A heat treatment method and product for improving the dynamic properties of TA15 titanium alloy

Abstract

A heat treatment method and product for improving the dynamic properties of TA15 titanium alloy not only retains high static strength, but also overcomes the problem that the average flow stress, maximum uniform plastic strain and impact absorption energy of the alloy under traditional annealing process are difficult to meet the use requirements. The method comprises: (1) solid solution treatment: heating the TA15 titanium alloy to Tβ-20℃~60℃ at a rate of 1~6℃ / min and holding the temperature for 2h~8h; the nominal chemical composition of the TA15 titanium alloy is: Ti-6.5Al-2Zr-1Mo-1V, and the microstructure of the TA15 titanium alloy includes primary α phase, short rod / lamellar α phase, and β phase matrix; (2) slow cooling and aging treatment: cooling the alloy material after solid solution to 550~650℃ at a rate of 5~15℃ / h and then air cooling to room temperature; adopting a higher aging temperature and a longer aging time for desolvation.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy preparation, and in particular to a heat treatment method for improving the dynamic properties of TA15 titanium alloy, and a titanium alloy product manufactured according to the heat treatment method for improving the dynamic properties of TA15 titanium alloy. Background Art

[0002] Titanium alloy has the advantages of stability, light weight, corrosion resistance, and high and low temperature resistance. It is one of the most ideal materials in aerospace, weapons industry, transportation and other fields. It is widely used in the manufacture of aircraft, missiles, warheads, locomotive traction and braking systems and other components, effectively reducing weight and improving economic and safety reliability.

[0003] The nominal composition of TA15 titanium alloy is Ti-6.5Al-2Zr-1Mo-1V. It is a near-α-type titanium alloy with high Al equivalent. It has good impact resistance and is widely used in aerospace, weapons industry, transportation and other fields that are subjected to high strain rate dynamic environments. TA15 titanium alloy is usually heat treated using a conventional annealing system (750-850℃ holding time for 1-4h, air cooling). The microstructure of the alloy is finely controlled by controlling the annealing temperature and holding time to achieve a match between strength and plasticity. After conventional annealing, the TA15 titanium alloy consists of a β matrix, a primary α phase and a short rod / lamellar α phase. -3 Dynamic strength at a strain rate of / s <1500MPa, dynamic strain <0.25%, impact absorption energy <360J / cm -3 . Dynamic performance, as an important indicator for evaluating the quality of a material's resistance to high-speed impact, has received widespread attention and research. However, with the continuous development of aerospace, weapons industry, transportation and other fields, higher requirements for high strain rate impact resistance have been put forward for materials. The research and development and engineering cycle of new materials is long and the cost is high. It is impossible to complete the replacement of existing materials in a short period of time. The traditional forging process has a long trial production cycle and high cost. Therefore, there is an urgent need to propose a simple, easy and reliable method to improve the dynamic performance of titanium alloys. Summary of the Invention

[0004] In order to overcome the defects of the prior art, the technical problem to be solved by the present invention is to provide a heat treatment method for improving the dynamic properties of TA15 titanium alloy, which not only retains a high static strength, but also overcomes the problem that the average flow stress, maximum uniform plastic strain and impact absorption energy of the alloy under the traditional annealing process are difficult to meet the use requirements.

[0005] The technical solution of the present invention is: this heat treatment method for improving the dynamic properties of TA15 titanium alloy comprises the following steps:

[0006] (1) Solution treatment: Heat the TA15 titanium alloy at a rate of 1-6°C / min to

[0007] Tβ-20°C to 60°C, holding temperature for 2h to 8h; the nominal chemical composition of the TA15 titanium alloy is: Ti-6.5Al-2Zr-1Mo-1V, and the microstructure of the TA15 titanium alloy includes primary α phase, short rod / lamellar α phase, and β phase matrix;

[0008] (2) Slow cooling and aging treatment: The alloy material after solid solution is cooled in the furnace at a rate of 5-15℃ / h to 550-650℃, and then air-cooled to room temperature; a higher aging temperature and a longer aging time are used for desolvation.

