Ti55531 high-strength titanium alloy and heat treatment method thereof

Abstract

This invention relates to the field of titanium alloy heat treatment technology, and discloses a heat treatment method for Ti55531 high-strength titanium alloy, comprising: placing the Ti55531 titanium alloy billet in a first temperature range for a first stage of heat treatment; heating to a second temperature range at a set rate for a second stage of heat treatment; cooling to a third temperature range at a set cooling rate for a third stage of heat treatment; heating to a fourth temperature range at a set rate for a fourth stage of heat treatment, followed by air cooling; wherein, the first temperature range is a temperature below the β phase transformation point, the second temperature range is a temperature above the β phase transformation point, and the third temperature range is a temperature below the β phase transformation point. The method of this invention significantly improves the strength and toughness balance of Ti55531 titanium alloy through an innovative multi-stage heat treatment process of "preheating homogenization → ultra-high temperature solution treatment → controlled cooling precipitation → rapid aging".

Description

Technical Field

[0001] This invention relates to the field of titanium alloy heat treatment technology, and in particular to a heat treatment method for Ti55531 high-strength titanium alloy. Background Technology

[0002] Titanium alloys, as a lightweight metal material, possess excellent comprehensive properties such as high specific strength, corrosion resistance, non-magnetic properties, and weldability, making them a key structural component material in the current aerospace field. High-strength titanium alloys generally refer to titanium alloys with a tensile strength of over 1000 MPa, such as TC18, Ti1023, and Ti55531, which are widely used in critical load-bearing components of aircraft.

[0003] Ti55531 high-strength titanium alloy, with its excellent specific strength, corrosion resistance, and structural stability, has become a core material for critical components such as landing gear and load-bearing structures in the aerospace field. The industry's requirements for the synergistic matching of strength and toughness are continuously increasing. Currently, Ti55531 titanium alloys are generally treated with conventional solution-aging heat treatment. While this process can achieve high strength levels, it easily leads to problems such as poor microstructure uniformity and continuous coarse α-phase at grain boundaries. When the tensile strength is ≥1300MPa, the impact toughness decreases significantly, making it difficult to meet the high safety and reliability requirements of aerospace components. Existing technologies improve performance through a composite process of "plastic deformation + heat treatment," requiring additional forging and cold deformation processes. This is not only cumbersome and costly, but also prone to fluctuations in the microstructure and properties of large-diameter bars, limiting industrial applications. Furthermore, existing heat treatment schemes lack segmented temperature control and cooling regimes suitable for Ti55531, making it impossible to achieve simultaneous optimization of strength and toughness without plastic deformation.

[0004] Therefore, there is a need to improve the heat treatment method for Ti55531 high-strength titanium alloy in the existing technology. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a heat treatment method for Ti55531 high-strength titanium alloy, which significantly improves impact toughness while ensuring high strength, and solves the problem of difficulty in achieving a balance between strength and toughness in existing processes.

[0006] To achieve the above objectives, this invention provides a heat treatment method for Ti55531 high-strength titanium alloy, comprising the following steps: S1 places the Ti55531 titanium alloy billet in the first temperature range for the first stage of heat preservation. S2 heats up to the second temperature range at a set heating rate for the second stage of heat preservation. S3 cools down to the third temperature range at a set cooling rate and performs the third stage of heat preservation. After the third stage of heat preservation in S4, the temperature is increased to the fourth temperature range at a set rate for the fourth stage of heat preservation, followed by air cooling. The first temperature range is the temperature below the β phase transition point, the second temperature range is the temperature above the β phase transition point, and the third temperature range is the temperature below the β phase transition point.

[0007] In some implementations, in S1, the first temperature range is β-(5~10)℃, and the first stage heat preservation time is 2h~3h.

[0008] In some embodiments, in S2, the heating rate is set to 10℃ / min~15℃ / min, the second temperature range is β+(30~70)℃, and the second stage holding time is determined according to the workpiece thickness.

