A heat treatment method to improve the room temperature plasticity of powder metallurgy Ti2AlNb alloy

Abstract

A heat treatment method for improving the room temperature plasticity of powder metallurgy Ti2AlNb alloy is disclosed. This invention aims to address the technical problems of severe elemental segregation, poor microstructure uniformity, shrinkage cavities, and poor room temperature plasticity in current Ti2AlNb alloy smelting technology. Using Ti-22Al-25Nb pre-alloyed powder as raw material, this invention prepares Ti2AlNb alloy using vacuum hot pressing sintering technology, obtaining a high-density Ti2AlNb alloy billet free of macroscopic defects. Subsequent solution heat treatment yields a microstructure with O+B2 dual-phase lamellar layers, significantly improving its room temperature plasticity without reducing its strength. The room temperature elongation of the heat-treated Ti2AlNb alloy reaches 10.5%, an increase of 518% compared to the sintered Ti2AlNb alloy, and its room temperature strength exceeds 950 MPa.

Description

Technical Field

[0001] This invention relates to a heat treatment method for Ti2AlNb alloy. Background Technology

[0002] The rapid development of the aerospace field has placed higher demands on the performance of high-temperature structural materials. Ti2AlNb alloys, with their high specific strength, high elastic modulus, and excellent resistance to high-temperature creep and oxidation, have become key materials for hot-end components of next-generation aero-engines. They are expected to partially replace nickel-based superalloys in the 650℃–750℃ operating temperature range, enabling lightweight aero-engines and improving their thrust-to-weight ratio. However, the room-temperature plasticity of Ti2AlNb alloys needs further improvement, and their high resistance to high-temperature deformation limits their application in the aerospace field. Research has found that Ti2AlNb alloys directly prepared by vacuum hot pressing sintering have poor plasticity and require further solution heat treatment to control their microstructure, thereby obtaining Ti2AlNb alloys with excellent room-temperature properties.

[0003] Powder metallurgy can effectively avoid defects such as shrinkage porosity, shrinkage cavities, and compositional segregation caused by traditional casting methods. Furthermore, by rationally controlling the hot pressing sintering process, alloys with high density, fine grains, uniform structure, and no macroscopic segregation can be obtained. Powder metallurgy also has advantages such as low production cost and the ability to produce large structural parts. Therefore, the preparation of Ti2AlNb alloys by powder metallurgy is currently widely used in high-end industries such as aerospace.

[0004] The phase composition of Ti2AlNb alloy is O+B2+α2 phase. Its microstructure, phase content, and grain size are highly sensitive to temperature, and these factors play a crucial role in the mechanical properties of the material. Therefore, subsequent optimized heat treatment processes are needed to control its microstructure and properties. Several typical microstructures exist in Ti2AlNb alloys: equiaxed structure, biphasic structure, fine lamellar structure, and coarse lamellar structure. Different microstructure characteristics exhibit different mechanical properties. Studies have shown that alloys with a single B2 phase or O phase have lower room temperature plasticity and strength than those with a B2+O biphasic lamellar structure. The lamellar O phase can play a precipitation strengthening role, while the B2 phase can effectively improve the toughness of the alloy. Therefore, optimizing the heat treatment process of Ti2AlNb alloy prepared by powder metallurgy to obtain reasonable heat treatment process parameters and control its microstructure will ultimately improve its comprehensive mechanical properties. Summary of the Invention

[0005] The present invention aims to address the technical problems of severe elemental segregation, poor microstructure uniformity, shrinkage cavities and porosity, and poor room temperature plasticity in the current Ti2AlNb alloy smelting technology, and provides a heat treatment method to improve the room temperature plasticity of powder metallurgy Ti2AlNb alloy.

