Ti8al sn based alloy castings and methods of making the same

Abstract

This disclosure provides a Ti8AlSn-based alloy casting and its preparation method. The preparation method includes: preheating a mold to obtain a preheated mold; simultaneously pouring molten alloy into the preheated mold and applying ultrasonic vibration to obtain an alloy billet; and performing heat treatment and post-treatment on the alloy billet to obtain the Ti8AlSn-based alloy casting, wherein the ultrasonic vibration is applied from the outer periphery and bottom of the mold into the interior of the mold. The method of this disclosure overcomes the problems of insufficient fluidity and casting defects caused by the high processing temperature and poor intrinsic plasticity of Ti8AlSn-based alloys, effectively avoids melt contamination, and significantly improves the microstructure uniformity and forming quality of the casting.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature resistant materials of intermetallic compounds, specifically relating to a Ti8AlSn-based alloy casting and its preparation method. Background Technology

[0002] To meet the development requirements of high thrust-to-weight ratio and high efficiency in aerospace engines, lightweight, high-strength, and high-temperature resistant materials have become crucial. While traditional high-temperature titanium alloys possess good overall performance below 600℃, they struggle to meet the long-term service requirements at higher temperatures. Ti-Al intermetallic compounds developed based on this, such as γ-TiAl and α2-Ti3Al, exhibit excellent high-temperature performance, but suffer from intrinsic room-temperature brittleness and poor processability. Ti2AlNb-based alloys, due to the addition of Nb, may experience microstructural instability degradation and performance decline during long-term high-temperature service.

[0003] To address the aforementioned issues, an intermetallic compound based on the Ti8AlSn phase has emerged, exhibiting superior high-temperature phase stability and resistance to structural degradation, providing a feasible technical path for the design of next-generation engine materials. However, as an ordered phase with a close-packed hexagonal structure, the intrinsically ordered structure of the Ti8AlSn phase significantly hinders dislocation movement, making the material highly susceptible to cracking and difficult to form during conventional hot working processes (such as forging).

[0004] On the other hand, the phase transformation point of Ti8AlSn-based alloys is higher than that of ordinary titanium alloys, which means that hot working must be carried out at higher temperatures, significantly increasing the difficulty of process control and production costs. Given its poor forging performance, casting has become the necessary method for manufacturing these alloy components. However, casting is prone to defects such as shrinkage porosity, hot cracking, and compositional segregation. Therefore, developing a method for manufacturing Ti8AlSn-based alloy castings to solve the problems of microstructure control and defect suppression during the casting process is of great significance for promoting the engineering application of this novel high-temperature material. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing Ti8AlSn-based alloy castings, so as to solve the problems of poor forming plasticity, high processing temperature, poor fluidity and easy generation of shrinkage cavities and cracks in the prior art, and improve the density and uniformity of the casting.

[0006] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, this disclosure provides a method for preparing Ti8AlSn-based alloy castings, the method comprising: The mold is preheated to obtain the preheated mold. While pouring the alloy melt into the treated mold, ultrasonic vibration is applied to obtain an alloy billet; and The alloy billet is subjected to heat treatment and post-treatment to obtain the Ti8AlSn-based alloy casting. The ultrasonic vibration is applied from the outer periphery and bottom of the mold into the interior of the mold.

[0007] In some embodiments, the ultrasonic vibration frequency of the outer periphery and bottom of the mold is controlled when the ultrasonic vibration is applied to apply uniform ultrasonic vibration to the alloy melt.

[0008] In some embodiments, the vibration frequency is 15-20 kHz, and the ultrasonic intensity per unit area is not less than 220 W·cm. -2 .

[0009] In some embodiments, applying the ultrasonic vibration includes: When the alloy melt is being poured and the mold is not yet completely filled, the ultrasonic vibration is applied only from the bottom of the mold to the interior of the mold to stabilize the liquid surface of the alloy melt and prevent splashing. After the alloy melt fills 80% of the mold volume, ultrasonic vibration is applied from the bottom and outer periphery of the mold into the interior of the mold to perform three-dimensional ultrasonic treatment on the alloy melt until the alloy melt is completely solidified.

[0010] In some embodiments, the preheating treatment includes preheating the mold to 800–1000°C.

