Method for preparing Ti2AlNb alloy based on spherical titanium alloy powder

Abstract

The invention belongs to the field of preparation of high-performance metal structure materials, and particularly relates to a method for preparing a Ti2AlNb alloy based on spherical titanium alloy powder. Commercial spherical titanium alloy pre-alloyed powder containing at least two elements of Al, Zr, Mo and V and pure niobium powder are selected as base materials, the spherical powder, the pure niobium powder and pure aluminum powder are evenly mixed according to the designed atomic proportion, a densification path of vacuum sintering or spark plasma sintering after cold isostatic pressing is adopted for preparing a consumable electrode blank, and the consumable electrode blank is prepared into a self-consumable electrode. And finally, a Ti2AlNb-based alloy cast ingot is obtained through vacuum self-consuming electric arc melting. According to the invention, not only is the technical bottleneck of inevitable gravity segregation in the smelting process of the Ti-Al intermetallic compound with high Nb content broken through, but also a brand new material preparation technical route with low cost, high performance and high stability is constructed; an industrialization feasible scheme is provided for solving the bottleneck problem of short-time high-temperature light structural materials in the aerospace field.

Description

Technical Field

[0001] This invention belongs to the field of high-performance metallic structural materials preparation, and specifically relates to a method for preparing Ti2AlNb alloys based on spherical titanium alloy powder. Specifically, this invention provides a method for preparing Ti2AlNb-based alloys with extremely low compositional segregation and high comprehensive performance at low cost and high efficiency by innovatively selecting specific commercially available spherical titanium alloy powder as raw material and combining it with specific powder metallurgy and smelting processes. Background Technology

[0002] Ti2AlNb alloy, as a new generation of high-temperature structural material, exhibits excellent high-temperature strength, creep resistance, and moderate density in the 600-750℃ temperature range due to its unique orthorhombic O-phase strengthening effect, making it an ideal candidate material for hot-end components of aerospace engines. Compared with traditional nickel-based superalloys, Ti2AlNb alloy has a lower density (approximately 5.0-5.5 g / cm³) and higher specific strength, enabling significant weight reduction in equipment. Furthermore, this alloy also possesses good oxidation resistance and fatigue performance, showing broad application prospects in components such as compressor disks, blades, and casings of aero-engines.

[0003] However, since its introduction, the engineering application of Ti2AlNb alloy has been limited by two interrelated core technical challenges: First, there is the serious problem of compositional segregation. This alloy system typically contains more than 20 at.% Nb. The density of Nb (8.57 g / cm³) is much higher than that of titanium melt (approximately 4.5 g / cm³). In traditional vacuum arc remelting, this significant density difference triggers strong gravity-driven convection within the molten pool, leading to the enrichment of high-density Nb at the bottom or core of the ingot, while the edges and upper parts are relatively depleted. This macroscopic segregation, and the resulting microscopic segregation, directly leads to the uneven distribution of brittle phases (such as Nb-rich β / B2 phase clusters or Nb-depleted α2 phase) in the alloy, severely impairing the uniformity of mechanical properties, plasticity, fatigue life, and long-term reliability of the material. Although remelting three or even more times can improve the situation to some extent, it cannot completely eliminate the problem and greatly increases energy consumption and time costs.

[0004] Secondly, the high cost of raw materials and manufacturing. To address segregation issues and precisely control composition, existing technologies often rely on high-purity elemental powders such as titanium, aluminum, niobium, and molybdenum as raw materials. However, high-purity, finely refined metal powders, especially niobium and molybdenum powders, are extremely expensive, keeping raw material costs high. Another approach involves using pre-alloyed Ti2AlNb spherical powders with precise composition prepared by gas atomization or plasma rotating electrode methods, followed by near-net-shape forming through hot isostatic pressing. While this method yields excellent microstructure and properties, the preparation of specialized pre-alloyed powders is difficult and extremely costly, limiting its application to extreme fields where cost is not a primary concern and failing to meet the demands of large-scale industrial applications.

[0005] Furthermore, if the route of simply mixing elemental powders and then sintering is adopted, problems such as poor mixing uniformity due to differences in powder density, shape, and particle size, as well as insufficient diffusion of refractory metals Nb and Mo during sintering, resulting in the formation of Kirkendall pores and brittle intermetallic compounds, will be encountered. Ultimately, it will be difficult to obtain dense, uniformly composed, and high-performance materials.

