Multi-scale alpha-phase regulation and control method for casting metastable beta titanium alloy
Through hot isostatic pressing and double annealing, a multi-scale α phase structure is formed, which solves the problem of plasticity caused by excessive fine needle-like α phases in cast titanium alloys and improves the mechanical properties of titanium alloys.
Patent Information
- Application Number
- CN202411376322.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-30
- Publication Date
- 2025-01-21
AI Technical Summary
There are a large number of triangularly distributed fine needle-shaped α phases in existing cast titanium alloys, which leads to a significant reduction in the plasticity of the titanium alloy and seriously affects the mechanical properties of the alloy.
Hot isostatic pressing and double annealing are used to control the temperature, pressure and holding time to form a multi-scale α phase structure, including fibrous, rod-shaped, nearly spherical and fine needle-shaped α phases.
By regulating the structure of the α phase, the yield strength, tensile strength and fracture elongation of the titanium alloy are improved, and it has the characteristics of strong plasticity matching.
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Figure CN119332187A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of heat treatment of titanium alloys, and more specifically, to a multi-scale α phase control method for casting metastable β titanium alloys. Background Art
[0002] Metastable β titanium alloys are widely used in the manufacture of aircraft main load-bearing components due to their high specific strength, low modulus, good fatigue properties and excellent processing properties. Among them, alloys such as Ti5553 (Ti-5Al-5V-5Mo-3Cr), Ti153 (Ti-15V-3Cr-3Al-3Sn), and Ti7333 (Ti-7Mo-3Al-3Nb-3Cr) not only have high strength but also have good filling fluidity. They are typical high-strength casting titanium alloys.
[0003] The mechanical properties and deformation behavior of metastable β titanium alloys mainly depend on the coupling effect between the α phase characteristics and the residual β matrix. Controlling the size, morphology and distribution of the α phase is crucial to improving the mechanical properties of metastable β titanium alloys. The high strength of multi-scale α phase metastable β titanium alloys originates from the nanoscale needle-like secondary α S The precipitation of phase introduces a large amount of α S / β interface can effectively hinder dislocation movement, reduce the mean free path of dislocation slip, and achieve interface strengthening; while the larger primary equiaxed α phase can produce obvious strain hardening to be compatible with the β transformation matrix to maintain uniform deformation and ensure ductility.
[0004] In the prior art, a (α+β) two-phase titanium alloy Ti-6.5Al-3.3Mo-1.2Mn-1.7Zr-0.6Fe-0.3Si-0.15Cr-0.1Ni prepared by laser directed energy deposition is subjected to a solid solution aging treatment at 950℃ / 1h AC+530℃ / 6h to obtain a special structure with a coarse root morphology of α phase and a triangularly distributed fine needle-shaped α phase, and the tensile strength of the titanium alloy reaches 1247MPa and the elongation is 9.2%. However, for cast titanium alloys, only a small amount of primary α phase can be obtained through the existing solid solution aging treatment, and a large amount of triangularly distributed fine needle-shaped α phase structure is precipitated, and the presence of a large amount of triangularly distributed fine needle-shaped α phase structure will greatly reduce the plasticity of the titanium alloy and seriously affect the mechanical properties of the alloy. Summary of the invention
[0005] The purpose of the present invention is to provide a multi-scale α phase control method for casting metastable β titanium alloy, which is used to solve the technical problem that the existing casting titanium alloy has a large number of triangularly distributed fine needle-shaped α phase structures, thereby greatly reducing the plasticity of the titanium alloy. In view of this, the present invention provides the following technical solutions.
[0006] In a first aspect, the present invention provides a multi-scale α phase control method for casting a metastable β titanium alloy, comprising: Obtaining a cast metastable beta titanium alloy; The titanium alloy is first subjected to hot isostatic pressing treatment, and then the furnace is cooled to room temperature; wherein the temperature of the hot isostatic pressing treatment is 20-40° C. lower than the β phase transformation point of the titanium alloy, the pressure of the hot isostatic pressing treatment is 110-150 MPa, and the holding time is 2-4 hours; The titanium alloy is subjected to a first annealing treatment: the temperature range is 25° C. lower than the β phase transformation point of the titanium alloy to 10° C. higher than the β phase transformation point of the titanium alloy, and the holding time is 0.5 to 1 hour; The titanium alloy is subjected to a second annealing treatment: the titanium alloy after the first annealing treatment is cooled to 550-650° C. and kept at this temperature for 3-8 hours; After the second annealing treatment, the titanium alloy is air-cooled to room temperature to obtain a titanium alloy with a multi-scale α phase; wherein the multi-scale α phase includes one or more of a fibrous α phase, a rod-like α phase, a nearly spherical α phase and a fine needle-like α phase.
