Preparation method of large-specification TC4 titanium alloy bar for aero-engine blade

Abstract

The invention belongs to the technical field of titanium alloy material processing, and particularly relates to a preparation method of a large-specification TC4 titanium alloy bar for an aero-engine blade. Compared with a traditional preparation process, on one hand, a large upsetting ratio is adopted in a single-phase region, the deformation amount is increased, the production heating number is reduced, and the production cost is reduced; on the other hand, reversing upsetting and drawing and diagonal forging processes are added, generation of difficult-to-deform areas is reduced, deformation is more uniform and sufficient, and the uniformity of the structure is guaranteed; and finally, a thermomechanical treatment process is added, the recrystallization process of the alloy is promoted, fine beta grains and a thin alpha lamellar structure are obtained, and preparation is made for subsequently obtaining fine and uniform equiaxed structures. The preparation method is simple and high in operability, and batch stable production can be achieved without equipment modification and the like; and the prepared TC4 titanium alloy bar is excellent in various properties and meets the technical index requirements, and the application field of the TC4 titanium alloy bar is further expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy material processing, and particularly relates to a method for preparing large-size TC4 titanium alloy bars for aircraft engine blades. Background Art

[0002] Titanium and titanium alloys are widely used in aviation, aerospace, petroleum, chemical industry, weapons, ships and other fields due to their high strength, low density, high / low temperature resistance and corrosion resistance. TC4 titanium alloy has become the ace alloy in the field of titanium alloy applications due to its advantages such as good comprehensive performance, formability and welding performance, and its usage accounts for more than 50% of all titanium alloys. In aircraft engines, TC4 titanium alloy is mainly used in parts such as fan disks, compressor disks and blades. Compared with steel products, it can significantly reduce the overall weight of the engine. Because the application environment of TC4 titanium alloy is complex, extremely high requirements are placed on its comprehensive performance. In particular, engine blades, as high-speed rotating structural parts, have more stringent requirements on the composition, structure, room temperature mechanical properties, high temperature endurance performance, high cycle fatigue life and other aspects of TC4 titanium alloy materials.

[0003] To meet these complex technical requirements, aircraft engine blades have traditionally been manufactured using small-sized TC4 bars. The maximum bar size specified in GJB 494A-2008, "Specification for Titanium Alloy Bars for Aircraft Engine Compressor Blades," is only 70 mm. However, with the rapid development of my country's aviation industry and the unstoppable trend toward larger aircraft, the production of larger TC4 titanium alloy bars has become increasingly urgent to meet the manufacturing needs of large aircraft engine blades.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a method for preparing large-sized TC4 titanium alloy bars for aircraft engine blades.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing large-sized TC4 titanium alloy bars for aircraft engine blades, which comprises the following specific steps:

[0008] Step 1: Forging: First heat the TC4 titanium alloy ingot to 800-850℃ and keep it warm for 100-150min, then heat it to T β+ 100-200℃ and keep warm for 120-180min, then forge the blank, perform two upsetting and two drawing, upsetting ratio is 1.6-1.9, final forging temperature is ≥850℃, water cooling after forging, and obtain forging blank A;

[0009] Step 2, intermediate forging: first heat the forging blank A to 800-850℃ and keep it at this temperature for 30-90min, then heat it to T β+ 50-100℃ and keep warm for 150-210min, then carry out intermediate forging, perform two upsetting and two drawing, upsetting ratio is 1.6-1.9, final forging temperature is ≥800℃, water cooling after forging, and obtain forging blank B;

[0010] It should be noted that both step 1 and step 2 are forged with a large upsetting ratio, and a large deformation is adopted in the single-phase region to further improve the forgeability of the billet, reduce the probability of the generation of the difficult-to-deform zone, enable the as-cast structure to be fully broken, and store energy for the subsequent deformation heat treatment. After the large deformation, rapid cooling is performed to increase the nucleation rate of the alloy, obtain finer β grains and martensite structure, and prepare for further refinement of the structure in the future.

[0011] Step 3: Two-phase zone forging: first heat the forging blank B to 800-850℃ and keep it at this temperature for 30-90min, then heat it to T β- 30-70℃ and keep warm for 180-270min, then carry out two-phase zone blank making, perform 3-5 fire upsetting and drawing process, among which 2 fires are reverse upsetting and drawing, two upsetting and two drawing in each fire, single upsetting ratio is 1.4-1.7, final forging temperature is ≥750℃, air cooling is carried out after forging, and forging blank C is obtained;

[0012] It should be noted that in step 3, in order to improve the forgeability of the billet, the forging billet B after the first fire upsetting is sawn into two equal sections, and the subsequent process flow is carried out separately; the forging billet B is repeatedly upset in the two-phase region to superimpose the deformation and further refine the grains. In this process, a reversing upsetting process is added to deform the billet from different directions to reduce the anisotropy of the bar; after this process, the original β grain boundary will be fully broken, and the structure formed by the processing of the two-phase region will be obtained, that is, the less equiaxed α and more elongated α structure on the β matrix are transformed. Since the deformation is not sufficient, the structure is not fully equiaxed;

[0013] Step 4: Drawing and forming: First, heat the forging blank C to T β- 30-70℃ and keep warm for 120-180min, then perform 3-5 fire drawing process, add diagonal forging process during the drawing process, total forging ratio ≥5.0, final forging temperature ≥750℃, air-cool after forging to obtain forging billet bar;

