Titanium alloy based on additive manufacturing and method for manufacturing thereof

Abstract

The application discloses a kind of titanium alloy based on additive manufacturing, the mass percentage of each component of the titanium alloy is as follows: Al: 4%-5.5%, Mo: 4%-5.5%, V: 4%-5.5%, Cr: 1%-1.5%, Fe: 1%-1.5%, B: 0.03%-0.15%, the balance is Ti;The microstructure of the titanium alloy is a basket structure, and TiB whiskers are discontinuously distributed at the grain boundary.The titanium alloy based on additive manufacturing has high strength and plasticity.The application also discloses a preparation method of the titanium alloy based on additive manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of metal alloys, and specifically relates to a titanium alloy based on additive manufacturing and its preparation method. Background Technology

[0002] TC18 (Ti-5Al-5Mo-5V-1Cr-1Fe) is an indispensable structural titanium alloy in the aerospace field. TC18 features low forging temperature, high hardenability, high strength, and high toughness, making it ideal for aerospace applications. Currently, TC18 is used in components of various aircraft models: the main landing gear torsion arms and left and right supports of the nose landing gear of the Su-27; landing gear, fuselage components, and flap rails of the Il-76; landing gear components, spars, and crossbeams of the Il-86 and Il-9; landing gear components, spars, crossbeams, fasteners, and springs of the An-124; and flap rails, pylons, and landing gear components of the Boeing 777. In addition, TC18 is also used to manufacture large load-bearing components for mainline passenger aircraft and large transport aircraft, as well as engine fan discs and blades operating in environments below 350°C.

[0003] Although TC18 alloy has obvious advantages in manufacturing aircraft components, its high strength brings a problem: sensitivity to defects. The uneven microstructure and segregation caused by traditional melting methods greatly reduce the utilization rate of cast TC18. In addition, as the main load-bearing structure of an aircraft, its design concept requires that the various properties of the materials used be matched. However, the inversion of strength and plasticity, an important problem that needs to be solved in the development of metallic materials, also restricts the development of TC18 titanium alloy. How to achieve simultaneous improvement of strength and plasticity is the research focus of TC18 and many other metallic materials.

[0004] Introducing reinforcing materials into a metallic matrix is ​​an effective method to improve mechanical properties, but a trade-off between strength and ductility remains. In such composite materials, the reinforcing agents are concentrated at the grain boundaries, so excessive reinforcing agents can form ceramic walls at the grain boundaries, hindering coordinated deformation between the matrix components and causing a rapid decrease in the material's plasticity. However, if the reinforcing agent content is too low, its strength-increasing effect cannot be fully realized. Therefore, it is desirable to introduce only a relatively small amount of reinforcing agent to influence the evolution of the microstructure in the matrix alloy, thereby simultaneously improving both the strength and plasticity of the matrix alloy.

[0005] Additive manufacturing of metals is a rapid manufacturing technology that integrates CAD technology and path algorithm theory. It enables rapid, free-form molding without molds, arbitrary composite manufacturing of multiple materials, and features full digitalization and high flexibility. Additive manufacturing is based on a 3D model, using software to slice and process the model, constructing a layer-by-layer printing path, and obtaining the final alloy part through layer-by-layer deposition. Laser metal deposition technology uses a laser as the energy source and argon gas to simultaneously feed powder. This technology offers advantages such as atmosphere protection, ease of operation, high forming efficiency, small size limitations of formed parts, and applicability for material repair. In recent years, additive manufacturing technology, especially laser metal deposition (LMD), has been considered a promising technology for producing complex geometric parts made of titanium alloys used in the aerospace industry.

[0006] Therefore, this paper mainly focuses on the introduction of an appropriate amount of reinforcing phase and the combination of laser metal deposition technology to regulate the microstructure of titanium alloys and optimize their mechanical properties. Summary of the Invention

[0007] This invention provides an additive manufacturing-based titanium alloy with high strength and ductility.

