A method for controlling multi-level alpha structure of metastable beta titanium alloy

Abstract

This disclosure provides a method for controlling the multi-level α microstructure of metastable β titanium alloys, including the following steps: Step 1: Metastable β titanium alloy at its β phase transformation point T β Solution treatment within ±50℃; Step 2: Perform multi-pass rolling deformation on the billet obtained in Step 1, with a single-pass deformation amount of 10-30%, and hold at the rolling temperature for 1-10 minutes after every 1-2 passes until the total alloy reduction reaches 70%-95%, then cool to room temperature; Step 3: The billet obtained in Step 2 is subjected to T β -40℃~T β Anneal for 2–120 minutes within the temperature range, then cool to room temperature; or first anneal at T β -80℃~T β Annealing at -40℃ for 20–120 min, then at T β -40℃~T β Annealing for 2–120 minutes within the temperature range, then cooling to room temperature; Step 4: The billet obtained in Step 3 is annealed at T... β -350℃~T β Multi-level α-structures were obtained after aging for 4–12 hours within a temperature range of -210℃. This disclosure enables coupling of primary α-structures. p Secondary α phases of different sizes and spacings s This phase allows metastable β-titanium alloys to possess high strength while retaining a certain degree of plasticity.

Description

Technical Field

[0001] The embodiments disclosed herein relate to the field of high-strength and high-toughness titanium alloy technology, and more specifically, to a method for controlling the multi-level α microstructure of metastable β titanium alloys. Background Technology

[0002] Metastable β-titanium alloys are widely used in the manufacture of main load-bearing components for aircraft due to their high specific strength, low modulus, good fatigue performance, and excellent machinability. These alloys contain a high content of β-stabilizing elements, which suppress the precipitation of the α-phase during quenching and cooling, thus retaining the metastable β matrix at room temperature. During subsequent aging, the high concentration of β-stabilizing elements causes the precipitation of fine and dispersed α-phase on the β matrix, resulting in a significant strengthening effect. By adjusting the size and morphology of the α-phase, the strength of these alloys can be increased to over 1400 MPa, but at the same time, plasticity and toughness are significantly reduced, causing a strength-plasticity mismatch under high strength conditions. Furthermore, the size and morphology of the precipitated α-phase are highly sensitive to composition and hot working processes, which is detrimental to achieving stable properties in high-strength titanium alloys.

[0003] In recent years, multi-level alpha microstructures have been proven to be a strategy to overcome the strength-ductility mismatch problem in metastable β-titanium alloys. However, most of these processes are complex, require sophisticated equipment, or are only applicable to alloys with specific compositions, making them difficult to apply in practice. Therefore, how to construct multi-level alpha microstructures through industrially feasible thermomechanical processing and heat treatment processes, while maintaining a certain degree of ductility, has become an urgent problem to be solved. Summary of the Invention

[0004] To address the existing problems, this disclosure provides a method for preparing multi-level α-structures by combining hot rolling and heat treatment. This method is applicable to metastable β-titanium alloys with various compositions, has a wide processing window, low equipment requirements, and can couple primary phases and secondary phases of different sizes and spacings, enabling metastable β-titanium alloys to have high strength while retaining a certain degree of plasticity.

[0005] This disclosure is achieved through the following technical solution:

[0006] According to the present disclosure, a method for controlling the multi-level α microstructure of metastable β titanium alloys is provided, comprising the following steps:

[0007] Step 1: Homogenization of alloy billet: Metastable β-titanium alloys near their β-phase transformation point (T β Solution treatment at ±50℃;

[0008] Step 2: Hot rolling: The billet obtained in Step 1 is subjected to multi-pass rolling deformation, with a single pass deformation amount of 10-30%. After every 1-2 passes of rolling, the billet is held at the rolling temperature for 1-10 minutes until the total reduction of the alloy reaches 70%-95%, and then cooled to room temperature.

