High-toughness titanium alloy based on structure spheroidizing regulation and preparation method thereof

Abstract

The invention discloses a high-strength and high-toughness titanium alloy based on structure spheroidizing regulation and a preparation method thereof, and the titanium alloy comprises the following components in percentage by mass: 5.5-6.0% of Al, 3.5-4.0% of V, 4.5-5.5% of Cu and the balance of Ti and inevitable impurities. The preparation method comprises the following steps: preparing the pre-alloyed powder of the components; forming by adopting a laser powder bed melting technology; and then carrying out solution treatment at 800-900 DEG C and carrying out water cooling. Through the synergistic effect of addition of the Cu element and solution treatment in a specific temperature interval, a needle-shaped / layered structure generated after fusion forming of a laser powder bed is effectively driven to be converted into a uniform spheroidized structure. The spheroidized structure is composed of an equiaxial or short-rod-shaped alpha phase and an intergranular alpha ''phase, so that the alloy has high strength and high plasticity at the same time at the room temperature, the tensile strength is larger than or equal to 1200 MPa, and the percentage elongation after fracture is larger than or equal to 14%. The process is simple, and the problem that the strength and plasticity of the additive manufacturing titanium alloy are difficult to synchronously improve is effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology for metallic materials, specifically relating to a high-strength and high-toughness titanium alloy based on microstructure spheroidization control and its preparation method. Background Technology

[0002] Ti6Al4V alloy, as an α+β type titanium alloy with excellent comprehensive performance, has become a key material for structural components in the aerospace field and implants in the biomedical field due to its high specific strength, good corrosion resistance and biocompatibility.

[0003] Laser bed melting (LPBF), a typical representative of metal additive manufacturing technology, uses a high-energy laser beam to selectively melt metal powder layer by layer, achieving near-net-shape forming from a 3D model to a dense metal component. It is particularly suitable for forming complex components with intricate internal flow channels, lattice structures, or topologically optimized morphologies. However, the inherently extremely high cooling rate (10^5-10^6 K / s) of LPBF technology, while refining grains and suppressing elemental segregation, also strongly inhibits the equilibrium α+β phase transformation of Ti6Al4V alloys, leading to metastable acicular α' martensite becoming the typical primary depositional structure. While this slender acicular martensite structure imparts high tensile strength (up to 1200 MPa), it also severely limits the material's plastic deformation capacity, resulting in an elongation after fracture often ≤10%, exhibiting a "high strength, low plasticity" characteristic. Simultaneously, the acicular / layered structure causes the component to exhibit significant anisotropy in mechanical properties. These inherent strength-plasticity contradictions and anisotropy issues greatly limit the application of LPBF-formed Ti6Al4V alloys in critical load-bearing structures.

[0004] To synergistically enhance the strength and toughness of materials, conventional alloying modification or heat treatment processes can optimize performance to some extent. However, simple compositional adjustments, without matching the corresponding thermal processes, make it difficult to precisely control microstructure evolution. Conventional heat treatment processes, on the other hand, have a wide processing window but insufficient control precision, easily forming coarse lamellar or basketweave structures, often sacrificing strength while improving plasticity. Therefore, exploring a method that combines specific compositional design with precise heat treatment processes, using their synergistic effect to accurately drive the spheroidization transformation of acicular / layered α-phase, thereby significantly improving plasticity while maintaining high strength, has significant scientific and engineering value. Summary of the Invention

[0005] The purpose of this invention is to address the problem of balancing strength and plasticity in existing laser powder bed fusion titanium alloys by providing a high-strength and high-toughness titanium alloy based on microstructure spheroidization control and its preparation method. This method, through the synergistic effect of optimized composition design and specific solution treatment processes, promotes the transformation of the original acicular / layered microstructure into a uniform spheroidized microstructure, thereby achieving a simultaneous improvement in alloy strength and plasticity.

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

[0007] A high-strength and high-toughness titanium alloy based on microstructure spheroidization regulation, wherein the alloy composition by mass percentage is: Al 5.5-6.0%, V 3.5-4.0%, Cu 4.5-5.5%, with the balance being Ti and unavoidable impurities; the alloy has a molybdenum equivalent (Moeq) of 10-15; the microstructure of the alloy consists of uniformly distributed equiaxed or short rod-shaped α phases and intergranular α" phases, wherein the average aspect ratio of the equiaxed α phase is less than 4, and its volume fraction accounts for more than 70% of the total α phase.

[0008] Furthermore, the room temperature mechanical properties of the alloy meet the following requirements: tensile strength ≥1200MPa, elongation after fracture ≥14%.

