Titanium alloy strength and toughness grading control method

Abstract

This invention discloses a method for graded control of the strength and toughness of titanium alloys, belonging to the field of metal material processing and heat treatment technology. Through multi-parameter synergistic control and graded heat treatment, a dual-state or basket-like hybrid microstructure is formed. The method regulates the temperature combination of high-temperature control and aging control to induce primary α-chromium formation in the final microstructure. p Phase content and secondary α s The lamination width satisfies three performance modes: high strength, balanced strength and toughness, and high toughness. After adjustment, the alloy tensile strength is ≥1015MPa and the impact absorption energy is ≥35J, breaking the inverse relationship between strength and toughness. According to the actual working conditions, different performance levels such as high strength and high toughness, balanced strength and toughness, and high toughness can be flexibly obtained to meet the requirements of customized component performance and high stability in high-end fields such as aerospace and medical.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing and heat treatment technology, and specifically relates to a method for graded control of the strength and toughness of titanium alloys. Background Technology

[0002] Ti-Al-V based α+β dual-phase titanium alloys are widely used in aerospace, shipbuilding, and biomedical engineering due to their high specific strength, excellent corrosion resistance, and good biocompatibility. However, there is a natural inverse relationship between the strength and toughness of this type of alloy. Its mechanical properties are determined by the microstructure characteristics such as the content and morphology of the primary α phase, the distribution of the transformed β phase, and the size and spacing of the secondary α phase. Microstructure control is the core means to achieve performance matching.

[0003] Currently, the commonly used heat treatment processes in the industry are mainly divided into two categories: annealing and solution-aging treatment. Annealing can eliminate processing stress and improve the plasticity and toughness of alloys, but the primary α phase is coarse, there is no secondary α phase strengthening, the dispersion strengthening effect is poor, and the strength is low, which cannot meet the high strength requirements of high-end load-bearing components. Although the traditional solution-aging process can significantly improve strength, it has prominent defects: this process uses high-temperature solution treatment in the α+β two-phase region, rapid cooling with water / oil cooling, and low-temperature aging to precipitate fine spherical secondary α phase strengthening, but it is easy to generate large internal stress, and even generate acicular brittle martensite phase, resulting in a significant decrease in toughness and plasticity, and a clear tendency to brittleness; at the same time, the cooling rate of large-size and irregularly shaped components is uneven, which can easily cause fluctuations in microstructure and properties, resulting in poor product stability and low yield.

[0004] In recent years, pulsed current heating technology has shown great potential in the field of heat treatment of metallic materials due to its unique electroplastic effect and non-thermal effect. However, existing technologies have not yet systematically integrated pulsed current technology with the entire forging-heat treatment process to achieve precise graded control of performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, a graded control method for the strength and toughness of titanium alloys is proposed. This method utilizes multi-parameter synergistic control and graded heat treatment to form a dual-state or basket-like hybrid microstructure. By controlling the temperature combination of high-temperature control and aging control, the primary α-phase in the final microstructure is optimized. p Phase content and secondary α s The lamination width satisfies three performance modes: high strength, balanced strength and toughness, and high toughness. After adjustment, the alloy tensile strength is ≥1015MPa and the impact absorption energy is ≥35J, breaking the inverse relationship between strength and toughness. According to the actual working conditions, different performance levels such as high strength and high toughness, balanced strength and toughness, and high toughness can be flexibly obtained to meet the requirements of customized component performance and high stability in high-end fields such as aerospace and medical.

