α+β type titanium alloy with high strength and low yield ratio and preparation method thereof

Abstract

The present invention relates to the field of titanium alloy materials, and specifically refers to an α+β titanium alloy with high strength and low yield ratio and a preparation method thereof. The chemical composition of the titanium alloy is Al: 5.0-7.0; V: 3.0-5.0; x: 0.1-10 (x is a eutectic β-stabilizing element such as Fe, Mn, Cr, Ni, Cu, etc.); the remainder is Ti. The preparation method of the titanium alloy is as follows: first, after keeping warm in the two-phase region for a period of time, it is rapidly cooled to room temperature to obtain a lamellar α″ martensite precursor; then the alloy with the lamellar α″ martensite precursor is cold rolled at room temperature, and the total strain is in the range of 10% to 50%. Finally, the cold-rolled plate is annealed for different times in the temperature range of 800-850°C to obtain an α+β titanium alloy with a two-stage equiaxed α phase structure. The α+β titanium alloy with high strength and low yield ratio prepared by the present invention can be widely used in important fields such as aerospace, marine engineering, petrochemical industry, automobile industry and biomedicine.

Description

Technical Field

[0001] The present invention relates to the field of titanium alloy materials, and in particular to an α+β titanium alloy with high strength and low yield ratio and a preparation method thereof. Background Art

[0002] At present, titanium alloys with light weight, high strength, excellent corrosion resistance and biocompatibility have been widely used in important fields such as aerospace, marine engineering, petrochemical industry, automobile industry and biomedicine. The yield strength ratio is an important mechanical index affecting the processing and engineering application of titanium alloys. However, the yield strength ratio (σ y / σ b ) is generally high, usually higher than 0.85, or even higher than 0.9, which is significantly higher than that of copper alloy (σ y / σ b =0.3~0.6)、aluminum alloy (σ y / σ b =0.5) and low and medium strength steel (σ y / σ b =0.6-0.8) and other traditional metal materials. Low yield ratios not only reduce the cold forming properties of titanium alloys but also reduce the material's ability to resist failure after yielding, thereby reducing the service safety and reliability of components. With the increasing demand for service safety and reliability in various advanced components, exploring effective methods to reduce the yield ratio of titanium alloys is of great significance for further expanding the application of titanium alloys.

[0003] At present, alloy design is usually used to reduce the stability of the β phase in titanium alloys, thereby reducing the yield ratio of titanium alloys by stress-induced martensitic transformation or β twinning. However, the above method is at the expense of the yield strength of the titanium alloy, so that the yield strength of the alloy is usually less than 600MPa. The lower yield strength not only fails to meet the design requirements of the component under certain working conditions, but also significantly reduces the utilization rate of the material, which is very unfavorable for the lightweighting of the component. Therefore, the research and development of new titanium alloys with both high strength and low yield ratio is crucial to further enhance the service performance of titanium alloy materials. Summary of the Invention

[0004] In response to the pain point that the strength and yield strength ratio of titanium alloys cannot be taken into account at the same time, the purpose of the present invention is to provide an α+β type titanium alloy with both high strength and low yield strength ratio and a preparation method thereof, which opens up a new way to further improve the performance and service performance of traditional titanium alloys.

[0005] In order to achieve the above objectives, the technical solution of the present invention is:

[0006] Disclosed is an α+β titanium alloy with high strength and low yield ratio. The titanium alloy has the following chemical compositions by weight: Al: 5.0-7.0, V: 3.0-5.0, x: 0.5-10, where x is a eutectic β-stabilizing element such as Fe, Mn, Cr, Ni, or Cu, and the remainder is Ti. The alloy also has a two-level equiaxed α phase.

[0007] A preparation method of an α+β titanium alloy with both high strength and low yield ratio, comprising the steps of: performing three smelting operations in a vacuum consumable furnace to obtain a raw material ingot with uniform composition; subjecting the ingot to grinding treatment, blanking forging, and precision forging into a blank; and subsequently undergoing solution treatment, cold rolling deformation, and annealing to obtain an α+β titanium alloy with both high strength and low yield ratio.

[0008] The preparation method of the α+β titanium alloy with both high strength and low yield ratio is as follows: the alloy billet obtained after precision forging is subjected to solid solution treatment, and after being kept in the α+β two-phase region for a period of time, it is rapidly cooled to room temperature to obtain an α″ martensite precursor. After the α″ martensite precursor is cold-rolled and deformed, a fine equiaxed α+β structure is formed during the annealing process. At the same time, due to the presence of the primary α phase, an α+β titanium alloy with a two-level equiaxed α phase is finally obtained.

[0009] In the method for preparing the α+β titanium alloy with both high strength and low yield ratio, the size distribution of the dual-scale equiaxed α phase is as follows: the size of the primary α phase is between 5 and 20 μm, and the size of the secondary α phase is between 200 and 500 nm.

