Heat treatment method for improving high-temperature strong plasticity of Ti2AlNb alloy

Abstract

The invention discloses a heat treatment method for improving high-temperature strong plasticity of a Ti2AlNb alloy. The method comprises the following steps: 1, gradually cooling and forging the Ti2AlNb alloy to obtain a Ti2AlNb alloy plate; secondly, the Ti2AlNb alloy plate is subjected to solution treatment; and thirdly, the solid solution state Ti2AlNb alloy plate is subjected to aging treatment. According to the heat treatment method, the Ti2AlNb alloy is subjected to solid solution and aging heat treatment after being subjected to successive cooling forging, a microscopic structure composed of equiaxial alpha2 phases and thick and thin alternate lath O phases is obtained, optimal matching of the high-temperature and high-plasticity performance of the alloy is achieved, meanwhile, the heat treatment method is simple in process, the Ti2AlNb alloy plate formed through forging is only subjected to solid solution and aging treatment, and the heat treatment cost is low. The tensile strength at high temperature is improved, meanwhile, better plasticity is still achieved, the structure is uniform, the performance is stable, the safety under the high-temperature service condition is guaranteed, and the requirements of the aviation field and the aerospace field for the high-temperature strong plasticity are met.

Description

Technical Field

[0001] The invention relates to the technical field of new materials, and in particular to a heat treatment method for improving high-temperature strength and plasticity of a Ti2AlNb alloy. Background Art

[0002] Ti2AlNb alloy has become the most promising high-temperature lightweight structural material due to its low density, high specific strength, excellent high-temperature oxidation resistance and creep resistance. It is expected to replace the nickel-based high-temperature alloy widely used in the aerospace industry. The application of Ti2AlNb alloy plays an important role in reducing the weight of aircraft, improving fuel efficiency and improving safe serviceability. The ambient temperature of Ti2AlNb alloy can reach 650℃~750℃, and the service conditions are complex, and it is susceptible to impact and overload. Therefore, higher requirements are placed on the performance of Ti2AlNb alloy, which requires not only sufficient strength but also a certain degree of plasticity to achieve safe service of formed parts under high temperature conditions. However, as an intermetallic compound, its inherent brittleness seriously limits its wide application due to its poor plasticity and low toughness.

[0003] Under certain alloy composition, the mechanical properties of materials depend on the microstructure characteristics. Ti2AlNb alloy castings have coarse grains, and the grain size is usually at the millimeter level. At the same time, Nb has a high density and a high melting point, while Al has a low melting point and a low density, which can easily cause Nb segregation and Al burning. Therefore, alloy ingots generally require thermal deformation to eliminate defects and refine the structure. Ti2AlNb alloys go through four phase regions from high temperature to low temperature, namely B2 / β, α2+B2, α2+B2+O, and O+B2. The phase transformation process between the main components B2 / β, α2 and O phases is very complex. Studies have shown that the phase composition, content and organizational morphology of the initial organization of the forged Ti2AlNb slab undergo significant changes when heat treated, indicating that the microstructure is very sensitive to the heat treatment process. The richness of this phase transformation and the sensitivity of the organization allow us to control the alloy microstructure and properties well by adjusting the heat treatment process. Therefore, studying a heat treatment process to improve the high-temperature strength and plasticity of Ti2AlNb-based alloys, while ensuring high strength and excellent plasticity, is of great significance to ensuring the high-quality development of my country's future aerospace industry. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a heat treatment method for improving the high-temperature strength and plasticity of Ti2AlNb alloy in view of the deficiencies of the above-mentioned prior art. The method obtains a Ti2AlNb alloy microstructure composed of an equiaxed α2 phase and a coarse and fine lath O phase by successively cooling and forging the Ti2AlNb alloy, combining solid solution and aging heat treatment, thereby improving the organizational stability of the Ti2AlNb alloy, achieving an optimized matching of the high-temperature strength and plasticity of the alloy, and solving the problem of poor strength and plasticity matching of the existing Ti2AlNb alloy under high temperature conditions.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a heat treatment method for improving the high temperature strength and plasticity of Ti2AlNb alloy, characterized in that the method comprises the following steps:

[0006] Step 1: forging the Ti2AlNb alloy at 1030° C. to 1150° C. in succession to obtain a Ti2AlNb alloy plate;

[0007] Step 2: placing the Ti2AlNb alloy plate obtained in step 1 in a box-type resistance furnace after reaching temperature for solid solution treatment to obtain a solid solution Ti2AlNb alloy plate;

[0008] Step 3: Place the solid solution Ti2AlNb alloy plate obtained in step 2 in a box-type resistance furnace after reaching temperature for aging treatment to obtain an aged Ti2AlNb alloy plate, i.e., a heat-treated Ti2AlNb alloy.

