An ultrahigh-strength and high-toughness titanium alloy and a preparation method thereof

Abstract

The application discloses a kind of super-high-strength high-toughness titanium alloy and preparation method thereof, it is related to metal material preparation technical field.The component of the super-high-strength high-toughness titanium alloy of the present application includes by mass percent: 4.8~5.4% of Al, 7.8~8.3% of Mo, 2.8~3.4% of Cr, 1.8~2.5% of Nb, the balance is Ti and unavoidable impurities;Preparation method specifically is: after mixing raw material is pressed into electrode, electrode is melted, and ingot is obtained;Ingot is heated and kept, then is upset deformation and elongation deformation treatment, and the upset and drawing forging processing after multi-stage is obtained;The upset and drawing forging processing after multi-stage is treated to three-stage elongation, then is rolled deformation, finally is aging treatment and solid solution treatment, and the super-high-strength high-toughness titanium alloy is obtained;The present application is prepared by the component design of atomic ratio constraint, gradient temperature control forging and rolling and segmented aging process coordination, improves beta phase stability, in combination with gradient temperature control forging and rolling and segmented aging process, realizes the preparation of super-high-strength high-toughness titanium alloy.

Description

Technical Field

[0001] This invention relates to an ultra-high strength and high toughness titanium alloy and its preparation method, belonging to the field of metal material preparation technology. Background Technology

[0002] Titanium alloys, due to their advantages of low density, high specific strength, and good corrosion resistance, have been widely used in aerospace, shipbuilding, and defense industries. However, with increasing demands for weight reduction and load-bearing capacity in aircraft manufacturing, traditional high-strength titanium alloys (such as TC4 and TC11, with strength grades of 900-1100 MPa) are no longer sufficient to meet the design requirements of main load-bearing components. In related technologies, achieving ultra-high strength in titanium alloys typically involves adding large amounts of β-stabilizing elements (such as V and Fe) combined with complex deformation heat treatment processes. However, such alloys suffer from a trade-off between strength and toughness. While adding β-stabilizing elements (such as V) can improve strength, excessive addition can lead to β-phase coarsening and uncontrolled secondary α-phase size, resulting in a sharp decline in toughness. Adding strong β-stabilizing elements like Mo and Cr can improve strength, but it significantly lowers the β-phase transformation point, narrowing the traditional β-forging window and making the β-grains highly susceptible to abnormal growth due to temperature fluctuations, thus degrading toughness. Furthermore, while β-forging alone can achieve high strength, it easily leads to coarse grains. Simple two-phase processing, while providing good plasticity, offers limited strength improvement. Heat treatment processes suffer from inefficiency, making it difficult to synergistically control the microstructure at both the micron and nanoscale. For example, refractory elements like Nb and Mo diffuse slowly, and conventional high-temperature single-stage large deformation processes cannot effectively break up the as-cast grain boundaries, leading to elemental segregation inherited into the final product and causing performance instability. Single solution aging treatments are insufficient to achieve stable precipitation and uniform distribution of the secondary α-phase, resulting in unstable strengthening effects and difficulty in achieving synergistic optimization of strength and toughness.

[0003] To address the aforementioned problems, this invention proposes a method for preparing ultra-high strength and high toughness titanium alloys through the synergistic effects of alloy composition atomic ratio, multi-stage upsetting and drawing forging, gradient temperature-controlled forging and rolling, and heat treatment. By synergistically combining atomic ratio-constrained composition design, gradient temperature-controlled forging and rolling, and segmented aging processes, a fracture toughness (KIC) ≥ 65 MPa·m is further achieved, in addition to achieving a tensile strength ≥ 1500 MPa and an elongation ≥ 8% for the titanium alloy. 1 / 2 The preparation of ultra-high strength and high toughness titanium alloys has achieved uniform microstructure and grain refinement of high alloy titanium alloys without sacrificing strength. Summary of the Invention

[0004] To address the shortcomings of related technologies, this invention provides an ultra-high strength and high toughness titanium alloy and its preparation method, which can achieve stable preparation of ultra-high strength and high toughness titanium alloys and solve the problem of balancing strength and toughness in titanium alloys.