[0007] Compared with the prior art, in the multi-scale α phase control method of the cast metastable β titanium alloy of the present invention, the cast metastable β titanium alloy is first subjected to hot isostatic pressing. During the hot isostatic pressing process, by controlling the temperature, pressure and holding time within the above range, the hole defects of the titanium alloy can be bridged, and the rod-shaped and near-spherical α phase organization can be obtained. After the hot isostatic pressing is completed, the titanium alloy is cooled to room temperature to release the residual stress. Then the titanium alloy is subjected to double annealing, that is, the titanium alloy is subjected to the above-mentioned first annealing and second annealing in sequence, and the temperature and time of each annealing are controlled within the above-mentioned reasonable range, so that the titanium alloy can further form a root-like coarse lamellar α phase, retain a part of the rod-shaped or near-spherical α phase formed during the hot isostatic pressing process, and precipitate a vertically or parallel fine needle-shaped α phase. After the above-mentioned regulation and treatment, the grain boundary α phase of the titanium alloy is a discontinuous layer, and a small amount of fine needle-shaped α phase is precipitated near the grain boundary. These small amounts of fine needle-shaped α phases are mostly distributed in a triangular shape, and the fine needle-shaped α phase precipitated in the β matrix is distributed in parallel or vertically. The yield strength of the titanium alloy is 1002~1030MPa, the tensile strength is 1060~1100MPa, and the elongation at break is 6.5~8%, which has the characteristics of strong plasticity matching. Further, in the above-mentioned technical solution, the β phase transformation point of the titanium alloy can be recorded as T β The temperature of hot isostatic pressing is T β -40℃~T β -20℃, the temperature of the first annealing treatment is T β -25℃~T β+10° C. Through the above technical solution of the present invention, the technical problem of how to obtain a multi-scale α phase structure with strong plasticity matching in a cast titanium alloy is solved.
[0008] Furthermore, in the multi-scale α phase control method of casting metastable β titanium alloy of the present invention, the titanium alloy includes Ti-5Al-5V-5Mo-3Cr titanium alloy, Ti-15V-3Cr-3Al-3Sn titanium alloy and Ti-7Mo-3Al-3Nb-3Cr titanium alloy.
[0009] Furthermore, in the multi-scale α phase control method for casting metastable β titanium alloy of the present invention, the thickness of the root-like α phase is 1-2 μm, and the thickness of the rod-like and / or nearly spherical α phase is 1-2 μm.
[0010] Furthermore, in the multi-scale α phase control method for casting metastable β titanium alloy of the present invention, the thickness of the fine needle-shaped α phase is 150-250 nm and the length is 0.75-1.25 μm.
[0011] Furthermore, in the multi-scale α phase control method for casting metastable β titanium alloy of the present invention, during the process of cooling the titanium alloy after the first annealing treatment to 550~650°C, the cooling rate is 3~10°C / min.
[0012] In the second aspect, the present invention provides a titanium alloy prepared by the multi-scale α phase control method of the above-mentioned cast metastable β titanium alloy; the titanium alloy has a multi-scale α phase, and the multi-scale α phase includes one or more of a fibrous α phase, a rod-like α phase, a nearly spherical α phase and a fine needle-like α phase.
[0013] Compared with the prior art, the beneficial effects of the titanium alloy of the present invention are the same as the beneficial effects of the multi-scale α phase control method for casting metastable β titanium alloy described in the above technical solution, which will not be repeated here.
