TC4 titanium alloy preformed blank, TC4 titanium alloy plate with full lamellar structure and preparation method of TC4 titanium alloy plate

Abstract

The invention discloses a TC4 titanium alloy preformed blank, a TC4 titanium alloy plate with a full lamellar structure and a preparation method of 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, solid solution and two-stage aging composite heat treatment are combined, the head and the tail are cut off, and the TC4 titanium alloy plate is obtained. The problem of tissue segregation of a traditional cast ingot is solved through powder metallurgy, the obdurability is improved, and the anisotropy is reduced; and meanwhile, the raw material cost is reduced, the production period is shortened, the yield is increased, the surface quality is improved, and a reliable scheme is provided for green and efficient preparation of high-performance titanium alloy plates in the aerospace field.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloy processing, and relates to a TC4 titanium alloy preform, a TC4 titanium alloy plate with a full lamellar structure, and a preparation method thereof, and specifically relates to a preparation method of a high-strength, high-toughness, wide-width TC4 plate by rolling a powder metallurgy preform through a single-stand rolling machine. Background Art

[0002] In the aerospace field, as the overall level of the industry continues to rise, the demand for personalized preparation of TC4 plates has gradually become prominent, and its preparation mode has also shifted from the traditional general process to the personalized preparation mode of special plates. Against this background, key performance indicators such as strong plasticity and toughness of aerospace-grade plates are steadily improving. At present, TC4 plates are mainly prepared through the following two process paths: one is to obtain slabs by forging after being melted into ingots in a VAR furnace three times; the other is to use an EB furnace to cast flat slabs. After the slab is prepared, it needs to undergo multiple reciprocating and cross-rolling passes to finally become a product.

[0003] Traditional forging billets exhibit dendritic segregation and poor microstructure uniformity, making them difficult to control for flaw detection pass rates, residual stresses, and plate shape in aviation and aerospace-grade titanium alloy plates. Furthermore, the production process is lengthy and the yield rate is low. According to statistics, the yield rate of domestic titanium manufacturers from ingot casting to finished plates measuring 3-6 mm (thickness) x 1400-2000 mm (width) is less than 60%. While EB furnace casting of flat slabs shortens the process to some extent, the as-cast microstructure, despite refined controlled rolling and controlled cooling methods, cannot meet the requirements for anisotropic and uniform microstructure in the plates. Limited by the multiple rolling passes of ingots and slabs and intermediate heat treatments, the long process can lead to structural inhomogeneity, plate warpage, residual stresses, and ultrasonic flaw detection issues. The performance pass rate of the finished product is also a technical challenge that restricts the application of titanium metal.

[0004] Although the existing patented technologies have proposed some improvement plans, they still have their own limitations. For example, CN120079718A discloses a method for rolling thin-gauge ultra-wide TC4 titanium alloy plates in one fire. In order to ensure the surface quality, the invented method adopts surface explosion to composite a layer of pure titanium plate, and the production environmental protection requirements are high; secondly, it adopts reversing rolling, which makes the on-site process difficult to execute and the production quality unstable. CN117066281A discloses a method for hot rolling a single TC4 titanium alloy plate, which adopts a three-fire rolling method to prepare TC4 plates, and the process flow is long. CN115971249A discloses a method for preparing ultra-thin TC4 titanium alloy plates. The ingot casting method adopts a multi-fire rolling method, and the slab structure control level is poor, which makes it difficult to meet the aviation-grade high structure uniformity requirements.

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

[0006] The technical problem to be solved by the present invention is the poor structural uniformity of the casting blank produced by the traditional forging process.

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

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

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

[0010] In the above preparation method, the hydrogenation and dehydrogenation powder preparation comprises: placing the small pieces in a closed reactor, introducing high-purity hydrogen to a pressure of 0.3-2.8 MPa, hydrogenating at 400-800 ° C for 8-18 hours, and then crushing and screening to obtain hydride powder; placing the hydride powder in a vacuum of ≤10 -2 Pa vacuum environment, dehydrogenation at 650-820 ° C for 8-18 hours, cooling to room temperature in vacuum or under inert atmosphere, and then performing plasma rotating electrode atomization treatment to obtain TC4 alloy powder.

[0011] Furthermore, the particle size of the TC4 alloy powder is 50-150 μm.

[0012] Furthermore, the contents of other elements in the TC4 alloy powder except oxygen content meet the requirements of GB / T3620.1.

