TC4 titanium alloy preformed blank, TC4 titanium alloy plate and preparation method of TC4 titanium alloy preformed blank

Abstract

The invention discloses a TC4 titanium alloy preformed blank, a TC4 titanium alloy plate and a preparation method of the TC4 titanium alloy preformed blank and the TC4 titanium alloy plate, and belongs to the technical field of titanium alloy machining. According to the method, TC4 alloy powder prepared through hydrogenation dehydrogenation and plasma rotating electrode atomization serves as a raw material, and a high-density binary structure preformed blank is prepared through a three-step type hot isostatic pressing technology; a pure titanium sheath is adopted for packaging, two-heating-number rolling is conducted through the sheath, and the plate shape is optimized through convexity design of a working roller and dynamic roller bending force control; and after rolling, the head and the tail are cut off in combination with composite heat treatment, and the TC4 titanium alloy plate is obtained. According to the method, the problem of traditional cast ingot structure segregation is solved through powder metallurgy, the preparation cost of the TC4 titanium alloy plate is reduced, the production period is shortened, the yield and the surface quality are improved, and a reliable scheme is provided for green and efficient preparation of the high-performance titanium alloy plate in the aerospace field.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy processing technology, and relates to a TC4 titanium alloy preform, a TC4 titanium alloy sheet and its preparation method, specifically to a method for preparing high-strength, high-toughness wide TC4 sheet by single-stand rolling of a powder metallurgy preform. Background Technology

[0002] In the aerospace field, with the continuous improvement of the overall industrial level, the demand for customized preparation of TC4 sheet metal is gradually becoming more prominent, and its preparation mode is also shifting from traditional general-purpose processes to customized preparation modes for special sheets. Against this backdrop, key performance indicators such as strength, plasticity, and toughness of aerospace-grade sheet metal are steadily improving. Currently, TC4 sheet metal is mainly prepared through two process routes: one is to obtain the slab by forging after three VAR furnace melting and casting into ingots; the other is to cast flat billets using an EB furnace. After the slab preparation is completed, it still needs to undergo multiple reciprocating and cross-rolling processes to finally become the finished product.

[0003] Traditional forged billets suffer from dendritic segregation and poor microstructure uniformity, posing significant challenges to aerospace-grade titanium alloy plates in terms of flaw detection pass rates, residual stress, and shape control. Furthermore, the production process is lengthy and yields low output. Statistics show that domestic titanium producers achieve a yield of less than 60% from ingots to finished plates measuring 3-6mm (thickness) × 1400-2000mm (width). While EB furnace casting shortens the process to some extent, even with refined controlled rolling and cooling methods, the as-cast microstructure cannot meet the requirements for anisotropy and microstructure uniformity. Limited by ingot and slab multi-pass rolling and intermediate heat treatment, issues such as microstructure inhomogeneity, plate warpage, residual stress, and ultrasonic flaw detection problems may arise during the long processing flow. The final product's performance pass rate remains a technical hurdle restricting the application of titanium metal.

[0004] While existing patented technologies have proposed some improvements, they still have their limitations. For example, CN120079718A discloses a method for single-pass rolling of thin, ultra-wide TC4 titanium alloy sheets. To ensure surface quality, this method uses a surface explosion bonding layer of pure titanium, which has high environmental protection requirements. Secondly, it employs reversing rolling, making on-site process execution difficult and resulting in unstable production quality. CN117066281A discloses a hot-rolling preparation method for single TC4 titanium alloy sheets, using a three-pass rolling process, which has a long process flow. CN115971249A discloses a method for preparing ultra-thin TC4 titanium alloy sheets, but this method uses a multi-pass rolling method for ingot casting, resulting in poor control of the slab microstructure and difficulty in meeting the high microstructure uniformity requirements for aerospace-grade products.

[0005] In summary, current TC4 sheet preparation technology still faces many challenges in pursuing high performance, high yield, and process stability. There is an urgent need to develop a low-cost preparation process that can simplify the process flow, improve the yield, and ensure uniform and stable product performance. Summary of the Invention

[0006] The technical problem to be solved by this invention is the poor uniformity of the microstructure of the cast billet produced by traditional forging processes.

[0007] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, the present invention provides a method for preparing TC4 titanium alloy preforms: TC4 recycled waste is pretreated, then hydrogenated and dehydrogenated to produce powder, and then atomized by plasma rotating electrode to obtain alloy powder with an oxygen content ≤0.15wt%; the alloy powder is subjected to three-step hot isostatic pressing to obtain TC4 titanium alloy preforms with a dual-state structure. The three-stage hot isostatic pressing process includes: a first stage where the temperature is increased to 150-250℃ at a rate of 5-10℃ / min, followed by vacuuming to ≤1×10⁻⁶. -2 Pa; In the second stage, the temperature is increased to 400-500℃ at a rate of 5-10℃ / min, and a vacuum is applied to ≤4×10⁻⁶ Pa. -2 Pa; In the third stage, the temperature is increased to 920-980℃ at a rate of 3-6℃ / min, and a static pressure of 100-140MPa is applied, and the temperature and pressure are maintained for 120-180min. The TC4 titanium alloy preform has a density ≥99.8%, a primary equiaxed α phase size ≤10μm, and an α lamellar spacing ≤10μm.

