A method for preparing dispersion-strengthened titanium alloy based on VAR melting

Abstract

The application discloses a dispersion strengthened titanium alloy preparation method based on VAR smelting and belongs to the technical field of titanium alloy material preparation. In view of the problems of easy agglomeration, uneven distribution and difficult large-scale production of reinforcing bodies in traditional dispersion strengthened titanium alloy preparation, the method takes coarse powder returned material generated in a titanium alloy atomization powder production process as a main raw material, calculates and proportionally mixes powders with different oxygen contents, and simultaneously adds micron or nanometer second-phase reinforcing bodies as strengthening phases. The uniformly mixed powders are loaded into a sheath, vacuumizing and sealing welding are performed, and sintering densification treatment is performed, so that a high-density, high-strength and reinforcing body uniformly distributed electrode rod for smelting is prepared. Finally, the electrode rod is subjected to VAR smelting, and a dispersion strengthened titanium alloy ingot with uniform structure and excellent performance is obtained. The method is simple in process and low in cost, realizes high-value utilization of titanium alloy returned material, and has important significance for promoting green circulation and low-cost manufacturing of the titanium industry.

Description

Technical Field

[0001] This invention relates to the field of advanced titanium alloy material preparation technology, and more specifically, to a method for preparing high-performance dispersion-strengthened titanium alloys by combining powder metallurgy and vacuum consumable arc melting using recycled titanium alloy materials. Background Technology

[0002] Titanium and titanium alloys hold an irreplaceable position in aerospace, marine engineering, biomedicine, and chemical industries due to their excellent specific strength, outstanding corrosion resistance, and good biocompatibility. However, their high production costs severely restrict their wider application. The costs mainly stem from two aspects: firstly, the complex and energy-intensive hot working process (accounting for approximately 50% of the total cost); and secondly, the extremely low material utilization rate from raw materials to finished products (typically only 20%-50%), generating a large amount of processing waste.

[0003] In recent years, additive manufacturing (3D printing) technology has provided a new approach for manufacturing complex titanium alloy components, significantly improving material utilization. However, in its industrial chain, both the powder preparation stage (such as gas atomization and plasma rotating electrode atomization) and the printing process itself generate a large amount of non-standard powder. Currently, various powder preparation methods and processes in 3D printing produce a large amount of coarse-particle powder. This spherical powder has poor pressing performance and cannot be pressed and sintered using traditional powder metallurgy. During vacuum melting, titanium alloy powder can be sucked away by the vacuum pump, leading to production accidents. With the large-scale application of 3D printing technology in industrial production, the recycling and reuse of waste generated by 3D printing has become a widely concerned issue.

[0004] Dispersion strengthening is an effective method for enhancing the strength and toughness of metallic materials. It significantly improves the strength, hardness, and wear resistance of materials at room temperature and high temperatures by uniformly introducing insoluble, thermally stable, hard second-phase particles (such as oxides, carbides, and nitrides) into the metal matrix. Powder metallurgy is an ideal process for preparing such materials, ensuring the uniform dispersion of the reinforcing phase. However, traditional dispersion strengthening methods are difficult to directly sinter to achieve density due to the presence of second-phase reinforcing particles. They mainly rely on hot isostatic pressing (HIP) for high-temperature, high-pressure sintering, which is costly and difficult to apply on a large scale. Currently, large electrode rods for smelting are mostly made of sponge titanium with added elements, which is difficult to incorporate second-phase reinforcing particles. Direct addition during smelting easily leads to agglomeration or segregation, affecting the quality of the final smelted billet. Traditional powder metallurgy methods (such as pressing and sintering, and HIP) face significant equipment limitations and high costs when preparing large-size, fully dense billets, making large-scale production difficult.