[0006] The heat treatment method of the present invention for improving the room temperature plasticity of powder metallurgy Ti2AlNb alloy is carried out according to the following steps:

[0007] 1. The Ti-22Al-25Nb pre-alloyed powder is loaded into a graphite mold, then sealed. The sealed graphite mold is placed in a vacuum hot-pressing sintering furnace and a vacuum is drawn. During the sintering process, the vacuum degree is maintained at 1×10⁻⁶. -3 The sintering temperature is 1200℃~1300℃, the holding time is 0.5h~2h, and the sintering pressure is 35MPa~45MPa. During the sintering process, the Ti2AlNb alloy is densified. After sintering, it is cooled with the furnace to obtain a high-density Ti2AlNb alloy billet.

[0008] 2. The Ti2AlNb alloy billet prepared in step 1 is ultrasonically cleaned, and then subjected to solution heat treatment at 930℃~970℃. After holding at the temperature for 0.5h~3h, it is water-quenched to obtain a Ti2AlNb alloy with O+B2 dual-phase lamellar structure.

[0009] This invention uses Ti-22Al-25Nb pre-alloyed powder as raw material and prepares a high-density Ti2AlNb alloy (step one) using a vacuum hot-pressing sintering method. The density is >99%, and the tensile strength and elongation are 963.5 MPa and 1.7%, respectively. This method offers high material utilization, low cost, and a uniform microstructure free from elemental segregation, macroscopic defects, shrinkage cavities, and other defects. However, the alloy exhibits poor room-temperature plasticity. Then, solution heat treatment at the O+B2 phase region (step two) is performed to regulate the microstructure of the Ti2AlNb alloy, obtaining a Ti2AlNb alloy with O+B2 dual-phase lamellar microstructure characteristics. This results in a Ti2AlNb alloy with excellent room-temperature plasticity, while maintaining its strength, effectively improving the room-temperature properties of the Ti2AlNb alloy prepared by vacuum hot-pressing sintering. This heat treatment method is simple and reduces the heat treatment cycle and cost. The heat-treated Ti2AlNb alloy exhibits a room temperature elongation of 10.5%, which is 518% higher than that of the Ti2AlNb alloy billet prepared in step one, and its room temperature strength exceeds 950 MPa. This invention employs a combination of powder metallurgy and solution heat treatment. Attached Figure Description

[0010] Figure 1 This is a microstructure of the sintered Ti2AlNb alloy prepared by vacuum hot pressing sintering in step one of Experiment 1;

[0011] Figure 2 This is a microstructure diagram of the Ti2AlNb alloy with O+B2 dual-phase lamellar structure obtained in step two of Experiment 1;

[0012] Figure 3 This is a schematic diagram of the heat treatment process in step two of the present invention;

[0013] Figure 4 This is the room temperature tensile stress-strain curve of the Ti2AlNb alloy prepared by vacuum hot pressing sintering in step one of Experiment 1;

[0014] Figure 5 This is the room temperature tensile stress-strain curve of the Ti2AlNb alloy after solution heat treatment in step two of Experiment 1. Detailed Implementation

[0015] Specific Implementation Method 1: This implementation method is a heat treatment method for improving the room temperature plasticity of powder metallurgy Ti2AlNb alloy, specifically carried out according to the following steps:

[0016] 1. The Ti-22Al-25Nb pre-alloyed powder is loaded into a graphite mold, then sealed. The sealed graphite mold is placed in a vacuum hot-pressing sintering furnace and a vacuum is drawn. During the sintering process, the vacuum degree is maintained at 1×10⁻⁶. -3 The sintering temperature is 1200℃~1300℃, the holding time is 0.5h~2h, and the sintering pressure is 35MPa~45MPa. During the sintering process, the Ti2AlNb alloy is densified. After sintering, it is cooled with the furnace to obtain a high-density Ti2AlNb alloy billet.

[0017] 2. The Ti2AlNb alloy billet prepared in step 1 is ultrasonically cleaned, and then subjected to solution heat treatment at 930℃~970℃. After holding at the temperature for 0.5h~3h, it is water-quenched to obtain a Ti2AlNb alloy with O+B2 dual-phase lamellar structure.

