A heat treatment method for regulating alpha+beta dual-phase structure and silicide precipitation in TC5751S titanium alloy

Abstract

The application discloses a heat treatment method for regulating alpha+beta dual-phase structure and silicide precipitation in TC5751S titanium alloy. β -45℃—T β -15℃ holding treatment and rapid cooling at a speed of 200-500 DEG C / s, while retaining a certain volume fraction of equiaxed primary alpha phase, the metastable beta matrix in the alloy will occur stress-induced alpha'' martensite phase transition when being stretched at room temperature, and double yield phenomenon occurs, at this time, the plastic deformation mechanism of the alloy is a multiple deformation mechanism formed by the combined action of phase transition induced plastic deformation and dislocation slip; the precipitated silicides are small and uniform, can significantly improve the strength of the alloy by pinning dislocations and have less influence on plasticity, and the heat treatment method makes the TC5751S titanium alloy realize synchronous improvement of strength and plasticity through the multiple deformation mechanism of the combined action of phase transition induced plastic deformation and dislocation slip and the precipitation strengthening effect of silicides when being stretched at room temperature, the tensile strength reaches 1255±11 MPa, the elongation reaches 21.7±1.3%, and the strength-plasticity product is not less than 25.3 GPa·%.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy heat treatment technology, specifically relating to a heat treatment method for regulating α+β dual-phase microstructure and silicide precipitation in TC5751S titanium alloy. Background Technology

[0002] In the development of modern weaponry, the requirements for material performance are becoming increasingly stringent. Traditional alloy steels, due to their insufficient corrosion resistance and high density, are inadequate in meeting the needs of high mobility and adapting to extreme environments, making them unsuitable for the development of intelligent combat platforms. In stark contrast, titanium alloys, with their outstanding high strength and low density, coupled with excellent corrosion resistance and low coefficient of thermal expansion, are hailed as the "metal of the 21st century" and have been widely used in many key industries such as aviation, aerospace, marine, and chemical engineering.

[0003] As the titanium alloy with the best comprehensive mechanical properties, the plastic deformation mechanism of α+β dual-phase titanium alloy has always been a key research focus for materials scientists. For α+β dual-phase titanium alloy, the main deformation mechanism during tensile testing of samples obtained under different heat treatment methods is stress-induced α'' martensitic phase transformation-induced plasticity and dislocation slip. However, as dislocations continue to slip, they intersect and entangle with each other, forming dislocation pile-ups, which continuously increases the resistance to dislocation movement. During continuous deformation, increasingly higher stresses are required for dislocations to continue slipping, and eventually, the material may fracture due to excessive stress. Silicides, as common trace elements in titanium alloys, can improve the strength of the alloy by pinning dislocations, but excessively large silicides can cause a decrease in the alloy's plasticity.

[0004] The novel alloy TC5751S is a high-strength, high-impact-toughness α+β dual-phase titanium alloy. However, there are currently no reports on how to simultaneously improve its plasticity and strength by controlling its internal structure. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention proposes a heat treatment method to regulate the microstructure of TC5751S titanium alloy by controlling the α+β dual-phase microstructure and silicide precipitation. This method allows the alloy to retain a certain volume fraction of equiaxed primary α phase and silicides, while the β phase can induce stress-induced α'' martensitic phase transformation during room temperature stretching. By controlling multiple deformation mechanisms and phase precipitation behavior, the strength and plasticity of TC5751S titanium alloy are simultaneously improved. This allows the heat-treated TC5751S titanium alloy forging bar to simultaneously improve the strength and plasticity of the material during room temperature stretching through phase transformation-induced plastic deformation, dislocation slip deformation mechanisms, and silicide precipitation strengthening effects, achieving a good balance between strength and plasticity.

[0006] To achieve the above-mentioned objective, this invention provides a heat treatment method for regulating the α+β dual-phase microstructure and silicide precipitation in TC5751S titanium alloy, the heat treatment method comprising the following steps: Step 1: Solution heat treatment; heat the heat treatment furnace to T. β -45℃~T β The TC5751S titanium alloy bar was placed in a heat treatment furnace at a constant temperature of -15℃ for a period of time; the nominal composition of the TC5751S titanium alloy is Ti-5Al-7.5V-0.5Mo-0.5Zr-0.5Si-0.25Fe-0.16O; the T β The β-phase transformation temperature of the TC5751S titanium alloy; Step 2: Cooling treatment; The TC5751S titanium alloy bar after solution heat treatment is removed from the heat treatment furnace and placed in a cooling medium, cooled to room temperature at a rate of 200-500℃ / s. The microstructure formed in the TC5751S titanium alloy consists of primary α phase, β transformation structure and silicide; the average size of the long axis of the primary α phase is 3.88-5.0μm; the average size of the short axis of the primary α phase is 2.53-2.99μm; the volume fraction of the primary α phase is 12%-14%; the volume fraction of the β transformation structure is 86%-88%; and the average size of the silicide is 235-283μm.