[0005] One objective of this invention is to provide an ultra-high strength and high toughness titanium alloy, wherein the composition of the ultra-high strength and high toughness titanium alloy, by mass percentage, comprises: 4.8~5.4% Al, 7.8~8.3% Mo, 2.8~3.4% Cr, 1.8~2.5% Nb, with the balance being Ti and unavoidable impurities, and the atomic ratio of the components is as follows: (Al+Cr) / Mo = 2.7~3.0; (Nb+Mo) / Ti=0.05~0.07.

[0006] Another objective of this invention is to provide a method for preparing ultra-high strength and high toughness titanium alloys, specifically including the following steps: (1) Raw material smelting: Weigh sponge titanium, pure Al particles, pure Cr particles, Ti-32Mo master alloy and Ti-45Nb master alloy raw materials according to the proportion, mix the raw materials and press them into electrodes, and smelt the electrodes to obtain ingots.

[0007] (2) Multi-stage upsetting and drawing forging: The ingot is heated and kept warm, and then upsetting and drawing deformation are carried out to obtain the forging blank after multi-stage upsetting and drawing forging.

[0008] (3) Gradient temperature controlled forging and rolling: The forging billet after multi-stage upsetting and drawing is subjected to three-stage elongation treatment to obtain forging bar. The forging bar is heated and kept at a constant temperature, and then rolled to obtain rolled bar.

[0009] (4) Heat treatment: The rolled bar is subjected to solution treatment and aging treatment in sequence to obtain ultra-high strength and high toughness titanium alloy.

[0010] More preferably, the electrode melting method in step (1) is vacuum self-consumable melting.

[0011] More preferably, the conditions for pressing the raw materials into electrodes in step (1) are as follows: bidirectional cold pressing at 300~350MPa and holding for 15~30s, followed by plasma welding in an inert atmosphere (such as argon atmosphere) to obtain the electrodes; the conditions for electrode melting are as follows: under a vacuum of 10 -2 ~10 -3 Melting is carried out at an arc temperature of 1700~2000℃ under Pa, followed by cooling, and the melting process is repeated three times.

[0012] Preferably, the conditions for heating and holding the ingot in step (2) are: heating the ingot to 1090~1110℃ at a heating rate of 8~10℃ / min and holding it for 2h.

[0013] Preferably, step (2), the upsetting deformation and elongation deformation treatment, is repeated twice; the total deformation amount of the upsetting deformation is 40~50%; the total deformation amount of the elongation deformation is 50~60%; and the strain rate of each deformation treatment is 0.01~0.1s. -1 .

[0014] More preferably, in step (2), after each upsetting and drawing deformation treatment, when the surface temperature of the forging billet is 600~700℃, it is kept in the furnace for 30~90 minutes.

[0015] Preferably, the three-stage elongation treatment in step (3) is as follows: First stage: first, keep warm at 870~910℃ for 30~60min, and then perform an elongation treatment with a deformation of 10~15%; Second stage: first, keep warm at 820~840℃ for 30~60min, and then perform an elongation treatment with a deformation of 10~15%; Third stage: first, keep warm at 780~800℃ for 30~60min, and then perform an elongation treatment with a deformation of 20~30%.

[0016] More preferably, the elongation treatment temperature in the third stage of step (3) is ≥760℃.

[0017] Preferably, the conditions for heating and holding the forging rod in step (3) are: holding at 790~810℃ for 20~40min.

[0018] Preferably, the conditions for rolling deformation in step (3) are: the deformation amount of a single rolling is 15~20%, and the total rolling deformation is 35~60%.

[0019] More preferably, the temperature of the rolls used for rolling deformation in step (3) is 150~200℃.

[0020] Preferably, the solution treatment conditions in step (4) are: solution treatment at 800~850℃ for 30~45 minutes, followed by cooling (e.g., air cooling).

[0021] Preferably, the conditions for the aging treatment in step (4) are as follows: the temperature is raised in stages, first at a rate of 5~10℃ / min to 325~535℃ and held for 0.5~1h, then raised to 475~635℃ and held for 6~8h, and then cooled (e.g., air cooling).

[0022] More preferably, the aging treatment in step (4) is performed under the following conditions: segmented heating is adopted, first heating at a heating rate of 5℃ / min to 420~500℃ and holding for 1h, then heating at a heating rate of 10℃ / min to 495~620℃ and holding for 6h, and then cooling (such as air cooling).

[0023] The upsetting and drawing deformation processes of this invention can achieve uniform deformation of the internal structure of the forging billet and avoid cracking.

[0024] The segmented heating method of this invention for aging treatment improves the uniformity of aging.