[0008] In the above preparation method, the pretreatment includes: cleaning the TC4 recovery waste with a 3% HNO3 solution and a 1% HF solution, annealing it under vacuum at 600~800℃, and then cutting or crushing it into small pieces of 3~15mm.

[0009] In the above preparation method, the TC4 recycled waste includes one or more of the following: processing scraps, molding residues, and metallurgical waste.

[0010] In the above preparation method, the hydrogenation dehydrogenation powdering includes: placing small pieces in a closed reactor, introducing high-purity hydrogen gas to a pressure of 0.3~2.8 MPa, hydrogenating at 400~800℃ for 8~18 h, and then crushing and sieving to obtain hydride powder; the hydride powder is then placed under a vacuum of ≤10 -2 In a vacuum environment of Pa, hydrogen is removed at 650~820℃ for 8~18h. After cooling to room temperature in a vacuum or under inert atmosphere protection, plasma rotating electrode atomization treatment is performed to obtain TC4 alloy powder.

[0011] In the above preparation method, the particle size of the TC4 alloy powder is 50~150μm.

[0012] In the above preparation method, the content of other elements in the TC4 alloy powder, except for oxygen content, meets the requirements of GB / T3620.1.

[0013] In the above preparation method, the hot isostatic pressing treatment further includes: loading the degassed TC4 alloy powder into a preheated 400~450℃ shroud, and then performing a three-step hot isostatic pressing treatment; after the hot isostatic pressing treatment, cooling it to below 450℃ in an argon environment with a cooling rate of ≥10℃ / min at a pressure of 45~65KPa, and then cooling it to room temperature in an argon environment with a pressure of 105~135KPa to obtain a TC4 titanium alloy preform with a dual-state structure.

[0014] In the above preparation method, the casing is made of pure titanium plate.

[0015] In the above preparation method, the wall thickness of the casing is 1~3mm.

[0016] In the above preparation method, the dimensions of the sleeve are: length 2000~2200mm × width 1800~2000mm × thickness 80~100mm.

[0017] In a second aspect, the present invention provides a method for preparing TC4 titanium alloy sheet: a TC4 titanium alloy preform with a dual-state structure is prepared by the above-mentioned method for preparing TC4 titanium alloy preform, and then hot rolling and composite heat treatment are performed to obtain a TC4 titanium alloy sheet with a dual-state structure or an equiaxed structure. The dual-state TC4 titanium alloy plate has a dual-scale α-phase structure, with the primary α-phase size ≤10μm and a volume fraction of 20~40%. The hot rolling process specifically involves two-fire rolling. The preform is heated to the rolling temperature in a gas atmosphere or electric heating furnace and then rolled. The rolling direction is along the width of the preform. The initial rolling temperature for both fires is 20~50℃ below the β phase transformation point of the preform, and the final rolling temperature is ≥750℃. The total deformation is 50~85% for both fires. The rolling speed for the first fire is 1.5~2.0m / s, and the rolling speed for the second fire is 1.2~1.8m / s.

[0018] Furthermore, the above-mentioned two-fire rolling is controlled in three temperature zones: the early rolling pass is 900℃~the initial rolling temperature, the middle rolling pass is 850~900℃, and the final rolling pass is 750~850℃. The middle rolling process compensates for the temperature drop at the edges. The deformation per pass in the two-fire rolling process is gradually reduced to 8~15%, the reduction rate of the final pass is <10%, and the rolling pass interval is <20s.

[0019] In the above preparation method, the hot rolling process adopts a six-roll reversible mill to dynamically control the plate shape. The work roll crown is designed to be +0.10~0.20mm. When the thickness is >16mm, the work roll crown is taken as the upper limit of +0.20mm. When the thickness is 6~16mm, the work roll crown is gradually reduced to +0.10mm. The maximum positive bending force of the work roll is +600kN and the maximum negative bending force is -450kN.

[0020] Furthermore, the above-mentioned single-fire rolling is carried out when the thickness is 60~100mm, the bending roll adopts positive bending, and the bending roll force is 70% of the maximum positive bending force.

[0021] Furthermore, the bending rolls in the above-mentioned two-fire rolling mill are adjusted from positive bending to balance, the bending roll force is gradually reduced from 50% of the maximum positive bending force to 30%, and a slight negative bending is introduced. The finished product pass is dominated by negative bending, the negative bending force is 40% of the maximum negative bending force, and the positive bending force is less than 20% of the maximum positive bending force.

[0022] In the above preparation method, after the hot rolling process is completed, cooling is performed. The cooling mode is selected according to the thickness of the rolled plate. When the thickness δ is 6≤δ≤15mm, air cooling is used, and when the thickness δ is 15<δ≤25mm, water cooling is used.

[0023] In the above preparation method, the composite heat treatment specifically involves: holding the rolled plate at 20-50°C below its β phase transformation point for 1-3 hours to complete the solution treatment, and then holding it at 580-620°C for 4-6 hours to complete the aging treatment; air cooling to room temperature, and after cooling, sawing off the snake head and tail to obtain a TC4 titanium alloy plate with a dual-state structure.

[0024] In the above preparation method, the composite heat treatment specifically involves: heating the rolled plate to 780~820℃ and holding it for 1~4h to complete recrystallization annealing, then holding it at 580~620℃ for 4~6h to complete aging treatment; air cooling to room temperature, and after cooling, sawing off the snake head and tail to obtain a TC4 titanium alloy plate with equiaxed structure.

