Rare earth modified cast high-temperature titanium alloy and preparation method and application thereof

Abstract

The invention discloses a rare earth modified cast high-temperature titanium alloy and a preparation method and application thereof, and belongs to the technical field of high-temperature titanium alloys. The alloy comprises the following components in percentage by mass: 5.50% to 6.50% of Al, 3.50% to 5.00% of Sn, 3.50% to 5.00% of Zr, 0.20% to 0.80% of Mo, 0.10% to 0.30% of Si, 0.25% to 0.55% of Nb, 0.20% to 0.40% of Ta, 0.40% to 0.60% of W, 0.25% to 0.35% of Nd and the balance of Ti and impurities. By adding narrow-interval rare earth Nd and utilizing the synergistic effect of structure purification and dispersion strengthening, the effective Al equivalent of an alpha phase is reduced, so that precipitation and growth of a Ti3Al brittle ordered phase in the high-temperature long-time service process are remarkably inhibited. The preparation method comprises a vacuum melting process and an innovative five-stage hot isostatic pressing process, and the process realizes densification, homogenization and structure stabilization integrated treatment through programmed temperature and pressure regulation and control. The obtained alloy has excellent high-temperature strength, plasticity and long-time structure stability at the temperature of 650 DEG C or above, and is suitable for high-temperature structural parts of aero-engines and gas turbines.

Description

Technical Field

[0001] This invention relates to the field of high-temperature titanium alloy materials technology, specifically to a rare-earth modified cast high-temperature titanium alloy, its preparation method, and its application. Background Technology

[0002] High-temperature titanium alloys, with their excellent specific strength, good high-temperature mechanical properties, and corrosion resistance, have become the preferred materials for key hot-end components of high-end equipment such as aerospace engines and gas turbines. Among them, near-α type titanium alloys have been widely researched and applied both domestically and internationally due to their good high-temperature strength and thermal stability, such as Ti-1100 from the United States, IMI834 from the United Kingdom, and Ti60 and Ti600 from my country.

[0003] However, with the rapid development of aerospace technology, the requirements for engine thrust-to-weight ratio and efficiency are constantly increasing, which leads to increasingly higher service temperatures for key components. Currently, the long-term stable service temperature of traditional high-temperature titanium alloys is generally limited to around 600℃. When the service temperature approaches or exceeds 650℃, existing alloys face two major challenges: First, titanium alloys are prone to forming a loose oxide layer at high temperatures, and oxygen atoms diffuse into the matrix to form a brittle "oxygen-rich α layer," severely impairing the material's plasticity, fatigue performance, and long-term lifespan. Second, and more critically, is the structural instability at high temperatures. In near-α titanium alloys based on the Ti-Al-Sn-Zr system, a high content of Al is usually added to obtain high-temperature strength. However, during long-term exposure (thermal exposure) at temperatures of 650℃ and above, Al, Sn, and other elements in the bulk tend to undergo ordering within the α phase, precipitating hexagonal close-packed (D0) phases. 19 The Ti3Al ordered phase (also known as the α2 phase) has a α2 structure. This phase is hard and brittle, and its extensive precipitation and coarsening can severely fracture the matrix, leading to a significant decrease in the alloy's plasticity, toughness, and creep properties, i.e., "heat exposure embrittlement." This is the fundamental scientific problem that restricts the service temperature window of high-temperature titanium alloys from exceeding the 650℃ bottleneck.

[0004] To overcome this problem, researchers have tried various methods. Alloying is an important approach, such as adding β-stabilizing elements like Nb, Ta, Mo, and W to improve high-temperature strength and thermal stability, and adding Si to improve creep properties. However, while these elements may improve one property, they can negatively impact other properties (such as plasticity and casting fluidity), and their effect on suppressing the precipitation of Ti3Al ordered phases is limited. Another approach is to use thermomechanical treatment to refine the microstructure, but this is often difficult to implement for castings with complex shapes.

[0005] Therefore, developing a novel high-temperature cast titanium alloy that possesses good casting processability while maintaining excellent microstructure stability and mechanical properties during long-term service at temperatures of 650℃ and above, and suppressing the precipitation of the brittle Ti3Al phase, has become a key technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the technical bottleneck of existing high-temperature titanium alloys experiencing microstructural instability and embrittlement due to the precipitation of Ti3Al ordered phases during long-term service at temperatures of 650℃ and above, this invention provides a rare-earth-modified cast high-temperature titanium alloy, its preparation method, and its applications. This invention aims to achieve microstructural purification while effectively suppressing the precipitation and growth of brittle ordered phases through unique alloy composition design and an innovative multi-stage hot isostatic pressing process, thereby obtaining a cast high-temperature titanium alloy material that possesses excellent high-temperature strength, good plasticity, and outstanding long-term microstructural stability.