[0013] In the above preparation method, the hot isostatic pressing treatment also includes: placing the degassed TC4 alloy powder into a package preheated to 400~450℃, and then performing a three-step hot isostatic pressing treatment; after the hot isostatic pressing treatment is completed, cooling to below 450℃ in an argon environment with a pressure of 45~65KPa at a cooling rate of ≥10℃ / min, and then cooling 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] Furthermore, the material of the above-mentioned sleeve is pure titanium plate.

[0015] Furthermore, the wall thickness of the above-mentioned sleeve is 1~3mm.

[0016] Furthermore, the dimensions of the above-mentioned package are: length 2000~2200mm×width 1800~2000mm×thickness 80~100mm.

[0017] In a second aspect, the present invention provides a method for preparing a TC4 titanium alloy plate: a TC4 titanium alloy preform having a dual-state structure is prepared using the above-mentioned method for preparing a TC4 titanium alloy preform, and then hot rolling and composite heat treatment are performed to obtain a TC4 titanium alloy plate having a full lamellar structure; The hot rolling process is specifically as follows: the preform is heated to the rolling temperature in a gas atmosphere or an electric heating furnace and then rolled out of the furnace, and two-fire rolling is adopted, and the rolling direction is along the width direction of the preform; the starting rolling temperature of the first fire rolling is 20-50°C above the β phase transformation point of the preform, the final rolling temperature is ≥750°C, the total deformation is 50-80%, and the rolling rate is 1.5-2.0 m / s; the starting rolling temperature of the second fire rolling is 20-50°C below the β phase transformation point of the preform, the final rolling temperature is ≥750°C, the total deformation is 50-85%, and the rolling rate is 1.2-1.8 m / s; The composite heat treatment is specifically as follows: heating the rolled plate to 20-50°C above its β phase transformation point and keeping it warm for 1 hour to complete solution treatment; then keeping it warm at 580-620°C for 4-6 hours and at 460-500°C for 4-6 hours to complete two-stage aging treatment; air cooling to room temperature, sawing off the snake head and tail, and obtaining a TC4 titanium alloy plate with a full lamellar structure.

[0018] Furthermore, the above-mentioned two-fire rolling is controlled in three temperature zones. The early rolling pass is 920℃~rolling start temperature, the middle rolling pass is 850~920℃, and the final rolling pass is 750~850℃. The temperature drop of the edge is compensated in the middle rolling; the deformation of the single pass of the two-fire rolling is gradually reduced to 8~15%, the reduction rate of the last pass is <10%, and the rolling pass interval is <20s.

[0019] In the above preparation method, the hot rolling process adopts a six-roll reversing rolling mill to dynamically control the plate shape, and the crown of the working roll is designed to be +0.10-0.20 mm. When the thickness is greater than 16 mm, the crown of the working roll is taken to an upper limit of +0.20 mm, and when the thickness is 6-16 mm, the crown of the working roll is gradually reduced to +0.10 mm; the maximum positive bending force of the working roll is +600 kN, and the maximum negative bending force is -450 kN; Furthermore, the above-mentioned single-heat rolling is carried out when the thickness is 60-100 mm, the bending roll adopts positive bending, and the bending roll force is 70% of the maximum positive bending force.

[0020] Furthermore, the above-mentioned two-fire rolling bending rolls 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.

[0021] In the above preparation method, cooling is performed after the hot rolling treatment is completed, and 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.

[0022] In a third aspect, the present invention provides a TC4 titanium alloy plate having a full lamellar structure, which is produced by the above-mentioned method for producing the TC4 titanium alloy plate.

[0023] Furthermore, the dimensions of the TC4 titanium alloy plate are: length 6000~15000 mm×width 2000~2200 mm×thickness 6~25 mm.

[0024] Furthermore, the mechanical properties of the TC4 titanium alloy plate are as follows: transverse tensile strength ≥970MPa, yield strength ≥890MPa, elongation ≥8%, cross-sectional shrinkage ≥15%, fracture toughness K in TL and LT directions IC All ≥85MPa·m 1 / 2 .

[0025] The beneficial effects of the present invention are as follows: Unlike conventional methods that increase the grade of titanium sponge and reduce the mass fraction of impurities and interstitial atoms to enhance the strength and toughness of TC4 sheet, the present method provides a green, low-cost powder metallurgy method for prefabricating TC4 slabs without titanium sponge screening or control of impurity elements in the intermediate alloy. This method combines two-stage hot rolling, solution treatment, and two-stage aging treatment to achieve the production of high-performance, highly uniform, wide-width TC4 sheet. Compared to traditional processes, this method simplifies the preparation process, improves yield efficiency, and significantly reduces production costs. The resulting titanium alloy sheet exhibits superior strength and toughness, meeting the application requirements of the aerospace field and possessing widespread application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the process control curve for hot isostatic pressing; Figure 2 The metallographic image of the dual-structure preform obtained in Example 1; Figure 3 This is the metallographic diagram of the TC4 titanium alloy plate obtained in Example 1; Figure 4 The metallographic image of the dual-structure preform obtained in Example 2; Figure 5 The microstructure of the preform prepared in Comparative Example 1. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clear, the application is further described in detail below in conjunction with the embodiments. Unless otherwise defined, all scientific and technical terms used herein have the same meanings as understood by ordinary technicians in this field.