[0025] Thirdly, the present invention provides a TC4 titanium alloy sheet prepared by the above-described method for preparing TC4 titanium alloy sheet.

[0026] Furthermore, the microstructure of the aforementioned TC4 titanium alloy sheet is a bimodal structure or an equiaxed structure; wherein, the bimodal TC4 titanium alloy sheet has a dual-scale α-phase structure, with the primary α-phase size ≤10μm and a volume fraction of 20~40%.

[0027] Furthermore, the dimensions of the aforementioned TC4 titanium alloy sheet are: length 6000~15000mm × width 2000~2200mm × thickness 6~25mm.

[0028] Furthermore, the mechanical properties of the aforementioned TC4 titanium alloy sheet are as follows: transverse tensile strength ≥990MPa, yield strength ≥910MPa, elongation ≥15%, and reduction of area ≥35%.

[0029] The beneficial effects of this invention are as follows: Unlike conventional methods that improve the strength and toughness of TC4 plates by increasing the grade of sponge titanium and reducing the mass fraction of impurities and interstitial atoms, this invention provides a method that does not require sponge titanium screening or intermediate alloy impurity element control. It utilizes green, low-cost powder metallurgy to prefabricate TC4 slabs, combined with two-stage rolling, solution treatment or recrystallization annealing, and a single-stage aging process to achieve the preparation of high-performance, highly uniform, wide-width TC4 plates. Compared to traditional processes, this invention simplifies the preparation process, improves yield efficiency, and significantly reduces production costs. The resulting titanium alloy plates exhibit good elongation and reduction of area, meeting the application requirements of the aerospace field and possessing significant potential for widespread application. Attached Figure Description

[0030] Figure 1 The process control curves for hot isostatic pressing (HIP) are shown. Figure 2 Scanning electron microscope (SEM) images of the bimorphic preform prepared in Example 1; Figure 3 Metallographic image of the TC4 titanium alloy sheet with a dual-state microstructure obtained in Example 1; Figure 4 Scanning electron microscope (SEM) images of the bimorphic preform prepared in Example 2; Figure 5 Metallographic image of the equiaxed TC4 titanium alloy sheet prepared in Example 2; Figure 6 To obtain the microstructure of the preform for Comparative Example 1; Figure 7 The microstructure of the finished board was obtained for Comparative Example 2. Detailed Implementation

[0031] To make the technical problems, solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with the embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as understood by one of ordinary skill in the art.

[0032] A method for preparing a high-performance, highly uniform wide-width TC4 titanium alloy sheet includes the following steps.

[0033] (1) After cleaning the TC4 recycled waste with a weak acid (3% HNO3 + 1% HF solution), vacuum anneal at 600~800℃ to remove surface impurities. Cut or crush large raw materials into small pieces with relatively uniform size of 3~15mm to increase the specific surface area of ​​the subsequent hydrogenation reaction and improve the hydrogenation efficiency and uniformity.

[0034] In one embodiment of the present invention, the TC4 recycled waste includes one or more of the following: machining scraps (such as turning chips and milling chips), forming waste (such as forging scraps and casting scraps), and metallurgical waste (such as substandard ingots and substandard bars). TC4 recycled waste is the main source of the economic efficiency of the method of the present invention. Recycling TC4 recycled waste as raw material can effectively reduce production costs.

[0035] (2) Place the pretreated TC4 raw material in a closed reactor (usually a high-temperature and high-pressure vacuum / atmosphere furnace). Introduce high-purity hydrogen (H2) and heat to a suitable hydrogenation temperature and hold. The hydrogenation reaction causes lattice expansion, generating huge internal stress, which makes the originally tough TC4 alloy very brittle (hydrogen embrittlement) and extremely easy to crush.

[0036] In one embodiment of the invention, the hydrogen pressure is typically in the range of 0.3 to 2.8 MPa, and the pressure affects the hydrogen absorption rate and the final hydrogen content. For TC4 alloy, the hydrogenation temperature is typically in the range of 400 to 800°C. Too low a temperature results in a slow hydrogenation rate, while too high a temperature may lead to coarsening of the microstructure or localized melting. The holding time is 8 to 18 hours to allow hydrogen to fully diffuse into the alloy and react with titanium to form titanium hydrides (mainly TiH2, as well as hydrides or solid solutions of aluminum and vanadium).

[0037] (3) Remove the brittle TC4 hydride block from the reactor after hydrogenation. Use a simple mechanical crushing method to crush the brittle hydride into powder of the required particle size. After crushing, the powder is sieved to separate the powder that meets the target particle size range (3~15mm). The powder that is too coarse is returned to continue crushing.

[0038] (4) Place the sieved TC4 hydride powder in a vacuum heat treatment furnace and keep it at a constant temperature to remove hydrogen. The hydride decomposes, hydrogen is removed, and the powder is restored to the state of titanium alloy (Ti-6Al-4V).

[0039] In one embodiment of the present invention, dehydrogenation is performed in a high vacuum environment (≤10). -2The dehydrogenation process is carried out at a temperature below 650°C (Pa) to ensure effective hydrogen extraction and prevent oxidation. For TC4 alloys, the dehydrogenation temperature must be high enough to drive hydrogen desorption and diffusion, while remaining below the β-transformation temperature (approximately 995°C for TC4) to avoid excessive grain growth and phase transformation. Excessively high temperatures can also introduce impurities such as oxygen and nitrogen. Therefore, the dehydrogenation temperature is typically in the range of 650–820°C. The holding time is 8–18 hours to allow for complete hydrogen desorption and diffusion from the powder.

