A preparation method for reducing anisotropy of near-alpha high-temperature titanium alloy plate

Abstract

The application discloses a preparation method for reducing anisotropy of a near-alpha high-temperature titanium alloy plate, and the method comprises the following steps: first, carrying out two-phase zone high-temperature part forging on a near-alpha high-temperature titanium alloy blank; second, heating, keeping warm and carrying out blooming rolling; third, taking out the blank after two-phase zone high-temperature heating and keeping warm and cooling; fourth, second fire rolling; and fifth, heat treatment. The application adopts two-phase zone high-temperature part forging to obtain a high-homogenized initial plate blank, then adopts heating and keeping warm and blooming rolling to obtain a small organization structure with sufficient deformation and store a higher distortion energy, adjusts the morphology and size of an alpha phase in the organization by two-phase zone high-temperature heating and keeping warm and water cooling, reduces the volume fraction of the alpha phase, avoids the formation of a single orientation of the alpha phase with a close-packed hexagonal structure in the rolling process, and further combines a double annealing heat treatment system to regulate the organization morphology and phase ratio, so that the anisotropy of the near-alpha high-temperature titanium alloy plate is reduced, and the demand of the aerospace field on the high-homogenized high-temperature titanium alloy plate is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium alloy preparation, and particularly relates to a preparation method for reducing anisotropy of near-alpha high-temperature titanium alloy plate. BACKGROUND

[0002] The research on near-alpha high-temperature titanium alloy has been one of the most important directions in the field of titanium alloy, and is also the focus of the research on titanium alloy in the field of aerospace in various countries. The near-alpha high-temperature titanium alloy is mainly applied to the manufacture of disc parts, blades and casings of compressors and fans of aeroengines, and can replace steel or high-temperature alloy to obviously reduce the weight of the aeroengine and improve the thrust-to-weight ratio of the aeroengine. With the improvement of application maturity, the application of the near-alpha high-temperature titanium alloy in the field of aerospace is further expanded, and the demand for the near-alpha high-temperature titanium alloy plate is increased, which is mainly used for the manufacture of high-temperature load-bearing structures of advanced aeroengines and hypersonic aircrafts.

[0003] The microstructure of the near-alpha high-temperature titanium alloy at room temperature is mainly composed of alpha phase and a small amount of beta phase. The alpha phase has a symmetrical hexagonal close-packed (HCP) crystal lattice structure, and the grains tend to form similar orientations in the plate rolling process, that is, the texture is easily formed, so that the mechanical properties of the material exhibit significant anisotropy, the uniformity and quality of the plate are poor, and the demand for the high-uniform near-alpha high-temperature titanium alloy plate cannot be met for advanced aircrafts. SUMMARY

[0004] The technical problem to be solved by the application is to provide a preparation method for reducing anisotropy of a near-alpha high-temperature titanium alloy plate in view of the deficiencies of the prior art. The method first adopts high-temperature forging in a two-phase region to obtain a high-uniform initial plate blank, then adopts opening and rolling after heating and heat preservation to obtain a small organizational structure with sufficient deformation and store a high distortion energy in the organizational structure, and adjusts the morphology and size of the alpha phase in the organizational structure by high-temperature heating and heat preservation in a two-phase region and water cooling, reduces the volume fraction of the alpha phase in the organizational structure, effectively avoids the formation of a single orientation of the alpha phase with a hexagonal close-packed structure in the rolling process, and combines a double annealing heat treatment system to control the organizational morphology and phase ratio, so as to reduce the anisotropy of the near-alpha high-temperature titanium alloy plate, and solve the problem that the anisotropy of the near-alpha high-temperature titanium alloy plate is significant and leads to poor uniformity and quality.

[0005] To solve the above technical problems, the technical scheme adopted by the application is as follows: a preparation method for reducing anisotropy of a near-alpha high-temperature titanium alloy plate, characterized in that the method comprises the following steps:

[0006] Step one, forging a near-alpha high-temperature titanium alloy blank in a high-temperature part of a two-phase region to obtain a near-alpha high-temperature titanium alloy plate blank; the near-alpha high-temperature titanium alloy plate blank is a typical equiaxed organizational structure;

[0007] Step 2: After the surface of the near-α high-temperature titanium alloy slab obtained in Step 1 is machined and heated and held at a certain temperature, it is then rolled to obtain a one-fire rolled slab.

[0008] Step 3: The one-fire rolled slab obtained in Step 2 is subjected to high-temperature heating and holding in the two-phase region, then cooled after being taken out of the furnace. The size and morphology of the α phase in the microstructure are controlled to obtain a near-α high-temperature titanium alloy slab with a uniform microstructure.