[0007] Furthermore, the TC5751S titanium alloy bar is obtained by two-stage forging in the β single-phase region and two-stage forging in the α+β two-phase region.

[0008] Furthermore, the heat preservation time mentioned in step one is ≥30 minutes.

[0009] Furthermore, the heat treatment furnace mentioned in step one is a box-type resistance furnace, the furnace atmosphere is air, and the heating rate of the heat treatment furnace is 10℃ / min.

[0010] Furthermore, the cooling medium mentioned in step two is water.

[0011] Furthermore, in step two, the interval between removing the TC5751S titanium alloy bar from the heat treatment furnace and placing it in the cooling medium shall not exceed 30 seconds.

[0012] Compared with the prior art, the present invention has the following beneficial technical effects: This invention involves T-processing of TC5751S titanium alloy forging rods. β -45℃—T βThe alloy is heat-treated at -15℃ and then rapidly cooled at a rate of 200-500℃ / s. While retaining a certain volume fraction of equiaxed primary α phase, the metastable β matrix in the alloy undergoes stress-induced α'' martensitic phase transformation during room temperature stretching, resulting in double yielding. At this time, the plastic deformation mechanism of the alloy is a multiple deformation mechanism formed by the combined action of phase transformation-induced plastic deformation and dislocation slip. Meanwhile, the silicides precipitated in the alloy during this heat treatment process are fine and uniform, which can significantly improve the strength of the alloy by pinning dislocations with little impact on plasticity.

[0013] The heat treatment method of this invention has successfully enabled TC5751S titanium alloy to achieve a tensile strength of 1255±11MPa and an elongation of 21.7±1.3% at room temperature, with a strength-ductility product of not less than 25.3GPa·; the method of this invention simultaneously improves the strength and ductility of the alloy, with simple steps, convenient operation, easy control of process parameters, and good repeatability. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings of the embodiments will be briefly described below. It should be understood that the drawings described below only relate to some embodiments of this disclosure and are not intended to limit this disclosure, wherein: Figure 1 This is a SEM image of the microstructure of the TC5751S titanium alloy provided in Embodiment 1 of the present invention.

[0015] Figure 2 This is a SEM image of the microstructure of the TC5751S titanium alloy provided in Comparative Example 1 of this invention.

[0016] Figure 3 This is a SEM image of the microstructure of the TC5751S titanium alloy provided in Comparative Example 2 of this invention.

[0017] Figure 4 This is a comparison chart of the room temperature tensile properties provided in Embodiment 1 and Comparative Examples 1-2 of the present invention.

[0018] Figure 5 This is the strain hardening rate curve of TC5751S titanium alloy provided in Embodiment 1 of the present invention. Detailed Implementation

[0019] 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.

[0020] 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 meanings consistent with their meanings 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.

[0021] 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.

[0022] This invention provides a heat treatment method for regulating the α+β dual-phase microstructure and silicide precipitation in TC5751S titanium alloy, comprising the following steps: Step 1: Solution heat treatment; the heat treatment furnace is heated at a rate of 10℃ / min, preferably to T. β -45℃~T β -15℃, for example, can be T β -45℃, T β -40℃, T β -35℃, T β -25℃, T β The TC5751S titanium alloy bar was placed in a heat treatment furnace at -15℃ and kept constant for at least 30 minutes; among which, T β The β-phase transformation temperature of TC5751S titanium alloy; In some embodiments of the present invention, the heat treatment furnace is preferably a box-type resistance furnace, and the furnace atmosphere is air.

[0023] Step 2: Cooling treatment; Remove the TC5751S titanium alloy bar after solution heat treatment from the heat treatment furnace and quickly place it in a cooling medium, preferably at a rate of 200-500℃ / s to room temperature. For example, the cooling rate can be 200℃ / s, 250℃ / s, 300℃ / s, 350℃ / s, 400℃ / s, 450℃ / s, or 500℃ / s.