[0009] In some implementations, the second-stage heat preservation time is 2 to 3 hours.

[0010] In some implementations, in S3, the cooling rate is set to 1℃ / min~2℃ / min, the third temperature range is 400℃~500℃, and the third stage heat preservation time is 2h~4h.

[0011] In some implementations, in S4, the fourth temperature range is 580°C to 650°C, and the fourth stage heat preservation time is 8h to 10h.

[0012] In some implementations, the heating rate in S4 is ≥10°C / min.

[0013] In some embodiments, the heat treatment process is carried out under a vacuum or inert gas protective atmosphere.

[0014] In some embodiments, the Ti55531 titanium alloy billet is a titanium alloy bar with a diameter of Φ200mm~Φ300mm.

[0015] In another aspect, the present invention provides a high-strength and high-toughness Ti55531 titanium alloy material prepared by the above method.

[0016] The present invention has at least the following beneficial technical effects: This invention significantly improves the strength and toughness balance of Ti55531 titanium alloy through an innovative multi-stage heat treatment process: preheating homogenization, ultra-high temperature solution treatment, controlled cooling precipitation, and rapid aging. The key technological breakthrough lies in: precisely controlling the ultra-high temperature solution treatment above the β phase transformation point and the slow controlled cooling rate to promote uniform solution of alloying elements and dispersed distribution of fine precipitates; combined with rapid heating and aging to suppress grain coarsening, achieving microstructure refinement and stress optimization. The resulting alloy maintains a tensile strength ≥1300MPa while maintaining an impact energy ≥20J, overcoming the bottleneck of traditional processes where strength and toughness are difficult to achieve simultaneously. This process, by optimizing the temperature range and heating / cooling rates, shortens the production cycle and improves efficiency, combining industrial feasibility and cost advantages. It provides titanium alloy materials with both ultra-high strength and excellent toughness for high-precision fields such as aerospace and energy, meeting the stringent performance requirements under extreme conditions and significantly expanding the engineering application boundaries of titanium alloys. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of an embodiment of a heat treatment method for Ti55531 high-strength titanium alloy provided by the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0020] The terms "comprising" and "having," and any variations thereof, used in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion; the terms "first," "second," etc., used in the specification, claims, and accompanying drawings are used to distinguish different objects, not to describe a particular order. "A plurality of" means two or more, unless otherwise explicitly specified.

[0021] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase 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.

[0022] like Figure 1 The above describes a heat treatment method for Ti55531 high-strength titanium alloy provided by the present invention, comprising the following steps: S1 places the Ti55531 titanium alloy billet in the first temperature range for the first stage of heat preservation. S2 heats up to the second temperature range at a set heating rate for the second stage of heat preservation. S3 cools down to the third temperature range at a set cooling rate and performs the third stage of heat preservation. After the third stage of heat preservation in S4, the temperature is increased to the fourth temperature range at a set rate for the fourth stage of heat preservation, followed by air cooling. The first temperature range is the temperature below the β phase transition point, the second temperature range is the temperature above the β phase transition point, and the third temperature range is the temperature below the β phase transition point.

[0023] Furthermore, in step S1, the first temperature range is β - (5~10)℃, and the first stage holding time is 2h~3h. In the heat treatment method of the present invention, the temperature of step S1 is controlled within the range of 5℃~10℃ below the β phase transformation point (i.e., β - (5~10)℃), combined with a holding time of 2h~3h, which has a significant preheating and microstructure homogenization effect. This temperature range is located at the high-temperature end of the (α+β) two-phase region, which can avoid the risk of grain coarsening caused by excessive temperature, and can also fully homogenize the internal microstructure of the alloy through long-term holding. Compared with direct cold furnace charging or preheating at higher temperatures, this parameter range can effectively eliminate residual stress inside the billet and provide a stable microstructure basis for subsequent rapid heating and ultra-high temperature solid solution, ensuring the consistency of the final product performance.