[0009] The above-mentioned heat treatment method for improving the high temperature strength and plasticity of Ti2AlNb alloy is characterized in that the Ti2AlNb alloy in step 1 is composed of the following components in mass percentage: Al 10% to 11.2%, Nb 39.0% to 42.0%, Mo 0.8% to 1.0%, O < 0.15%, N < 0.04%, H < 0.01%, and the rest is Ti and unavoidable impurities. The heat treatment method of the present invention has a significant effect on the Ti2AlNb alloy of the above composition.

[0010] The above-mentioned heat treatment method for improving the high-temperature strength and plasticity of Ti2AlNb alloy is characterized in that the number of successive cooling forging fires in step 1 is not less than seven times.

[0011] The above-mentioned heat treatment method for improving the high-temperature strength and plasticity of Ti2AlNb alloy is characterized in that the successive cooling forging in step one includes blank forging, intermediate forging and finished product forging, wherein the temperature of blank forging is 1150°C, the temperature of intermediate forging is 1080°C~1100°C, the temperature of finished product forging is 1030°C~1050°C, and the deformation amount of each fire is 20%~50%.

[0012] The above-mentioned heat treatment method for improving the high-temperature strength and plasticity of Ti2AlNb alloy is characterized in that the thickness of the Ti2AlNb alloy plate in step 1 is 100 mm to 150 mm.

[0013] The above-mentioned heat treatment method for improving the high-temperature strength and plasticity of Ti2AlNb alloy is characterized in that the system of the solid solution treatment in step 2 is: keeping the temperature at 980°C to 1030°C for 0.5h to 1.5h, and air cooling to room temperature.

[0014] The above-mentioned heat treatment method for improving the high-temperature strength and plasticity of Ti2AlNb alloy is characterized in that the aging treatment system in step three is: keeping the temperature at 860°C to 890°C for 6h to 8h, and air cooling to room temperature.

[0015] The above-mentioned heat treatment method for improving the high-temperature strength and plasticity of Ti2AlNb alloy is characterized in that the tensile strength of the Ti2AlNb alloy after the heat treatment in step three is above 944MPa at 650°C and the elongation is above 14%.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The present invention firstly performs forging at a lower temperature step by step, that is, forging at a higher temperature first increases the plasticity of the Ti2AlNb alloy, and then gradually reduces the forging temperature to refine the grains, thereby obtaining a Ti2AlNb alloy plate having an initial forged structure consisting of an equiaxed α2 phase and a lath O phase, and then further heat-treating the plate to form a short rod-shaped O phase structure while retaining the equiaxed primary α2 phase through a solid solution treatment, thereby improving the strength of the Ti2AlNb alloy, and in the subsequent aging treatment process, B2 / β precipitates a secondary needle-shaped fine O phase structure to form a coarse and fine alternating O phase lath structure, so that the microstructure of the Ti2AlNb alloy after heat treatment consists of an equiaxed α2 phase and a coarse and fine alternating lath O phase, and the O phase content is greater than 60%, thereby improving the organizational stability of the Ti2AlNb alloy and achieving an optimized matching of the high-temperature strength and plasticity properties of the alloy.

[0018] 2. The heat treatment method of the present invention enables the Ti2AlNb alloy to obtain excellent high-temperature strength and plasticity, and the tensile strength and elongation at 650°C can reach 944MPa-958MPa and 14%-15.5% respectively.

[0019] 3. The heat treatment method of the present invention has a simple process. After forging, the Ti2AlNb alloy plate is only subjected to solid solution + aging treatment, and the tensile strength at high temperature is improved while still obtaining good plasticity, and the structure is uniform and the performance is stable, thereby ensuring the safety under high temperature service conditions and meeting the requirements of the aviation and aerospace fields for the high temperature strength and plasticity of Ti2AlNb alloy.