[0011] In some embodiments, the heat treatment includes hot isostatic pressing of the alloy billet under heat and pressure to eliminate internal micro-shrinkage cavities and porosity.

[0012] In some embodiments, the temperature of the hot isostatic pressing treatment is 1100~1200°C.

[0013] In some embodiments, the pressure of the hot isostatic pressing process is 100~200MPa.

[0014] In some implementations, the heat preservation and pressure holding are carried out for 1 to 2 hours.

[0015] In some embodiments, the post-processing includes annealing the alloy blank to remove internal stresses.

[0016] In some embodiments, the alloy is a titanium-based intermetallic compound material with a Ti8AlSn phase as its matrix, and the chemical composition of the alloy, by atomic percentage, comprises: Al: 5-15 at% Sn: 5-15 at%, and Balance: Ti and unavoidable impurity elements.

[0017] In some embodiments, the Ti8AlSn phase is an ordered phase with a close-packed hexagonal structure, wherein the atomic ratio of Ti, Al, and Sn is 8:1:1.

[0018] In a second aspect, this disclosure provides a Ti8AlSn-based alloy casting, which is prepared by the method described in the first aspect.

[0019] In some embodiments, the Ti8AlSn-based alloy casting has an average grain width of 5-10 μm, an aspect ratio of 8-10, and the grains have parallel growth directions.

[0020] Compared with the prior art, the present invention has the following beneficial effects: This disclosure effectively solves the problems of high processing temperature, poor intrinsic plasticity, insufficient fluidity, and casting defects in Ti8AlSn-based alloys by applying ultrasonic vibration from the outer periphery and bottom of the mold to the interior of the mold. This method, by applying ultrasonic vibration from the outer periphery and bottom of the mold to the interior of the mold and utilizing the mold wall to conduct the vibration, avoids the high-temperature erosion and contamination of the alloy melt caused by traditional probe insertion ultrasonic treatment.

[0021] Furthermore, the use of three-dimensional ultrasonic waves creates a multi-directional superimposed field within the alloy melt, eliminating the dead zone of the acoustic field caused by single-sided vibration and significantly improving the uniformity of the casting structure. Moreover, preheating the mold at 800-1000℃ further enhances the melt's ability to fill the mold, effectively reducing shrinkage cavities, porosity, and hot cracking tendencies while ensuring mold filling integrity. Attached Figure Description

[0022] Figure 1 The macroscopic morphology of the alloy casting prepared according to Example 1 of this disclosure; Figure 2 The metallographic structure of the alloy casting prepared according to Example 1 of this disclosure; Figure 3 The metallographic structure of the alloy casting prepared according to Comparative Example 1 of this disclosure. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present disclosure, the technical solutions of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present disclosure, and not all embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present disclosure.

[0024] The terms “comprising” or “including” as used herein should be interpreted as having a non-exhaustive meaning and allowing for the addition or reference to further elements, such as adding features or method steps or members or components to anything that includes the listed elements. “Comprising” may be replaced by “including” if the practice of a given language variant requires it, or may be limited to “consistently consisting of” if other elements besides those listed are not essential to the practice of this disclosure, or may be limited to “consisting of” in the absence of any other elements.

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to those ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Terms defined in dictionaries should be interpreted as having the same meaning as those disclosed in relevant technical literature and not as having an idealized or overly formal meaning.

[0027] To meet the development requirements of high thrust-to-weight ratio and high efficiency in aerospace engines, lightweight, high-strength, and high-temperature resistant materials have become crucial. Current technology has proposed an intermetallic compound based on the Ti8AlSn phase, which combines superior high-temperature phase stability and resistance to structural degradation, providing a feasible technical path for the design of next-generation engine materials. However, as an ordered phase with a close-packed hexagonal structure, the intrinsically ordered structure of the Ti8AlSn phase significantly hinders dislocation movement, making the material highly susceptible to cracking during conventional hot working (such as forging) and difficult to form.

