Ultrahigh-strength alpha + beta titanium alloy suitable for being used at 600 DEG C and preparation method of ultrahigh-strength alpha + beta titanium alloy

Abstract

The invention discloses an ultrahigh-strength alpha + beta titanium alloy suitable for 600 DEG C and a preparation method thereof, and belongs to the technical field of titanium alloys, the titanium alloy comprises the following alloy components in percentage by weight: 5.5-7.0% of Al, 11.0-14.0% of Zr, 1.0-2.5% of Mo, 1.0-2.5% of Nb, 2.5-4.0% of Ta, 2.5-4.0% of W, 0.05-0.2% of Si and the balance of Ti and other inevitable impurities, and the following synergistic change relationship is met: Ti + 0.9 Zr is greater than or equal to 86.6 wt% and less than or equal to 92.8 wt%, Al + Si is greater than or equal to 5.7 wt% and less than or equal to 7.0 wt%, Mo + Nb + 0.6 Ta + 0.6 W is greater than or equal to 5.7 wt% and less than or equal to 8.6 wt%, the novel titanium alloy is designed through multi-element alloying on the basis of a solid solution cluster and connecting atom model, low-diffusion elements Mo, Nb, Ta and W are added into the alloy to achieve fine secondary alpha-phase precipitation, and the high-temperature stability of the alloy is improved; meanwhile, the high-content Zr element and the trace Si element are added, and synergistic enhancement of solid solution strengthening and precipitation strengthening is achieved. The titanium alloy prepared by the method shows an excellent strength and plasticity synergistic effect, has excellent comprehensive mechanical properties and hot working formability, and can be used as an alternative material for medium-high temperature structural components.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloys, and relates to an ultra-high strength α + β titanium alloy applicable to 600 °C and a preparation method thereof. Background Art

[0002] At present, α + β type titanium alloys have high strength and low density, stable high-temperature performance, good creep resistance and oxidation resistance, and can meet the various requirements of aerospace vehicles in harsh environments. They are mainly used in medium and high-temperature structural components such as aero-engine turbine blades and compressors, and are one of the key materials in this field. As early as 1954, the United States successfully developed the first aviation dual-phase high-temperature Ti-6Al-4V. Its dual-phase microstructure is formed by the synergistic effect of Al (α-phase stabilizing element) and V (β-phase stabilizing element), combining the high-temperature stability of the α-phase and the excellent processing performance of the β-phase, enabling its tensile strength to reach 800 - 1000 MPa and the elongation rate to exceed 10%, and it can serve for a long time at a temperature of 350 - 400 °C. However, with the rapid development of the aerospace industry, the room-temperature performance and service temperature of the current α + β titanium alloys can no longer meet the working conditions requirements of aero-engines.

[0003] In Chinese invention patent CN102978440A, Northwest Institute for Nonferrous Metal Research proposed a short-time high-temperature high-strength titanium alloy with excellent high-temperature strength and hot processability. This alloy is a Ti-Al-Sn-Zr-W-Mo-Cr-C system α + β two-phase titanium alloy. After heat treatment, the tensile strength of the alloy reaches 900 MPa at 500 °C and 810 MPa at 600 °C, having higher strength than existing commercial high-temperature titanium alloys in the high-temperature range and meeting the performance requirements of short-time high-temperature applications for titanium alloys; however, there are relatively coarse secondary α-phases in the alloy structure, resulting in its room-temperature tensile strength not exceeding 1300 MPa and the room-temperature yield strength not exceeding 1200 MPa.

[0004] In Chinese invention patent CN107043870B, Guangdong Institute of Materials and Processing proposed a high-Si-content high-temperature titanium alloy. This alloy system is Ti-Al-Si-Zr-Mo-Sn, and the composition design aims to improve the high-temperature strength and creep performance of the alloy by adding a high content of Si (1.0 - 1.5%); after heat treatment, the room-temperature tensile strength of this alloy can reach 1300 MPa and the elongation rate reaches 7%, with excellent room-temperature performance, but at 600 °C, its tensile strength does not exceed 800 MPa.