[0018] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the particle size of the Ti-22Al-25Nb pre-alloyed powder mentioned in step one is 75μm to 125μm. Everything else is the same as in Specific Implementation Method One.

[0019] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: uniformly coating the inner wall of the graphite mold described in step one with boron nitride powder facilitates demolding after the Ti2AlNb alloy is formed. Everything else is the same as in Specific Implementation Method One or Two.

[0020] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the sintering temperature in step one is 1300℃, the holding time is 2 hours, and the sintering pressure is 40MPa. Everything else is the same as in Specific Implementation Methods One to Three.

[0021] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the ultrasonic cleaning solution in step two is acetone. Everything else is the same as in Specific Implementation Method Four.

[0022] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the ultrasonic cleaning time in step two is 3 to 5 minutes. Everything else is the same as in Specific Implementation Method Five.

[0023] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that: in step two, solution heat treatment is performed at 950℃, followed by water quenching after holding at that temperature for 1 hour. Everything else is the same as in Specific Implementation Method Six.

[0024] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the quenching transfer time is less than or equal to 4 seconds. Everything else is the same as Specific Implementation Method Seven.

[0025] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the quenching transfer time is 2 seconds. Everything else is the same as Specific Implementation Method Eight.

[0026] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the quenching medium is water. Everything else is the same as in Specific Implementation Method Nine.

[0027] The invention was verified using the following experiments:

[0028] Experiment 1: This experiment is a heat treatment method to improve the room temperature plasticity of powder metallurgy Ti2AlNb alloy, specifically carried out according to the following steps:

[0029] 1. The Ti-22Al-25Nb pre-alloyed powder is loaded into a graphite mold, then sealed. The sealed graphite mold is placed in a vacuum hot-pressing sintering furnace and a vacuum is drawn. During the sintering process, the vacuum degree is maintained at 1×10⁻⁶. -3 The sintering temperature is 1300℃, the holding time is 2h, and the sintering pressure is 40MPa. During the sintering process, the Ti2AlNb alloy is densified. After sintering, it is cooled with the furnace to obtain a high-density Ti2AlNb alloy billet.

[0030] The particle size of the Ti-22Al-25Nb pre-alloyed powder mentioned in step one is 75μm to 125μm;

[0031] The uniform coating of boron nitride powder on the inner wall of the graphite mold described in step one is beneficial for demolding the Ti2AlNb alloy after molding.

[0032] 2. The Ti2AlNb alloy billet prepared in step 1 is ultrasonically cleaned for 5 minutes using acetone as the ultrasonic cleaning solution; then, it is subjected to solution heat treatment at 950℃, held for 1 hour, and then water-quenched. The quenching transfer time is 2 seconds, and the quenching medium is water, to obtain a Ti2AlNb alloy with an O+B2 dual-phase lamellar structure.

[0033] The room temperature tensile strength and elongation of the Ti2AlNb alloy after heat treatment in step two were 967.4 MPa and 10.5%, respectively. Compared with the sintered Ti2AlNb alloy prepared in step one, its elongation increased by 518%.

[0034] Experiment 2: The difference between this experiment and Experiment 1 is that in step 2, a solution heat treatment is performed at 960℃ and held for 2 hours. Everything else is the same as Experiment 1.

[0035] The heat-treated Ti2AlNb alloy obtained in Experiment 2 has a tensile strength of 958.1 MPa and an elongation of 10.7%, which is 529% higher than that of the sintered Ti2AlNb alloy prepared in Step 1.

[0036] Figure 1 The image shows the microstructure of the sintered Ti2AlNb alloy prepared by vacuum hot pressing in step one of Experiment 1. The O phase has an irregular shape.