[0040] (5) After dehydrogenation, the powder is cooled to room temperature under vacuum or an inert atmosphere (such as argon) to prevent oxidation of the hot powder. Then, it is subjected to plasma rotating electrode atomization treatment to obtain TC4 alloy powder. The chemical composition of the powder is analyzed, including the content of major elements (Ti, Al, V) and key impurity elements (O, H, N, C, Fe). The particle size of the TC4 alloy powder is 50~150μm, the oxygen content is ≤0.15wt%, and the remaining element ranges meet the requirements of GB / T3620.1.

[0041] In one embodiment of the present invention, the dehydrogenated powder may experience slight agglomeration or changes in particle size distribution due to shrinkage or other reasons, and usually needs to be screened again or batched to ensure batch uniformity.

[0042] (6) After degassing the TC4 alloy powder, it is placed into a preheated packaging bag and subjected to three-stage temperature control under vacuum. The first stage controls the heating rate at 5~10℃ / min, raising the temperature to 150~250℃. While removing impurities, the vacuum is slowly evacuated to ≤1×10 -2 Pa; The second stage involves heating to 400~500℃ and then further evacuating to a vacuum level ≤4×10⁻⁶. -2 Pa; The three-stage heating rate is controlled at 3~6℃ / min, reducing the heating rate to avoid temperature unevenness, raising the temperature to 920~980℃, and applying a static pressure of 100~140MPa within this temperature range, holding for 120~180min. After holding, under argon gas medium, first apply argon gas at a pressure of 45~65KPa, and gradually cool to below 450℃ at a rate of ≥10℃ / min; then apply argon gas at a pressure of 105~135KPa, and continue cooling to room temperature. The process control curve for hot isostatic pressing is shown below. Figure 1 As shown, a bimodal preform with a density ≥99.8% and a microstructure consisting of primary equiaxed α-lamellae with a size ≤10μm and an interlamellar spacing ≤10μm was obtained.

[0043] In one embodiment of the present invention, the sheath is made of pure titanium plate, and the dimensions of the sheath are 80~100mm (thickness) × 1800~2000mm (width) × 2000~2200mm (length), the wall thickness of the sheath is 1~3mm, and the preheating temperature is 400~450℃. The process control curve for hot isostatic pressing is shown below. Figure 1 As shown, the temperature of hot isostatic pressing is lower than the β-transformation temperature T. β (998℃), holding time 120~180min, after which rapid cooling is performed, followed by pressure gradient loading under argon medium to suppress α phase growth. The advantages of the above method are that it avoids the problem of α phase coarsening, improves density, and enhances powder bonding strength; the use of pure titanium sheathing eliminates the need for demolding, preventing severe surface oxidation in the subsequent heating medium; and the sheathed rolling process avoids the long process of conventional acid and alkali washing, while also ensuring surface quality.

[0044] In this invention, to address the problems of poor microstructure uniformity and low flaw detection pass rate in traditional processes, powder metallurgy preforms are used to replace traditional ingots. Recycled waste is hydrogenated and dehydrogenated to produce powder, which is then atomized using a plasma rotating electrode to prepare low-oxygen TC4 alloy powder. This powder is then solidified using a three-step hot isostatic pressing (HIP) process to form a bimodal microstructure preform, thus preventing macroscopic segregation at its source. The high-temperature, high-pressure environment of HIP promotes powder diffusion and bonding, refining grains while eliminating internal defects and significantly improving material density. This method completely eliminates dendritic segregation in ingots, achieving ultra-fine microstructure and high uniformity, meeting aerospace-grade flaw detection requirements.

[0045] (7) The billet is heated to the rolling temperature in a gas atmosphere or electric heating furnace and then rolled. It is formed by two-fire rolling, with the rolling direction along the width of the preform. The total deformation of the first-fire rolling is 50~85%, the initial rolling temperature is 20~50℃ below the β phase transformation point of the preform, the final rolling temperature is ≥750℃, and the rolling speed is 1.5~2.0m / s; the total deformation of the second-fire rolling is 50~85%, the initial rolling temperature is 20~50℃ below the β phase transformation point of the preform, the final rolling temperature is ≥750℃, and the rolling speed is 1.2~1.8m / s. After rolling, the plate is cooled to obtain the rolled plate. The cooling mode is selected according to the thickness of the rolled plate. Air cooling is used when the thickness δ is 6≤δ≤15mm, and water cooling is used when the thickness δ is 15<δ≤25mm.

[0046] This invention employs a two-stage rolling process instead of the traditional multi-stage forging and rolling. Through precise temperature control (avoiding harmful phase transformation zones), efficient deformation is achieved, reducing the number of intermediate heat treatments. This effectively improves yield, shortens the process, and reduces energy consumption, solving the problems of low yield and high energy consumption caused by the long production process of traditional methods. The rolling process includes a cladding system; the pure titanium cladding isolates oxidation, and plastic deformation during rolling is synchronized with the substrate. The surface is free from acid and alkali washing, improving surface quality.