[0014] Furthermore, the titanium alloy of the present invention has a yield strength of 1002-1030 MPa, a tensile strength of 1060-1100 MPa, and an elongation at break of 6.5-8%. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 This is a SEM schematic diagram of the multi-scale α-structure area of the titanium alloy after regulation in Example 1 of the present invention; Figure 2It is a magnified SEM schematic diagram of the intracrystalline root-like α phase, rod-like α phase, nearly spherical α phase and fine needle-like α phase region of the titanium alloy after regulation in Example 1 of the present invention; Figure 3 This is a SEM schematic diagram of the fine needle-shaped α phase near the grain boundary and the discontinuous grain boundary α phase region of the titanium alloy after regulation in Example 1 of the present invention; Figure 4 Schematic diagram of the engineering stress-engineering strain tensile curve of the titanium alloy after regulation in Example 1 of the present invention; Figure 5 Schematic diagram of the engineering stress-engineering strain tensile curve of the titanium alloy after regulation in Example 2 of the present invention; Figure 6 This is a SEM schematic diagram of the titanium alloy after adjustment in Example 3 of the present invention; Figure 7 Schematic diagram of the engineering stress-engineering strain tensile curve of the titanium alloy after regulation in Example 3 of the present invention; Figure 8 This is a SEM schematic diagram of the titanium alloy after adjustment in Example 4 of the present invention; Fig. 9 This is a SEM schematic diagram of the titanium alloy after regulation in Comparative Example 1 of the present invention; Fig.10 It is a schematic diagram of the engineering stress-engineering strain tensile curve of the titanium alloy after regulation in Comparative Example 1 of the present invention; Fig.11 This is a SEM schematic diagram of the titanium alloy after regulation in Comparative Example 2 of the present invention; Fig.12 It is a schematic diagram of the engineering stress-engineering strain tensile curve of the titanium alloy after regulation in Comparative Example 2 of the present invention. DETAILED DESCRIPTION
[0016] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.
[0017] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.
[0018] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. The meaning of "several" is one or more, unless otherwise clearly and specifically defined.
[0019] In the prior art, a (α+β) two-phase titanium alloy Ti-6.5Al-3.3Mo-1.2Mn-1.7Zr-0.6Fe-0.3Si-0.15Cr-0.1Ni prepared by laser directed energy deposition is subjected to a solid solution aging treatment at 950℃ / 1h AC+530℃ / 6h to obtain a special structure with a coarse root morphology of α phase and a triangularly distributed fine needle-shaped α phase, and the tensile strength of the titanium alloy reaches 1247MPa and the elongation is 9.2%. However, for cast titanium alloys, only a small amount of primary α phase can be obtained through the existing solid solution aging treatment, and a large amount of triangularly distributed fine needle-shaped α phase structure is precipitated, and the presence of a large amount of triangularly distributed fine needle-shaped α phase structure will greatly reduce the plasticity of the titanium alloy and seriously affect the mechanical properties of the alloy.
[0020] In order to solve the above technical problems, in a first aspect, the present invention provides a multi-scale α phase control method for casting a metastable β titanium alloy, comprising: Obtaining a cast metastable beta titanium alloy; The titanium alloy is first subjected to hot isostatic pressing treatment, and then the furnace is cooled to room temperature; wherein the temperature of the hot isostatic pressing treatment is 20-40° C. lower than the β phase transformation point of the titanium alloy, the pressure of the hot isostatic pressing treatment is 110-150 MPa, and the holding time is 2-4 hours; The titanium alloy is subjected to a first annealing treatment: the temperature range is 25° C. lower than the β phase transformation point of the titanium alloy to 10° C. higher than the β phase transformation point of the titanium alloy, and the holding time is 0.5 to 1 hour; The titanium alloy is subjected to a second annealing treatment: the titanium alloy after the first annealing treatment is cooled to 550-650° C. and kept at this temperature for 3-8 hours; After the second annealing treatment, the titanium alloy is air-cooled to room temperature to obtain a titanium alloy with a multi-scale α phase; wherein the multi-scale α phase includes one or more of a fibrous α phase, a rod-like α phase, a nearly spherical α phase and a fine needle-like α phase.