[0028] A method for preparing a high-performance, high-uniformity wide-width TC4 titanium alloy plate comprises the following steps.

[0029] (1) The TC4 recycled waste is cleaned with weak acid (3% HNO3 + 1% HF solution) and then vacuum annealed at 600-800°C to remove surface impurities. The large raw materials are cut or crushed into relatively uniform small pieces of 3-15 mm in size to increase the specific surface area for the subsequent hydrogenation reaction and improve the hydrogenation efficiency and uniformity.

[0030] In one embodiment of the present invention, the TC4 recycled waste includes one or more of machining shavings (e.g., turnings and milling shavings), molding residues (e.g., forging scraps and casting scraps), and metallurgical waste (e.g., substandard ingots and bar stock). TC4 recycled waste is the primary source of economic efficiency for the present method. Reusing TC4 recycled waste as raw material effectively reduces production costs.

[0031] (2) The pretreated TC4 raw material is placed in a sealed reactor (usually a high-temperature and high-pressure vacuum / atmosphere furnace). High-purity hydrogen (H2) is introduced and heated to the appropriate hydrogenation temperature and maintained. The hydrogenation reaction causes the lattice to expand, generating huge internal stresses, making the originally tough TC4 alloy extremely brittle (hydrogen embrittlement) and easily crushed.

[0032] In one embodiment of the present invention, the hydrogen pressure is typically within the range of 0.3-2.8 MPa. Pressure affects the hydrogen absorption rate and final hydrogen content. For TC4 alloy, the hydrogenation temperature is typically between 400°C and 800°C. Lower temperatures slow the hydrogenation rate, while higher temperatures may lead to microstructure coarsening or localized melting. The holding time is 8-18 hours to allow the hydrogen to fully diffuse into the alloy and react with titanium to form titanium hydrides (primarily TiH2, as well as aluminum and vanadium hydrides or solid solutions).

[0033] (3) The brittle TC4 hydride block after hydrogenation is removed from the reactor. A simple mechanical crushing method is used to crush the brittle hydride into powder. The crushed powder is sieved to separate the powder that meets the target particle size range (3~15mm). The coarse powder is returned for further crushing.

[0034] (4) The sieved TC4 hydride powder is placed in a vacuum heat treatment furnace for heat preservation and dehydrogenation. The hydride decomposes, the hydrogen is removed, and the powder returns to the titanium alloy (Ti-6Al-4V) state.

[0035] In one embodiment of the present invention, dehydrogenation is carried out in a high vacuum environment (≤10 -2 The dehydrogenation process is carried out at a pressure of 1000 Pa (Pa) to ensure efficient hydrogen extraction and prevent oxidation. For TC4 alloy, the dehydrogenation temperature must be high enough to drive hydrogen desorption and diffusion, while remaining below the β-transus temperature (TC4's β-transus temperature is approximately 995°C) to prevent excessive grain growth and phase transformation. Excessively high temperatures can also easily introduce impurities such as oxygen and nitrogen. Therefore, the dehydrogenation temperature is typically between 650°C and 820°C. The holding time is 8 to 18 hours to allow hydrogen to fully desorb and diffuse out of the powder.

[0036] (5) After dehydrogenation, the powder is cooled to room temperature under vacuum or inert atmosphere (such as argon) to prevent oxidation of the hot powder. The powder is then atomized using a plasma rotating electrode to obtain TC4 alloy powder. The powder is tested for chemical composition, including the contents of major elements (Ti, Al, V) and key impurity elements (O, H, N, C, Fe). The TC4 alloy powder has a particle size of 50-150 μm, an oxygen content of ≤0.15 wt%, and the remaining elements meet the requirements of GB / T3620.1.

[0037] In one embodiment of the present invention, the dehydrogenated powder may cause slight agglomeration or change in particle size distribution due to shrinkage or other reasons, and usually needs to be screened again or batched to ensure batch uniformity.