[0005] Therefore, there is an urgent need to develop a new method that can prepare dispersion-strengthened titanium alloys at low cost and on a large scale, and can effectively utilize recycled titanium alloy materials, so as to open up the technology chain from waste recycling and material upgrading to high-end applications. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing dispersion-strengthened titanium alloys based on VAR melting. This method aims to achieve the following objectives: 1. To achieve efficient and high-value recycling of titanium alloy reclaimed materials (especially coarse powder / waste powder generated from 3D printing), reducing raw material costs. 2. To solve the problem of uniform dispersion of the dispersion-strengthening phase in the titanium alloy matrix, achieving in-situ uniform distribution of the strengthening phase through powder metallurgy precursors. 3. To combine the material design flexibility of powder metallurgy with the large-scale, high-quality ingot production capacity of VAR melting, providing a process route for the scalable preparation of high-performance dispersion-strengthened titanium alloys. 4. To simplify the process flow, reduce dependence on expensive hot isostatic pressing equipment, and improve production economics.

[0007] The technical solution of the present invention: A method for preparing dispersion-strengthened titanium alloy based on VAR melting includes the following steps: S1. Raw material preparation and mixing: Using recycled titanium alloy as the base material, calculate and weigh powders with different oxygen contents according to the target composition and mix them in proportion; add a second phase reinforcement as a reinforcing phase to the proportioned base powder, and mix it thoroughly in a mixer to obtain a mixed powder with uniform composition. S2. Packaging and encapsulation: The mixed powder is filled into a metal sleeve, the sleeve is vacuumed, and then sealed by welding after reaching a predetermined vacuum level; S3. Sintering densification: The sealed casing is sintered at a temperature of 800℃~1100℃ and a holding time of 2~5 hours to obtain a dense sintered blank; S4. Electrode rod preparation: The sintered blank obtained in step S3 is machined to produce a consumable electrode rod that meets the requirements of VAR melting. S5. VAR melting: The consumable electrode rod is subjected to vacuum consumable arc melting to obtain a dispersion-strengthened titanium alloy ingot.

[0008] In step S1, the titanium alloy return material is selected from coarse powder produced by titanium alloy atomization powder production or coarse powder produced by titanium alloy 3D printing; the second phase reinforcement is one or more of carbides, nitrides, and borides.

[0009] The second phase reinforcement is TiC, TiB, SiC or B4C, and its addition amount is 0.5% to 5.0% of the total mass of the matrix titanium alloy powder.

[0010] In step S1, the mixing is carried out in a planetary ball mill for 2 to 8 hours.

[0011] In step S2, the metal sheath is made of low-carbon steel, stainless steel, or titanium alloy; the vacuum level after evacuation is not less than 1×10⁻⁶. -2 Pa.

[0012] In step S3, the sintering is carried out in a vacuum sintering furnace or a hot isostatic pressing device.

[0013] The electrode rod prepared by S4 is formed by sintering titanium alloy return material with uniformly distributed reinforcing phase. The titanium alloy ingot prepared by S5 has micron or nano-scale second phase reinforcing particles uniformly distributed in it.

[0014] Prepare a larger enclosure, place the sintered blank in the larger enclosure, and repeat steps S2-S3 to obtain a larger sintered blank.

[0015] Beneficial effects: 1. Resource recycling and cost advantages: Using low-cost recycled titanium alloy materials as raw materials, turning waste into treasure, significantly reducing the raw material cost of high-performance titanium alloys, which is in line with the concepts of green manufacturing and sustainable development.

[0016] 2. Excellent material properties: By mixing the reinforcement with the titanium alloy in advance through the powder mixing process, the global problem of easy agglomeration and segregation of the reinforcing phase in the molten alloy is fundamentally solved, and the uniform dispersion distribution of the reinforcing phase in the titanium alloy matrix is ​​achieved, which significantly improves the strength, hardness and high temperature performance of the ingot.

[0017] 3. Excellent process compatibility and easy scaling: It cleverly combines the advantages of two mature processes: powder metallurgy (material design and homogenization) and VAR smelting (large-scale, high-quality ingot production). It avoids the dependence on ultra-large hot isostatic pressing equipment when using powder metallurgy alone to prepare large-size billets, and can realize the large-scale production of dispersion-strengthened titanium alloys using existing VAR capacity.

[0018] 4. High flexibility: By adjusting the proportion of recycled materials, the content of impurity elements (such as oxygen) in the final product can be precisely controlled; by selecting different types and contents of reinforcements, a series of dispersion-strengthened titanium alloys with specific properties can be designed and prepared to meet diverse application needs; and the sintering size limit of existing technologies can be broken through by using a multi-layer nested sintering method. Attached Figure Description

[0019] Figure 1 Microscopic view of HDH TC4 coarse powder return material.

