A method for preparing TC4 titanium alloy supercritical specification bars with equiaxed microstructure uniformity for aircraft engines

Abstract

The present invention discloses a method for preparing TC4 titanium alloy supercritical gauge rods for aircraft engines with equiaxed microstructure uniformity. The method uses a TC4 titanium alloy ingot, forging it with two upsetting and two drawing cycles per fire, and fully deforming the rods through multi-dimensional upsetting and drawing in the radial and transverse directions. The deformation amount per fire is 80-95%, and the upsetting temperature is carried out in the β phase or two-phase region. The result is an equiaxed microstructure rod with a diameter of 600-900 mm and a supercritical microstructure. The present invention utilizes a composite forging process of two upsetting and two drawing cycles per fire and multi-dimensional reversing upsetting and drawing to increase the material deformation, more fully break up the core microstructure, improve the microstructure uniformity of large-size TC4 titanium alloy rods, achieve equiaxed microstructure, and obtain forged rods with performance that meets the technical requirements of aircraft engines. This allows for industrialized production and expands the processing and application potential of titanium alloys.

Description

Technical Field

[0001] The invention belongs to the field of metallurgy and relates to a titanium alloy hot processing technology, in particular to a method for preparing a TC4 titanium alloy supercritical specification bar with equiaxed structural uniformity for aircraft engines. Background Art

[0002] As aircraft engines evolve toward higher thrust-to-weight ratios and longer lifespans, and to meet the trend toward larger, more integrated structural designs, the dimensions of forgings for these engines are constantly surpassing traditional specifications, resulting in supercritical bar sizes. The diameters of these bars often exceed the critical size (over 500mm) that can be reliably produced using conventional forging processes, making controlling the uniformity of their internal structure a key challenge that limits material performance. As one of the most commonly used titanium alloys in aviation, TC4 titanium alloy offers advantages such as lightweight, high specific strength, and excellent machinability. Its application performance is closely related to the material's microstructure.

[0003] In order to ensure the reliability and long life of key components, the structural uniformity of TC4 titanium alloy for aviation must be strictly controlled to ensure the stability of titanium alloy under different temperatures and environments. During the forging process, the refinement of titanium alloy grains and structural homogenization can be achieved by controlling the temperature and deformation degree. The uniformity of grain size and distribution can improve the plasticity and toughness of the material and reduce anisotropy, thereby ensuring the performance stability of aircraft engine components under complex loads. The present invention adopts a composite forging process of single-fire two-upsetting and two-drawing and multi-dimensional reversing, and the operation replaces the original unidirectional upsetting and drawing, increases the degree of material deformation, and contributes to the crushing of grains and the transformation of structural morphology. It can more fully crush the core structure, achieve equiaxed, and improve the structural uniformity of large-size TC4 alloy bars. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing TC4 titanium alloy supercritical specification bars for aircraft engines with equiaxed structural uniformity. The method for preparing such TC4 titanium alloy supercritical specification bars for aircraft engines with equiaxed structural uniformity is intended to solve the technical problems in the prior art of TC4 titanium alloy bars being small in size, having elongated α structure in the longitudinal direction, and having insufficient equiaxility.

[0005] The present invention provides a method for preparing a TC4 titanium alloy supercritical specification bar for an aero-engine with equiaxed structural uniformity, comprising the following steps:

[0006] S1, a step of preparing a TC4 titanium alloy ingot, wherein the diameter of the TC4 titanium alloy ingot is Φ860-1000 mm;

[0007] S2, a step of preparing a forging blank,

[0008] Determining the original radial height direction Z, transverse width direction X, and thickness direction Y of the TC4 titanium alloy ingot;

[0009] S21, adding the TC4 titanium alloy ingot when the furnace temperature is 800-900° C., and holding the ingot at 1100-1200° C. for 8-12 hours, first performing upsetting deformation on the TC4 titanium alloy ingot along the radial height Z direction, then flipping 90° with the thickness Y direction as the axis, stretching it along the Z direction, and flipping 90° on the transverse extension surface perpendicular to the Z direction to obtain an intermediate billet, then chamfering the small edges, flipping 90° with the thickness Y direction as the axis, and continuing to perform upsetting deformation in the Z direction, then stretching it along the original transverse width X direction, and flipping 45° on the YZ extension surface perpendicular to the X direction to obtain a first octagonal billet of Φ680-980 mm;

[0010] S22, the first octagonal billet of Φ680-980 mm obtained in step S21 is put into a furnace at a furnace temperature of 700-850° C., and after the temperature reaches 1010-1070° C., it is kept warm for 2-6 hours, and the billet is first subjected to upsetting deformation along the width X direction, and then flipped 90° with the thickness Y direction as the axis, stretched along the X direction, and flipped 90° in the YZ extension surface to obtain an intermediate square billet, and then the small edges are chamfered, and then flipped 90° with the thickness Y direction as the axis, and then continued to be subjected to upsetting deformation along the X direction, and then stretched along the radial height Z direction, and flipped 45° in the transverse extension surface to obtain a second octagonal billet of Φ680-980 mm;

[0011] The upsetting deformation in any of the above steps is controlled to be 80~95%;

[0012] S3, a step of forging bars,

[0013] The second octagonal billet is forged through 4 to 8 fires to obtain an octagonal billet with a diameter of 680 to 980 mm. The deformation of each fire is 80 to 95%. The upsetting process of forging includes a reversing operation of drawing length. The billet is heated and kept warm in the β phase region or the two-phase region before each upsetting process. The temperature of the β phase region is 1010 to 1070°C, and the temperature of the two-phase region is 930 to 980°C. Finally, TC4 titanium alloy supercritical specification bars with a diameter of 600 to 900 mm and uniform equiaxed structure for aircraft engines are obtained.