[0009] The TA15 titanium alloy structure selected by the present invention is prepared by traditional two-phase zone forging and heat treatment process, and is composed of β matrix, equiaxed α phase and lamellar α phase. The equiaxed α phase in the structure is formed during the thermal deformation process, and its content is small. The lamellar α phase has a small width and a large number. The selection of the above structure can provide a basis for finely regulating the content and size of the equiaxed α phase and the lamellar α phase during subsequent heat treatment, thereby achieving the purpose of regulating the dynamic properties of the alloy; the solution treatment adopts a slow heating rate, a near-β holding temperature and a long holding time to ensure that there is enough time for the α phase to be melted back, and as the holding time of the solution treatment is extended, the concentration of α-stabilizing elements in the lamellar α phase is reduced, the β phase is wedged into the α lamella, and the straight separation of the internal grain boundaries causes the large lamella to decompose into several small lamellae. The interface of the small lamellae migrates due to diffusion, causing the surface The energy is minimized, resulting in the spheroidization of small lamellar α. The spheroidized lamellar α phase dissolves because it is smaller than the average size. As the slow cooling treatment proceeds, the lower supercooling inhibits the β→α” transformation process, allowing β to transform into more α phase. In addition, the long cooling time allows the alloy elements to diffuse more and the structure to be more uniform. At the same time, during the cooling process, the lamellar α phase that is not fractured and dissolved continues to coarsen due to Oswald ripening, thereby increasing the thickness of the secondary lamellar α, shortening the length and reducing the number. The above heat treatment ensures the precipitation of more equiaxed α phase in the alloy. The use of higher aging temperature and longer aging time promotes the dissolution process of β phase and α” phase, eliminates the ω phase, and further increases the number and grain size of the α phase, thereby increasing the coordinated deformation ability of the alloy and achieving the purpose of increasing the dynamic properties of the alloy.

[0010] Also provided is a titanium alloy material manufactured using the heat treatment method for improving the dynamic properties of the TA15 titanium alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the microscopic morphology of the TA15 titanium alloy sample prepared in Example 1 of the present invention.

[0012] Figure 2This is the microscopic morphology of the TA15 titanium alloy sample in the normal annealed state used in Example 1 of the present invention.

[0013] Figure 3 This is the microscopic morphology of the TA15 titanium alloy sample prepared in Example 2 of the present invention.

[0014] Figure 4 This is the microscopic morphology of the TA15 titanium alloy sample in the normal annealed state prepared in Example 2 of the present invention.

[0015] Figure 5 This is the microscopic morphology of the TA15 titanium alloy sample prepared in Example 3 of the present invention.

[0016] Figure 6 This is the microscopic morphology of the TA15 titanium alloy sample in the normal annealing state prepared in Example 3 of the present invention.

[0017] Figure 7 The figure is a flow chart of the heat treatment method for improving the dynamic properties of TA15 titanium alloy according to the present invention. DETAILED DESCRIPTION

[0018] like Figure 7 As shown, the heat treatment method for improving the dynamic properties of TA15 titanium alloy comprises the following steps:

[0019] (1) Solution treatment: Heat the TA15 titanium alloy at a rate of 1-6°C / min to

[0020] Tβ-20°C to 60°C, holding temperature for 2h to 8h; the nominal chemical composition of the TA15 titanium alloy is: Ti-6.5Al-2Zr-1Mo-1V, and the microstructure of the TA15 titanium alloy includes primary α phase, short rod / lamellar α phase, and β phase matrix;

[0021] (2) Slow cooling and aging treatment: The alloy material after solid solution is cooled in the furnace at a rate of 5-15℃ / h to 550-650℃, and then air-cooled to room temperature; a higher aging temperature and a longer aging time are used for desolvation.

