Preparation method of lamellar structure metastable beta titanium alloy plasticized by rod-like alpha phase

Abstract

The invention belongs to the technical field of preparation of high-strength and high-plasticity titanium alloys, and particularly relates to a preparation method of a layered-structure metastable beta titanium alloy plasticized by a rod-shaped alpha phase. The lamellar structure metastable beta titanium alloy provided by the invention comprises the following elements in percentage by mass: 6.0-8.0% of Mo, 2.0-4.0% of Nb, 2.0-4.0% of Cr, 0.5-3% of Al and 1.0-3.0% of Zr except Ti, a lamellar structure in which coarse grains and fine grains are alternately distributed is obtained in a system through three-stage forging and pressing, and the lamellar structure is obtained through a two-way forging process. A primary equiaxial alpha phase is separated out in a layered mode in the finish forging drawing-out direction and stretched into a rod shape, meanwhile, a nanoscale needle-shaped secondary alpha phase is separated out in the air cooling process of the alloy, the nanoscale needle-shaped secondary alpha phase provides an extraordinary strengthening effect for an alloy beta matrix, the yield strength of the alloy is 1,300 MPa or above, the tensile strength of the alloy is 1,400 MPa or above, and the ductility of the alloy is 10% or above.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-strength plastic titanium alloy preparation, and more particularly relates to a method for preparing a layered metastable beta titanium alloy plasticized by a rod-shaped alpha phase. Background Art

[0002] Titanium alloys have broad application prospects in aerospace, biomedicine, petrochemicals and other fields due to their low density, high specific strength, low elastic modulus and excellent corrosion resistance. However, as the application environment becomes increasingly harsh, higher requirements are placed on the performance of titanium alloys. Traditional metastable β-titanium alloys are mainly improved by combining forging, solid solution + aging treatment to improve yield strength, but this traditional process has obvious limitations: the deformation incompatibility between α-phase precipitates and β-phase matrix will be significantly aggravated, resulting in the alloy plasticity usually being less than 10%, forming an inverted relationship between strength and plasticity that restricts each other, which seriously hinders the further development and application expansion of titanium alloy materials. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a layered metastable β titanium alloy plasticized by a rod-shaped α phase, so as to solve the problems existing in the above-mentioned prior art.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention is to provide a metastable β titanium alloy with a layered structure plasticized by a rod-shaped α phase, wherein the element composition, in addition to Ti, comprises, by mass percentage:

[0006] Mo 6.0~8.0%, Nb 2.0~4.0%, Cr 2.0~4.0%, Al 0.5~3% and Zr 1.0~3.0%.

[0007] The second technical solution of the present invention is to provide a method for preparing the above-mentioned layered metastable β titanium alloy plasticized by the rod-shaped α phase, comprising the following steps:

[0008] uniformly melting the titanium alloy raw material to prepare a titanium alloy ingot;

[0009] The titanium alloy ingot is subjected to a first heat treatment at a first preset temperature, followed by blank forging, and then subjected to a second heat treatment at a second preset temperature, followed by β phase → α + β phase cross-zone forging, and after remelting and heat preservation treatment, a small downward pressure deformation treatment is performed, and the layered structure metastable β titanium alloy is obtained after cooling.

[0010] Furthermore, the β / (α+β) phase transition temperature of the titanium alloy ingot is 750±5°C.

[0011] Furthermore, the first preset temperature is 100-200° C. higher than the β / (α+β) phase transition point temperature.

[0012] Furthermore, the first heat treatment lasts for 30-60 minutes.

[0013] By performing the first heat treatment at the first preset temperature, the sample can be brought to the temperature required for forging and ensured to remain above the phase transformation point during the forging process.

[0014] Furthermore, the pressing rate of the blank forging is 4-6 mm / s, and the titanium alloy ingot is first forged along the height Z direction with a deformation of 40-60%, and then forged in the X and Y directions with deformations of 20-40% respectively.

[0015] Open forging can homogenize the sample structure, improve the original structure of the ingot, reduce segregation, and refine the grains to a certain extent.