[0014] During the upsetting process, the upsetting operation in the Z direction is performed first, and then the upsetting operation in the X direction, and the upsetting operations are performed alternately in sequence;

[0015] When operating in the Z direction, heat preservation is carried out in the β phase region for 2 to 6 hours or in the two-phase region for 4 to 8 hours, and the xth octagonal billet is upset and stretched along the radial height Z direction. During the stretching process, the horizontal extension surface is flipped 90 degrees, where x is an integer, 2≤x≤7. After obtaining the intermediate square billet, the small edges are chamfered, and the billet is flipped 90 degrees with the thickness Y direction as the axis, upset deformation is performed in the Z direction, and then stretched along the X direction. The billet is flipped 45 degrees on the YZ extension surface to obtain the (x+1)th octagonal billet with a diameter of 680 to 980 mm.

[0016] When operating in the X direction, keep warm in the β phase region for 2 to 6 hours or in the two-phase region for 4 to 8 hours, upset and draw along the X direction, flip 90° on the YZ extension surface during the drawing process to obtain the intermediate square billet, then chamfer the small edges, flip 90° with the thickness Y direction as the axis, upset along the X direction, and then draw along the Z direction, flip 45° on the transverse extension surface to obtain the (x+2) octagonal billet with a diameter of 680~980mm; then air cool for 4 to 8 hours.

[0017] Preferably, in the step of preparing the TC4 titanium alloy ingot in step S1, the titanium alloy ingot is obtained by at least three vacuum consumable melting processes.

[0018] Preferably, a step of preparing the blank in step S2 is:

[0019] In step S3, at least one process of heating and keeping warm in the β phase region is included, and at least one process of heating and keeping warm in the two-phase region is included.

[0020] Preferably, in step S3, the step of obtaining a rod with a diameter of Φ600-900 mm by upsetting the second octagonal blank six times is as follows:

[0021] S31, adding the second octagonal billet when the furnace temperature is 600-700° C., and holding the temperature after reaching 930-980° C. for 4-8 hours, upsetting and stretching the second octagonal billet along the radial height Z direction, flipping 90° in the transverse extension surface during the stretching process to obtain an intermediate square billet, chamfering the small edges, flipping 90° along the thickness Y direction as the axis, performing upsetting deformation in the Z direction, and then stretching in the X direction, and flipping 45° in the YZ extension surface to obtain a third octagonal billet of Φ680-980 mm;

[0022] S32, adding the third octagonal billet when the furnace temperature is 600-700°C, holding the temperature after reaching 930-980°C for 4-8h, upsetting and stretching in the X direction, flipping 90° in the YZ extension surface during the stretching process to obtain an intermediate square billet, chamfering the small edges, flipping 90° along the thickness Y direction as the axis, upsetting and deforming in the X direction, and then stretching in the Z direction, flipping 45° in the transverse extension surface to obtain a fourth octagonal billet of Φ680-980mm; and then air cooling for 4-8h;

[0023] S33, adding the fourth octagonal billet when the furnace temperature is 700-850° C., and holding the temperature after reaching 1010-1070° C. for 2-6 hours, upsetting and stretching the billet in the radial height Z direction, flipping 90° in the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, performing upsetting deformation in the Z direction, and then stretching in the X direction, and flipping 45° in the YZ extension surface to obtain a fifth octagonal billet of Φ680-980 mm;

[0024] S34, adding the fifth octagonal billet when the furnace temperature is 600-700° C., holding the temperature after reaching 930-980° C. for 4-8 hours, upsetting and stretching in the X direction, flipping 90° in the YZ extension plane during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, upsetting and deforming in the X direction, and then stretching in the Z direction, flipping 45° in the transverse extension plane, to obtain a sixth octagonal billet of Φ680-980 mm;

[0025] S35, adding the sixth octagonal billet when the furnace temperature is 700-850° C., and holding the temperature after reaching 1010-1070° C. for 2-6 hours, upsetting and stretching the billet in the radial height Z direction, flipping 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° along the thickness Y direction as the axis, performing upsetting deformation in the Z direction, and then stretching in the X direction, and flipping 45° on the YZ extension surface to obtain a seventh octagonal billet with a diameter of 680-980 mm;

[0026] S36. Add the seventh octagonal billet when the furnace temperature is 600-700°C. After the temperature reaches 930-980°C, keep it warm for 4-8 hours. Upset and stretch the billet along the X direction. During the stretching process, flip it 90° on the YZ extension surface once to obtain the intermediate square billet, chamfer the small edges, flip it 90° with the thickness Y direction as the axis, perform upsetting deformation along the X direction, and then stretch it along the Z direction. Finally, return to the radial height Z direction, and radial forge to obtain large-size bars of Φ600-900mm. Then, air cool it for 4-8 hours to finally obtain TC4 bars with a diameter of Φ600-900mm.

[0027] The present invention also provides a TC4 titanium alloy supercritical specification bar for aircraft engines with equiaxed structural uniformity, which is prepared by the above method. The weight percentages of the components in the TC4 titanium alloy supercritical specification bar are as follows: Al: 6.5-6.8%, V: 4.1-4.5%, Fe≤0.2%, C≤0.05%, N≤0.05%, H≤0.0125%, O≤0.20%, the balance being Ti, a single impurity ≤0.1%, and a total impurity content ≤0.2%.

[0028] Furthermore, the grain size of the TC4 titanium alloy supercritical specification bar is ≤23 μm, the grain size is 11-13 grades according to the GB / T 6394-2017 standard, and the primary α phase content is 70-90%.

[0029] Furthermore, the tensile strength of the TC4 titanium alloy supercritical specification bar is ≥960MPa, the yield strength is ≥920MPa, the elongation is ≥12.5%, and the cross-sectional shrinkage is ≥36%; the tensile strength at 400°C is ≥630MPa, the elongation is ≥16%, and the cross-sectional shrinkage is ≥48%. The endurance test at 570MPa and 400°C meets the requirement of 101h without breaking, and the diameter of the flat-bottom hole in the ultrasonic flaw detection is less than or equal to 3.2mm.