[0005] In summary, there is an urgent need for a titanium alloy material with ultra-high room-temperature strength and applicable to 600 °C. Summary of the Invention

[0006] The present invention provides a super-high-strength α+β titanium alloy applicable to 600°C and a preparation method thereof, aiming to solve the technical problems of insufficient room-temperature performance and low service temperature of existing α+β titanium alloys. Alloying is an effective means to improve the room-temperature strength and temperature-bearing capacity of alloys. Precise alloy composition design requires finding the structural units that carry alloy components. The α+β titanium alloy contains two solid-solution phases, α and β, and the solid-solution phases are characterized by chemical short-range order. The present invention introduces the cluster-plus-connected-atom model that describes the chemical short-range order of the solid solution. Based on this model, the widely used α+β titanium alloy composition formula Ti-6Al-4V can be expressed as 12[Al-Ti 12 (AlTi2)+5[Al-Ti 14 (V2Ti). Based on this composition formula, the stability of the α and β phases is enhanced through multi-element alloying. After the alloy designed by the present invention is solution-treated and aged, the room-temperature tensile strength is ≥1450 MPa, the room-temperature yield strength is ≥1400 MPa, the room-temperature elongation is ≥7.5%, and the tensile strength at 600°C is ≥800 MPa, showing a certain strength-ductility match.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A super-high-strength α+β titanium alloy applicable to 600°C, the super-high-strength α+β titanium alloy includes elements Ti, Al, Zr, Mo, Nb, Ta, W and Si, and the mass percentages (wt.%) of its alloy components are as follows:

[0009] Al: 5.5 - 7.0, Zr: 11.0 - 14.0, Mo: 1.0 - 2.5, Nb: 1.0 - 2.5, Ta: 2.5 - 4.0, W: 2.5 - 4.0, Si: 0.05 - 0.2, and the balance is Ti element and other inevitable impurities; and the alloy elements satisfy the following co-variation relationship: 86.6 wt.% ≤ Ti + 0.9Zr ≤ 92.8 wt.%, 5.7 wt.% ≤ Al + Si ≤ 7.0 wt.%, 5.7 wt.% ≤ Mo + Nb + 0.6Ta + 0.6W ≤ 8.6 wt.%, where Ti, Al, and Mo are the main elements.

[0010] The composition of the super-high-strength α+β titanium alloy is high-content zirconium element and trace silicon element, which constitutes the core element difference from existing α+β titanium alloys, and the given composition co-variation relationship can more precisely guide the actual alloy production.

[0011] The ultra-high strength α+β titanium alloy applicable to 600 °C has a specific microstructure: it is a lamellar structure when solution-treated above the phase transformation point, and an equiaxed structure and a duplex structure when solution-treated below the phase transformation point. Among them, for the lamellar structure, the α phase has a width of 67 - 211 nm. For the equiaxed structure and the duplex structure, they are composed of primary α phase and β transformation structure. Among them, the volume fraction of the primary α phase is 20 - 50%, and there are finer secondary α phases with a width of 30 - 125 nm in the β transformation structure. At the same time, Ti3Al phases are uniformly precipitated inside the primary α phase with a size of 2 - 3 nm. (Ti,Zr)5Si3 type silicides are precipitated at grain boundaries and within grains in all three types of microstructures (lamellar structure, equiaxed structure, duplex structure), presenting a round or oval shape with a size of 200 - 250 nm, and no harmful phases are generated in the microstructure.

[0012] The ultra-high strength α+β titanium alloy applicable to 600 °C has good room-temperature strength and plasticity and high-temperature properties. The typical properties of the alloy are: room-temperature tensile strength ≥ 1450 MPa, room-temperature yield strength ≥ 1400 MPa, room-temperature elongation ≥ 7.5%, and 600 °C tensile strength ≥ 800 MPa.

[0013] A preparation method of an ultra-high strength α+β titanium alloy applicable to 600 °C includes the following steps:

[0014] First, according to the mass percentages of the alloy component elements, high-purity alloy materials are weighed, and the accurately weighed metal ingredients are placed in a vacuum arc melting furnace and added separately according to the melting points of the elements. The elements with lower melting points, such as titanium, aluminum, and zirconium, are placed at the bottom, and the elements with higher melting points, such as molybdenum, niobium, tantalum, tungsten, and silicon, are placed on top of them.

[0015] Subsequently, the air in the furnace cavity is pumped to a vacuum, and high-purity argon gas is introduced to melt the high-purity alloy materials to obtain an alloy ingot. During the melting process, the total number of flipping and melting times is 5 - 7 times, and the electromagnetic stirring system is turned on 3 - 5 times.