[0008] A specific embodiment of the present invention provides a titanium alloy based on additive manufacturing, wherein the mass percentage of each component of the titanium alloy is as follows: Al: 4%-5.5%, Mo: 4%-5.5%, V: 4%-5.5%, Cr: 1%-1.5%, Fe: 1%-1.5%, B: 0.03%-0.15%, with the balance being Ti;

[0009] The titanium alloy has a basket mesh structure, with TiB whiskers discontinuously distributed at the grain boundaries.

[0010] Furthermore, the TiB whiskers are smaller than 1 μm in size and are short rod-shaped.

[0011] Furthermore, the raw materials for preparing the titanium alloy are nano-sized B powder and micron-sized TC18 powder.

[0012] Furthermore, the average grain size of the titanium alloy is 20-110 μm.

[0013] This invention adjusts the mass ratio of nano-sized boron powder in a mixed powder, causing boron to react with titanium (Ti) to form short, rod-shaped TiB whiskers with a size less than 1 μm. These whiskers form a discontinuous reinforcing phase at the grain boundaries of the titanium alloy. The inhibitory effect of TiB whiskers on grain growth effectively refines the grains, thereby improving the tensile strength of the titanium alloy. Simultaneously, due to the small size of the TiB whiskers, they effectively passivate cracks and hinder crack propagation during tensile fracture, increasing the elongation of the titanium alloy. Furthermore, the discontinuous formation of TiB whiskers at the grain boundaries also eliminates some grain boundary α and enhances grain boundary cohesion, suppressing intergranular fracture. Therefore, the goal of synergistically improving the strength and plasticity of the titanium alloy is achieved.

[0014] Furthermore, when the mass ratio of the nano-sized B powder to the micron-sized TC18 powder is 0-0.03%, the average grain size of the titanium alloy is 75-110 μm, the tensile strength is 1550-1660 MPa, and the elongation is 2.5-4.9%.

[0015] Furthermore, when the mass ratio of the nano-sized B powder to the micron-sized TC18 powder is 0.03%–0.05%, the average grain size of the titanium alloy is 50–75 μm, the tensile strength is 1660–1720 MPa, and the elongation is 4.5%–4.9%.

[0016] Furthermore, when the mass ratio of the nano-sized B powder to the micron-sized TC18 powder is 0.05%–0.15%, the average grain size of the titanium alloy is 20–50 μm, the tensile strength is 1720–1770 MPa, and the elongation is 4.5–4.9%.

[0017] The present invention also provides a method for preparing the aforementioned additive manufacturing-based titanium alloy, comprising:

[0018] Nano-sized B powder and micron-sized TC18 powder are mixed according to the mass percentage of each component of the additive manufacturing-based titanium alloy to obtain a mixed powder.

[0019] The mixed powder is ball-milled, dried, and sieved.

[0020] The mixed powder obtained after sieving is deposited layer by layer on a substrate using laser additive manufacturing to obtain a multilayer additive manufacturing-based titanium alloy.

[0021] Furthermore, the process parameters for laser additive manufacturing are as follows: laser power of 800-1000W, scanning speed of 500-800mm / min, laser scanning path spacing set to 40-60% of the cross-sectional size of a single-pass molten pool, slice layer thickness set to 60-80% of the cross-sectional size of a single-pass molten pool, and powder feed rate fixed at 3-5g / min. When the laser power is moderate, the width, height, and depth of the molten pool formed by the metal powder deposition are all moderate. Appropriate powder feed rate and scanning rate ensure that the time the laser acts on the metal powder during scanning is moderate, and the laser energy absorbed by the powder is moderate, thus forming a suitable powder melting range. The cladding layer surface is smooth, which is beneficial for subsequent pass overlap, thereby affecting the geometry, density, and microstructure of the material, giving the material excellent mechanical properties.

[0022] Furthermore, the mixed powder is ball-milled, wherein the ball-milling process is as follows: the steel balls are made of 316L steel, the diameter of the steel balls is 3-6 mm, the ball milling speed is 150-250 r / min, and the ball milling time is 2-4 h. A suitable ball milling speed allows the nano-sized B powder to adhere uniformly to the surface of the TC18 powder, and the powder can maintain a good spherical shape without deformation.