[0020] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the microstructure diagram of the Ti2AlNb alloy after heat treatment in Example 1 of the present invention.

[0022] Figure 2 This is the microstructure diagram of the Ti2AlNb alloy after heat treatment in Example 2 of the present invention.

[0023] Figure 3 This is the microstructure diagram of the Ti2AlNb alloy after heat treatment in Example 3 of the present invention. DETAILED DESCRIPTION

[0024] Example 1

[0025] This embodiment includes the following steps:

[0026] Step 1, forging the Ti2AlNb alloy at 1150°C, 1100°C, 1070°C, 1050°C, and 1030°C respectively, with the forging number of not less than 7 times, and the deformation amount of each fire is 20% to 50%, to obtain a Ti2AlNb alloy plate with a thickness of 100 mm;

[0027] The Ti2AlNb alloy is composed of the following components in mass percentage: Al 10.38%, Nb 39.64%, Mo 0.88%, O 0.074%, N 0.01%, H 0.0023%, and the rest is Ti and unavoidable impurities;

[0028] Step 2: placing the Ti2AlNb alloy plate obtained in step 1 in a box-type resistance furnace after reaching temperature for solid solution treatment, keeping the temperature at 980°C for 1.5 hours, and air cooling to room temperature to obtain a solid solution Ti2AlNb alloy plate;

[0029] Step 3: Place the solid solution Ti2AlNb alloy plate obtained in step 2 in a box-type resistance furnace after heating for aging treatment, keep it at 860°C for 8 hours, and air cool it to room temperature to obtain an aged Ti2AlNb alloy plate, that is, the heat-treated Ti2AlNb alloy.

[0030] Figure 1 The microstructure of the Ti2AlNb alloy after heat treatment in this embodiment is shown in FIG. Figure 1 It can be seen that the microstructure of the heat-treated Ti2AlNb alloy consists of an equiaxed α2 phase and coarse and fine lath O phases, and the O phase content is greater than 60%.

[0031] Example 2

[0032] This embodiment includes the following steps:

[0033] Step 1, forging the Ti2AlNb alloy at 1150°C, 1100°C, 1070°C, 1050°C, and 1030°C respectively, with the forging number of not less than 7 times, and the deformation amount of each fire is 20% to 50%, to obtain a Ti2AlNb alloy plate with a thickness of 120 mm;

[0034] The Ti2AlNb alloy is composed of the following components in mass percentage: Al 11.2%, Nb 41.3%, Mo 0.92%, O 0.061%, N 0.01%, H 0.0006%, and the rest is Ti and unavoidable impurities;

[0035] Step 2: placing the Ti2AlNb alloy plate obtained in step 1 in a box-type resistance furnace after reaching temperature for solution treatment, keeping the temperature at 1010°C for 1 hour, and air cooling to room temperature to obtain a solid solution Ti2AlNb alloy plate;

[0036] Step 3: Place the solid solution Ti2AlNb alloy plate obtained in step 2 in a heated box-type resistance furnace for aging treatment, keep it at 880°C for 7 hours, and air cool it to room temperature to obtain an aged Ti2AlNb alloy plate, i.e., the heat-treated Ti2AlNb alloy.

[0037] Figure 2 The microstructure of the Ti2AlNb alloy after heat treatment in this embodiment is shown in FIG. Figure 2 It can be seen that the microstructure of the heat-treated Ti2AlNb alloy consists of an equiaxed α2 phase and coarse and fine lath O phases, and the O phase content is greater than 60%.

[0038] Example 3

[0039] This embodiment includes the following steps:

[0040] Step 1, forging the Ti2AlNb alloy at 1150°C, 1100°C, 1070°C, 1050°C, and 1030°C respectively, with the forging number of not less than 7 times, and the deformation amount of each fire is 20% to 50%, to obtain a Ti2AlNb alloy plate with a thickness of 150 mm;

[0041] The Ti2AlNb alloy is composed of the following components in mass percentage: Al 10.15%, Nb 39.08%, Mo 0.96%, O 0.062%, N 0.007%, H 0.0022%, and the rest is Ti and unavoidable impurities;

[0042] Step 2: placing the Ti2AlNb alloy plate obtained in step 1 in a box-type resistance furnace after reaching temperature for solution treatment, keeping the temperature at 1030° C. for 0.5 h, and air cooling to room temperature to obtain a solid solution Ti2AlNb alloy plate;

[0043] Step 3: Place the solid solution Ti2AlNb alloy plate obtained in step 2 in a box-type resistance furnace after heating for aging treatment, keep it at 890°C for 6 hours, and air cool it to room temperature to obtain an aged Ti2AlNb alloy plate, that is, the heat-treated Ti2AlNb alloy.