[0006] Therefore, there is an urgent need in this field for an innovative technical solution that can simultaneously and synergistically address the two major bottlenecks of "compositional segregation" and "high cost." However, under the guidance of existing technologies, reducing costs often means sacrificing performance and uniformity, while pursuing high performance inevitably involves high costs; the two seem to be in an irreconcilable contradiction. This invention is a creative design aimed at breaking this deadlock.

[0007] 2. Existing Technological Attempts and Limitations In recent years, researchers have explored various methods to improve the preparation process of Ti2AlNb alloys. For example: Pre-alloyed powders can be prepared by mechanical alloying, but this method is prone to introducing impurities, and has high energy consumption and low yield. While multiple remeltings and electromagnetic stirring can improve compositional uniformity, the effect is limited and energy consumption is increased. While hot isostatic pressing (HIP) near-net-shape forming technology can achieve a uniform microstructure, it requires significant equipment investment and is costly.

[0008] These methods all struggle to simultaneously resolve the conflict between component segregation and cost control. Especially in fields like aerospace where material performance requirements are extremely high, how to reduce costs while ensuring material performance remains a pressing technical challenge.

[0009] 3. Technological gaps and innovation needs Currently, there are no research reports on methods for preparing Ti2AlNb alloys using commercially available spherical titanium alloy powder as a raw material. The main reason for this technological gap is: 1) The compositions of commercial titanium alloy powders of different grades are fixed and differ significantly from the composition of the target Ti2AlNb alloy; 2) The lack of systematic composition design and process control methods makes it difficult to achieve effective conversion from commercial powder to target alloy; 3) Insufficient understanding of the role mechanism of commercial powder in the preparation process of Ti2AlNb alloy.

[0010] Therefore, developing a new method to fully utilize the advantages of commercially available spherical titanium alloy powder while overcoming its limitations to achieve low-cost preparation of high-performance Ti2AlNb alloys has significant theoretical and engineering value. Summary of the Invention

[0011] Purpose of this invention: The primary objective of this invention is to provide a preparation method that fundamentally solves the problem of compositional segregation in Ti2AlNb alloys. By innovatively selecting commercially available spherical titanium alloy powder with specific components as the base raw material, and combining it with an optimized process route, macroscopic and microscopic uniformity of the alloy composition is achieved.

[0012] The second objective of this invention is to significantly reduce the production cost of Ti2AlNb alloys. By using relatively inexpensive commercially available spherical titanium alloy powder instead of specialized pre-alloyed powders or pure element powders, raw material costs can be reduced by 40-60% while ensuring material performance.

[0013] The third objective of this invention is to provide a flexible and adaptable method for preparing Ti2AlNb alloys. By designing multiple process routes, this method can adapt to different production conditions and technical requirements, and has good prospects for industrialization.

[0014] Technical solution of the present invention: To achieve the above objectives, this invention, through in-depth research, breaks away from the traditional mindset of "must start mixing from the element level" or "must use special pre-alloyed powders," and creatively proposes a completely new technical paradigm: using commercially available spherical titanium alloy pre-alloyed powders with specific element combinations as prefabricated modules for constructing high-performance Ti2AlNb alloys.

[0015] 1. A method for preparing low-segregation Ti2AlNb alloy based on spherical titanium alloy powder, characterized by comprising the following steps: Step 1: Precision ingredient formulation and powder mixing: Using spherical titanium alloy pre-alloyed powder, pure niobium powder and pure aluminum powder as raw materials, the raw materials are accurately calculated and weighed based on the composition of the target Ti2AlNb alloy. The weighed powder raw materials are placed in a powder mixing device and mixed until a mixed powder with uniform composition is obtained. Step 2: Forming and densification of the electrode blank: The mixed powder obtained in step 1 is shaped and densified using cold isostatic pressing or spark plasma sintering to prepare a consumable electrode blank. Step 3: Vacuum consumable arc melting: The electrode blank prepared in step 2 is used as a consumable electrode and is melted once or multiple times in a vacuum consumable arc furnace to finally obtain a Ti2AlNb alloy ingot with uniform chemical composition.

[0016] The cold isostatic pressing technique specifically involves: controlling the pressing pressure within the range of 200 MPa to 400 MPa to obtain a compact; subsequently, vacuum sintering the compact at a temperature range of 1100°C to 1300°C, with a vacuum degree higher than 10. -2 Pa, the holding time is 1 to 4 hours, and finally a sintered electrode blank with a density of not less than 95% of the theoretical density is obtained.