[0023] Furthermore, the mass ratio of the mixed powder to the steel ball is 1:3. This suitable mass ratio allows the nano-sized B powder to adhere uniformly to the surface of the TC18 powder.

[0024] Furthermore, the drying of the mixed powder includes:

[0025] Place the ball-milled mixed powder into a vacuum drying oven, evacuate the container until the pressure inside is less than 1 Pa, and dry at 100-120℃ for 4-8 hours.

[0026] Furthermore, the mixed powder is sieved multiple times through a sieve with a mesh size of 80-200.

[0027] Furthermore, before the mixed powder obtained after sieving is deposited layer by layer onto the substrate using laser additive manufacturing, the substrate is sequentially polished and cleaned. Polishing and cleaning result in a substrate with a smooth and glossy surface.

[0028] Furthermore, the substrate is a TC4 substrate with a thickness of 10-20 mm. Selecting a TC4 substrate of appropriate thickness is more conducive to the effective deposition of metal powder, promoting a moderate molten pool width and depth, thereby affecting the geometry, density, microstructure, and mechanical properties of the material.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] This invention utilizes a suitable amount of boron (B) to create a Ti alloy with a basket-like structure and discontinuous distribution of TiB whiskers at grain boundaries. This results in a Ti alloy with smaller grain size and higher tensile strength. During tensile fracture, the TiB whiskers effectively passivate cracks and hinder crack propagation, improving the ductility of the titanium alloy. Furthermore, the formation of TiB whiskers also eliminates some grain boundary α and enhances grain boundary cohesion, suppressing intergranular fracture. Therefore, a synergistic improvement in the strength and ductility of the titanium alloy is achieved.

[0031] The preparation method provided by this invention is universal, the preparation process is simple, the production cycle is short, and the repeatability is high. It can be widely applied to improve the mechanical properties of TC18 titanium alloy. Attached Figure Description

[0032] Figure 1 The images show the laser-printed bulk materials of titanium alloys based on additive manufacturing prepared in Examples 1-3 and Comparative Example 1 of this invention.

[0033] Figure 2 The images show the grain morphology of the titanium alloys prepared by additive manufacturing in Examples 1-3 and Comparative Example 1 of this invention.

[0034] Figure 3 The grain size statistics of the titanium alloys based on additive manufacturing prepared in Examples 1-3 and Comparative Example 1 of this invention are shown in the figure.

[0035] Figure 4 Backscattered electron (BSE) microstructures of the titanium alloys prepared by additive manufacturing in Examples 1-3 and Comparative Example 1 of this invention;

[0036] Figure 5 The image shows backscattered electron (BSE) TiB whisker patterns of the additively manufactured titanium alloys prepared in Examples 1-3 of this invention.

[0037] Figure 6 The mechanical properties of the high-strength titanium alloys based on additive manufacturing prepared in Examples 1-3 and Comparative Example 1 of this invention are shown in the figure. Detailed Implementation

[0038] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of this application, and not all of them.

[0039] Example 1

[0040] TC18 powder and nano-sized B powder were obtained as powder raw materials for laser metal deposition. The particle size of TC18 powder was 50-150 μm.

[0041] The TC18 powder weighs 199.98 g, and the nano-sized B powder weighs 0.02 g, accounting for 0.03 wt.%. The TC18 powder and nano-sized B powder are mixed and placed in a stainless steel ball mill jar with a diameter of... The 316L steel balls were used, and the mass ratio of the steel balls to the alloy powder was 3:1. The mixed powder was then placed in a stainless steel ball mill jar for ball milling at a speed of 200 r / min for 5 hours.

[0042] The mixed powder obtained after ball milling is placed in a vacuum drying oven, and the oven is evacuated until the pressure inside is less than 1 Pa. The drying temperature is 120℃ and the drying time is 8 hours. After drying, the powder is sieved twice using a 100-mesh sieve. Then the mixed powder is loaded into the powder feeder of the laser additive manufacturing equipment.

[0043] Take a 10*10cm TC4 substrate with a thickness of 10mm, sand the surface with sandpaper to expose a flat and shiny upper surface, clean and dry it with ethanol after sanding, and then put it into the laser additive manufacturing equipment.