[0020] Figure 2 To improve the microstructure of dispersion-strengthened titanium alloy electrode rods.

[0021] Figure 3 This is a schematic diagram of multi-layer nested sintering. Detailed Implementation

[0022] Example 1: A method for preparing dispersion-strengthened titanium alloys based on VAR melting includes: Step 1: Raw material calculation and mixing: The coarse powder recycled material generated during the titanium alloy atomization powder production process is used as the matrix raw material. First, based on the target oxygen content requirements of the final titanium alloy ingot, the recycled powders with different oxygen contents are precisely calculated and weighed in proportion. Then, a predetermined amount of micron- or nano-sized second-phase reinforcing particles are added to the proportioned matrix powder as a reinforcing phase. All the above powders are thoroughly mixed to ensure that the matrix powder and reinforcing particles are uniformly distributed.

[0023] Step 2: Encapsulation and Vacuum Sealing The uniformly mixed powder is filled into a pre-prepared metal sheath. The sheath is typically cylindrical and can be made of low-carbon steel, stainless steel, or a titanium alloy with the same composition as the matrix. Vibration or other methods can be used during filling to increase the powder density. After filling, a high-vacuum evacuation is performed inside the sheath using a vacuum tube welded to it. The vacuum level is maintained until a predetermined requirement is met (typically better than 1×10⁻⁶). -2 After Pa), immediately weld the extraction pipe to place the mixed powder in a highly clean vacuum environment.

[0024] Step 3: Sintering and densification The sealed cladding is placed in a sintering apparatus. The sintering temperature is set between 800℃ and 1100℃, and the holding time is 2 to 5 hours. During this process, the titanium alloy powder particles diffuse to form a metallurgical bond, achieving densification. Simultaneously, the reinforcing particles are "locked" within the dense titanium alloy matrix, forming a sintered billet with uniformly distributed reinforcement. After sintering, the cladding and the internal billet may form a metallurgical bond or be easily separated.

[0025] Step 4: Electrode rod processing The sintered billet obtained in step three is subjected to necessary machining (such as turning and grinding), the cladding is removed (if necessary), and it is machined into a cylindrical consumable electrode rod with a smooth surface, accurate dimensions, and meeting the requirements of the VAR furnace. This electrode rod itself is a high-density, high-strength composite material with a uniformly distributed reinforcing phase.

[0026] Step 5: VAR Melting The processed consumable electrode rods are loaded into a vacuum consumable arc furnace (VAR) for conventional VAR melting. During the melting process, the tip of the electrode rod is gradually melted by the arc and dripped into a water-cooled copper crucible to solidify into an ingot. Because the reinforcing particles have been pre-uniformly solidified within the titanium alloy matrix of the electrode rod, and during the relatively rapid solidification process of VAR melting, these fine, thermodynamically stable particles can be well retained and redistributed in the new as-cast matrix, thus obtaining a titanium alloy ingot with a uniform microstructure and dispersion strengthening effect.

[0027] Example 2: Preparation of TiC dispersion-strengthened TC4 titanium alloy.

[0028] 1. Raw Material Preparation: Two types of TC4 titanium alloy gas-atomized coarse powder return materials (particle size 50-150μm) with oxygen contents of 0.08 wt.% and 0.15 wt.%, respectively, were selected. Based on the target ingot oxygen content requirement of 0.12 wt.%, the two powders were calculated and weighed, and mixed at a mass ratio of 1:1. TiC powder with an average particle size of 1.0μm was added to the mixed matrix powder as a reinforcing phase, at an addition amount of 2.0% of the total matrix mass. The proportioned powder was thoroughly mixed to ensure that the reinforcement was uniformly distributed in the titanium alloy powder.

[0029] 2. Sleeve assembly and sealing: After mixing, the mixture is filled into the pre-prepared sleeve, and the sleeve is vacuumed to a vacuum degree of 1×10⁻⁶. -3 After Pa, sealing welding is performed to ensure a vacuum environment within the cladding during sintering.