[0010] The preparation method of the α+β type titanium alloy with both high strength and low yield ratio has the following characteristics: when heat preservation in the two-phase region, the heat preservation temperature is 800° C. to 900° C., and the heat preservation time is 30 minutes to 60 minutes.

[0011] The method for preparing the α+β type titanium alloy with both high strength and low yield ratio is as follows: the obtained blank is kept in the two-phase region for a period of time and then rapidly cooled to room temperature; the cooling rate of the rapid cooling is between 25 and 200°C / s.

[0012] The method for preparing the α+β type titanium alloy with both high strength and low yield ratio is as follows: the α″ martensite precursor is cold rolled at room temperature at a strain rate of 0.5 to 5s -1 The total deformation is between 10% and 50%. Preferably, the strain rate is between 1 and 3s -1 , the total deformation is between 10% and 40%.

[0013] In the method for preparing the α+β titanium alloy with both high strength and low yield ratio, the annealing temperature after cold rolling is 800-850°C and the annealing time is 0.5-4 hours. Preferably, the annealing temperature is 800-830°C and the annealing time is 0.5-3 hours.

[0014] The method for preparing the α+β type titanium alloy with both high strength and low yield ratio has a yield strength of not less than 700 MPa, a tensile strength of not less than 1200 MPa, and a yield ratio of not more than 0.82.

[0015] The design concept of the present invention is:

[0016] The present invention adds a eutectic β-stabilizing element to the titanium alloy so that the alloy forms an α″ martensite phase after solution treatment. The α″ martensite phase, as an important precursor, will evolve into a secondary equiaxed α phase with a size of several hundred nanometers after subsequent cold deformation and annealing. The micron-scale primary equiaxed α phase combined with the secondary equiaxed α phase will make the alloy have both high strength and low yield ratio.

[0017] In the chemical composition design of the α+β titanium alloy with both high strength and low yield ratio of the present invention, a eutectic β-stabilizing element is added to form an α″ martensite precursor after solution treatment, thereby preparing the structure for subsequent cold rolling and annealing treatments.

[0018] In the preparation process of this titanium alloy, the alloy billet is first heated to the two-phase region for solid solution treatment, and then cold deformation is used in combination with appropriate annealing process to obtain the microstructure characteristics of α phase with two-level scale or above. While ensuring that the yield strength of the alloy is not less than 700MPa and the tensile strength is not less than 1200MPa, the yield strength ratio of the alloy is significantly reduced to 0.60-0.82.

[0019] The advantages and beneficial effects of the present invention are:

[0020] 1. Different from the microstructure of existing engineering titanium alloys, the titanium alloy provided by the present invention has a unique two-level size equiaxed α phase microstructure feature. The two-level size refers to the presence of both micron-scale and nano-scale equiaxed α phases. The size of the primary α phase is between 5 and 20 μm, and the size of the secondary α phase is between 200 and 500 nm.

[0021] 2. The method of the present invention can significantly reduce the yield strength ratio of the alloy while ensuring the yield strength and tensile strength of the alloy, further increasing the service safety and reliability of the alloy while meeting the lightweight requirements of the components.

[0022] 3. Titanium alloy bars, wires, plates, etc. can be prepared by the method of the present invention.

[0023] 4. The method of the present invention can be used to prepare titanium alloys with both high strength and low yield ratio, which can be widely used in many important fields such as aerospace, marine engineering, petrochemical industry, automobile industry and biomedicine.-1 , the total deformation is 20% to 40%) and under the conditions of annealing process (800 to 830°C, 0.5 to 3h), the yield strength of the prepared α+β titanium alloy with multi-level equiaxed α phase is not less than 700MPa, the tensile strength is not less than 1200MPa, the yield strength ratio is not higher than 0.82, and the elongation is not less than 11%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a scanning electron microscope image of an α″ martensite precursor.

[0025] Figure 2 This is a scanning electron microscope photograph of the equiaxed α phase with two levels of size after annealing. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and effects of this application clearer and more specific, this application is further described in detail below with reference to the accompanying drawings and examples.

[0027] In practice, the present invention provides a novel titanium alloy processing and preparation technology with both high strength and low yield ratio. The titanium alloy has the following chemical composition: Al: 5.0-7.0; V: 3.0-5.0; x: 0.5-10 (x is a eutectic β-stabilizing element such as Fe, Mn, Cr, Ni, Cu, etc.); and the balance is Ti. The impurity element content in the alloy must meet the corresponding requirements of the national titanium alloy standard.

