Low-molybdenum equivalent low-cost lightweight super-high-strength titanium alloy and preparation method thereof

Abstract

The application discloses a low-molybdenum equivalent low-cost light-weight super-high-strength titanium alloy and a preparation method thereof, and belongs to the technical field of titanium alloys. The alloy is composed of the following elements in the following mass percentages: Al: 6-8%, Mo: 0.5-1.5%, V: 0.5-1.5%, Cr: 0.5-2%, Zr: 0.5-3%, C: 0.1-0.5%, and the balance of Ti and inevitable impurities. The application further discloses a preparation method of the low-molybdenum equivalent low-cost light-weight super-high-strength titanium alloy. The application uses the low-density interstitial element C and the alpha-stabilizing element Al as the main strengthening elements, replaces or reduces the use of the conventional high-density or high-cost beta-stabilizing elements such as Mo, V, W, Fe, Nb and Mn, and simultaneously uses the Cr element to refine the secondary alpha phase aged and precipitated, so that the low-molybdenum equivalent low-cost light-weight super-high-strength titanium alloy is prepared, the strength and plasticity of the alloy are superior to those of the conventional high-molybdenum equivalent high-strength titanium alloy, the density and raw material cost of the alloy are also significantly reduced, and the application has important engineering application significance.

Description

Technical Field

[0001] This invention relates to a low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent and its preparation method, belonging to the field of titanium alloy technology. Background Technology

[0002] High-strength titanium alloys generally refer to titanium alloys with a room temperature strength greater than 1100 MPa after heat treatment. High-strength titanium alloys possess advantages such as low density, high specific strength, high damage tolerance, and good wear and corrosion resistance. They are widely used in important structural components such as aerospace fasteners, aircraft landing gear, and fuselage load-bearing beams, reducing the weight of structural components by 30% to 40%. With the rapid development of the aerospace industry and increasingly demanding service conditions, higher requirements are being placed on the performance of high-strength titanium alloys. β-type titanium alloys, with their age-hardening characteristics and good strength-toughness matching, have become the best choice for ultra-high-strength titanium alloys. Molybdenum equivalent ([Mo]) eq [Mo] is an important parameter for measuring the β phase content and stability in high-strength titanium alloys, and also an important criterion for the design of high-strength β titanium alloys. eq The higher the [Mo] content, the higher the stability of the β phase, and the more significant its precipitation strengthening effect. eq A Mo content of 8.0 or higher is required to obtain stable β-type titanium alloys and achieve high strength. Commonly used [Mo]... eq The calculation formula is:

[0003] [Mo] eq = [Mo]+0.28[Nb]+0.2[Ta]+0.4[W]+1.25[Cr]+1.7[Mn]+0.67[V]+2.5[Fe]+1.7[Co]+1.25[Ni], where [X] is the mass fraction of element X in the titanium alloy.

[0004] Based on the molybdenum equivalent criterion, a series of ultra-high-strength titanium alloys with room-temperature strength exceeding 1350 MPa have been developed, such as Ti-3Al-8V-6Cr-4Mo-4Zr (β-C), Ti-15Mo-3Al-2.7Nb-0.25Si (β-21S), Ti-6.5Mo-4.5Al-2.6Nb-2Cr-2Zr-1V-1Sn (TB17), Ti-5Al-4Mo-4V-4Cr-3Zr (Ti-1300), and Ti-5Al-5Mo-5V-3Cr (Ti-5553). A common characteristic of these ultra-high-strength titanium alloys is the addition of large amounts of β-stabilizing elements such as Mo, V, and Cr for solid solution strengthening, thereby improving the alloy's room-temperature strength. However, this also leads to common disadvantages of such titanium alloys: (1) poor plasticity: high content of β-stabilizing elements results in a high molybdenum equivalent in the alloy, which leads to high strength after solution aging, but significantly deteriorates plasticity (less than 5%); (2) high cost: the raw materials for β-stabilizing elements are generally various intermediate alloys, which are expensive, resulting in a 50% to 250% increase in raw material cost compared to traditional TC4 titanium alloys; (3) high density: β-stabilizing elements such as Mo, Nb, and Fe have high density, and the addition of high content of β-stabilizing elements will increase the density of the alloy by 5% to 20% compared to traditional TC4 titanium alloys. The above shortcomings greatly limit the engineering application of such ultra-high strength titanium alloys. Therefore, it is urgent to develop a low-cost, lightweight ultra-high strength titanium alloy with low molybdenum equivalent. Summary of the Invention