[0006] To achieve the above objectives, the present invention provides a method for graded control of the strength and toughness of titanium alloys, the method comprising the following steps: S1. Preparation of titanium alloy ingots; S2, High-temperature forging; heating the ingot to T β The first forging is carried out at 180℃~220℃, and then heated to T. β A second forging is performed at (80℃~120℃), followed by reheating to T. β The first billet is obtained by forging at (50℃~70℃) for the third time. All three forging processes involve repeated upsetting and drawing. After each forging, the billet is air-cooled to room temperature to obtain the first billet. S3, forging near the phase transformation point; heating the first billet to T β The material is subjected to repeated upsetting and drawing forging at ±10℃ for 1 to 2 cycles, and then water-cooled to room temperature to obtain the second billet. S4, Low-temperature forging; heating the second billet to T β - (10℃~30℃) Repeated upsetting and drawing forging 2~4 times, and air-cooled to room temperature after each forging to obtain titanium alloy billet with equiaxed α+β dual-phase structure; S5. Regulate pulse current to assist in graded heat treatment. The graded heat treatment consists of high temperature regulation and aging treatment. The target performance titanium alloy is as follows: for high strength type, the high temperature regulation temperature is 955℃±3℃ and the aging temperature is 500℃±3℃. For the robust and balanced type, the high temperature control temperature is 960℃±3℃, and the aging temperature is 520℃±3℃. For the high-toughness type, the high-temperature control temperature is 965℃±3℃, and the aging temperature is 510℃±3℃. The pulse parameters are: pulse voltage 10V~100V, pulse current density 10A / mm²~100A / mm², pulse frequency 50Hz~500Hz, and heating time 10s~300s.

[0007] Preferably, in step S1, the titanium alloy is composed of the following elements by mass percentage: Al 6.02%–6.30%, V 4.11%–4.37%, Fe ≤0.030%, Si ≤0.015%, C ≤0.010%, H ≤0.0015%, N ≤0.005%, O 0.171%–0.190%, with the balance being Ti and unavoidable impurities; the β-phase transformation point T of the titanium alloy is... β The temperature ranges from 970℃ to 985℃.

[0008] Preferably, in step S4, the volume fraction of the primary α phase in the titanium alloy billet is 35% to 45%.

[0009] Preferably, in step S5, after high-temperature control and heat preservation for 0.5h to 2h, the temperature is rapidly cooled to room temperature at a cooling rate of ≥50℃ / s, and after aging and heat preservation for 4h to 8h, the temperature is air-cooled to room temperature.

[0010] Preferably, in step S5, the parameters of the pulse current assisted graded heat treatment are selected according to the target performance of the titanium alloy as follows: high strength type: pulse voltage 50V~80V, pulse current density 50A / mm²~80A / mm², pulse frequency 200Hz~300Hz, heating time 30s~60s; Strong and balanced type: pulse voltage 30V~50V, pulse current density 30A / mm²~50A / mm², pulse frequency 150Hz~250Hz, heating time 60s~90s; High toughness type: pulse voltage 20V~40V, pulse current density 20A / mm²~40A / mm², pulse frequency 100Hz~200Hz, heating time 90s~120s.

[0011] Preferably, in step S5, the content of primary α phase and the width of secondary α lamellars in the regulated titanium alloy microstructure satisfy the following: High-strength type: primary α phase content and secondary α lamellar width. p Phase content 15%–20%, secondary α s Average lamellar width < 0.5 μm; Strong and balanced type: nascent α p Phase content 8%–12%, secondary α s The average width of the lamellar sheets is 0.5 μm to 0.8 μm; High toughness type: primary α p Phase content ≤5%, secondary α s The average width of the sheets is 0.8 μm to 1.2 μm.

[0012] Preferably, the mechanical properties of the regulated titanium alloy meet the following requirements: High strength type: tensile strength ≥1030MPa, yield strength ≥910MPa, elongation after fracture ≥15%, impact absorption energy ≥35J; Strong and balanced type: tensile strength ≥1020MPa, yield strength ≥900MPa, elongation after fracture ≥15%, impact energy absorption ≥40J; High toughness type: tensile strength ≥1015MPa, yield strength ≥885MPa, elongation after fracture ≥14%, impact energy absorption ≥44J.

[0013] Preferably, in step S2, the upsetting deformation amount for each forging is 45% to 50%.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention obtains three titanium alloy performance modes—high strength, balanced strength and toughness, and high toughness—by adjusting the parameter combination within the range of high temperature control (940℃~970℃) and aging control (480℃~540℃), thus meeting the customized needs of different working conditions such as aerospace load-bearing components, general engineering structural components, and impact-resistant components. The parameter sensitivity window, with an impact absorption energy change of ≥3J for every 5℃ temperature change, allows the performance control accuracy to reach ±3J.