[0007] To achieve the above objectives, the specific solution adopted by the present invention is as follows: In a first aspect, the present invention provides a rare earth modified cast high-temperature titanium alloy, comprising the following components by mass percentage: Al 5.50%–6.50%, Sn 3.50%–5.00%, Zr 3.50%–5.00%, Mo 0.20%–0.80%, Si 0.10%–0.30%, Nb 0.25%–0.55%, Ta 0.20%–0.40%, W 0.40%–0.60%, Nd 0.25%–0.35%, with the remainder being Ti and unavoidable impurity elements; The addition of Nd element achieves tissue purification and diffusion enhancement, thereby suppressing the precipitation of Ti3Al ordered phase.

[0008] Furthermore, by mass percentage, it comprises the following components: Al 5.9%, Sn 4.5%, Zr 4.0%, Mo 0.5%, Si 0.2%, Nb 0.4%, Ta 0.3%, W 0.5%, Nd 0.3%, with the remainder being Ti and unavoidable impurity elements.

[0009] Secondly, the present invention provides a method for preparing rare earth modified cast high-temperature titanium alloy, comprising the following steps: S1. Raw material smelting: Weigh each raw material according to the above composition ratio, and obtain a uniform alloy ingot through vacuum arc melting and multiple ingot turning and remelting. S2. Microstructure-controlled hot isostatic pressing: The alloy ingot is placed in a hot isostatic pressing apparatus and subjected to the following five stages of treatment under a protective atmosphere: (1) First stage: Under the conditions of temperature of 900~920℃ and pressure of 220~250MPa, keep warm for 0.3~0.6 hours; (2) Second stage: Raise the temperature to 970~990℃, adjust the pressure to 80~100MPa, and keep it warm for 1.0~1.8 hours; (3) Third stage: Reduce the temperature to 940~960℃, and then control the pressure in the following order: (a) First, increase the pressure to 170~180MPa and maintain it for 0.15~0.3 hours; (b) Then reduce the pressure to 130-140 MPa and maintain it for 0.15-0.3 hours; (c) Increase the pressure again to 150~160MPa and maintain it for 0.2~0.4 hours; (4) Fourth stage: lower the temperature to 910~930℃, raise the pressure to 190~210MPa, and keep it at that temperature for 1.5~2.2 hours; (5) Fifth stage: During the process of linearly reducing the pressure from 190~210MPa to 100MPa, the temperature is cooled from the end temperature of the fourth stage to 850℃ at a rate of no more than 5℃ / min. S3. Final cooling: Cool the alloy from 850°C to room temperature.

[0010] Furthermore, step S1 specifically includes: S11. Raw material weighing and preparation: Weigh the raw materials Ti, Al, Zr, Sn, Mo, Si, Nb, Ta, W and Nd respectively, and store the rare earth Nd blocks separately in a sealed container. S12. Loading and Vacuum Preparation: Mix all raw materials except the Nd block thoroughly, and place them together with the Nd block wrapped in titanium foil in a water-cooled copper crucible of a vacuum arc melting furnace, with the Nd block placed in the middle of the mixed raw materials; evacuate the furnace to a vacuum level not exceeding 5 × 10⁻⁶. -3 After Pa, high-purity argon gas was introduced to a concentration of 5 × 10⁻⁶. -2 Pa, then evacuate again, repeat this process 2-3 times to remove residual gas in the furnace; S13. Melting and stirring: Melting is carried out under argon protection, the melting current is controlled at 600~800A, the temperature is raised to 2200~2500℃, the melting time is 2~3min each time, and electromagnetic stirring is applied for 30~40s in the molten state of the alloy. S14. Ingot flipping and remelting and ingot cooling: After completing one melting, flip the ingot 180° and repeat the melting operation of step S13. The number of ingot flipping and remelting is 4 to 6 times, and the cooling interval between two adjacent meltings is 2 to 3 minutes. After completing the last melting, the ingot is naturally cooled to below 200°C under argon protection for 20 to 30 minutes. Then the cast alloy ingot is taken out.

[0011] Furthermore, in step S3, the cooling rate above 500°C is no more than 30°C / min.

[0012] Thirdly, this invention provides an application of rare earth modified casting high-temperature titanium alloy in the preparation of structural components for aero-engines or gas turbines that operate at temperatures of 650°C and above for extended periods.