[0024] Further, in S2, the heating rate is set to 10℃ / min~15℃ / min, the second temperature range is β+(30~70)℃, and the second stage holding time is determined according to the workpiece thickness. In some preferred embodiments, the second stage holding time is 2h~3h. The heating rate of 10℃ / min~15℃ / min and the second temperature range of β+(30~70)℃ are defined in this step. Rapid heating can shorten the residence time of the billet in the intermediate temperature zone and minimize the time the sample stays above the β phase transformation point. Setting the temperature in the range of 30℃~70℃ above the β phase transformation point can promote the full solid solution of a large number of alloying elements (such as Mo, V, etc.) into the β matrix, significantly improving the stability of the β phase. Combined with the holding time of 2h~3h, it ensures that the α phase is completely transformed into the β phase. At the same time, it does not cause abnormal grain growth due to excessive temperature, laying a solid foundation for subsequent toughening.

[0025] Furthermore, in S3, the cooling rate is set to 1℃ / min~2℃ / min, the third temperature range is 400℃~500℃, and the holding time in the third stage is 2h~4h. In this step, cooling to 400℃~500℃ at a controlled rate of 1℃ / min~2℃ / min and holding at that temperature serves a dual purpose of "microstructure regulation and stress buffering." Compared to direct quenching or furnace cooling, this specific slow cooling rate guides the α phase to precipitate in the β matrix in a specific morphology (such as fine lamellar or needle-like structures), forming a diffusely distributed primary α phase lamellar layer with a certain thickness. This ensures high strength while retaining a certain degree of ductility and toughness. Simultaneously, this process effectively releases the thermal and microstructural stresses generated by rapid heating in stage S2, preventing workpiece deformation or cracking. Holding the material at 400℃~500℃ for 2h~4h creates conditions for the formation of the ω phase. The ω phase will decompose into the β phase and fine lamellar or needle-like α phase during the subsequent aging process. Together with the primary α phase lamellar with a certain thickness and the lamellar α phase precipitated from the β matrix during the aging process, they form a multi-scale structure, which synergistically optimizes the material's strength and toughness.

[0026] Furthermore, in S4, the fourth temperature range is 580℃~650℃, and the fourth stage holding time is 8h~10h. The heating rate is ≥10℃ / min. The aging temperature range of 580℃~650℃ and the holding time of 8h~10h in this step represent the "peak aging" window for achieving the best match between strength and plasticity of Ti55531 titanium alloy. Within this temperature range, the secondary α phase precipitated in the β matrix is ​​of moderate size and sufficient quantity, preventing a sharp decrease in plasticity due to excessive or large precipitates; the ω phase also decomposes into the β phase and fine lamellar α phase, further strengthening the material. The long holding time (8~10 hours) ensures sufficient growth of the precipitates and stability of the interfacial energy, achieving a perfect balance of strength, plasticity, and toughness. This parameter combination allows the alloy to maintain an impact energy above 20J while achieving a tensile strength greater than 1300MPa, fully verifying its excellent comprehensive mechanical properties.

[0027] Furthermore, all heat treatment processes are conducted under a vacuum or inert gas protective atmosphere. The primary purpose of limiting the heat treatment process to a vacuum or inert gas (such as argon) protective atmosphere is to prevent surface contamination of the titanium alloy at high temperatures. Titanium is chemically reactive and readily reacts with oxygen, nitrogen, and hydrogen in the air at high temperatures, forming a brittle surface layer, leading to a decrease in material surface quality and deterioration of fatigue performance. Using a vacuum or inert gas protection effectively isolates reactive gases, ensuring the surface finish and compositional purity of the workpiece, preventing surface oxygen embrittlement, and thus ensuring the reliability and long service life of high-strength titanium alloy components during actual service. This is particularly suitable for critical aerospace components with extremely high surface quality requirements.

[0028] Furthermore, the Ti55531 titanium alloy billet is a titanium alloy bar with a diameter of Φ200mm~Φ300mm.