[0025] The alloy composition and preparation process of this invention have a synergistic effect. The atomic ratio of the components in this invention enables the alloy to have a suitable phase transformation temperature and β-phase stability during subsequent hot working and heat treatment. Combined with multi-stage upsetting and drawing forging, uniform deformation of the internal structure of the forging billet can be achieved, avoiding uneven deformation and insufficient grain fragmentation caused by unidirectional forging. On this basis, gradient temperature-controlled forging and rolling achieve cooling and elongation. Combined with the deformation amount, the grains are gradually refined in different temperature ranges, which can effectively suppress β-grain coarsening and promote the dispersed precipitation of primary α-phase. Finally, the segmented aging process allows the alloy elements to be pre-homogenized at a lower temperature, and then promotes the uniform and dispersed precipitation of nanoscale secondary α-phase at a higher temperature. Through the coordinated processes of composition, deformation, and heat treatment, a dual-phase microstructure comprising micron-scale primary α phase and nano-scale secondary α phase is ultimately obtained. The two α phases at different scales synergistically exert strengthening and toughening effects, thereby enabling the titanium alloy to simultaneously possess tensile strength >1500 MPa, yield strength >1450 MPa, elongation >8%, and fracture toughness KIC ≥65 MPa·m. 1 / 2 Its comprehensive mechanical properties.

[0026] Mechanism of the invention: The synergistic effect of the alloy composition atomic ratio, multi-stage upsetting and forging, gradient temperature-controlled forging and rolling, and heat treatment (solution and aging) in this invention enhances the strength and toughness of the titanium alloy. This invention achieves a balance between the stability of the β phase and the volume fraction of the α phase through the synergistic effect of the alloy composition and preparation process, preventing the precipitation of brittle phases (such as Ti3Al), strengthening the α phase, and inhibiting β grain growth. Furthermore, the excellent solid solution strengthening effect of the β matrix avoids the deterioration of the alloy material's toughness, and this invention achieves significant refinement of the β grains, inhibiting the formation of the brittle ω phase. Due to the synergistic effect of the alloy composition atomic ratio, multi-stage upsetting and forging, gradient temperature-controlled forging and rolling, and heat treatment processes, the titanium alloy product contains micron-sized primary α phase and nano-sized secondary α phase, which synergistically strengthen the titanium alloy, resulting in ultra-high strength and excellent toughness. The synergistic effect between the preparation processes in this invention refines the grains of the prepared titanium alloy, resulting in uniform internal microstructure deformation. The solution treatment of this invention facilitates the full dissolution of alloying elements in the β phase, forming a uniform solid solution, which provides a good microstructure basis for subsequent aging treatment. The aging treatment causes fine and dispersed strengthening phases to precipitate in the supersaturated solid solution after solution treatment, promoting the dispersed distribution of nanoscale secondary α phases and improving the strength and hardness of the alloy. In addition, the aging treatment of this invention achieves a uniform distribution of alloying elements at a lower temperature, reducing the nucleation barrier during subsequent high-temperature aging, which is conducive to the uniform precipitation of fine and dispersed secondary α precipitates and improves the uniformity of the aging effect.

[0027] The beneficial effects of this invention are: (1) The titanium alloy prepared by the present invention forms a uniform dual-state structure due to the combined effect of dynamic recrystallization and strain-induced refinement, which includes: primary α phase (volume fraction 10~20%, average size ≤5μm); β transformation structure (nanoscale secondary α precipitates dispersed in the β matrix, size 50~200nm); the synergistic strengthening of the micron-scale primary α phase and the nanoscale secondary α phase of the present invention provides a basis for improving the strength and toughness of the titanium alloy.

[0028] (2) The ultra-high strength and high toughness titanium alloy prepared by this invention has a tensile strength >1500MPa, a yield strength >1450MPa, an elongation >8%, and a three-point bending fracture toughness greater than 65MPa·m. 1 / 2 It has broad application prospects.

[0029] (3) Through the synergistic effect of alloy composition, atomic ratio and preparation process, the present invention has successfully prepared a titanium alloy with ultra-high strength and high toughness, breaking the limitations of traditional titanium alloys in terms of strength and toughness balance.

[0030] (4) The preparation and heat treatment methods of the present invention have good repeatability and stability, and can be industrialized, providing a process basis for the widespread application of high-performance titanium alloys. Attached Figure Description

[0031] Figure 1 The images show the tensile stress-strain curves of titanium alloys prepared in Examples 1-3 and Comparative Examples 1-2 of this invention.