[0013] The role of each element is explained below. The core of the alloy composition design in this invention lies in constructing an "α / β multi-component strengthening system" and achieving a breakthrough in microstructure stability through "rare earth Nd micro-alloying modification". The synergistic principle is as follows: (1) Roles and challenges of Al, Sn, and Zr: Al, Sn, and Zr are the main α-stabilizing elements and solid solution strengthening elements. Maintaining a high content of Al, Sn, and Zr (corresponding to a high nominal Al equivalent) is the basis for ensuring that the alloy has sufficient high-temperature strength. However, this design itself brings an inherent challenge: an excessively high Al equivalent will significantly increase the thermodynamic driving force for the precipitation of Ti3Al ordered phase, which may lead to the microstructure instability of the alloy under long-term high-temperature service.

[0014] (2) Synergistic stabilizing effect of Mo, Nb, Ta, and W: Mo, Nb, Ta, and W are all β-stabilizing elements, which together constitute a multi-component β-stabilizing system. Mo, Nb, and W mainly play a solid solution strengthening role and can improve the stability of the β phase. The addition of Ta helps to improve the melt thermal stability and plasticity of the alloy. The synergistic effect of these elements can improve the high-temperature strength of the alloy, improve its processability, and maintain a certain plasticity reserve, but its effect on inhibiting the precipitation of Ti3Al ordered phase inside the α phase is limited.

[0015] (3) The role of Si: As a eutectic forming element, the addition of trace amounts of Si (0.10%~0.30%) can significantly improve the high-temperature creep resistance of the alloy.

[0016] (4) The core modifying role of rare earth Nd: The introduction of rare earth Nd is precisely to fundamentally solve the risk of embrittlement caused by the high nominal Al equivalent that must be faced in order to maintain high strength. Its mechanism of action is the core of the invention to improve the long-term structural stability of the alloy, specifically including: (a) Rare earth Nd has extremely strong chemical activity. During the melting and heat treatment process, it preferentially combines with interstitial atoms O and solute atoms such as Sn and Zr in the matrix or enriches around them. This "capture" effect effectively reduces the concentration of elements such as O, Sn, and Zr dissolved in the α phase matrix. Since Sn and Zr are elements that directly contribute to the calculation of Al equivalent, the "fixation" or "segregation" of them by Nd actually reduces the "effective Al equivalent" in the local α phase matrix. According to the phase transformation thermodynamics of titanium alloys, this directly reduces the actual thermodynamic driving force for the precipitation of Ti3Al ordered phase. (b) Trace amounts of Nd can be dispersed in the matrix and phase boundaries in the form of fine Nd-rich phase or oxide particles. These particles can, on the one hand, pin dislocations and grain boundaries, producing a dispersion strengthening effect and supplementing strength; on the other hand, they can act as a physical barrier to the heterogeneous nucleation of the Ti3Al phase, kinetically inhibiting its precipitation and hindering its growth and coarsening. (c) This invention strictly limits the Nd content to a narrow range of 0.25% to 0.35%. Below 0.25%, the above-mentioned purification and dispersion effects are insufficient; above 0.35%, excessive Nd easily forms a continuous brittle phase at grain boundaries, impairing plasticity. This design ensures that Nd exerts its optimal synergistic effect.

[0017] Therefore, this invention, through unique composition and process design, achieves a triple synergistic mechanism: ensuring basic high-temperature strength with sufficient α-stabilizing elements (Al, Sn, Zr) and multiple β-stabilizing elements (Mo, Nb, Ta, W); reducing the 'effective Al equivalent' of the α phase by utilizing the purification effect of rare earth Nd to suppress the driving force for brittle phase precipitation; and further hindering the nucleation and growth of brittle phases kinetically by leveraging the dispersed phase of Nd. This systematically solves the problem of long-term microstructural stability of traditional high-strength titanium alloys at temperatures of 650℃ and above from both thermodynamic and kinetic perspectives.

[0018] Beneficial effects Compared with existing technologies, the rare earth-modified cast high-temperature titanium alloy and its preparation method provided by this invention have the following significant advantages: (1) Through the synergistic effect of rare earth Nd in “purification-reduction of Al equivalent-dispersion strengthening”, the precipitation and growth of Ti3Al(α2) ordered hard and brittle phase during long-term service at temperatures of 650℃ and above are fundamentally suppressed, solving the core problem that traditional high aluminum equivalent titanium alloys are prone to thermal exposure embrittlement in this temperature range, thus improving the long-term service temperature window of the alloy.

[0019] (2) Based on the composite strengthening mechanism of "multi-element β-stabilized synergistic strengthening" and "rare earth dispersion strengthening", the alloy of the present invention maintains good casting performance while also possessing high room temperature strength, high high temperature strength and good plasticity. Examples show that the titanium alloy prepared by the present invention has a room temperature tensile strength of over 1000 MPa, a yield strength of over 930 MPa, and an elongation after fracture of over 13%.