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Example 1 The nominal composition of the TC5751S titanium alloy used in this embodiment is Ti-5Al-7.5V-0.5Mo-0.5Zr-0.5Si-0.25Fe-0.16O. The TC5751S titanium alloy bar obtained by two-stage forging in the β single-phase region and two-stage forging in the α+β two-phase region is selected as the raw material. Its β transformation point is measured to be 910℃ by metallographic method.

[0026] The specific steps are as follows: Step 1: Heat the heat treatment furnace to 30°C below the β transformation point of TC5751S titanium alloy material, i.e., 880°C.

[0027] Step 2: After the furnace temperature of the heat treatment furnace has stabilized, place the TC5751S titanium alloy material into the furnace and hold it at that temperature for 30 minutes for solution treatment.

[0028] Step 3: Remove the solution-treated TC5751S titanium alloy material from the heat treatment furnace and quickly immerse it in water to cool it rapidly at a rate of 200-500℃ / s.

[0029] The microstructure obtained had an average major axis size of 4.27 μm, an average minor axis size of 2.59 μm, a primary α phase volume fraction of 13.2%, and a β-transformation tissue volume fraction of 86.8%. Furthermore, precipitates with an average size of 235 nm were observed to be uniformly dispersed throughout the field of view. The microstructure results are attached. Figure 1 As shown.

[0030] The aforementioned heat treatment furnace is a box-type resistance furnace with an air atmosphere in the furnace chamber; during the cooling process, the interval between removing the TC5751S titanium alloy material from the furnace chamber and placing it into the cooling medium shall not exceed 30 seconds.

[0031] The gauge length of the tensile test specimen for mechanical property testing is 8 mm, the width is 2 mm, and the thickness is 1.5 mm. The stress-strain curve after room temperature tensile testing is attached. Figure 4 As shown in the attached figure, the strain hardening rate curve is as follows. Figure 5 As shown.

[0032] Appendix Figure 4 The medium curve exhibits a double yield phenomenon, with a tensile strength reaching 1244 MPa, an elongation of 22.6%, and a strength-ductility product of 28.1 GPa·%, demonstrating good strength-ductility matching. (See attached image) Figure 4The heat treatment curve exhibited three stages: the work hardening rate decreased rapidly in the first stage, increased to its maximum during plastic deformation in the second stage, and finally decreased to failure in the third stage. The peak work hardening rate reached 10.2 GPa, indicating that stress-induced α'' martensitic phase transformation occurred during this process. This means that the plastic deformation mechanism at this temperature includes not only dislocation slip within the equiaxed primary α phase but also phase transformation-induced plastic deformation. The silicides precipitated in the alloy microstructure are small in size and relatively uniformly distributed. While pinning dislocations and improving material strength, they also prevent the deterioration of plasticity caused by larger silicides. Therefore, this heat treatment method can simultaneously improve the strength and plasticity of TC5751S titanium alloy by controlling the α+β dual-phase microstructure and silicide precipitation, and regulating multiple deformation mechanisms and silicide precipitation behavior.

[0033] Example 2 The raw materials used are the same as in Example 1, and the specific steps are as follows: Step 1: Heat the heat treatment furnace to 15°C below the β transformation point of TC5751S titanium alloy material, i.e., 895°C.

[0034] Step 2: After the furnace temperature of the heat treatment furnace has stabilized, place the TC5751S titanium alloy material into the furnace and hold it at that temperature for 30 minutes for solution treatment.

[0035] Step 3: Remove the solution-treated TC5751S titanium alloy material from the heat treatment furnace and quickly immerse it in water to cool it rapidly at a rate of 200-500℃ / s.

[0036] The microstructure obtained had an average major axis size of 4.06 μm, an average minor axis size of 2.79 μm, a primary α phase volume fraction of 12.0%, and a β-transformation tissue volume fraction of 88%. Furthermore, precipitates with an average size of 265 nm were observed to be diffusely and uniformly distributed within the field of view.

[0037] The aforementioned heat treatment furnace is a box-type resistance furnace with an air atmosphere in the furnace chamber; during the cooling process, the interval between removing the TC5751S titanium alloy material from the furnace chamber and placing it into the cooling medium shall not exceed 30 seconds.