[0038] (6) After degassing, the TC4 alloy powder was placed in a preheated package and subjected to three-step temperature control under vacuum. The first stage controlled the heating rate to 5-10°C / min and heated to 150-250°C. While removing impurities, the powder was slowly vacuumed to ≤1×10 -2 Pa; in the second stage, the temperature is raised to 400~500℃ and the vacuum is further evacuated to ≤4×10 -2 Pa; the three-stage heating rate is controlled at 3~6℃ / min, and the heating rate is reduced to avoid temperature unevenness, and the temperature is raised to 920~980℃. A static pressure of 100~140MPa is applied in this temperature range, and the holding time is 120~180min. After the holding is completed, under the argon medium, the argon pressure is first applied to 45~65kPa, and the temperature is gradually cooled to below 450℃ at a rate of ≥10℃ / min; then the argon pressure is applied to 105~135kPa and continued to cool to room temperature. The density is ≥99.8%, and the microstructure is composed of a primary equiaxed α size ≤10μm and an α lamellae spacing ≤10μm.

[0039] In one embodiment of the present invention, the material of the sheath is pure titanium plate, the size of the sheath is 80-100 mm (thickness) × 1800-2000 mm (width) × 2000-2200 mm (length), the wall thickness of the sheath is 1-3 mm, and the preheating temperature is 400-450°C. The process control curve of hot isostatic pressing treatment is as follows Figure 1 As shown, the hot isostatic pressing temperature is lower than the β transformation temperature T β (998°C), holding time 120-180 minutes, rapid cooling after the end of the holding period, and pressure gradient loading under argon medium to inhibit α phase growth. The advantages of this method are that it avoids α phase coarsening, improves density, and enhances powder bonding strength. The use of a pure titanium sheath eliminates the need for mold release and prevents severe surface oxidation in subsequent heating media. Rolling with the sheath avoids the conventional lengthy acid and alkali cleaning process while also ensuring surface quality.

[0040] In the present invention, in order to solve the problems of poor uniformity of structure and low qualified rate of flaw detection in traditional processes, powder metallurgy preforms are used to replace traditional ingots. The recycled waste is subjected to hydrogenation and dehydrogenation treatment to prepare powder, and then atomized by a plasma rotating electrode to prepare TC4 alloy powder with low oxygen content, and then consolidated by three-step hot isostatic pressing to form a dual-state structure preform, thereby avoiding macro segregation from the source. The high temperature and high pressure environment of hot isostatic pressing promotes powder diffusion and bonding, refines grains while eliminating internal defects, and significantly improves the density of the material. This method completely eliminates the dendritic segregation of the ingot, achieves ultra-fine microstructure and high uniformity, and meets the requirements of aviation-grade flaw detection.

[0041] (7) The billet is heated to the rolling temperature in a gas atmosphere or an electric heating furnace and then rolled out of the furnace. Two-fire rolling is used for forming, and the rolling direction is along the width direction of the preform. The total deformation of the first fire rolling is 50~80%, the starting rolling temperature is 20~50℃ above the β phase transformation point of the preform, the final rolling temperature is ≥750℃, and the rolling rate is 1.5~2.0m / s; the total deformation of the second fire rolling is 50~85%, the starting rolling temperature is 20~50℃ below the β phase transformation point of the preform, the final rolling temperature is ≥750℃, and the rolling rate is 1.2~1.8m / s. After rolling, cooling is performed to obtain the rolled plate; 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.

[0042] This invention uses a two-pass rolling process, replacing the traditional multi-pass forging and rolling process. Precise temperature control (avoiding harmful phase transition zones) achieves efficient deformation and reduces the number of intermediate heat treatments, effectively improving yield rates, shortening processes, and reducing energy consumption. This addresses the low yield rates and high energy consumption associated with lengthy production processes in traditional processes. Furthermore, the use of a jacketed rolling process, with the pure titanium jacket providing oxidation isolation, synchronizes plastic deformation with the substrate during rolling, and eliminates the need for acid or alkali cleaning, improving surface quality.

[0043] In one embodiment of the present invention, the two-fire rolling is controlled in three temperature zones, the early rolling pass is 920°C~rolling temperature, the middle rolling pass is 850~920°C, and the final rolling pass is 750~850°C. Edge heaters are used in the middle rolling to compensate for the edge temperature drop; the deformation of the two-fire single pass is gradually reduced to 8~15%, the reduction rate of the final pass is <10% to ensure the plate shape, and the rolling pass interval is <20s.