[0020] (3) After simulating long-term high-temperature service with a heat exposure treatment of 650℃ / 100h, the room temperature mechanical properties of the alloy of the present invention decreased significantly less than those of the comparative alloy without Nd. This directly confirms the key role of Nd in maintaining the stability of the microstructure and properties of the alloy under high-temperature conditions, ensuring the service safety and reliability of the components under extreme conditions.

[0021] (4) The five-stage programmed hot isostatic pressing (HIP) process of the invention upgrades the traditional single densification treatment into a composite treatment that integrates "densification, homogenization, microstructure control, stress relaxation, and stabilization". The process parameters are scientifically designed, the purpose of each stage is clear, the synergistic effect is significant, and it can be stably realized on industrial standard HIP equipment, providing a reliable and advanced process route for the industrial production of high-performance cast titanium alloy components.

[0022] (5) This invention provides a novel rare earth modified casting high-temperature titanium alloy with novel composition design, advanced preparation process, excellent comprehensive performance, and is especially suitable for long-term safe service in temperature environments of 650℃ and above. It has broad application prospects in aerospace, energy and power fields. Attached Figure Description

[0023] Figure 1 These are SEM microstructure comparison images of the alloys prepared in the as-cast state in Example 1 and Comparative Example 1 of the present invention; (a) is the SEM image of the alloy of Example 1 (containing Nd) in the conventional state; (b) is the SEM image of the alloy of Comparative Example 1 (excluding Nd) in the conventional state; (c) is the SEM image of the alloy of Example 1 (containing Nd) after being exposed to heat at 650℃ for 100h; (d) is the SEM image of the alloy of Comparative Example 1 (excluding Nd) after being exposed to heat at 650℃ for 100h.

[0024] Figure 2 This is a TEM microstructure image of the alloy prepared in Example 1 of this invention after being subjected to heat exposure treatment at 650℃ for 100h. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0026] This invention provides a rare-earth modified casting high-temperature titanium alloy suitable for long-term service at 650℃ and above, and its preparation method. The high-temperature titanium alloy comprises the following essential components: Al 5.50%–6.50%, Sn 3.50%–5.00%, Zr 3.50%–5.00%, Mo 0.20%–0.80%, Si 0.10%–0.30%, Nb 0.25%–0.55%, Ta 0.20%–0.40%, W 0.40%–0.60%, Nd 0.25%–0.35%, with the remainder being Ti and impurity elements unavoidably introduced during the preparation process. Specifically, by adding 0.25%–0.35% rare-earth Nd, its extremely strong chemical reactivity and interfacial segregation ability preferentially capture elements such as O, Sn, and Zr in the matrix during smelting and heat treatment, achieving microstructural purification. At the same time, this reduces the effective Al equivalent of the α phase matrix, thermodynamically reducing the precipitation driving force of the harmful ordered phase Ti3Al(α2), and together with the dispersion strengthening effect of Nd, it inhibits the precipitation and growth of this brittle phase in the initial state and during subsequent long-term service.

[0027] Next, the preparation method of rare earth modified casting high-temperature titanium alloy is described in detail.

[0028] S1, Raw material smelting This step aims to obtain alloy ingots with uniform composition and no contamination. The specific steps are as follows: S11. Raw material preparation: Select high-purity raw materials, including OA grade sponge titanium, titanium foil, Al particles, sponge zirconium, and metal blocks of Sn, Mo, Si, Nb, Ta, W, and Nd. Rare earth Nd blocks need to be sealed and stored separately. S12. Loading the furnace: Mix all raw materials except Nd blocks evenly and place them together with the Nd blocks wrapped in titanium foil in a water-cooled copper crucible of a vacuum arc melting furnace. Wrapping the Nd blocks in titanium foil can reduce burn-off during the melting process and reduce pre-reaction with other raw materials. S13. Atmosphere purification: Start the vacuum system and evacuate the furnace to a vacuum level not exceeding 5×10⁻⁶. -3 Pa, then high-purity argon gas was introduced to 5 × 10⁻⁶. -2 Pa, then evacuate again. Repeat this process 2-3 times to thoroughly remove residual oxygen, nitrogen, and other harmful gases from the furnace; S14. Melting and Stirring: Under argon protection, control the melting current at 600-800A and heat to 2200-2500℃ for melting, with each melting session lasting 2-3 minutes. While the alloy is in the molten state, apply electromagnetic stirring for 30-40 seconds to ensure thorough and uniform mixing of all alloying elements. S15. Turning and Cooling: After one melting operation, turn the ingot 180° and repeat the above melting operation. The number of times the ingot is turned and remelted is 4 to 6, with a cooling time of 2 to 3 minutes between adjacent melting operations. After the last melting operation, allow the ingot to cool naturally to below 200°C (about 20 to 30 minutes) under argon protection, and then remove the as-cast alloy ingot.