[0030] In the manufacturing method of the present invention:

[0031] The present invention uses TC4 titanium alloy ingots with a diameter of Φ860~1000mm, which are obtained through at least three vacuum self-consumption processes, and uses large ingots to meet the needs of large-size bar forging. However, the cross-sectional dimensions of large ingots are relatively large. During the forging process, due to the forgeability of TC4 titanium alloy, it is more difficult to control the uniformity of heat transfer and metal deformation. In order to obtain equiaxed structure after forging, higher requirements need to be placed on the forging process. In contrast, due to the smaller size of small-size ingots, heat transfer and deformation are more uniform under the same forging process conditions, and it is easier to obtain equiaxed structure. Therefore, the use of large ingots for upsetting to obtain equiaxed structure significantly increases the difficulty of forging.

[0032] The present invention controls the deformation of each fire in the β phase region and the α+β region to 80-95%. The large deformation in the β phase region can break up the original coarse as-cast structure of the ingot, achieve grain refinement, and provide an easily breakable structure for subsequent upsetting. The large deformation in the α+β region can transform the α phase from a coarse lamellar structure to a fine equiaxed structure. The equiaxed α phase structure has better isotropy, while strengthening the α / β phase interface bonding force, refining the β phase grains, improving the material strength while maintaining good plasticity and toughness, thereby obtaining a TC4 titanium alloy forged rod with excellent comprehensive mechanical properties.

[0033] The present invention employs a gradient temperature field design and a segmented heating strategy. Preferably, during the heating process of the upsetting and drawing blank, the bar is first preheated at a low temperature to slowly raise its overall temperature, minimizing the internal and external temperature differential and preventing cracking. The temperature is then gradually raised to the appropriate forging temperature. This insulation maintains a consistent internal and external temperature, reducing the risk of cracking. This process effectively ensures uniform temperature across the bar, preventing uneven deformation during forging due to localized overheating or cooling, which can compromise the quality of the forged bar.

[0034] During the forging process, the present invention adopts high-temperature pre-forging in the β phase region and forging in the α+β two-phase region to form a gradient deformation field. During the forging process in the β phase region, the broken β grains are recrystallized to form new, fine grains, which helps to break up the original cast structure, refine the β grains, and build the basic structure morphology. During the forging in the α+β two-phase region, the temperature is reduced to below the β transformation temperature, the β phase transforms to the α phase through the nucleation and growth mechanism, and the α phase nuclei are preferentially formed inside the β grains and at the grain boundaries. This process helps to finely control the structure and optimize the final performance.

[0035] The forging process of the present invention adopts an air cooling method. Compared with water cooling, it can effectively avoid excessive thermal stress inside the TC4 large-size bar due to excessive cooling speed, thereby reducing the risk of defects such as deformation and cracking in the bar. Compared with air cooling, the cooling rate of air cooling is conducive to improving the nucleation rate, inhibiting the growth of grains, and preventing further coarsening of the core structure during the cooling process. Therefore, air cooling helps to obtain a fine grain structure in the TC4 large-size bar, which can not only improve the strength and hardness of the material, but also improve its plasticity and toughness, reduce anisotropy, and make the performance of the bar in different directions more uniform and stable, meeting the strict requirements of engineering applications for material properties. In addition, air cooling can shorten the cooling time, which can significantly improve production efficiency for large-scale production, reduce the production cycle, and facilitate the timely implementation of the next step.

[0036] In the present invention, during the upsetting operation in the Z direction or the X direction, the cross-section of the intermediate square billet after the small edges are chamfered is octagonal, and the billets after single-fire forging all have an octagonal cross-section: compared with the square cross-section, the metal flow is better guided, ensuring that the metal flow is relatively uniform in the next upsetting operation, reducing the stress concentration phenomenon at the corners and edges, and helping to reduce cracks and folds.

[0037] The multi-dimensional reversing upsetting process employed in this invention enables the TC4 titanium alloy billet to be fully deformed in multiple directions, thereby improving microstructure uniformity and reducing differences in the horizontal and vertical directions. This reversing upsetting refines grain size, eliminates internal defects, improves material properties, reduces cracking, and increases the yield rate of bar forging.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1) The present invention adopts a forging process of reversing upsetting and drawing, which replaces the original upsetting and drawing, increases the degree of material deformation, can more fully crush the core structure, and achieve equiaxed. In addition, the temperature of the forging blank is gradually reduced during the subsequent operation, which is conducive to the crushing of grains and the transformation of microstructure, thereby improving the microstructure uniformity of large-size TC4 alloy bars.

[0040] 2) The large-scale TC4 titanium alloy rods prepared by this method have broken through the bottleneck of controlling the uniformity of the microstructure of supercritical-sized rods. The microstructure of the TC4 titanium alloy rods is a uniformly distributed equiaxed structure with a grain size of ≤23μm, an isometry KD ≤1.5, and a primary α-phase content of 70-90%. The TC4 rods with this uniform structure can be applied to many titanium alloy fields and have significant application value.

[0041] 3) By reversing the drawing process, the forgeability is improved, the production cost and material loss are reduced, the uniformity of the structure of large-sized bars is improved, and TC4 titanium alloy bars with equiaxed structure are obtained.