[0009] The present invention also provides a method for preparing the above-mentioned high-strength and high-toughness titanium alloy, comprising the following steps:

[0010] (1) Powder preparation: According to the composition of the alloy, prepare pre-alloyed spherical powder with a particle size of 15-53 μm;

[0011] (2) Laser powder bed melting forming: The powder obtained in step (1) is formed by laser powder bed melting technology to obtain a dense alloy sample;

[0012] (3) Solution treatment: The alloy sample obtained in step (2) is solution treated at 800-900℃ and held for 60-120 min, and then cooled at a rate of 500-800℃ / s.

[0013] Furthermore, in step (2), the process parameters for the laser powder bed melting are: laser power 130-160W, scanning speed 1000-1500mm / s, powder layer thickness 30-50μm, and scanning spacing 50-100μm.

[0014] Furthermore, in step (3), the heating rate of the solution treatment is 5-15℃ / min.

[0015] The advantages of this invention are:

[0016] (1) By adding a specific amount of Cu element (4.5-5.5 wt.%) and precisely controlling the solution treatment temperature at 800-900℃, the two work together to effectively drive the transformation of the original acicular α' martensite into uniform equiaxed / short rod-shaped α and α” structures after LPBF forming, thus realizing the active spheroidization control of the structure.

[0017] (2) Excellent performance: The obtained spheroidized structure achieves an excellent match between high strength and high plasticity at room temperature. The tensile strength is not less than 1200MPa, while the elongation after fracture is not less than 14%, which effectively solves the common problem of "inversion of strength and plasticity" in LPBF titanium alloy.

[0018] (3) Simple and efficient process: The heat treatment method of this invention is a one-step solution treatment with a clear process window, simple process flow, and easy implementation and control in industrial production, which helps to ensure the stability of product performance. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation and microstructure spheroidization control of the high-strength and high-toughness titanium alloy of this invention.

[0020] Figure 2 This is a comparative diagram showing the microstructure of the alloy compared to that of the embodiments of the present invention.

[0021] Figure 3 This is a comparative diagram showing the room temperature tensile mechanical properties of the alloys in the embodiments of the present invention. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] like Figure 1-3 As shown:

[0024] Comparative Example 1 (Standard Ti6Al4V Alloy Formulation)

[0025] (1) Alloy powder preparation: First, pre-alloyed spherical powder was prepared by vacuum induction melting gas atomization method according to the composition of Al: 6.0%, V: 4.0% by mass percentage, with the balance being Ti. Then, the powder with a particle size in the range of 15-53 μm was screened out using a sieve and used for subsequent laser powder bed melting and forming. The molybdenum equivalent of this composition was calculated to be approximately 2.5-3.5.

[0026] (2) Laser powder bed melting: The alloy powder prepared above is loaded into a laser powder bed melting device and formed under an argon protective atmosphere (oxygen content less than 100ppm) with the following process parameters: laser power 130-160W, scanning speed 1000-1500mm / s, powder layer thickness 30-50μm, scanning spacing 50-100μm, using a 67° layered stripe scanning strategy, and forming a dense bulk sample with a size of 12mm×20mm×10mm.

[0027] (3) Solution heat treatment: Place the LPBF-formed block sample into a box-type heat treatment furnace. Heat to 700-900℃ at a heating rate of 10℃ / min, and hold at this temperature for 1-2 hours to allow the acicular α' martensite to fully decompose and the elements to diffuse. After the holding time is completed, quickly remove the sample and immerse it in room temperature water for quenching.

[0028] (4) Characterization of structure and properties: The heat-treated samples were observed for structure and tested for mechanical properties.

[0029] a. Microstructure: such as Figure 2 As shown in (a), the original acicular α' martensite of the alloy after step (3) has been completely transformed into layered α structure.

[0030] b. Mechanical properties: Samples were taken along the construction direction for room temperature tensile testing. Results showed (e.g.) Figure 3 The alloy has a tensile strength of approximately 950 MPa and an elongation after fracture of approximately 17%, which is relatively low compared to the control.

[0031] Comparative Example 2 (Contains Cu, but the solution heat treatment temperature is too low)

[0032] (1) Alloy powder preparation: First, pre-alloyed spherical powder was prepared by vacuum induction melting gas atomization method according to the following composition by mass percentage: Al: 5.5%–6.0%, V: 3.5%–4.0%, Cu: 4.5%–5.5%, with the balance being Ti. Then, powder with a particle size in the range of 15–53 μm was screened using a sieve for subsequent laser powder bed melting and forming. The calculated molybdenum equivalent of this composition is approximately 9–15.