[0044] In one embodiment of the present invention, a six-roll reversible rolling mill is used for rolling. To control the plate shape, the crown design and bending roll force are taken into consideration. The crown of the working roll is treated to compensate for the thermal expansion and wear of the roll, thereby offsetting the bending deformation caused by the rolling force. The crown of the working roll is designed to be +0.10~0.20mm (concave roll). When the thickness is greater than 16mm, the crown of the working roll is taken to an upper limit of +0.20mm to resist bending under high rolling forces. When the thickness is 6~16mm, the crown of the working roll is gradually reduced to +0.10mm to avoid excessive edge thinning. The maximum positive bending force of the working roll is +600kN, and the maximum negative bending force is -450kN. The bending rolls of the first-heat rolling adopt positive bending, and the bending roll force is 70% of the maximum positive bending force to compensate for the insufficient thermal crown of the rolls. The bending rolls of the second-heat rolling 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%. Then, a slight negative bending is introduced to prevent edge waves. The bending roller force in the finished product pass is dominated by negative bending, and the negative bending force is increased to 40% of the maximum negative bending force, and the positive bending force is controlled to be less than 20% of the maximum positive bending force.

[0045] In this method, gradient rolling is used to suppress local stress concentration. Two-stage aging promotes uniform precipitation of the secondary α phase, optimizing the lamellar microstructure ratio and simultaneously improving both strength and toughness. Edge heaters are used mid-roll to compensate for temperature drops along the edges of wide plates, reducing microstructure unevenness caused by lateral temperature differences, maintaining stable performance, and minimizing fluctuations. The combined use of concave roll crown and bending force dynamically compensates for roll thermal deformation, balancing the lateral distribution of the roll gap and ensuring the shape and surface quality of wide plates. This results in a finished product free of warpage and edge wave defects, resulting in improved surface quality.

[0046] (8) After rolling, the plate is kept at 20~50℃ above its β phase transformation point for 1h to complete the solution treatment, and then subjected to two stages of aging (580~620℃)×(4~6h)+(460~500℃)×(4~6h), AC; after cooling, the snake head and tail are sawed off, and finally a finished plate with a size of 6~25mm (thickness)×2000~2200mm (width)×6000~15000mm (length) is obtained, with good surface quality and full lamellar structure.

[0047] The mechanical properties of the TC4 plate prepared by the above method are tested in accordance with GB / T228.1: transverse tensile strength ≥970MPa, yield strength ≥890MPa, elongation ≥8%, cross-sectional shrinkage ≥15%, and fracture toughness TL and LT directions are tested in accordance with GB / T4161 K IC ≥85MPa·m 1 / 2 .

[0048] Specific examples will be listed below to explain the scheme of the present invention. Those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product specifications. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0049] The present invention provides two sets of Examples 1 and 2, each of which utilizes the method of the present invention to produce TC4 sheet materials. Examples 1 and 2 utilize pretreated recycled TC4 waste as raw material. The pretreatment method involves cleaning the recycled TC4 waste with a weak acid solution (3% HNO3 + 1% HF solution) and then vacuum annealing at 600°C to remove surface impurities. The bulk material is then cut or crushed into relatively uniform small pieces of 3-15 mm for later use.

[0050] Example 1 1) The pretreated TC4 raw material is placed in a closed reactor, high-purity hydrogen is introduced to a pressure of 2.8 MPa, and hydrogenation is carried out at 400°C for 8 hours. The brittle TC4 hydride block after hydrogenation is removed from the reactor and crushed into powder using a simple mechanical crushing method. The hydride powder of 3~15 mm is separated by screening.

[0051] 2) Place the hydride powder at 650℃ and vacuum ≤10 -2 Pa heat treatment furnace for 18 h to dehydrogenate, and after cooling to room temperature in vacuum, plasma rotating electrode atomization treatment was performed to obtain TC4 alloy powder with an average particle size of 50 μm.

[0052] The chemical composition of TC4 alloy powder was tested, 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%.

[0053] 3) After degassing, the TC4 alloy powder was placed in a pure titanium can with a size of 80 mm (thickness) × 2000 mm (width) × 2200 mm (length) (the thickness of the titanium plate in the can was 1.0 mm). The can was preheated to 400 °C. A three-step hot isostatic pressing treatment was performed under vacuum: in the first stage, the heating rate was controlled at 5 °C / min, the temperature was raised to 150 °C, and the vacuum was slowly evacuated to ≤1×10 -2 Pa; in the second stage, the heating rate was controlled at 5℃ / min, the temperature was raised to 400℃, and the vacuum was further evacuated to ≤4×10 -2Pa, three-stage controlled heating rate of 3 ° C / min, heating to 920 ° C, and applying 140 MPa static pressure in this temperature range, and holding time is 180 minutes. After the holding period, under argon medium, argon pressure of 45 kPa is applied, and gradient cooling is carried out at a rate of 10 ° C / min to below 400 ° C; then argon pressure is applied to 105 kPa, and cooling is continued to room temperature to obtain a dual-structure preform.