[0042] 4) The supercritical bars produced by this method have a transverse room temperature tensile strength ≥950 MPa and an elongation ≥12%, meeting the performance requirements of large-scale titanium alloy forgings for aircraft engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a schematic diagram of the forging of an octagonal billet according to the present invention;

[0044] Figure 2 This is a low-magnification microstructure photograph of a Φ600 mm TC4 titanium alloy bar obtained in Example 1 of the present invention;

[0045] Figure 3 This is a high-magnification microstructure photograph of a Φ600 mm TC4 titanium alloy bar obtained in Example 1 of the present invention;

[0046] Figure 4 This is a low-magnification microstructure image of the Φ800 mm TC4 titanium alloy bar obtained in Example 2 of the present invention;

[0047] Figure 5 This is a high-magnification microstructure image of the Φ800mm TC4 titanium alloy bar obtained in Example 2 of the present invention;

[0048] Figure 6 This is a low-magnification microstructure image of the Φ900 mm TC4 titanium alloy bar obtained in Example 3 of the present invention;

[0049] Figure 7 This is a high-magnification microstructure image of the Φ900 mm TC4 titanium alloy bar obtained in Example 3 of the present invention;

[0050] Figure 8 This is a low-magnification microstructure image of the TC4 titanium alloy bar obtained in the comparative example;

[0051] Figure 9 This is a high-magnification microstructure image of the TC4 titanium alloy bar obtained in the comparative example. DETAILED DESCRIPTION

[0052] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] Example 1 A method for preparing a TC4 titanium alloy supercritical specification rod with a diameter of Φ600 mm and uniform equiaxial structure for use in aircraft engines, the chemical composition ratio of which is shown in Table 1, comprises the following steps:

[0054] S1. Preparation of TC4 titanium alloy ingot

[0055] Prepare TC4 titanium alloy ingot with a diameter of Φ860mm;

[0056] S2. Preparation of forging blank

[0057] S21, put the TC4 titanium alloy ingot into the furnace at a temperature of 800℃, keep the temperature at 1100℃ for 8 hours, and upset the TC4 titanium alloy ingot along the radial height Z direction ( Figure 1 Middle a), pull long ( Figure 1 In the middle b), during the drawing process, the horizontal extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are inverted. After the thickness Y direction is used as the axis, the billet is turned 90° and upsetting deformation is performed along the Z direction ( Figure 1 c) and then stretch along the X direction ( Figure 1 Middle (d) A single 45° flip on the YZ extension plane yields the first octagonal blank with a diameter of 680 mm.

[0058] S22, put the first octagonal billet into the furnace at a temperature of 700℃, keep it warm for 2h after the temperature reaches 1010℃, and upset it along the X direction ( Figure 1 Middle e), pull long ( Figure 1 In the middle f), during the drawing process, the YZ extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are inverted. The billet is turned 90° along the thickness Y direction and upsetting deformation is performed along the X direction ( Figure 1 Middle g) and then stretch along the Z direction ( Figure 1 (h) A single 45° flip on the transverse extension surface was performed to obtain the second octagonal blank with a diameter of 680 mm;

[0059] S3, Forged Bars

[0060] S31, put the second octagonal billet into the furnace at a temperature of 600℃, keep it warm for 4 hours after the temperature reaches 930℃, and upset the second octagonal billet along the radial height Z direction ( Figure 1 Middle a), pull long ( Figure 1 In the middle b), during the drawing process, the horizontal extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are chamfered. The billet is turned 90° along the thickness Y direction and upsetting is performed along the Z direction ( Figure 1 c) After deformation, it is stretched along the X direction ( Figure 1 Middle (d) A single 45° flip on the YZ extension plane yields the third octagonal blank with a diameter of 680 mm.

[0061] S32, put the third octagonal billet into the furnace at a temperature of 600℃, keep it at 930℃ for 4 hours, and upset it along the X direction ( Figure 1 Middle e), pull long ( Figure 1 In the middle f), during the drawing process, the YZ extension surface is turned 90° once, and the intermediate billet is obtained and then the small edges are chamfered. The billet is turned 90° along the thickness Y direction and upsetting is performed along the X direction ( Figure 1 g) after deformation and then stretched along the Z direction ( Figure 1 (h) A single 45° flip on the transverse extension surface was performed to obtain the fourth octagonal blank of Φ680mm; and then air-cooled for 4h;

[0062] S33, put the fourth octagonal billet into the furnace at a temperature of 700℃, keep it at that temperature for 2 hours after the temperature reaches 1010℃, and upset the billet along the radial height Z direction ( Figure 1 Middle a), pull long ( Figure 1 In the middle b), during the drawing process, the horizontal extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are inverted. After the thickness Y direction is used as the axis, the billet is turned 90° and upsetting deformation is performed along the Z direction ( Figure 1 c) and then stretch along the X direction ( Figure 1 Middle (d) A single 45° flip on the YZ extension plane yields the fifth octagonal blank with a diameter of 680 mm.

[0063] S34, put the 5th octagonal billet into the furnace at a temperature of 600℃, keep it at 930℃ for 4 hours, and upset it along the X direction ( Figure 1 Middle e), pull long ( Figure 1 In the middle f), during the drawing process, the YZ extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are inverted. The billet is turned 90° along the thickness Y direction and upsetting deformation is performed along the X direction ( Figure 1 Middle g) and then stretch along the Z direction ( Figure 1 (h) A single 45° flip on the transverse extension surface was performed to obtain the sixth octagonal blank with a diameter of 680 mm;

[0064] S35, put the 6th octagonal billet into the furnace at a temperature of 700℃, keep it at that temperature for 2 hours after the temperature reaches 1010℃, and upset the billet along the radial height Z direction ( Figure 1 Middle a), pull long ( Figure 1 In the middle b), during the drawing process, the horizontal extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are inverted. After the thickness Y direction is used as the axis, the billet is turned 90° and upsetting deformation is performed along the Z direction ( Figure 1 c) and then stretch along the X direction ( Figure 1 Middle (d) A single 45° flip on the YZ extension plane yields the seventh octagonal blank with a diameter of 680 mm.