[0016] Second, the alloy ingot is placed in a muffle furnace heated to 890 °C - 910 °C and held for 30 - 50 min, and the alloy ingot after the heat treatment is subjected to 5 - 10 passes of unidirectional rolling with a total reduction of 80% - 90% to prepare an alloy plate.

[0017] Finally, after solution treatment at 820 - 930 °C / 30 - 90 min, aging treatment at 600 °C / 4 h is carried out to obtain the final product. In addition, a scanning electron microscope (SEM) and a transmission electron microscope (TEM) are used to detect the alloy microstructure morphology, and a UTM5504 electronic universal tensile testing machine is used to test the tensile properties of the alloy specimens at room temperature, 500 °C, 550 °C, and 600 °C.

[0018] The concept of the present invention to achieve the above technical solution is as follows:

[0019] 1) The cluster-based composition design method of the applicant is used to design the composition of a super-high-strength α + β titanium alloy applicable to 600 °C. The types of elements in titanium alloys are complex, and there are obvious partitioning effects in the α and β phases, and there are interactions between different elements. This makes it very difficult to accurately design the composition of titanium alloys. To address the above problems, the present invention uses the cluster plus connecting atom model that describes the chemical short-range order of solid solutions, gives the structural unit carrying the alloy composition, and forms an alloy cluster formula according to the interaction between elements: [cluster](connecting atom) x , where the cluster is a coordination polyhedron formed by any solute atom as the center and the matrix atoms in the nearest neighbor shell around it, and the connecting atoms in the next nearest neighbor shell are used to match the average density of the alloy. The cluster composition formula of the typical α + β titanium alloy Ti-6Al-4V can be expressed as: α-{[Al-Ti 12 (AlTi2)} 12 +β-{[Al-Ti 14 (V2Ti)}5. This dual cluster formula provides a basis for understanding existing α + β titanium alloys and designing high-performance α + β titanium alloys.

[0020] 2) According to the applicant's previous research work, in the titanium alloy system, according to the element action and the mixing enthalpy between elements and matrix elements, elements can be divided into Ti-like elements (including Ti, Zr), Al-like elements (including Al, Si), and Mo-like elements (including Mo, Nb, Ta, W). For simplicity of expression later, the three elements entering the cluster formula are replaced by _T__i_, _A__l_, and __M__o_. Among them, the mixing enthalpy of the _A__l_ element with the matrix element is relatively negative, and the interaction is strong, so it preferentially occupies the central atomic position; the _T__i_ element will preferentially occupy the cluster position; the __M__o_ element with a relatively positive mixing enthalpy and weak interaction with the matrix element occupies the connecting atom position. At the same time, to maintain the same good processing performance and dual-phase characteristics as the Ti-6Al-4V alloy, the number of {α} and {β} in the cluster formula of the new α + β titanium alloy is the same as that of Ti-6Al-4V to ensure the dual-phase characteristics.

[0021] 3) To improve the high-temperature strength of the alloy, the main alloying elements are Mo, Nb, Ta, W, and Si. First, Mo, Nb, Ta, and W are used to replace V in the double-cluster type {β} unit. These four elements have a lower diffusion rate than V, which will endow the alloy with better high-temperature stability. At the same time, an appropriate amount of Al element is added to keep the β unit in balance. In addition, the Nb element helps the alloy to form a continuous Al2O3 oxide film, improving the oxidation resistance of the alloy. Second, the Si element is added to the composition to replace part of Al in the cluster shell, so as to improve the high-temperature performance of the alloy by solid solution strengthening and precipitation strengthening. At the same time, its content needs to be controlled within 0.5 wt.%, otherwise, due to the segregation of Si, coarse silicides will be formed, reducing the plasticity of the alloy.

[0022] 4) To improve the room-temperature strength of the alloy, the main alloying element is Zr. Since Zr and Ti belong to the same transition metal group and have similar chemical properties and infinite solid solubility in the α and β phases, Zr is used to partially replace Ti in the double-cluster type to strengthen the alloy by solid solution strengthening; and when the Zr content exceeds 6 wt.%, it can provide inhomogeneous nucleation particles for the silicides, promoting the precipitation of silicides in the α phase; at the same time, the synergistic addition of high contents of Zr and Si can promote the activation of the α-phase cone slip system, which enables the alloy to have good ductility while maintaining high strength.