[0028] On the other hand, the phase transformation point of Ti8AlSn-based alloys is higher than that of conventional titanium alloys, meaning that hot working must be carried out at higher temperatures, significantly increasing the difficulty of process control and production costs. Given its poor forging performance, casting has become the necessary method for manufacturing these alloy components. However, casting is highly susceptible to defects such as shrinkage porosity, hot cracking, and compositional segregation. Therefore, developing a method for manufacturing Ti8AlSn-based alloy castings to address the issues of microstructure control and defect suppression during the casting process is of great significance for promoting the engineering application of this novel high-temperature material.

[0029] In order to overcome the shortcomings of the prior art, this disclosure provides a Ti8AlSn-based alloy casting and its preparation method, so as to solve the problems of poor forming plasticity, high processing temperature, poor fluidity and easy generation of shrinkage cavities and cracks in the prior art, and improve the density and uniformity of the casting.

[0030] The first aspect of this disclosure provides a method for preparing Ti8AlSn-based alloy castings, the method comprising: The mold is preheated to obtain the preheated mold. While pouring the alloy melt into the treated mold, ultrasonic vibration is applied to obtain an alloy billet; and The alloy billet is subjected to heat treatment and post-treatment to obtain the Ti8AlSn-based alloy casting. The ultrasonic vibration is applied from the outer periphery and bottom of the mold into the interior of the mold.

[0031] This disclosure effectively solves the problems of high processing temperature, poor intrinsic plasticity, insufficient fluidity, and casting defects in Ti8AlSn-based alloys by applying ultrasonic vibration from the outer periphery and bottom of the mold to the interior of the mold.

[0032] This method applies ultrasonic vibrations from the outer periphery and bottom of the mold to the interior of the mold, and uses the mold wall to conduct the vibrations, thereby avoiding the high-temperature erosion and contamination of the alloy melt caused by traditional probe insertion ultrasonic treatment.

[0033] In some embodiments, the ultrasonic vibration frequency of the outer periphery and bottom of the mold is controlled when the ultrasonic vibration is applied to apply uniform ultrasonic vibration to the alloy melt.

[0034] In some implementations, the vibration frequency is 15-20 kHz. As an example, the vibration frequency can be 15 kHz, 15.5 kHz, 16 kHz, 16.5 kHz, 17 kHz, 17.5 kHz, 18 kHz, 18.5 kHz, 19 kHz, 19.5 kHz, 20 kHz, and any number between any two of the above values.

[0035] In some implementations, the ultrasonic intensity per unit area is not less than 220 W·cm. -2 .

[0036] In some embodiments, applying the ultrasonic vibration includes: When the alloy melt is being poured and the mold is not yet completely filled, the ultrasonic vibration is applied only from the bottom of the mold to the interior of the mold to stabilize the liquid surface of the alloy melt and prevent splashing. After the alloy melt fills 80% of the mold volume, ultrasonic vibration is applied from the bottom and outer periphery of the mold into the interior of the mold to perform three-dimensional ultrasonic treatment on the alloy melt until the alloy melt is completely solidified.

[0037] This disclosure effectively solves the problems of high processing temperature, poor intrinsic plasticity, insufficient fluidity, and casting defects in Ti8AlSn-based alloys by applying ultrasonic vibration from the outer periphery and bottom of the mold to the interior of the mold, combined with a step-by-step start-up strategy.

[0038] In addition, by using three-dimensional ultrasonic action, ultrasonic waves are formed into a multi-directional superimposed field inside the alloy melt, eliminating the dead zone of the acoustic field of single-sided vibration and significantly improving the uniformity of the casting structure.

[0039] In some embodiments, the preheating treatment includes preheating the mold to 800–1000°C. For example, the mold can be preheated to 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, and any number between any two of the above values.

[0040] This disclosure improves the filling capacity of the melt by preheating the mold to 800-1000℃, thereby effectively reducing shrinkage cavities and hot cracking tendency while ensuring the integrity of the filling process.

[0041] In some embodiments, the heat treatment includes hot isostatic pressing of the alloy billet under heat and pressure to eliminate internal micro-shrinkage cavities and porosity.

[0042] In some embodiments, the hot isostatic pressing (HIP) temperature is 1100~1200°C. For example, the HIP temperature can be 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, or any number between any two of the above values.

[0043] In some embodiments, the pressure of the hot isostatic pressing (HIP) is 100-200 MPa. For example, the HIP pressure can be 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, 200 MPa, or any number between any two of the above values.

