High-performance TiAl alloy based on periodic stacking fault strengthening and preparation method of high-performance TiAl alloy

Abstract

According to the high-performance TiAl alloy based on periodic stacking fault strengthening and the preparation method of the high-performance TiAl alloy based on periodic stacking fault strengthening, proper alpha2 / gamma double-phase TiAl alloy components are selected, a proper method is adopted for preparing a block material, and the microscopic structure of the TiAl alloy is regulated and controlled to be a fully lamellar structure through a post-heat treatment process; and a periodic stacking fault structure is induced to be generated in the full-lamellar TiAl alloy by adopting a stress induction method. Compared with the prior art, the method has the advantages that the microscopic structure of the TiAl alloy is further optimized, and the mechanical property of the TiAl alloy is improved.

Description

Technical Field

[0001] The invention relates to a lightweight metal structural material, in particular to a high-performance TiAl alloy based on periodic stacking fault strengthening and a preparation method thereof. Background Art

[0002] The development of high thrust-to-weight ratio, high service temperature and long life aircraft engines is of great significance to promoting the development of the national economy and enhancing the country's core competitiveness. The breakthrough of key materials will directly promote the upgrading of aircraft engines, and then promote the progress of the aviation industry. TiAl alloy, as the only lightweight metal structural material that can be used for a long time in an oxidizing environment above 600°C, has successfully replaced nickel-based high-temperature alloys in aircraft engine low-pressure turbine blades, significantly improving the engine's propulsion efficiency, and achieving 20% ​​fuel saving, 50% noise reduction, and NO reduction. x However, the poor room temperature plasticity and low high temperature strength of TiAl alloys have severely limited their wider application in aircraft engines. Improving the strength, plasticity and service temperature of TiAl alloys can promote their application in compressors, medium / high pressure turbine blades and other occasions, which will help to fully realize the weight reduction and efficiency improvement of aircraft engines.

[0003] Improving the mechanical properties of TiAl alloys through traditional methods such as composition control and heat treatment has reached a bottleneck. Microstructure (dislocation, stacking fault, etc.) control has become another means to further improve the performance of TiAl alloys. The periodic stacking fault structure is a new microstructure that helps to improve the room temperature and high temperature mechanical properties of the material (X. Zhang, C. Li, Q. Wang, M. Zheng, Z. Ye, J. Gu, Unusual ordered phases with long periodic stacking structures in an additively manufactured TiAl alloy, Mater. Res. Lett. 8 (12), 454–461 (2020).).

[0004] However, it is currently difficult to prepare a full-lamellar TiAl alloy containing a periodic stacking fault structure by ordinary processing methods (such as heat treatment, etc.). The present invention develops a new processing method based on the principle of stacking fault formation to induce a periodic stacking fault structure in TiAl alloy, providing a basis for improving the mechanical properties of TiAl alloy. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a high-performance TiAl alloy with stress-induced periodic stacking faults and a preparation method thereof. The method can obtain a full-lamellar TiAl alloy with a periodic stacking fault structure, so that the material has excellent comprehensive mechanical properties.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] In one aspect, the present invention provides a method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening, comprising the following steps:

[0008] (1) Preparation of TiAl alloy with full lamellar structure;

[0009] (2) Applying stress to the TiAl alloy induces the formation of a periodic stacking fault structure with a strengthening effect in the TiAl alloy, thereby obtaining a high-performance TiAl alloy.

[0010] Furthermore, the process for preparing the TiAl alloy is any one of arc melting, powder metallurgy, and additive manufacturing.

[0011] Furthermore, the TiAl alloy with full lamellar structure is prepared by the following method:

[0012] Firstly, an α2 / γ dual-phase TiAl alloy is prepared, and then heat-treated to form a full lamellar structure;

[0013] Alternatively, a TiAl alloy with a full lamellar structure can be directly prepared according to a selected alloy ratio by using additive manufacturing or other methods.

[0014] Furthermore, the heat treatment temperature should be higher than the high-temperature α phase transformation temperature in the TiA1 alloy (i.e., the temperature at which the α phase is transformed), and the material should be kept warm for a sufficient time (usually not less than 0.5 h) so that the material can be completely transformed into the α phase at high temperature, followed by furnace cooling or air cooling to obtain a TiAl alloy structure with a full lamellar structure.

[0015] Furthermore, the Al content of the α2 / γ dual-phase TiAl alloy is between 42 and 50 at.%, and the room temperature microstructure is mainly composed of α2 and γ phases.

[0016] Furthermore, the microstructure of the TiAl alloy after post-heat treatment is a full lamellar structure.

