High-density fine-grain TiAl alloy and preparation method thereof

Abstract

The invention discloses a high-density fine-grain TiAl alloy and a preparation method thereof, and belongs to the technical field of powder metallurgy. The TiAl alloy comprises the following components in atomic percent: 41%-48% of Al, 1%-8% of Nb, 0.1%-5% of In and the balance of Ti. According to the method, low-melting-point In element powder is introduced to form a low-temperature instantaneous liquid phase in the rapid sintering densification process, TiAl alloy powder particles are connected in a solid-liquid infiltration mode to promote formation of a sintering neck, and the high-performance high-density fine-grain TiAl alloy material is obtained under the conditions of low sintering temperature and sintering pressure.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology and relates to a high-density fine-grained TiAl alloy and its preparation method. Background Technology

[0002] Lightweighting of high-performance structural materials is key to improving the performance and lifespan of aerospace vehicles, reducing energy consumption and costs, and directly determines the sustainable development of the aerospace industry in the future.

[0003] TiAl alloys have advantages such as low density, high specific strength, excellent high-temperature oxidation resistance and creep resistance. Their density is only about half that of nickel-based superalloys, making them the preferred material for replacing nickel-based superalloys to achieve large-scale weight reduction in aerospace vehicles.

[0004] With the development of technologies in related application fields, the demand for complex alloy structural parts is increasing. However, traditional melting-forging-machining techniques cannot achieve precise forming, and metallurgical defects such as segregation and shrinkage porosity in precision casting are difficult to control, resulting in low yields and failing to meet the manufacturing requirements of complex structural parts. Therefore, powder metallurgy technology has attracted widespread attention in the manufacture of complex TiAl alloy structural parts.

[0005] Powder metallurgy technology based on rapid sintering offers excellent formability and microstructure, making it a promising candidate for the efficient fabrication of complex TiAl alloy components. However, TiAl alloy powders exhibit poor sinterability and low self-diffusion rates, typically requiring sintering temperatures close to the alloy's melting point and higher pressures to accelerate element migration and improve sintering density. Higher sintering temperatures and pressures, however, consume significant energy and impose stringent requirements on equipment and preparation conditions, leading to increased TiAl alloy production costs. Higher sintering temperatures also cause rapid α-phase growth, forming large lamellar structures. Grain coarsening significantly reduces the room-temperature mechanical properties of TiAl alloys. Furthermore, while TiAl alloys, as intermetallic compounds, possess excellent high-temperature mechanical properties, their room-temperature mechanical properties are relatively poor, and microstructure coarsening further degrades these properties. High-pressure sintering makes it difficult to form complex structures, limiting the production to simple blanks with poor formability. Additionally, higher sintering pressures can cause stress concentration within the sintered alloy, weakening its microstructure advantages and increasing the difficulty of subsequent processing. Therefore, although higher sintering temperatures and pressures can improve the density of the alloy to some extent, they can lead to coarsening of the alloy structure and stress concentration, significantly deteriorating the room temperature mechanical properties of TiAl alloys, weakening the forming and microstructure advantages of rapidly solidified TiAl alloy powders, and hindering the assembly, subsequent processing and application of TiAl alloys and components.

[0006] Therefore, it is necessary to provide a high-density fine-grained TiAl alloy and its preparation method to achieve rapid sintering densification of the high-density fine-grained TiAl alloy under low temperature and low pressure conditions, so that the alloy has excellent room temperature mechanical properties, simplifies the alloy preparation process, and promotes the widespread application of TiAl alloy and complex structural parts in the aerospace field. Summary of the Invention

[0007] To overcome the problems in the prior art, this invention introduces In element powder into TiAl alloy powder to form an In-containing transient liquid phase. At a lower temperature, the wettability of the In-containing transient liquid phase on the surface of TiAl alloy powder particles is utilized to achieve rapid bonding between TiAl alloy powders, thereby promoting the formation and growth of sintering necks. Simultaneously, in conjunction with spark plasma rapid sintering technology, a high-density fine-grained TiAl alloy is successfully prepared under low-temperature and low-pressure conditions, significantly improving the room-temperature mechanical properties of TiAl alloy and simplifying the alloy preparation process.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: In one aspect, this invention proposes a high-density, fine-grained TiAl alloy, wherein the alloy composition, by atomic percentage, comprises: 41%~48% Al, 1%~8% Nb, 0.1%~5% In, and the balance is Ti.

[0009] In another aspect, the present invention provides a method for preparing the above-mentioned alloy, the method comprising the following steps: S1: Under an inert gas protective atmosphere, Ti, Al, and Nb raw materials are melted and cast to obtain TiAl alloy ingots.