[0044] In some implementations, the heat preservation and pressure holding process lasts for 1 to 2 hours. For example, the heat preservation and pressure holding time can be 1 hour, 1.5 hours, 2 hours, or any number between any two of the above values.

[0045] In some embodiments, the post-processing includes annealing the alloy blank to remove internal stresses.

[0046] In some embodiments, the alloy is a titanium-based intermetallic compound material with a Ti8AlSn phase as its matrix, and the chemical composition of the alloy, by atomic percentage, comprises: Al: 5-15 at% Sn: 5-15 at%, and Balance: Ti and unavoidable impurity elements.

[0047] In some embodiments, the Ti8AlSn phase is an ordered phase with a close-packed hexagonal structure, wherein the atomic ratio of Ti, Al, and Sn is 8:1:1.

[0048] The second aspect of this disclosure provides a Ti8AlSn-based alloy casting, which is prepared by the method described in the first aspect.

[0049] In some embodiments, the average grain width of the Ti8AlSn-based alloy casting is 5-10 μm. For example, the average grain width of the Ti8AlSn-based alloy casting can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, and any number between any two of the above values.

[0050] The castings disclosed herein have a smooth surface and clear outline, and are free from macroscopic casting defects such as incomplete pouring, cold shuts, and hot cracks. The average grain width of the castings is 5-10 μm, with uniform distribution and no abnormally large grains.

[0051] In some embodiments, the aspect ratio of the casting grains is 8-10. For example, as an example, the aspect ratio of the casting grains can be 8, 8.5, 9, 9.5, 10, or any number between any two of the above values.

[0052] Therefore, the castings described in this disclosure have a consistent aspect ratio of approximately 8-10, and the grain growth direction has good parallelism.

[0053] To make the embodiments of this disclosure easier to understand, the present disclosure will be described in detail below with reference to the embodiments. These embodiments are for illustrative purposes only and are not limited to the application scope of this disclosure.

[0054] Unless otherwise specified, the specific operations and processing methods or conditions not described in the following embodiments are conventional methods in the art or are performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0055] Unless otherwise specified, all reagents or instruments used in the following examples that do not specify the manufacturer are commercially available products and conventional instruments in the field.

[0056] In the following examples, unless otherwise specified, all percentages are atomic percentages.

[0057] None of the chemicals underwent secondary purification.

[0058] The specific testing methods disclosed herein are as follows: The metallographic structure was measured using a CX40M optical metallographic microscope in accordance with GB / T 13298-2015 "Methods for Examination of Metallic Microstructures" and GB / T 6394-2017 "Methods for Determination of Average Grain Size of Metals".

[0059] Example 1 The raw materials used in this embodiment, by atomic percentage, have the following target components: Ti content of 90.0%, Al content of 5.0%, and Sn content of 5.0%.

[0060] An aluminum alloy mold, matching the shape of the target casting, was prepared by machining. After cleaning and removing contaminants from the mold surface, it was immersed in molten wax at a temperature controlled at 75±5℃ for approximately 15 seconds, forming a uniform wax layer approximately 0.2 mm thick. Subsequently, a surface layer and a reinforcing layer were sequentially fabricated on the wax mold surface: the surface layer slurry was prepared from yttrium oxide powder and zirconium sol, and fine yttrium oxide sand was used for sprinkling; the reinforcing layer used mullite powder and silica sol, and coarse mullite sand was used for sprinkling, for a total of three layers. The mold shell was fired at 950℃ for 2 hours, cooled, washed with water to remove residual ash, and dried for later use.

[0061] Subsequently, the mold shell is placed in a resistance furnace and heated to 1000℃ at a rate of 5℃ / min, and held at that temperature for 1.5 hours to ensure uniform temperature distribution.

[0062] Afterward, the preheated shell is transferred into a vacuum arc furnace and fixed to an ultrasonic vibration platform. The ultrasonic vibration platform is equipped with a bottom ultrasonic transducer and two ultrasonic transducers on opposite sides, all controlled by a synchronization signal generator. The casting process employs a step-by-step ultrasonic activation: initially, only the bottom ultrasonic transducer is activated at a frequency of 15 kHz and an ultrasonic intensity of 250 W·cm. - ²; When the melt fills about 80% of the shell volume, immediately turn on the side ultrasonic transducer, maintaining the same frequency and intensity as the bottom, and continue the three-dimensional ultrasonic action until the melt is completely solidified.