[0016] Furthermore, the second preset temperature is 40 to 60° C. higher than the β / (α+β) phase transition point temperature.

[0017] Furthermore, the second heat treatment time is 10-30 minutes.

[0018] Performing the second heat treatment at the second preset temperature can ensure that the alloy temperature remains near the phase transformation point.

[0019] Furthermore, the cross-region forging of the β phase → α + β phase is performed by first forging in the Z direction with a deformation of 40-60%, and then switching to forging in the X and Y directions with deformations of 20-40% respectively.

[0020] Through cross-zone forging, an appropriate amount of α phase can be introduced to hinder the growth of β grains, achieve the effect of refining β grains, and strengthen the alloy through the introduced α phase.

[0021] Furthermore, the time for the reheating and heat preservation treatment is 10-30 minutes.

[0022] The sample temperature will drop during the forging process, and returning to the furnace for heat preservation can keep the sample at a temperature near the phase transition point.

[0023] Furthermore, the small downward pressure deformation process is to continuously reverse the X and Y directions to perform small downward pressure deformation, and the deformation amounts in the two directions are 20-40% respectively.

[0024] Through continuous reversing deformation treatment in two directions (deformation treatment with small downward pressure), the alloy is stretched along the Z direction.

[0025] For metastable β titanium alloys, the elemental composition and content (especially β phase stabilizing elements, such as Mo, Cr, Nb, etc.) determine the stability of the β phase, which in turn affects the phase transition point of the alloy. The forging temperature needs to be designed in combination with the phase transition point temperature to obtain a layered metastable β titanium alloy plasticized by the rod-shaped α phase.

[0026] The third technical solution of the present invention is to provide an application of the above-mentioned layered metastable β titanium alloy plasticized by rod-shaped α phase in the fields of aerospace, biomedicine and petrochemical industry.

[0027] The layered metastable β-titanium alloy prepared by the present invention has the characteristics of high specific strength, low elastic modulus, excellent corrosion resistance, etc., and has high application prospects in the fields of aerospace, biomedicine and petrochemical industry. Mechanical properties are one of the indicators for judging its application feasibility. The strength of the titanium alloy prepared by this process reaches the standard of ultra-high-strength titanium alloy, and it also has excellent ductility (greater than 10%). In addition, the process flow is simple and can greatly reduce production costs.

[0028] The present invention discloses the following technical effects:

[0029] The method for preparing a layered metastable β titanium alloy plasticized by a rod-shaped α phase, proposed in the present invention, does not require a post-forging heat treatment process. Instead, the high-strength plastic titanium alloy preparation process can be completed through forging and post-forging air cooling (cooling). This greatly shortens the process flow, reduces production costs, and significantly improves the plasticity while ensuring the alloy's strength. The present invention constructs a structural combination of a layered structure and a rod-shaped α phase, achieving synergistic optimization of strength and plasticity. This opens up a new path for the development of metastable β titanium alloy materials with excellent comprehensive performance, which can meet the urgent needs of fields such as aerospace, biomedicine, and petrochemicals.

[0030] The present invention obtains a layered structure with alternating coarse and fine grains in the system by subjecting the ingot to three-stage forging. Through the bidirectional forging process, the primary equiaxed α phase is separated and precipitated in layers along the final forging drawing direction and elongated into rods. At the same time, the alloy precipitates nano-sized needle-shaped secondary α phase during air cooling. The nano-sized needle-shaped secondary α phase provides an extraordinary strengthening effect for the alloy β matrix. At the same time, the layered rod-shaped α phase can hinder the expansion of planar slip, and the stress of the rod-shaped α phase induces the transformation of the HCP structure to the FCC structure to relieve the stress concentration at the α / β phase interface, inhibit crack initiation, and significantly improve the plasticity of the alloy. The unique layered structure effect and the coupling of the rod-shaped α phase and the needle-shaped α phase enable the alloy to maintain high strength while also having excellent plasticity. Its yield strength is above 1300MPa, the tensile strength is above 1400MPa, and the elongation is above 10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0032] Figure 1 This is a physical picture of the layered metastable β titanium alloy prepared in Example 1.