[0009] Step 3: Annealing: The billet obtained in Step 2 is annealed at T... β -40℃~T β Anneal for 2–120 minutes within the temperature range, then cool to room temperature; or first anneal at T β -80℃~T β Annealing at -40℃ for 20–120 min, then at T β -40℃~T β Anneal for 2–120 minutes within the temperature range, then cool to room temperature;

[0010] Step 4: Aging: The billet obtained in Step 3 is aged at T β -350℃~T β After aging for 4 to 12 hours within a temperature range of -210℃, multi-level α tissue was obtained.

[0011] As a further explanation of this disclosure, the homogenization time in step 1 is not less than 30 min, to ensure the formation of a fully β-equiaxed structure or a β-equiaxed structure containing a small amount of primary phase.

[0012] As a further explanation of this disclosure, the rolling temperature in step 2 is controlled at T. β If the rolling temperature is within ±40℃ and the rolling temperature is in the β single-phase region, the holding time after each 1 to 2 rolling passes shall not exceed 2 minutes.

[0013] As a further explanation of this disclosure, the annealing in step 3 must ensure the formation of an incompletely recrystallized structure, retaining some substructures, in order to ensure the formation of multi-level and multi-morphological α structures during subsequent aging processes.

[0014] As a further explanation of this disclosure, when the hot rolling temperature is low or the rolling deformation is large, first at T β -80℃~T β Annealing within a temperature range of -40℃ ensures partial recrystallization, consuming some of the dislocation and deformation energy stored, and then at T... β -40℃~T β Annealing within a specific temperature range ensures the formation of a finer, more uniform microstructure while preventing the rapid growth of β-grains or complete recrystallization during single-step annealing.

[0015] As a further explanation of this disclosure, the aging process in step 4 must ensure the formation of secondary α with different spacings and sizes. s The morphology of the phase should be considered to avoid the formation of a uniform and fine secondary phase due to excessively low temperature, which would reduce plasticity.

[0016] Compared with the prior art, the technical solution disclosed herein has the following beneficial technical effects:

[0017] This invention provides a method for controlling the multilayered α microstructure of metastable β-titanium alloys and achieving a balance between strength and ductility. The method involves forming a lamellar streamline microstructure through multiple hot rolling passes near the phase transformation point and obtaining sufficiently high deformation energy storage. Then, partial recrystallization occurs through temperature annealing above the two-phase region, retaining a portion of the α-phase. p Simultaneously, a heterogeneous β structure is formed, mainly consisting of fully recrystallized equiaxed β grains, elongated deformed β grains containing residual dislocations, and partially recrystallized β subgrains. Finally, aging yields a multi-layered α structure and achieves a strong-plasticity match. Due to the state differences between different regions of the non-uniform heterogeneous β structure, lamellar α structures form within the fully recrystallized equiaxed β grains after aging. l Phases with a length greater than 2 μm and a large aspect ratio, α l The interlamellar spacing is relatively wide; while needle-like α-grains are formed in the elongated β-grains containing residual dislocations and in the partially recrystallized β-subgrains. s Phase and discontinuous grain boundary α GB Phase, where α s The lamellar structures are less than 2 μm in length and densely distributed with small interlamellar spacing. This multi-scale, multi-morphological hierarchical structure interacts with dislocations during deformation, which is beneficial for strain distribution and thus leads to excellent performance.

[0018] The metastable β-titanium alloy multi-level α microstructure provided by this invention includes equiaxed α p Phase, lamellae α l Phase, fine α s Phase and discontinuous α GB This microstructure utilizes multi-scale, multi-morphological interactions with dislocations to generate significant strain distribution during deformation, thereby maintaining a certain level of plasticity (EL>5%) while ensuring strength (UTS>1300MPa), avoiding the strength-plasticity mismatch problem in high-strength titanium alloys. Furthermore, the process of this invention has low equipment requirements, is applicable to metastable β-titanium alloys of various compositions, has a wide processing window, and shows promising application prospects in industrial fields. Attached Figure Description

[0019] 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:

[0020] Figure 1 Here are SEM images of the alloy microstructure of Example 1 of the present invention, wherein, Figure 1 (a) is a SEM image of a multi-level α-tissue region. Figure 1 (b) is a magnified SEM image of the lamellar phase region. Figure 1 (c) is fine α S Phase and discontinuous α GB Phase region SEM image.