[0021] In the case of adopting the above technical scheme, in the multi-scale α phase control method of the cast metastable β titanium alloy of the present invention, the cast metastable β titanium alloy is first subjected to hot isostatic pressing. During the hot isostatic pressing process, by controlling the temperature, pressure and holding time within the above range, the hole defects of the titanium alloy can be bridged, and the rod-shaped and near-spherical α phase organization can be obtained. After the hot isostatic pressing is completed, the titanium alloy is cooled to room temperature to release the residual stress. Then the titanium alloy is subjected to double annealing, that is, the titanium alloy is subjected to the above-mentioned first annealing and second annealing in sequence, and the temperature and time of each annealing are controlled within the above-mentioned reasonable range, so that the titanium alloy can further form a root-like coarse lamellar α phase, and retain a part of the rod-shaped or near-spherical α phase formed during the hot isostatic pressing process, and precipitate a vertically or parallel fine needle-shaped α phase. After the above-mentioned regulation and treatment, the grain boundary α phase of the titanium alloy is a discontinuous layer, and a small amount of fine needle-shaped α phase is precipitated near the grain boundary. These small amounts of fine needle-shaped α phases are mostly distributed in a triangular shape, and the fine needle-shaped α phase precipitated in the β matrix is distributed in parallel or vertically. The yield strength of the titanium alloy is 1002~1030MPa, the tensile strength is 1060~1100MPa, and the elongation at break is 6.5~8%, which has the characteristics of strong plasticity matching. Further, in the above-mentioned technical solution, the β phase transformation point of the titanium alloy can be recorded as T β The temperature of hot isostatic pressing is T β -40℃~T β -20℃, the temperature of the first annealing treatment is T β -25℃~T β +10° C. Through the above technical solution of the present invention, the technical problem of how to obtain a multi-scale α phase structure with strong plasticity matching in a cast titanium alloy is solved.
[0022] By way of example, the titanium alloy includes Ti-5Al-5V-5Mo-3Cr titanium alloy, Ti-15V-3Cr-3Al-3Sn titanium alloy or Ti-7Mo-3Al-3Nb-3Cr titanium alloy; by way of another example, the titanium alloy may be Ti-5Al-5V-5Mo-3Cr titanium alloy, or may be Ti-15V-3Cr-3Al-3Sn titanium alloy or Ti-7Mo-3Al-3Nb-3Cr titanium alloy. Among them, for Ti-5Al-5V-5Mo-3Cr titanium alloy, it means that the titanium alloy contains 5wt% aluminum, 5wt% vanadium, 5wt% molybdenum and 3wt% chromium, and the balance is titanium and trace impurities; for Ti-15V-3Cr-3Al-3Sn titanium alloy, it means that the titanium alloy contains 15wt% vanadium, 3wt% chromium, 3wt% aluminum and 3wt% tin; for Ti-7Mo-3Al-3Nb-3Cr titanium alloy, it means that the titanium alloy contains 7wt% molybdenum, 3wt% aluminum, 3wt% niobium and 3wt% chromium, and the balance is titanium and trace impurities.
[0023] By way of example, the thickness of the fibrous α phase may be 1-2 μm, and the thickness of the rod-shaped and / or nearly spherical α phase may be 1-2 μm; by way of another example, the thickness of the fibrous α phase may be 1 μm, 1.5 μm or 2 μm, and the thickness of the rod-shaped and / or nearly spherical α phase may be 1 μm, 1.5 μm or 2 μm.
[0024] For example, the thickness of the fine needle-shaped α phase may be 150-250 nm, and the length may be 0.75-1.25 μm; for another example, the thickness of the fine needle-shaped α phase may be 150 nm, 200 nm or 250 nm, and the length may be 0.75 μm, 1 μm or 1.25 μm.
[0025] As a possible implementation method, in the multi-scale α phase control method of the cast metastable β titanium alloy of the present invention, the cooling rate is 3~10℃ / min in the process of cooling the titanium alloy after the first annealing treatment to 550~650℃. In the case of adopting the above technical solution, the cooling rate is one of the key factors affecting the precipitation morphology and distribution of the above titanium alloy phase. Within the cooling rate range, it can be ensured that the cooling process is neither too rapid nor too slow. Too rapid may form too many nucleation particles, resulting in the precipitation of too many fine needle-shaped α phases after the second annealing treatment, thereby reducing the plasticity of the titanium alloy. Too slow will cause the α phase to be coarse, affecting the distribution of multi-scale α phases. For example, the above cooling rate can be 3℃ / min, 5℃ / min, 8℃ / min or 10℃ / min.
[0026] In the second aspect, the present invention provides a titanium alloy prepared by the multi-scale α phase control method of the above-mentioned cast metastable β titanium alloy; the titanium alloy has a multi-scale α phase, and the multi-scale α phase includes one or more of a fibrous α phase, a rod-like α phase, a nearly spherical α phase and a fine needle-like α phase.