[0022] The TA15 titanium alloy structure selected by the present invention is prepared by traditional two-phase zone forging and heat treatment process, and is composed of β matrix, equiaxed α phase and lamellar α phase. The equiaxed α phase in the structure is formed during the thermal deformation process, and its content is small. The lamellar α phase has a small width and a large number. The selection of the above structure can provide a basis for finely regulating the content and size of the equiaxed α phase and the lamellar α phase during subsequent heat treatment, thereby achieving the purpose of regulating the dynamic properties of the alloy; the solution treatment adopts a slow heating rate, a near-β holding temperature and a long holding time to ensure that there is enough time for the α phase to be melted back, and as the holding time of the solution treatment is extended, the concentration of α-stabilizing elements in the lamellar α phase is reduced, the β phase is wedged into the α lamella, and the straight separation of the internal grain boundaries causes the large lamella to decompose into several small lamellae. The interface of the small lamellae migrates due to diffusion, causing the surface The energy is minimized, resulting in the spheroidization of small lamellar α. The spheroidized lamellar α phase dissolves because it is smaller than the average size. As the slow cooling treatment proceeds, the lower supercooling inhibits the β→α” transformation process, allowing β to transform into more α phase. In addition, the long cooling time allows the alloy elements to diffuse more and the structure to be more uniform. At the same time, during the cooling process, the lamellar α phase that is not fractured and dissolved continues to coarsen due to Oswald ripening, thereby increasing the thickness of the secondary lamellar α, shortening the length and reducing the number. The above heat treatment ensures the precipitation of more equiaxed α phase in the alloy. The use of higher aging temperature and longer aging time promotes the dissolution process of β phase and α” phase, eliminates the ω phase, and further increases the number and grain size of the α phase, thereby increasing the coordinated deformation ability of the alloy and achieving the purpose of increasing the dynamic properties of the alloy.

[0023] Preferably, in the desolventizing step (2), the alloy is heated to 500-550°C at a rate of 5-10°C / min, kept at that temperature for 4-8 hours, and then air-cooled to room temperature.

[0024] Preferably, a TA15 titanium alloy hot-forged bar of Φ100mm×200mm is used, and after the β-transus temperature of the bar is determined to be 995±5°C, the alloy bar is heated to 970°C in a furnace at a rate of 5°C / min and kept warm for 3 hours in step (1); and the alloy bar is cooled in a furnace to 580°C at a cooling rate of 15°C / h and then air-cooled, and the alloy bar is heated to 540°C in a furnace at a rate of 6°C / min, kept warm for 4 hours, and then air-cooled to room temperature in step (2).

[0025] Preferably, a TA15 titanium alloy hot-forged bar of Φ200mm×300mm is used, and after the β-transus temperature of the bar is determined to be 995±5°C, the alloy bar is heated to 960°C in a furnace at a rate of 4°C / min and kept warm for 4 hours in step (1); and the alloy bar is cooled to 600°C in a furnace at a cooling rate of 13°C / h and then air-cooled in step (2), and the alloy bar is heated to 530°C in a furnace at a rate of 8°C / min, kept warm for 6 hours, and then air-cooled to room temperature in step (2).

[0026] Preferably, a TA15 titanium alloy hot-forged bar of Φ450mm×500mm is used, and after the β-transus temperature of the bar is measured to be 995±5°C, the alloy bar is heated to 950°C in a furnace at a rate of 3°C / min and kept warm for 7 hours in step (1); and the alloy bar is cooled in a furnace to 640°C at a cooling rate of 12°C / h and then air-cooled, and the alloy bar is heated to 520°C in a furnace at a rate of 8°C / min, kept warm for 8 hours, and then air-cooled to room temperature in step (2).

[0027] Preferably, after heat treatment, an equiaxed α phase with a content of ≥85%, a small amount of β matrix and a coarse short rod / lamellar secondary α phase structure are formed.

[0028] Also provided is a titanium alloy material manufactured using the heat treatment method for improving the dynamic properties of the TA15 titanium alloy.

[0029] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0030] (1) The selected TA15 titanium alloy microstructure is obtained by traditional two-phase forging and heat treatment processes and consists of a β matrix, an equiaxed α phase, and a lamellar α phase. The equiaxed α phase in the microstructure is formed during the thermal deformation process and has a small content. The lamellar α phase is small in width and has a large number. The selection of the above microstructure provides a basis for finely controlling the content and size of the equiaxed α phase and the lamellar α phase during subsequent heat treatment, thereby achieving the purpose of regulating the dynamic properties of the alloy.