[0005] To address the shortcomings of existing ultra-high strength titanium alloys, this invention aims to provide a low-cost, lightweight ultra-high strength titanium alloy with low molybdenum equivalent and its preparation method. This method enables the production of ultra-high strength titanium alloys under low molybdenum equivalent conditions, while maintaining the alloy's plasticity within an acceptable range. The raw material cost and density of this alloy are significantly reduced compared to existing ultra-high strength titanium alloys, and this alloy has broad application prospects in the aerospace field.

[0006] The technical solution of the present invention is as follows:

[0007] A low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent has the following alloy composition by mass percentage: Al: 6%–8%, Mo: 0.5%–1.5%, V: 0.5%–1.5%, Cr: 0.5%–2%, Zr: 0.5%–3%, C: 0.1%–0.5%, with the balance being Ti and unavoidable impurities.

[0008] The low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy provided by this invention uses Al, a low-density α-stabilizing element, as the main alloying element to reduce the molybdenum equivalent, lower the alloy density, and provide solid solution strengthening. Simultaneously, the high Al content causes the precipitation of nano-ordered Ti3Al(α2) phases in the alloy, achieving a significant dispersion strengthening effect. Furthermore, the active introduction of interstitial element C further enhances the solid solution strengthening and precipitation strengthening effects in the alloy. The addition of small amounts of β-stabilizing elements Mo, V, and Cr is for solid solution strengthening of the β phase, lowering the phase transformation point, increasing hardenability, and improving the alloy's machinability. Cr also refines the secondary α phase precipitated during aging, thereby significantly improving the alloy's strength. Zr, as a near-neutral element, provides solid solution strengthening and can improve the overall room temperature strength of the alloy.

[0009] This invention uses inexpensive and low-density Al and C elements as the main strengthening elements, replacing the high-content, high-cost, and high-density β-stabilizing elements in traditional high-strength titanium alloys, such as Mo, V, W, Fe, Nb, and Mn. This yields an ultra-high-strength titanium alloy with a room-temperature strength greater than 1500 MPa under lower molybdenum equivalent conditions, while significantly reducing cost and density. Simultaneously, the introduction of the interstitial element C strengthens the primary α phase (α...). p This improved the primary α phase and β transformation tissue (β). T The ability to coordinate deformation avoids α p / β T Stress concentration at the interface leads to premature material failure, thus preventing a significant deterioration (greater than 8%) in the plasticity of the ultra-high strength titanium alloy. This invention addresses the problems of low plasticity, high cost, and high density in traditional ultra-high strength titanium alloys through optimization of alloying elements. It provides a low-molybdenum equivalent, low-cost, lightweight ultra-high strength titanium alloy with a room temperature strength ≥1500MPa and an elongation ≥8%, while simultaneously exhibiting significantly lower raw material costs and density compared to traditional high-molybdenum equivalent ultra-high strength titanium alloys.

[0010] This invention also provides a method for preparing the above-mentioned low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent, comprising the following steps:

[0011] (1) Smelting: Using sponge titanium, Al source, Mo source, V source, Cr source, Zr source and C source as raw materials, the raw materials are mixed and stirred evenly, and then pressed into alloy rods. The alloy rods are welded into vacuum self-consuming electrodes by argon arc welding, and the electrodes are vacuum self-consuming smelting 2 to 4 times to form titanium alloy ingots.

[0012] The Al source is elemental Al.

[0013] The Mo source is an intermediate alloy formed by Mo and Ti.

[0014] The intermediate alloy formed by V source V and Al.

[0015] The Cr source is elemental Cr.

[0016] The Zr source is elemental Zr.

[0017] The C source is C elemental powder.

[0018] (2) Hot deformation: The phase transformation point temperature of the titanium alloy ingot obtained in step (1) is measured by metallographic method; the titanium alloy ingot is forged into a flat ingot by 1 to 2 forging passes, with the forging temperature 100℃ to 200℃ above the phase transformation point, in order to break up the coarse cast grains; the flat ingot is rolled to a specified thickness in 9 to 13 passes, with the rolling temperature 30℃ to 50℃ below the phase transformation point, and the deformation amount per pass is controlled at 10% to 25%, finally obtaining the plate.