[0054] The density of the dual-state structure preform is 99.89%, and the microstructure is a dual-state structure with a primary equiaxed α size of 8 μm and an α lamella spacing of 6 μm. The metallographic structure photo is shown in Figure 2 .

[0055] 4) The rolling process adopts two-fire forming, the rolling mill is a six-roll reversing rolling mill, and the crown of the working roll is designed to be +0.10mm (concave roll).

[0056] The β phase transition point of the dual-state structure preform was measured to be 1008℃. First, the billet was heated to 1028℃ in a gas atmosphere heating furnace for single-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 direction of the preform, the total deformation was 50%, the rolling line speed was 1.5m / s, the rolling thickness was 40mm, and the rolling size was 40×2040×4310mm.

[0057] Then, the preform was cut into 40×2040×2155mm pieces for the second hot rolling. The second hot rolling temperature was 988℃ and the final rolling temperature was 760℃. The rolling direction was along the width direction of the preform. The total deformation was 50%. The rolling pass interval was 20s and the rolling line speed was 1.2m / s. In the early stage, the thickness is rolled from 40mm to 15mm, and the temperature is maintained at 920~988℃; in the middle stage of rolling, the thickness is rolled from 15mm to 10mm, and the temperature is maintained at 850~920℃. Edge heaters are used to compensate for the temperature drop at the edges, 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 waves; in the final stage of rolling, the thickness is rolled from 10mm to 6mm, and the last pass is rolled from 6.4mm to 6mm. The temperature is maintained at 750~850℃, and the bending roll force is dominated by negative bending. The negative bending force is increased to 180KN, the positive bending force is 120KN, the last pass reduction rate is 6.7%, the rolling size is 6×2210×13200mm, and air cooling is performed after rolling.

[0058] 5) After rolling, the plate is kept at 1028℃ for 1h to complete the solution treatment, and then two stages of aging are carried out at 580℃×6h+460℃×6h, AC. After cooling, the snake head and tail are sawed off, and finally a finished plate with a thickness of 6mm (thickness) × 2200mm (width) × 13200mm (length) is obtained, with good surface quality and full lamellar structure. Its metallographic structure is as follows Figure 3 shown.

[0059] The mechanical properties of the TC4 plate prepared by the above method are tested according to GB / T228.1, with the transverse tensile strength of 978MPa, the yield strength of 898MPa, the elongation of 9.7%, the cross-sectional shrinkage of 28.9%, and the fracture toughness in the TL and LT directions according to GB / T4161. IC The measured value is 89 MPa·m 1 / 2 and 92 MPa·m 1 / 2 .

[0060] Example 2 1) The pretreated TC4 raw material is placed in a closed reactor, high-purity hydrogen is introduced to a pressure of 0.3 MPa, and hydrogenation is carried out at 800°C for 18 hours. The brittle TC4 hydride block after hydrogenation is removed from the reactor and crushed into powder using a simple mechanical crushing method. The hydride powder of 3-15 mm is separated by screening.

[0061] 2) Place the hydride powder in a vacuum chamber at 820°C and ≤10 -2 Pa heat treatment furnace for 8 h to dehydrogenate, cooled to room temperature in vacuum, and then subjected to plasma rotating electrode atomization treatment to obtain TC4 alloy powder with an average particle size of 150 μm.

[0062] The chemical composition of TC4 alloy powder was tested, 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%.

[0063] 3) After degassing, the TC4 alloy powder was placed in a pure titanium can with a size of 100 mm (thickness) × 1800 mm (width) × 2000 mm (length) (the thickness of the titanium plate is 3.0 mm), and the can was preheated to 450 ° C. A three-step hot isostatic pressing treatment was performed under a vacuum environment: the first stage was controlled to heat up at a rate of 10 ° C / min, and the temperature was raised to 250 ° C. The vacuum was slowly evacuated to ≤ 1 × 10 -2 Pa; the second stage controlled the heating rate to 10℃ / min, heated to 500℃, and further vacuumed to ≤4×10 - 2 Pa, three-stage controlled heating rate of 6 ° C / min, heating to 980 ° C, and applying 100 MPa static pressure in this temperature range, and holding time is 120 minutes. After the holding period, under argon medium, argon pressure of 65 kPa is applied, and the temperature is gradually cooled at a rate of 15 ° C / min to below 450 ° C; then argon pressure of 135 kPa is applied, and cooling is continued to room temperature to obtain a dual-structure preform.