[0032] Figure 2 This is a SEM image of the ultra-high strength and high toughness titanium alloy prepared in Example 1 of the present invention.

[0033] Figure 3 This is a SEM image of the ultra-high strength and high toughness titanium alloy prepared in Example 2 of the present invention.

[0034] Figure 4 This is a SEM image of the ultra-high strength and high toughness titanium alloy prepared in Comparative Example 1 of this invention.

[0035] Figure 5 This is a SEM image of the ultra-high strength and high toughness titanium alloy prepared in Comparative Example 2 of this invention. Detailed Implementation

[0036] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. In the embodiments and comparative examples of this invention, unless otherwise specified, all chemical reagents used were commercially available analytical grade reagents. The plasma welding splicing in the embodiments and comparative examples of this invention is a conventional operation in the art, and its purpose is to achieve the welding of high-density electrode blocks.

[0037] Example 1 A method for preparing an ultra-high strength and high toughness titanium alloy specifically includes the following steps: (1) Raw material smelting: Sponge titanium, pure Al particles, pure Cr particles, Ti-32Mo master alloy and Ti-45Nb master alloy raw materials were weighed according to the proportion. The components included by mass percentage: 4.8% Al, 7.8% Mo, 2.8% Cr, 1.8% Nb, with the balance being Ti and unavoidable impurities. The atomic ratio of the components was (Al+Cr) / Mo=2.85, (Nb+Mo) / Ti=0.058. After mixing the raw materials, a high-density electrode block was obtained by bidirectional cold pressing at 300MPa for 30s. The high-density electrode block was then plasma welded and spliced ​​under an argon atmosphere to obtain the electrode. The electrode was then sent into a vacuum arc furnace, and the furnace body was pre-evacuated to 10 - 2 Pa is smelted at an arc temperature of 1800℃. After uniform smelting, it is slowly cooled in the furnace to 200℃ and then removed from the furnace. The smelting process is repeated three times to obtain an ingot.

[0038] (2) Multi-stage upsetting and drawing forging: The ingot is heated to 1090℃ at a heating rate of 8℃ / min and held for 2h. Then, upsetting and drawing deformation are performed. The upsetting and drawing deformation are repeated twice. The total deformation of upsetting is 40% and the total deformation of drawing is 50%. After each upsetting and drawing deformation, when the surface temperature of the forging billet is 600℃, it is returned to the furnace and held for 30min. The strain rate of each deformation is 0.01s. -1 The forged billet is obtained after multi-stage upsetting and drawing forging.

[0039] (3) Gradient temperature controlled forging and rolling: The forging billet after multi-stage upsetting and drawing is subjected to three-stage elongation treatment at 870℃ (holding temperature for 30 min, deformation amount of 10%), 830℃ (holding temperature for 30 min, deformation amount of 10%), and 800℃ (holding temperature for 30 min, deformation amount of 20%). The temperature of the third stage elongation treatment is 800℃ to obtain a forging bar. The forging bar is held at 800℃ for 30 min and then rolled. The deformation amount of a single rolling is 15%, the total deformation amount of rolling is 60%, the roll temperature is 150℃, and the rolling pressure is 50kN to obtain a rolled bar with a diameter of 20mm.

[0040] (4) Heat treatment: The rolled bar is solution treated at 800℃ for 30 min, then air-cooled to room temperature, then heated to 420℃ at a heating rate of 5℃ / min and held for 1 h, then heated to 495℃ at a heating rate of 10℃ / min and held for 6 h, and finally air-cooled to room temperature to obtain ultra-high strength and high toughness titanium alloy.

[0041] The prepared alloy was subjected to microstructure observation and property testing, such as... Figure 1 and Figure 2 As shown, the microstructure is a two-phase structure, with the primary α phase having a volume fraction of 11% and an average size of 2 μm; the secondary α precipitates in the β-transformation microstructure have a size of 50 nm. The alloy has a tensile strength of 1541 MPa, a yield strength of 1485 MPa, and an elongation of 8.1% (This invention). Figure 1 The performance corresponds to the performance in the embodiments and comparative examples. This performance test uses the average value of three tensile specimens from the same sample, and the plots are drawn. Figure 1 The performance graph was plotted by selecting one of the three sample curves. The three-point bending fracture toughness was 66 MPa·m. 1 / 2 .