[0009] Step 4: Grind the surface of the near-α high-temperature titanium alloy slab obtained in Step 3, repair the damage, and then perform a second rolling process to obtain a two-fire rolled slab.

[0010] Step 5: Heat treat the double-rolled slab obtained in Step 4 to obtain a near-α high-temperature titanium alloy plate with a two-phase microstructure.

[0011] The above-mentioned method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy is characterized in that the forging heating temperature of the high-temperature part of the two-phase region in step one is 15℃~30℃ below the β phase transformation point, and the total deformation is not less than 80%.

[0012] The above-mentioned method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy is characterized in that, in step two, the heating and holding temperature is a two-phase region heating temperature, which is 40℃~50℃ below the β phase transformation point, and the holding time is t1=H1min, where H1 is the thickness of the near-α high-temperature titanium alloy plate surface after machining, in mm; and the total deformation of the billet rolling is not less than 60%.

[0013] The above-mentioned method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy is characterized in that, in step three, the high-temperature heating and holding temperature in the two-phase region is 15℃~20℃ below the β phase transformation point, the holding time is t2=H2min, H2 is the thickness of the one-fire rolled slab in mm; and the cooling method is water cooling.

[0014] The above-mentioned method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy is characterized in that the volume fraction of the α phase in the microstructure of the near-α high-temperature titanium alloy plate in step three is 10% to 15%.

[0015] The above-mentioned method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy is characterized in that, in step four, the second heat rolling is a reversing rolling, that is, the rolling direction of the near-α high-temperature titanium alloy slab after repair is rotated by 90° compared with the initial rolling.

[0016] The above-mentioned method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy is characterized in that, in step four, the heating temperature of the second heat rolling is 20°C to 30°C below the β phase transformation point, and the holding time is t3 = H3 min, where H3 is the thickness of the near-α high-temperature titanium alloy plate after repair, in mm; the total deformation of the second heat rolling is not less than 60%.

[0017] The above-mentioned method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy is characterized in that the heat treatment regime in step five is 1010℃ / 2h, AC+800℃ / 2h, AC.

[0018] The above-mentioned method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy is characterized in that the microstructure of the near-α high-temperature titanium alloy plates in step five is a uniform and fine equiaxed α-phase biphase microstructure.

[0019] The above-mentioned method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy is characterized in that the difference between the transverse and longitudinal strengths of the near-α high-temperature titanium alloy plates with two-phase microstructures in step five is not greater than 10 MPa.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. This invention involves forging near-α high-temperature titanium alloy billets in the high-temperature part of the two-phase region. By controlling the forging heating temperature and deformation amount, the content and morphology of the isometric α phase in the billet are adjusted, making the initial microstructure of the billet more uniform and fine, thus obtaining a near-α high-temperature titanium alloy billet with a typical isometric microstructure.

[0022] 2. This invention involves machining the surface of a near-α high-temperature titanium alloy slab, then heating and holding it at a certain temperature before rolling it into a blank. By controlling the heating and holding temperature and combining it with large deformation rolling, the lamellar α phase in the slab's microstructure undergoes greater plastic deformation, resulting in maximum bending and spheroidization. The lower heating temperature avoids the formation of overheated structures. At the same time, due to the severe deformation of the lamellar α phase, a large amount of distortion energy is stored inside the microstructure, laying the foundation for obtaining a near-α high-temperature titanium alloy slab with a uniform microstructure after subsequent heating and holding.

[0023] 3. This invention employs a two-phase region low-temperature heating combined with large deformation billet rolling, which not only fully breaks down the microstructure but also stores high distortion energy within it. Building upon this, the invention further performs high-temperature heating and holding in the two-phase region. This high-temperature heating combined with high distortion energy alters the morphology of the α-phase within the microstructure of the first-fire rolled slab, reducing the volume of the primary α-phase and causing the bent and broken secondary α-phase to spheroidize and dissolve. This achieves the goal of controlling the size, morphology, and volume fraction of the α-phase in the microstructure. Simultaneously, the invention uses water cooling after high-temperature heating and holding in the two-phase region, limiting the precipitation of the secondary α-phase during cooling and reducing the overall proportion of the α-phase in the microstructure. Because the α phase has a poorly symmetrical HCP crystal lattice structure, the grains tend to form similar orientations during the rolling process of the sheet metal, which easily leads to the formation of texture. This results in the material exhibiting strong anisotropy. Therefore, this invention, based on fully breaking down the microstructure and refining the grains, combines the control of the size, morphology, and volume fraction of the α phase in the microstructure with water cooling to further reduce the proportion of the α phase in the microstructure. This eliminates the orientation formed in the early deformation stage and reduces the tendency of the α phase to easily form orientations in subsequent deformations, thereby improving the uniformity and consistency of the microstructure of near-α high-temperature titanium alloy sheets.