[0014] It should be noted that in step 4, a diagonal forging process is used during the drawing process to eliminate the difficult-to-deform area in the surface area of the billet, reduce the anisotropy of the bar, and through sufficient drawing deformation, make the elongated α structure completely equiaxed through recrystallization. In this step, since there are clear requirements for the content of primary α phase in the microstructure, the heating temperature must be strictly controlled to ensure that the content of primary α phase meets the requirements;

[0015] Step 5, annealing: heating the forging billet to 750-850° C., keeping the temperature for 1-3 hours, and then air-cooling to room temperature to finally obtain the desired TC4 titanium alloy bar;

[0016] It should be noted that the annealing equipment uses a box-type resistance furnace with a furnace temperature uniformity of ≤ (±10)°C, and the furnace is put into use when the temperature reaches the required level.

[0017] Specifically, in step 1, the TC4 titanium alloy ingot is obtained by three times of vacuum consumable arc furnace melting, and its chemical composition meets the following requirements in terms of mass percentage: Al: 6.1-6.5%, V: 3.95-4.35%, O: 0.18-0.20%, Fe≤0.3%, C≤0.05%, N≤0.03%, H≤0.008%, Si≤0.15%, Bi≤0.0014%, Y≤0.001%, single impurity element≤0.1%, total impurity elements≤0.3%, and the remainder is Ti.

[0018] On the other hand, the present invention provides a TC4 titanium alloy bar prepared by a method for preparing a large-size TC4 titanium alloy bar for aircraft engine blades. The tensile strength R m ≥950MPa, yield strength R P0.2 ≥860MPa, elongation A≥15%, section shrinkage Z≥35%, room temperature impact energy KU2≥33J, rotary bending fatigue test at room temperature σ=460N / mm 2 、Nf≥2×10 6 Weeks, no fracture occurred;

[0019] After testing at a high temperature of 400°C, its tensile strength R m ≥620MPa, yield strength R P0.2 ≥490MPa, elongation A≥15%, section shrinkage Z≥50%, high temperature endurance test σ=570N / mm at 400℃ 2 , when τ≥100h, no fracture occurs.

[0020] It should be noted that the T β+ Indicates the temperature above the phase transition point, T β- Indicates the temperature below the phase transition point.

[0021] On the other hand, the present invention provides an application of a method for preparing large-sized TC4 titanium alloy bars for aircraft engine blades, characterized in that it is applied to the preparation of large-sized TC4 titanium alloy bars for aircraft engine blades.

[0022] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0023] Compared with the traditional preparation process, the preparation method of the present invention adopts a large upsetting ratio in the single-phase zone, increases the deformation amount to reduce the number of production fires, and reduces the production cost; on the other hand, it adds reversing upsetting and diagonal forging processes to reduce the generation of difficult-to-deform areas, makes the deformation more uniform and sufficient, and ensures the uniformity of the organization and the consistency of performance; finally, it adds a deformation heat treatment process to promote the recrystallization process of the alloy, obtains relatively fine β grains and thinner α lamellar organization, and prepares for the subsequent acquisition of fine and uniform equiaxed organization.

[0024] The macrostructure of the TC4 titanium alloy bar prepared by the preparation method of the present invention complies with the requirements of GJB 494A-2008. Figure 1 Grade 1 to 2; the microstructure is evenly distributed in an equiaxed structure, and the primary α phase content is ≥ 65%, which meets the requirements of GJB 494A-2008 Figure 2 Grade 1 to 2; the size of the long α phase is ≤ 0.06mm, in line with GJB 494A-2008 Figure 5 Level 1 to 2.

[0025] The TC4 titanium alloy bar prepared by the preparation method of the present invention has a tensile strength R m ≥950MPa, yield strength R P0.2 ≥860MPa, elongation A≥15%, section shrinkage Z≥35%, room temperature impact energy KU2≥33J, rotary bending fatigue test at room temperature σ=460N / mm 2 、Nf≥2×10 6 Weeks, no fracture occurred, meeting the requirements;

[0026] At 400℃, its tensile strength R m ≥620MPa, yield strength R P0.2 ≥490MPa, elongation A≥15%, section shrinkage Z≥50%, high temperature endurance test σ=570N / mm at 400℃ 2 , when τ≥100h, no fracture occurs, which meets the requirements.

[0027] Furthermore, the preparation method of the present invention is simple and highly operational, and can achieve stable batch production without the need for equipment modification, etc., and the prepared TC4 titanium alloy rods have excellent performance and meet the technical index requirements, further expanding the application field of TC4 titanium alloy rods. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, serve to explain the principles of the invention.

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0030] Figure 1 is a flow chart of the preparation method of the present invention;

[0031] Figure 2 This is a low-magnification microstructure diagram of the head and bottom of the rod prepared in Example 1 of the present invention;

[0032] Figure 3 The microstructure diagrams of the head and tail of the rod prepared in Example 1 of the present invention are as follows;

[0033] Figure 4 This is a low-magnification microstructure diagram of the head and tail of the rod prepared in Example 2 of the present invention;

[0034] Figure 5 The microstructure diagrams of the head and tail of the rod prepared in Example 2 of the present invention are as follows;

[0035] Figure 6 This is a low-magnification microstructure diagram of the head and tail of the rod prepared in Example 3 of the present invention;

[0036] Figure 7 The microstructure diagrams of the head and tail of the rod prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0037] Exemplary embodiments will now be described in detail, with examples shown in the accompanying drawings. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present invention. Instead, they are merely examples consistent with some aspects of the present invention as detailed in the appended claims.