[0042] Example 2 A method for preparing an ultra-high strength and high toughness titanium alloy specifically includes the following steps: (1) Raw material smelting: Weigh sponge titanium, pure Al particles, pure Cr particles, Ti-32Mo master alloy and Ti-45Nb master alloy raw materials according to the proportion. Each component includes, by mass percentage: 5.0% Al, 8.0% Mo, 3.0% Cr, 2.3% Nb, with the balance being Ti and unavoidable impurities. The atomic ratio of the components is: (Al+Cr) / Mo=2.91, (Nb+Mo) / Ti=0.063. After mixing the raw materials, use a bidirectional cold pressing at 320MPa for 25s to obtain a high-density electrode block. The high-density electrode block is then plasma welded and spliced ​​under an argon atmosphere to obtain the electrode. The electrode is then sent into a vacuum consumable arc furnace, and the furnace body is pre-evacuated to 10. -3 Pa is smelted at an arc temperature of 1900℃. After uniform smelting, it is slowly cooled in the furnace to 200℃ and then removed from the furnace. The smelting process is repeated three times to obtain the ingot.

[0043] (2) Multi-stage upsetting and drawing forging: The ingot is heated to 1100℃ at a heating rate of 10℃ / min and held for 2 hours. Then, upsetting and drawing deformation are performed. The upsetting and drawing deformation are repeated twice. The total deformation of upsetting is 45% and the total deformation of drawing deformation is 55%. After each upsetting and drawing deformation, when the surface temperature of the forging billet is 650℃, it is returned to the furnace and held for 60 minutes. The strain rate of each deformation is 0.05s. -1 The forged billet is obtained after multi-stage upsetting and drawing forging.

[0044] (3) Gradient temperature controlled forging and rolling: The forging billet after multi-stage upsetting and drawing is subjected to three-stage elongation treatment at 880℃ (holding temperature for 45 min, deformation amount 12%), 840℃ (holding temperature for 45 min, deformation amount 12%), and 790℃ (holding temperature for 45 min, deformation amount 25%). The temperature of the third stage elongation treatment is 790℃ to obtain a forging bar. The forging bar is held at 810℃ for 20 min and then rolled. The deformation amount of a single rolling is 17%, the total rolling deformation is 50%, the roll temperature is 175℃, and the rolling pressure is 50kN to obtain a rolled bar with a diameter of 20mm.

[0045] (4) Heat treatment: The rolled bar was solution treated at 815℃ for 38 min, then air-cooled to room temperature, then heated to 470℃ at a heating rate of 5℃ / min and held for 1 h, then heated to 580℃ at a heating rate of 10℃ / min and held for 6 h, and finally air-cooled to room temperature to obtain ultra-high strength and high toughness titanium alloy.

[0046] The microstructure and properties of the prepared alloy were observed and tested. Figure 3The SEM microstructure of Example 2 is presented. The microstructure exhibits a two-phase structure, with abundant acicular α phase and a small amount of equiaxed α phase precipitated within the β grains. Most of the acicular α phases interweave, forming a basket-like pattern. The primary α phase has a volume fraction of 12% and an average size of 2.5 μm; the secondary α precipitates in the β-transformation microstructure have a size of 120 nm. The alloy exhibits a tensile strength of 1530 MPa, a yield strength of 1470 MPa, an elongation of 8.5%, and a three-point bending fracture toughness of 68 MPa·m. 1 / 2 .

[0047] Example 3 A method for preparing an ultra-high strength and high toughness titanium alloy specifically includes the following steps: (1) Raw material smelting: Sponge titanium, pure Al particles, pure Cr particles, Ti-32Mo master alloy and Ti-45Nb master alloy raw materials were weighed according to the proportion. The components included by mass percentage: 5.2% Al, 8.2% Mo, 3.2% Cr, 2.2% Nb, with the balance being Ti and unavoidable impurities. The atomic ratio of the components was (Al+Cr) / Mo=2.98, (Nb+Mo) / Ti=0.064. After mixing the raw materials, a high-density electrode block was obtained by bidirectional cold pressing at 340MPa for 15s. The high-density electrode block was then plasma welded and spliced ​​under an argon atmosphere to obtain the electrode. The electrode was then sent into a vacuum arc furnace, and the furnace body was pre-evacuated to 10 -3 Pa is smelted at an arc temperature of 2000℃. After uniform smelting, it is slowly cooled in the furnace to 200℃ and then removed from the furnace. The smelting process is repeated three times to obtain an ingot.