[0065] S36, put the 7th octagonal billet into the furnace at a temperature of 600℃, keep it warm for 4 hours after the temperature reaches 930℃, and upset the billet along the X direction ( Figure 1 Middle e), pull long ( Figure 1 In the middle f), during the drawing process, the YZ extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are inverted. The billet is turned 90° along the thickness Y direction and upsetting deformation is performed along the X direction ( Figure 1 Middle g) and then stretch along the Z direction ( Figure 1 The rod is cut into the shape of a rod (middle h) to Φ600mm, and finally returned to the original radial height Z direction, and then air-cooled for 4h to finally obtain a large-sized bar with a diameter of Φ600mm.

[0066] The obtained rods were subjected to microstructure and mechanical property tests, and the properties are shown in Table 2;

[0067] Figure 2 The microstructure photograph of the Φ600mm TC4 titanium alloy bar obtained at low magnification shows that there are no visible cracks, shrinkage cavities, pores, folds, inclusions, segregation or other defects that affect use in the microstructure. There are no obvious, visually visible clear grains in the low-magnification microstructure.

[0068] Figure 3 These are the microstructure photos of the Φ600mm TC4 titanium alloy rod obtained under high magnification. It can be seen from the pictures that the microstructure is equiaxed, the content of primary α phase in the microstructure reaches more than 80%, and the equiaxed primary α phase is distributed on the matrix of the β transformation microstructure. All the original β grain boundaries are fully broken, and there is no continuous network of α phase on the original β grain boundaries.

[0069] Example 2 A method for preparing a TC4 titanium alloy supercritical specification rod with a diameter of Φ800 mm and uniform equiaxial structure for use in aircraft engines, the chemical composition ratio of which is shown in Table 1, comprises the following steps:

[0070] S1. Preparation of TC4 titanium alloy ingot

[0071] Preparing a TC4 titanium alloy ingot with a diameter of Φ960 mm;

[0072] S2. Preparation of forging blank

[0073] S21, placing the TC4 titanium alloy ingot into a furnace at a temperature of 850° C., holding the ingot at 1150° C. for 10 hours, upsetting and stretching the ingot in the radial height Z direction, flipping the ingot 90° in the transverse extension surface during the stretching process to obtain an intermediate square billet, chamfering the small edges, flipping the ingot 90° with the thickness Y direction as the axis, upsetting the ingot in the Z direction, stretching the ingot in the X direction, and flipping the ingot 45° in the YZ extension surface to obtain a first octagonal billet of Φ880 mm;

[0074] S22, placing the first octagonal billet into a furnace at a temperature of 800° C., holding the temperature after reaching 1050° C. for 4 hours, upsetting and stretching in the X direction, flipping 90° in the YZ extension plane during the stretching process to obtain an intermediate billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, upsetting and deforming in the X direction, and then stretching in the Z direction, flipping 45° in the transverse extension plane to obtain a second octagonal billet of Φ880 mm;

[0075] S3, Forged Bars

[0076] S31, placing the second octagonal billet into the furnace at a temperature of 650° C., holding the temperature after reaching 960° C. for 6 hours, upsetting and stretching the billet in the radial height Z direction, flipping 90° in the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, performing upsetting deformation in the Z direction, and then stretching in the X direction, flipping 45° in the YZ extension surface, to obtain a third octagonal billet of Φ880 mm;

[0077] S32, placing the third octagonal billet into a furnace at a temperature of 650° C., holding the temperature after reaching 960° C. for 6 hours, upsetting and stretching in the X direction, flipping 90° in the YZ extension plane during the stretching process to obtain an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, upsetting and deforming in the X direction, and then stretching in the Z direction, flipping 45° in the transverse extension plane to obtain a fourth octagonal billet of Φ880 mm; and then air cooling for 6 hours;

[0078] S33, placing the fourth octagonal billet into the furnace at a temperature of 800° C., holding the temperature after reaching 1050° C. for 4 hours, upsetting and stretching the billet in the radial height Z direction, flipping 90° in the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, flipping 45° in the YZ extension surface, to obtain a fifth octagonal billet of Φ880 mm;

[0079] S34, placing the fifth octagonal billet into a furnace at a temperature of 650° C., holding the temperature after reaching 960° C. for 6 hours, upsetting and stretching in the X direction, flipping 90° in the YZ extension plane during the stretching process to obtain an intermediate billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, upsetting and deforming in the X direction, and then stretching in the Z direction, flipping 45° in the transverse extension plane to obtain a sixth octagonal billet of Φ880 mm;

[0080] S35, placing the sixth octagonal billet into the furnace at a temperature of 800° C., holding the temperature after reaching 1050° C. for 6 hours, upsetting and stretching the billet in the radial height Z direction, flipping 90° in the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, performing upsetting deformation in the Z direction, and then stretching in the X direction, flipping 45° in the YZ extension surface, to obtain a seventh octagonal billet of Φ880 mm;

[0081] S36. The 7th octagonal billet is put into the furnace at a furnace temperature of 650°C. After the temperature reaches 960°C, it is kept warm for 6 hours. The billet is upset and stretched along the X direction. During the stretching process, it is flipped 90° on the YZ extension surface once to obtain the intermediate square billet. After the small edge is chamfered, it is flipped 90° with the thickness Y direction as the axis and upset and deformed along the X direction. Then it is stretched to Φ800mm along the Z direction. Finally, it is switched back to the radial height Z direction, and then air-cooled for 6 hours to finally obtain a large-sized bar with a diameter of Φ800mm.

[0082] The obtained rods were subjected to microstructure and mechanical property tests, and the properties are shown in Table 2;

[0083] Figure 4 The microstructure photograph of the Φ800mm TC4 titanium alloy bar obtained at low magnification shows that there are no visible cracks, shrinkage cavities, pores, folds, inclusions, segregation or other defects that affect use in the microstructure. There are no obvious, visually visible clear grains in the low magnification microstructure.

[0084] Figure 5 These are the microstructure photos of the Φ800mm TC4 titanium alloy rod obtained under high magnification. It can be seen from the pictures that the microstructure is equiaxed, the content of primary α phase in the microstructure reaches more than 80%, and the equiaxed primary α phase is distributed on the matrix of the β transformation microstructure. All the original β grain boundaries are fully broken, and there is no continuous network of α phase on the original β grain boundaries.