[0029] In another aspect, the present invention provides a high-strength and high-toughness Ti55531 titanium alloy material prepared by the above method.

[0030] The present invention will be further explained below with reference to specific embodiments. The raw material used in the embodiments is a Ф200mm Ti55531 titanium alloy bar with a phase transformation point of 845℃. Before heat treatment, the bar is sawn into blanks of the corresponding size according to the processing requirements of tensile and impact test specimens. The heat treatment process includes the following steps; Step 1: After the furnace temperature is raised to β-(5~10)℃, load the furnace and keep it at that temperature for 2~3 hours.

[0031] ② Step 2: After step 1 is completed, immediately heat up to β+(30~70)℃ at a heating rate of 10~15℃ / min, then cool down to 400~500℃ at a cooling rate of 1~2℃ / min, and keep warm for 2~4 hours.

[0032] ③ Step 3: After step 2, heat the temperature to 580~650℃ at a rate of ≥10℃ / min, hold for 8~10 hours, and then air cool.

[0033] After heat treatment, the specimens are processed into test pieces for tensile and impact testing, and then the impact and tensile properties are tested.

[0034] Example 1 Step 1: After the furnace temperature is raised to 835℃, load the furnace and keep it at that temperature for 2 hours.

[0035] Step 2: Heat to 875℃ at a heating rate of 10℃ / min, then cool to 400℃ at a cooling rate of 2℃ / min, and hold for 3 hours.

[0036] Step 3: Heat to 580℃ at a rate of 10℃ / min, hold for 10 hours, and then air cool.

[0037] Example 2 Step 1: After the furnace temperature is raised to 835℃, load the furnace and keep it at that temperature for 2 hours.

[0038] Step 2: Heat to 895℃ at a heating rate of 10℃ / min, then cool to 400℃ at a cooling rate of 2℃ / min, and hold for 3 hours.

[0039] Step 3: Heat to 580℃ at a rate of 10℃ / min, hold for 10 hours, and then air cool.

[0040] Example 3 Step 1: After the furnace temperature is raised to 835℃, load the furnace and keep it at that temperature for 2 hours.

[0041] Step 2: Heat to 915℃ at a heating rate of 10℃ / min, then cool to 400℃ at a cooling rate of 2℃ / min, and hold for 3 hours.

[0042] Step 3: Heat to 580℃ at a rate of 10℃ / min, hold for 10 hours, and then air cool.

[0043] Example 4 Step 1: After the furnace temperature is raised to 835℃, load the furnace and keep it at that temperature for 2 hours.

[0044] Step 2: Heat to 895℃ at a heating rate of 10℃ / min, then cool to 400℃ at a cooling rate of 2℃ / min, and hold for 3 hours.

[0045] Step 3: Heat to 620℃ at a rate of 10℃ / min, hold for 10 hours, and then air cool.

[0046] Example 5 Step 1: After the furnace temperature is raised to 835℃, load the furnace and keep it at that temperature for 2 hours.

[0047] Step 2: Heat to 895℃ at a heating rate of 10℃ / min, then cool to 400℃ at a cooling rate of 2℃ / min, and hold for 3 hours.

[0048] Step 3: Heat to 650℃ at a rate of 10℃ / min, hold for 10 hours, and then air cool.

[0049] Comparative Example 1 The comparative example uses the current conventional β-annealing heat treatment process for Ti55531.

[0050] Step 1: After the furnace temperature is raised to 860℃, load the furnace and keep it at that temperature for 2 hours.

[0051] Step 2: Furnace cool to 600℃ at 2℃ / min, hold for 8 hours, then air cool.

[0052] Comparative Example 2 The comparative example uses the current conventional β-annealing heat treatment process for Ti55531.

[0053] Step 1: After the furnace temperature is raised to 860℃, load the furnace and keep it at that temperature for 2 hours.

