Ultrahigh-strength titanium alloy capable of being directly printed

Abstract

The invention discloses an ultrahigh-strength titanium alloy capable of being directly printed. The ultrahigh-strength titanium alloy comprises the following chemical components in percentage by mass: less than or equal to 0.1% of C, 5.5-6.8% of Al, 3.5-4.5% of V, less than or equal to 0.3% of Fe, 0.1-0.2% of Mo, 0.2-0.4% of O, less than or equal to 0.015% of H, less than or equal to 0.05% of N and the balance of Ti and inevitable impurities. The ultrahigh-strength titanium alloy is prepared on the basis of a laser powder bed melting technology. The ultrahigh-strength titanium alloy capable of being directly printed is obtained through component regulation and control and additive manufacturing process adjustment, the subsequent heat treatment process is not needed, the preparation cost of the ultrahigh-strength titanium alloy is reduced, and the production efficiency is remarkably improved. The density of the obtained ultrahigh-strength titanium alloy reaches 99.8% or above, the tensile strength is larger than or equal to 1400 MPa, the yield strength is larger than or equal to 900 MPa, and the ductility is larger than or equal to 7.0%.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy technology, and in particular relates to an ultra-high strength titanium alloy that can be directly printed. Background Technology

[0002] Titanium and titanium alloys are widely used in aerospace, biomedicine, and mechanical engineering due to their excellent corrosion resistance, low density, good biocompatibility, and high specific strength. Among them, ultra-high-strength titanium alloys with a room temperature tensile strength >1300 MPa possess ultra-high strength, high specific strength, and corrosion resistance, making them a key focus in the development of the titanium alloy field and a structural material with great application prospects. Currently, the preparation of ultra-high-strength titanium alloys still mainly relies on traditional smelting, forging, and multi-stage subsequent heat treatment processes. However, this process cannot achieve low-cost and efficient fabrication of complex structural parts. Laser powder bed melting (LPBF) technology, a type of additive manufacturing (AM), is currently the most widely used technology in titanium alloy additive manufacturing. Compared with traditional manufacturing processes, it has significant advantages, such as free design of part shapes, near-net-shape or net-shape production, and high material utilization. However, the following problems still exist in the preparation of ultra-high strength titanium alloys by LPBF technology: (1) Traditional ultra-high strength titanium alloys all require the addition of a large number of β phase stabilizing elements (Mo, Nb, Cr, Fe, V, etc.) for alloying, and under forging + heat treatment conditions, high-density secondary α phase is precipitated to achieve ultra-high strength. However, due to the rapid cooling process characteristics of LPBF, the titanium alloys produced are usually acicular martensite (a typical structure of titanium alloys that are rapidly cooled), and secondary α phase cannot be obtained, so the strength cannot reach the ultra-high strength level; (2) The plasticity of the printed parts is usually significantly worse than that of titanium alloys prepared by traditional processes due to the influence of internal residual stress, making it difficult to achieve a balance between strength and plasticity, thus limiting its application and development in this field. At present, the most common solution is to perform subsequent heat treatment on the printed parts of traditional ultra-high strength titanium alloys to regulate the microstructure of the titanium alloy and eliminate residual stress, thereby improving the strength and elongation of the printed parts. However, the heat treatment process is prone to causing deformation of the parts, that is, the dimensional accuracy is difficult to control, and it also increases the preparation cost and production cycle, which is not conducive to green and sustainable development. Summary of the Invention

[0003] In view of the above technical problems, the present invention provides an ultra-high strength titanium alloy that can be directly printed. By controlling the composition and adjusting the additive manufacturing process, it eliminates the need for subsequent heat treatment, and realizes a short-process and low-cost preparation of ultra-high strength titanium alloys through additive manufacturing. This solves the problems of high cost and difficulty in controlling shape and size that currently require subsequent heat treatment processes.

[0004] The objective of this invention is mainly achieved through the following technical solutions: On one hand, the present invention provides a method for preparing ultra-high strength titanium alloy, wherein the chemical composition of the ultra-high strength titanium alloy comprises, by mass percentage (wt.%): C≤0.1%, Al: 5.5%~6.8%, V: 3.5%~4.5%, Fe≤0.3%, Mo: 0.1%~0.2%, O: 0.2%~0.4%, H≤0.015%, N≤0.05%, with the balance being Ti and unavoidable impurities; the method is based on laser powder bed melting technology to prepare ultra-high strength titanium alloy.