[0030] 3. Sintering: Place the sealed sleeve into the sintering furnace, set the sintering temperature to 950℃, and the sintering time to 3 hours.

[0031] 4. Electrode processing: After sintering, the cladding is machined to remove excess material, resulting in electrode rods for VAR melting.

[0032] 5. VAR melting: The electrode rod is subjected to two VAR melting processes to obtain an ingot with a diameter of 400mm.

[0033] Results: Sampling analysis of the ingots showed that TiC particles were uniformly dispersed and without obvious agglomeration.

[0034] Example 3: Preparation of TiB dispersion-strengthened TA15 titanium alloy (small-size electrode).

[0035] For the fabrication of small-sized electrode rods, the proportions of recycled titanium alloy powder with different oxygen contents were first precisely calculated and weighed accordingly. Next, an appropriate amount of micron-sized TiB was added to the powder as a reinforcing phase to enhance the mechanical properties of the final product. The mixed powders were thoroughly blended to ensure uniform distribution of the reinforcement within the titanium alloy powder. After blending, the mixture was filled into a small-sized sheath, and the sheath was vacuum-treated to a vacuum degree of 1×10⁻⁶. -3 After Pa, the sheath is sealed. The sealed sheath is then placed in a sintering furnace, and the sintering temperature is set to 850℃ for 2 hours. After sintering, the sheath is machined to remove excess material, yielding a small electrode rod for VAR melting. Finally, the electrode rod is subjected to VAR melting to obtain a dispersion-strengthened titanium alloy. This method not only effectively utilizes recycled titanium alloy material, reducing production costs, but also improves the performance of the titanium alloy by adding a strengthening phase, solving the problem of large-scale application of dispersion-strengthened titanium alloys in traditional methods.

[0036] Example 4: Preparation of SiC dispersion-strengthened high-temperature titanium alloy.

[0037] Using Ti-Al-Sn-Zr-Mo-Si series high-temperature titanium alloy recycled coarse powder with varying oxygen contents as the matrix, the target oxygen content after formulation was 0.07 wt.%. 0.8 wt.% of nano-SiC powder (average particle size 50 nm) was added as a reinforcement. A large low-carbon steel sheath (Φ300 mm × 600 mm) was used, and a vacuum sintering process was performed at 1050℃ / 5 h. Large electrode rods were obtained through machining, and three VAR melting processes were performed to obtain extremely pure and uniform ingots. This material maintains excellent high-temperature strength and creep resistance even at 750℃.

[0038] Example 5: Optimized process for preparing B4C dispersion-strengthened titanium alloy. The matrix is ​​a proportioned recycled TC11 titanium alloy powder. 3.0 wt.% micron-sized B4C powder is added. After homogeneous mixing, a cladding is made using a TC11 titanium plate of the same composition as the matrix, intended to prevent separation after sintering and serve as a common electrode. Vacuum sintering parameters: 920℃, 3 hours. The clad sintered billet is directly processed and subjected to VAR melting. The final ingot exhibits a uniform TiB and TiC mixed reinforcing phase, resulting in good overall mechanical properties.

[0039] Example 6: Large-size titanium alloy electrode rod with multiple nested layers.

[0040] Matrix: TC4 return material coarse powder.

[0041] Reinforcing phase: nano-TiC powder (average particle size 50nm), added at 1.0wt.% of the matrix mass.

[0042] The TC4 powder and TiC powder were mixed in a planetary ball mill for 4 hours under argon protection to achieve uniform dispersion of nanoparticles.

[0043] Prepare the sleeves: Prepare three stainless steel cylindrical sleeves, with the following dimensions: Small size sleeve: inner diameter Φ100mm, height 500mm, wall thickness 3mm.

[0044] Medium-sized sleeve: inner diameter Φ250mm, height 600mm, wall thickness 3mm.

[0045] Large size sleeve: inner diameter Φ400mm, height 700mm, wall thickness 3mm.

[0046] All the packaging sleeves have one end welded and sealed, and the other end has an opening for filling with powder.