[0048] (2) Multi-stage upsetting and drawing forging: The ingot is heated to 1110℃ at a heating rate of 9℃ / min and held for 2h. Then, upsetting and drawing deformation are performed. The upsetting and drawing deformation are repeated twice. The total deformation of upsetting is 50% and the total deformation of drawing is 60%. After each upsetting and drawing deformation, when the surface temperature of the forging billet is 700℃, it is returned to the furnace and held for 90min. The strain rate of each deformation is 0.1s. -1 The forged billet is obtained after multi-stage upsetting and drawing forging.

[0049] (3) Gradient temperature controlled forging and rolling: The forging billet after multi-stage upsetting and drawing is subjected to three-stage elongation treatment at 910℃ (holding temperature for 60 min, deformation amount 15%), 820℃ (holding temperature for 60 min, deformation amount 15%), and 780℃ (holding temperature for 60 min, deformation amount 30%). The elongation treatment temperature of the third stage is 780℃ to obtain a forging bar. The forging bar is held at 790℃ for 40 min and then rolled. The deformation amount of a single rolling is 20%, the total rolling deformation amount is 40%, the roll temperature is 200℃, and the rolling pressure is 50kN to obtain a rolled bar with a diameter of 20mm.

[0050] (4) Heat treatment: The rolled bar is solution treated at 830℃ for 45 min, and then air-cooled to room temperature; then the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h, then the temperature is increased to 620℃ at a rate of 10℃ / min and held for 6 h, and finally air-cooled to room temperature to obtain ultra-high strength and high toughness titanium alloy.

[0051] The prepared alloy was subjected to microstructure observation and property testing. The microstructure was a two-phase structure, with a primary α phase volume fraction of 13% and an average size of 3 μm; the secondary α precipitate in the β-transformation microstructure had a size of 200 nm. The alloy exhibited a tensile strength of 1520 MPa, a yield strength of 1450 MPa, an elongation of 8.8%, and a three-point bending fracture toughness of 70 MPa·m. 1 / 2 .

[0052] The present invention discloses a method for preparing and heat-treating ultra-high strength and high toughness titanium alloys. Through the synergistic effect of raw material selection, smelting process, hot working process, and heat treatment, a titanium alloy material with excellent comprehensive properties is prepared with high stability. Its strength and toughness indicators meet or even exceed the standards of similar products in the industry, satisfying the stringent requirements of aerospace and high-end equipment manufacturing fields for high-performance titanium alloy materials, and has broad application prospects.

[0053] Comparative Example 1 A method for preparing a titanium alloy specifically includes the following steps: (1) Raw material smelting: Sponge titanium, pure Al particles, pure Cr particles, Ti-32Mo master alloy and Ti-45Nb master alloy raw materials were weighed according to the proportion. The components included by mass percentage: 4.8% Al, 7.8% Mo, 2.8% Cr, 1.8% Nb, with the balance being Ti and unavoidable impurities. The atomic ratio of the components was (Al+Cr) / Mo=2.85, (Nb+Mo) / Ti=0.058. After mixing the raw materials, a high-density electrode block was obtained by bidirectional cold pressing at 300MPa for 30s. The high-density electrode block was then plasma welded and spliced ​​under an argon atmosphere to obtain the electrode. The electrode was then sent into a vacuum arc furnace, and the furnace body was pre-evacuated to 10 -2Pa is smelted at an arc temperature of 1800℃. After uniform smelting, it is slowly cooled in the furnace to 200℃ and then removed from the furnace. The smelting process is repeated three times to obtain an ingot.

[0054] (2) Forging: The ingot is heated to 1090℃ at a heating rate of 8℃ / min and held for 2h. Then, unidirectional elongation forging is carried out with a deformation of 50% and a strain rate of 0.01s during the elongation process. -1 The forged billet is obtained after forging.

[0055] (3) Gradient temperature control forging and rolling: The forged billet after forging is subjected to three stages of elongation treatment in sequence at 870℃ (holding temperature for 30 min, deformation amount of 10%), 830℃ (holding temperature for 30 min, deformation amount of 10%), and 800℃ (holding temperature for 30 min, deformation amount of 20%). The elongation treatment temperature of the third stage is 800℃ to obtain a forged bar. The forged bar is held at 800℃ for 30 min and then rolled. The deformation amount of a single rolling is 15%, the total deformation amount of rolling is 60%, the roll temperature is 150℃, and the rolling pressure is 50kN to obtain a rolled bar with a diameter of 20mm.