[0063] After casting, the mold shell is kept in the vacuum arc furnace and cooled to room temperature. The ultrasonic vibration system is turned off, the furnace door is opened, and the mold shell is removed. The mold shell is broken and removed using mechanical vibration or high-pressure water jet to remove any remaining mold shell residue from the casting surface. The casting is then sandblasted to remove surface oxide scale and impurities, thus obtaining the Ti8AlSn-based alloy billet.

[0064] The deshelled alloy billet is subjected to hot isostatic pressing at 1200℃ and 100MPa for 2 hours to eliminate internal micro-shrinkage cavities and porosity. Subsequently, stress-relief annealing is performed to remove casting and machining stresses, ultimately obtaining the titanium alloy casting.

[0065] Example 2 The raw materials used in this embodiment, by atomic percentage, have the following target components: Ti content 70.0%, Al content 15.0%, and Sn content 15.0%.

[0066] An aluminum alloy mold, matching the shape of the target casting, was prepared by machining. After cleaning and removing contaminants from the mold surface, it was immersed in molten wax at a temperature controlled at 75±5℃ for approximately 15 seconds, forming a uniform wax layer approximately 0.2 mm thick. Subsequently, a surface layer and a reinforcing layer were sequentially fabricated on the wax mold surface: the surface layer slurry was prepared from yttrium oxide powder and zirconium sol, and fine yttrium oxide sand was used for sprinkling; the reinforcing layer used mullite powder and silica sol, and coarse mullite sand was used for sprinkling, for a total of three layers. The mold shell was fired at 950℃ for 2 hours, cooled, washed with water to remove residual ash, and dried for later use.

[0067] Subsequently, the mold shell is placed in a resistance furnace and heated to 800°C at a rate of 5°C / min, and held at that temperature for 2 hours to ensure uniform temperature distribution.

[0068] Afterward, the preheated shell is transferred into a vacuum arc furnace and fixed to an ultrasonic vibration platform. The ultrasonic vibration platform is equipped with a bottom ultrasonic transducer and two ultrasonic transducers on opposite sides, all controlled by a synchronization signal generator. The casting process employs a step-by-step ultrasonic activation: initially, only the bottom ultrasonic transducer is activated at a frequency of 20 kHz and an ultrasonic intensity of 250 W·cm. - ²; When the melt fills about 80% of the shell volume, immediately turn on the side ultrasonic transducer, maintaining the same frequency and intensity as the bottom, and continue the three-dimensional ultrasonic action until the melt is completely solidified.

[0069] After casting, the mold shell is kept in the vacuum arc furnace and cooled to room temperature. The ultrasonic vibration system is turned off, the furnace door is opened, and the mold shell is removed. The mold shell is broken and removed using mechanical vibration or high-pressure water jet to remove any remaining mold shell residue from the casting surface. The casting is then sandblasted to remove surface oxide scale and impurities, thus obtaining the Ti8AlSn-based alloy billet.

[0070] The unshelled billet is subjected to hot isostatic pressing at 1100℃ and 200MPa for 1 hour to eliminate internal micro-shrinkage cavities and porosity. Subsequently, stress-relief annealing is performed to remove casting and machining stresses, ultimately yielding the titanium alloy casting.

[0071] Example 3 The raw materials used in this embodiment, by atomic percentage, have the following target components: Ti content of 80.0%, Al content of 10.0%, and Sn content of 10.0%.

[0072] An aluminum alloy mold, matching the shape of the target casting, was prepared by machining. After cleaning and removing contaminants from the mold surface, it was immersed in molten wax at a temperature controlled at 75±5℃ for approximately 15 seconds, forming a uniform wax layer approximately 0.2 mm thick. Subsequently, a surface layer and a reinforcing layer were sequentially fabricated on the wax mold surface: the surface layer slurry was prepared from yttrium oxide powder and zirconium sol, and fine yttrium oxide sand was used for sprinkling; the reinforcing layer used mullite powder and silica sol, and coarse mullite sand was used for sprinkling, for a total of three layers. The mold shell was fired at 950℃ for 2 hours, cooled, washed with water to remove residual ash, and dried for later use.