[0038] The tensile test specimens for mechanical property testing had a gauge length of 8 mm, a width of 2 mm, and a thickness of 1.5 mm. The curves showed a double yield phenomenon, with a tensile strength of 1247 MPa, an elongation of 21.3%, and a strength-ductility product of 26.5 GPa·%, indicating good strength-ductility matching.

[0039] Comparative Example 1 The raw materials used are the same as in Example 1, and the specific steps are as follows: Step 1: Heat the heat treatment furnace to 760°C, which is 150°C below the β transformation point of the TC5751S titanium alloy material.

[0040] Step 2: After the furnace temperature of the heat treatment furnace has stabilized, place the TC5751S titanium alloy material into the furnace and hold it at that temperature for 30 minutes for solution treatment.

[0041] Step 3: Remove the solution-treated TC5751S titanium alloy material from the heat treatment furnace and quickly place it in a cooling medium to cool it rapidly at a rate of 250℃ / s.

[0042] The microstructure obtained had an average major axis size of 7.39 μm, an average minor axis size of 5.03 μm, a primary α phase volume fraction of 79.3%, and a β-transformation volume fraction of 21.7%. Furthermore, it was observed that silicides with an average size of 394 nm were abundant, large in size, and unevenly distributed near the phase boundaries. The microstructure results are shown in the attached figure. Figure 2 As shown.

[0043] The aforementioned heat treatment furnace is an electric resistance furnace with an air atmosphere in the furnace chamber; during the cooling process, the interval between removing the TC5751S titanium alloy material from the furnace chamber and placing it into the cooling medium shall not exceed 30 seconds.

[0044] The gauge length of the tensile test specimen for mechanical property testing is 8 mm, the width is 2 mm, and the thickness is 1.5 mm. The stress-strain curve after room temperature tensile testing is attached. Figure 4 As shown.

[0045] No double yield phenomenon was observed in the curve. The tensile strength was 1076 MPa, the elongation was 16.2%, and the strength-ductility product was 17.4 GPa·s.

[0046] Comparative Example 2 The raw materials used are the same as in Example 1, and the specific steps are as follows: Step 1: Heat the heat treatment furnace to 30°C below the β transformation point of TC5751S titanium alloy material, i.e., 880°C.

[0047] Step 2: After the furnace temperature of the heat treatment furnace has stabilized, place the TC5751S titanium alloy material into the furnace and hold it at that temperature for 30 minutes for solution treatment.

[0048] Step 3: Remove the solution-treated TC5751S titanium alloy material from the heat treatment furnace and cool it at room temperature at a rate of 1-10℃ / s. This yields a microstructure with an average primary α-phase major axis size of 3.96 μm, an average primary α-phase minor axis size of 2.37 μm, a primary α-phase volume fraction of 12.6%, and a β-transformation volume fraction of 87.4%. Furthermore, a large number of relatively large silicides with an average size of 327 nm are observed within the field of view. The microstructure results are shown in the attached figure. Figure 3 As shown.

[0049] The aforementioned heat treatment furnace is an electric resistance furnace, and the furnace atmosphere is air.

[0050] The gauge length of the tensile test specimen for mechanical property testing is 8 mm, the width is 2 mm, and the thickness is 1.5 mm. The stress-strain curve after room temperature tensile testing is attached. Figure 4 As shown in the figure, no double yield phenomenon was observed in the curve. Its tensile strength was 1213 MPa, elongation was 9.17%, and strength-ductility product was 11.1 GPa·%.

[0051] Based on the above embodiments and comparative examples, it can be found that in T β -45℃—T β After heat treatment of TC5751S titanium alloy forging bar within the temperature range of -15℃ and rapid cooling at a rate of 200-500℃ / s, the alloy microstructure retains equiaxed primary α phase with a volume fraction of 13±1%, while the β phase has low stability. During room temperature stretching, it can achieve the combined effect of dislocation slip and phase transformation-induced plasticity mechanism.

[0052] Furthermore, precipitated silicides can significantly improve room temperature tensile strength through precipitation strengthening mechanisms. This is because dispersed silicide particles, acting as second-phase particles, can hinder dislocation movement and increase dislocation slip resistance. However, excessively large silicide particles become local stress concentration points during deformation, easily inducing microcrack nucleation and propagation, thereby deteriorating the material's performance. Based on the above embodiments and comparative examples, it can be found that at T... β -45℃—T β After heat preservation treatment of TC5751S titanium alloy forging bar within the temperature range of -15℃ and rapid cooling at a rate of 200-500℃ / s, the size of silicide in the alloy microstructure can be controlled to be below 300nm and the distribution is relatively uniform.