[0056] (4) Heat treatment: The rolled bar is solution treated at 800℃ for 30 min, then air-cooled to room temperature, then heated to 420℃ at a heating rate of 5℃ / min and held for 1 h, then heated to 495℃ at a heating rate of 10℃ / min and held for 6 h, and finally air-cooled to room temperature to obtain titanium alloy.

[0057] The prepared alloy was subjected to microstructure observation and property testing, such as... Figure 1 and Figure 4 As shown, the microstructure is a two-phase structure, with a primary α phase volume fraction of 9% and an average size of 3 μm; the secondary α precipitate in the β-transformation microstructure has a size of 47 nm. The alloy has a tensile strength of 1328 MPa, a yield strength of 1291 MPa, an elongation of 4.7%, and a three-point bending fracture toughness of 42 MPa·m. 1 / 2 .

[0058] The mechanical properties of Comparative Example 1 are lower than those of Example 1. The main reasons are: conventional forging only involves unidirectional elongation, the deformation direction is singular, the coarse grains in the cast state are not sufficiently broken, and the grain size is significantly larger than that of Example 1; conventional forging has insufficient deformation and uneven deformation, and the deformation degree of the core and surface of the forging billet is very different, resulting in uneven microstructure and thus unstable performance.

[0059] Comparative Example 2 A method for preparing a titanium alloy specifically includes the following steps: (1) Raw material smelting: Sponge titanium, pure Al particles, pure Cr particles, Ti-32Mo master alloy and Ti-45Nb master alloy raw materials were weighed according to the proportion. The components included by mass percentage: 4.8% Al, 7.8% Mo, 2.8% Cr, 1.8% Nb, with the balance being Ti and unavoidable impurities. The atomic ratio of the components was (Al+Cr) / Mo=2.85, (Nb+Mo) / Ti=0.058. After mixing the raw materials, a high-density electrode block was obtained by bidirectional cold pressing at 300MPa for 30s. The high-density electrode block was then plasma welded and spliced ​​under an argon atmosphere to obtain the electrode. The electrode was then sent into a vacuum arc furnace, and the furnace body was pre-evacuated to 10 -2 Pa is smelted at an arc temperature of 1800℃. After uniform smelting, it is slowly cooled in the furnace to 200℃ and then removed from the furnace. The smelting process is repeated three times to obtain an ingot.

[0060] (2) Multi-stage upsetting and drawing forging: The ingot is heated to 1090℃ at a heating rate of 8℃ / min and held for 2h. Then, upsetting and drawing deformation are performed. The upsetting and drawing deformation are repeated twice. The total deformation of upsetting is 40% and the total deformation of drawing is 50%. After each upsetting and drawing deformation, when the surface temperature of the forging billet is 600℃, it is returned to the furnace and held for 30min. The strain rate of each deformation is 0.01s. -1 The forged billet is obtained after multi-stage upsetting and drawing forging.

[0061] (3) Forging and rolling: The forging billet after multi-stage upsetting and drawing is heated at 870℃ (30 min, deformation amount 40%) to obtain a forging bar. The forging bar is heated at 800℃ for 30 min, and then rolled and deformed. The deformation amount of a single rolling is 15%, the total rolling deformation is 60%, the roll temperature is 150℃, the rolling pressure is 50kN, and a rolled bar with a diameter of 20mm is obtained.

[0062] (4) Heat treatment: The rolled bar is solution treated at 800℃ for 30 min, then air-cooled to room temperature, then heated to 420℃ at a heating rate of 5℃ / min and held for 1 h, then heated to 495℃ at a heating rate of 10℃ / min and held for 6 h, and finally air-cooled to room temperature to obtain titanium alloy.

[0063] The prepared alloy was subjected to microstructure observation and property testing, such as... Figure 1 and Figure 5 As shown, the microstructure is a two-phase structure, with a primary α phase volume fraction of 8.8% and an average size of 3 μm; the secondary α precipitate in the β-transformation microstructure has a size of 48 nm. The alloy has a tensile strength of 1317 MPa, a yield strength of 1285 MPa, an elongation of 5.4%, and a three-point bending fracture toughness of 40 MPa·m.1 / 2 .