[0033] Figure 2 This is the metallographic structure diagram of the layered metastable β titanium alloy prepared in Example 1.

[0034] Figure 3 This is the XRD pattern of the layered metastable β titanium alloy prepared in Example 1.

[0035] Figure 4 This is the metallographic structure diagram of the layered metastable β titanium alloy prepared in Comparative Example 1.

[0036] Figure 5 This is the SEM image of the layered metastable β titanium alloy prepared in Example 1 before stretching.

[0037] Figure 6 This is an SEM image of the layered metastable β titanium alloy prepared in Example 1 after tensile fracture.

[0038] Figure 7 This is the TEM image of the rod-shaped α phase of the layered metastable β titanium alloy prepared in Example 1 after stretching.

[0039] Figure 8 Schematic diagram of the plasticization principle of rod-shaped α phase.

[0040] Figure 9 Mechanical properties diagram of the materials prepared for Example 1 and Comparative Example 1.

[0041] Figure 10 This is a flow chart for preparing a layered metastable β titanium alloy according to Example 1. DETAILED DESCRIPTION

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0044] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0045] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0046] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0047] Unless otherwise specified, the raw materials and reagents used in the specific embodiments of the present invention are all commercially available products.

[0048] Unless otherwise specified, the "%" of raw materials involved in the specific embodiments of the present invention are all mass percentages; the "room temperature" and "normal temperature" involved both refer to 20-30°C.

[0049] Example 1

[0050] The preparation steps of the layered metastable β titanium alloy plasticized by the rod-shaped α phase include:

[0051] S1. Weigh the corresponding raw materials (the β / (α+β) phase transition temperature of the titanium alloy ingot is 750±5°C) containing, by weight, 7.5% Mo, 2.7% Nb, 3.3% Cr, 1.4% Al, and 2.3% Zr, with the remainder being Ti.

[0052] S2. The raw materials are melted evenly in a vacuum induction melting furnace (the raw materials are melted once in a crucible, and then turned over and melted again after cooling. This is repeated five times to ensure that the raw materials are completely melted and evenly distributed), and cast into titanium alloy round bars with an aspect ratio of 2:1;

[0053] S3. Place the titanium alloy round bar in a muffle furnace at 850°C for 30 minutes, then place it on a hydraulic press for forging, deform it by 50% in the height Z direction, and then reverse the direction to deform it by 30% in the X and Y directions respectively to form a square billet;

[0054] S4. Place the billet in a muffle furnace and keep it at 800°C for 30 minutes. Then perform cross-forging from β phase to α+β phase, first deforming it in the Z direction by 50%, then changing the direction and deforming it in the X and Y directions by 30% respectively.

[0055] S5. After the cross-zone forging is completed, the furnace is returned to heat preservation for 30 minutes, and then the X and Y directions are continuously reversed to perform small downward pressure deformation treatment. The total deformation in the two directions is maintained at 30%, and finally a square long rod is made. It is air-cooled to room temperature to obtain a layered metastable β titanium alloy.

[0056] Figure 1 This is a physical picture of the layered metastable β titanium alloy prepared in Example 1.

[0057] Figure 2 This is the metallographic structure diagram of the layered metastable β titanium alloy prepared in Example 1. As can be seen from the figure, according to the metallographic structure diagram, a layered structure with alternating coarse and fine grains is obtained in the system through three-stage forging, and the coarse grains are lamellar.

[0058] Figure 3 This is the XRD pattern of the layered metastable β titanium alloy prepared in Example 1. As can be seen from the figure, after the cross-zone forging is completed and air-cooled, the matrix contains α and β phases.

[0059] Figure 10 This is a flow chart for preparing a layered metastable β titanium alloy according to Example 1.

[0060] Example 2

[0061] The preparation steps of the layered metastable β titanium alloy plasticized by the rod-shaped α phase include:

[0062] S1. Weigh the corresponding raw materials (the β / (α+β) phase transition temperature of the titanium alloy ingot is 750±5°C) containing, by weight, 7.5% Mo, 2.7% Nb, 3.3% Cr, 1.4% Al, and 2.3% Zr, with the remainder being Ti.