[0023] 5) By changing the ratios of Ti, Al, Zr, Mo, Nb, Ta, W, and Si in the cluster type, the optimal multi-element alloying effect is achieved. Finally, the mass percentages of the main components of the new ultra-high-strength α + β titanium alloy applicable to 600 °C are determined as follows: Al: 5.5 - 7.0, Zr: 11.0 - 14.0, Mo: 1.0 - 2.5, Nb: 1.0 - 2.5, Ta: 2.5 - 4.0, W: 2.5 - 4.0, Si: 0.05 - 0.2, and the balance is Ti element and other inevitable impurities; and the alloying elements satisfy the following co-variation relationships: 86.6 wt.% ≤ Ti + 0.9Zr ≤ 92.8 wt.%, 5.7 wt.% ≤ Al + Si ≤ 7.0 wt.%, 5.7 wt.% ≤ Mo + Nb + 0.6Ta + 0.6W ≤ 8.6 wt.%, where Ti, Al, and Mo are the main elements.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1) The present invention is a super-high-strength α+β titanium alloy applicable to 600 °C, which is designed and developed according to the cluster composition method independently developed by the applicant. On the basis of maintaining the same number of {α} and {β} in the Ti-6Al-4V cluster type, by replacing the V element in the original {β} unit with elements such as Mo, Nb, Ta, and W with low diffusion coefficients, the high-temperature stability of the alloy is significantly improved. At the same time, in order to further improve the high-temperature strength of the alloy, a trace amount of Si element is introduced, which is dissolved in the α-phase matrix to produce lattice distortion strengthening, and (Ti,Zr)5Si3-type silicide is precipitated dispersedly. Finally, in order to break through the room-temperature strength bottleneck of the 1400 MPa level, a high content of Zr element is added to the alloy to achieve solid solution strengthening by inducing lattice distortion, at the same time, it serves as a heterogeneous nucleation substrate for silicide to promote its uniform distribution, and activates the cone-plane slip system of the α-phase through the synergistic effect with the Si element, ultimately achieving an excellent match between strength and plasticity.

[0026] 2) The novel super-high-strength α+β titanium alloy applicable to 600 °C provided by the present invention has a specific microstructure: it is a lamellar structure when solution-treated above the phase transformation point and an equiaxed structure and a duplex structure when solution-treated below the phase transformation point. Among them, for the lamellar structure, there is an α-phase with a width of 67 - 211 nm. For the equiaxed structure and the duplex structure, it is composed of primary α-phase and β-transformed structure. Among them, the volume fraction of the primary α-phase is 20 - 50%, and there is a finer secondary α-phase with a width of 30 - 125 nm in the β-transformed structure. At the same time, Ti3Al phase is evenly precipitated in the primary α-phase with a size of 2 - 3 nm. (Ti,Zr)5Si3-type silicide is precipitated at the grain boundaries and within the grains in all three types of microstructures, showing a circular or elliptical shape with a size of 200 - 250 nm, and no harmful phases are generated in the microstructure. And according to the cluster composition design method, the elemental synergistic variation relationship is given, which is beneficial to the composition control in actual production.

[0027] 3) The novel super-high-strength α+β titanium alloy applicable to 600 °C provided by the present invention has an ultra-high room-temperature tensile strength and excellent tensile properties at 600 °C. The typical performance indicators are: room-temperature tensile strength ≥ 1450 MPa, room-temperature yield strength ≥ 1400 MPa, room-temperature elongation ≥ 7.5%, and 600 °C tensile strength ≥ 800 MPa; and the alloy has excellent hot strength, good strength-plasticity matching, and can be used as an alternative material for medium- and high-temperature structural components. Description of the Drawings

[0028] Figure 1 SEM microstructural morphology diagram of the alloy prepared in Example 1: The microstructure is an equiaxed structure, composed of primary α-phase and β-transformed structure, the volume fraction of the primary α-phase is ~50%, there is a finer secondary α-phase with a width of ~30 nm, and silicide exists in the microstructure;

[0029] Figure 2SEM microstructure morphology diagram of the alloy prepared in Example 2: The microstructure is a bimodal structure, consisting of primary α phase and β transformation structure. The volume fraction of the primary α phase is ~20%, and there are secondary α phases with two width ranges, ~45 nm and ~125 nm respectively. At the same time, there are silicides in the microstructure;

[0030] Figure 3 SEM microstructure morphology diagram of the alloy prepared in Example 3: The microstructure is a lamellar structure, with α phases having two width ranges, ~67 nm and ~211 nm respectively. At the same time, there are silicides in the microstructure. Detailed implementation manners

[0031] The following details the specific implementation manners of the present invention in combination with the technical solutions.