[0005] In a preferred embodiment, the particle size of the raw material powder used in the laser powder bed melting technology for preparing ultra-high strength titanium alloy is 15~53 μm.

[0006] In some specific embodiments, the raw material powder used in the laser powder bed melting technology to prepare ultra-high strength titanium alloys may contain a low oxygen content, for example, 0.1 wt.%, and then the O content may be increased to 0.2~0.4 wt.% by heating in an argon-oxygen atmosphere. The heating temperature is 400~600℃; the heating time is 5~30 min.

[0007] In some specific embodiments, the flowability of the raw material powder used in the laser powder bed melting technology to prepare ultra-high strength titanium alloy is 30~45 s / 50 g.

[0008] In a preferred embodiment, the laser power for preparing ultra-high strength titanium alloys using the laser powder bed melting technology is 200~400 W.

[0009] In a preferred embodiment, the scanning speed for preparing ultra-high strength titanium alloys using the laser powder bed melting technology is 700~1000 mm / s.

[0010] In a preferred embodiment, the pass spacing of the laser powder bed melting technology for preparing ultra-high strength titanium alloy is 80~120 μm.

[0011] In a preferred embodiment, the powder bed thickness of the ultra-high strength titanium alloy prepared by the laser powder bed melting technology is 30~90 μm.

[0012] In a preferred embodiment, the interlayer dwell time for preparing ultra-high strength titanium alloys using the laser powder bed melting technology is 5-10 seconds.

[0013] As a preferred embodiment, the laser powder bed melting technology for preparing ultra-high strength titanium alloys is carried out in a protective atmosphere; the protective atmosphere is high-purity argon (99.99%).

[0014] On the other hand, the present invention provides a directly printable ultra-high strength titanium alloy obtained by the above method.

[0015] The technical effects of this invention are as follows: This invention designs a directly printable ultra-high-strength titanium alloy through composition control and additive manufacturing process adjustments. This eliminates the need for subsequent heat treatment, significantly reducing the manufacturing cost and improving production efficiency. The resulting ultra-high-strength titanium alloy products exhibit strength and elongation comparable to commonly used ultra-high-strength titanium alloys. Furthermore, the direct printing capability greatly reduces manufacturing costs, achieving a balance between low cost and high performance, and is suitable for mass production.

[0016] (1) This invention modifies the microstructure of the printed ultra-high strength titanium alloy by adjusting its composition. The addition of β-stabilizing elements (Fe, Mo, V) expands the β-phase region and lowers the β→α phase transition point, which is beneficial for retaining the residual β-phase during printing, resulting in an α+β dual-phase structure in the printed state. Furthermore, by introducing oxygen as a strengthening element into the titanium alloy, it is enriched in the β-phase and precipitates a nano-second phase, improving strength while maintaining good elongation.

[0017] (2) The present invention uses LPBF forming process to directly form, which reduces material waste, lowers the preparation cost, and can also be used to prepare complex shapes.

[0018] (3) The room temperature tensile strength of the direct-printed ultra-high strength titanium alloy obtained by the present invention is >1400 MPa, yield strength is >900 MPa, and elongation at break is >7%. Attached Figure Description

[0019] Figure 1 This is a physical image of the LPBF molded part in Embodiment 1 of the present invention; Figure 2 This is a SEM image of the microstructure of the LPBF molded part in Embodiment 2 of the present invention; Figure 3 This is the room temperature tensile stress-strain curve of the LPBF molded part in Embodiment 3 of the present invention. Detailed Implementation

[0020] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0022] This invention provides a directly printable ultra-high strength titanium alloy with the following chemical composition by mass percentage (wt.%): C≤0.1%, Al: 5.5%~6.8%, V: 3.5%~4.5%, Fe≤0.3%, Mo: 0.1%~0.2%, O: 0.2%~0.4%, H≤0.015%, N≤0.05%, with the balance being Ti and unavoidable impurities.

[0023] The composition design of this invention is based on the following principles: Carbon: As an interstitial solid solution atom, carbon can improve the overall strength of titanium alloys. However, while increasing strength, it also impairs the ductility, toughness, and weldability of titanium alloys. Carbon is generally considered an impurity element in titanium alloys. Taking all factors into consideration, the carbon content of the titanium alloy in this invention is controlled to be less than 0.1%.