[0021] Figure 2 This is a tensile curve of the alloy engineering stress-engineering strain in Embodiment 1 of the present invention.

[0022] Figure 3 This is a tensile curve of alloy engineering stress-engineering strain in Embodiment 2 of the present invention.

[0023] Figure 4 Here is a SEM image of the alloy microstructure of Example 3 of the present invention, wherein, Figure 4 (a) is a SEM image of a multi-level α-tissue region. Figure 4 (b) represents α growing perpendicular to grain boundaries. WGB Enlarged SEM images of layered phases.

[0024] Figure 5 This is a tensile curve of the alloy engineering stress-engineering strain in Embodiment 3 of the present invention.

[0025] Figure 6 This is a tensile curve of alloy engineering stress-engineering strain in Embodiment 4 of the present invention. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] Example 1:

[0029] A method for controlling the multi-level α-structure of a metastable β-titanium alloy, using the metastable β-titanium alloy Ti-7333 (Ti-7Mo-3Nb-3Cr-3Al), whose β-phase transformation point is approximately 845℃, includes the following steps:

[0030] Step 1: Hold the 20mm thick Ti-7333 block sample at 880℃ for 40min and then water cool it to room temperature;

[0031] Step 2: The sample from Step 1 was hot rolled at 850℃. Before hot rolling, it was held at the temperature for 10 minutes. The reduction in pressure was 15% per pass. After each pass, it was held at 850℃ for 1 minute. After 11 passes, the total reduction in pressure reached 83%. After the last pass, it was cooled to room temperature.

[0032] Step 3: After hot rolling, the sample is annealed at 820℃ for 10 min;

[0033] Step 4: After annealing, the sample was aged at 520℃ for 6 hours to obtain a multi-level α-structure.

[0034] like Figure 1 As shown, the obtained tissue contains equiaxed α-cells of 0–2 μm. p discontinuous α phases at grain boundaries GB Phase, α-lamellae with a length greater than 2 μm and cross-distributed l Phase, α with a size less than 1 μm and finely distributed s Phase, α l The interlamellar spacing is significantly greater than α. s The interlamellar spacing was measured. Tensile property tests were performed on the microstructure, revealing a yield strength of 1360 MPa, a tensile strength of 1430 MPa, and an elongation at break of 8%. The tensile curve is shown below. Figure 2 As shown.

[0035] Example 2:

[0036] A method for controlling the multi-level α-structure of a metastable β-titanium alloy, using the metastable β-titanium alloy Ti-7333 (Ti-7Mo-3Nb-3Cr-3Al), whose β-phase transformation point is approximately 845℃, includes the following steps:

[0037] Step 1: Hold the 20mm thick Ti-7333 block sample at 820℃ for 40min;

[0038] Step 2: Then take out the sample and hot roll it at 820℃, with a reduction of 15% per pass. After each pass, hold at 820℃ for 1 minute. After 11 passes, the total reduction reaches 84%. After the last pass, cool to room temperature.

[0039] Step 3: After hot rolling, the sample is annealed at 820℃ for 5 minutes;

[0040] Step 4: After annealing, the sample was aged at 520℃ for 6 hours to obtain a multi-level α-structure.

[0041] Tensile property tests were performed on the specimen, and the yield strength reached 1230 MPa, the tensile strength was 1425 MPa, and the elongation at break reached 12%. Its tensile curve is shown below. Figure 3 As shown.

[0042] Example 3:

[0043] A method for controlling the multi-level α-structure of a metastable β-titanium alloy, using the metastable β-titanium alloy Ti-7333 (Ti-7Mo-3Nb-3Cr-3Al), whose β-phase transformation point is approximately 845℃, includes the following steps:

[0044] Step 1: Hold the 20mm thick Ti-7333 block sample at 820℃ for 40min;

[0045] Step 2: Then take out the sample and hot roll it at 820℃, with a reduction of 15% per pass. After each pass, hold at 820℃ for 1 minute. After 11 passes, the total reduction reaches 84%. After the last pass, cool to room temperature.