[0032] Example 1:

[0033] This example is a super-high-strength α + β titanium alloy applicable to 600 °C. The mass percentages (wt.%) of each component in the titanium alloy are: Al: 7.0 wt.%, Zr: 11.0 wt.%, Mo: 2.5 wt.%, Nb: 1.0 wt.%, Ta: 2.5 wt.%, W: 2.5 wt.%, Si: 0.05 wt.%, and the balance is Ti element and other inevitable impurities, corresponding to the upper limit of the main element content and the lower limit of the content of other elements within the given co-variation range. The mass purities of titanium, aluminum, zirconium, molybdenum, niobium, tantalum, tungsten, and silicon are all 99.98%.

[0034] Step 1: Alloy preparation

[0035] Using high-purity raw materials, 80 g of raw materials are mixed according to the mass percentage and placed in a vacuum arc furnace, and added separately according to the melting points of the elements. The elements with lower melting points, titanium, aluminum, and zirconium, are placed at the bottom, and the elements with higher melting points, molybdenum, niobium, tantalum, tungsten, and silicon, are placed on top. Subsequently, the air in the furnace cavity is pumped to vacuum, and high-purity argon is introduced to melt the metal materials. The total number of flipping and melting times during the process is 5 times, and the electromagnetic stirring system is turned on 5 times during this period. After that, the alloy ingot is placed in a muffle furnace heated to 890 °C and kept warm for 50 min. The alloy ingot after heat preservation treatment is subjected to 5 passes of unidirectional rolling with a total reduction of 80% to prepare alloy plates. Finally, the alloy plates are heat-treated, subjected to solution treatment at 820 °C / 90 min, and then aged at 600 °C / 4 h to obtain the final product.

[0036] Step 2: Alloy microstructure and mechanical property testing

[0037] The morphology of the alloy microstructure was detected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the alloy consisted of primary α phase and transformed β phase, and there were round or oval silicides and Ti3Al phase precipitates in the microstructure. Among them, the volume fraction of the primary α phase was ~50%, the size was ~2.3 μm, and there was secondary α phase with a size of ~30 nm; the silicides precipitated in the microstructure were of the (Ti,Zr)5Si3 type, with a size of ~250 nm, incoherent with the matrix, and the size of the Ti3Al phase precipitated in the primary α phase was ~3 nm, coherent with the matrix, see attachment Figure 1 . The tensile property data of the alloy specimens were measured by a UTM5504 electronic universal tensile testing machine at room temperature, 500 °C, 550 °C and 600 °C: the yield strength YS at room temperature = 1446 MPa, the ultimate tensile strength UTS at room temperature = 1496 MPa, and the elongation after fracture EI at room temperature = 7.8%; the ultimate tensile strength UTS at 500 °C = 976 MPa, the ultimate tensile strength UTS at 550 °C = 882 MPa, and the ultimate tensile strength UTS at 600 °C = 845 MPa.

[0038] Example 2:

[0039] This example is a super-high-strength α+β titanium alloy applicable to 600 °C. The mass percentages (wt.%) of each component in the titanium alloy are: Al: 5.5 wt.%, Zr: 14.0 wt.%, Mo: 1.0 wt.%, Nb: 2.5 wt.%, Ta: 4.0 wt.%, W: 4.0 wt.%, Si: 0.2 wt.%, and the balance is Ti element and other inevitable impurities, corresponding to the lower limit of the main element content and the upper limit of the other element content within the given co-variation range. The mass purities of titanium, aluminum, zirconium, molybdenum, niobium, tantalum, tungsten, and silicon are all 99.98%.

[0040] Step 1: Alloy preparation

[0041] High-purity raw materials were used. 80 g of raw materials were mixed according to the mass percentage and put into a vacuum arc furnace, and were added separately according to the melting points of the elements. The elements with lower melting points, such as titanium, aluminum, and zirconium, were placed at the bottom, and the elements with higher melting points, such as molybdenum, niobium, tantalum, tungsten, and silicon, were placed on top of them. Subsequently, the air in the furnace cavity was pumped to vacuum, and high-purity argon gas was introduced to melt the metal materials. The total number of flipping and melting times during the process was 7 times, and the electromagnetic stirring system was turned on 3 times during this period. After that, the alloy ingot was placed in a muffle furnace heated to 910 °C and kept warm for 30 min. The heat-treated alloy ingot was subjected to 10 passes of unidirectional rolling with a total reduction of 90% to prepare an alloy plate. Finally, the alloy plate was heat-treated. After solution treatment at 930 °C / 30 min, aging treatment at 600 °C / 4 h was carried out to obtain the final product.