[0019] (3) Heat treatment: The plate obtained in step (2) is kept at 30℃~100℃ below the phase transformation point temperature of the titanium alloy ingot for 20min~60min, then water-cooled to room temperature, and then kept at 450℃~600℃ for 4h~8h, and naturally cooled in air to obtain a low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent as described in this invention.

[0020] Beneficial effects:

[0021] (1) The present invention provides a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy, wherein the weight percentage of alloying elements is: Al: 6%–8%, Mo: 0.5%–1.5%, V: 0.5%–1.5%, Cr: 0.5%–2%, Zr: 0.5%–3%, C: 0.1%–0.5%, with the balance being Ti and unavoidable impurities. The high content of Al, as the main alloying element, reduces the molybdenum equivalent, lowers the alloy density, and provides significant solid solution strengthening and Ti3Al dispersion strengthening effects; the active introduction of the interstitial element C provides significant solid solution strengthening and Ti3Al dispersion strengthening effects. x C precipitation enhances the effect, and also strengthens the primary α phase (α). p ), making α p and β T Improved coordinated deformation capability, avoiding α p / β T Premature material failure caused by stress concentration at the interface prevents significant deterioration of the plasticity of the ultra-high strength titanium alloy. The addition of Cr can significantly refine the secondary α phase precipitated during aging and improve the alloy strength. The addition of small amounts of β-stabilizing elements Mo and V is to strengthen the β phase through solid solution, lower the phase transformation point, increase hardenability, and improve the machinability of the alloy. Meanwhile, Zr, as a near-neutral element, provides solid solution strengthening and enhances the room temperature strength of the alloy.

[0022] (2) The titanium alloy of the present invention has a room temperature strength ≥1500MPa and an elongation ≥8%, achieving an excellent balance of strength and plasticity.

[0023] (3) The [Mo] in the ultra-high strength titanium alloy of the present invention eq The [Mo] content is 0.46–5.0, while that of traditional ultra-high strength titanium alloys is much lower. eq Typically above 10, lower [Mo] eq This makes the raw material cost and density of the alloy much lower than those of traditional ultra-high strength titanium alloys.

[0024] (4) The low molybdenum equivalent low-cost lightweight ultra-high strength titanium alloy of the present invention has significant advantages in strength, plasticity, cost and density compared with the commonly used ultra-high strength titanium alloys, and is expected to become a candidate material for ultra-high strength titanium alloys in the aerospace field. Attached Figure Description

[0025] Figure 1 Microstructure images of the low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy described in Example 1: (a) SEM image; (b) high-magnification SEM image; (c) primary α phase (α p TEM image; (d) Secondary α phase (α s TEM image; (e) α after 2% strain p Photograph; (f) α after 2% strain s photo;

[0026] Figure 2 The room temperature quasi-static tensile stress-strain curve of the low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy described in Example 2 is shown.

[0027] Figure 3 This is a schematic diagram comparing the raw material costs and density of the low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy described in Example 3 with that of traditional high-strength titanium alloys. Detailed Implementation

[0028] The technical solution of the present invention, a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy and its preparation method, will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] The raw material cost accounting basis for the low-cost, lightweight, ultra-high-strength titanium alloys with low molybdenum equivalent in Examples 1-3 of this invention is shown in Table 1 below.

[0030] Table 1. Raw material costs for titanium alloy smelting

[0031] 1 Titanium sponge Ti 65 2 Aluminum Bean Al 27 3 Titanium molybdenum Ti-32Mo 420 4 Aluminum Vanadium Al-85V 380 5 chromium Cr 110 6 zirconium Zr 245 7 Nano carbon powder C 2531 8 Titanium Niobium Ti-60Nb 680 9 aluminum silicon Al-10Si 120 10 Titanium Iron Ti-32Fe 155 11 Titanium Tin Ti-80Sn 290 12 Aluminum molybdenum Al-60Mo 200 13 Aluminum Vanadium Al-55V 280

[0032] Example 1

[0033] This embodiment of a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy is composed of the following components by mass percentage: Al 7%, Mo 0.5%, V 0.7%, Cr 1.5%, Zr 1%, C 0.4%, with the balance being Ti and unavoidable impurities.

