Preparation method of TiAl alloy with honeycomb shell structure

Abstract

The invention discloses TiA with a honeycomb shell structure as well as a preparation method, a product and application of the TiA. The method comprises the steps that mixed powder is loaded into a pure titanium tube to be subjected to vacuum packaging, hot isostatic pressing treatment is conducted for 4-6 hours at the temperature of 1200-1300 DEG C and the pressure of 150-200 MPa, then near-isothermal forging is conducted at the temperature of 1250-1300 DEG C at the pressing speed of 0.5-2 mm / s, and the single-pass deformation is 15-25%. The obtained honeycomb shell structure is formed by distributing a W-rich beta phase along a grain boundary and is of a net-shaped wrapping alpha < 2 + > gamma structure. By means of the structure, the yield strength and the tensile strength of the TiAl alloy from the room temperature to 900 DEG C are remarkably improved by about 8%-10%, and meanwhile the room-temperature plasticity of the alloy is basically kept. The method avoids the problems of resource waste and brittle phase increase caused by excessive addition of rare metal elements in a traditional method, has the dual advantages of resource saving and performance optimization, and is suitable for preparing high-temperature structural parts of aerospace engines.

Description

Technical Field

[0001] This application belongs to the field of titanium-aluminum alloy microstructure control technology, and particularly relates to a method for preparing a novel honeycomb shell microstructure to improve the room temperature / high temperature strength of TiAl alloy, as well as its products and applications. Background Technology

[0002] TiAl alloys possess low density, high high-temperature strength, and excellent fatigue and creep resistance. They are currently the only known lightweight, high-strength material that can replace nickel-based superalloys at 650-850℃ in the fabrication of high-temperature structural components for aerospace and automation industries. Their lightweight and high-strength characteristics can effectively improve the efficiency of heat engines and significantly reduce CO2 and NO emissions. x Emissions of polluting gases such as SO2.

[0003] As a material used in high-temperature environments, improving its high-temperature tensile and yield strength can ensure the safety and stability of important heat-resistant structural components in service environments, expand its application range, and is very beneficial to the development of the aerospace industry.

[0004] There have been two main approaches to improving the high-temperature strength of TiAl alloys:

[0005] One approach is to refine the lamellar microstructure through heat treatment, thereby improving the high-temperature strength of the alloy through the grain refinement strengthening effect. However, refining the lamellar microstructure leads to a significant decrease in the alloy's room-temperature plasticity and microstructural instability during service.

[0006] Another approach is to add a large amount of refractory metal elements such as Nb, Ta, and Mo to enhance the high-temperature strength of TiAl alloys by solid solution strengthening, which hinders dislocation movement. However, extensive alloying has the following drawbacks: (1) it severely wastes the valuable resources of rare metals; (2) it introduces a large amount of brittle β-metals into TiAl alloys. o (3) During service, the β→ω+γ phase transformation is induced, which leads to a serious reduction in the creep resistance.

[0007] To avoid the adverse effects of excessive alloying of β-stabilizing elements, grain boundary engineering can be used to improve the high-temperature strength of TiAl alloys. This not only reduces the unnecessary waste of rare metal resources, but also provides a new paradigm for improving the high-temperature strength of TiAl alloys. Summary of the Invention

[0008] The purpose of this invention is to address the aforementioned technical problems by providing a method for preparing a novel honeycomb shell microstructure that simultaneously improves the room temperature and high temperature strength of TiAl alloys, along with its products and applications.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] A method for preparing a TiAl alloy with a honeycomb shell structure, characterized by comprising the following steps:

[0011] (1) Mixing: TiAl alloy powder and W powder are mixed at a mass ratio of 98:2 to 95:5 to obtain mixed powder;

[0012] (2) Packaging: The mixed powder is loaded into a pure titanium tube and vacuum-sealed;

[0013] (3) Hot isostatic pressing: The packaged sample is subjected to hot isostatic pressing at 1200-1300℃ and 150-200MPa, held for 4-6 hours, and then cooled to room temperature in the furnace to obtain a densified billet.

[0014] (4) Near-isothermal forging: The densified billet is forged at 1250-1300℃ with a pressing speed of 0.5-2mm / s and a single-pass deformation of 15-20%.

[0015] Furthermore, in step (1), the mass ratio of the W powder is 2%-5%.

[0016] Furthermore, in step (1), the mixing is carried out using a gravity-free vibration mixer or a high-energy ball mill.

[0017] Furthermore, in step (2), the inner diameter of the pure titanium tube is 20-40 mm and the length does not exceed 1500 mm.

[0018] Furthermore, in step (2), the vacuum sealing includes vacuuming in stages at room temperature, 200°C and 600°C, with each stage lasting no less than 1 hour.

[0019] Furthermore, in step (2), the packaging process uses a high-frequency vibrator to vibrate the pure titanium tube to compact the powder.

[0020] Furthermore, in step (3), the temperature of the hot isostatic pressing treatment is 1200-1300℃, and the pressure is...