[0028] The preparation method of the titanium alloy is as follows: a vacuum consumable furnace is used to carry out three smelting to obtain a raw material ingot with uniform composition, the ingot is ground and then subjected to blanking forging and precision forging into a blank, which is then subjected to solid solution treatment, cold rolling deformation and annealing to obtain an α+β titanium alloy with both high strength and low yield ratio. First, after keeping warm in the two-phase region for a period of time, it is rapidly cooled to room temperature to obtain a lamellar α″ martensite precursor; then the alloy with the lamellar α″ martensite precursor is cold rolled at room temperature, and the total strain is in the range of 10% to 50%. Finally, the cold-rolled plate is annealed for different times in the temperature range of 800 to 850°C to obtain an α+β titanium alloy with two-stage equiaxed α phase structure characteristics.

[0029] See also Figures 1-2 . Figure 1 This is the microstructure containing primary α phase and α″ martensite formed after the blank in Example 1 of the present invention is rapidly cooled after solution treatment. It can be seen from the SEM photo that the width of the α″ martensite lath is about 2 to 3 μm. Figure 2It is a microstructure with a two-level equiaxed α phase formed after the solution treated billet in Example 3 of the present invention is cold rolled and heat treated. It can be seen from the SEM photo that the size of the primary α phase is between 5 and 10 μm, and the size of the secondary α phase is between 300 and 500 nm.

[0030] The present application will be described and explained below through several groups of specific embodiments and comparative examples, but they should not be used to limit the scope of the present application.

[0031] Examples: Examples 1 to 5 are alloys obtained by making appropriate adjustments according to the preparation steps in the summary of the invention.

[0032] Table 1 Chemical composition and cold rolling annealing process of the example materials

[0033]

[0034] Tensile properties test

[0035] The room temperature tensile mechanical properties of the example materials were tested using a Zwick Z150 tensile testing machine at a tensile rate of 0.3 mm / min. Three replicates were taken from each set of heat-treated samples. The mechanical properties obtained from the experiments included yield strength, tensile strength, and elongation. The results are shown in Table 2.

[0036] Table 2 Mechanical properties of Examples 1 to 5

[0037]

[0038] The results in Table 2 show that the alloys in Examples 1-5 exhibit high yield strength, tensile strength, and ductility, while also exhibiting a low yield strength ratio. Within the heat treatment time range specified in this invention, the yield strength and yield strength ratio gradually increase with increasing annealing time, while elongation does not significantly change.

[0039] The results of the embodiment show that the α+β titanium alloy with high strength and low yield ratio and a two-level equiaxed α phase obtained by the present invention can be widely used in important fields such as aerospace, marine engineering, petrochemical industry, automobile industry and biomedicine.

[0040] The above description is only an implementation method of the present application and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the description and drawings of this application, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. An α+β titanium alloy with both high strength and low yield ratio, characterized in that: The titanium alloy has a chemical composition of Al: 5.0-7.0, V: 3.0-5.0, x: 0.5-10, x is one of the eutectoid β-stabilizing elements Fe, Mn, Cr, Ni or Cu, and the balance is Ti, and has a two-level equiaxed α phase; The alloy billet obtained after the precision forging process is subjected to a solution treatment, wherein the solution treatment comprises: holding the alloy billet in the α+β two-phase region for a period of time, and then rapidly cooling the alloy billet to room temperature to obtain an α´´ martensitic precursor; the α´´ martensitic precursor is subjected to cold rolling and then annealing to form a fine equiaxed α+β structure. At the same time, due to the presence of the primary α phase, an α+β titanium alloy with a dual-scale equiaxed α phase is finally obtained. The size distribution of the two-level equiaxed α phase is as follows: the size of the primary α phase is between 5 and 20 μm, and the size of the secondary α phase is between 200 and 500 nm; the yield strength of the titanium alloy is not less than 700 MPa, the tensile strength is not less than 1200 MPa, and the low yield strength ratio is not higher than 0.

82.

2. A method for preparing the α+β titanium alloy with high strength and low yield ratio according to claim 1, characterized in that: A vacuum consumable furnace is used for three smelting processes to obtain raw material ingots with uniform composition. The ingots are ground and then forged and precision forged into billets. Subsequently, they undergo solution treatment, cold rolling and annealing to obtain α+β titanium alloy with both high strength and low yield ratio.

3. The method for preparing an α+β titanium alloy having both high strength and low yield ratio according to claim 2, characterized in that: When holding in the two-phase region, the holding temperature is 800°C~900°C, and the holding time is 30 min~60 min.

4. The method for preparing an α+β titanium alloy having both high strength and low yield ratio according to claim 2, wherein: The obtained billet is kept in the two-phase region for a period of time and then rapidly cooled to room temperature, with a cooling rate of 25-200°C / s.

5. The method for preparing an α+β titanium alloy having both high strength and low yield ratio according to claim 2, wherein: The α´´ martensite precursor is cold rolled at room temperature with a strain rate of 0.5~5S -1 , the total deformation is between 10% and 50%.

6. The method for preparing an α+β titanium alloy having both high strength and low yield ratio according to claim 2, wherein: The annealing temperature after cold rolling deformation is 800~850℃, and the annealing time is 0.5~4 h.

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