[0085] Example 3 A method for preparing a TC4 titanium alloy supercritical specification rod with a diameter of Φ900 mm and uniform equiaxial structure for use in aircraft engines, the chemical composition ratio of which is shown in Table 1, comprises the following steps:

[0086] S1. Preparation of TC4 titanium alloy ingot

[0087] Prepare TC4 titanium alloy ingot with a diameter of Φ1000mm;

[0088] S2. Preparation of forging blank

[0089] S21, placing the TC4 titanium alloy ingot into a furnace at a temperature of 900° C., holding the ingot at 1200° C. for 12 h, upsetting and stretching the ingot in the radial height Z direction, flipping the ingot 90° in the transverse extension surface during the stretching process to obtain an intermediate billet, chamfering the small edges, flipping the ingot 90° along the thickness Y direction as an axis, upsetting the ingot in the Z direction, stretching the ingot in the X direction, and flipping the ingot 45° in the YZ extension surface to obtain a first octagonal billet of Φ980 mm;

[0090] S22, placing the first octagonal billet into a furnace at a temperature of 850° C., holding the temperature after reaching 1070° C. for 6 hours, upsetting and stretching in the X direction, flipping 90° in the YZ extension plane during the stretching process to obtain an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, upsetting and deforming in the X direction, and then stretching in the Z direction, flipping 45° in the transverse extension plane to obtain a second octagonal billet of Φ980 mm;

[0091] S3, Forged Bars

[0092] S31, placing the second octagonal billet into the furnace at a temperature of 700° C., holding the temperature after reaching 980° C. for 8 hours, upsetting and stretching the billet in the radial height Z direction, flipping 90° in the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, performing upsetting deformation in the Z direction, and then stretching in the X direction, flipping 45° in the YZ extension surface, to obtain a third octagonal billet of Φ980 mm;

[0093] S32, placing the third octagonal billet into the furnace at a temperature of 700° C., holding the temperature after reaching 980° C. for 8 hours, upsetting and stretching in the X direction, flipping 90° in the YZ extension plane during the stretching process to obtain an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, upsetting and deforming in the X direction, and then stretching in the Z direction, flipping 45° in the transverse extension plane to obtain a fourth octagonal billet of Φ980 mm; and then air cooling for 8 hours;

[0094] S33, placing the fourth octagonal billet into the furnace at a temperature of 850° C., holding the temperature after reaching 1070° C. for 6 hours, upsetting and stretching the billet in the radial height Z direction, flipping 90° in the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, performing upsetting deformation in the Z direction, and then stretching in the X direction, flipping 45° in the YZ extension surface, to obtain a fifth octagonal billet of Φ980 mm;

[0095] S34, placing the fifth octagonal billet into a furnace at a temperature of 700° C., holding the temperature after reaching 980° C. for 8 hours, upsetting and stretching in the X direction, flipping 90° in the YZ extension plane during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, upsetting and deforming in the X direction, and then stretching in the Z direction, flipping 45° in the transverse extension plane, to obtain a sixth octagonal billet of Φ980 mm;

[0096] S35, placing the sixth octagonal billet into the furnace at a temperature of 850° C., holding the temperature after reaching 1070° C. for 8 hours, upsetting and stretching the billet in the radial height Z direction, flipping 90° in the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, performing upsetting deformation in the Z direction, and then stretching in the X direction, flipping 45° in the YZ extension surface, to obtain a seventh octagonal billet of Φ980 mm;

[0097] S36, placing the seventh octagonal billet into a furnace at a temperature of 700° C., holding the temperature after reaching 980° C. for 8 hours, upsetting and stretching in the X direction, flipping 90° in the YZ extension plane during the stretching process to obtain an intermediate square billet, chamfering the small edges, flipping 90° along the thickness Y direction as an axis, upsetting and deforming in the X direction, and then stretching in the Z direction, flipping 45° in the transverse extension plane to obtain an eighth octagonal billet of Φ980 mm; and then air cooling for 8 hours;

[0098] S37, placing the eighth octagonal billet into a furnace at a temperature of 850° C., holding the temperature after reaching 1070° C. for 6 hours, upsetting and stretching the billet in the radial height Z direction, flipping 90° in the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness Y direction as the axis, performing upsetting deformation in the Z direction, and then stretching in the X direction, flipping 45° in the YZ extension surface, to obtain a ninth octagonal billet of Φ980 mm;

[0099] S38. The ninth octagonal billet is put into the furnace at a temperature of 700°C. After the temperature reaches 980°C, it is kept warm for 8 hours. The billet is upset and stretched along the X direction. During the stretching process, it is flipped 90° on the YZ extension surface once to obtain an intermediate square billet, and then the small edges are chamfered. The billet is flipped 90° with the thickness Y direction as the axis, upset and deformed along the X direction, and then stretched to Φ900mm along the Z direction. Finally, it is switched back to the radial height Z direction, and then air-cooled for 8 hours to finally obtain a large-sized bar with a diameter of Φ900mm.

[0100] The obtained rods were subjected to microstructure and mechanical property tests, and the properties are shown in Table 2;

[0101] Figure 6 The microstructure photograph of the Φ900mm TC4 titanium alloy bar obtained at low magnification shows that there are no visible cracks, shrinkage cavities, pores, folds, inclusions, segregation or other defects that affect use in the microstructure. There are no obvious, visually visible clear grains in the low magnification microstructure.

[0102] Figure 7 They are the microstructure photos of the Φ900mm TC4 titanium alloy rod obtained under high magnification. It can be seen from the pictures that the microstructure is equiaxed, the content of primary α phase in the microstructure reaches more than 85%, and the primary α phase grain size rating reaches level 13 in the GB / T6394-2017 metal average grain size determination method. Equiaxed primary α phase is distributed on the matrix of β transformation structure, all original β grain boundaries are fully broken, and there is no continuous network of α phase on the original β grain boundaries.