[0063] S2. The raw materials are melted evenly in a vacuum induction melting furnace (the raw materials are melted once in a crucible, and then turned over and melted again after cooling. This is repeated five times to ensure that the raw materials are completely melted and evenly distributed), and cast into titanium alloy round bars with an aspect ratio of 2:1;

[0064] S3. Place the titanium alloy round bar in a muffle furnace at 850°C for 20 minutes, then place it on a hydraulic press for forging, deform it by 40% in the Z direction, and then deform it by 20% in the X and Y directions respectively to form a square billet;

[0065] S4. Place the billet in a muffle furnace and keep it at 790°C for 20 minutes. Then perform cross-forging from β phase to α+β phase, first deforming it in the Z direction by 40%, then changing the direction and deforming it in the X and Y directions by 20% respectively.

[0066] S5. After the cross-zone forging is completed, the furnace is returned to heat preservation for 20 minutes, and then the X and Y directions are continuously reversed to perform small downward pressure deformation treatment. The total deformation in the two directions is maintained at 20%, and finally a square long rod is made. It is air-cooled to room temperature to obtain a layered metastable β titanium alloy.

[0067] Example 3

[0068] The preparation steps of the layered metastable β titanium alloy plasticized by the rod-shaped α phase include:

[0069] S1. Weigh the corresponding raw materials (the β / (α+β) phase transition temperature of the titanium alloy ingot is 750±5°C) containing, by weight, 7.5% Mo, 2.7% Nb, 3.3% Cr, 1.4% Al, and 2.3% Zr, with the remainder being Ti.

[0070] S2. The raw materials are melted evenly in a vacuum induction melting furnace (the raw materials are melted once in a crucible, and then turned over and melted again after cooling. This is repeated five times to ensure that the raw materials are completely melted and evenly distributed), and cast into titanium alloy round bars with an aspect ratio of 2:1;

[0071] S3. Place the titanium alloy round bar in a muffle furnace at 900°C for 30 minutes, then place it on a hydraulic press for forging, deform it by 60% in the height Z direction, and then reverse the direction to deform it by 40% in the X and Y directions respectively to form a square billet;

[0072] S4. Place the billet in a muffle furnace and keep it at 810°C for 30 minutes. Then perform cross-forging from β phase to α+β phase, first deforming it in the Z direction by 60%, then changing the direction and deforming it in the X and Y directions by 40% respectively.

[0073] S5. After the cross-zone forging is completed, the furnace is returned to heat preservation for 30 minutes, and then the X and Y directions are continuously reversed to perform small downward pressure deformation treatment. The total deformation in the two directions is maintained at 40%, and finally a square long rod is made. It is air-cooled to room temperature to obtain a layered metastable β titanium alloy.

[0074] Comparative Example 1

[0075] Compared with Example 1, the only difference is that the total deformation amounts in the three directions of X, Y and Z in the small downward pressure deformation process in step S5 are respectively maintained at 20%.

[0076] Figure 4 This is the metallographic microstructure of the layered metastable β titanium alloy prepared in Comparative Example 1. As can be seen from the figure, while Example 1 was forged in two directions, X and Y, with a deformation of 30% in each direction, for a total of 60%, Comparative Example 1 was forged in three directions, X, Y, and Z, with a deformation of 20% in each direction, also for a total of 60%, the equiaxed microstructure formed by three-direction forging in Comparative Example 1 is compared with the properties of the layered microstructure in Example 1 (Table 1). It can be seen that the layered microstructure has superior performance.

[0077] Comparative Example 2

[0078] Compared with Example 2, the only difference is that the total deformation amounts in the X, Y and Z directions of the small downward pressure deformation process in step S5 are respectively maintained at 15%.

[0079] Comparative Example 3

[0080] Compared with Example 3, the only difference is that the total deformation amounts in the three directions of X, Y and Z in the small downward pressure deformation process in step S5 are respectively maintained at 25%.

[0081] Test example

[0082] The materials prepared in the examples and comparative examples were made into bone-shaped tensile parts (gauge size: 10.0 mm×3.5 mm×1.5 mm), and their yield strength, tensile strength and total elongation were tested. The results are shown in Table 1.