[0042] Step 2: Detection of alloy microstructure and mechanical properties

[0043] The morphology of the alloy microstructure was detected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the alloy was composed of primary α phase and transformed β phase, and there were circular or elliptical silicides and Ti3Al phase precipitates in the microstructure. Among them, the volume fraction of the primary α phase was ~20%, the size was ~2.5 μm, and there were fine and coarse secondary α phases of ~45 nm and ~125 nm; the silicides precipitated in the microstructure were of the (Ti,Zr)5Si3 type, with a size of ~200 nm, non-coherent with the matrix, and the size of the Ti3Al phase existing in the primary α phase was ~2 nm, coherent with the matrix. See the appendix Figure 2 The tensile property data of the alloy specimens were measured by a UTM5504 electronic universal tensile testing machine at room temperature, 500 °C, 550 °C and 600 °C: the yield strength YS at room temperature was 1430 MPa, the ultimate tensile strength UTS was 1473 MPa, and the elongation after fracture EL was 8%; the ultimate tensile strength UTS at 500 °C was 1043 MPa, the ultimate tensile strength UTS at 550 °C was 947 MPa, and the ultimate tensile strength UTS at 600 °C was 850 MPa.

[0044] Example 3:

[0045] This example is a super high-strength α+β titanium alloy applicable to 600 °C. The mass percentages (wt.%) of each component in the titanium alloy are: Al: 6.25 wt.%, Zr: 12.5 wt.%, Mo: 1.75 wt.%, Nb: 1.75 wt.%, Ta: 3.25 wt.%, W: 3.25 wt.%, Si: 0.125 wt.%, and the balance is Ti element and other inevitable impurities, corresponding to the median value of the content of each element within the given co-variation range. The mass purities of titanium, aluminum, zirconium, molybdenum, niobium, tantalum, tungsten, and silicon are all 99.98%.

[0046] Step 1: Alloy preparation

[0047] High-purity raw materials were used. 80 g of raw materials were mixed according to the mass percentage and placed in a vacuum arc furnace, and were added separately according to the melting points of the elements. The elements with lower melting points, such as titanium, aluminum and zirconium, were placed at the bottom, and the elements with higher melting points, such as molybdenum, niobium, tantalum, tungsten and silicon, were placed on top. Subsequently, the air in the furnace cavity was pumped to vacuum, and high-purity argon was introduced to melt the metal materials. The total number of flipping and melting times during the process was 6 times, and the electromagnetic stirring system was turned on 4 times. After that, the alloy ingot was placed in a muffle furnace heated to 900 °C and kept warm for 40 min. The heat-treated alloy ingot was subjected to 7 passes of single-pass rolling with a total reduction of 85% to prepare an alloy plate. Finally, the alloy plate was heat-treated. After solution treatment at 875 °C / 60 min, aging treatment at 600 °C / 4 h was carried out to obtain the final product.

[0048] Step 2: Detection of alloy microstructure and mechanical properties

[0049] The morphology of the alloy microstructure was detected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the alloy has a lamellar microstructure, and circular or elliptical silicides precipitate in the microstructure. Among them, the volume fraction of the α phase is ~68%, and there are finer α regions and coarser α regions, which are ~67 nm and ~211 nm respectively. The silicide precipitated in the microstructure is of the (Ti,Zr)5Si3 type, with a size of ~239 nm, and is incoherent with the matrix. See Appendix Figure 3 . The tensile property data of the alloy specimens were measured by a UTM5504 electronic universal tensile testing machine at room temperature, 500 °C, 550 °C, and 600 °C: the yield strength YS at room temperature = 1410 MPa, the ultimate tensile strength UTS = 1480 MPa, and the elongation after fracture EI = 8.2%; the ultimate tensile strength UTS at 500 °C = 1004 MPa, the ultimate tensile strength UTS at 550 °C = 973 MPa, and the ultimate tensile strength UTS at 600 °C = 840 MPa.