[0103] Comparative Example A method for preparing a TC4 titanium alloy rod with a diameter of Φ800mm, the chemical composition ratio of which is shown in Table 1,

[0104] Table 1 Chemical composition of 600~900mm TC4 titanium alloy bars Unit: mass percentage

[0105]

[0106] The preparation method comprises the following steps:

[0107] S1. Preparation of TC4 titanium alloy ingot

[0108] Preparing a TC4 titanium alloy ingot with a diameter of Φ960 mm;

[0109] S2. Preparation of forging blank

[0110] S21, placing the TC4 titanium alloy ingot into a furnace at a temperature of 850° C., holding the ingot at 1150° C. for 10 hours, and deforming the ingot by upsetting and drawing to obtain a first ingot of 880 mm;

[0111] S22, placing the blank into a furnace at a temperature of 800° C., holding the temperature at 1050° C. for 4 hours, and deforming the blank by upsetting and drawing to obtain a second blank of Φ880 mm;

[0112] S3, Forged Bars

[0113] S31, placing the second blank into the furnace at a temperature of 650° C., holding the temperature at 960° C. for 6 hours, and deforming the blank by upsetting and drawing to obtain a third blank of Φ880 mm;

[0114] S32. The third blank is placed in the furnace at a temperature of 650°C. After the temperature reaches 960°C, it is kept warm for 6 hours. The blank is deformed by upsetting and drawing to obtain a fourth blank of Φ880mm; and then air-cooled.

[0115] S33, placing the fourth blank into the furnace at a temperature of 800° C., holding the temperature at 1050° C. for 4 hours, and deforming the blank by upsetting and drawing to obtain a fifth blank of Φ880 mm;

[0116] S34, placing the fifth blank into the furnace at a temperature of 650° C., holding the temperature at 960° C. for 6 hours, and deforming the blank by upsetting and drawing to obtain a sixth blank of Φ880 mm;

[0117] S35, placing the sixth blank into the furnace at a temperature of 800° C., holding the temperature at 1050° C. for 4 hours, and deforming the blank by upsetting and drawing to obtain a seventh blank of Φ880 mm;

[0118] S36. The seventh billet is put into the furnace at a temperature of 650°C. After the temperature reaches 960°C, it is kept warm for 6 hours. The billet is deformed by upsetting and drawing, and then air-cooled to finally obtain a large-sized bar with a diameter of Φ800mm.

[0119] The obtained rods were subjected to microstructure and mechanical property tests, and the properties are shown in Table 2;

[0120] Table 2 Tensile properties of Φ600~900mm TC4 titanium alloy bars

[0121]

[0122] As can be seen from Table 2, the diameter of the rods prepared in Examples 1 to 3 of the present invention can reach Φ600 to 900 mm, the tensile strength of the rods is ≥960 MPa, the yield strength is ≥920 MPa, the elongation is ≥12.5%, and the cross-sectional reduction rate is ≥36%. At a high temperature of 400°C, the tensile strength of the TC4 titanium alloy rod is ≥630 MPa, the elongation is ≥16%, and the cross-sectional reduction rate is ≥48%. This shows that the TC4 titanium alloy rod prepared by the method of the present invention has high strength and high plasticity while having a larger specification, and can meet the requirements of large-size rods for aircraft engines.

[0123] In the preparation process of the comparative example, only a single upsetting and drawing process was performed, the upsetting and drawing direction was unidirectional (along the Z direction), and the cooling method was air cooling with a low cooling rate, resulting in a coarse core structure. The yield strength of the obtained rod was 921 MPa and the high-temperature tensile strength was 819 MPa, which were lower than the mechanical properties of the rod obtained by upsetting and drawing in the X direction.

[0124] Figure 8 The microstructure of the Φ800mm TC4 titanium alloy bar obtained for the comparative example at low magnification is shown in the picture. It can be seen from the picture that the microstructure is uneven at low magnification and does not meet the requirements of the bar in GJB1538.

[0125] Figure 9 This is a high-magnification microstructure photograph of a Φ800mm TC4 titanium alloy rod obtained for comparison. It can be seen from the picture that the content of primary α phase in the structure is about 60%, there is little primary equiaxed α phase, long strips of α phase are distributed on the matrix of the β transformation structure, the original β grain boundaries are not fully broken, and the microstructure uniformity is poor.