[0034] The preparation method of a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy in this embodiment is as follows:

[0035] (1) Smelting: According to the above composition ratio, sponge titanium, aluminum briquettes, Ti-Mo master alloy, Al-V master alloy, elemental Cr, elemental Zr, and C powder are selected as raw materials for batching. After the raw materials are mixed evenly, they are pressed into alloy rods by a hydraulic press. Then, the alloy rods are welded into electrodes by argon arc welding. Vacuum consumable melting is performed three times, and the melting vacuum degree is 2×10. -2 Pa, melting voltage of 32V, melting current of 3000A, finally obtained a titanium alloy ingot with a diameter of 220mm and a weight of 100kg;

[0036] (2) Hot deformation: The phase transformation temperature of the titanium alloy ingot obtained in step (1) was measured to be 1130℃ by metallographic method; the titanium alloy ingot was forged radially in one pass at a forging temperature of 1250℃, and finally a flat ingot with a thickness of 70mm was obtained; the flat ingot was rolled and deformed to 8mm in 9 passes at a rolling temperature of 1080℃, and the deformation amount per pass was controlled at 10%-25% to obtain a plate.

[0037] (3) Heat treatment: The plate obtained in step (2) is kept at 1080℃ for 30 minutes, quenched in water to room temperature, kept at 500℃ for 6 hours, and naturally cooled in air to obtain the final sample, which is a low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent as described in this invention.

[0038] The room temperature tensile properties of the low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy prepared in this embodiment are as follows: tensile strength of 1536 MPa, yield strength of 1412 MPa, and elongation of 8.2%.

[0039] The low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy prepared in this embodiment has a density of 4.42 g / cm³. 3 .

[0040] According to calculations, the raw material cost of a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy in this embodiment is 78.5 yuan / kg.

[0041] Figure 1 This is a microstructure photograph of the low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy described in this embodiment. As shown in the figure, the titanium alloy in this embodiment exhibits a bimodal microstructure, consisting of equiaxed α-phase... pThe grains, β grains, and nanoscale needle-like α particles precipitated within the β matrix s Composition. Nanoscale needle-like α s The precipitation of these elements significantly increases the α / β phase interface within the alloy, hindering dislocation slip and thus significantly improving the alloy's strength. Simultaneously, high contents of Al, Zr, and C elements significantly strengthen the α phase. p Grains, making α p Grains and β T The tissue can deform in a coordinated manner, with needle-like α-shaped structures. s It also participates in deformation, which gives the alloy good elongation.

[0042] Example 2

[0043] This embodiment of a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy is composed of the following components by mass percentage: Al 8%, Mo 0.5%, V 0.5%, Cr 2%, Zr 2%, C 0.1%, with the balance being Ti and unavoidable impurities.

[0044] The preparation method of a low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent in this embodiment is as follows:

[0045] (1) Smelting: According to the above composition ratio, sponge titanium, aluminum briquettes, Ti-Mo master alloy, Al-V master alloy, elemental Cr, elemental Zr, and C powder are selected as raw materials for batching. After the raw materials are mixed evenly, they are pressed into alloy rods by a hydraulic press. Then, the alloy rods are welded into electrodes by argon arc welding. Vacuum consumable melting is performed four times, and the melting vacuum degree is 2.5×10 -2 Pa, melting voltage of 35V, melting current of 2800A, finally obtained a titanium alloy ingot with a diameter of 230mm and a weight of 100kg;

[0046] (2) Hot deformation: The phase transformation temperature of the titanium alloy ingot obtained in step (1) was measured to be 1035℃ by metallographic method; the titanium alloy ingot was ground radially and then forged in two passes at forging temperatures of 1200℃ and 1150℃ respectively, finally obtaining a flat ingot with a thickness of 70mm; the flat ingot was rolled and deformed to 8mm in 11 passes at a rolling temperature of 1000℃, and the deformation amount per pass was controlled at 10%-25%, to obtain a plate.

[0047] (3) Heat treatment: The plate obtained in step (2) is kept at 1000℃ for 40 min, quenched in water to room temperature, kept at 550℃ for 5 h, and naturally cooled in air to obtain the final sample, which is a low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent as described in this invention.

[0048] The room temperature tensile properties of the low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy prepared in this embodiment are as follows: tensile strength of 1503 MPa, yield strength of 1394 MPa, and elongation of 9.1%. Its room temperature tensile stress-strain curve is shown below. Figure 2 As shown.