[0038] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is described in further detail below with reference to the accompanying drawings and embodiments.

[0039] The present invention provides a method for preparing large-sized TC4 titanium alloy bars for aircraft engine blades, which comprises the following specific steps:

[0040] Step 1: Forging: First heat the TC4 titanium alloy ingot to 800-850℃ and keep it warm for 100-150min, then heat it to T β+ 100-200℃ and keep warm for 120-180min, then forge the blank, perform two upsetting and two drawing, upsetting ratio is 1.6-1.9, final forging temperature is ≥850℃, water cooling after forging, and obtain forging blank A;

[0041] Step 2, intermediate forging: first heat the forging blank A to 800-850℃ and keep it at this temperature for 30-90min, then heat it to T β+ 50-100℃ and keep warm for 150-210min, then carry out intermediate forging, perform two upsetting and two drawing, upsetting ratio is 1.6-1.9, final forging temperature is ≥800℃, water cooling after forging, and obtain forging blank B;

[0042] It should be noted that both step 1 and step 2 are forged with a large upsetting ratio, and a large deformation is adopted in the single-phase region to further improve the forgeability of the billet, reduce the probability of the generation of the difficult-to-deform zone, enable the as-cast structure to be fully broken, and store energy for the subsequent deformation heat treatment. After the large deformation, rapid cooling is performed to increase the nucleation rate of the alloy, obtain finer β grains and martensite structure, and prepare for further refinement of the structure in the future.

[0043] Step 3: Two-phase zone forging: first heat the forging blank B to 800-850℃ and keep it at this temperature for 30-90min, then heat it to T β- 30-70℃ and keep warm for 180-270min, then carry out two-phase zone blank making, perform 3-5 fire upsetting and drawing process, among which 2 fires are reverse upsetting and drawing, two upsetting and two drawing in each fire, single upsetting ratio is 1.4-1.7, final forging temperature is ≥750℃, air cooling is carried out after forging, and forging blank C is obtained;

[0044] It should be noted that in step 3, in order to improve the forgeability of the billet, the forging billet B after the first fire upsetting is sawn into two equal sections, and the subsequent process flow is carried out separately; the forging billet B is repeatedly upset in the two-phase region to superimpose the deformation and further refine the grains. In this process, a reversing upsetting process is added to deform the billet from different directions to reduce the anisotropy of the bar; after this process, the original β grain boundary will be fully broken, and the structure formed by the processing of the two-phase region will be obtained, that is, the less equiaxed α and more elongated α structure on the β matrix are transformed. Since the deformation is not sufficient, the structure is not fully equiaxed;

[0045] Step 4: Drawing and forming: First, heat the forging blank C to T β- 30-70℃ and keep warm for 120-180min, then perform 3-5 fire drawing process, add diagonal forging process during the drawing process, total forging ratio ≥5.0, final forging temperature ≥750℃, air-cool after forging to obtain forging billet bar;

[0046] It should be noted that in step 4, a diagonal forging process is used during the drawing process to eliminate the difficult-to-deform area in the surface area of the billet, reduce the anisotropy of the bar, and through sufficient drawing deformation, make the elongated α structure completely equiaxed through recrystallization. In this step, since there are clear requirements for the content of primary α phase in the microstructure, the heating temperature must be strictly controlled to ensure that the content of primary α phase meets the requirements;

[0047] Step 5, annealing: heating the forging billet to 750-850° C., keeping the temperature for 1-3 hours, and then air-cooling to room temperature to finally obtain the desired TC4 titanium alloy bar;

[0048] It should be noted that the annealing equipment uses a box-type resistance furnace with a furnace temperature uniformity of ≤ (±10)°C, and the furnace is put into use when the temperature reaches the required level.

[0049] Specifically, in step 1, the TC4 titanium alloy ingot is obtained by three times of vacuum consumable arc furnace melting, and its chemical composition meets the following requirements in terms of mass percentage: Al: 6.1-6.5%, V: 3.95-4.35%, O: 0.18-0.20%, Fe≤0.3%, C≤0.05%, N≤0.03%, H≤0.008%, Si≤0.15%, Bi≤0.0014%, Y≤0.001%, single impurity element≤0.1%, total impurity elements≤0.3%, and the remainder is Ti.

[0050] In order to prove the effect of the present invention, the following examples are provided for verification.