[0027] In the case of adopting the above technical solution, the titanium alloy is prepared by the multi-scale α phase control method of the above-mentioned cast metastable β titanium alloy. In the control method, the cast metastable β titanium alloy is first subjected to hot isostatic pressing. During the hot isostatic pressing process, by controlling the temperature, pressure and holding time within the above range, the hole defects of the titanium alloy can be bridged, and the rod-shaped and near-spherical α phase organization can be obtained. After the hot isostatic pressing is completed, the titanium alloy is cooled to room temperature to release the residual stress. Then the titanium alloy is subjected to double annealing, that is, the titanium alloy is subjected to the above-mentioned first annealing and second annealing in sequence, and the temperature and time of each annealing are controlled within the above-mentioned reasonable range, so that the titanium alloy can further form a root-like coarse lamellar α phase, and retain a part of the rod-shaped or near-spherical α phase formed during the hot isostatic pressing process, and precipitate a vertically or parallel fine needle-shaped α phase. After the above-mentioned regulation and control treatment, the grain boundary α phase of the titanium alloy is a discontinuous layer, and a small amount of fine needle-shaped α phase is precipitated near the grain boundary. These small amounts of fine needle-shaped α phases are mostly distributed in a triangular shape, and the fine needle-shaped α phase precipitated in the β matrix is distributed in parallel or vertically. The yield strength of the titanium alloy is 1002~1030MPa, the tensile strength is 1060~1100MPa, and the elongation at break is 6.5~8%, which has the characteristics of strong plasticity matching. For example, the yield strength of the titanium alloy can be 1020MPa, 1030MPa or 1002MPa, the tensile strength can be 1080MPa, 1100MPa or 1060MPa, and the elongation at break can be 8%, 7.5% or 6.5%.
[0028] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific embodiments, but the content of the present invention is not limited to the following embodiments.
[0029] Unless otherwise specified, the raw materials used in the following examples are commercially available. Example 1
[0030] This embodiment provides a multi-scale α phase control method for casting a metastable β titanium alloy, comprising: S100, obtaining the cast metastable β titanium alloy Ti-5553 (Ti-5Al-5Mo-5V-3Cr), the β phase transformation point of the titanium alloy is 855℃; S200, the Ti-5553 sample cast by investment casting is subjected to hot isostatic pressing at a temperature of 820°C, a pressure of 130 MPa, and a holding time of 2 hours. After the holding is completed, the furnace is cooled to room temperature and the sample is taken out; S300, subjecting the sample after hot isostatic pressing in step S200 to a first annealing treatment, that is, maintaining the temperature at 865°C for 0.5h; S400, performing a second annealing treatment on the sample in step S300, that is, the sample after the first annealing treatment in step S300 is furnace cooled to 600°C at a cooling rate of 5°C / min, and kept at this temperature for 4 hours, and then air-cooled to room temperature to obtain a titanium alloy Ti-5553 with a multi-scale α phase.
[0031] See also Figures 1 to 3 In this embodiment, a coarse lamellar α phase with a root shape is obtained in the titanium alloy Ti-5553, and there is a small amount of rod-shaped and nearly spherical α phase. The grain boundary α phase is discontinuous, and a small amount of fine needle-shaped α phase is precipitated near the grain boundary, which is mostly distributed in a triangular shape. The fine needle-shaped α phase precipitated in the β matrix is distributed in parallel or vertically. The average thickness of the root-shaped and rod-shaped or nearly spherical α phase exceeds 1 μm, the average thickness of the grain boundary α phase exceeds 1.5 μm, and the thickness of the fine needle-shaped α phase in the crystal is about 150~250nm, and the length is 0.75~1.25μm.
[0032] See also Figure 4 The titanium alloy Ti-5553 obtained in step S400 of this embodiment is subjected to a tensile property test. The yield strength of the titanium alloy Ti-5553 reaches 1020 MPa, the tensile strength reaches 1080 MPa, and the elongation at break reaches 8%. The specific tensile curve is as follows: Figure 4 shown. Example 2
[0033] This embodiment provides a multi-scale α phase control method for casting a metastable β titanium alloy, comprising: S100, obtaining the cast metastable β titanium alloy Ti-5553 (Ti-5Al-5Mo-5V-3Cr), the β phase transformation point of the titanium alloy is 855℃; S200, the Ti-5553 sample cast by investment casting is subjected to hot isostatic pressing at a temperature of 820°C, a pressure of 130 MPa, and a holding time of 2 hours. After the holding is completed, the furnace is cooled to room temperature and the sample is taken out; S300, subjecting the sample after hot isostatic pressing in step S200 to a first annealing treatment, that is, keeping the temperature at 855°C for 1 hour; S400, performing a second annealing treatment on the sample in step S300, that is, the sample after the first annealing treatment in step S300 is furnace cooled to 600°C at a cooling rate of 5°C / min, and kept at this temperature for 4 hours, and then air-cooled to room temperature to obtain a titanium alloy Ti-5553 with a multi-scale α phase.