[0021] 150-200MPa, heat preservation time is 4-6 hours, furnace cool to room temperature.

[0022] Furthermore, in step (3), the hot isostatic pressing process is carried out at a vacuum level higher than 10. -3 The experiment was conducted in an environment of Pa, with high-purity argon gas used as a protective atmosphere.

[0023] Furthermore, in step (4), the near-isothermal forging temperature is 1300℃, and the pressing speed is 0.5-2.

[0024] mm / s, with a single-pass deformation of 15-20%.

[0025] A TiAl alloy material with a honeycomb shell structure prepared by the above preparation method.

[0026] Furthermore, the matrix composition of the TiAl alloy material is Ti-48Al-2Nb-2Cr or Ti-45Al-8Nb.

[0027] The above-mentioned TiAl alloy materials are used in the manufacture of high-temperature structural components for aerospace engines.

[0028] The beneficial effects of this invention are:

[0029] (1) The strengthening effect can be achieved by adding a small amount of W powder (2%-5%), which saves resources significantly compared with the traditional method of adding a large amount of rare metal elements.

[0030] (2) The honeycomb shell structure can simultaneously improve the room temperature and high temperature strength of TiAl alloy (by about 8%-10%), while basically maintaining room temperature plasticity;

[0031] (3) It avoids the problems of increased brittle phase and decreased plasticity caused by excessive addition of β-stabilizing elements in traditional methods;

[0032] (4) The process route is clear, the parameters are controllable, and it is easy to promote and apply it in industrial applications. Attached Figure Description

[0033] Figure 1 This is a microstructure diagram of the TiAl alloy prepared by the method of the present invention. Detailed Implementation

[0034] To better understand the above-mentioned objectives, features and advantages of this application, the application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Implementation Case 1

[0036] Ti-48Al-2Nb-2Cr (TiAl4822) powder and high-purity W (99.95% purity) powder were mixed at a mass ratio of 98:2 and vibrated for 2 hours. The mixture was then placed into a pure titanium tube with an inner diameter of 30 mm and a length of 500 mm and vibrated in a high-frequency vibrator for 5 hours. Afterward, the mixture was evacuated using a vacuum pump for 1.5 hours at room temperature, 200℃, and 600℃. Next, hot isostatic pressing was performed at 1250℃ and 200 MPa for 4 hours, followed by furnace cooling to room temperature. Finally, near-isothermal forging was carried out at 1300℃, a strain rate of 1 mm / s, and a single-pass deformation of 20%, to obtain the TiAl4822-2%W honeycomb shell structure. Tensile tests at room temperature and 670°C showed (see Table 1) that the novel TiAl4822-W honeycomb shell structure exhibited 10% higher room temperature and high temperature strength than pure TiAl4822 from room temperature to 670°C, while maintaining almost no loss of its room temperature plasticity.

[0037] Table 1. Tensile properties of pure TiAl4822 and TiAl4822-2%W at room temperature and 670℃

[0038]

[0039] Implementation Case 2

[0040] Ti-48Al-2Nb-2Cr (TiAl4822) alloy powder and high-purity W powder were mixed at a mass ratio of 95:5 and continuously mixed for 2 hours using a vibratory mixer. The mixed powder was then filled into a pure titanium sheath with an inner diameter of 30 mm and a length of 500 mm, and subjected to densification treatment in a high-frequency vibration device for 8 hours. Subsequently, under vacuum conditions, staged degassing was performed sequentially at room temperature, 200℃, and 600℃, each stage lasting 2 hours to ensure thorough degassing. Next, a hot isostatic pressing process was implemented, with a temperature of 1250℃ and a pressure of 200 MPa. After holding at this temperature for 4 hours, the furnace was cooled to room temperature to complete densification. Finally, near-isothermal forging was performed at 1300℃ with a strain rate of 1 mm / s, and the deformation per pass was controlled at 20%, successfully preparing a TiAl4822-5%W alloy with a honeycomb shell structure. The results of room temperature and 750℃ high temperature tensile tests (data shown in Table 2) show that the strength of the new honeycomb shell structure TiAl4822-W alloy from room temperature to 750℃ is increased by about 8.6% compared with TiAl4822 without W, and the room temperature plasticity is not significantly reduced.