[0053] In T β -45℃—T βWhen TC5751S titanium alloy forging bars are heat-treated at 120℃ below -15℃ and rapidly cooled at a rate of 200-500℃ / s, the alloy microstructure retains equiaxed primary α phase with a volume fraction of 76.6±3%. The content of stabilizing elements in the β phase increases, resulting in higher stability. Stress-induced α'' martensite transformation is relatively difficult. The deformation mechanism under room temperature tension is still the plastic deformation mechanism dominated by dislocation slip, which has certain limitations.

[0054] In T β -45℃—T β When TC5751S titanium alloy forged bars are held at -15℃ and cooled at a rate of 1-10℃ / s, atoms have more time to diffuse. During cooling, alloying elements can redistribute according to differences in solubility in different phases, making the microstructure closer to equilibrium, with higher stability in the β phase. This relatively stable β phase is less likely to reach the energy and stress conditions required for transformation to α'' martensite under tensile stress, thus making stress-induced α'' martensite transformation difficult. Furthermore, a slower cooling rate can cause coarsening of silicides, thereby deteriorating the material's plasticity.

[0055] Compared to the embodiments, although the same TC5751S titanium alloy material was subjected to solution heat treatment, the solution temperature of Comparative Example 1 was not within the protection range of this application, and the cooling rate of Comparative Example 2 was not within the protection range of this application. This resulted in a simpler plastic deformation mechanism, and the precipitation behavior of a large number of silicides with large size and uneven distribution also resulted in a poor match between strength and plasticity compared to the embodiments.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A heat treatment method for regulating the α+β dual-phase microstructure and silicide precipitation in TC5751S titanium alloy, characterized in that, The heat treatment method includes the following steps: Step 1: Solution heat treatment; heat the heat treatment furnace to T. β -45℃~T β The TC5751S titanium alloy bar was placed in a heat treatment furnace at a constant temperature of -15℃ for a period of time; the nominal composition of the TC5751S titanium alloy is Ti-5Al-7.5V-0.5Mo-0.5Zr-0.5Si-0.25Fe-0.16O; the T β The β-phase transformation temperature of the TC5751S titanium alloy; Step 2: Cooling treatment; The TC5751S titanium alloy bar after solution heat treatment is removed from the heat treatment furnace and placed in a cooling medium, cooled to room temperature at a rate of 200-500℃ / s. The microstructure formed in the TC5751S titanium alloy consists of primary α phase, β transformation structure, and silicides; the average size of the long axis of the primary α phase is 3.88-5.0 μm; the average size of the short axis of the primary α phase is 2.53-2.99 μm; the volume fraction of the primary α phase is 12%-14%; the volume fraction of the β transformation structure is 86%-88%; and the average size of the silicides is 235-283 nm. The TC5751S titanium alloy has a tensile strength of 1255±11MPa and an elongation of 21.7±1.3% at room temperature, with a strength-ductility product of not less than 25.3GPa·.

2. The heat treatment method for regulating α+β dual-phase microstructure and silicide precipitation in TC5751S titanium alloy according to claim 1, characterized in that, The TC5751S titanium alloy bar is obtained by two-stage forging in the β single-phase region and two-stage forging in the α+β two-phase region.

3. The heat treatment method for regulating α+β dual-phase microstructure and silicide precipitation in TC5751S titanium alloy according to claim 1, characterized in that, The heat preservation time mentioned in step one is ≥30 minutes.

4. The heat treatment method for regulating α+β dual-phase microstructure and silicide precipitation in TC5751S titanium alloy according to claim 1, characterized in that, The heat treatment furnace mentioned in step one is a box-type resistance furnace with air in the furnace chamber and a heating rate of 10℃ / min.

5. The heat treatment method for regulating α+β dual-phase microstructure and silicide precipitation in TC5751S titanium alloy according to claim 1, characterized in that, The cooling medium mentioned in step two is water.

6. The heat treatment method for regulating α+β dual-phase microstructure and silicide precipitation in TC5751S titanium alloy according to claim 1, characterized in that, In step two, the TC5751S titanium alloy bar is removed from the heat treatment furnace and placed in the cooling medium within an interval of no more than 30 seconds.

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