Preparation method of high-strength damage tolerance type TC21 titanium alloy for anti-fatigue performance design

Abstract

The invention provides a preparation method of a high-strength damage tolerance type TC21 titanium alloy for anti-fatigue performance design. The preparation method comprises the following steps: step 1, carrying out homogenization heat treatment on a TC21 titanium alloy cast ingot; 2, beta single-phase region forging cogging is conducted, specifically, the homogenized TC21 titanium alloy cast ingot is discharged out of a furnace and heated to the temperature above the phase transformation point T beta, four-drawing and three-upsetting forging is conducted, and a first TC21 titanium alloy forging stock is obtained; (3) upsetting and drawing in an alpha + beta two-phase region: heating the first TC21 titanium alloy forging stock to be below a phase transformation point T beta, and performing forging, four-drawing and three-upsetting to obtain a second TC21 titanium alloy forging stock; fourthly, quasi-beta-phase region die forging is conducted, specifically, the second TC21 titanium alloy forging stock is heated to the temperature below the phase transformation point T beta to be subjected to die forging, and a TC21 titanium alloy die forging is obtained; and fifthly, strengthening and toughening heat treatment is conducted on the TC21 titanium alloy die forging, and the high-strength damage tolerance type TC21 titanium alloy is prepared and obtained. Strengthening and toughening matching can be achieved, and the fatigue performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy thermal processing, and in particular to a method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance. Background Art

[0002] With the continuous development of space exploration technology, rockets are an important means of transportation to the space field. Although their recovery technology saves launch costs, it increases the potential risk of fatigue damage to components, so strict requirements are put forward for the fatigue resistance of load-bearing components. Generally, improving the tensile strength of materials can effectively improve fatigue strength. However, the influence of microstructure on fatigue performance is easily overlooked. For example, for two materials with the same tensile strength, the fatigue resistance of lamellar structure is better than that of equiaxed grain structure. This is because the lamellar structure can more effectively guide the propagation of fatigue cracks, form a curved path, and prolong the crack growth time.

[0003] The damage-tolerant TC21 alloy has good strength and ductility and is widely used in load-bearing parts in the aerospace field. At present, the TC21 alloy is not heat-insulated by the jacketing process during hot deformation processing, which leads to a large number of reheating times and low efficiency. Subsequent heat treatment usually adopts a multi-level system to generate equiaxed α phase and fine needle-shaped β phase that is prone to brittle fracture, and the fatigue resistance needs to be improved. By adjusting the volume fraction of the equiaxed α phase in the microstructure and increasing the lamellar structure with a certain toughness, it is possible to achieve strength-toughness matching and improve fatigue performance. Summary of the invention

[0004] In response to the technical problems raised above, a method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance is provided.

[0005] The technical means adopted by the present invention are as follows:

[0006] A preparation method of a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance comprises the following steps:

[0007] Step 1, performing homogenization heat treatment on the TC21 titanium alloy ingot;

[0008] Step 2, forging in the β single-phase region: taking the homogenized TC21 titanium alloy ingot out of the furnace, and heating it to above the phase transformation point Tβ to perform four-drawing and three-upsetting forging to obtain the first TC21 titanium alloy forging billet;

[0009] Step 3, α+β two-phase region upsetting and drawing: heating the first TC21 titanium alloy forging billet to below the phase transition point Tβ, forging four times and drawing and three times upsetting, to obtain a second TC21 titanium alloy forging billet;

[0010] Step 4: Quasi-β phase region die forging: heating the second TC21 titanium alloy forging blank to below the phase transformation point Tβ for die forging to obtain a TC21 titanium alloy die forging;

[0011] Step 5: Perform toughening heat treatment on the TC21 titanium alloy die forgings to prepare high-strength damage-tolerant TC21 titanium alloy.

[0012] Furthermore, in the step 1, the TC21 titanium alloy ingot is heated to 1000-1080° C. above the phase transition point Tβ for homogenization treatment, and the holding time of the homogenization heat treatment is 0.8-1.5 h;

[0013] The TC21 titanium alloy ingot is a cylinder with a diameter φ of 600-800 mm and a length of 600-1600 mm.

[0014] Furthermore, in the step 2, the homogenized TC21 titanium alloy ingot is subjected to one-fire four-drawing and three-upsetting forging at a starting forging temperature of 100 to 150° C. above the phase transformation point Tβ, and an octagonal ingot with a diagonal of 500 to 580 mm is formed after forging.