[0064] The mechanical properties of Comparative Example 2 are significantly lower than those of Example 1. The main reason is that conventional forging and rolling concentrates all elongation deformation (40%) at 870°C in one go. Although the rolling temperature is subsequently reduced to 800°C, the total deformation time in the early high-temperature stage is significantly prolonged. The long duration of high temperature (870°C) causes coarsening of β grains, and the grain size is significantly larger than that of Example 1. Conventional forging and rolling only deforms at two temperatures: 870°C and 800°C. The deformation at 870°C is too large (40%). At this temperature, a large amount of β-stabilizing elements dissolve in the β matrix, inhibiting the precipitation of the primary α phase. This results in a lower volume fraction and larger size of the final primary α phase, thereby reducing the plasticity and toughness of the alloy.

[0065] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A high-strength, high-toughness titanium alloy, characterized in that, The ultra-high strength and high toughness titanium alloy comprises, by mass percentage: 4.8–5.4% Al, 7.8–8.3% Mo, 2.8–3.4% Cr, 1.8–2.5% Nb, with the balance being Ti and unavoidable impurities, and the atomic ratios of the components are as follows: (Al+Cr) / Mo = 2.7~3.0; (Nb+Mo) / Ti=0.05~0.

07.

2. The method for preparing the ultra-high strength and high toughness titanium alloy according to claim 1, characterized in that, Specifically, the following steps are included: (1) Raw material smelting: Weigh sponge titanium, pure Al particles, pure Cr particles, Ti-32Mo master alloy and Ti-45Nb master alloy raw materials according to the proportion, mix the raw materials and press them into electrodes, and smelt the electrodes to obtain ingots; (2) Multi-stage upsetting and drawing forging: The ingot is heated and kept warm, and then upsetting and drawing deformation are carried out to obtain the forging billet after multi-stage upsetting and drawing forging. (3) Gradient temperature controlled forging and rolling: The forging billet after multi-stage upsetting and drawing is subjected to three-stage elongation treatment to obtain forging bar. The forging bar is heated and kept at a certain temperature, and then rolled to obtain rolled bar. (4) Heat treatment: The rolled bar is subjected to solution treatment and aging treatment in sequence to obtain ultra-high strength and high toughness titanium alloy.

3. The method for preparing the ultra-high strength and high toughness titanium alloy according to claim 2, characterized in that, The conditions for heating and holding the ingot in step (2) are as follows: the ingot is heated to 1090~1110℃ at a heating rate of 8~10℃ / min and held for 2h.

4. The method for preparing the ultra-high strength and high toughness titanium alloy according to claim 2, characterized in that, Step (2), the upsetting deformation and elongation deformation treatment, are repeated twice; the total deformation of the upsetting deformation is 40~50%; the total deformation of the elongation deformation is 50~60%; the strain rate of each deformation treatment is 0.01~0.1s. -1 .

5. The method for preparing the ultra-high strength and high toughness titanium alloy according to claim 2, characterized in that, The three-stage elongation treatment in step (3) is as follows: First stage: first, keep warm at 870~910℃ for 30~60min, and then perform an elongation treatment with a deformation of 10~15%; The second stage: First, keep it at 820~840℃ for 30~60 minutes, and then perform a stretching treatment with a deformation amount of 10~15%. The third stage: First, keep it at 780~800℃ for 30~60 minutes, and then perform a stretching treatment with a deformation amount of 20~30%.

6. The method for preparing the ultra-high strength and high toughness titanium alloy according to claim 2, characterized in that, The conditions for heating and holding the forging rod in step (3) are: holding at 790~810℃ for 20~40min.

7. The method for preparing the ultra-high strength and high toughness titanium alloy according to claim 2, characterized in that, The conditions for rolling deformation in step (3) are: the deformation amount of a single rolling is 15~20%, and the total deformation amount of rolling is 35~60%.

8. The method for preparing the ultra-high strength and high toughness titanium alloy according to claim 2, characterized in that, The conditions for the solution treatment in step (4) are: solution treatment at 800~850℃ for 30~45 minutes, followed by cooling.

9. The method for preparing the ultra-high strength and high toughness titanium alloy according to claim 2, characterized in that, The conditions for the aging treatment in step (4) are as follows: the temperature is raised in stages, first at a rate of 5~10℃ / min to 325~535℃ and held for 0.5~1h, then raised to 475~635℃ and held for 6~8h, and then cooled.

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