[0017] The discharge plasma sintering technology specifically involves: loading the mixed powder into a conductive mold, applying an axial pressure of 15 MPa to 50 MPa under vacuum or inert atmosphere protection, and simultaneously heating it to a sintering temperature of 600°C to 1100°C using pulsed DC electricity, and holding it at this temperature for 5 to 20 minutes to directly obtain an electrode blank with a density of not less than 95% of the theoretical density.

[0018] The spherical titanium alloy powder is a pre-alloyed powder whose chemical composition, by weight percentage, includes at least two of the following four elements: aluminum (A), zirconium (Zr), molybdenum (Mo), and vanadium (V), with each element having a content of not less than 0.5 wt%, and the balance being titanium (Ti) and impurities.

[0019] The spherical titanium alloy pre-alloyed powder has a particle size D10 ≥ 53 μm.

[0020] The composition of the spherical titanium alloy pre-alloyed powder, pure niobium powder, and pure aluminum powder is 40~55:35~45:8~15 by mass percentage.

[0021] The Ti2AlNb alloy ingot prepared from the ingredients, after thermomechanical processing and heat treatment, has a room temperature tensile strength and elongation after fracture of not less than 1100 MPa and 6%, respectively.

[0022] The chemical composition deviation of the Ti2AlNb alloy ingot is as follows: Al≤0.8%, Nb≤0.3%, and other alloying elements≤0.2%.

[0023] Beneficial effects of the invention This invention is based on a precise mass ratio of titanium alloy pre-alloyed powder, pure Nb powder, and pure Al powder to form a Ti2AlNb alloy composition. A mixer is used to ensure macroscopic compositional uniformity. Then, two technical paths are used to achieve the forming and densification of the electrode blank. Path one uses cold isostatic pressing to obtain a high-density green blank, followed by high-temperature vacuum sintering to achieve metallurgical bonding between powder particles and preliminary interdiffusion of alloying elements. This path has relatively low equipment investment and is suitable for large-scale continuous production. Path two uses spark plasma sintering technology, utilizing the plasma activation effect and Joule heating generated by pulsed high current to achieve rapid densification of the powder at a lower temperature and in a shorter time, minimizing the loss of volatile elements such as Al and V. Finally, the densified electrode blank is used as a consumable electrode for melting. Since the electrode is already a highly homogeneous "pre-alloyed block," each drop of molten material during melting is a small, fixed-composition alloy melt, thus cutting off the element separation mechanism caused by density differences in traditional processes at the source, ultimately obtaining an ingot with extremely homogeneous composition. Compared with existing technologies, this invention has the following outstanding advantages: 1. A revolutionary solution to the segregation problem: By using pre-alloyed spherical powder with uniform composition as a base, the solution to the segregation problem is brought forward to the powder preparation stage, rather than relying on the downstream melting and stirring. The Nb element composition fluctuation range of the final ingot can be controlled within ±0.3 at.%.

[0024] 2. Extremely significant cost-effectiveness: Taking TA15 spherical powder as an example, the cost of purchasing 53~150μm TA15 spherical powder, niobium powder, and aluminum powder from the market is far lower than the combined cost of TiNb, Al-Mo, AlV master alloys of the same quality, as well as sponge titanium, sponge zirconium, and aluminum wire. Raw material costs can be reduced by about 40%-60%. At the same time, the optimization of the process flow also reduces energy consumption and time costs.

[0025] 3. Excellent and stable comprehensive performance: Due to the high uniformity of composition, the alloy prepared by this invention exhibits extremely stable mechanical properties. Examples show that its room temperature tensile strength is stable at 1100-1200 MPa, its elongation after fracture is stable at 6%-10%, its high temperature strength at 750℃ remains above 750 MPa, and it has good batch repeatability. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0027] A method for preparing Ti2AlNb-based alloys based on spherical titanium alloy powder includes the following steps: Step 1: Precision ingredient formulation and powder mixing Using spherical titanium alloy pre-alloyed powder, pure niobium powder, and pure aluminum powder as raw materials, the mass ratio of spherical titanium alloy pre-alloyed powder, pure niobium powder, and pure aluminum powder is 40~55:35~45:8~15; the final atomic percentage composition of the target Ti2AlNb alloy is accurately calculated and weighed. The spherical titanium alloy powder is a pre-alloyed powder with a particle size D10 ≥ 53 μm. The powder chemical composition, by weight percentage, includes at least two of the following four elements: aluminum (Al), zirconium (Zr), molybdenum (Mo), and vanadium (V), and the content of each element is not less than 0.5 wt%, with the balance being titanium (Ti) and impurities.