[0015] (2) This invention establishes for the first time a quantitative correspondence between the content of primary α phase, the width of secondary α lamellars, and three performance modes, making performance regulation predictable and repeatable. Existing technologies only focus on process parameters and do not establish a direct correlation between microstructure parameters and performance. This invention fills this technological gap.

[0016] (3) The core properties of the alloy after regulation in this invention: high-strength type: tensile strength ≥1030MPa, impact absorption energy ≥35J; strong and tough balanced type: tensile strength ≥1020MPa, impact absorption energy ≥40J; high-toughness type: tensile strength ≥1015MPa, impact absorption energy ≥44J. Compared with the untreated forged sample: tensile strength increased by ≥41MPa, impact absorption energy increased by ≥64%, while maintaining a high strength level, the toughness was significantly improved, and the risk of brittle fracture was reduced; compared with the 700℃ low-temperature annealing process: tensile strength increased by ≥157MPa, yield strength increased by ≥140MPa, and the impact toughness was not lower than or even better than that of the annealed state, overcoming the shortcomings of the traditional annealing process that caused a significant decrease in strength; compared with the 940℃ low-temperature solution-aging process: under the premise of obtaining equivalent or higher tensile strength, the impact absorption energy increased by 20.6%, achieving a significant increase in toughness without reducing strength, effectively improving the matching relationship between alloy strength and toughness.

[0017] (4) The present invention uses conventional equipment and only includes two steps: high temperature control and aging control. The heat preservation time is uniform. Water quenching and air cooling are conventional cooling methods in the industry. No special consumables or complicated operations are required, and the cost is controllable. The cooling rate is clear (≥50℃ / s), which can effectively avoid the fluctuation of the structure and performance of large-sized and irregularly shaped components. The system has high stability and is easy to promote and implement on existing industrial production lines. Attached Figure Description

[0018] Figure 1 This is a microstructure diagram of the titanium alloy provided in Embodiment 1 of the present invention.

[0019] Figure 2 This is a microstructure diagram of the titanium alloy provided in Embodiment 2 of the present invention.

[0020] Figure 3 This is a microstructure diagram of the titanium alloy provided in Embodiment 3 of the present invention.

[0021] Figure 4 This is a microstructure diagram of the titanium alloy provided in Comparative Example 1 of the present invention.

[0022] Figure 5 This is a microstructure diagram of the titanium alloy provided in Comparative Example 2 of the present invention.

[0023] Figure 6 This is a microstructure diagram of the titanium alloy provided in Comparative Example 3 of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are also within the scope of protection of this disclosure.

[0025] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this subject matter pertains. It will be further understood that terms such as those defined in commonly used dictionaries shall be interpreted as having the meaning consistent with their meaning in the context of the specification and in the relevant art, and shall not be interpreted in an idealized or overly formal form unless otherwise explicitly defined herein.

[0026] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of the phrase "embodiment" in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] The method for graded control of strength and toughness of titanium alloys provided by this invention includes the following steps: S1. Preparation of titanium alloy ingots; the titanium alloy is composed of the following elements by mass percentage: Al 6.02%–6.30%, V 4.11%–4.37%, Fe ≤0.030%, Si ≤0.015%, C ≤0.010%, H ≤0.0015%, N ≤0.005%, O 0.171%–0.190%, with the balance being Ti and unavoidable impurities; wherein, the β-phase transformation point T of the titanium alloy is... β The temperature ranges from 970℃ to 985℃.

[0028] In some embodiments of the present invention, during the ingot preparation process in step S1, sponge titanium, aluminum-vanadium master alloy and high-purity aluminum are pressed into electrode blocks as raw materials, and three VAR meltings are carried out in a vacuum arc remelting furnace. The three meltings effectively reduce the content of impurity elements and compositional segregation in the alloy, and obtain ingots with high purity and high uniformity.