[0029] The process involves multiple vacuuming and argon purging to ensure a clean smelting environment; electromagnetic stirring and multiple ingot remelting greatly promote the compositional uniformity of the alloy melt and ensure the uniform distribution of the active element Nd, providing a uniform as-cast microstructure basis for subsequent processing.

[0030] S2, Tissue-controlled hot isostatic pressing (HIP) treatment This step is the core innovative process of this invention. Its design breaks through the single function of traditional hot isostatic pressing, which is only used to eliminate porosity. It designs a composite microstructure engineering method integrating "active densification, depth uniformity, microstructure control, stress relaxation, and structural stability." The programmed design of five consecutive stages, each targeting the specific physicometallurgical behavior of the alloy under high temperature and high pressure, aims to maximize the modification potential of rare earth Nd and obtain a long-term stable and ideal microstructure. The specific steps are as follows: S21, First Stage (Ultra-High Pressure Densification): Holding at 900-920℃ and 220-250MPa for 0.3-0.6 hours; the core objective of this stage is to achieve complete densification of the alloy. A relatively low temperature (approximately 100℃ below the alloy's β-transformation point) is chosen to ensure the alloy matrix has high yield strength. Under these conditions, applying extremely high hydrostatic pressure of 220-250MPa generates a strong plastic compression effect on casting defects such as micro-shrinkage cavities and interdendritic porosity in the as-cast microstructure, forcing them to rapidly weld and close in the solid state through creep and diffusion mechanisms. This process is akin to "micro-forging" the material, not only eliminating potential crack sources in subsequent service and significantly improving the material's density and reliability, but also providing a defect-free matrix for subsequent atomic diffusion and phase transformation. The short holding time (0.3-0.6 hours) is sufficient to close the main defects while avoiding unnecessary grain growth. S22. Second Stage (High-Temperature Diffusion Homogenization): The temperature is raised to 970-990℃, and the pressure is adjusted to 80-100MPa, held for 1.0-1.8 hours. The core objective of this stage is to promote the full diffusion and homogenization of alloying elements, especially to activate the role of rare earth Nd. Raising the temperature to 970-990℃ significantly improves the diffusion coefficients of all alloying elements, especially Al, Sn, Zr, and Nd. Simultaneously, the pressure is significantly reduced from the ultra-high pressure of the first stage to 80-100MPa. This reduces the constraint of high pressure on atomic diffusion and migration while still maintaining sufficient hydrostatic pressure to prevent the formation of new defects. Under this "high-temperature-medium-pressure" environment: on the one hand, rare earth Nd atoms can undergo long-range diffusion, more effectively "searching" for and segregating around grain boundaries, phase boundaries, and solute atoms such as O and Sn, achieving their microstructural purification effect. On the other hand, the distribution of major alloying elements such as Al, Sn, and Zr in the α and β phases is further homogenized, reducing microsegregation. Furthermore, the increased proportion of the β phase at high temperatures facilitates the formation of a more uniform and finer β-transformation structure during subsequent cooling. Sufficient holding time (1.0-1.8 hours) is crucial to ensuring the full progress of the aforementioned diffusion process. S23. Third Stage (Medium-Temperature Multi-Stage Pressure Control): The temperature is lowered to 940-960℃, followed by a stepped pressure control process of "high pressure-low pressure-medium pressure," lasting 0.5-1.0 hours in total. This stage is crucial for fine-tuning the microstructure, its core being the use of dynamic changes in pressure parameters to "condition" the alloy's substructure. First, maintaining a relatively high pressure (170-180 MPa) for 0.15-0.3 hours helps to further compact the micro-interfaces, promoting dislocation rearrangement and annihilation. Subsequently, the pressure is lowered to a lower level (130-140 MPa), providing a brief "relaxation" window for atoms, which helps release local stress and allows some diffusion processes suppressed under high pressure to occur. Finally, the pressure is restored to a moderate level (150-160 MPa) for stabilization. This stepwise cyclical change in pressure can disrupt the precipitation and growth path of phases (such as coarse Ti3Al phases or continuous brittle phases) that may occur under a single steady-state condition and are detrimental to performance, while simultaneously promoting the heterogeneous nucleation of more fine, dispersed strengthening phases (such as Nd-rich nanophases). This is equivalent to performing a "micromechanical oscillation treatment" on the material, aiming to obtain a more uniform and stable dispersed strengthening structure; S24, Fourth stage (low temperature and high pressure stabilization): The temperature is reduced to 910~930℃ and the pressure is increased to 190~210MPa, and the temperature is maintained for 1.5~2.2 hours. The core objective of this stage is to achieve deep stabilization of the structure and complete relaxation of residual stress. After experiencing the previous stages, especially the changes in temperature and pressure, a certain amount of micro-strain and thermal stress will accumulate inside the material. Setting the temperature at 910~930℃, while applying a higher pressure (190-210MPa) and maintaining it for a sufficient time (1.5-2.2 hours), this combination of conditions can: (1) High hydrostatic pressure combined with long-term heat preservation provides a strong driving force and sufficient time for dislocation climb, grain boundary slip and phase boundary adjustment, thereby effectively eliminating residual stress inside the material and improving dimensional stability and fatigue resistance. (2) It makes the metastable structures formed in the preceding stage (such as supersaturated solid solutions and fine precipitate nuclei) more thermodynamically stable, but because the temperature is relatively low and the pressure is high, it inhibits them from becoming excessively coarsened or transforming into harmful phases. This stage is crucial for the purification and dispersion enhancement effect brought about by "locking in" Nd elements; S25, Fifth Stage (Programmed Cooling): During the linear reduction of pressure from 190~210MPa to 100MPa, the temperature is slowly cooled to 850℃ at a rate not exceeding 5℃ / min. This stage serves as a bridge from the processing temperature to subsequent cooling, aiming to "freeze" the optimized microstructure. Traditional HIP processes typically employ furnace cooling or air cooling after completion, resulting in rapid cooling rates that may lead to microcracks due to thermal stress or induce unfavorable secondary phase transformations during cooling. This invention employs a strategy of coordinated and gradual pressure and temperature reduction: the linear reduction of pressure provides a smooth unloading process, avoiding microscopic springback or damage that may be caused by a sudden pressure drop. The extremely slow cooling rate (≤5℃ / min) ensures that the material remains in a near-equilibrium state throughout the cooling process from the end temperature of the fourth stage to 850℃, minimizing new thermal and internal stresses generated by rapid cooling. This controlled cooling environment allows the phase composition and microstructure of the alloy to be finalized in a smooth and controllable manner, thus "intactly" preserving the ideal microstructure obtained through the careful regulation of the first four stages and transferring it to the final product.