[0028] The weighed powder raw materials are placed in a mixing device and mixed until a uniformly distributed mixed powder is obtained. Step 2: Forming and densification of the electrode blank The mixed powder obtained in step 1 is shaped and densified using cold isostatic pressing or spark plasma sintering to prepare a consumable electrode blank. The cold isostatic pressing technique specifically involves: controlling the pressing pressure within the range of 200 MPa to 400 MPa to obtain a compact; subsequently, vacuum sintering the compact at a temperature range of 1100°C to 1300°C, with a vacuum degree higher than 10. - 2 Pa, the holding time is 1 to 4 hours, and finally a sintered electrode blank with a density of not less than 95% of the theoretical density is obtained.

[0029] The discharge plasma sintering technology specifically involves: loading the mixed powder into a conductive mold, applying an axial pressure of 15 MPa to 50 MPa under vacuum or inert atmosphere protection, and simultaneously heating it to a sintering temperature of 600°C to 1100°C using pulsed DC electricity, and holding it at this temperature for 5 to 20 minutes to directly obtain an electrode blank with a density of not less than 95% of the theoretical density.

[0030] Step 3: Vacuum consumable arc melting: The electrode blank prepared in step 2 is used as a consumable electrode and is melted once or multiple times in a vacuum consumable arc furnace to finally obtain a Ti2AlNb-based alloy ingot with uniform chemical composition and dense structure.

[0031] The chemical composition deviation of the obtained Ti2AlNb alloy ingot is: Al≤0.8%, Nb≤0.3%, and other alloying elements≤0.2%.

[0032] After thermomechanical processing and heat treatment, the room temperature tensile strength and elongation after fracture of the Ti2AlNb alloy ingot obtained by smelting are not less than 1100MPa and 6%, respectively.

[0033] Example 1: Using TA15 powder and CIP+ sintering path Target composition: Ti-23Al-24Nb-1Mo-1.2Zr-1V (at.%) Raw materials: gas-atomized TA15 spherical powder (particle size: 53-150 μm, oxygen content <1000 ppm), high-purity niobium powder (particle size <45 μm), and high-purity aluminum powder (particle size <75 μm).

[0034] step: 1. Ingredient mixing: Based on the target composition, weigh TA15 powder, Nb powder, and Al powder, place them in a three-dimensional mixer, and mix at 30 rpm for 6 hours under argon protection.

[0035] 2. CIP forming: The mixed powder is loaded into a rubber sleeve, vacuum sealed, and then held under pressure of 300 MPa for 3 minutes to obtain a green compact.

[0036] 3. Vacuum sintering: The green billet was placed in a vacuum sintering furnace and heated to 1250℃ at a rate of 5℃ / min, held at that temperature for 2.5 hours, and then cooled to below 300℃ before being removed from the furnace. The density of the sintered billet was measured to be 97.5% of the theoretical density.

[0037] 4. VAR melting: The sintered electrode blank is machined into a standard electrode and then subjected to a vacuum self-consuming arc melting process with a melting current of 8 kA and a stable arc magnetic field strength of 0.05 T.

[0038] 5. Subsequent processing: The ingot is forged in the β phase region (Tβ+30℃), then rolled at (Tβ-40℃), and finally subjected to heat treatment at 1020℃ / 1h / OQ (solution) + 760℃ / 8h / AC (aging).

[0039] Example 2: Using TA15 powder and SPS pathway Target ingredient: Same as in Example 1.

[0040] Raw materials: Same as in Example 1.

[0041] step: 1. Ingredient mixing: Same as in Example 1.

[0042] 2. SPS Densification: The mixed powder was loaded into a φ110 mm graphite mold and densified in an SPS (Silicon-Pulsed Fiber Optics) apparatus. Process parameters: vacuum degree <10⁻² Pa, pressure 15 MPa, temperature increased to 750℃ at 100 ℃ / min, held for 15 minutes, and then cooled in the furnace. The density of the SPS preform was measured to be 97% of the theoretical density.

[0043] 3. VAR smelting and subsequent processing: Same as in Example 1.

[0044] Comparative Example 1: Traditional Electrode Pressing Method Using sponge titanium, TiNb master alloy, pure Al wire, and Al-Mo, Al-V, and Al-Zr master alloy particles with the same final target composition as in Example 1 as raw materials, a comparative alloy was prepared by weighing, pressing electrodes, and VAR one-time melting (process is the same as in Example 1).