[0047] In one embodiment of the present invention, the two-pass rolling is controlled in three temperature zones: 900°C to the initial rolling temperature in the early rolling stage, 850°C to 900°C in the middle rolling stage, and 750°C to 850°C in the final rolling stage. An edge heater is used in the middle rolling stage to compensate for the temperature drop at the edge. The deformation per pass in the two-pass rolling is gradually reduced to 8-15%, and the reduction rate in the final pass is <10% to ensure the plate shape. The interval between rolling passes is <20s.

[0048] In one embodiment of the invention, a six-roll reversible rolling mill is used for rolling. To control the strip shape, considering the crown design and bending force, the work roll crown is compensated for by heat expansion and wear treatment to counteract bending deformation under rolling force. The work roll crown is designed to be +0.10~0.20mm (concave roll). When the thickness is >16mm, the work roll crown is set to the upper limit of +0.20mm to resist bending under high rolling force. When the thickness is 6~16mm, the work roll crown is gradually reduced to +0.10mm to avoid excessive edge thinning. The maximum positive bending force of the work roll is +600kN, and the maximum negative bending force is -450kN. The bending roll in the first rolling mill adopts positive bending, and the bending force is 70% of the maximum positive bending force to compensate for insufficient thermal crown of the roll. In the second rolling mill, the bending roll is adjusted from positive bending to balance, and the bending force is gradually reduced from 50% of the maximum positive bending force to 30%, and then a slight negative bending is introduced to prevent edge waviness. The bending force of the finished product is dominated by negative bending, with the negative bending force increasing to 40% of the maximum negative bending force, and the positive bending force controlled to be less than 20% of the maximum positive bending force.

[0049] In this invention, gradient rolling suppresses local stress concentration; two-stage aging promotes uniform precipitation of the secondary α phase, optimizes the lamellar structure ratio, and simultaneously improves strength and toughness; during the rolling process, an edge heater is used to compensate for the temperature drop at the edges of the wide plate, reducing microstructure inhomogeneity caused by transverse temperature differences, maintaining stable performance, and minimizing fluctuations. Dynamic compensation for roll thermal deformation is achieved through concave roll crown and bending roll force, balancing the transverse distribution of the roll gap and ensuring the shape and surface quality of the wide plate. This results in a finished product free of warping and edge waviness defects, with improved surface quality.

[0050] (8) The rolled plate is kept at 20~50℃ below the β phase transformation point for 1~3h to complete the solution treatment, and then subjected to a period of aging (580~620℃)×(4~6h), AC; after cooling, the snake head and tail are cut off to finally obtain TC4 titanium alloy plate with good surface quality and dual-state structure of 6~25mm (thickness)×2000~2200mm (width)×6000~15000mm (length); wherein the dual-state structure of TC4 titanium alloy plate has a dual-scale α phase structure, the size of the primary α phase is ≤10μm, and the volume fraction is 20~40%.

[0051] Alternatively, the rolled sheet is heated to 780~820℃ and held for 1~4h to complete recrystallization annealing, followed by a period of aging (580~620℃) × (4~6h), AC; air-cooled to room temperature, and after cooling, the snake head and tail are sawn off to obtain TC4 titanium alloy sheet with equiaxed structure.

[0052] The room temperature mechanical properties of bimodal and equiaxed structures are similar. TC4 plates prepared using the above method exhibit the following mechanical properties according to GB / T228.1: transverse tensile strength ≥970 MPa, yield strength ≥890 MPa, elongation ≥8%, reduction of area ≥15%, and fracture toughness in the TL and LT directions according to GB / T4161. IC ≥85MPa·m 1 / 2 .

[0053] The following specific embodiments will be provided to explain the solution of the present invention. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0054] This invention provides an embodiment of preparing TC4 sheets using the method of this invention, wherein pretreated TC4 recycled waste is used as raw material. The pretreatment method is as follows: the TC4 recycled waste is washed with a weak acid (3% HNO3 + 1% HF solution), and then annealed under vacuum at 600°C to remove surface impurities. Then, large pieces of raw material are crushed into relatively uniform small pieces of 3-15 mm for later use.

[0055] Example 1 1) Place the pretreated TC4 raw material in a closed reactor, introduce high-purity hydrogen gas to a pressure of 2.8 MPa, and hydrogenate at 400℃ for 8 hours. Remove the brittle TC4 hydride block after hydrogenation from the reactor and crush the brittle hydride into powder using a simple mechanical crushing method. Separate the hydride powder of 3~15mm by sieving.

[0056] 2) Place the hydride powder at 650℃ and a vacuum degree ≤10 -2 The TC4 alloy powder was dehydrogenated by holding it at a high temperature for 18 hours in a Pa heat treatment furnace, and then cooled to room temperature in a vacuum. After that, it was subjected to plasma rotating electrode atomization treatment to obtain TC4 alloy powder with an average particle size of 50 μm.

[0057] The chemical composition of TC4 alloy powder was analyzed, and the mass fractions of the main elements were: Al 5.6%, V 4.0%, O 0.06%, H 0.003%, N 0.006%, C 0.012%, and Fe 0.11%.