[0051] Example 1

[0052] See also Figure 1 As shown, this embodiment provides a method for preparing large-sized TC4 titanium alloy bars for aircraft engine blades, and the specific steps are as follows:

[0053] Step 1, open forging: using a natural gas heating furnace (furnace temperature uniformity ± 10 ° C), first heat the TC4 titanium alloy ingot melted in a vacuum consumable arc furnace three times to 850 ° C, keep it warm for 120 minutes, then heat it to 1150 ° C and keep it warm for 150 minutes, and then open forging is carried out. Due to the poor thermal conductivity of titanium alloy, the TC4 titanium alloy ingot is heated in sections to ensure uniform heating, so as to prepare for the subsequent uniform plastic deformation; open forging is carried out on a 45 / 50MN fast forging unit, and the upsetting and drawing process is performed, with two upsetting and two drawing, and a single upsetting ratio of 1.85. A large forging ratio is used to fully crush the as-cast structure, and the upsetting is followed by drawing. The billet height-to-diameter ratio is 2:1, and the final forging temperature is 855 ° C. After forging, water cooling is used for rapid cooling to increase the nucleation rate of the crystal, form relatively fine β grains and martensite structure, and prepare for the subsequent expected structure to obtain forging billet A;

[0054] Step 2, intermediate forging: using a natural gas heating furnace (furnace temperature uniformity ±10°C), first heat the forging blank A to 850°C, hold it for 60 minutes, then raise the temperature to 1050°C and hold it for 180 minutes, and then perform intermediate forging on a 45 / 50MN fast forging unit. The heating temperature of the intermediate forging is 100°C lower than that of the open forging. The main reason is that β grains in the single-phase region are very easy to grow. In order to prevent the coarsening of the β grains that have been refined in the open forging, the heating temperature is lowered; this fire performs an upsetting and drawing process, two upsetting and two drawing, with a single upsetting ratio of 1.85, to further refine the β grains. After upsetting, the blank is drawn, and the billet height-to-diameter ratio is 2:1. The final forging temperature is 812°C, and the blank is water-cooled after forging to obtain the forging blank B;

[0055] Step 3, two-phase zone reforming forging: a total of 3 fires of two-phase zone reforming forging process;

[0056] The third heat was conducted in a resistance heating furnace (temperature uniformity ±10°C). The forging blank B was first heated to 850°C, held for 60 minutes, then raised to 950°C, held for 270 minutes, and forged on a 45 / 50MN fast forging unit. The upsetting and drawing process was performed, with two upsetting and two drawing operations and a single upsetting ratio of 1.6. The blank was forged to a size of 450×1800 mm and air-cooled after forging.

[0057] In order to further improve the forging permeability of the blank, the blank was sawn and divided into two equal parts to obtain two blanks of Ø450×900mm. The subsequent process flow was carried out on the two blanks respectively.

[0058] The 4th and 5th fires were conducted in a resistance heating furnace (furnace temperature uniformity ±10°C) to heat the billet to 850°C, hold the temperature for 60 minutes, then raise the temperature to 950°C, hold the temperature for 180 minutes, and then forge on a 45 / 50MN fast forging unit. A reversing upsetting and drawing process was used to plastically process the billet from multiple directions to make the structure more uniform. Two upsetting and two drawing operations were performed per fire, with a single upsetting ratio of 1.5. The final forging temperature was ≥750°C, and the billet was air-cooled after forging to obtain the forging billet C.

[0059] The single upsetting ratio was appropriately reduced during forging in the two-phase region. The main reason is that the plasticity of TC4 titanium alloy in the two-phase region is much worse than that in the single-phase region. The forging ratio was appropriately reduced to ensure the surface quality of the billet, ensure that the single-fire process can proceed smoothly, reduce invisible losses, and improve material utilization and production efficiency. To ensure the deformation amount, repeated upsetting and drawing in the two-phase region are used to superimpose the deformation amount to obtain the expected structure;

[0060] Step 4, drawing and forming: performing a three-fire drawing process on the forging blank C;

[0061] The sixth heat was conducted in a resistance heating furnace (temperature uniformity ±10°C) to heat the forging billet C to 950°C, hold the temperature for 180 minutes, and then remove it from the furnace. The billet was then drawn on a 45 / 50MN fast forging machine with a forging ratio of 1.7 until the billet was 240 mm in diameter. After forging, the billet was air-cooled to room temperature.

[0062] The seventh heat was conducted in a resistance heating furnace (temperature uniformity ±10°C) to heat the billet to 940°C after the sixth heat. After holding the temperature for 150 minutes, the billet was taken out of the furnace and drawn on a 45 / 50MN fast forging machine with a forging ratio of 2.2. The diagonal forging process was incorporated into the drawing process to eliminate the hard-to-deform area on the billet surface and make the structure and properties more uniform. The billet was drawn to Ø180mm and air-cooled to room temperature after forging.

[0063] The eighth heat is heated to 940°C in a resistance heating furnace (temperature uniformity ±10°C) after the seventh heat. After holding for 120 minutes, the billet is taken out of the furnace and finally formed using a 45 / 50MN fast forging machine with a spring hammer of 110-170mm in diameter. The forging ratio is 1.1, and the billet is drawn to 165mm in diameter. A machining allowance of 7.5mm is left on one side. The tolerance meets ±3mm and the curvature is ≤3mm / m. After forging, the billet is air-cooled to room temperature to obtain the forged bar.

[0064] Since there are strict requirements on the content, morphology and size of primary α phase in the microstructure of forging billets and bars, the forming process of 7 and 8 fires has been adjusted to make the microstructure of the bars meet the technical requirements;

[0065] Step 5, annealing: using a resistance heating furnace (furnace temperature uniformity ±10°C), after the furnace temperature rises to 800°C, the forging billet is placed in the effective heating zone of the heating furnace, kept warm for 3 hours, and then air-cooled to room temperature, finally obtaining a TC4 titanium alloy bar X with a specification of Ø150 mm.