[0044] The laser power for laser metal deposition was set to 900W, and the scanning speed was set to 600mm / min. A single pass was pre-scanned and printed, and the cross-sectional dimensions of the molten pool were measured. Based on the dimensions of the single pass molten pool, the path spacing was set to 1.38mm, the slice layer thickness was set to 0.4mm, and the powder feeding rate was fixed at 3g / min. Multi-pass, multi-layer titanium alloy blocks without macroscopic cracks were thus prepared.

[0045] Example 2

[0046] TC18 powder and nano-sized B powder were obtained as powder raw materials for laser metal deposition. The particle size of TC18 powder was 50-150 μm.

[0047] The TC18 powder weighs 199.9g, and the nano-sized B powder weighs 0.1g, accounting for 0.05wt.%. The TC18 powder and nano-sized B powder are mixed and placed in a stainless steel ball mill jar with a diameter of... The 316L steel balls were used, and the mass ratio of the steel balls to the alloy powder was 3:1. The mixed powder was then placed in a stainless steel ball mill jar for ball milling at a speed of 200 r / min for 5 hours.

[0048] The mixed powder obtained after ball milling is placed in a vacuum drying oven, and the oven is evacuated until the pressure inside is less than 1 Pa. The drying temperature is 120℃ and the drying time is 8 hours. After drying, the powder is sieved twice using a 100-mesh sieve. Then the mixed powder is loaded into the powder feeder of the laser additive manufacturing equipment.

[0049] Take a 10*10cm TC4 substrate with a thickness of 10mm, sand the surface with sandpaper to expose a flat and shiny upper surface, clean and dry it with ethanol after sanding, and then put it into the laser additive manufacturing equipment.

[0050] The laser power for laser metal deposition was set to 900W, and the scanning speed was set to 600mm / min. A single pass was pre-scanned and printed, and the cross-sectional dimensions of the molten pool were measured. Based on the dimensions of the single pass molten pool, the path spacing was set to 1.38mm, the slice layer thickness was set to 0.4mm, and the powder feeding rate was fixed at 3g / min. Multi-pass, multi-layer titanium alloy blocks without macroscopic cracks were thus prepared.

[0051] Example 3

[0052] TC18 powder and nano-sized B powder were obtained as powder raw materials for laser metal deposition. The particle size of TC18 powder was 50-150 μm.

[0053] The TC18 powder weighs 199.7g, and the nano-sized B powder weighs 0.3g, accounting for 0.15wt.%. The TC18 powder and nano-sized B powder are mixed and placed in a stainless steel ball mill jar. The 316L steel balls were used, and the mass ratio of the steel balls to the alloy powder was 3:1. The mixed powder was then placed in a stainless steel ball mill jar for ball milling at a speed of 200 r / min for 5 hours.

[0054] The mixed powder obtained after ball milling is placed in a vacuum drying oven, and the oven is evacuated until the pressure inside is less than 1 Pa. The drying temperature is 120℃ and the drying time is 8 hours. After drying, the powder is sieved twice using a 100-mesh sieve. Then the mixed powder is loaded into the powder feeder of the laser additive manufacturing equipment.

[0055] Take a 10*10cm TC4 substrate with a thickness of 10mm, sand the surface with sandpaper to expose a flat and shiny upper surface, clean and dry it with ethanol after sanding, and then put it into the laser additive manufacturing equipment.

[0056] The laser power for laser metal deposition was set to 900W, and the scanning speed was set to 600mm / min. A single pass was pre-scanned and printed, and the cross-sectional dimensions of the molten pool were measured. Based on the dimensions of the single pass molten pool, the path spacing was set to 1.38mm, the slice layer thickness was set to 0.4mm, and the powder feeding rate was fixed at 3g / min. Multi-pass, multi-layer titanium alloy blocks without macroscopic cracks were thus prepared.

[0057] Comparative Example 1

[0058] The difference between this example and the previous one is that no nano-sized B powder was added in the comparative example.