[0073] Subsequently, the mold shell is placed in a resistance furnace and heated to 900℃ at a rate of 5℃ / min, and held at that temperature for 1.5 hours to ensure uniform temperature distribution.

[0074] Afterward, the preheated shell is transferred into a vacuum arc furnace and fixed to an ultrasonic vibration platform. The ultrasonic vibration platform is equipped with a bottom ultrasonic transducer and two ultrasonic transducers on opposite sides, all controlled by a synchronization signal generator. The casting process employs a step-by-step ultrasonic activation: initially, only the bottom ultrasonic transducer is activated at a frequency of 20 kHz and an ultrasonic intensity of 220 W·cm. - ²; When the melt fills about 80% of the shell volume, immediately turn on the side ultrasonic transducer, maintaining the same frequency and intensity as the bottom, and continue the three-dimensional ultrasonic action until the melt is completely solidified.

[0075] After casting, the mold shell is kept in the vacuum arc furnace and cooled to room temperature. The ultrasonic vibration system is turned off, the furnace door is opened, and the mold shell is removed. The mold shell is broken and removed using mechanical vibration or high-pressure water jet to remove any remaining mold shell residue from the casting surface. The casting is then sandblasted to remove surface oxide scale and impurities, thus obtaining the Ti8AlSn-based alloy billet.

[0076] The unshelled billet is subjected to hot isostatic pressing at 1150℃ and 150MPa for 1.5 hours to eliminate internal micro-shrinkage cavities and porosity. Subsequently, stress-relief annealing is performed to remove casting and machining stresses, ultimately yielding the titanium alloy casting.

[0077] Ti8AlSn-based alloy castings were prepared using the methods described in Examples 1-3. The resulting Ti8AlSn-based alloy castings had smooth surfaces, clear outlines, and were free from macroscopic casting defects such as incomplete pouring, cold shuts, and hot cracks. Figure 1 As shown.

[0078] Comparative Example 1 The raw materials used in this comparative example, on an atomic percentage basis, have the following target components: Ti content 80.0%, Al content 5.0%, and Sn content 5.0%.

[0079] The aluminum alloy module was prepared using the same machining method as in Example 3. After cleaning and removing contaminants from the module surface, it was immersed in molten wax at a temperature controlled at 75±5℃ for approximately 15 seconds, forming a uniform wax layer with a thickness of approximately 0.2 mm. Subsequently, a surface layer and a reinforcing layer were sequentially fabricated on the wax model surface: the surface layer slurry was prepared from yttrium oxide powder and zirconium sol, and fine yttrium oxide sand was used for sprinkling; the reinforcing layer used mullite powder and silica sol, and coarse mullite sand was used for sprinkling, for a total of 3 layers. The shell was fired at 950℃ for 2 hours, cooled, washed with water to remove residual ash, and dried for later use.

[0080] Subsequently, the mold shell is placed in a resistance furnace and heated to 900℃ at a rate of 5℃ / min, and held at that temperature for 1.5 hours to ensure uniform temperature distribution.

[0081] The preheated shell was then transferred into a vacuum arc furnace and fixed on the same ultrasonic vibration platform as in Example 3, but without activating any ultrasonic transducers during the casting process. The melt was cast and solidified naturally under normal static conditions without the application of ultrasonic vibration assistance.

[0082] After casting, the mold shell is kept in the vacuum arc furnace and cooled to room temperature. The ultrasonic vibration system is turned off, the furnace door is opened, and the mold shell is removed. The mold shell is broken and removed using mechanical vibration or high-pressure water jet to remove any remaining mold shell residue from the casting surface. The casting is then sandblasted to remove surface oxide scale and impurities, thus obtaining the Ti8AlSn-based alloy billet.

[0083] The unshelled blank was subjected to hot isostatic pressing at 1150℃ and 150MPa for 1.5 hours. Stress-relief annealing was then performed to obtain the final titanium alloy casting.

[0084] The Ti8AlSn-based alloy casting prepared in Comparative Example 1 showed significant differences in surface quality and internal structure compared to the examples. Obvious macroscopic casting defects were observed in some areas of the casting, including incomplete filling at thin-walled sections, cold shuts, and hot cracks at corners. The surface finish was poor, and the outline clarity was reduced.