[0066] The TC4 titanium alloy rod X obtained in Example 1 was subjected to structural observation. The original macroscopic structure of the head of the TC4 titanium alloy rod is shown in FIG. Figure 2 (a) shows the original low-magnification structure of the tail. Figure 2 As shown in (b), the low-magnification tissues all conform to GJB 494A-2008. Figure 1 Level 2 in the test meets the use requirements; the microstructure of the TC4 titanium alloy bar X head is shown in Figure 3 (a) shows the microstructure of the tail. Figure 3 As shown in (b), it can be seen that the microstructure of TC4 titanium alloy bar X is uniformly distributed in an equiaxed structure, and the primary α phase content is ≥65%, which is in line with GJB 494A-2008. Figure 2 The size of the long α phase is ≤0.06mm, which is in line with GJB 494A-2008 Figure 5 Level 1 in.

[0067] Example 2

[0068] See also Figure 1 As shown, this embodiment provides a method for preparing large-sized TC4 titanium alloy bars for aircraft engine blades, and the specific steps are as follows:

[0069] Step 1, open forging: using a natural gas heating furnace (furnace temperature uniformity ± 10 ° C), first heat the TC4 titanium alloy ingot melted in a vacuum consumable arc furnace three times to 800 ° C, keep it for 90 minutes, then heat it to 1150 ° C and keep it for 120 minutes, and then open forging. Due to the poor thermal conductivity of titanium alloy, the TC4 titanium alloy ingot is heated in sections to ensure uniform heating, so as to prepare for the subsequent uniform plastic deformation; open forging is carried out on a 45 / 50MN fast forging unit, and the upsetting and drawing process is performed, with two upsetting and two drawing, and a single upsetting ratio of 1.9. A large forging ratio is used to fully crush the as-cast structure, and the upsetting is followed by drawing. The billet height-to-diameter ratio is 2:1, and the final forging temperature is 867 ° C. After forging, water cooling is used for rapid cooling to increase the nucleation rate of the crystal, form relatively fine β grains and martensite structure, and prepare for the subsequent expected structure to obtain forging billet A;

[0070] Step 2, intermediate forging: using a natural gas heating furnace (furnace temperature uniformity ±10°C), first heat the forging blank A to 800°C, hold it for 90 minutes, then raise the temperature to 1050°C and hold it for 150 minutes, and then perform intermediate forging on a 45 / 50MN fast forging unit. The heating temperature of the intermediate forging is 100°C lower than that of the open forging. The main reason is that β grains in the single-phase region are very easy to grow. In order to prevent the coarsening of the β grains that have been refined in the open forging, the heating temperature is lowered; this fire performs an upsetting and drawing process, two upsetting and two drawing, with a single upsetting ratio of 1.7, to further refine the β grains. After upsetting, the blank is drawn, and the billet height-to-diameter ratio is 2:1. The final forging temperature is 808°C, and the blank is water-cooled after forging to obtain the forging blank B;

[0071] Step 3, two-phase zone reforming forging: a total of 3 fires of two-phase zone reforming forging process;

[0072] The third heat was conducted in a resistance heating furnace (temperature uniformity ±10°C). The forging blank B was first heated to 800°C, held for 60 minutes, then raised to 940°C, held for 270 minutes, and forged on a 45 / 50MN fast forging unit. The upsetting and drawing process was performed, with two upsetting and two drawing operations and a single upsetting ratio of 1.4. The blank was forged to a size of 480 × 1600 mm and air-cooled after forging.

[0073] In order to further improve the forging permeability of the blank, the blank was sawed and divided into two equal parts to obtain two blanks of Ø480×800mm. The subsequent process flow was carried out on the two blanks respectively.

[0074] The 4th and 5th heats were conducted in a resistance heating furnace (temperature uniformity ±10°C) to heat the billet to 800°C, hold the temperature for 60 minutes, then raise the temperature to 940°C, hold the temperature for 180 minutes, and then forge on a 45 / 50MN fast forging unit. A reversing upsetting and drawing process was used to plastically process the billet from multiple directions to make the structure more uniform. Two upsetting and two drawing operations were performed per fire, with a single upsetting ratio of 1.8. The final forging temperature was 769°C, and the billet was air-cooled after forging to obtain the forging billet C.

[0075] The single upsetting ratio was appropriately reduced during forging in the two-phase region. The main reason is that the plasticity of TC4 titanium alloy in the two-phase region is much worse than that in the single-phase region. The forging ratio was appropriately reduced to ensure the surface quality of the billet, ensure that the single-fire process can proceed smoothly, reduce invisible losses, and improve material utilization and production efficiency. To ensure the deformation amount, repeated upsetting and drawing in the two-phase region are used to superimpose the deformation amount to obtain the expected structure;

[0076] Step 4, drawing and forming: performing a three-fire drawing process on the forging blank C;

[0077] The sixth heat was conducted by heating the forging billet C to 930°C in a resistance heating furnace (temperature uniformity ±10°C), holding the temperature for 180 minutes, and then removing the billet from the furnace. The billet was then drawn on a 45 / 50MN fast forging machine with a forging ratio of 2.0 until the billet was 210 mm in diameter. The billet was then air-cooled to room temperature after forging.