[0034] See also Figure 5 The titanium alloy Ti-5553 obtained in step S400 of this embodiment is subjected to a tensile property test, and its yield strength reaches 1030 MPa, the tensile strength reaches 1100 MPa, and the elongation at break reaches 7.5%. The specific tensile curve is as follows Figure 5 shown. Example 3
[0035] This embodiment provides a multi-scale α phase control method for casting a metastable β titanium alloy, comprising: S100, obtaining a cast metastable β titanium alloy Ti-7333 (Ti-7Mo-3Al-3Nb-3Cr), the β phase transition point of the titanium alloy is 845°C; S200, the Ti-7333 sample cast by investment casting is subjected to hot isostatic pressing at a temperature of 820°C, a pressure of 140 MPa, and a holding time of 2 hours. After the holding time is completed, the furnace is cooled to room temperature and the sample is taken out; S300, subjecting the sample after hot isostatic pressing in step S200 to a first annealing treatment, that is, keeping the temperature at 845°C for 1 hour; S400, performing a second annealing treatment on the sample in step S300, that is, furnace cooling the sample after the first annealing treatment in step S300 to 650°C at a cooling rate of 5°C / min, keeping it warm for 4 hours, and then air cooling it to room temperature to obtain a titanium alloy Ti-7333 with a multi-scale α phase.
[0036] See also Figure 6 In this embodiment, a root-like coarse lamellar α phase and a small amount of rod-shaped and nearly spherical α phase are obtained in the titanium alloy Ti-7333. At the same time, fine needle-shaped α phase precipitates in the β matrix and presents a multi-scale α phase structure with parallel or vertical distribution. Please refer to Figure 7 The tensile properties of the titanium alloy Ti-7333 were tested, and the yield strength reached 1002MPa, the tensile strength reached 1060MPa, and the elongation at break reached 6.5%. The specific tensile curve is as follows Figure 7 shown. Example 4
[0037] This embodiment provides a multi-scale α phase control method for casting a metastable β titanium alloy, comprising: S100, obtaining a cast metastable β titanium alloy Ti-7333 (Ti-7Mo-3Al-3Nb-3Cr), the β phase transition point of the titanium alloy is 845°C; S200, the Ti-7333 sample cast by investment casting is subjected to hot isostatic pressing at a temperature of 825°C, a pressure of 110 MPa, and a holding time of 4 hours. After the holding is completed, the furnace is cooled to room temperature and the sample is taken out; S300, subjecting the sample after the hot isostatic pressing treatment in step S200 to a first annealing treatment, that is, keeping the temperature at 820° C. for 1 hour; S400, performing a second annealing treatment on the sample in step S300, that is, furnace cooling the sample after the first annealing treatment in step S300 to 550°C at a cooling rate of 10°C / min, keeping it warm for 8 hours, and then air cooling it to room temperature to obtain a titanium alloy Ti-7333 with a multi-scale α phase.
[0038] See also Figure 8 In this embodiment, a root-like coarse lamellar α phase and a small amount of rod-shaped and nearly spherical α phase are obtained in the titanium alloy Ti-7333, and at the same time, a fine needle-shaped α phase is precipitated in the β matrix and a multi-scale α phase is distributed in parallel or vertically. The yield strength of the titanium alloy Ti-7333 reaches 1010MPa, the tensile strength reaches 1070MPa, and the elongation at break reaches 7%.
[0039] Comparative Example 1 The multi-scale α phase control method for casting metastable β titanium alloy provided in this comparative example is basically the same as that in Example 2, except that the annealing treatment of step S300 and step S400 is not performed in this comparative example.
[0040] See also Fig. 9 The titanium alloy Ti-5553 of this comparative example contains rod-shaped and nearly spherical lamellar α phases, no fine needle-shaped α phase precipitates on the β matrix, and the average thickness of the lamellar α phase is 0.74±0.20μm. Fig.10 The tensile properties of the titanium alloy Ti-5553 were tested, and the yield strength was 930MPa, the tensile strength was 1007MPa, and the elongation at break was 10%. The comprehensive tensile properties were significantly worse than those of Example 2. The specific tensile curve is as follows Fig.10 shown.