[0010] S2: Using the TiAl alloy ingot obtained in step S1 as a rotating electrode, spherical TiAl alloy powder is prepared by plasma rotating electrode atomization powder preparation method in an inert gas protective atmosphere.

[0011] S3: In an inert gas protective atmosphere, the TiAl alloy powder obtained in step S2 is mixed and ball-milled with In powder to obtain a mixed powder.

[0012] S4: In an inert gas protective atmosphere, the mixed powder obtained in step S3 is subjected to spark plasma segmented sintering, and after being cooled to room temperature in the furnace, a high-density fine-grained TiAl alloy is obtained. Preferably, in step S1, the melting temperature is 1560~1600℃ and the holding time is 30~40min.

[0013] During the heat preservation process, electromagnetic stirring is used to promote uniform mixing of the components of the melt. During the melting process, a high-purity argon atmosphere is used to protect the alloy melt. After melting and casting, the melt is cooled to room temperature with the furnace to obtain TiAl alloy ingots.

[0014] Preferably, in step S2, the electrode rotation speed is 16000~20000rpm, the current is 1200~1800A, the electrode melting rate is 1.5~3.0mm / s, and the inert gas protective atmosphere positive pressure is ≥0.05MPa.

[0015] More preferably, during the plasma rotating electrode atomization powder preparation process, the electrode rotation speed is 17000~19000rpm, the current is 1400~1600A, the electrode melting rate is 1.5~2.0mm / s, and the inert gas protective atmosphere positive pressure is ≥0.08MPa.

[0016] Within the control parameters of this invention, the particle size of the prepared TiAl alloy powder can be within 80 μm.

[0017] Preferably, in step S3, the ball-to-material ratio is 1:1 to 4:1, the ball milling speed is ≥240 rpm, and the ball milling time is 3.5 to 10 h.

[0018] More preferably, the ball milling time is 3.5 to 8 hours.

[0019] Through prolonged high-energy ball milling, the In element powder is plastically deformed and fully metallurgically bonded with the TiAl alloy powder.

[0020] Preferably, in step S4, the specific process of the spark plasma segmented sintering includes: first, raising the sintering temperature to an intermediate temperature of 400-800℃ at a heating rate of 60-100℃ / min, holding at that temperature for 5-15 minutes; then, raising the temperature to a sintering temperature of 1000-1250℃ at a heating rate of 60-100℃ / min, holding at that temperature for 5-15 minutes. During the segmented sintering process, the sintering pressure does not exceed 20MPa.

[0021] To avoid uneven composition of the sintered body caused by the flow of the In-containing liquid phase under gravity, a rapid segmented sintering process is adopted. First, the temperature is raised to an intermediate temperature at an extremely fast heating rate. The In element powder is melted and rapidly wetted on the surface of TiAl alloy powder particles by holding the temperature for a very short time. Solid-liquid diffusion is used to promote effective bonding at the interface and avoid directional flow of the liquid phase. Then, the temperature is raised to the sintering temperature to obtain a TiAl alloy sintered body with a uniform distribution of the In metastable phase.

[0022] Preferably, in step S1, the Ti raw material is sponge titanium powder with a particle size ≤3mm and a purity ≥99.9%; the Al raw material is industrial pure aluminum block with a purity ≥99.99% and length, width and height dimensions ≤5×5×5mm; and the Nb raw material is high-purity niobium shavings with a particle size of 3~6mm and a purity ≥99.95%.

[0023] Preferably, in step S3, the In element powder has a particle size ≤ 65 μm and a purity ≥ 99.99%.

[0024] The beneficial effects of this invention are: 1. This invention introduces In element powder into TiAl alloy powder to form a low-temperature transient liquid phase, which generates solid-liquid wetting and interfacial reaction between the liquid phase and TiAl alloy powder particles, rapidly connecting the TiAl alloy powder particles to promote the formation of sintering necks. As the sintering process progresses, the sintering necks evolve, elements diffuse, and pores close, causing the TiAl alloy powder to shrink, resulting in a highly dense, fine-grained TiAl alloy sintered body.

[0025] 2. This invention introduces In element powder into TiAl alloy powder, utilizing the solid solution strengthening effect of In element, the second phase strengthening and dislocation strengthening effect generated by the precipitation of metastable phase containing In compounds, and the fine grain strengthening effect of segmented rapid sintering to form a fine grain structure, which can significantly improve the room temperature mechanical properties of TiAl alloy.