[0033] (2) Laser powder bed melting and forming: The process parameters are the same as those of Comparative Example 1.

[0034] (3) Solution heat treatment: The sample was heated to 650℃ at 10℃ / min, held for 90min, and then water quenched.

[0035] (4) Organization and performance: such as Figure 2 As shown in (b), the microstructure consists of a lamellar α-matrix with fine Ti₂Cu intermetallic compound particles distributed on it. Room temperature tensile properties ( Figure 3 The results showed a tensile strength of approximately 1080 MPa, but an elongation after fracture of only about 3%, indicating brittle fracture. In this comparative example, insufficient heat treatment temperature resulted in incomplete solidification of Cu, forming a brittle phase and leading to extremely poor plasticity.

[0036] Example 1 (Invention)

[0037] (1) Alloy powder preparation: First, pre-alloyed spherical powder was prepared by vacuum induction melting gas atomization method according to the following composition by mass percentage: Al: 5.5%–6.0%, V: 3.5%–4.0%, Cu: 4.5%–5.5%, with the balance being Ti. Then, powder with a particle size in the range of 15–53 μm was screened using a sieve for subsequent laser powder bed melting and forming. The calculated molybdenum equivalent of this composition is approximately 9–15.

[0038] (2) Laser powder bed melting and forming: The process parameters are the same as those of Comparative Example 1.

[0039] (3) Solution heat treatment: Place the LPBF-formed block sample into a box-type heat treatment furnace. Heat to 800-900℃ at a heating rate of 10℃ / min, and hold at this temperature for 1-2 hours to allow the acicular α' martensite to fully decompose and the elements to diffuse. After holding, quickly remove the sample and immerse it in room temperature water for quenching at a cooling rate of 500-800℃ / s.

[0040] (4) Characterization of structure and properties: The heat-treated samples were observed for structure and tested for mechanical properties.

[0041] a. Microstructure: such as Figure 2 As shown in (c), the original acicular α' martensite in the alloy treated by this method has been completely transformed into uniformly distributed equiaxed or short rod-shaped α phases (bright white) and intergranular α" phases (dark). Image analysis statistics show that the average aspect ratio of the equiaxed α phase is about 2.5, and its volume fraction accounts for more than 70% of the total α phase.

[0042] b. Mechanical properties: Samples were taken along the construction direction for room temperature tensile testing. Results showed (e.g.) Figure 3 The alloy has a tensile strength greater than 1200 MPa and an elongation after fracture greater than 14%, achieving an excellent match between high strength and high plasticity.

[0043] The above examples demonstrate that only when the specific composition range (especially Cu content) of the present invention and the specific solution treatment temperature (800-900°C) work synergistically can an ideal spheroidized structure be obtained, thereby simultaneously improving the strength and plasticity of the alloy.

[0044] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A high-strength and high-toughness titanium alloy based on microstructure spheroidization regulation, characterized in that: The alloy composition, by mass percentage, is: Al 5.5-6.0%, V 3.5-4.0%, Cu 4.5-5.5%, with the balance being Ti and unavoidable impurities; the alloy has a molybdenum equivalent (Moeq) of 10-15; the alloy's microstructure consists of uniformly distributed equiaxed or short rod-shaped α phases and intergranular α" phases, wherein the average aspect ratio of the equiaxed α phase is less than 4, and its volume fraction accounts for more than 70% of the total α phase.

2. The high-strength and high-toughness titanium alloy based on microstructure spheroidization regulation according to claim 1, characterized in that: The room temperature mechanical properties of the alloy meet the following requirements: tensile strength ≥ 1200 MPa, elongation after fracture ≥ 14%.

3. A method for preparing a high-strength and high-toughness titanium alloy as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Powder preparation: According to the composition of the alloy, prepare pre-alloyed spherical powder with a particle size of 15-53 μm; (2) Laser powder bed melting forming: The powder obtained in step (1) is formed by laser powder bed melting technology to obtain a dense alloy sample; (3) Solution treatment: The alloy sample obtained in step (2) is solution treated at 800-900℃ and held for 60-120 min, and then cooled at a rate of 500-800℃ / s.

4. The method for preparing the high-strength and high-toughness titanium alloy according to claim 3, characterized in that: In step (2), the process parameters for laser powder bed melting are: laser power 130-160W, scanning speed 1000-1500mm / s, powder layer thickness 30-50μm, and scanning spacing 50-100μm.

5. The method for preparing the high-strength and high-toughness titanium alloy according to claim 3, characterized in that: In step (3), the heating rate of the solution treatment is 5-15℃ / min.

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