[0126] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for preparing TC4 titanium alloy supercritical specification bars for aircraft engines with equiaxed structural uniformity, characterized in that The steps include: S1. Prepare a TC4 titanium alloy ingot, wherein the diameter of the TC4 titanium alloy ingot is Φ860-1000 mm; S2, prepare forging blank, Determining the radial height direction Z, the transverse width direction X, and the thickness direction Y of the TC4 titanium alloy ingot; S21, adding the TC4 titanium alloy ingot when the furnace temperature is 800-900°C, and holding the ingot at 1100-1200°C for 8-12 hours, first performing upsetting deformation on the TC4 titanium alloy ingot along the radial height direction Z, then flipping 90° with the thickness direction Y as the axis, stretching along the radial height direction Z, and flipping 90° on the XY extension plane perpendicular to the radial height direction Z to obtain an intermediate billet, then chamfering the small edges, flipping 90° with the thickness direction Y as the axis, and continuing to perform upsetting deformation along the radial height direction Z, then stretching along the transverse width direction X, and flipping 45° on the YZ extension plane perpendicular to the transverse width direction X to obtain a first octagonal billet of Φ680-980 mm; S22, the first octagonal billet of Φ680-980 mm obtained in step S21 is put into a furnace at a furnace temperature of 700-850° C., and after the temperature reaches 1010-1070° C., it is kept warm for 2-6 hours, and the first octagonal billet is first subjected to upsetting deformation along the transverse width direction X, and then flipped 90° with the thickness direction Y as the axis, and then stretched along the transverse width direction X, and flipped 90° in the YZ extension surface to obtain an intermediate square billet, and then the small edges are chamfered, and then flipped 90° with the thickness direction Y as the axis, and then continued to be subjected to upsetting deformation along the transverse width direction X, and then stretched along the radial height direction Z, and flipped 45° in the XY extension surface to obtain a second octagonal billet of Φ680-980 mm; The upsetting deformation in any of the above steps is controlled to be 80~95%; S3, forging bars. The second octagonal billet is forged for 6 times to obtain bars with a diameter of Φ600~900mm. The specific steps are as follows: S31, adding the second octagonal billet when the furnace temperature is 600-700°C, and keeping the temperature at 930-980°C for 4-8h, upsetting and stretching the second octagonal billet in the radial height direction Z, flipping 90° in the XY extension plane during the stretching process, obtaining an intermediate billet, chamfering the small edges, flipping 90° with the thickness direction Y as the axis, and then performing upsetting deformation in the radial height direction Z, and then stretching it in the transverse width direction X, and flipping 45° in the YZ extension plane to obtain a third octagonal billet of Φ680-980mm; S32, adding the third octagonal billet when the furnace temperature is 600-700° C., and holding the temperature after reaching 930-980° C. for 4-8 hours, upsetting and stretching the third octagonal billet in the transverse width direction X, flipping 90° in the YZ extension plane during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness direction Y as the axis, performing upsetting deformation in the transverse width direction X, and then stretching in the radial height direction Z, flipping 45° in the XY extension plane, to obtain a fourth octagonal billet of Φ680-980 mm; and then air-cooling for 4-8 hours; S33, adding the fourth octagonal billet when the furnace temperature is 700-850° C., and holding the temperature after reaching 1010-1070° C. for 2-6 hours, upsetting and stretching the fourth octagonal billet in the radial height direction Z, flipping 90° in the XY extension plane during the stretching process, obtaining an intermediate billet, chamfering the small edges, flipping 90° with the thickness direction Y as the axis, performing upsetting deformation in the radial height direction Z, and then stretching in the transverse width direction X, and flipping 45° in the YZ extension plane to obtain a fifth octagonal billet of Φ680-980 mm; S34, adding the fifth octagonal billet when the furnace temperature is 600-700° C., and holding the temperature after reaching 930-980° C. for 4-8 hours, upsetting and stretching the fifth octagonal billet in the transverse width direction X, flipping 90° in the YZ extension plane during the stretching process, obtaining an intermediate square billet, chamfering the small edges, flipping 90° with the thickness direction Y as the axis, performing upsetting deformation in the transverse width direction X, and then stretching in the radial height direction Z, flipping 45° in the XY extension plane, to obtain a sixth octagonal billet of Φ680-980 mm; S35, adding the sixth octagonal billet when the furnace temperature is 700-850° C., and holding the temperature after reaching 1010-1070° C. for 2-6 hours, upsetting and stretching the sixth octagonal billet in the radial height direction Z, flipping 90° in the XY extension plane during the stretching process, obtaining an intermediate billet, chamfering the small edges, flipping 90° with the thickness direction Y as the axis, performing upsetting deformation in the radial height direction Z, and then stretching in the transverse width direction X, and flipping 45° in the YZ extension plane to obtain a seventh octagonal billet of Φ680-980 mm; S36. Add the 7th octagonal billet when the furnace temperature is 600-700°C, and keep it warm for 4-8 hours after the temperature reaches 930-980°C. Upset and stretch the 7th octagonal billet along the transverse width direction X. During the stretching process, flip it 90° on the YZ extension surface once to obtain an intermediate square billet, chamfer the small edges, flip it 90° with the thickness direction Y as the axis, and then perform upsetting deformation along the transverse width direction X and then stretch it along the radial height direction Z. Finally, switch back to the radial height direction Z to obtain large-size bars of Φ600-900 mm, which are then air-cooled for 4-8 hours to finally obtain TC4 titanium alloy supercritical size bars for aircraft engines with equiaxed microstructure uniformity.

2. The method for preparing a TC4 titanium alloy supercritical specification bar for an aero-engine with equiaxed structural uniformity according to claim 1, characterized in that: In the step S1 of preparing the TC4 titanium alloy ingot, at least three vacuum consumable melting processes are performed to obtain the TC4 titanium alloy ingot having a diameter of 860 to 1000 mm.

3. A TC4 titanium alloy supercritical bar for aircraft engines with equiaxed microstructure homogeneity prepared by the method according to any one of claims 1 to 2, characterized in that: The weight percentages of the components in the TC4 titanium alloy supercritical specification bar are: Al: 6.5~6.8%, V: 4.1~4.5%, Fe≤0.2%, C≤0.05%, N≤0.05%, H≤0.0125%, O≤0.20%, the balance is Ti, a single impurity is ≤0.1%, and the total impurity amount is ≤0.2%.

4. The TC4 titanium alloy supercritical standard bar for aircraft engines with equiaxed structural uniformity according to claim 3, characterized in that: The grain size of the TC4 titanium alloy supercritical specification bar is ≤23 μm, the grain size is 11 to 13 grades according to the GB / T 6394-2017 standard, and the primary α phase content is 70 to 90%.

5. The TC4 titanium alloy supercritical standard bar for aircraft engines with equiaxed structural uniformity according to claim 3, characterized in that: The tensile strength of the TC4 titanium alloy supercritical specification bar is ≥960MPa, the yield strength is ≥920MPa, the elongation is ≥12.5%, and the cross-sectional shrinkage is ≥36%; the tensile strength at 400°C is ≥630MPa, the elongation is ≥16%, and the cross-sectional shrinkage is ≥48%.

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