[0017] Furthermore, the treatment temperature when applying stress is lower than the recrystallization temperature of the TiAl alloy. More preferably, the treatment temperature when applying stress is between room temperature and 800°C, and the temperature selected here should ensure that the whole layer of TiAl alloy does not recrystallize at this temperature.

[0018] Furthermore, when stress is applied, the original structure of the TiAl alloy after post-heat treatment is divided into the following two cases:

[0019] a) applying a uniaxial tensile or compressive stress with an angle of 30 to 60° to the lamellar structure to a polylamellar twin TiAl alloy having a single lamellar cluster or a directional lamellar TiAl alloy having a directional solidification condition;

[0020] b) For a polycrystalline TiAl alloy, a uniaxial tensile or compressive stress is applied to the material three times, and the angle between the second and third applied stresses and the previous stress is between 30 and 60 degrees, and the directions of the second applied stress and the third applied stress satisfy: the two applied stresses are applied along two mutually perpendicular planes. For example, taking the direction of the first applied stress along the x-axis as an example, the second applied stress can be in the xy plane and at an angle of 30 to 60 degrees to the x-axis, and the third applied stress can be in the xz plane and at an angle of 30 to 60 degrees to the x-axis.

[0021] Furthermore, in the stress inducing method, each uniaxial tensile or compressive stress is maintained for no less than 0.5 h.

[0022] Furthermore, the stress of uniaxial tension or compression is 0.4 to 0.8σ y , σ y is the yield strength of the material at the current temperature.

[0023] On the other hand, the present invention also provides a high-performance TiAl alloy based on periodic stacking fault strengthening, which is prepared by using any of the preparation methods described above.

[0024] Compared with the prior art, the present invention forms a special periodic stacking fault structure in a full-lamellar TiAl alloy in a stress-induced manner, provides a new method for optimizing the microstructure of TiAl alloy and developing high-performance TiAl alloy, and makes up for the shortcomings of current research. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of stress-induced periodic stacking faults in TiAl alloy;

[0026] Figure 2 The room temperature tensile properties and comparison diagram of TiAl alloy containing periodic stacking fault structure;

[0027] Figure 3 is the periodic stacking fault structure formed in the sample in Example 1;

[0028] Figure 4 is the periodic stacking fault structure formed in the sample in Example 2;

[0029] Figure 5 There is no periodic stacking fault structure in the sample layer structure in Comparative Example 1;

[0030] Figure 6 There is no periodic stacking fault structure in the sample layer structure in Comparative Example 2; DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0032] In order to improve the mechanical properties of TiAl alloy, the present invention forms a special periodic stacking fault structure in the full-lamellar TiAl alloy in a stress-induced manner, which provides a new method for optimizing the microstructure of TiAl alloy and developing high-performance TiAl alloy, making up for the shortcomings of current research. Figure 2 It can be seen that when the TiAl alloy contains a periodic stacking fault structure, it has a significant improvement in strength and plasticity compared to the TiAl alloy without a periodic stacking fault structure.

[0033] In the following examples, raw materials or processing techniques, unless otherwise specified, are conventional commercially available raw materials or conventional processing techniques in the art.

[0034] Example 1

[0035] This embodiment provides a method for preparing a TiAl alloy based on periodic stacking fault strengthening, comprising the following steps:

[0036] Step S1, selecting the alloy composition as Ti-47Al-2Cr-2Nb alloy;

[0037] Step S2, using laser additive manufacturing to directly prepare a block sample with oriented lamellar structure by adjusting process parameters (laser power 400 W, scanning speed 4 mm / s, layer height 0.3 mm);

[0038] Step S3, applying a tensile stress of 400 MPa at an angle of 45° to the sheet layer to the sample at room temperature, and maintaining the tensile stress for 0.5 h.

[0039] Figure 1 Flow chart of TiAl alloy preparation based on periodic stacking fault strengthening.

[0040] Figure 3The microstructure of the TiAl alloy sample shows that a periodic stacking fault structure appears inside the lamellar layer. This example proves that a periodic stacking fault structure can be induced in a directional lamellar TiAl alloy or a polylamellar twin TiAl alloy by applying stress only once.

[0041] Example 2

[0042] This embodiment provides a method for preparing a TiAl alloy based on periodic stacking fault strengthening, comprising the following steps:

[0043] Step S1, selecting the alloy composition as Ti-47Al-2Cr-2Nb alloy;

[0044] Step S2, preparing a TiAl alloy block by arc melting (melting current 200A);

[0045] Step S3, post-heat treatment (1350° C., 30 min) is performed to adjust the microstructure of the TiAl alloy to a full lamellar structure;

[0046] Step S4, applying 300 MPa tensile stress to the sample at 800°C and maintaining it for 1 hour.