[0058] 3) After degassing, TC4 alloy powder is packed into a pure titanium sheath measuring 80mm (thickness) × 2000mm (width) × 2200mm (length) (the titanium plate of the sheath is 1.0mm thick). The sheath is preheated to 400℃. A three-stage hot isostatic pressing process is then performed under vacuum: the first stage controls the heating rate at 5℃ / min, heating to 150℃, and then slowly evacuating to a vacuum level ≤1×10⁻⁶. -2 Pa; the second stage controls the heating rate at 5℃ / min, raising the temperature to 400℃, and then further evacuating to ≤4×10 -2 The heating process was carried out in three stages with a heating rate of 3℃ / min, reaching 920℃. A static pressure of 140MPa was applied within this temperature range, and the holding time was 180min. After holding, under argon gas conditions, an argon pressure of 45KPa was applied, and the temperature was gradually cooled to below 400℃ at a rate of 10℃ / min. Then, an argon pressure of 105KPa was applied, and the temperature was further cooled to room temperature to obtain a bimodal preform.

[0059] The preform with the dual-phase microstructure has a density of 99.89% and a microstructure consisting of a primary equiaxed α-lamellae with a size of 8 μm and an α-lamellae spacing of 6 μm. Its metallographic photograph is shown below. Figure 2 .

[0060] 4) The rolling process adopts two-fire forming, and the rolling mill is a six-roll reversible rolling mill with a work roll crown design of +0.10mm (concave roll).

[0061] The β phase transformation point of the bimodal preform was measured to be 1008℃. First, the billet was heated to 982℃ in a gas atmosphere furnace for one-fire rolling, and the final rolling temperature was 750℃. The bending roll force was set to positive bending, and the bending roll force was 420KN. The rolling direction was along the width of the preform, the total deformation was 50%, the rolling line speed was 1.5m / s, the rolling thickness was 40mm, and the rolling dimensions were 40×2040×4310mm.

[0062] Then, the preform is cut into 40×2040×2155mm sections for a second rolling process. The initial rolling temperature is 982℃ and the final rolling temperature is 750℃. The rolling direction is along the width of the preform, the total deformation is 85%, the rolling pass interval is 20s, and the rolling speed is 1.2m / s. In the initial stage, 40mm is rolled to 15mm, with the temperature maintained at 900~982℃; in the middle stage, 15mm is rolled to 10mm, with the temperature maintained at 850~900℃. An edge heater is used to compensate for the temperature drop at the edge, and the bending roll force is adjusted from positive bending to balance. The positive bending force is gradually reduced from 300KN to 120KN, and a slight negative bending is introduced to prevent edge waviness; in the final stage, 10mm is rolled to 6mm, and the last pass is rolled from 6.4mm to 6mm, with the temperature maintained at 750~850℃. The bending roll force is dominated by negative bending, with the negative bending force increased to 180KN and the positive bending force at 120KN. The reduction rate of the last pass is 6.7%, and the rolling size is 6×2210×13200mm. After rolling, the rolls are air-cooled.

[0063] 5) The β-phase transformation point of the rolled sheet was measured to be 1002℃. The rolled sheet was solution treated at 980℃ for 1 hour, followed by aging at 620℃ for 4 hours, AC. After cooling, the head and tail of the sheet were removed, resulting in a TC4 titanium alloy sheet with a thickness of 6mm × 2200mm × 13200mm (length), good surface quality, a dual-scale α-phase structure, an average primary α-phase size of 10μm, and a volume fraction of 28%. Its microstructure is as follows: Figure 3 As shown.

[0064] The TC4 sheet prepared by the above method has the following mechanical properties as tested according to GB / T228.1: transverse tensile strength 992 MPa, yield strength 915 MPa, elongation 15.6%, and reduction of area 35.8%.

[0065] Example 2 1) Place the pretreated TC4 raw material in a closed reactor, introduce high-purity hydrogen gas to a pressure of 0.3 MPa, and hydrogenate at 800℃ for 18 hours. Remove the brittle TC4 hydride block after hydrogenation from the reactor and crush the brittle hydride into powder using a simple mechanical crushing method. Separate the hydride powder of 3~15 mm by sieving.

[0066] 2) Place the hydride powder at 820℃ and a vacuum degree ≤10 -2 The TC4 alloy powder was dehydrogenated by holding it at a high temperature for 8 hours in a Pa heat treatment furnace, and then cooled to room temperature in a vacuum. After that, it was subjected to plasma rotating electrode atomization treatment to obtain TC4 alloy powder with an average particle size of 150 μm.

[0067] The chemical composition of TC4 alloy powder was analyzed, and the mass fractions of the main elements were: Al 5.8%, V 3.9%, O 0.04%, H 0.004%, N 0.005%, C 0.014%, and Fe 0.11%.

[0068] 3) After degassing, TC4 alloy powder is packed into a pure titanium sheath measuring 100mm (thickness) × 1800mm (width) × 2000mm (length) (the titanium plate of the sheath is 3.0mm thick). The sheath is preheated to 450℃. A three-stage hot isostatic pressing process is then performed under vacuum: the first stage controls the heating rate at 10℃ / min, heating to 250℃, and then slowly evacuating to a vacuum level ≤1×10⁻⁶. -2 Pa; the second stage controls the heating rate at 10℃ / min, raising the temperature to 500℃, and then further evacuating to ≤4×10 - 2 The heating process was carried out in three stages with a heating rate of 6℃ / min, reaching 980℃. A static pressure of 100MPa was applied within this temperature range, and the holding time was 120min. After holding, under argon gas conditions, an argon pressure of 65KPa was applied, and the temperature was gradually cooled to below 450℃ at a rate of 15℃ / min. Then, an argon pressure of 135KPa was applied, and the temperature was further cooled to room temperature to obtain a bimodal preform.