[0044] Figure 3 The microstructure of the Ti2AlNb alloy after heat treatment in this embodiment is shown in FIG. Figure 3 It can be seen that the microstructure of the heat-treated Ti2AlNb alloy consists of an equiaxed α2 phase and coarse and fine lath O phases, and the O phase content is greater than 60%.

[0045] The tensile strength and tensile properties of the heat-treated Ti2AlNb alloys at 650°C in Examples 1 to 3 of the present invention were tested, and the results are shown in Table 1 below.

[0046] Table 1

[0047] Example Tensile strength / MPa Elongation / % Example 1 949 14.0 Example 2 958 14.5 Example 3 944 15.5

[0048] It can be seen from Table 1 that the Ti2AlNb alloy after heat treatment in Examples 1 to 3 of the present invention has a tensile strength of more than 944 MPa at 650°C and an elongation of more than 14%, which meets the requirements of aviation and aerospace fields for its strong plasticity.

[0049] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A heat treatment method for improving the high temperature strength and plasticity of Ti2AlNb alloy, characterized in that: The method comprises the following steps: Step 1: forging the Ti2AlNb alloy at 1030° C. to 1150° C. in succession to obtain a Ti2AlNb alloy plate; Step 2: placing the Ti2AlNb alloy plate obtained in step 1 in a box-type resistance furnace after reaching temperature for solid solution treatment to obtain a solid solution Ti2AlNb alloy plate; Step 3: Place the solid solution Ti2AlNb alloy plate obtained in step 2 in a box-type resistance furnace after reaching temperature for aging treatment to obtain an aged Ti2AlNb alloy plate, i.e., a heat-treated Ti2AlNb alloy.

2. A heat treatment method for improving high temperature strength and plasticity of Ti2AlNb alloy according to claim 1, characterized in that: The Ti2AlNb alloy in step 1 is composed of the following components in mass percentage: Composition: Al 10%~11.2%, Nb39.0%~42.0%, Mo 0.8%~1.0%, O<0.15%, N<0.04%, H<0.01%, and the rest are Ti and unavoidable impurities.

3. A heat treatment method for improving high temperature strength and plasticity of Ti2AlNb alloy according to claim 1, characterized in that: The number of successive cooling forgings in step 1 is not less than seven times.

4. A heat treatment method for improving high temperature strength and plasticity of Ti2AlNb alloy according to claim 1, characterized in that: The successive cooling forging in step 1 includes blank forging, intermediate forging and finished product forging, wherein the temperature of blank forging is 1150°C, the temperature of intermediate forging is 1080°C to 1100°C, the temperature of finished product forging is 1030°C to 1050°C, and the deformation amount of each fire is 20% to 50%.

5. A heat treatment method for improving high temperature strength and plasticity of Ti2AlNb alloy according to claim 1, characterized in that: The thickness of the Ti2AlNb alloy plate in step 1 is 100 mm to 150 mm.

6. A heat treatment method for improving high temperature strength and plasticity of Ti2AlNb alloy according to claim 1, characterized in that: The solution treatment system in step 2 is: keeping the temperature at 980° C. to 1030° C. for 0.5 h to 1.5 h, and air cooling to room temperature.

7. A heat treatment method for improving high temperature strength and plasticity of Ti2AlNb alloy according to claim 1, characterized in that: The aging treatment system in step 3 is: keeping the temperature at 860° C. to 890° C. for 6 h to 8 h, and air cooling to room temperature.

8. A heat treatment method for improving high temperature strength and plasticity of Ti2AlNb alloy according to claim 1, characterized in that: The tensile strength of the Ti2AlNb alloy after the heat treatment in step 3 is above 944 MPa at 650°C, and the elongation is above 14%.

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