[0083] Uniaxial tensile tests were carried out at room temperature using an INSTRON 5982 testing machine at a test speed of 5 × 10 -4 s -1 ,All tests were repeated three times to ensure the reproducibility of the data.

[0084] Table 1

[0085]

[0086]

[0087] Figure 5 This is the SEM image of the layered metastable β titanium alloy prepared in Example 1 before stretching. It can be seen from the figure that the primary equiaxed α phase precipitates in layers along the final forging drawing direction and is elongated into rods. At the same time, the alloy precipitates nano-scale needle-like secondary α phase during the air cooling process.

[0088] Figure 6 This is an SEM image of the layered metastable β titanium alloy prepared in Example 1 after tensile fracture. It can be seen from the figure that the layered rod-shaped α phase can hinder the propagation of planar slip.

[0089] Figure 7 This is a TEM image of the rod-shaped α phase after stretching in the layered metastable β titanium alloy prepared in Example 1. As can be seen from the image, the stress-induced HCP structure transformation of the rod-shaped α phase to the FCC structure alleviates stress concentration at the α / β phase interface, inhibits crack initiation, and significantly improves the alloy's plasticity.

[0090] Figure 8 Schematic diagram of the plasticization mechanism of the rod-shaped α phase. As can be seen from the figure, the alloy's deformation mode is primarily slip. Furthermore, the lamellar distribution of the rod-shaped α phase hinders the propagation of planar slip. The stress-induced transformation of the rod-shaped α phase into an FCC structure alleviates stress concentration at the α / β phase interface, inhibiting crack initiation and significantly improving the alloy's plasticity.

[0091] Figure 9 Mechanical properties diagram of the materials prepared for Example 1 and Comparative Example 1.

[0092] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0093] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A metastable β titanium alloy with a layered structure plasticized by a rod-shaped α phase, characterized in that: In terms of mass percentage, excluding Ti, the elemental composition includes: Mo 6.0~8.0%, Nb 2.0~4.0%, Cr 2.0~4.0%, Al 0.5~3% and Zr 1.0~3.0%.

2. A method for preparing a layered metastable β titanium alloy plasticized by a rod-shaped α phase according to claim 1, characterized in that the steps include: uniformly melting the titanium alloy raw material to prepare a titanium alloy ingot; The titanium alloy ingot is subjected to a first heat treatment at a first preset temperature, followed by blank forging, and then subjected to a second heat treatment at a second preset temperature, followed by β phase → α + β phase cross-zone forging, and after remelting and heat preservation treatment, a small downward pressure deformation treatment is performed, and the layered structure metastable β titanium alloy is obtained after cooling.

3. The preparation method according to claim 2, wherein The first preset temperature is 100-200° C. higher than the β / (α+β) phase transition point temperature; and / or the first heat treatment time is 30-60 min.

4. The preparation method according to claim 2, wherein The pressing rate of the blank forging is 4-6 mm / s. The titanium alloy ingot is first forged along the height Z direction with a deformation of 40-60%, and then forged in the X and Y directions with deformations of 20-40% respectively.

5. The preparation method according to claim 2, wherein The second preset temperature is 40-60° C. higher than the β / (α+β) phase transition point temperature.

6. The preparation method according to claim 2, wherein The second heat treatment time is 10-30 minutes.

7. The preparation method according to claim 2, wherein The cross-region forging of the β phase → α + β phase is performed by first forging in the Z direction with a deformation of 40-60%, and then switching to forging in the X and Y directions with deformations of 20-40% respectively.

8. The preparation method according to claim 2, wherein The time for the reheating and heat preservation treatment is 10-30 minutes.

9. The preparation method according to claim 2, wherein The small downward pressure deformation process is to continuously reverse the X and Y directions to perform small downward pressure deformation, and the deformation amounts in the two directions are 20-40% respectively.

10. Application of the layered metastable β titanium alloy plasticized by rod-shaped α phase according to claim 1 in the fields of aerospace, biomedicine and petrochemical industry.

Images