[0024] 4. In the second rolling process, the present invention adopts reversing rolling, that is, the transverse and longitudinal directions of the rolled plate are reversed, and the total deformation of the second rolling is controlled to be not less than 60%, which changes the stress state of the α phase and β phase in the microstructure, thereby affecting the initiation of different slip systems, further avoiding the inheritance of the early deformation microstructure and reducing the risk of forming a single orientation.

[0025] 5. Compared with the prior art, the present invention adopts a double annealing heat treatment system. First, a high-temperature annealing treatment is adopted to further adjust the proportion and morphology of the isoaxial α phase in the microstructure, reduce the orientation of the microstructure, and reduce the anisotropy of the plate. On the other hand, it allows the silicon element in the microstructure to be fully dissolved. Then, an air-cooled heat treatment system of 800℃ / 2h is adopted to further control the proportion and size of the precipitated silicides and α2 phase, thereby improving the room temperature plasticity of near-α high-temperature titanium alloy plates.

[0026] 6. Compared with the prior art, the preparation method of the present invention significantly reduces the anisotropy of high-temperature titanium alloy plates, so that the difference between the transverse and longitudinal strength of the plates is no more than 10 MPa.

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0028] Figure 1 This is a microstructure diagram of the near-α high-temperature titanium alloy plate prepared in Example 1 of the present invention. Detailed Implementation

[0029] Example 1

[0030] This embodiment includes the following steps:

[0031] Step 1: Forging the near-α high-temperature titanium alloy billet in the high-temperature part of the two-phase region to obtain a near-α high-temperature titanium alloy slab; the forging heating temperature of the high-temperature part of the two-phase region is 1030℃, the total deformation is 85%, and the near-α high-temperature titanium alloy slab has a typical equiaxed microstructure.

[0032] Step 2: After the surface of the near-α high-temperature titanium alloy slab obtained in Step 1 is machined and heated and held at a certain temperature, it is then rolled to obtain a one-fire rolled slab; the heating and holding temperature is 1010℃, and the holding time is t1 = 210min; the total deformation of the rolling process is 65%.

[0033] Step 3: The one-fire rolled slab obtained in Step 2 is subjected to high-temperature heating and holding in the two-phase region, then cooled after being removed from the furnace. The size and morphology of the α phase in the microstructure are controlled to obtain a near-α high-temperature titanium alloy slab with a uniform microstructure. The high-temperature heating and holding temperature in the two-phase region is 1010℃, the holding time is t2 = 80 min, and the cooling method is water cooling. The volume fraction of the α phase in the microstructure of the near-α high-temperature titanium alloy slab is 10%.

[0034] Step 4: Grind the surface of the near-α high-temperature titanium alloy slab obtained in Step 3, repair the damage, and then perform a second-fire rolling to obtain a two-fire rolled slab. The second-fire rolling is a reversing rolling, that is, the rolling direction of the near-α high-temperature titanium alloy slab after repair is rotated by 90° compared with the initial rolling. The heating temperature of the second-fire rolling is 1025℃, and the holding time is t3 = 80min. The total deformation of the second-fire rolling is 60%.

[0035] Step 5: Heat treat the two-phase rolled slab obtained in Step 4 to obtain a near-α high-temperature titanium alloy plate with a two-phase microstructure; the heat treatment regime is 1010℃ / 2h, AC+800℃ / 2h, AC; the microstructure of the near-α high-temperature titanium alloy plate with a two-phase microstructure is a uniform and fine equiaxed α phase dual-state microstructure, and the difference in strength between the transverse and longitudinal directions is 6MPa.

[0036] Figure 1 The image shows the microstructure of the near-α high-temperature titanium alloy sheet prepared in this embodiment. Figure 1 It can be seen that the microstructure of the near-α high-temperature titanium alloy plate is uniform and fine, consisting of equiaxed α phase and β transformation microstructure, with the equiaxed α phase having a volume fraction of about 15%, which is a typical bimodal microstructure.

[0037] Example 2

[0038] This embodiment includes the following steps:

[0039] Step 1: Forging the near-α high-temperature titanium alloy billet in the high-temperature part of the two-phase region to obtain a near-α high-temperature titanium alloy slab; the forging heating temperature of the high-temperature part of the two-phase region is 1025℃, the total deformation is 82%, and the near-α high-temperature titanium alloy slab has a typical equiaxed microstructure.