[0047] Primary sintering: Uniformly dispersed nanoparticle powder is filled into a small sleeve, vibrated to compact it, and then vacuumed. The open end is then welded and sealed. The sealed sleeve is placed in a vacuum sintering furnace, and the temperature is increased to 1000℃ at a rate of 10℃ / min, under a vacuum degree better than 1×10⁻⁶. -2 The sample was held at a temperature of 3 Pa for 3 hours, then cooled in the furnace at a rate of 5 °C / min to below 200 °C before being removed from the furnace. A dense primary preform was obtained and the cladding was removed.

[0048] Two-stage nested sintering: The primary preform is placed in the center of a medium-sized sleeve, and the surrounding annular gap is filled with the same coarse powder. After vibration to compact the powder, the sleeve is sealed under vacuum. A second sintering process is then performed using the exact same method to obtain the secondary preform, and the sleeve is removed.

[0049] Three-stage nested sintering and finished product: The secondary preform is placed in the center of the large casing, surrounded by coarse powder, sealed, and then sintered again using the same process. After sintering, the casing is removed to obtain a large TC4 integral sintered electrode rod with a final size smaller than [size missing].

[0050] Performance tests show that, compared with pure TC4 sintered parts without added reinforcing phase, the sintered parts prepared in this embodiment have an increased room temperature hardness of about 11% and an increased high-temperature compressive strength at 600°C of about 15%.

Claims

1. A method for preparing dispersion-strengthened titanium alloy based on VAR melting, characterized in that... Includes the following steps: S1. Raw material preparation and mixing: Using recycled titanium alloy as the base material, calculate and weigh powders with different oxygen contents according to the target composition and mix them in proportion; add a second phase reinforcement as a reinforcing phase to the proportioned base powder, and mix it thoroughly in a mixer to obtain a mixed powder with uniform composition. S2. Packaging and encapsulation: The mixed powder is filled into a metal sleeve, the sleeve is vacuumed, and then sealed by welding after reaching a predetermined vacuum level; S3. Sintering densification: The sealed metal cladding is sintered at a temperature of 800℃~1100℃ and a holding time of 2~5 hours to obtain a dense sintered blank; S4. Electrode rod preparation: The sintered blank obtained in step S3 is machined to produce a consumable electrode rod that meets the requirements of VAR melting. S5. VAR melting: The consumable electrode rod is subjected to vacuum consumable arc melting to obtain a dispersion-strengthened titanium alloy ingot.

2. The method for preparing dispersion-strengthened titanium alloy based on VAR melting according to claim 1, characterized in that: In step S1, the titanium alloy return material is selected from coarse powder produced by titanium alloy atomization powder production or coarse powder produced by titanium alloy 3D printing; the second phase reinforcement is one or more of carbides, nitrides, and borides.

3. The method for preparing dispersion-strengthened titanium alloy based on VAR melting according to claim 2, characterized in that: The second phase reinforcement is TiC, TiB, SiC or B4C, and its addition amount is 0.5% to 5.0% of the total mass of the matrix powder.

4. The method for preparing dispersion-strengthened titanium alloy based on VAR melting according to claim 1, characterized in that, In step S1, the mixing is carried out in a planetary ball mill for 2 to 8 hours.

5. The method for preparing dispersion-strengthened titanium alloy based on VAR melting according to claim 1, characterized in that, In step S2, the metal sheath is made of low-carbon steel, stainless steel, or titanium alloy; the vacuum level after evacuation is not less than 1×10⁻⁶. -2 Pa.

6. The method for preparing dispersion-strengthened titanium alloy based on VAR melting according to claim 1, characterized in that: In step S3, the sintering is carried out in a vacuum sintering furnace or a hot isostatic pressing device.

7. The method for preparing dispersion-strengthened titanium alloy based on VAR melting according to claim 1, characterized in that: The consumable electrode rod prepared by S4 is formed by sintering titanium alloy return material with uniformly distributed reinforcing phase. The titanium alloy ingot obtained by S5 has micron- or nano-sized second phase reinforcing particles uniformly distributed in it.

8. The method for preparing dispersion-strengthened titanium alloy based on VAR melting according to claim 1, characterized in that: Prepare a larger enclosure, place the sintered blank in the larger enclosure, and repeat steps S2-S3 to obtain a larger sintered blank.

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