[0078] The seventh heat was conducted in a resistance heating furnace (temperature uniformity ±10°C) to heat the billet to 930°C after the sixth heat. After holding the temperature for 150 minutes, the billet was taken out of the furnace and drawn on a 45 / 50MN fast forging machine with a forging ratio of 2.2. The diagonal forging process was incorporated into the drawing process to eliminate the hard-to-deform area on the billet surface and make the structure and properties more uniform. The billet was drawn to Ø160mm and air-cooled to room temperature after forging.

[0079] The eighth heat is heated to 930°C in a resistance heating furnace (temperature uniformity ±10°C) after the seventh heat. After holding for 120 minutes, the billet is taken out of the furnace and finally formed using a 45 / 50MN fast forging machine with a spring hammer of 110-170mm in diameter. The forging ratio is 1.3, and the billet is drawn to 140mm in diameter with a machining allowance of 10mm on one side. The tolerance meets ±3mm and the curvature is ≤3mm / m. After forging, the billet is air-cooled to room temperature to obtain the forged bar.

[0080] Because there are strict requirements on the content, morphology and size of the primary α phase in the microstructure of the forging billet bar, the forming process of 6 to 8 fires is adjusted to make the microstructure of the bar meet the technical requirements;

[0081] Step 5, annealing: using a resistance heating furnace (furnace temperature uniformity ±10°C), after the furnace temperature rises to 750°C, the forging billet is placed in the effective heating zone of the heating furnace, kept warm for 2 hours, and then air-cooled to room temperature, finally obtaining a TC4 titanium alloy bar Y with a specification of Ø120 mm.

[0082] The TC4 titanium alloy rod Y obtained in Example 2 was subjected to microstructure observation. The original macrostructure of the head of the TC4 titanium alloy rod Y is shown in FIG. Figure 4 (a) shows the original low-magnification structure of the tail. Figure 4 As shown in (b), the low-magnification tissues all meet the requirements of GJB494A-2008 Figure 1 The 2nd level meets the use requirements; the microstructure of the Y head of TC4 titanium alloy bar is shown in Figure 5 (a) shows the microstructure of the tail. Figure 5 As shown in (b), it can be seen that the microstructure of TC4 titanium alloy bar Y is uniformly distributed in an equiaxed structure, and the primary α phase content is ≥65%, which is in line with GJB 494A-2008. Figure 2 The size of the long α phase is ≤0.06mm, which is in line with GJB494A-2008 Figure 5 Level 1 in.

[0083] Example 3

[0084] See also Figure 1 As shown, this embodiment provides a method for preparing large-sized TC4 titanium alloy bars for aircraft engine blades, and the specific steps are as follows:

[0085] Step 1, cogging forging: using a natural gas heating furnace (furnace temperature uniformity of ±10°C), first heat the TC4 titanium alloy ingot that has been melted in a vacuum consumable arc furnace for three times to 820°C, keep it warm for 120 minutes, then raise the temperature to 1180°C and keep it warm for 180 minutes, and then perform cogging forging. Due to the poor thermal conductivity of titanium alloy, the TC4 titanium alloy ingot is heated in sections to ensure uniform heating, so as to prepare for subsequent uniform plastic deformation; cogging forging is performed on a 45 / 50MN fast forging unit, and an upsetting and drawing process is performed, with two upsetting and two drawing, and a single upsetting ratio of 1.9. A large forging ratio is used to fully crush the as-cast structure, and the billet is drawn after upsetting. The height-to-diameter ratio of the billet is 2:1, and the final forging temperature is 860°C. After forging, water cooling is used for rapid cooling to increase the nucleation rate of the crystal, form relatively fine β grains and martensite structure, and prepare for the subsequent expected structure to obtain forging billet A;

[0086] Step 2, intermediate forging: Using a natural gas heating furnace (furnace temperature uniformity of ±10°C), the forging blank A is first heated to 820°C, held at that temperature for 90 minutes, then raised to 1080°C and held at that temperature for 210 minutes, and then intermediate forging is performed on a 45 / 50MN fast forging unit. The heating temperature for intermediate forging is 100°C lower than that for open forging. The main reason is that β grains in the single-phase region are very easy to grow. In order to prevent the coarsening of the β grains that have been refined in open forging, the heating temperature is lowered; this fire is performed with an upsetting and drawing process, two upsetting and two drawing, with a single upsetting ratio of 1.9, to further refine the β grains. After upsetting, the blank is drawn to a height-to-diameter ratio of 2.1. The final forging temperature is 812°C, and the blank is water-cooled after forging to obtain the forging blank B;

[0087] Step 3, two-phase zone reforming forging: a total of 7 fires of two-phase zone reforming forging process;

[0088] The third heat was conducted in a resistance heating furnace (temperature uniformity ±10°C). The forging blank B was first heated to 820°C, held at that temperature for 90 minutes, then raised to 960°C, held at that temperature for 270 minutes, and forged on a 45 / 50MN fast forging unit. The upsetting and drawing process was performed, with two upsetting and two drawing operations and a single upsetting ratio of 1.4. The blank was forged to a size of 500 × 2000 mm and air-cooled after forging.

[0089] In order to further improve the forging permeability of the blank, the blank is sawn and divided into two equal parts to obtain two blanks of Ø500×1000mm. The subsequent process flow is carried out on the two blanks respectively.