[0031] In summary, these five stages constitute a logically rigorous and functionally progressive process chain: densification (laying the foundation) → homogenization and Nd activation (playing a core role) → multi-level pressure fine control (optimizing substructure) → high-pressure stabilization (relieving stress and stabilizing the microstructure) → programmed slow cooling (locking in the final state). This process, in close synergy with the specific alloy composition of this invention (especially the narrow-range Nd), jointly ensures that the alloy achieves high strength while possessing excellent long-term high-temperature microstructural stability and service safety.

[0032] S3, Final Cooling The alloy that has undergone the above five-stage HIP treatment is cooled from 850°C to room temperature to obtain the final product.

[0033] The rare-earth Nd-modified cast high-temperature titanium alloy prepared based on this invention exhibits excellent high-temperature strength, good plasticity, and outstanding long-term structural stability at temperatures of 650°C and above through the synergistic effect of the aforementioned composition and process. Therefore, this alloy is particularly suitable for manufacturing key hot-end structural components for equipment such as aero-engines and gas turbines that require long-term operation at temperatures of 650°C and above, such as integrally cast casings and guide vane supports, meeting the stringent requirements of advanced equipment for weight reduction, high-temperature resistance, and long service life.

[0034] The following description, in conjunction with specific embodiments and comparative examples, provides further explanation.

[0035] Example 1 The titanium alloy composition (mass percentage) in this embodiment is as follows: Al 5.9%, Sn 4.5%, Zr 4.0%, Mo 0.5%, Si 0.2%, Nb 0.4%, Ta 0.3%, W 0.5%, Nd 0.3%, with the balance being Ti and impurities.

[0036] Preparation method: S1. Raw Material Smelting: Weigh the raw materials according to the above composition (Nd blocks are wrapped in titanium foil). Load the raw materials into a vacuum arc furnace and evacuate to 5×10⁻⁶. -3 After Pa, argon gas was added to a pressure of 5 × 10⁻⁶. -2 Pa, then evacuate again, repeat 3 times. Under argon protection, melt at a current of 700A, temperature of approximately 2350℃, each melting time 2.5 minutes, with electromagnetic stirring for 35 seconds. Repeat this melting process and turn the ingot 5 times. Finally, cool with the furnace to approximately 150℃ and remove the ingot. S2. Five-stage HIP treatment: Parameters are as follows: Stage 1: 910℃, 235MPa, 0.5h; Stage 2: 980℃, 90MPa, 1.5h; Stage 3: 950℃, followed by 175MPa / 0.25h, 135MPa / 0.25h, and 155MPa / 0.3h; Stage 4: 920℃, 200MPa, 2.0h; Stage 5: Pressure linearly decreases from 200MPa to 100MPa, while temperature cools from 920℃ to 850℃ at a rate of 4℃ / min. S3, Final Cooling: Air cooling from 850°C to room temperature.