[0069] The preform with the dual-phase microstructure has a density of 99.92% and a microstructure consisting of a primary equiaxed α-lamellae with a size of 10 μm and an α-lamellae spacing of 8 μm. Its metallographic photograph is shown below. Figure 4 .

[0070] 4) The rolling process adopts two-fire forming, and the rolling mill is a six-roll reversible rolling mill with a work roll crown design of +0.10mm (concave roll).

[0071] The β phase transformation point of the bimodal preform was measured to be 1000℃. First, the billet was heated to 952℃ in a gas atmosphere furnace for one-fire rolling, and the final rolling temperature was 780℃. The bending roll force was set to positive bending, and the bending roll force was 420KN. The rolling direction was along the width of the preform, the total deformation was 50%, the rolling line speed was 2.0m / s, the rolling thickness was 50mm, and the rolling dimensions were 50×2040×3529mm.

[0072] Then, a second rolling process is carried out, with an initial rolling temperature of 952℃ and a final rolling temperature of 770℃; the rolling direction is along the width of the preform, the total deformation is 50%, the rolling pass interval is 20s, and the rolling line speed is 1.8m / s. In the initial stage, 50mm is rolled to 34mm, with the temperature maintained at 900~952℃; in the middle stage, 34mm is rolled to 30mm, with the temperature maintained at 850~900℃. An edge heater is used to compensate for the temperature drop at the edge, and the bending roll force is adjusted from positive bending to balance. The positive bending force is gradually reduced from 300KN to 120KN, and a slight negative bending is introduced to prevent edge waviness; in the final stage, 30mm is rolled to 25mm, and the last pass is rolled from 27mm to 25mm, with the temperature maintained at 750~850℃. The bending roll force is dominated by negative bending, with the negative bending force increasing to 180KN and the positive bending force at 120KN. The reduction rate of the last pass is 7.4%, and the rolling size is 25×2080×6920mm. The rolling is water-cooled after rolling.

[0073] 5) After rolling, the sheet is held at 820℃ for 1 hour to complete recrystallization annealing, followed by a period of aging at 620℃ for 4 hours, AC treatment, and after cooling, the head and tail are removed, finally obtaining a finished sheet with good surface quality and equiaxed structure, measuring 25mm (thickness) × 2080mm (width) × 6920mm (length). Its metallographic structure is as follows: Figure 5 As shown. The mechanical properties of the TC4 sheet prepared by the above method were tested according to GB / T228.1, with a transverse tensile strength of 1010 MPa, a yield strength of 924 MPa, an elongation of 17.1%, and a reduction of area of ​​38.8%.

[0074] Comparative Example 1: A preform was prepared according to steps 1) to 3) of Example 1, the difference being that in step 3), the hot isostatic pressing treatment did not involve a three-step heating process, but instead directly controlled the heating rate at 6℃ / min, directly heating to 1000℃ and holding under pressure to obtain the preform. The microstructure of the obtained preform is as follows: Figure 6 As shown, the bimodal preform cannot be made equiaxed, resulting in poor microstructure uniformity.

[0075] Comparative Example 2: A finished sheet was prepared according to steps 1) to 5) of Example 2, the difference being that in step 5), the rolled sheet was subjected to recrystallization annealing at 840℃ for 1 hour to obtain the finished sheet. The microstructure of the obtained finished sheet is as follows: Figure 7 As shown, excessively coarse equiaxed structures will reduce the mechanical properties of the finished sheet material.

Claims

1. A method for preparing TC4 titanium alloy preforms, characterized in that: After pretreatment, TC4 recycled waste is pulverized by hydrogenation and dehydrogenation, and then atomized by plasma rotating electrode to obtain alloy powder with an oxygen content of ≤0.15wt%. The alloy powder is then subjected to three-step hot isostatic pressing to obtain TC4 titanium alloy preforms with a dual-state structure. The TC4 titanium alloy preform has a density ≥99.8%, a primary equiaxed α phase size ≤10μm and an α lamellar spacing ≤10μm; The three-stage hot isostatic pressing process includes: a first stage where the temperature is increased to 150-250℃ at a rate of 5-10℃ / min, followed by vacuuming to ≤1×10⁻⁶. -2 Pa; In the second stage, the temperature is increased to 400-500℃ at a rate of 5-10℃ / min, and a vacuum is applied to ≤4×10⁻⁶ Pa. -2 Pa; in the third stage, the temperature is increased to 920~980℃ at 3~6℃ / min, a static pressure of 100~140MPa is applied, and the temperature and pressure are maintained for 120~180min.

2. The method for preparing TC4 titanium alloy preforms according to claim 1, characterized in that: The pretreatment includes: cleaning the TC4 recycled waste with a 3% HNO3 solution and a 1% HF solution, annealing it under vacuum at 600~800℃, and then cutting or crushing it into small pieces of 3~15mm. The TC4 recycled waste includes one or more of the following: processing scraps, molding waste, and metallurgical waste.

3. The method for preparing TC4 titanium alloy preforms according to claim 1, characterized in that: The hydrogenation and dehydrogenation powdering process includes: placing small pieces in a closed reactor, introducing high-purity hydrogen gas to a pressure of 0.3~2.8 MPa, hydrogenating at 400~800℃ for 8~18 hours, and then crushing and sieving to obtain hydride powder; the hydride powder is then placed under a vacuum of ≤10... -2 In a vacuum environment of Pa, dehydrogenation was carried out at 650~820℃ for 8~18h. After cooling to room temperature in a vacuum or under inert atmosphere protection, plasma rotating electrode atomization treatment was performed to obtain TC4 alloy powder. The particle size of the TC4 alloy powder is 50~150μm; The content of elements other than oxygen in the TC4 alloy powder meets the requirements of GB / T3620.