[0029] S2, High-temperature forging; the ingot is heated to a specific temperature (T). β The first forging is carried out at (180℃~220℃), for example, it can be T. β +180, T β +200, T β +220, reheating preferably to T β A second forging is performed at (80℃~120℃), for example, for T... β +80, T β +100, T β +120, reheat preferably to T β A third forging process is performed at (50℃~70℃), for example, for T. β +50, T β +60, T β +70, all three forging methods are repeated upsetting and drawing, and the upsetting deformation of each forging is preferably 45% to 50%, for example, 45%, 48%, and 50%; after each forging, air cool to room temperature, and then draw using a transverse axis to obtain the first billet; In some embodiments of the present invention, repeated upsetting and drawing with three gradual cooling stages during the high-temperature billet forging stage, combined with air cooling after each forging, effectively breaks up coarse grains in the cast state, promotes the homogenization of the microstructure, and avoids abnormal grain growth.

[0030] S3, forging near the phase transformation point; heating the first billet to T... β The material is subjected to repeated upsetting and drawing forging at ±10℃ for 1 to 2 times, and then water-cooled to room temperature at a cooling rate of ≥100℃ / s, so as to refine the grains while retaining some deformation energy to obtain the second billet. S4. Low-temperature forging; the second billet is preferably heated to T. β -(10℃~30℃), for example, it can be T β -10, T β -20, T β The titanium alloy billet is subjected to repeated upsetting and drawing forging 2 to 4 times at -30°C, and air-cooled to room temperature after each forging to obtain a titanium alloy billet with a fine grain and uniform distribution of primary α phase and an equiaxed α+β dual-phase structure. The volume fraction of primary α phase in the titanium alloy billet is 35% to 45%, which provides an ideal microstructure basis for subsequent heat treatment.

[0031] S5. Pulse current-assisted graded heat treatment, wherein the graded heat treatment is high-temperature control and aging treatment. The high-temperature control temperature range is 940℃~970℃ in the α+β two-phase region. During this stage, pulse current-assisted heating is applied, and after holding at this temperature for 0.5h~2h, it is rapidly cooled to room temperature at a cooling rate ≥50℃ / s. The aging treatment temperature range is 480℃~540℃, and after holding at this temperature for 4h~8h, it is air-cooled to room temperature. The pulse current-assisted parameters are: pulse voltage 10V~100V, pulse current density 10A / mm²~100A / mm², pulse frequency 50Hz~500Hz, and heating time 10s~300s. In some embodiments of the present invention, during the staged heat treatment, a supersaturated β phase and a martensitic α' phase are obtained by high-temperature control in the two-phase region and rapid cooling at a rate of ≥50℃ / s. This provides high-density nucleation sites for subsequent aging precipitation, while suppressing excessive growth of the primary α phase. Subsequently, within the intermediate-temperature aging range, the decomposition of the supersaturated β phase and the secondary α phase are precisely controlled. s The nucleation and growth of lamellae are precisely controlled through a specific combination of high-temperature regulation temperatures (955℃ / 960℃ / 965℃) and aging regulation temperatures (500℃ / 520℃ / 510℃), achieving precise control over the content of primary α phase and the width of secondary α lamellae, ultimately forming a structure composed of an appropriate amount of equiaxed α phase. p and diffusely distributed fine α s The dual-state or basket-like hybrid structure composed of lamellar layers achieves a controllable balance between high strength and high toughness.

[0032] The specific titanium alloys used for matching to achieve the target performance are as follows: High-strength type, the preferred high-temperature control temperature is 955℃±3℃, the aging temperature is 500℃±3℃; the pulse voltage is 50V~80V, the pulse current density is 50A / mm²~80A / mm², the pulse frequency is 200Hz~300Hz, and the heating time is 30s~60s. Strong and balanced type, high temperature control temperature is 960℃±3℃, aging temperature is 520℃±3℃; pulse voltage is 30V~50V, pulse current density is 30A / mm²~50A / mm², pulse frequency is 150Hz~250Hz, heating time is 60s~90s. High toughness type, high temperature control temperature is 965℃±3℃, aging temperature is 510℃±3℃; pulse voltage is 20V~40V, pulse current density is 20A / mm²~40A / mm², pulse frequency is 100Hz~200Hz, and heating time is 90s~120s.