[0040] Step 2: After the surface of the near-α high-temperature titanium alloy slab obtained in Step 1 is machined and heated and held at a certain temperature, it is then rolled to obtain a one-fire rolled slab; the heating and holding temperature is 1000℃, and the holding time is t1 = 190min; the total deformation of the rolling process is 62%.

[0041] Step 3: The one-fire rolled slab obtained in Step 2 is subjected to high-temperature heating and holding in the two-phase region, then cooled after being removed from the furnace. The size and morphology of the α phase in the microstructure are controlled to obtain a near-α high-temperature titanium alloy slab with a uniform microstructure. The high-temperature heating and holding temperature in the two-phase region is 1025℃, the holding time is t2 = 72 min, and the cooling method is water cooling. The volume fraction of the α phase in the microstructure of the near-α high-temperature titanium alloy slab is 12%.

[0042] Step 4: Grind the surface of the near-α high-temperature titanium alloy slab obtained in Step 3, repair the damage, and then perform a second-fire rolling to obtain a second-fire rolled slab. The second-fire rolling is a reverse rolling, that is, the rolling direction of the near-α high-temperature titanium alloy slab after repair is rotated by 90° compared with the initial rolling. The heating temperature of the second-fire rolling is 1015℃, and the holding time is t3 = 72min. The total deformation of the second-fire rolling is 65%.

[0043] Step 5: Heat treat the two-phase rolled slab obtained in Step 4 to obtain a near-α high-temperature titanium alloy plate with a two-phase microstructure; the heat treatment regime is 1010℃ / 2h, AC+800℃ / 2h, AC; the microstructure of the near-α high-temperature titanium alloy plate with a two-phase microstructure is a uniform and fine equiaxed α phase dual-state microstructure with a transverse and longitudinal strength difference of 8MPa.

[0044] Example 3

[0045] This embodiment includes the following steps:

[0046] Step 1: Forging the near-α high-temperature titanium alloy billet in the high-temperature part of the two-phase region to obtain a near-α high-temperature titanium alloy slab; the forging heating temperature of the high-temperature part of the two-phase region is 1015℃, the total deformation is 85%, and the near-α high-temperature titanium alloy slab has a typical equiaxed microstructure.

[0047] Step 2: After the surface of the near-α high-temperature titanium alloy slab obtained in Step 1 is machined and heated and held at a certain temperature, it is then rolled to obtain a one-fire rolled slab; the heating and holding temperature is 1015℃, and the holding time is t1=195min; the total deformation of the rolling process is 65%.

[0048] Step 3: The one-fire rolled slab obtained in Step 2 is subjected to high-temperature heating and holding in the two-phase region, then cooled after being removed from the furnace. The size and morphology of the α phase in the microstructure are controlled to obtain a near-α high-temperature titanium alloy slab with a uniform microstructure. The high-temperature heating and holding temperature in the two-phase region is 1027℃, the holding time is t2 = 68 min, and the cooling method is water cooling. The volume fraction of the α phase in the microstructure of the near-α high-temperature titanium alloy slab is 15%.

[0049] Step 4: Grind the surface of the near-α high-temperature titanium alloy slab obtained in Step 3, repair the damage, and then perform a second-fire rolling to obtain a two-fire rolled slab. The second-fire rolling is a reversing rolling, that is, the rolling direction of the near-α high-temperature titanium alloy slab after repair is rotated by 90° compared with the initial rolling. The heating temperature of the second-fire rolling is 1020℃, and the holding time is t3 = 68min. The total deformation of the second-fire rolling is 60%.

[0050] Step 5: Heat-treat the two-phase rolled slab obtained in Step 4 to obtain a near-α high-temperature titanium alloy plate with a two-phase microstructure; the heat treatment regime is 1010℃ / 2h, AC+800℃ / 2h, AC; the microstructure of the near-α high-temperature titanium alloy plate with a two-phase microstructure is a uniform and fine equiaxed α phase dual-state microstructure with a transverse and longitudinal strength difference of 9MPa.

[0051] Example 4

[0052] This embodiment includes the following steps:

[0053] Step 1: Forging the near-α high-temperature titanium alloy billet in the high-temperature part of the two-phase region to obtain a near-α high-temperature titanium alloy slab; the forging heating temperature of the high-temperature part of the two-phase region is 1025℃, the total deformation is 80%, and the near-α high-temperature titanium alloy slab has a typical equiaxed microstructure.

[0054] Step 2: After the surface of the near-α high-temperature titanium alloy slab obtained in Step 1 is machined and heated and held at a certain temperature, it is then rolled to obtain a one-fire rolled slab; the heating and holding temperature is 1010℃, and the holding time is t1 = 200min; the total deformation of the rolling process is 62%.