[0090] In the 4th to 9th heats, a resistance heating furnace (temperature uniformity ±10°C) is used to heat the billet to 820°C, hold the temperature for 60 minutes, then raise the temperature to 960°C, hold the temperature for 240 minutes, and then forge on a 45 / 50MN fast forging unit. A reversing upsetting and drawing process is used to plastically process the billet from multiple directions to make the structure more uniform. Two upsetting and two drawing operations are performed per fire, with a single upsetting ratio of 1.5. The final forging temperature is ≥750°C, and the billet is air-cooled after forging to obtain a forging billet C.

[0091] The single upsetting ratio was appropriately reduced during forging in the two-phase region. The main reason is that the plasticity of TC4 titanium alloy in the two-phase region is much worse than that in the single-phase region. The forging ratio was appropriately reduced to ensure the surface quality of the billet, ensure that the single-fire process can proceed smoothly, reduce invisible losses, and improve material utilization and production efficiency. To ensure the deformation amount, repeated upsetting and drawing in the two-phase region are used to superimpose the deformation amount to obtain the expected structure;

[0092] Step 4, drawing and forming: performing a three-fire drawing process on the forging blank C;

[0093] In the 10th heat, a resistance heating furnace (temperature uniformity ±10°C) is used to heat the forging billet C to 950°C, hold the temperature for 180 minutes, and then remove it from the furnace. The billet is then drawn on a 45 / 50MN fast forging machine with a forging ratio of 1.7 until the billet is 300 mm in diameter. After forging, the billet is air-cooled to room temperature.

[0094] The 11th heat was conducted in a resistance heating furnace (temperature uniformity ±10°C). The billet was heated to 950°C after 10 heats and held at this temperature for 150 minutes before being taken out of the furnace. The billet was then drawn on a 45 / 50MN fast forging machine with a forging ratio of 2.2. The diagonal forging process was incorporated into the drawing process to eliminate the hard-to-deform area on the billet surface and make the structure and properties more uniform. The billet was drawn to Ø230mm and air-cooled to room temperature after forging.

[0095] The 12th heat is heated to 950℃ in a resistance heating furnace (temperature uniformity ±10℃) after 7 heats. After holding for 120 minutes, the billet is taken out of the furnace and finally formed using a 45 / 50MN fast forging machine with a spring hammer of 110-220mm in diameter. The forging ratio is 1.3. The billet is drawn to 200mm in diameter, with a machining allowance of 10mm on one side. The tolerance meets ±3mm and the curvature is ≤3mm / m. After forging, it is air-cooled to room temperature to obtain the forged billet bar.

[0096] Because there are strict requirements on the content, morphology and size of the primary α phase in the microstructure of the forging billet bar, the forming process of 10 to 12 fires was adjusted to make the microstructure of the bar meet the technical requirements;

[0097] Step 5, annealing: using a resistance heating furnace (furnace temperature uniformity ±10°C), after the furnace temperature rises to 780°C, the forging billet is placed in the effective heating zone of the heating furnace, kept warm for 2.5 hours, and then air-cooled to room temperature, finally obtaining a TC4 titanium alloy bar Z with a specification of Ø180 mm.

[0098] The TC4 titanium alloy rod Z obtained in Example 3 was subjected to microstructure observation. The original macrostructure of the head of the TC4 titanium alloy rod Z is shown in FIG. Figure 6 (a) shows the original low-magnification structure of the tail. Figure 6 As shown in (b), the low-magnification tissues all meet the requirements of GJB494A-2008 Figure 1 The 2nd level meets the use requirements; the microstructure of the Z head of TC4 titanium alloy bar is shown in Figure 7 (a) shows the microstructure of the tail. Figure 7 As shown in (b), it can be seen that the microstructure of TC4 titanium alloy bar Z is uniformly distributed in an equiaxed structure, and the primary α phase content is ≥65%, which is in line with GJB 494A-2008. Figure 2 The size of the long α phase is ≤0.06mm, which is in line with GJB494A-2008 Figure 5 Level 1 in.

[0099] In order to further verify the effectiveness of the technical solution provided by the present invention, the following mechanical property tests were performed on the TC4 titanium alloy bar X, TC4 titanium alloy bar Y, and TC4 titanium alloy bar Z prepared above:

[0100] (1) The tensile strength, yield strength, elongation, cross-sectional shrinkage, room temperature impact energy, and rotary bending fatigue tests were performed at room temperature. The test results are shown in Table 1.

[0101] (2) The tensile strength, yield strength, elongation, cross-sectional shrinkage, and high-temperature durability tests were carried out at a high temperature of 400°C. The test results are shown in Table 2.

[0102] Table 1 Room temperature mechanical properties test

[0103]

[0104] Table 2 High temperature mechanical properties test

[0105]

[0106] In summary, it can be seen from Table 1 and Table 2 that the TC4 titanium alloy bar X, TC4 titanium alloy bar Y, and TC4 titanium alloy bar Z prepared by the preparation method of the present invention are tested at room temperature, and the tensile strength R m All ≥950MPa, yield strength R P0.2 All ≥860MPa, elongation A ≥15%, section shrinkage Z ≥35%, room temperature impact energy KU2 ≥33J, room temperature rotation bending fatigue test σ=460N / mm 2 、Nf≥2×10 6 During the week, no fracture occurred;

[0107] After testing at 400℃, the tensile strength R m All ≥620MPa, yield strength R P0.2 All are ≥490MPa, elongation A is ≥15%, section shrinkage Z is ≥50%, high temperature endurance test σ=570N / mm at 400℃ 2 , τ≥100h, no fracture occurred;

[0108] Therefore, the TC4 titanium alloy bar prepared by the preparation method of the present invention meets the use requirements of aircraft engine blades.