[0033] Among them, the high-temperature control temperature difference between the high-strength type and the strong-toughness balanced type is 5℃±1℃; the high-temperature control temperature difference between the strong-toughness balanced type and the high-toughness type is 5℃±1℃; the high-temperature control temperature difference between the high-strength type and the high-toughness type is 10℃±1℃; the aging control temperature difference between the high-strength type and the strong-toughness balanced type is 20℃±3℃; and the aging control temperature difference between the strong-toughness balanced type and the high-toughness type is 10℃±3℃.

[0034] In some embodiments of the present invention, the titanium alloy workpiece / material is a bar, plate, tube or forging, and the prepared titanium alloy material can be used for aerospace engine blades, landing gear, fuselage connectors or medical device implants.

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments:

[0036] Example 1 The titanium alloy used in this embodiment is composed of the following elements by mass percentage: Al 6.12%, V 4.17%, Fe 0.026%, Si 0.012%, C 0.010%, H 0.0010%, N 0.003%, O 0.172%, with the balance being Ti; its β-phase transformation point T was determined. β It is 975℃.

[0037] The preparation process is as follows: S1. Sponge titanium, aluminum-vanadium master alloy and high-purity aluminum are pressed into electrode blocks as raw materials, and three VAR meltings are carried out in a vacuum consumable arc furnace to obtain ingots with uniform composition. S2. Heat the ingot to T. β The first forging was carried out at +190℃, using repeated upsetting and drawing. The upsetting deformation was 50%, and the drawing was done horizontally. After forging, the billet was air-cooled to room temperature. Then, the billet was heated to T. β The billet is then subjected to a second forging at +90℃, using a repeated upsetting and drawing method, with an upsetting deformation of 48%, followed by air cooling; the billet is then heated to T... β The third forging was carried out at +50℃, and the forging method was repeated upsetting and drawing. The upsetting deformation was 45%, and the material was air-cooled to obtain the first billet. S3. Heat the first billet to T β The material is forged in one pass using a repeated upsetting and drawing method, with an upsetting deformation of 45%. After forging, it is water-quenched and cooled to room temperature (cooling rate of 100℃ / s) to obtain the second billet. S4. Heat the second billet to T β The first forging was carried out at -10℃, using repeated upsetting and drawing methods, with an upsetting deformation of 50%. After forging, it was air-cooled to room temperature; then reheated to T. β The second forging was carried out at -10℃, using repeated upsetting and drawing methods, with an upsetting deformation of 48%, followed by air cooling; then reheated to T.β The third forging was carried out at -20℃, and the forging method was repeated upsetting and drawing. The upsetting deformation was 45%, and the material was air-cooled. Finally, it was processed into a bar and used as the original billet for the experiment. Its original structure was an equiaxed α+β dual-phase structure with fine grains and uniform distribution of primary α phase. The volume fraction of primary α phase was 35%.

[0038] S5. Heat the titanium alloy bar to 955℃ while applying a pulsed current with a pulse voltage of 65V, a pulse current density of 70A / mm², a pulse frequency of 250Hz, a heating time of 50s, and hold for 1h. Then, quench the alloy in water to room temperature. Next, heat the water-quenched alloy to 500℃ and hold for 6h. Then, air-cool the alloy to room temperature to obtain a high-strength titanium alloy.

[0039] The microstructure of the alloy obtained in this embodiment was observed, and the results are as follows: Figure 1 As shown, from Figure 1 It can be seen that its organizational characteristics are approximately 15%-20% equiaxed primary α phase (α... p ) evenly distributed on the β-transformed tissue matrix, secondary α-lamellae (α s The particles are extremely fine and dense, with an average width of less than 0.5 μm. Mechanical property testing revealed a tensile strength of 1032 MPa, a yield strength of 918 MPa, an elongation after fracture of 15.8%, a reduction of area of ​​55%, and an impact absorption energy of 38 J.