[0045] Performance testing and results analysis: The final heat-treated alloys obtained in Examples 1, 2 and Comparative Example 1 were tested: Compositional uniformity: Nb content was measured at 10 points along the diameter direction by electron probe microanalysis (EPMA) at the head, middle, and tail of the ingot. The standard deviation of Nb content in Examples 1 and 2 was <0.25 at.%, while the standard deviation of Comparative Example 1 was >1.8 at.%, demonstrating the overwhelming advantage of the method of the present invention in solving segregation.

[0046] Mechanical properties: Room temperature tensile testing: The strengths of Examples 1 and 2 were both around 1150 MPa, with elongations ranging from 6% to 9%, showing little data dispersion. Comparative Example 1 exhibited large strength fluctuations (1000-1150 MPa) and an average elongation of only 4.5%, verifying the inherent defects in uniformity of traditional smelting methods.

Claims

1. A method for preparing low-segregation Ti2AlNb alloy based on spherical titanium alloy powder, characterized in that, Includes the following steps: Step 1: Precision ingredient formulation and powder mixing: Using spherical titanium alloy pre-alloyed powder, pure niobium powder and pure aluminum powder as raw materials, the raw materials are accurately calculated and weighed based on the composition of the target Ti2AlNb alloy. The weighed powder raw materials are placed in a powder mixing device and mixed until a mixed powder with uniform composition is obtained. Step 2: Forming and densification of the electrode blank: The mixed powder obtained in step 1 is shaped and densified using cold isostatic pressing or spark plasma sintering to prepare a consumable electrode blank. Step 3: Vacuum consumable arc melting: The electrode blank prepared in step 2 is used as a consumable electrode and is melted once or multiple times in a vacuum consumable arc furnace to finally obtain a Ti2AlNb alloy ingot with uniform chemical composition.

2. The method for preparing low-segregation Ti2AlNb alloy based on spherical titanium alloy powder according to claim 1, characterized in that, The cold isostatic pressing technique specifically involves: controlling the pressing pressure within the range of 200 MPa to 400 MPa to obtain a compact; subsequently, vacuum sintering the compact at a temperature range of 1100°C to 1300°C, with a vacuum degree higher than 10. -2 Pa, the holding time is 1 to 4 hours, and finally a sintered electrode blank with a density of not less than 95% of the theoretical density is obtained.

3. The method for preparing low-segregation Ti2AlNb alloy based on spherical titanium alloy powder according to claim 1, characterized in that, The discharge plasma sintering technology specifically involves: loading the mixed powder into a conductive mold, applying an axial pressure of 15 MPa to 50 MPa under vacuum or inert atmosphere protection, and simultaneously heating it to a sintering temperature of 600°C to 1100°C using pulsed DC electricity, and holding it at this temperature for 5 to 20 minutes to directly obtain an electrode blank with a density of not less than 95% of the theoretical density.

4. The method for preparing low-segregation Ti2AlNb alloy based on spherical titanium alloy powder according to claim 1, characterized in that, The spherical titanium alloy powder is a pre-alloyed powder whose chemical composition, by weight percentage, includes at least two of the following four elements: aluminum (A), zirconium (Zr), molybdenum (Mo), and vanadium (V), with each element having a content of not less than 0.5 wt%, and the balance being titanium (Ti) and impurities.

5. The method for preparing low-segregation Ti2AlNb alloy based on spherical titanium alloy powder according to claim 1, characterized in that, The particle size D10 of the spherical titanium alloy pre-alloyed powder is ≥53μm.

6. The method for preparing low-segregation Ti2AlNb alloy based on spherical titanium alloy powder according to claim 1, characterized in that, The composition of spherical titanium alloy pre-alloyed powder, pure niobium powder and pure aluminum powder is 40~55:35~45:8~15 by mass percentage.

7. The method for preparing low-segregation Ti2AlNb alloy based on spherical titanium alloy powder according to claim 1, characterized in that, The Ti2AlNb alloy ingot prepared from the ingredients, after thermomechanical processing and heat treatment, has a room temperature tensile strength and elongation after fracture of not less than 1100 MPa and 6%, respectively.

8. The method for preparing low-segregation Ti2AlNb alloy based on spherical titanium alloy powder according to claim 1, characterized in that, The chemical composition deviation of the Ti2AlNb alloy ingot is as follows: Al≤0.8%, Nb≤0.3%, and other alloying elements≤0.2%.