[0050] The above-described embodiments only represent the implementation modes of the present invention, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A super-high-strength α+β titanium alloy applicable to 600°C, characterized in that, The described ultra-high strength α+β titanium alloy comprises elements Ti, Al, Zr, Mo, Nb, Ta, W and Si, and the mass percentages wt.% of its alloy components are as follows: Al: 5.5 - 7.0, Zr: 11.0 - 14.0, Mo: 1.0 - 2.5, Nb: 1.0 - 2.5, Ta: 2.5 - 4.0, W: 2.5 - 4.0, Si: 0.05 - 0.2, with the balance being Ti element and other inevitable impurities.

2. An ultra-high strength α+β titanium alloy applicable to 600°C according to claim 1, characterized in that, The alloying elements in the described ultra-high strength α+β titanium alloy satisfy the following co-variation relationships: 86.6wt.% ≤ Ti + 0.9Zr ≤ 92.8wt.%, 5.7wt.% ≤ Al + Si ≤ 7.0wt.%, 5.7wt.% ≤ Mo + Nb + 0.6Ta + 0.6W ≤ 8.6wt.%, where Ti, Al, and Mo are the main elements.

3. An ultra-high strength α+β titanium alloy applicable to 600°C, characterized in that, The described ultra-high strength α+β titanium alloy has a specific microstructure morphology: it is a lamellar structure when solution-treated above the phase transformation point, and an equiaxed structure and a duplex structure when solution-treated below the phase transformation point.

4. An ultra-high strength α+β titanium alloy applicable to 600 °C according to claim 3, characterized in that In the described microstructure morphology: For the lamellar structure, there is an α-phase with a width of 67 - 211 nm; For the equiaxed structure and the duplex structure, they are composed of primary α-phase and β-transformed structure. Among them, the volume fraction of the primary α-phase is 20 - 50%, and there are finer secondary α-phases with a width of 30 - 125 nm in the β-transformed structure. At the same time, Ti3Al phases are uniformly precipitated within the primary α-phase, with a size of 2 - 3 nm; (Ti,Zr)5Si3 type silicides are precipitated at grain boundaries and within grains in all three types of microstructures, with a size of 200 - 250 nm, and no harmful phases are generated in the microstructure.

5. An ultra-high strength α+β titanium alloy applicable to 600 °C according to claim 1, characterized in that, The described ultra-high strength α+β titanium alloy has good room temperature strength and plasticity and high temperature properties. The typical properties of the alloy are: room temperature tensile strength ≥ 1450 MPa, room temperature yield strength ≥ 1400 MPa, room temperature elongation ≥ 7.5%, and 600°C tensile strength ≥ 800 MPa.

6. A method for preparing a super-high-strength α+β titanium alloy applicable to 600°C according to any one of claims 1-5, characterized in that, It includes the following steps: First step, according to the mass percentages of the alloy component elements, weigh high-purity alloy materials, and place the accurately weighed metal ingredients in a vacuum arc melting furnace, and add them separately according to the melting points of the elements. The titanium, aluminum, and zirconium elements with lower melting points are placed at the bottom, and the molybdenum, niobium, tantalum, tungsten, and silicon elements with higher melting points are placed on top of them; Second step, evacuate the air in the furnace cavity to vacuum, introduce high-purity argon gas, and melt the high-purity alloy materials to obtain an alloy ingot; Third step, place the alloy ingot in a muffle furnace heated to 890°C - 910°C and keep it warm for 30 - 50 min, and process the alloy ingot after the heat preservation treatment to prepare an alloy plate; Fourth step, after solution treatment and aging treatment, the final product is obtained.

7. The preparation method of the ultra-high strength α+β titanium alloy applicable to 600 °C according to claim 6, characterized in that, During the melting process in the second step, the total number of flipping and melting times is 5 - 7 times, and the electromagnetic stirring system is turned on 3 - 5 times during this period.

8. The preparation method of the ultra-high strength α+β titanium alloy applicable to 600 °C according to claim 6, characterized in that, In the third step, the alloy ingot after heat preservation treatment is subjected to 5 - 10 passes of single-direction rolling, and the total reduction is 80% - 90%.

9. The preparation method of the ultra-high strength α+β titanium alloy applicable to 600°C according to claim 6, characterized in that, In the fourth step, the temperature of the solution treatment is 820 - 930°C, and the time is 30 - 90 min.

10. The preparation method of the ultra-high strength α+β titanium alloy applicable to 600°C according to claim 6, characterized in that In the fourth step, the temperature of the aging treatment is 600 °C and the time is 4 h.

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