[0085] Reference Figure 3 Metallographic observation of the castings obtained from the comparative examples shows that the average grain width is 20~50μm; the aspect ratio is approximately 1. 30. The grain structure of the casting is coarse and uneven, with abnormally large columnar crystals in some areas.

[0086] However, refer to Figure 2 Metallographic observation of the castings obtained from the examples shows that the average grain width of the castings is 5~10μm, uniformly distributed, and without any abnormally large grains; the aspect ratio is consistent, approximately 8. 10. The grain growth direction has good parallelism.

[0087] The above-mentioned effect is due to the three-dimensional ultrasonic vibration-assisted solidification technology adopted in this disclosure. Through the multi-directional synergistic effect of ultrasonic vibration from the bottom surface and the outer periphery to the inside of the mold, primary dendrites are continuously broken, grains are promoted to detach, and feeding channels are enhanced during the solidification process of the melt. At the same time, the step-by-step start-up strategy effectively avoids liquid surface disturbance and air entrapment in the early stage of pouring, thereby achieving synergistic optimization of casting forming quality and internal structure.

[0088] Therefore, the method disclosed herein overcomes the problems of insufficient fluidity and casting defects caused by high processing temperature and poor intrinsic plasticity of Ti8AlSn-based alloys, effectively avoids melt contamination, and significantly improves the microstructure uniformity and forming quality of castings.

[0089] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing Ti8AlSn-based alloy castings, characterized in that, The method includes: The mold is preheated to obtain the preheated mold. While pouring the alloy melt into the treated mold, ultrasonic vibration is applied to obtain an alloy billet; and The alloy billet is subjected to heat treatment and post-treatment to obtain the Ti8AlSn-based alloy casting. The ultrasonic vibration is applied from the outer periphery and bottom of the mold into the interior of the mold.

2. The method according to claim 1, characterized in that, The ultrasonic vibration frequency of the outer periphery and bottom of the mold is controlled during the application of the ultrasonic vibration to apply uniform ultrasonic vibration to the alloy melt, wherein the vibration frequency is 15-20 kHz and the ultrasonic intensity per unit area is not less than 220 W·cm. -2 .

3. The method according to claim 1, characterized in that, Applying the ultrasonic vibration includes: When the alloy melt is being poured and the mold is not yet completely filled, the ultrasonic vibration is applied only from the bottom of the mold to the interior of the mold to stabilize the liquid surface of the alloy melt and prevent splashing. After the alloy melt fills 80% of the mold volume, ultrasonic vibration is applied from the bottom and outer periphery of the mold into the interior of the mold to perform three-dimensional ultrasonic treatment on the alloy melt until the alloy melt is completely solidified.

4. The method according to claim 1, characterized in that, The preheating treatment includes preheating the mold to 800-1000°C.

5. The method according to claim 1, characterized in that, The heat treatment includes hot isostatic pressing (HIP) of the alloy billet to eliminate internal micro-shrinkage cavities and porosity, wherein the HIP temperature is 1100~1200℃, the HIP pressure is 100~200MPa, and / or the heat and pressure holding is performed for 1~2 hours.

6. The method according to claim 1, characterized in that, The post-processing includes annealing the alloy blank to remove internal stress.

7. The method according to claim 1, characterized in that, The alloy is a titanium-based intermetallic compound material with Ti8AlSn phase as the matrix. The chemical composition of the alloy, by atomic percentage, includes: Al: 5-15 at% Sn: 5-15 at%, and Balance: Ti and unavoidable impurity elements.

8. The method according to claim 7, characterized in that, The Ti8AlSn phase is an ordered phase with a close-packed hexagonal structure, wherein the atomic ratio of Ti, Al, and Sn is 8:1:

1.

9. A Ti8AlSn-based alloy casting, characterized in that, The Ti8AlSn-based alloy casting is prepared by the method according to any one of claims 1 to 8.

10. The Ti8AlSn-based alloy casting according to claim 9, characterized in that, The average grain width of the Ti8AlSn-based alloy casting is 5-10 μm, and the aspect ratio of the grains is 8-10.

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