[0040] Example 2 The main difference between this embodiment and embodiment 1 is that in step S5, the alloy is heated to 960°C while a pulsed current is applied. The pulse voltage is 45V, the pulse current density is 40A / mm², the pulse frequency is 200Hz, the heating time is 80s, the holding time is 1h, the alloy is water-quenched to room temperature, then heated to 520°C for aging for 6h, and air-cooled to room temperature. The remaining steps are the same as in embodiment 1; thus, a strong and tough titanium alloy with balanced properties is obtained.

[0041] The microstructure of the alloy obtained in this embodiment was observed, and the results are as follows: Figure 2 As shown, from Figure 2 It is evident that as the solution temperature increases, the content of the primary α phase decreases (by about 10%) and becomes finer; the secondary α lamellae further coarsen and exhibit a certain degree of clustering characteristics.

[0042] Mechanical property tests were conducted, yielding a tensile strength of 1026 MPa, a yield strength of 906 MPa, an elongation after fracture of 15.1%, a reduction of area of ​​52%, and an impact absorption energy of 41.4 J.

[0043] Example 3 The main difference between this embodiment and embodiment 1 is that in step S5, the alloy is heated to 965°C while a pulsed current is applied. The pulse voltage is 30V, the pulse current density is 30A / mm², the pulse frequency is 150Hz, the heating time is 100s, the holding time is 1h, the alloy is water-quenched to room temperature, then heated to 510°C for aging for 6h, and air-cooled to room temperature. The remaining steps are the same as in embodiment 1, resulting in a high-toughness titanium alloy.

[0044] The microstructure of the alloy obtained in this embodiment was observed, and the results are as follows: Figure 3 As shown, from Figure 3 It is evident that the primary α phase content is extremely low (≤5%), and the main body of the microstructure consists of coarsened secondary α lamellae and β matrix, exhibiting a typical basket-like structure. Mechanical property testing revealed a tensile strength of 1021 MPa, a yield strength of 889 MPa, an elongation after fracture of 14.2%, a reduction of area of ​​49%, and an impact absorption energy of 44.5 J.

[0045] Comparative Example 1 The main difference between this comparative example and Example 1 is that the graded heat treatment in step S5 is omitted; the remaining steps are the same as in Example 1. The resulting titanium alloy microstructure is shown in the image below. Figure 4 As shown, the primary α p The phase is a flat, equiaxed shape elongated along the forging direction, accounting for 15% to 20%, and is preferentially distributed along the rheological direction; the β matrix is ​​a deformed structure with high-density dislocations and deformed twins inside, retaining significant work hardening energy storage, and without secondary α-lamellae precipitation.

[0046] Mechanical property testing revealed a tensile strength of 904 MPa, a yield strength of 821 MPa, an elongation after fracture of 12.0%, a reduction of area of ​​40.0%, and an impact absorption energy of 25.0 J. Compared to the mechanical properties of Examples 1-3, the titanium alloy prepared in this comparative example exhibits higher strength but extremely poor plasticity and impact toughness. Dislocation entanglement and deformation defects easily lead to brittle fracture, failing to meet the requirements for high-end load-bearing components.

[0047] Comparative Example 2 The main difference between this comparative example and Example 1 is that in step S5, the alloy sample was heated to 700°C, held at that temperature for 2 hours, and then air-cooled to room temperature. The remaining steps are the same as in Example 1. The resulting titanium alloy microstructure is shown in the figure below. Figure 5 As shown, the primary α p The phases are spheroidized, with rounded shapes and uniform distribution, and forging deformation marks are completely eliminated; the β matrix undergoes recrystallization, the grains are refined, and there is no obvious secondary α phase. s Laminar precipitation results in a weak diffusion enhancement effect.