[0064] The density of the dual-state structure preform is 99.92%, and the microstructure is a dual-state structure with a primary equiaxed α size of 10 μm and an α lamella spacing of 8 μm. The metallographic structure photo is shown in Figure 4 .

[0065] 4) The rolling process adopts two-fire forming, the rolling mill is a six-roll reversing rolling mill, and the crown of the working roll is designed to be +0.20mm (concave roll).

[0066] The β phase transition point of the dual-state structure preform was measured to be 1000℃. First, the billet was heated to 1050℃ in a gas atmosphere heating furnace for single-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 direction of the preform, the total deformation was 50%, the rolling line speed was 2.0m / s, the rolling thickness was 50mm, and the rolling size was 50×2040×3529mm.

[0067] Then, the second hot rolling is carried out, the second hot rolling temperature is 950℃, and the final rolling temperature is 770℃; the rolling direction is along the width direction of the preform, the total deformation is 50%, the rolling pass interval is 18s, and the rolling line speed is 1.8m / s. In the early stage, the thickness is rolled from 40mm to 34mm, and the temperature is maintained at 920~950℃; in the middle stage of rolling, the thickness is rolled from 34mm to 30mm, and the temperature is maintained at 850~920℃. Edge heaters are used to compensate for the temperature drop at the edges, and the bending roll force is adjusted from positive bending to balance. The positive bending force of 300KN is gradually reduced to 120KN, and a slight negative bending is introduced to prevent edge waves; in the final stage of rolling, the thickness is rolled from 30mm to 25mm, and the last pass is rolled from 27mm to 25mm. The temperature is maintained at 750~850℃, and the bending roll force is dominated by negative bending. The negative bending force is increased to 180KN, the positive bending force is 120KN, the reduction rate of the last pass is 7.4%, the rolling size is 25×2080×6920mm, and it is water-cooled after rolling.

[0068] 5) After rolling, the plate was kept at 1050℃ for 1h to complete the solution treatment, and then subjected to two-stage aging treatment at 620℃×4h+500℃×4h, AC. After cooling, the snake head and tail were sawed off to finally obtain a finished plate with a thickness of 25mm (thickness)×2080mm (width)×6920mm (length) and good surface quality and full lamellar structure.

[0069] The mechanical properties of the TC4 plate prepared by the above method are tested according to GB / T228.1. The transverse tensile strength is 982MPa, the yield strength is 901MPa, the elongation is 11.6%, the cross-sectional shrinkage is 30.4%, and the fracture toughness in TL and LT directions is tested according to GB / T4161. IC The measured value is 91 MPa·m 1 / 2 and 95 MPa·m 1 / 2 .

[0070] Comparative Example 1: A preform was prepared according to steps 1) to 3) of Example 1. The difference from Example 1 is that in step 3), the hot isostatic pressing process was not performed in three steps. Instead, the temperature was directly raised to 1000°C and the temperature was kept at this temperature and pressure at a controlled rate of 6°C / min to obtain a preform. The microstructure of the obtained preform is shown in FIG. Figure 5 As shown, it can be seen that the dual-state structure preform cannot be isometric and the structure uniformity is poor.

Claims

1. A method for preparing a TC4 titanium alloy preform, characterized in that: After pretreatment, the recycled TC4 waste is pulverized by hydrogenation and dehydrogenation, and then atomized by a plasma rotating electrode to obtain an alloy powder with an oxygen content of ≤0.15wt%. The alloy powder is then subjected to a three-step hot isostatic pressing process to obtain a TC4 titanium alloy preform with a dual-state structure. The density of the TC4 titanium alloy preform is ≥99.8%, the size of the primary equiaxed α phase is ≤10 μm, and the spacing between α lamellae is ≤10 μm; The three-step hot isostatic pressing treatment includes: in the first stage, heating to 150-250°C at 5-10°C / min, vacuuming to ≤1×10 -2 Pa; in the second stage, the temperature was raised to 400-500°C at a rate of 5-10°C / min, and vacuumed to ≤4×10 -2 Pa; in the third stage, the temperature is raised to 920~980℃ at a rate of 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 a TC4 titanium alloy preform according to claim 1, wherein: The pretreatment comprises: washing the TC4 recovery waste with a 3% HNO3 solution and a 1% HF solution, annealing at 600-800°C under vacuum conditions, and then cutting or crushing into small pieces of 3-15 mm; The TC4 recycled waste includes one or more of machining chips, molding residues, and metallurgical waste.