[0015] Furthermore, in the step 2, the axial deformation of the four-drawing and three-upsetting forging is 40-60%, and the radial deformation is 30-40%.

[0016] Furthermore, in the step three, the first TC21 titanium alloy forging billet is subjected to three rounds of four drawing and three upsetting at a starting forging temperature of 40 to 50° C. below the phase transformation point Tβ, and is returned to the furnace for insulation for 1 to 1.5 hours after each round of heating.

[0017] Furthermore, in the step three, the axial deformation of the four-drawing and three-upsetting process is 40-50%, and the radial deformation is 20-40%.

[0018] Furthermore, in the step 4, the die forging temperature is 5 to 20° C. below the single-phase region Tβ, the deformation amount is 10 to 30%, and after die forging, a TC21 titanium alloy die forging with a size of φ100 to 150 mm is formed.

[0019] Furthermore, in the step 4, the second TC21 titanium alloy forging blank is sheathed before die forging.

[0020] Furthermore, in the step five, the TC21 titanium alloy die forging is heated to below the phase transformation point Tβ for strengthening and toughening heat treatment, and then cooled.

[0021] Furthermore, in step five, the temperature of the toughening heat treatment is 10 to 30°C below the single-phase region Tβ, and the holding time is 1 to 2 hours; the cooling method of the toughening heat treatment is furnace cooling, or first furnace cooling to 400 to 650°C and then air cooling.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The present invention adopts the jacketing process, which can delay the temperature drop of the blank during the subsequent homogenization treatment and transportation to the forging process.

[0024] 2. The present invention adopts a step-by-step heat treatment, and the microstructure forms an equiaxed α phase and a (α+β) lamellar structure with good toughness.

[0025] 3. The present invention adopts a step-by-step heat treatment to control the equiaxed α phase content by adjusting the solution temperature and the holding time, and the aging temperature and the holding time to control the (α+β) sheet thickness.

[0026] Based on the above reasons, the present invention can be widely promoted in the fields of alloy hot processing and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 Flow chart of the method of the present invention.

[0029] Figure 2 This is the microstructure diagram of the TC21 titanium alloy rod in Example 1 of the present invention.

[0030] Figure 3 This is the microstructure diagram of the TC21 titanium alloy rod in Example 2 of the present invention. DETAILED DESCRIPTION

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0034] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present invention. Meanwhile, it should be clear that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0035] The present invention provides a method for preparing a high-strength damage-tolerant TC21 titanium alloy (200-400 mm) designed for fatigue resistance, the method comprising the following steps:

[0036] Step 1: Homogenization heat treatment: Heat the TC21 titanium alloy ingot to 1000-1080°C above the phase transition point Tβ for microstructure homogenization.

[0037] Preferably, in step 1, the homogenization holding time of the TC21 titanium alloy ingot is 0.8 to 1.5 hours. The homogenization heat treatment can improve element segregation, enhance the structural uniformity of the ingot, and reduce the strength deviation of each position of the ingot.

[0038] Preferably, in step 1, the TC21 titanium alloy ingot is a cylinder, and the diameter φ of the cylinder is 600-800 mm and the length is 600-1600 mm.

[0039] Step 2: Forging in the β single-phase region: The homogenized TC21 titanium alloy ingot is taken out of the furnace and subjected to four-drawing and three-upsetting forging, which causes the coarse and deformed grains to break and the dynamic recrystallization to refine the grains.

[0040] Preferably, in step 2, the TC21 titanium alloy ingot is forged by four drawing and three upsetting forgings, for a total of one fire, and the start forging temperature is Tβ+100-150°C.

[0041] Preferably, in step 2, the axial deformation is 40-60%, and the radial deformation is 30-40%.

[0042] Preferably, in step 2, the blank is forged to form an octagonal ingot with a diagonal size of 500 to 580 mm.

[0043] Step 3: α+β two-phase region upsetting and drawing: Heat the TC21 titanium alloy forging billet to below the phase transformation point Tβ and forge it for four times and draw it for three times. The grains can be further refined based on step 2.

[0044] Preferably, in step three, the start forging temperature is 40 to 50° C. below the phase transformation point Tβ.

[0045] Preferably, in step three, four drawing and three upsetting are performed, for a total of three firings, and after each firing, the steel is returned to the furnace and kept warm for 1 to 1.5 hours.