[0037] Figure 2 This is a microstructure diagram of the Ti2AlNb alloy with O+B2 dual-phase lamellar structure obtained in step two of Experiment 1. It can be seen that the O phase is lamellar and forms a lamellar structure with the B2 phase.

[0038] Figure 3 This is a schematic diagram of the heat treatment process in step two of the present invention. It can be seen that the process is simple and the cycle is short.

[0039] Figure 4 The figure shows the room temperature tensile stress-strain curve of the Ti2AlNb alloy prepared by vacuum hot pressing sintering in step one of Experiment 1. It can be seen that the alloy has poor room temperature plasticity.

[0040] Figure 5 The figure shows the room temperature tensile stress-strain curve of the Ti2AlNb alloy after solution heat treatment in step two of Experiment 1. It can be seen that the plasticity of the Ti2AlNb alloy is greatly improved after heat treatment compared with the sintered alloy in step one.

Claims

1. A heat treatment method for improving the room temperature ductility of a powder metallurgy Ti2AlNb alloy, characterized in that The heat treatment method for improving the plasticity of the powder metallurgy Ti2AlNb alloy at room temperature is performed according to the following steps: I. Ti-22Al-25Nb pre-alloy powder is loaded into a graphite mold, then packaged, and the packaged graphite mold is placed as a whole in a vacuum hot-pressing sintering furnace and vacuumized, and the vacuum degree is maintained at 1×10 -3 The sintering temperature is 1200-1300℃, the holding time is 0.5-2h, and the sintering pressure is 35-45MPa, so that the Ti2AlNb alloy is densified during sintering, and the high-density Ti2AlNb alloy blank is obtained after sintering and furnace cooling. II. The Ti2AlNb alloy blank prepared in step I is subjected to ultrasonic cleaning, and then is subjected to solid solution heat treatment at 930-970 DEG C, is kept for 0.5-3 hours, and is water quenched to obtain the Ti2AlNb alloy with O+B2 dual-phase lamellar structure; The elongation of the Ti2AlNb alloy after heat treatment reaches 10.5% at room temperature, and the strength at room temperature is higher than 950 MPa.

2. The heat treatment method for improving the room temperature plasticity of a powder metallurgy Ti2AlNb alloy according to claim 1, characterized in that The particle size of the Ti-22Al-25Nb pre-alloy powder in step I is 75-125 mu m.

3. The heat treatment method for improving the room temperature plasticity of a powder metallurgy Ti2AlNb alloy according to claim 1, characterized in that The inner wall of the graphite mold in step I is uniformly coated with boron nitride powder.

4. The heat treatment method for improving the room temperature plasticity of a powder metallurgy Ti2AlNb alloy according to claim 1, characterized in that The sintering temperature in step I is 1300 DEG C, the holding time is 2 hours, and the sintering pressure is 40 MPa.

5. The heat treatment method for improving the room temperature plasticity of a powder metallurgy Ti2AlNb alloy according to claim 1, characterized in that The ultrasonic cleaning liquid in step II is acetone.

6. The heat treatment method for improving the room temperature plasticity of a powder metallurgy Ti2AlNb alloy according to claim 1, characterized in that The ultrasonic cleaning time in step II is 3-5 minutes.

7. The heat treatment method for improving the room temperature plasticity of a powder metallurgy Ti2AlNb alloy according to claim 1, characterized in that The solid solution heat treatment in step II is performed at 950 DEG C, is kept for 1 hour, and is water quenched.

8. The heat treatment method for improving the room temperature plasticity of a powder metallurgy Ti2AlNb alloy according to claim 1, characterized in that The transfer time of quenching is less than or equal to 4 seconds.

9. The heat treatment method for improving the room temperature plasticity of a powder metallurgy Ti2AlNb alloy according to claim 8, characterized in that The transfer time of quenching is 2 seconds.

10. The heat treatment method for improving the room temperature plasticity of a powder metallurgy Ti2AlNb alloy according to claim 1, characterized in that The quenching medium is water.

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