[0026] 3. This invention utilizes spark plasma sintering to rapidly melt In element powder within an extremely short time, forming a transient liquid phase under low temperature and low pressure conditions. This liquid phase, through solid-liquid wetting, connects TiAl alloy powder particles while simultaneously promoting the formation of sintering necks to stabilize the transient liquid phase position. The rapid sintering characteristics of spark plasma sintering prevent the transient liquid phase from flowing due to gravity. Simultaneously, it significantly reduces the sintering temperature and pressure of the TiAl alloy, greatly improving the sinterability of the TiAl alloy powder. The lower sintering temperature enables rapid solidification and sintering, maximizing the preservation of the microstructure characteristics of the TiAl alloy powder, facilitating the formation of a uniform, fine-grained structure, and preventing microstructure coarsening. The lower sintering pressure helps achieve near-net-shape forming of TiAl alloys and their components, reducing stress concentration within the alloy sintered body. When the sintering pressure approaches pressureless sintering conditions, near-net-shape preparation of complex TiAl alloy components can be achieved.

[0027] 4. The TiAl alloy prepared by this invention has an average grain size of 5.93 μm, a density of 99.48%, and a room temperature ultimate tensile strength of 635.96 MPa. The grains are fine and the density is high, and the alloy has excellent room temperature mechanical properties.

[0028] 5. The alloy composition of this invention is simple, the cost is low, the preparation method is convenient, and it is suitable for industrial promotion and application. Attached Figure Description

[0029] Figure 1 This is a SEM image of the morphology of TiAl alloy spherical powder prepared in Example 1 of the present invention; Figure 2This is a SEM image of the mixed powder prepared in Example 1 of the present invention; Figure 3 This is a SEM image of the sintered microstructure of the TiAl alloy prepared in Example 1 of this invention; Figure 4 This is a SEM image of the mixed powder prepared in Example 2 of the present invention; Figure 5 This is a SEM image of the sintered microstructure of the TiAl alloy prepared in Example 2 of this invention; Figure 6 The image shows the sintered microstructure (OM) of the TiAl alloy prepared in Comparative Example 1 of this invention. Figure 7 The table shows the room temperature tensile properties of the TiAl alloys prepared in Examples 1 and 2 of this invention. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0031] Unless otherwise specified, all chemical reagents used in the embodiments and comparative examples of this invention were commercially available analytical grade reagents.

[0032] In this embodiment of the invention, the atomic percentages of the TiAl alloy components are shown in Table 1.

[0033] Table 1 Example 1 This embodiment prepares the TiAl alloy according to the following steps: S1: Weigh the sponge titanium, industrial pure aluminum, and niobium scrap according to the composition in Table 1, and add the raw materials to a suspension furnace to melt and cast into TiAl alloy ingots. The melting temperature is 1560℃, and the holding time is 30min. During the holding process, electromagnetic stirring is used to promote uniform mixing of the components in the melt. The alloy melt is protected by a high-purity argon atmosphere during the melting process. After melting and casting, the TiAl alloy ingot is cooled to room temperature in the furnace to obtain the TiAl alloy ingot.

[0034] S2: Using TiAl alloy ingots as rotating electrodes, spherical TiAl alloy powders were prepared by plasma rotating electrode atomization technology in an argon protective atmosphere (electrode rotation speed was 16000 rpm, current was 1200 A, electrode melting speed was 1.5 mm / s, and positive pressure of argon protective atmosphere was 0.10 MPa), resulting in TiAl alloy powders with a particle size not exceeding 80 μm.

[0035] S3: Weigh the TiAl alloy powder and high-purity In powder according to the components in Table 1. Add the TiAl alloy powder and In powder to the stainless steel ball mill jar, lock the ball mill jar, and evacuate the ball mill jar using a vacuum pump. When the air pressure inside the ball mill jar is less than 10... -2 At MPa, stop evacuation and fill with argon gas to make the pressure inside the container equal to the external atmospheric pressure. Repeat the above evacuation and venting process 2-3 times to ensure that the mixed powder is in an argon atmosphere. Then, place the ball mill jar in a ball mill for high-energy ball milling (milling speed 240 rpm, ball-to-material ratio 3:1, milling time 3.5 h) to obtain the mixed powder.

[0036] S4: The mixed powder is loaded into a graphite mold. Then, the graphite mold containing the mixed powder is placed in a spark plasma sintering furnace to sinter and densify the TiAl alloy billet. First, the temperature is raised to 700°C at a heating rate of 80°C / min and held at this temperature for 5 min. The sintering pressure is 20 MPa. Then, the temperature is raised to the final sintering temperature at a heating rate of 80°C / min. The final sintering temperature is 1200°C, the sintering pressure is 20 MPa, and the holding time is 10 min. After sintering, the alloy is cooled to room temperature with the furnace. The furnace is then opened and the TiAl alloy is obtained.