[0048] Mechanical property testing revealed a tensile strength of 864 MPa, a yield strength of 749 MPa, an elongation after fracture of 13.6%, a reduction of area of ​​46.7%, and an impact absorption energy of 32.0 J. The titanium alloy prepared in this comparative example can eliminate processing stress, and its plasticity and toughness are slightly improved compared to the untreated forged state. However, the primary α phase is coarse, and there is no effective secondary phase reinforcement, resulting in significantly lower strength indicators. Therefore, it is only suitable for ordinary components where strength is not a requirement.

[0049] Comparative Example 3 The main difference between this comparative example and Example 1 is that in step S5, the alloy sample was heated to 940°C, held at that temperature for 2 hours, then water-quenched to room temperature, subsequently heated to 520°C, held for 6 hours, and then air-cooled to room temperature. The remaining steps are the same as in Example 1. The resulting titanium alloy microstructure is shown in the figure below. Figure 6 As shown, the equiaxed primary α p The proportion of secondary α-phosphorus is 20%~25%, with a round shape and uniform distribution; s The lamellar density is better than that of the low-temperature annealing process, and it is diffusely distributed in the β matrix. However, the lamellar density is still relatively coarse, and the proportion of primary α phase is relatively high, and no basket-like structure is formed.

[0050] Mechanical property testing revealed a tensile strength of 1000 MPa, a yield strength of 923 MPa, an elongation after fracture of 12.5%, a reduction of area of ​​48.0%, and an impact absorption energy of 34.0 J. The titanium alloy prepared in this comparative example exhibited significantly improved plasticity compared to the untreated forged state and the low-temperature annealing process, while its strength was improved somewhat by the low-temperature annealing process. However, due to the low solution temperature and excessively high proportion of primary α phase, the strength still did not meet the requirements for high-end components, and the improvement in impact toughness was limited, resulting in poor strength-toughness matching. Therefore, although the 940℃ solution-aging process can achieve high strength, its improvement in impact toughness is limited, indicating that under these process parameters, the synergistic optimization effect of strength and toughness is poor, making it difficult to meet the stringent requirements of applications demanding comprehensive mechanical properties.

[0051] Comparative Example 4 The main difference between this comparative example and Example 1 is that in step S5, the titanium alloy bar was heated to 955°C and held for 1 hour, then water-quenched to room temperature. Next, the water-quenched alloy was heated to 500°C and held for 6 hours, then air-cooled to room temperature. Mechanical property testing revealed a tensile strength of 1020 MPa, a yield strength of 905 MPa, an elongation after fracture of 13.8%, a reduction of area of ​​50%, and an impact absorption energy of 33 J.

[0052] In summary, compared with Comparative Example 3, Example 1, with a solution temperature increase of only 15°C to 955°C, not only increased the tensile strength from 1000MPa to 1032MPa, but also significantly increased the impact absorption energy from 34J to 38J, demonstrating a marked improvement in the strength-toughness match. This indicates that precisely controlling the solution temperature at a specific point of 955°C is the key to overcoming the performance bottleneck of traditional processes. Example 2 showed a 21.8% increase in impact absorption energy compared to Comparative Example 3, making it suitable for general-purpose aerospace structural components and core components of engineering machinery that require both high strength and toughness. Example 3 showed a 34.8% increase in impact absorption energy compared to Comparative Example 3, while maintaining a high level of tensile strength ≥1020MPa, completely breaking the bottleneck of the contradiction between strength and toughness. It is suitable for aerospace impact-resistant components and vulnerable parts of engineering machinery that withstand high impact loads.