[0031] (2) Compared with the traditional heat treatment system, the solid solution treatment + slow cooling and aging treatment method is adopted. The solid solution treatment adopts a slow heating rate, a near β holding temperature and a long holding time to ensure that there is enough time for the α phase to melt back. As the holding time of the solid solution treatment is prolonged, the concentration of α-stabilizing elements in the lamellar α phase decreases, the β phase is wedged into the α lamellae, and the straight separation of the internal grain boundaries causes the large lamellae to decompose into several small lamellae. Diffusion at the interfaces of the small lamellars minimizes surface energy, leading to spheroidization of the small α-phases. The spheroidized α-phases dissolve due to their smaller-than-average size. As the slow cooling treatment proceeds, the lower degree of undercooling inhibits the β→α” transformation, allowing β to transform into more α-phase. Furthermore, the longer cooling time allows for greater diffusion of alloying elements and a more uniform structure. Simultaneously, during the cooling process, the α-phases that fracture and dissolve before fracture continuously coarsen due to Oswald ripening, resulting in an increase in the thickness of the secondary α-phases, a decrease in length, and a decrease in number. The above heat treatment ensures the precipitation of more equiaxed α-phase in the alloy. The use of higher aging temperatures and longer aging times promotes the dissolution of the β- and α”-phases, eliminating the ω-phase and further increasing the amount and grain size of the α-phase, thereby enhancing the alloy's coordinated deformation capability and improving its dynamic properties.

[0032] The specific embodiments of the present invention are described in detail below.

[0033] Implementation Example 1

[0034] The hot forged TA15 titanium alloy bar with a size of Φ100mm×200mm was used. The β transformation temperature of the bar was measured to be 995±5℃. In the first step, the alloy bar was heated to 970℃ at a rate of 5℃ / min in the furnace, kept warm for 3h, then cooled to 580℃ at a cooling rate of 15℃ / h and then air-cooled; in the second step, the alloy bar was heated to 540℃ at a rate of 6℃ / min in the furnace, kept warm for 4h, then air-cooled to room temperature. After this heat treatment, Figure 1 The microstructure of the steel is composed of 85% or more equiaxed α phase, a small amount of β matrix, and coarse short rods / lamellar α phase. Its dynamic properties and room temperature tensile properties are shown in Table 1.

[0035] Comparative Example 1:

[0036] The β-transformation temperature of the hot-forged TA15 titanium alloy bar with a diameter of 100 mm × 200 mm was measured to be 995 ± 5 °C. The first step was to heat the alloy bar to 760 °C, keep it at this temperature for 4 hours, and then air-cool it to room temperature. Figure 2 The microstructure of the steel is a typical two-phase processed structure, consisting of a β matrix and an equiaxed α phase and a lamellar α phase with a content of about 23%. Its dynamic properties and room temperature tensile properties are shown in Table 1.

[0037] Table 1

[0038]

[0039] Implementation Example 2

[0040] Using Φ200mm×300mm TA15 titanium alloy hot forging bar, the β transformation temperature of the bar was measured to be 995±5℃. In the first step, the alloy bar was heated to 960℃ at a rate of 4℃ / min in the furnace, kept at this temperature for 4h, then cooled to 600℃ at a cooling rate of 13℃ / h and then air-cooled; in the second step, the alloy bar was heated to 530℃ at a rate of 8℃ / min in the furnace, kept at this temperature for 6h, then air-cooled to room temperature. After this heat treatment, Figure 3 The microstructure of the steel is composed of 85% or more equiaxed α phase, a small amount of β matrix, and coarse short rods / lamellar α phase. Its dynamic properties and room temperature tensile properties are shown in Table 2.

[0041] Comparative Example 2:

[0042] The β-transformation temperature of the hot-forged TA15 titanium alloy bar of Φ200mm×300mm was measured to be 995±5℃. The first step was to heat the alloy bar to 800℃, keep it at this temperature for 4 hours, and then air-cool it to room temperature. Figure 4The microstructure of the steel is a typical two-phase processed structure, consisting of a β matrix and an equiaxed α phase and a lamellar α phase with a content of about 20%. Its dynamic properties and room temperature tensile properties are shown in Table 2.

[0043] Table 2

[0044]

[0045] Implementation Example 3

[0046] Using Φ450mm×500mm TA15 titanium alloy hot forging bar, the β transformation temperature of the bar was measured to be 995±5℃. In the first step, the alloy bar was heated to 950℃ at a rate of 3℃ / min in the furnace, kept warm for 7h, then cooled to 640℃ at a cooling rate of 12℃ / h and then air-cooled; in the second step, the alloy bar was heated to 520℃ at a rate of 8℃ / min in the furnace, kept warm for 8h, then air-cooled to room temperature. After this heat treatment, Figure 5 The microstructure of the steel is composed of 85% or more equiaxed α phase, a small amount of β matrix, and coarse short rods / lamellar α phase. Its dynamic properties and room temperature tensile properties are shown in Table 3.