1.

4. The method for preparing TC4 titanium alloy preforms according to claim 1, characterized in that: The hot isostatic pressing process further includes: loading the degassed TC4 alloy powder into a preheated 400~450℃ shroud, and then performing a three-step hot isostatic pressing process; after the hot isostatic pressing process, cooling the powder to below 450℃ in an argon atmosphere at a pressure of 45~65KPa at a cooling rate of ≥10℃ / min, and then cooling it to room temperature in an argon atmosphere at a pressure of 105~135KPa to obtain a TC4 titanium alloy preform with a dual-state structure; The casing is made of pure titanium plate; The wall thickness of the sheath is 1~3mm; The dimensions of the sleeve are: length 2000~2200mm × width 1800~2000mm × thickness 80~100mm.

5. A method for preparing TC4 titanium alloy sheet, characterized in that: A TC4 titanium alloy preform with a dual-phase microstructure is prepared by the preparation method of any one of claims 1 to 4, and then hot rolling and composite heat treatment are performed to obtain a TC4 titanium alloy plate with a dual-phase microstructure or an equiaxed microstructure. The dual-state TC4 titanium alloy plate has a dual-scale α-phase structure, with the primary α-phase size ≤10μm and a volume fraction of 20~40%. The hot rolling process specifically involves two-fire rolling. The preform is heated to the rolling temperature in a gas atmosphere or electric heating furnace and then rolled. The rolling direction is along the width of the preform. The initial rolling temperature for both fires is 20~50℃ below the β phase transformation point of the preform, and the final rolling temperature is ≥750℃. The total deformation is 50~85% for both fires. The rolling speed for the first fire is 1.5~2.0m / s, and the rolling speed for the second fire is 1.2~1.8m / s.

6. The method for preparing TC4 titanium alloy sheet according to claim 5, characterized in that: The two-stage rolling process is controlled in three temperature zones: 900℃ to the initial rolling temperature in the early stage, 850℃ to 900℃ in the middle stage, and 750℃ to 850℃ in the final stage. The temperature drop at the edges is compensated during the middle stage. The deformation per pass in the two-stage rolling process is gradually reduced to 8% to 15%, the reduction rate in the final pass is <10%, and the interval between rolling passes is <20s.

7. The method for preparing TC4 titanium alloy sheet according to claim 5, characterized in that: The hot rolling process uses a six-roll reversible mill to dynamically control the plate shape. The work roll crown is designed to be +0.10~0.20mm. When the thickness is >16mm, the work roll crown is taken as the upper limit of +0.20mm. When the thickness is 6~16mm, the work roll crown is gradually reduced to +0.10mm. The maximum positive bending force of the work roll is +600kN, and the maximum negative bending force is -450kN; The single-pass rolling is carried out when the thickness is 60~100mm, the bending roll adopts positive bending, and the bending roll force is 70% of the maximum positive bending force; The bending rolls in the second heat rolling process are adjusted from positive bending to balance, and the bending roll force is gradually reduced from 50% of the maximum positive bending force to 30%, and a slight negative bending is introduced. The finishing passes are dominated by negative bending, with the negative bending force being 40% of the maximum negative bending force and the positive bending force being less than 20% of the maximum positive bending force.

8. The method for preparing TC4 titanium alloy sheet according to claim 5, characterized in that: After the hot rolling process is completed, cooling is performed. The cooling mode is selected according to the thickness of the rolled plate. When the thickness δ is 6≤δ≤15mm, air cooling is used, and when the thickness δ is 15<δ≤25mm, water cooling is used.

9. The method for preparing TC4 titanium alloy sheet according to claim 5, characterized in that: The composite heat treatment satisfies any one of the following: The rolled sheet was kept at 20-50℃ below its β phase transformation point for 1-3 hours to complete the solution treatment, and then kept at 580-620℃ for 4-6 hours to complete the aging treatment; it was air-cooled to room temperature, and the head and tail of the snake were sawed off after cooling to obtain TC4 titanium alloy sheet with dual-state structure. The rolled sheet is heated to 780~820℃ and held for 1~4h to complete recrystallization annealing, and then held at 580~620℃ for 4~6h to complete aging treatment; air-cooled to room temperature, and after cooling, the snake head and tail are sawn off to obtain TC4 titanium alloy sheet with equiaxed structure.

10. A TC4 titanium alloy sheet, characterized in that: It is prepared by the preparation method of TC4 titanium alloy sheet according to any one of claims 5 to 9; The microstructure of the TC4 titanium alloy sheet is a bimodal structure or an equiaxed structure; wherein the bimodal structure is a dual-scale α-phase structure, the primary α-phase size is ≤10μm, and the volume fraction is 20~40%; The dimensions of the TC4 titanium alloy plate are: length 6000~15000mm × width 2000~2200mm × thickness 6~25mm; The mechanical properties of the TC4 titanium alloy sheet are: transverse tensile strength ≥990MPa, yield strength ≥910MPa, elongation ≥15%, and reduction of area ≥35%.

Images