GCr15 steel balls, and the grinding balls are mixed with two sizes of steel balls. The size of the large steel balls is φ15 mm, the size of the small steel balls is φ10 mm, and the quantity ratio of the large steel balls to the small steel balls is 1:(2 - 4).
8. The preparation method of the low-temperature superplastic TiAl alloy with a duplex fine-grained structure according to claim 7, characterized in that: During the high-energy ball milling process in step (2), in order to prevent the ball milling tank body from heating up, it is stopped for cooling for 2 h every 5 h, and 2 - 3 drops of alcohol are added as a process control agent to prevent excessive cold welding of the powder during the mechanical alloying process; in order to avoid or reduce air pollution as much as possible, all operations such as powder grinding, transportation, and storage are carried out under the protection of inert gas Ar.