[0109] It should also be noted that the “□” appearing in the text indicates that the shape of the blank is a square bar.

[0110] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0111] It should be understood that the present invention is not limited to the above description and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing large-sized TC4 titanium alloy bars for aircraft engine blades, characterized in that: The following steps are involved: Step 1: Forging: First heat the TC4 titanium alloy ingot and keep it warm, then heat it to T β+ The forging blank A is obtained by heating the forging blank to a specific temperature and keeping the temperature. Then, the forging blank is forged, and the upsetting and drawing process is performed. The forging blank is cooled after forging. Step 2, intermediate forging: first heat the forging blank A and keep it warm, then raise the temperature to T β+ The forging blank B is obtained by heating the forging blank to a specific temperature and keeping the temperature, then performing intermediate forging, performing upsetting and drawing processes, and cooling after forging. Step 3: Two-phase zone forging: first heat the forging blank B and keep it warm, then raise the temperature to T β- The forging blank C is obtained by heating the forging blank to a specific temperature and keeping the temperature, then performing the two-phase zone blanking process, performing the upsetting and drawing process, and cooling after forging; Step 4: Drawing and forming: First, heat the forging blank C to T β- The forging process is carried out at a specific temperature and kept warm, and then the drawing process is carried out, and the forging blank bar is obtained after cooling; Step 5, annealing: heating and holding the forged billet bar, and then cooling the forged billet bar to room temperature to obtain the desired TC4 titanium alloy bar.

2. The preparation method according to claim 1, characterized in that In step 1, the TC4 titanium alloy ingot is obtained by three times of vacuum consumable arc furnace melting, and its chemical composition meets the following requirements in terms of mass percentage: Al: 6.1-6.5%, V: 3.95-4.35%, O: 0.18-0.20%, Fe≤0.3%, C≤0.05%, N≤0.03%, H≤0.008%, Si≤0.15%, Bi≤0.0014%, Y≤0.001%, single impurity element≤0.1%, total impurity elements≤0.3%, and the remainder is Ti.

3. The preparation method according to claim 1, characterized in that Step 1 is as follows: first heat the TC4 titanium alloy ingot to 800-850℃ and keep it at this temperature for 100-150min, then heat it to T β+ 100-200℃ and keep warm for 120-180min, then carry out blank forging, perform upsetting and drawing process, upsetting ratio is 1.6-1.9, final forging temperature is ≥850℃, water cooling is carried out after forging, and forging blank A is obtained.

4. The preparation method according to claim 1, characterized in that Step 2 is as follows: first heat the forging blank A to 800-850°C and keep it at this temperature for 30-90 minutes, then heat it to T β+ 50~100℃ and keep warm for 150~210min, then carry out intermediate forging, perform upsetting and drawing process, upsetting ratio is 1.6~1.9, final forging temperature is ≥800℃, water cooling is carried out after forging, and forging billet B is obtained.

5. The preparation method according to claim 1, characterized in that Step 3 is as follows: first heat the forging blank B to 800-850°C and keep it at this temperature for 30-90 minutes, then heat it to T β- 30-70℃ and keep warm for 180-270min, then carry out two-phase zone billet making, perform 3-5 fire upsetting and drawing processes, of which 2 fires are reverse upsetting and drawing, two upsetting and two drawing in each fire, single upsetting ratio is 1.4-1.7, final forging temperature is ≥750℃, air cooling is carried out after forging, and forging billet C is obtained.

6. The preparation method according to claim 5, characterized in that In step 3, the forging blank B after the first upsetting is sawn into two equal sections, and the subsequent process flow is carried out separately.

7. The preparation method according to claim 1, characterized in that Step 4 is as follows: first, heat the forging blank C to T β- 30-70℃ and keep warm for 120-180min, then perform 3-5 fire drawing process, add diagonal forging process during the drawing process, total forging ratio ≥5.0, final forging temperature ≥750℃, air cool after forging to obtain forging billet bar.

8. The preparation method according to claim 1, characterized in that Step 5 is specifically as follows: heating the forging billet to 750-850° C., keeping the temperature for 1-3 hours, and then air-cooling to room temperature.

9. The TC4 titanium alloy bar prepared by the preparation method according to any one of claims 1 to 8, characterized in that: After testing at room temperature, its tensile strength R m ≥950MPa, yield strength R P0.2 ≥860MPa, elongation A≥15%, section shrinkage Z≥35%, room temperature impact energy KU2≥33J, rotary bending fatigue test at room temperature σ=460N / mm 2 、Nf≥2×10 6 During the Zhou period, it was not broken; After testing at a high temperature of 400°C, its tensile strength R m ≥620MPa, yield strength R P0.2 ≥490MPa, elongation A≥15%, section shrinkage Z≥50%, high temperature endurance test σ=570N / mm at 400℃ 2 , when τ≥100h, no fracture occurs.

10. The use of the preparation method according to any one of claims 1 to 8, characterized in that: Used in the preparation of large-sized TC4 titanium alloy bars for aircraft engine blades.

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