[0049] The low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy prepared in this embodiment has a density of 4.41 g / cm³. 3 .

[0050] According to calculations, the raw material cost of a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy in this embodiment is 72.1 yuan / kg.

[0051] Example 3

[0052] This embodiment of a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy is composed of the following components by mass percentage: Al 8%, Mo 1%, V 1%, Cr 0.5%, Zr 0.5%, C 0.2%, with the balance being Ti and unavoidable impurities.

[0053] The preparation method of a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy in this embodiment is as follows:

[0054] (1) Smelting: According to the above composition ratio, sponge titanium, aluminum briquettes, Ti-Mo master alloy, Al-V master alloy, elemental Cr, elemental Zr, and C powder are selected as raw materials for batching. After the raw materials are mixed evenly, they are pressed into alloy rods by a hydraulic press. Then, the alloy rods are welded into electrodes by argon arc welding. Vacuum consumable melting is performed three times, and the melting vacuum degree is 2.8×10 -2 Pa, melting voltage of 28V, melting current of 3200A, finally obtained a titanium alloy ingot with a diameter of 234mm and a weight of 100kg;

[0055] (2) Hot deformation: The phase transformation temperature of the titanium alloy ingot obtained in step (1) was measured to be 1090℃ by metallographic method; the titanium alloy ingot was forged in one heat at a temperature of 1200℃ to obtain a flat ingot with a thickness of 70mm; the flat ingot was rolled to 8mm in 13 passes at a rolling temperature of 1050℃, and the deformation amount per pass was controlled at 10%-25% to obtain a plate.

[0056] (3) Heat treatment: The plate obtained in step (2) is kept at 1050℃ for 60 min, quenched in water to room temperature, kept at 450℃ for 8 h, and naturally cooled in air to obtain the final sample, which is a low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent as described in this invention.

[0057] The room temperature tensile properties of the low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy prepared in this embodiment are as follows: tensile strength of 1564 MPa, yield strength of 1428 MPa, and elongation of 8.3%.

[0058] The low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy prepared in this embodiment has a density of 4.38 g / cm³. 3 .

[0059] According to calculations, the raw material cost of a low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy in this embodiment is 74.6 yuan / kg.

[0060] Figure 3 This diagram illustrates the comparison of raw material costs and densities between the low-molybdenum equivalent, low-cost, lightweight, ultra-high-strength titanium alloy described in this embodiment and traditional high-strength titanium alloys. It can be seen that the titanium alloy in this embodiment, while possessing ultra-high strength and good elongation, has a density and raw material cost that are far lower than those of traditional high-strength titanium alloys, and thus has broad application prospects.

[0061] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent, characterized in that, The alloy composition, by mass percentage, is: Al: 6.0%–8.0%; Mo: 0.5%~1.5%; V: 0.5%~1.5%; Cr: 0.5%~2.0%; Zr：0.5%～3.0%； C: 0.2%–0.5%, balance being Ti and unavoidable impurities; the preparation method includes the following steps: Step 1: Mix and stir the raw materials evenly, press and weld them into vacuum self-consuming electrodes, and then vacuum self-consuming melt the electrodes into titanium alloy ingots. Step 2: The titanium alloy ingot obtained in Step 1 is subjected to multiple forging and deformation processes to form a flat ingot; the flat ingot is then subjected to multiple rolling and deformation processes to a preset thickness to obtain a plate. Step 3: Heat treat the plate obtained in Step 2 to obtain the low-cost, lightweight, ultra-high-strength titanium alloy with low molybdenum equivalent. The melting described in step one is vacuum self-consumable melting, and the melting is carried out 2 to 4 times to ensure uniform composition. Step two involves 1-2 forging passes at a temperature 100-200°C above the phase transformation point to break up coarse cast grains. Step two also involves 9-13 rolling passes at a temperature 30-50°C below the phase transformation point, with deformation controlled at 10%-25% in each pass. The heat treatment described in step three is as follows: the plate obtained in step two is kept at 30℃~100℃ below the phase transformation temperature of the titanium alloy ingot for 20min~60min, then water-cooled to room temperature, and then kept at 450℃~600℃ for 4h~8h, and then naturally cooled in air.

Images