[0041] Table 2 Tensile properties of pure TiAl4822 and TiAl4822-5%W at room temperature and 670℃

[0042]

[0043] Implementation Case 3

[0044] Ti-45Al-8Nb (TNB alloy) powder and high-purity W powder were mixed at a mass ratio of 98:2 and mixed in a vibratory mixer for about 2 hours. Then, the resulting mixed powder was loaded into a pure titanium tube with an inner diameter of about 30 mm and a length of about 500 mm and placed in a high-frequency vibrator for about 6 hours. After that, the tube was degassed in a vacuum environment at room temperature, about 200 °C and about 600 °C for about 2 hours each. Next, the degassed titanium tube was subjected to hot isostatic pressing (HIP) densification treatment, held at a temperature of about 1250 °C and a pressure of about 200 MPa for about 4 hours, and then cooled to room temperature in the furnace to obtain a dense billet. Finally, the billet was subjected to near isothermal forging at about 1250 °C, with a single-pass deformation of about 20% at a strain rate of about 1 mm / s, thereby forming a TNB-2%W (mass fraction) material with a honeycomb shell structure. The TNB-2%W honeycomb shell structure prepared by this method exhibits excellent mechanical properties, as shown in Table 3. Its tensile strength at room temperature, 800℃ and 900℃ is significantly improved compared with pure TNB material, with an average strength increase of about 8%, while basically maintaining the room temperature plasticity level of pure TNB material.

[0045] Table 3 Tensile properties of pure TNB and TNB-2%W at room temperature, 800℃, and 900℃

[0046]

[0047] Example 4

[0048] Ti-48Al-2Nb-2Cr (TiAl4822) alloy powder and high-purity W powder were mixed at a mass ratio of 97:3 and mixed for 2 hours using a gravity-free vibrating mixer. The mixed powder was then placed into a pure titanium tube with an inner diameter of 30 mm and a length of 500 mm and vibrated in a high-frequency vibrator for 6 hours. After that, degassing was carried out by vacuum pumping for 1.5 hours at room temperature, 200℃, and 600℃, respectively.

[0049] Subsequently, hot isostatic pressing (HIP) densification was performed with the following parameters: temperature 1300℃, pressure 150MPa, and holding time 6 hours. The alloy was then cooled to room temperature in the furnace. Finally, near-isothermal forging was carried out at 1250℃ with a pressing speed of 0.5mm / s and a single-pass deformation of 25%, successfully producing a TiAl4822-3%W alloy with a honeycomb shell structure.

[0050] Tensile tests at room temperature and 800℃ showed (data in Table 4) that the alloy exhibited significantly improved strength compared to pure TiAl4822 at both temperatures, with room temperature yield strength increasing by approximately 7.8% and tensile strength by approximately 9.2%, while maintaining good plasticity. The results indicate that a high-performance honeycomb shell structure can still be obtained under hot isostatic pressing conditions with higher temperatures and longer holding times, combined with a forging process using lower pressing speeds and larger deformation amounts.

[0051] Table 4. Tensile properties of pure TiAl4822 and TiAl4822-3%W at room temperature and 800℃

[0052]

Claims

1. A method for preparing a TiAl alloy with a honeycomb shell structure, characterized in that, Includes the following steps: (1) Mixing: TiAl alloy powder and W powder are mixed in a mass ratio of 98:2 to 95:5 to obtain mixed powder; (2) Packaging: The mixed powder is loaded into a pure titanium tube and vacuum-sealed; (3) Hot isostatic pressing: The packaged sample is subjected to hot isostatic pressing at 1200-1300℃ and 150-200MPa, held for 4-6 hours, and then cooled to room temperature in the furnace to obtain a densified billet. (4) Near-isothermal forging: The densified billet is forged at 1250-1300℃ with a pressing speed of 0.5-2mm / s and a single-pass deformation of 15-25%.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the W powder is 2%-5%.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the mixing method is carried out by a gravity-free vibration mixer or a high-energy ball mill.

4. The preparation method according to claim 1, characterized in that, In step (2), the inner diameter of the pure titanium tube is 10-100 mm and the length does not exceed 1500 mm.

5. The preparation method according to claim 1 or 4, characterized in that, In step (2), the vacuum sealing includes vacuuming in stages at room temperature, 200°C, and 600°C, with each stage lasting at least 1 hour, achieving a vacuum level of 10. -3 Pa.

6. The preparation method according to claim 1, 4, or 5, characterized in that, In step (2), the packaging process uses a high-frequency vibrator to vibrate the pure titanium tube to compact the powder.

7. The preparation method according to claim 1, characterized in that, In step (3), the temperature of the hot isostatic pressing treatment is 1250-1300℃, the pressure is 150-200MPa, the holding time is 4-5 hours, and the furnace is cooled to room temperature.

8. The preparation method according to claim 1, characterized in that, In step (3), the hot isostatic pressing process is carried out at a vacuum level higher than 10. -3 The experiment was conducted in an environment of Pa, with high-purity argon gas used as a protective atmosphere.

9. The preparation method according to claim 1, characterized in that, In step (4), the near-isothermal forging temperature is 1200-1300℃, the pressing speed is 0.5-2mm / s, and the deformation per pass is not higher than 15-20%.

10. A TiAl alloy material having a honeycomb shell structure prepared by the preparation method according to any one of claims 1-9.

11. The TiAl alloy material according to claim 10, characterized in that, The matrix composition of the TiAl alloy material is Ti-48Al-2Nb-2Cr or Ti-45Al-8Nb.

12. The application of the TiAl alloy material according to claim 10 or 11 in the preparation of high-temperature structural components for aerospace engines.

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