[0037] Example 2 The titanium alloy composition (mass percentage) in this embodiment is as follows: Al 5.50%, Sn 3.50%, Zr 3.50%, Mo 0.20%, Si 0.10%, Nb 0.25%, Ta 0.20%, W 0.40%, Nd 0.25%, with the balance being Ti and impurities.

[0038] Preparation method: Except for weighing the raw materials according to the ingredients in this embodiment, the other process steps and parameters are exactly the same as in Example 1.

[0039] Example 3 The titanium alloy composition (mass percentage) in this embodiment is as follows: Al 6.50%, Sn 5.00%, Zr 5.00%, Mo 0.80%, Si 0.30%, Nb 0.55%, Ta 0.40%, W 0.60%, Nd 0.35%, with the balance being Ti and impurities.

[0040] Preparation method: Except for weighing the raw materials according to the ingredients in this embodiment, the other process steps and parameters are exactly the same as in Example 1.

[0041] Comparative Example 1 (without Nd comparison) The alloy composition of this comparative example is exactly the same as that of Example 1, except that no Nd element is added (i.e., the Nd content is 0%).

[0042] Preparation method: Except for the absence of Nd blocks in the raw materials, all smelting parameters and five-stage HIP process parameters are strictly consistent with those in Example 1.

[0043] Performance Testing and Results Analysis Samples were cut from the final alloys (HIP state) prepared in Examples 1, 2, 3, and Comparative Example 1, and processed into standard room temperature tensile specimens to test their "normal state" properties. Separate samples were taken from the final alloys prepared in Examples 1, 2, 3, and Comparative Example 1, and subjected to heat exposure treatment at 650℃ / 100h in a muffle furnace. After air cooling, they were processed into tensile specimens to test their simulated "long-term service" performance. The test results are shown in Table 1 below.

[0044] Table 1 Performance test results of alloys in each embodiment and comparative example As shown in Table 1, (1) comparing the "normal state" data of Example 1 (containing 0.3% Nd) and Comparative Example 1 (without Nd), it can be seen that under the same preparation process, the addition of trace amounts of Nd increased the yield strength of the alloy by 73 MPa (approximately 8.4%), the tensile strength by 65 MPa (approximately 6.7%), and the elongation was also improved. This directly proves that rare earth Nd has a significant contribution to improving the basic strength and plasticity of the alloy through its synergistic effect of microstructure purification and dispersion strengthening. (2) Comparing the data after heat exposure treatment, the role of Nd is more critical and prominent. After heat exposure at 650℃ / 100h, the yield strength and tensile strength of Comparative Example 1 without Nd plummeted by 313 MPa and 360 MPa, respectively, and the elongation also dropped to a low level, showing typical heat exposure embrittlement characteristics. All Nd-containing Examples 1-3, under the same heat exposure conditions, showed only a slight decrease in strength (approximately 4-5%), and the tensile strength after heat exposure (UTS≥940MPa) was much higher than that of Comparative Example 1 (UTS=610MPa), while maintaining good plasticity (E1≥9.0%). This strongly confirms that Nd element fundamentally ensures the microstructure stability and performance reliability of the alloy during long-term high-temperature service by reducing the effective Al equivalent of the α phase and inhibiting the precipitation and growth of the Ti3Al ordered phase. (3) The test results of Examples 2 (lower limits for each component) and 3 (upper limits for each component) prove that within the composition range required by this invention, alloys with excellent performance can be obtained by the preparation method, and the composition design is feasible and versatile. Specifically: Example 2 showed better plasticity (conventional state E1=14.5%). Example 3 achieved the highest conventional strength (conventional YS=955MPa, UTS=1050MPa), but its plasticity and plasticity retention rate after heat exposure were slightly lower than those of Example 1. Example 1 (preferred composition) achieved the best balance among strength (conventional UTS=1035MPa), plasticity (conventional E1=13.8%), and performance retention rate after heat exposure (strength retention rate>94%, plasticity retention rate>74%), resulting in the most outstanding overall service performance.

[0045] Depend on Figure 1 and Figure 2 It can be seen that both Example 1 and Comparative Example 1 yielded titanium alloys containing α and β phases in both the conventional and hot-exposed states. However, after adding the rare earth element Nd, the microstructure became finer in both the conventional and hot-exposed states. This directly demonstrates that the addition of rare earth Nd significantly inhibits microstructure coarsening and harmful phase precipitation during long-term high-temperature exposure, thereby ensuring excellent thermal stability.