[0059] Performance comparison:

[0060] See Figure 1 , Figure 1 Macroscopic morphology images of titanium alloy blocks for Comparative Example 1 and Examples 1-3 are shown. TC18, TC18+0.03B, TC18+0.05B, and TC18+0.15B correspond to Comparative Example 1 and Examples 1, 2, and 3, respectively. As can be seen from the figures, the printed titanium alloy blocks exhibit a layered characteristic along the direction of metal deposition from bottom to top.

[0061] See Figure 2 , Figure 2 The grain morphology diagrams of Comparative Example 1 and Examples 1-3 are shown. TC18, TC18+0.03B, TC18+0.05B, and TC18+0.15B correspond to Comparative Example 1 and Examples 1, 2, and 3, respectively. It can be seen from the figures that the grain size of the TC18 titanium alloy without nano-sized B powder is relatively large. As the amount of nano-sized B powder added increases, the grain size of the titanium alloy gradually becomes finer. When the amount of nano-sized B powder added is 0.15 wt.%, the grain size refinement effect is the most significant, and it can be clearly observed that the grain morphology gradually becomes spherical due to the addition of nano-sized B powder.

[0062] See Figure 3 , Figure 3 The following graphs show the grain size statistics of Comparative Example 1 and Examples 1-3, as well as the variation curves of the average grain size of the titanium alloy. Figure 3 of (a), Figure 3 (b) Figure 3 (c) Figure 3 (d) represents the grain size statistics of Comparative Example 1 and Examples 1-3, respectively. Figure 3 (e) is a graph showing the grain size variation of the titanium alloy. From Figure 3 of (a), Figure 3 (b) Figure 3 (c) Figure 3 As can be seen from (d), the average grain size of TC18 titanium alloy without added nano-sized boron powder is 110 μm, and the grain size is very uneven. When the amount of nano-sized boron powder added is 0.03% wt., the average grain size of TC18+0.03B titanium alloy is 75 μm. When the amount of nano-sized boron powder added is 0.05% wt., the average grain size of TC18+0.05B ​​titanium alloy is 50 μm, and the grain size distribution is relatively uniform. When the amount of nano-sized boron powder added is 0.15% wt., the average grain size of TC18+0.05B ​​titanium alloy is 20 μm, and the grain size distribution is very uniform, with approximately 90% of the grains ranging from 10 to 30 μm. Figure 3(e) clearly shows that the average grain size of the titanium alloy gradually decreases with the increase of the amount of nano-sized B powder added, indicating that the addition of nano-sized B powder can effectively refine the grain size of TC18 titanium alloy and make it more uniform.

[0063] See Figure 4 , Figure 4 Microstructure diagrams of Comparative Example 1 and Examples 1-3 are shown. TC18, TC18+0.03B, TC18+0.05B, and TC18+0.15B correspond to Comparative Example 1 and Examples 1, 2, and 3, respectively. As can be seen from the figures, all four titanium alloys have a basket structure. Nanoscale B powder and TC18 titanium alloy matrix generate TiB whiskers in situ, and the TiB whiskers are mainly distributed at the grain boundaries. This indicates that TiB whiskers effectively refine the grain size by inhibiting grain growth.

[0064] See Figure 5 , Figure 5 The diagrams show TiB whisker patterns from Examples 1-3. TC18+0.03B, TC18+0.05B, and TC18+0.15B correspond to Examples 1, 2, and 3, respectively. Clearly, the reaction of B with Ti forms short, rod-shaped TiB whiskers with a size less than 1 μm, generating a discontinuous network reinforcing phase in situ at the grain boundaries of the titanium alloy. These small-sized TiB whiskers effectively refine the grains by inhibiting grain growth, thereby improving the tensile strength of the titanium alloy. Simultaneously, TiB whiskers effectively passivate cracks and hinder crack propagation during tensile fracture, improving the ductility of the titanium alloy. Furthermore, the formation of TiB whiskers also eliminates some grain boundary α and enhances grain boundary cohesion, suppressing intergranular fracture. Therefore, the addition of nano-sized B powder enables the in-situ generation of discontinuous network reinforcing TiB whiskers at the grain boundaries, achieving the goal of synergistically improving the strength and ductility of the titanium alloy.