[0046] Preferably, in step three, the axial deformation is 40-50%, and the radial deformation is 20-40%.

[0047] Step three of the present invention can reduce the generation of hot working cracks.

[0048] Step 4: Quasi-β phase die forging: Heat the TC21 titanium alloy forging billet to near the phase transition point Tβ and die forge it. This can make the structure more uniform and the appearance of the bar product regular and smooth.

[0049] Preferably, in step 4, the die forging temperature is 5 to 20° C. below Tβ in the single-phase region.

[0050] Preferably, in step 4, sheathing treatment is performed before die forging.

[0051] Preferably, in step 4, the deformation amount each time is 10 to 30%.

[0052] Preferably, in step 4, the die forging is formed to a size of φ100-150 mm.

[0053] Based on the above multiple processing steps, the grains have been refined step by step. The finer the grains, the more difficult they are to process and the more likely they are to crack. Therefore, as the last step of deformation processing, the deformation amount of die forging should not be too large.

[0054] Step 5: Post-forging strengthening and toughening treatment: Heat the TC21 titanium alloy die forging to below the phase transformation point Tβ for strengthening and toughening heat treatment.

[0055] Preferably, in step five, the toughening heat treatment temperature is 10 to 30° C. below the single-phase region Tβ, and the temperature is maintained for 1 to 2 hours.

[0056] Preferably, in step 5, the toughening heat treatment cooling method is furnace cooling, or first furnace cooling to 400-650°C and then air cooling. By adjusting the single zone heat treatment system (solution temperature and holding time), the control of the equiaxed α phase content is achieved, and the toughening treatment (aging temperature and holding time) can control the (α+β) sheet thickness.

[0057] The present invention develops corresponding microstructures based on anti-fatigue design ideas, has strong professionalism and good prospects.

[0058] Example 1

[0059] The present embodiment provides a method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance, comprising the following steps:

[0060] (1) Homogenization heat treatment:

[0061] The TC21 titanium alloy ingot with a size of φ650*700mm was heated to 1050°C, kept warm for 1h, and subjected to a microstructure homogenization treatment.

[0062] (2) Forging in β single phase region:

[0063] The ingot obtained in step (1) is subjected to four-drawing and three-upsetting forging, the start forging temperature is Tβ+100°C, the deformation amount is controlled at 40-50%, and an octagonal ingot with a diagonal of 500-530 mm is obtained.

[0064] (3) Upsetting in α+β two-phase region:

[0065] The TC21 titanium alloy forging blank obtained in step (2) is heated to 40° C. below the phase transformation point Tβ, and subjected to four-drawing and three-upsetting forging with a deformation amount of 30-40%, for a total of three firings, and each firing is completed by re-melting and heat preservation for 1 hour.

[0066] (4) Quasi-β phase die forging:

[0067] The TC21 titanium alloy forging blank obtained in step (3) is sheathed, heated to 5-10°C below the phase transformation point Tβ, and die forged, with the deformation amount controlled at 10-20%, and the finished product size is φ100-120 mm.

[0068] (5) Post-forging toughening treatment:

[0069] The TC21 titanium alloy product obtained in step (4) is kept at 15-30° C. below the single-phase region Tβ for 2 h, first furnace-cooled to 400-650° C. and then air-cooled.

[0070] Example 2

[0071] The present embodiment provides a method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance, comprising the following steps:

[0072] (1) Homogenization heat treatment:

[0073] The TC21 titanium alloy ingot with a size of φ750*800mm was heated to 110°C, kept warm for 1h, and subjected to a microstructure homogenization treatment.

[0074] (2) Forging in β single phase region:

[0075] The ingot obtained in step (1) is subjected to four-drawing and three-upsetting forging, the start forging temperature is Tβ+150°C, the deformation amount is controlled at 50-60%, and an octagonal ingot with a diagonal of 540-580 mm is obtained.

[0076] (3) Upsetting in α+β two-phase region:

[0077] The TC21 titanium alloy forging blank obtained in step (2) is heated to 50°C below the phase transformation point Tβ, and subjected to four-draw and three-upsetting forging with a deformation amount of 40-50%, for a total of three firings. The first two firings are completed by re-melting and heat preservation for 1.5 hours, and the third re-melting and heat preservation for 1 hour.