[0046] The above data and analysis show that the cast high-temperature titanium alloy successfully prepared by combining "specific composition design (including narrow-range Nd)" and "innovative five-stage HIP process" not only has excellent conventional mechanical properties, but more importantly, it possesses outstanding long-term microstructural stability at 650℃, fully achieving the design objectives of this invention. Among them, the composition ratio represented by Example 1 exhibits the optimal comprehensive performance.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A rare-earth modified cast high-temperature titanium alloy, characterized in that, By mass percentage, it comprises the following components: Al 5.50%–6.50%, Sn 3.50%–5.00%, Zr 3.50%–5.00%, Mo 0.20%–0.80%, Si 0.10%–0.30%, Nb 0.25%–0.55%, Ta 0.20%–0.40%, W 0.40%–0.60%, Nd 0.25%–0.35%, with the remainder being Ti and unavoidable impurity elements; The addition of Nd element achieves tissue purification and diffusion enhancement, thereby suppressing the precipitation of Ti3Al ordered phase.

2. The rare earth modified cast high-temperature titanium alloy according to claim 1, characterized in that, By mass percentage, it comprises the following components: Al 5.9%, Sn 4.5%, Zr 4.0%, Mo 0.5%, Si 0.2%, Nb 0.4%, Ta 0.3%, W 0.5%, Nd 0.3%, with the remainder being Ti and unavoidable impurity elements.

3. A method for preparing a rare-earth modified cast high-temperature titanium alloy, characterized in that, Includes the following steps: S1. Raw material smelting: Weigh each raw material according to the composition ratio described in any one of claims 1-2, and obtain an alloy ingot with uniform composition by vacuum arc melting and multiple ingot turning and remelting. S2. Microstructure-controlled hot isostatic pressing: The alloy ingot is placed in a hot isostatic pressing apparatus and subjected to the following five stages of treatment under a protective atmosphere: (1) First stage: Under the conditions of temperature of 900~920℃ and pressure of 220~250MPa, keep warm for 0.3~0.6 hours; (2) Second stage: Raise the temperature to 970~990℃, adjust the pressure to 80~100MPa, and keep it warm for 1.0~1.8 hours; (3) Third stage: Reduce the temperature to 940~960℃, and then control the pressure in the following order: (a) First, increase the pressure to 170~180MPa and maintain it for 0.15~0.3 hours; (b) Then reduce the pressure to 130-140 MPa and maintain it for 0.15-0.3 hours; (c) Increase the pressure again to 150~160MPa and maintain it for 0.2~0.4 hours; (4) Fourth stage: lower the temperature to 910~930℃, raise the pressure to 190~210MPa, and keep it at that temperature for 1.5~2.2 hours; (5) Fifth stage: During the process of linearly reducing the pressure from 190~210MPa to 100MPa, the temperature is cooled from the end temperature of the fourth stage to 850℃ at a rate of no more than 5℃ / min. S3. Final cooling: Cool the alloy from 850°C to room temperature.

4. The preparation method according to claim 3, characterized in that, Step S1 specifically includes: S11. Raw material weighing and preparation: Weigh the raw materials Ti, Al, Zr, Sn, Mo, Si, Nb, Ta, W and Nd respectively, and store the rare earth Nd blocks separately in a sealed container. S12. Loading and Vacuum Preparation: Mix all raw materials except the Nd block thoroughly, and place them together with the Nd block wrapped in titanium foil in a water-cooled copper crucible of a vacuum arc melting furnace, with the Nd block placed in the middle of the mixed raw materials; evacuate the furnace to a vacuum level not exceeding 5 × 10⁻⁶. -3 After Pa, high-purity argon gas was introduced to a concentration of 5 × 10⁻⁶. -2 Pa, then evacuate again, repeat this process 2-3 times to remove residual gas in the furnace; S13. Melting and stirring: Melting is carried out under argon protection, the melting current is controlled at 600~800A, the temperature is raised to 2200~2500℃, the melting time is 2~3min each time, and electromagnetic stirring is applied for 30~40s in the molten state of the alloy. S14. Ingot flipping and remelting and ingot cooling: After completing one melting, flip the ingot 180° and repeat the melting operation of step S13. The number of ingot flipping and remelting is 4 to 6 times, and the cooling interval between two adjacent meltings is 2 to 3 minutes. After completing the last melting, the ingot is naturally cooled to below 200°C under argon protection for 20 to 30 minutes. Then the cast alloy ingot is taken out.

5. The preparation method according to claim 3, characterized in that, In step S3, the cooling rate above 500°C shall not exceed 30°C / min.

6. The application of a rare earth modified cast high-temperature titanium alloy according to any one of claims 1-2 or a rare earth modified cast high-temperature titanium alloy prepared by the preparation method according to any one of claims 3-5 in the preparation of structural components for aero-engines or gas turbines that operate at temperatures of 650°C and above for extended periods.

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