3. The method for preparing a TC4 titanium alloy preform according to claim 1, wherein: The hydrogenation and dehydrogenation powder preparation comprises: placing small pieces in a closed reactor, introducing high-purity hydrogen to a pressure of 0.3-2.8 MPa, hydrogenating at 400-800°C for 8-18 hours, and then crushing and screening to obtain hydride powder; placing the hydride powder in a vacuum of ≤10 -2 Pa vacuum environment, dehydrogenation at 650-820 ° C for 8-18 hours, cooling to room temperature in vacuum or under inert atmosphere, and then performing plasma rotating electrode atomization treatment to obtain TC4 alloy powder; The particle size of the TC4 alloy powder is 50-150 μm; The contents of other elements of the TC4 alloy powder except oxygen content meet the requirements of GB / T3620.

1.

4. The method for preparing a TC4 titanium alloy preform according to claim 1, wherein: The hot isostatic pressing treatment further comprises: placing the degassed TC4 alloy powder into a can preheated to 400-450° C., and then performing a three-step hot isostatic pressing treatment; after the hot isostatic pressing treatment, cooling the powder to below 450° C. in an argon environment at a pressure of 45-65 kPa at a cooling rate of 10° C. / min, and then cooling the powder to room temperature in an argon environment at a pressure of 105-135 kPa, to obtain a TC4 titanium alloy preform having a dual-state structure; The material of the sheath is pure titanium plate; The wall thickness of the sleeve is 1-3 mm; The dimensions of the package are: length 2000~2200mm×width 1800~2000mm×thickness 80~100mm.

5. The preparation method of TC4 titanium alloy plate is characterized by: A TC4 titanium alloy preform with a dual-state structure is prepared by the method for preparing a TC4 titanium alloy preform according to any one of claims 1 to 4, and then a TC4 titanium alloy plate with a full lamellar structure is obtained by hot rolling and composite heat treatment. The hot rolling process is specifically as follows: the preform is heated to the rolling temperature in a gas atmosphere or an electric heating furnace and then rolled out of the furnace, and two-fire rolling is adopted, and the rolling direction is along the width direction of the preform; the starting rolling temperature of the first fire rolling is 20-50°C above the β phase transformation point of the preform, the final rolling temperature is ≥750°C, the total deformation is 50-80%, and the rolling rate is 1.5-2.0 m / s; the starting rolling temperature of the second fire rolling is 20-50°C below the β phase transformation point of the preform, the final rolling temperature is ≥750°C, the total deformation is 50-85%, and the rolling rate is 1.2-1.8 m / s; The composite heat treatment is specifically as follows: heating the rolled plate to 20-50°C above its β phase transformation point and keeping it warm for 1 hour to complete solution treatment; then keeping it warm at 580-620°C for 4-6 hours and at 460-500°C for 4-6 hours to complete two-stage aging treatment; air cooling to room temperature, sawing off the snake head and tail, and obtaining a TC4 titanium alloy plate with a full lamellar structure.

6. The method for preparing the TC4 titanium alloy sheet according to claim 5, characterized in that: The two-pass rolling is controlled in three temperature zones, with the early rolling pass being 920°C to the start rolling temperature, the mid-pass rolling pass being 850~920°C, and the final rolling pass being 750~850°C. The mid-pass rolling compensates for the edge temperature drop; the deformation of a single pass of the two-pass rolling is gradually reduced to 8~15%, the reduction rate of the final pass is <10%, and the rolling pass interval is <20s.

7. The method for preparing the TC4 titanium alloy sheet according to claim 5, wherein: The hot rolling process adopts a six-roll reversing rolling mill to dynamically control the plate shape, and the crown of the working roll is designed to be +0.10-0.20 mm. When the thickness is greater than 16 mm, the crown of the working roll is taken to an upper limit of +0.20 mm, and when the thickness is 6-16 mm, the crown of the working roll is gradually reduced to +0.10 mm. The maximum positive bending force of the working roll is +600kN, and the maximum negative bending force is -450kN.

8. The method for preparing the TC4 titanium alloy sheet according to claim 7, wherein: The first heat rolling is carried out when the thickness is 60-100 mm, the bending roll adopts positive bending, and the bending roll force is 70% of the maximum positive bending force; The second-fire rolling bending roll is 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 finished product pass is dominated by negative bending, and 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.

9. The method for preparing the TC4 titanium alloy sheet according to claim 5, wherein: 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.

10. A TC4 titanium alloy sheet with a full lamellar structure, characterized by: Prepared by the preparation method of the TC4 titanium alloy plate according to any one of claims 5 to 9; 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 plate are as follows: transverse tensile strength ≥970MPa, yield strength ≥890MPa, elongation ≥8%, section shrinkage ≥15%, fracture toughness K in TL and LT directions IC All ≥85MPa·m 1 / 2 .

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