[0065] See Figure 6 , Figure 6 The stress-strain curves for Comparative Example 1 and Examples 1-3 are shown. Specifically, the curve corresponding to TC18 is the stress-strain curve for Comparative Example 1; the curve corresponding to TC18+0.03B is the stress-strain curve for Example 1; the curve corresponding to TC18+0.05B ​​is the stress-strain curve for Example 2; and the curve corresponding to TC18+0.15B is the stress-strain curve for Example 3. Figure 5As shown, the tensile strength of TC18 titanium alloy without the addition of nano-sized B powder is 1550 MPa, and the elongation is 2.5%. When the amount of nano-sized B powder added is 0.03 wt.%, 0.05 wt.%, and 0.15 wt.%, the tensile strength of the titanium alloy is 1660 MPa, 1720 MPa, and 1770 MPa, respectively, and the elongation is 4.9%, 4.9%, and 4.5%, respectively. Obviously, the tensile strength and elongation of TC18 titanium alloy increase with the increase of the amount of nano-sized B powder added, effectively achieving a synergistic improvement in strength and plasticity.

Claims

1. A titanium alloy based on additive manufacturing, characterized in that, The mass percentage of each component of the titanium alloy is: Al: 4%-5.5%, Mo: 4%-5.5%, V: 4%-5.5%, Cr: 1%-1.5%, Fe: 1%-1.5%, B: 0.03%-0.15%, and the balance is Ti; The microstructure of the titanium alloy is a basket structure, and the TiB whiskers at the grain boundary are discontinuously distributed; The size of the TiB whisker is less than 1 μm, and the TiB whisker is a short rod; The raw material for preparing the titanium alloy is nano-sized B powder and micron-sized TC18 powder.

2. The additive manufacturing based titanium alloy of claim 1, wherein, When the mass ratio of the nano-sized B powder and the micron-sized TC18 powder is 0-0.03%, the average grain size is 75-110 μm, the tensile strength of the titanium alloy is 1550-1660 MPa, and the elongation is 2.5-4.9%.

3. The additive manufacturing based titanium alloy of claim 1, wherein, When the mass ratio of the nano-sized B powder and the micron-sized TC18 powder is 0.03%-0.05%, the average grain size is 50-75 μm, the tensile strength of the titanium alloy is 1660-1720 MPa, and the elongation is 4.5%-4.9%.

4. The additive manufacturing based titanium alloy of claim 1, wherein, When the mass ratio of the nano-sized B powder and the micron-sized TC18 powder is 0.05%-0.15%, the average grain size is 20-50 μm, the tensile strength of the titanium alloy is 1720-1770 MPa, and the elongation is 4.5-4.9%.

5. The additive manufacturing based titanium alloy of claim 1, wherein, The average grain size of the titanium alloy is 20-110 μm.

6. A method of producing a titanium alloy based on additive manufacturing according to any one of claims 1 to 5, characterized in that Comprising: The nano-sized B powder and the micron-sized TC18 powder are proportioned according to the mass percentage of each component of the titanium alloy based on additive manufacturing according to any one of claims 1-5 to obtain a mixed powder; The mixed powder is ball milled, dried, and sieved; The mixed powder obtained after sieving is deposited on a substrate by laser additive manufacturing to obtain a multi-layer titanium alloy based on additive manufacturing.

7. The method of producing a titanium alloy based on additive manufacturing according to claim 6, characterized in that, The process parameters of the laser additive manufacturing are: laser power is 800-1000 W, scanning speed is 500-800 mm / min, path spacing of laser scanning is set to 40-60% of the single-track molten pool cross-sectional size, slice layer thickness is set to 60-80% of the single-track molten pool cross-sectional size, and the powder feeding rate is fixed at 3-5 g / min.

8. The method of producing a titanium alloy based on additive manufacturing according to claim 7, characterized in that, The mixed powder is ball milled, wherein the process of the ball milling is: the material of the steel ball is 316L, the diameter of the steel ball is 3-6 mm, the ball milling speed is 150-250 r / min, and the ball milling time is 2-4 h.

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