Claims

1. A method for graded control of the strength and toughness of titanium alloys, characterized in that, The method includes the following steps: S1. Preparation of titanium alloy ingots; S2, High-temperature forging; heating the ingot to T β The first forging is carried out at 180℃~220℃, and then heated to T. β A second forging is performed at (80℃~120℃), followed by reheating to T. β The first billet is obtained by forging at (50℃~70℃) for the third time. All three forging processes involve repeated upsetting and drawing. After each forging, the billet is air-cooled to room temperature to obtain the first billet. S3, forging near the phase transformation point; heating the first billet to T β The material is subjected to repeated upsetting and drawing forging at ±10℃ for 1 to 2 cycles, and then water-cooled to room temperature to obtain the second billet. S4, Low-temperature forging; heating the second billet to T β - (10℃~30℃) Repeated upsetting and drawing forging 2~4 times, and air-cooled to room temperature after each forging to obtain titanium alloy billet with equiaxed α+β dual-phase structure; S5. Regulate pulse current to assist in graded heat treatment. The graded heat treatment consists of high temperature regulation and aging treatment. The target performance titanium alloy is as follows: for high strength type, the high temperature regulation temperature is 955℃±3℃ and the aging temperature is 500℃±3℃. For the robust and balanced type, the high temperature control temperature is 960℃±3℃, and the aging temperature is 520℃±3℃. For the high-toughness type, the high-temperature control temperature is 965℃±3℃, and the aging temperature is 510℃±3℃. The pulse parameters are: pulse voltage 10V~100V, pulse current density 10A / mm²~100A / mm², pulse frequency 50Hz~500Hz, and heating time 10s~300s.

2. The method for graded control of strength and toughness of titanium alloys according to claim 1, characterized in that, In step S1, the titanium alloy comprises the following elements by mass percentage: Composition: Al 6.02%–6.30%, V 4.11%–4.37%, Fe ≤0.030%, Si ≤0.015%, C ≤0.010%, H ≤0.0015%, N ≤0.005%, O 0.171%–0.190%, balance being Ti and unavoidable impurities; the β-phase transformation point T of the titanium alloy is... β The temperature ranges from 970℃ to 985℃.

3. The method for graded control of strength and toughness of titanium alloys according to claim 1, characterized in that, In step S4, the volume fraction of the primary α phase in the titanium alloy billet is 35% to 45%.

4. The method for graded control of strength and toughness of titanium alloys according to claim 1, characterized in that, In step S5, after high-temperature control and heat preservation for 0.5h to 2h, the temperature is rapidly cooled to room temperature at a cooling rate of ≥50℃ / s, and then aged and heat preservation for 4h to 8h, followed by air cooling to room temperature.

5. The method for graded control of strength and toughness of titanium alloys according to claim 1, characterized in that, In step S5, the parameters of the pulsed current-assisted graded heat treatment are selected based on the target properties of the titanium alloy as follows: High-intensity type: pulse voltage 50V~80V, pulse current density 50A / mm²~80A / mm², pulse frequency 200Hz~300Hz, heating time 30s~60s; Strong and balanced type: pulse voltage 30V~50V, pulse current density 30A / mm²~50A / mm², pulse frequency 150Hz~250Hz, heating time 60s~90s; High toughness type: pulse voltage 20V~40V, pulse current density 20A / mm²~40A / mm², pulse frequency 100Hz~200Hz, heating time 90s~120s.

6. The method for graded control of strength and toughness of titanium alloys according to claim 1, characterized in that, In step S5, the primary α phase content and secondary α lamellar width in the regulated titanium alloy microstructure satisfy the following: High-strength type: primary α phase content and secondary α lamellar width. p Phase content 15%–20%, secondary α s Average lamellar width < 0.5 μm; Strong and balanced type: nascent α p Phase content 8%–12%, secondary α s The average width of the lamellar sheets is 0.5 μm to 0.8 μm; High toughness type: primary α p Phase content ≤5%, secondary α s The average width of the sheets is 0.8 μm to 1.2 μm.

7. The method for graded control of strength and toughness of titanium alloys according to claim 1, characterized in that, The mechanical properties of the regulated titanium alloy meet the following requirements: High strength type: tensile strength ≥1030MPa, yield strength ≥910MPa, elongation after fracture ≥15%, impact absorption energy ≥35J; Strong and balanced type: tensile strength ≥1020MPa, yield strength ≥900MPa, elongation after fracture ≥15%, impact energy absorption ≥40J; High toughness type: tensile strength ≥1015MPa, yield strength ≥885MPa, elongation after fracture ≥14%, impact energy absorption ≥44J.

8. The method for graded control of the strength and toughness of titanium alloys according to claim 1, characterized in that, In step S2, the upsetting deformation amount for each forging is 45% to 50%.

Images