[0024] Aluminum: Aluminum is the most commonly used α-stabilizing element in titanium alloys. By strengthening titanium alloys through substitution solid solution, adding an appropriate amount of aluminum can improve the room temperature and high temperature strength, as well as the thermoplasticity. Generally, an appropriate amount of aluminum is added to almost all types of titanium alloys both domestically and internationally. However, if too much aluminum is added, it can easily form a brittle Ti3Al phase in the titanium alloy, significantly reducing its ductility and toughness. Therefore, excessive aluminum addition should be avoided during alloy design. In this invention, the aluminum content of the titanium alloy is controlled within 5.5% to 6.8%.

[0025] Vanadium: Vanadium is the most widely used β-phase stabilizing element in titanium alloys, strengthening the β-phase through substitutional solid solution. Adding vanadium can significantly lower the α-β phase transformation point, increase the hardenability of titanium alloys, and thus enhance the heat treatment strengthening effect. Furthermore, compared with other β-stabilizing elements (Fe), vanadium is less prone to segregation and exhibits good microstructural stability at high temperatures. However, vanadium is a strategic element and is very expensive. Adding excessive vanadium to titanium alloys will significantly increase the cost. Therefore, the cost associated with adding vanadium needs to be considered in alloy design. In summary, the vanadium content of the titanium alloy in this invention is controlled at 3.5%~4.5%.

[0026] Oxygen: Oxygen is an interstitial solid solution element in titanium alloys, playing a role in solid solution strengthening. Simultaneously, the interaction between oxygen and dislocations in titanium alloys can significantly improve their strength. However, most studies report that while the addition of oxygen increases the strength of titanium alloys, it also results in a loss of ductility and toughness, leading to a significant decrease in elongation. Excessive oxygen content can also promote the formation of the brittle Ti3Al phase in titanium alloys, making them brittle. This invention uses oxygen as the main strengthening element for titanium alloys, overturning the traditional understanding that oxygen content and ductility are inversely proportional. It achieves a synergistic balance between strength and ductility, providing a new approach for the design of high-performance metallic materials. The main reason is that the rapid cooling rate of LPBF technology enriches oxygen in the formed titanium alloy parts, forming an oxygen-rich phase, allowing the titanium alloy to maintain a certain level of ductility and toughness while achieving high strength. In summary, the oxygen content of the titanium alloy in this invention is controlled at 0.2%~0.4%.

[0027] Nitrogen and hydrogen: Nitrogen and hydrogen are generally considered impurity elements in titanium alloys. They can improve the strength of titanium alloys but significantly reduce their ductility and toughness. Hydrogen's effect on the mechanical properties of titanium is also reflected in hydrogen embrittlement. When the hydrogen content reaches a certain level, it will increase the notch sensitivity of the titanium alloy, thereby drastically reducing the impact toughness and other properties of the notched specimen. Therefore, the nitrogen and hydrogen content in titanium must be strictly controlled. In this invention, the nitrogen and hydrogen contents of the titanium alloy are controlled to within 0.05% and 0.015%, respectively.

[0028] Iron and molybdenum: Iron and molybdenum are also added as β-phase stabilizing elements. Among them, iron is the element with the strongest β-phase stability in titanium alloys, strengthening the β-phase through substitution solid solution. The addition of iron and molybdenum further expands the β-phase region, lowers the β→α phase transformation point, and is beneficial for the retention of residual β-phase during the printing process, resulting in an α+β dual-phase microstructure in the printed state.

[0029] Example 1 The chemical composition of the ultra-high strength titanium alloy prepared in this embodiment is C: 0.08%, Al: 6.3%, V: 4.0%, Fe: 0.2%, Mo: 0.1%, O: 0.30%, H: 0.013%, N: 0.018%, with the balance being Ti and unavoidable impurities.

[0030] This embodiment utilizes laser powder bed fusion (LPBF) technology to prepare ultra-high strength titanium alloys. The particle size range of the raw material powder used for printing is 15–53 μm, and the flowability is 33.5 s / 50 g. The printing process is carried out in a high-purity argon atmosphere, with the following printing parameters: laser power 200 W, scanning speed 800 mm / s, pass spacing 110 μm, powder thickness 60 μm, and interlayer residence time 6 s.

[0031] Figure 1This is a photograph of the LPBF formed part prepared in this embodiment. The microstructure of the LPBF-formed titanium alloy sample was observed, and then it was machined into tensile bars for room temperature mechanical property testing. The tensile strength was 1425 MPa, the yield strength was 912 MPa, and the elongation after fracture was 8.9%.