[0078] (4) Quasi-β phase die forging:

[0079] The TC21 titanium alloy forging blank obtained in step (3) is sheathed, heated to 10-20°C below the phase transformation point Tβ, and die forged, with the deformation amount controlled at 20-30%, and the finished product size is φ130-150mm.

[0080] (5) Post-forging toughening treatment:

[0081] The TC21 titanium alloy product obtained in step (4) is kept at 10-15°C below the single-phase region Tβ for 1 hour, first furnace-cooled to 400-650°C and then air-cooled.

[0082] Table 1 Mechanical properties of TC21 forged rods in the embodiment (unit: MPa)

[0083]

[0084] The present invention can achieve strengthening and toughening matching by regulating the volume fraction of the equiaxed α phase and the thickness of the (α+β) layer in the microstructure. m ) and high ductility (A), and fatigue limit (σ w ) is higher.

[0085] Figure 2-3 The results show that the content of isoaxial α phase in the tissue is different and the thickness of (α+β) lamellae is different. Figure 2 In terms of Figure 3 The organization is obtained after a short holding time in a single zone, and its characteristics are less equiaxed α phase content and greater (α+β) lamella thickness.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance, characterized in that: The steps include: Step 1, performing homogenization heat treatment on the TC21 titanium alloy ingot; Step 2, forging in the β single-phase region: taking the homogenized TC21 titanium alloy ingot out of the furnace, and heating it to above the phase transformation point Tβ to perform four-drawing and three-upsetting forging to obtain the first TC21 titanium alloy forging billet; Step 3, α+β two-phase region upsetting and drawing: heating the first TC21 titanium alloy forging billet to below the phase transition point Tβ, forging four times and drawing and three times upsetting to obtain a second TC21 titanium alloy forging billet; Step 4: Quasi-β phase region die forging: heating the second TC21 titanium alloy forging blank to below the phase transformation point Tβ for die forging to obtain a TC21 titanium alloy die forging; Step 5: Perform toughening heat treatment on the TC21 titanium alloy die forgings to prepare high-strength damage-tolerant TC21 titanium alloy.

2. The method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance according to claim 1, characterized in that: In the step 1, the TC21 titanium alloy ingot is heated to 1000-1080° C. above the phase transition point Tβ for homogenization treatment, and the holding time of the homogenization heat treatment is 0.8-1.5 h; The TC21 titanium alloy ingot is a cylinder with a diameter φ of 600-800 mm and a length of 600-1600 mm.

3. The method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance according to claim 1, characterized in that: In the step 2, the homogenized TC21 titanium alloy ingot is subjected to one-fire four-drawing and three-upsetting forging at a starting forging temperature of 100-150° C. above the phase transformation point Tβ, and an octagonal ingot with a diagonal of 500-580 mm is formed after forging.

4. The method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance according to claim 3, characterized in that: In the step 2, the axial deformation of the four-draw and three-upset forging is 40-60%, and the radial deformation is 30-40%.

5. The method for preparing the high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance according to claim 1, characterized in that: In the step three, the first TC21 titanium alloy forging billet is subjected to three rounds of four drawing and three upsetting at a starting forging temperature of 40-50°C below the phase transformation point Tβ, and is returned to the furnace for insulation for 1-1.5 hours after each round of heating.

6. The method for preparing the high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance according to claim 5, characterized in that: In the step three, the axial deformation of the four-drawing and three-upsetting process is 40-50%, and the radial deformation is 20-40%.

7. The method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance according to claim 1, characterized in that: In the step 4, the die forging temperature is 5-20° C. below the single-phase region Tβ, the deformation amount is 10-30%, and after die forging, a TC21 titanium alloy die forging with a size of φ100-150 mm is formed.

8. The method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance according to claim 1, characterized in that: In the step 4, the second TC21 titanium alloy forging blank is sheathed before die forging.

9. The method for preparing a high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance according to claim 1, characterized in that: In the step five, the TC21 titanium alloy die forging is heated to below the phase transformation point Tβ for toughening heat treatment, and then cooled.

10. The method for preparing the high-strength damage-tolerant TC21 titanium alloy designed for fatigue resistance according to claim 9, characterized in that: In the step 5, the temperature of the toughening heat treatment is 10-30°C below the single-phase region Tβ, and the holding time is 1-2h; the cooling method of the toughening heat treatment is furnace cooling, or first furnace cooling to 400-650°C and then air cooling.

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