[0047] Comparative Example 3:

[0048] The β-transformation temperature of the hot-forged TA15 titanium alloy bar of Φ450mm×500mm was measured to be 995±5℃. The first step was to heat the alloy bar to 840℃, keep it at this temperature for 7h, and then air-cool it to room temperature. Figure 6 The microstructure of the steel is a typical two-phase processed structure, consisting of a β matrix and an equiaxed α phase and a lamellar α phase with a content of about 19%. Its dynamic properties and room temperature tensile properties are shown in Table 3.

[0049] Table 3

[0050]

[0051]

[0052] The titanium alloys obtained by the three embodiments of the present invention have a static room temperature tensile strength comparable to that of titanium alloys prepared by conventional heat treatment processes, but their plasticity has been greatly improved. -3 At the same strain rate, the dynamic plastic strain increased from 0.20% to more than 0.27%, the dynamic flow stress increased from 1485MPa to more than 1580MPa, and the dynamic absorbed energy increased from 330J / cm -3 Increased to 410J / cm -3 The above provides a new heat treatment method for aerospace, weapons industry, transportation and other fields that are subjected to high strain rate dynamic environments.

[0053] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of protection of the technical solution of the present invention.

Claims

1. A heat treatment method for improving the dynamic properties of TA15 titanium alloy, characterized by: It includes the following steps: (1) Solution treatment: heating the TA15 titanium alloy to Tβ- (20°C~60°C) at a rate of 1~6°C / min and holding the temperature for 2h~8h; the nominal chemical composition of the TA15 titanium alloy is: Ti-6.5Al-2Zr-1Mo-1V, and the microstructure of the TA15 titanium alloy includes primary α phase, short rod / lamellar α phase, and β phase matrix; (2) Slow cooling and aging treatment: The alloy material after solid solution is cooled in the furnace at a rate of 5-15℃ / h to 550-650℃, and then air-cooled to room temperature; The following aging temperature and aging time are used for precipitation: the alloy is heated to 500-550°C at a rate of 5-10°C / min, kept at this temperature for 4-8 hours, and then air-cooled to room temperature.

2. The heat treatment method for improving the dynamic properties of TA15 titanium alloy according to claim 1, characterized in that: A 100 mm × 200 mm TA15 titanium alloy hot-forged bar is used. After the β-transus temperature of the bar is determined to be 995±5°C, the alloy bar is heated to 970°C in a furnace at a rate of 5°C / min and kept warm for 3 hours in the step (1); and the alloy bar is cooled to 580°C in a furnace at a cooling rate of 15°C / h and then air-cooled, and the alloy bar is heated to 540°C in a furnace at a rate of 6°C / min, kept warm for 4 hours, and then air-cooled to room temperature in the step (2).

3. The heat treatment method for improving the dynamic properties of TA15 titanium alloy according to claim 1, characterized in that: A 200 mm × 300 mm TA15 titanium alloy hot-forged bar is used. After the β-transus temperature of the bar is measured to be 995±5°C, the step (1) heats the alloy bar to 960°C in a furnace at a rate of 4°C / min and keeps it warm for 4 hours. The step (2) cools the alloy bar to 600°C in a furnace at a cooling rate of 13°C / h and then air cools it. The alloy bar is heated to 530°C in a furnace at a rate of 8°C / min, keeps it warm for 6 hours, and then air cools it to room temperature.

4. The heat treatment method for improving the dynamic properties of TA15 titanium alloy according to claim 1, characterized in that: A TA15 titanium alloy hot-forged bar of Φ450mm×500mm is used. After the β-transformation temperature of the bar is measured to be 995±5°C, the alloy bar is heated to 950°C in a furnace at a rate of 3°C / min and kept warm for 7h in the step (1); and the alloy bar is cooled to 640°C in a furnace at a cooling rate of 12°C / h and then air-cooled in the step (2). The alloy bar is heated to 520°C in a furnace at a rate of 8°C / min, kept warm for 8h, and then air-cooled to room temperature in the step (2).

5. The heat treatment method for improving the dynamic properties of TA15 titanium alloy according to any one of claims 1 to 4, characterized in that: After heat treatment, an equiaxed α phase with a content of ≥85%, a small amount of β matrix and coarse short rod / lamellar secondary α phase structure are formed.

6. Titanium alloy material manufactured according to the heat treatment method for improving the dynamic properties of TA15 titanium alloy according to any one of claims 1 to 4.

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