[0047] Step S5, applying 300 MPa tensile stress to the sample at 800°C, with the tensile stress direction being at an angle of 45° to the tensile stress direction in S4, and maintaining for 1 hour;

[0048] Step S6, continue to apply 300 MPa tensile stress to the sample at 800°C, with the tensile stress direction being at an angle of 45° to the tensile stress direction in S4 (and being in two perpendicular planes to the tensile stress direction in S5), and maintain for 1 hour.

[0049] Figure 1 Flow chart of TiAl alloy preparation based on periodic stacking fault strengthening.

[0050] Figure 4 The microstructure of the TiAl alloy sample is shown in Figure 1. It can be observed that a periodic stacking fault structure appears inside the lamella. This embodiment proves that a large number of periodic stacking fault structures can be generated in polycrystalline TiAl alloy by using a multi-step stress induction method.

[0051] Comparative Example 1:

[0052] According to steps S1 and S2 in Example 1, a TiAl alloy block with oriented lamellar characteristics was prepared by laser additive manufacturing, but no stress was applied, and no periodic stacking fault structure was found in its microstructure.

[0053] Figure 5 It is the lamellar structure of TiAl alloy under this condition, and there is no periodic stacking fault structure inside the lamellar structure.

[0054] Comparative Example 2:

[0055] A polycrystalline TiAl alloy sample was prepared according to steps S1, S2 and S3 in Example 2. The microstructure was observed to reveal that there was no periodic stacking fault structure in the microstructure.

[0056] Figure 6 It is the lamellar structure of TiAl alloy under this condition, and there is no periodic stacking fault structure inside the lamellar structure.

[0057] Comparative Examples 1 and 2 show that applying stress conditions is a direct and effective means to induce a periodic stacking fault structure, and is a key technology for preparing TiAl alloys based on periodic stacking fault strengthening in the present invention.

[0058] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening, characterized in that: The following steps are involved: (1) Preparation of TiAl alloy with full lamellar structure; (2) Applying stress to the TiAl alloy induces the formation of a periodic stacking fault structure with a strengthening effect in the TiAl alloy, thereby obtaining a high-performance TiAl alloy.

2. The method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening according to claim 1, characterized in that: The TiAl alloy is prepared by any process such as arc melting, powder metallurgy, additive manufacturing, etc.

3. The method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening according to claim 1, characterized in that: The TiAl alloy with full lamellar structure is prepared by the following method: Firstly, an α2 / γ dual-phase TiAl alloy is prepared, and then heat-treated to form a full lamellar structure; Alternatively, a TiAl alloy with a full lamellar structure can be directly prepared according to the selected alloy ratio.

4. The method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening according to claim 3, characterized in that: The heat treatment temperature is higher than the high temperature α phase transformation temperature of the TiAl alloy, and the heat treatment time is sufficient to allow the TiAl alloy to completely transform into the α phase, followed by furnace cooling or air cooling to obtain a TiAl alloy structure with a full lamellar structure; Methods for directly preparing TiAl alloys with full lamellar structure include additive manufacturing.

5. The method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening according to claim 3, characterized in that: The Al element content of the α2 / γ dual-phase TiAl alloy is between 42 and 50 at.%.

6. The method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening according to claim 1, characterized in that: The treatment temperature when the stress is applied is lower than the recrystallization temperature of the TiAl alloy.

7. The method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening according to claim 6, characterized in that: The treatment temperature when applying stress is room temperature to 800°C.

8. The method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening according to claim 1, characterized in that: When stress is applied, the original structure of the TiAl alloy after post-heat treatment is divided into the following two cases: a) applying a uniaxial tensile or compressive stress with an angle of 30 to 60° to the lamellar structure to a polylamellar twin TiAl alloy having a single lamellar cluster or a directional lamellar TiAl alloy having a directional solidification condition; b) For a polycrystalline TiAl alloy, uniaxial tensile or compressive stress is applied to the material three times, the angles between the second and third applied stresses and the previous stress are between 30 and 60 degrees, and the directions of the second applied stress and the third applied stress satisfy: the two applied stresses are applied along two mutually perpendicular planes respectively.

9. The method for preparing a high-performance TiAl alloy based on periodic stacking fault strengthening according to claim 8, characterized in that: In the stress induction method, the uniaxial tensile or compressive stress is maintained for no less than 0.5h each time; the uniaxial tensile or compressive stress is 0.4~0.8σ y , σ y is the yield strength of the material at the current temperature.

10. A high performance TiAl alloy based on periodic stacking fault strengthening, prepared by the preparation method according to any one of claims 1 to 9.

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