[0046] Step 3: After hot rolling, the sample is first annealed at 800℃ for 30 min and then water-cooled, and then annealed at 820℃ for 10 min.

[0047] Step 4: After annealing, the sample was aged at 520℃ for 6 hours to obtain a multi-level α-structure.

[0048] like Figure 4 As shown, the obtained tissue contains equiaxed α-cells of 0–2 μm. p α phases at grain boundaries GB α phase and partial vertical grain boundary growth WGB Lamellae, α-lamellae with a length greater than 2 μm and cross-distributed l Phase, α with a size less than 1 μm and finely distributed s Phase, and α l The interlamellar spacing is significantly greater than α. s Laminar spacing. Tensile property tests were performed on the microstructure, revealing a yield strength of 1270 MPa, a tensile strength of 1420 MPa, and an elongation at break of 9%. The tensile curve is shown below. Figure 5 As shown.

[0049] Example 4:

[0050] A method for controlling the multi-level α-microstructure of a metastable β-titanium alloy, using the metastable β-titanium alloy TB18 (Ti-4Al-5Mo-5V-5Cr-1Nb), whose β-phase transformation point is approximately 810℃, includes the following steps:

[0051] Step 1: Hold the 20mm thick TB18 block sample at 780℃ for 60 minutes;

[0052] Step 2: Then take out the sample and hot roll it at 780℃, with a reduction of 15% per pass. After each pass, hold at 780℃ for 1 minute. After 11 passes, the total reduction reaches 84%. After the last pass, cool to room temperature.

[0053] Step 3: After hot rolling, the sample is annealed at 780℃ for 10 min;

[0054] Step 4: After annealing, the sample was aged at 530℃ for 4 hours to obtain a multi-level α-structure.

[0055] Tensile property tests were performed on the specimen, revealing a yield strength of 1320 MPa, a tensile strength of 1345 MPa, and an elongation at break of 11.9%. The tensile curve is shown below. Figure 6 As shown.

[0056] The multi-level α-structure obtained by the present invention can significantly improve plasticity without sacrificing strength, breaking the problem of the mismatch between strength and plasticity in high-strength titanium alloys. It is applicable to high-strength titanium alloys with different compositions and is of great significance for the further application of metastable β-titanium alloys in the industrial field.

[0057] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for controlling the multi-level α microstructure of metastable β-titanium alloys, characterized in that, Includes the following steps: Step 1: Homogenization of alloy billet: Metastable β-titanium alloy at its β-phase transformation point Solid solution within the range; Step 2: Hot rolling: The billet obtained in Step 1 is subjected to multi-pass rolling deformation, with a single pass deformation of 10-30%. After every 1-2 passes, the billet is held at the rolling temperature for 1-10 minutes until the total alloy reduction reaches 70%-95%, then cooled to room temperature. The rolling temperature is controlled at... If the rolling temperature is in the β single-phase region, the holding time after each 1-2 rolling passes shall not exceed 2 minutes. Step 3: Annealing: The billet obtained in step 2 is subjected to... Anneal for 2-120 minutes within the temperature range, then cool to room temperature; or first anneal within the temperature range. Annealing at a temperature range of 20-120 minutes, then... Anneal for 2-120 minutes within the temperature range, then cool to room temperature; Step 4: Aging time: The billet obtained in step 3 is in After aging for 4 to 12 hours within the temperature range, multi-level α tissue was obtained.

2. The method according to claim 1, characterized in that, The homogenization time in step 1 shall not be less than 30 minutes to ensure the formation of a full β-equiaxed structure or a β-equiaxed structure containing a small amount of primary phase.

3. The method according to claim 1, characterized in that, In step 3, the annealing process must ensure the formation of an incompletely recrystallized structure, retaining some substructures.

4. The method according to claim 1, characterized in that, The aging process in step 4 must ensure the formation of secondary structures with varying spacing and dimensions. Appearance of a face.

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