[0054] Step 2: Furnace cool to 650℃ at 2℃ / min, hold for 8 hours, then air cool.

[0055] As can be seen from Table 1, compared with conventional heat treatment, the heat treatment technology in this invention patent can achieve an impact energy of over 20J while ensuring a tensile strength greater than 1300MPa.

[0056] Table 1. Tensile and impact properties at room temperature

[0057] As can be seen from the data in Table 1, using the process of the present invention (Examples 1-5), while ensuring a high strength level of tensile strength greater than 1300 MPa, the impact energy generally reaches over 20 J, with a maximum of 28.7 J. This indicates that the present invention has successfully solved the technical problem of high-strength titanium alloys being brittle despite their high strength.

[0058] Although the strength of Comparative Example 1 (conventional process) is similar, its impact toughness fluctuates significantly, reaching a minimum of only 15.0 J, and its elongation (6.5%) is significantly lower than that of the embodiment of the present invention. The present invention significantly improves the comprehensive mechanical properties of the material, particularly its fracture toughness, through multiple heat treatment processes.

[0059] Examples 1-5 cover a wide range of parameters in the claims, such as solution temperature of 875~915℃ and aging temperature of 580~650℃. All examples have achieved excellent performance, proving that the present invention has a wide process window, good repeatability, and is easy to implement in industrial applications.

[0060] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0061] It should be understood that, as used herein, unless the context clearly supports an exception. It should also be understood that, as used herein, "and / or" means any and all possible combinations of one or more of the associated listed items.

[0062] The embodiment numbers disclosed in the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0063] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A heat treatment method for Ti55531 high-strength titanium alloy, characterized in that, include: S1 places the Ti55531 titanium alloy billet in the first temperature range for the first stage of heat preservation. S2 heats up to the second temperature range at a set heating rate for the second stage of heat preservation. S3 cools down to the third temperature range at a set cooling rate and performs the third stage of heat preservation. After the third stage of heat preservation in S4, the temperature is increased to the fourth temperature range at a set rate for the fourth stage of heat preservation, followed by air cooling. The first temperature range is the temperature below the β phase transition point, the second temperature range is the temperature above the β phase transition point, and the third temperature range is the temperature below the β phase transition point.

2. The heat treatment method for Ti55531 high-strength titanium alloy according to claim 1, characterized in that, In S1, the first temperature range is β-(5~10)℃, and the first stage heat preservation time is 2h~3h.

3. The heat treatment method for Ti55531 high-strength titanium alloy according to claim 1, characterized in that, In S2, the set heating rate is 10℃ / min~15℃ / min, the second temperature range is β+(30~70)℃, and the second stage holding time is determined according to the workpiece thickness.

4. The heat treatment method for Ti55531 high-strength titanium alloy according to claim 3, characterized in that, The second stage of heat preservation time is 2 to 3 hours.

5. The heat treatment method for Ti55531 high-strength titanium alloy according to claim 1, characterized in that, In S3, the set cooling rate is 1℃ / min to 2℃ / min, the third temperature range is 400℃ to 500℃, and the third stage heat preservation time is 2h to 4h.

6. The heat treatment method for Ti55531 high-strength titanium alloy according to claim 1, characterized in that, In S4, the fourth temperature range is 580℃~650℃, and the fourth stage heat preservation time is 8h~10h.

7. The heat treatment method for Ti55531 high-strength titanium alloy according to claim 1, characterized in that, In S4, the heating rate is ≥10℃ / min.

8. The heat treatment method for Ti55531 high-strength titanium alloy according to claim 1, characterized in that, All heat treatment processes are carried out under a vacuum or inert gas protective atmosphere.

9. The heat treatment method for Ti55531 high-strength titanium alloy according to claim 1, characterized in that, The Ti55531 titanium alloy billet is a titanium alloy bar with a diameter of Φ200mm~Φ300mm.

10. A high-strength and high-toughness Ti55531 titanium alloy material prepared by the method according to any one of claims 1 to 9.

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