[0041] Comparative Example 2 The multi-scale α phase control method for casting metastable β titanium alloy provided in this comparative example is basically the same as that in Example 2, except that in this comparative example S300, the sample is kept at a temperature of 870° C. for 0.5 h.
[0042] See also Fig.11 When the temperature of the first annealing treatment is higher (10°C higher than the β phase transformation point of the titanium alloy Ti-5553), although the same root-like coarse lamellar α phase is obtained, the fine needle-like α phase precipitated on the β matrix is mostly distributed in a triangular shape. Fig.12 , the tensile properties of the titanium alloy Ti-5553 were tested. Although the yield strength reached 1150MPa and the tensile strength reached 1200MPa, the elongation at break was only 2%, showing an obvious mismatch between strength and plasticity. The specific tensile curve is as follows: Fig.12 shown.
[0043] It should be noted that the above embodiments and comparative examples only take titanium alloy Ti-5553 (Ti-5Al-5Mo-5V-3Cr) and titanium alloy Ti-7333 (Ti-7Mo-3Al-3Nb-3Cr) as examples to illustrate the present invention. For titanium alloy Ti-5553 (Ti-5Al-5Mo-5V-3Cr), it means that the titanium alloy contains 5wt% aluminum, 5wt% molybdenum, 5wt% vanadium and 3wt% chromium, and the balance is titanium and trace impurities; for titanium alloy Ti-7333 (Ti-7Mo-3Al-3Nb-3Cr), it means that the titanium alloy contains 7wt% molybdenum, 3wt% aluminum, 3wt% niobium and 3wt% chromium, and the balance is titanium and trace impurities.
[0044] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.
[0045] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.
Claims
1. A multi-scale α phase control method for casting metastable β titanium alloy, characterized in that: include: Obtaining a cast metastable beta titanium alloy; The titanium alloy is first subjected to hot isostatic pressing treatment, and then the furnace is cooled to room temperature; wherein the temperature of the hot isostatic pressing treatment is 20-40° C. lower than the β phase transformation point of the titanium alloy, the pressure of the hot isostatic pressing treatment is 110-150 MPa, and the holding time is 2-4 hours; The titanium alloy is subjected to a first annealing treatment: the temperature range is 25° C. lower than the β phase transformation point of the titanium alloy to 10° C. higher than the β phase transformation point of the titanium alloy, and the holding time is 0.5 to 1 hour; The titanium alloy is subjected to a second annealing treatment: the titanium alloy after the first annealing treatment is cooled to 550-650° C. and kept at this temperature for 3-8 hours; After the second annealing treatment, the titanium alloy is air-cooled to room temperature to obtain a titanium alloy with a multi-scale α phase; wherein the multi-scale α phase includes one or more of a fibrous α phase, a rod-like α phase, a nearly spherical α phase and a fine needle-like α phase.
2. The multi-scale α phase control method for casting metastable β titanium alloy according to claim 1, characterized in that: The titanium alloys include Ti-5Al-5V-5Mo-3Cr titanium alloy, Ti-15V-3Cr-3Al-3Sn titanium alloy and Ti-7Mo-3Al-3Nb-3Cr titanium alloy.
3. The multi-scale α phase control method for casting metastable β titanium alloy according to claim 1 or 2, characterized in that: The thickness of the root-like α phase is 1-2 μm, and the thickness of the rod-like and / or nearly spherical α phase is 1-2 μm.
4. The multi-scale α phase control method for casting metastable β titanium alloy according to claim 3, characterized in that: The fine needle-shaped α phase has a thickness of 150-250 nm and a length of 0.75-1.25 μm.
5. The multi-scale α phase control method for casting metastable β titanium alloy according to claim 4, characterized in that: In the process of cooling the titanium alloy after the first annealing treatment to 550-650° C., the cooling rate is 3-10° C. / min.
6. A titanium alloy, characterized in that: The titanium alloy is prepared by the multi-scale α phase control method of the cast metastable β titanium alloy described in any one of claims 1 to 5; the titanium alloy has a multi-scale α phase, and the multi-scale α phase includes one or more of a fibrous α phase, a rod-like α phase, a nearly spherical α phase and a fine needle-like α phase.
7. The titanium alloy according to claim 6, characterized in that The titanium alloy has a yield strength of 1002-1030 MPa, a tensile strength of 1060-1100 MPa, and a fracture elongation of 6.5-8%.