[0055] Step 3: The one-fire rolled slab obtained in Step 2 is subjected to high-temperature heating and holding in the two-phase region, then cooled after being removed from the furnace. The size and morphology of the α phase in the microstructure are controlled to obtain a near-α high-temperature titanium alloy slab with a uniform microstructure. The high-temperature heating and holding temperature in the two-phase region is 1025℃, the holding time is t2=76min, and the cooling method is water cooling. The volume fraction of the α phase in the microstructure of the near-α high-temperature titanium alloy slab is 15%.

[0056] Step 4: Grind the surface of the near-α high-temperature titanium alloy slab obtained in Step 3, repair the damage, and then perform a second-heat rolling to obtain a two-heat rolled slab. The second-heat rolling is a reversing rolling, that is, the rolling direction of the near-α high-temperature titanium alloy slab after repair is rotated by 90° compared with the initial rolling. The heating temperature of the second-heat rolling is 1015℃, and the holding time is t3 = 76min. The total deformation of the second-heat rolling is 65%.

[0057] Step 5: Heat treat the two-phase rolled slab obtained in Step 4 to obtain a near-α high-temperature titanium alloy plate with a two-phase microstructure; the heat treatment regime is 1010℃ / 2h, AC+800℃ / 2h, AC; the microstructure of the near-α high-temperature titanium alloy plate with a two-phase microstructure is a uniform and fine equiaxed α phase dual-state microstructure, and the difference in strength between the transverse and longitudinal directions is 6MPa.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy, characterized in that, The method includes the following steps: Step 1: Forging the near-α high-temperature titanium alloy billet in the high-temperature part of the two-phase region to obtain a near-α high-temperature titanium alloy slab; the near-α high-temperature titanium alloy slab has a typical equiaxed microstructure; the forging heating temperature for the high-temperature part of the two-phase region is 15℃~30℃ below the β phase transformation point, and the total deformation is not less than 80%; Step 2: After the surface of the near-α high-temperature titanium alloy slab obtained in Step 1 is machined and then heated and held at a certain temperature, it is then subjected to initial rolling to obtain a one-fire rolled slab. The heating and holding temperature is the two-phase region heating temperature, which is 40℃~50℃ below the β phase transformation point. The holding time is t1=H1min, where H1 is the thickness of the near-α high-temperature titanium alloy slab surface after machining, in mm. The total deformation of the initial rolling is not less than 60%. Step 3: The one-fire rolled slab obtained in Step 2 is subjected to high-temperature heating and holding in the two-phase region, then cooled after removal from the furnace. The size and morphology of the α phase in the microstructure are controlled to obtain a near-α high-temperature titanium alloy slab with a uniform microstructure. The high-temperature heating and holding temperature in the two-phase region is 15℃~20℃ below the β phase transformation point, and the holding time is t2 = H2min, where H2 is the thickness of the one-fire rolled slab in mm. The cooling method is water cooling. Step 4: Grind the surface of the near-α high-temperature titanium alloy slab obtained in Step 3, repair the damage, and then perform a second rolling process to obtain a two-fire rolled slab. Step 5: Heat treat the double-rolled slab obtained in Step 4 to obtain a near-α high-temperature titanium alloy plate with a two-phase microstructure.

2. The method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy according to claim 1, characterized in that, The volume fraction of the α phase in the microstructure of the near-α high-temperature titanium alloy slab described in step three is 10%~15%.

3. The method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy according to claim 1, characterized in that, In step four, the second heat rolling is a reversing rolling, that is, the rolling direction of the near-α high-temperature titanium alloy slab after repair is rotated by 90° compared with the initial rolling.

4. The method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy according to claim 1, characterized in that, In step four, the heating temperature of the second heat rolling is 20°C to 30°C below the β phase transformation point, and the holding time is t3 = H3 min, where H3 is the thickness of the near-α high-temperature titanium alloy slab after the repair, in mm; the total deformation of the second heat rolling is not less than 60%.

5. The method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy according to claim 1, characterized in that, The heat treatment regime described in step five is 1010℃ / 2h, AC + 800℃ / 2h, AC.

6. The method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy according to claim 1, characterized in that, The microstructure of the near-α high-temperature titanium alloy plate described in step five is characterized by a uniform and fine equiaxed α phase biphase microstructure.

7. The method for preparing near-α high-temperature titanium alloy plates with reduced anisotropy according to claim 1, characterized in that, The difference in transverse and longitudinal strength of the near-α high-temperature titanium alloy plate with two-phase microstructure described in step five is no greater than 10 MPa.

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