[0032] Example 2 The chemical composition of the ultra-high strength titanium alloy prepared in this embodiment is C: 0.07%, Al: 6.1%, V: 3.9%, Fe: 0.3%, Mo: 0.2%, O: 0.32%, H: 0.012%, N: 0.002%, with the balance being Ti and unavoidable impurities.

[0033] This embodiment utilizes laser powder bed fusion (LPBF) technology to prepare ultra-high strength titanium alloys. The particle size range of the raw material powder used for printing is 15–53 μm, and the flowability is 33.5 s / 50 g. The printing process is carried out in a high-purity argon atmosphere, with the following printing parameters: laser power 350 W, scanning speed 700 mm / s, pass spacing 100 μm, powder thickness 90 μm, and interlayer residence time 8 s.

[0034] Microstructural observation of the titanium alloy sample after LPBF forming, such as Figure 2 As shown, the microstructure of the ultra-high strength titanium alloy formed by LPBF consists of acicular α' martensite interspersed within the primary β grains. α' martensite is a non-equilibrium phase; the rapid cooling during the LPBF process leads to a non-equilibrium phase transformation from the primary β phase to α' martensite. Numerous studies have shown that acicular α' microstructure can effectively improve the strength of titanium alloy formed parts. In addition to acicular martensite, short rod-shaped β microstructure also exists, which can effectively improve the elongation of the formed parts. The formed parts were then machined into tensile bars for room temperature mechanical property testing. The tensile strength was 1474 MPa, the yield strength was 1050 MPa, and the elongation after fracture was 8.0%.

[0035] Example 3 The chemical composition of the ultra-high strength titanium alloy prepared in this embodiment is C: 0.05%, Al: 6.5%, V: 3.5%, Fe: 0.29%, Mo: 0.1%, O: 0.28%, H: 0.010%, N: 0.019%, with the balance being Ti and unavoidable impurities.

[0036] This embodiment utilizes laser powder bed fusion (LPBF) technology to prepare ultra-high strength titanium alloys. The particle size range of the raw material powder used for printing is 15~53 μm, and the flowability is 33.5 s / 50g. The printing process is carried out in a high-purity argon atmosphere, with the following printing parameters: laser power 280W, scanning speed 1000 mm / s, pass spacing 120 μm, powder thickness 30 μm, and interlayer dwell time 9 s.

[0037] The microstructure of the LPBF-formed titanium alloy sample was observed, and then it was machined into tensile bars for room temperature mechanical property testing. The tensile strength was 1449 MPa, the yield strength was 1100 MPa, and the elongation after fracture was 7.0%. Its stress-strain curve is shown below. Figure 3 As shown.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of making an ultra-high strength titanium alloy, characterized by, The chemical composition of the ultra-high-strength titanium alloy includes, in terms of mass percentage (wt.%): C≤0.1%, Al: 5.5%-6.8%, V: 3.5%-4.5%, Fe≤0.3%, Mo: 0.1%-0.2%, O: 0.2%-0.4%, H≤0.015%, N≤0.05%, the balance being Ti and inevitable impurities; and the method is based on a laser powder bed melting technique to prepare the ultra-high-strength titanium alloy.

2. The method of claim 1, wherein, The particle size of the raw material powder used in the laser powder bed melting technique to prepare the ultra-high-strength titanium alloy is 15-53 μm.

3. The method of claim 1, wherein, The flowability of the raw material powder used in the laser powder bed melting technique to prepare the ultra-high-strength titanium alloy is 30-45 s / 50 g.

4. The method of claim 1, wherein, The laser power used in the laser powder bed melting technique to prepare the ultra-high-strength titanium alloy is 200-400 W.

5. The method of claim 1, wherein, The scanning speed used in the laser powder bed melting technique to prepare the ultra-high-strength titanium alloy is 700-1000 mm / s.

6. The method of claim 1, wherein, The path distance used in the laser powder bed melting technique to prepare the ultra-high-strength titanium alloy is 80-120 μm.

7. The method of claim 1, wherein, The powder laying thickness used in the laser powder bed melting technique to prepare the ultra-high-strength titanium alloy is 30-90 μm.

8. The method of claim 1, wherein, The interlayer residence time used in the laser powder bed melting technique to prepare the ultra-high-strength titanium alloy is 5-10 s.

9. The method of claim 1, wherein, The laser powder bed melting technique to prepare the ultra-high-strength titanium alloy is carried out in a protective atmosphere; and the protective atmosphere is high-purity argon.

10. A directly printable ultra-high-strength titanium alloy obtained by the method of any one of claims 1-9.

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