[0037] In this embodiment, the SEM image of the prepared TiAl alloy powder morphology is as follows: Figure 1 As shown.

[0038] pass Figure 1 It can be seen that the powder has a regular shape and good sphericity.

[0039] The morphology of the mixed powder obtained by ball milling in this embodiment is as follows: Figure 2 As shown, through Figure 2 It can be seen that the mixed powder has a relatively uniform particle size and good dispersion uniformity. The In powder is broken and undergoes plastic deformation, and is uniformly embedded in the surface of the TiAl alloy powder.

[0040] The microstructure of the TiAl alloy prepared in this embodiment is as follows: Figure 3 As shown, through Figure 3 It can be seen that the average grain size of the alloy is 5.93 μm. At the same time, In element is dissolved in the TiAl alloy and forms metastable phases containing In element such as Ti2In5.

[0041] The TiAl alloy prepared in this embodiment was subjected to performance testing, and the results are as follows: Figure 7 As shown, according to Figure 7 The quantitative test results are shown in Table 2.

[0042] Example 2 This embodiment prepares the TiAl alloy according to the following steps: S1: Weigh sponge titanium, industrial pure aluminum and niobium scrap according to the components in Table 1, and add the raw materials to a suspension furnace to melt and cast TiAl alloy ingots. The melting temperature is 1560℃ and the holding time is 30min. During the holding process, electromagnetic stirring is used to promote uniform mixing of the components of the melt. The alloy melt is protected by a high-purity argon atmosphere during the melting process. After melting and casting, the TiAl alloy ingots are cooled to room temperature with the furnace to obtain TiAl alloy ingots.

[0043] S2: Using TiAl alloy ingots as rotating electrodes, spherical TiAl alloy powders were prepared by plasma rotating electrode atomization technology in an argon protective atmosphere (electrode rotation speed was 20000 rpm, current was 1800 A, electrode melting speed was 3.0 mm / s, and positive pressure of argon protective atmosphere was 0.20 MPa), resulting in TiAl alloy powders with a particle size not exceeding 80 μm.

[0044] S3: Weigh the TiAl alloy powder and high-purity In powder according to the components in Table 1. Add the TiAl alloy powder and In powder to the stainless steel ball mill jar, lock the ball mill jar, and evacuate the ball mill jar using a vacuum pump. When the air pressure inside the ball mill jar is less than 10... -2 At MPa, stop evacuation and fill with argon gas to make the pressure inside the container equal to the external atmospheric pressure. Repeat the above evacuation and venting process 2-3 times to ensure that the mixed powder is in an argon atmosphere. Then, place the ball mill jar in a ball mill for high-energy ball milling (milling speed 240 rpm, ball-to-material ratio 4:1, milling time 8 h) to obtain the mixed powder.

[0045] S4: The mixed powder is loaded into a graphite mold. Then, the graphite mold containing the mixed powder is placed in a spark plasma sintering furnace to sinter and densify the TiAl alloy billet. First, the temperature is raised to 700°C at a heating rate of 80°C / min and held at this temperature for 5 min. The sintering pressure is 20 MPa. Then, the temperature is raised to the final sintering temperature at a heating rate of 80°C / min. The final sintering temperature is 1200°C, the sintering pressure is 20 MPa, and the holding time is 10 min. After sintering, the alloy is cooled to room temperature with the furnace. The furnace is then opened and the TiAl alloy is obtained.

[0046] In this embodiment, the morphology of the prepared mixed powder is as follows: Figure 4 As shown, through Figure 4 It can be seen that the mixed powder has a relatively uniform particle size and good dispersion uniformity. The In powder is broken and undergoes plastic deformation, embedding itself into the surface of the TiAl alloy powder and fully combining with it.

[0047] The microstructure of the TiAl alloy prepared in this embodiment is as follows: Figure 5 As shown, through Figure 5 It can be seen that the TiAl alloy sintered structure has fewer pores and smaller grain size.

[0048] The TiAl alloy prepared in this embodiment was subjected to performance testing, and the results are as follows: Figure 7 As shown, according to Figure 7 The quantitative test results are shown in Table 2.

[0049] Example 3 This embodiment prepares the TiAl alloy according to the following steps: S1: Weigh sponge titanium, industrial pure aluminum and niobium scrap according to the components in Table 1, and add the raw materials to a suspension furnace to melt and cast TiAl alloy ingots. The melting temperature is 1560℃ and the holding time is 30min. During the holding process, electromagnetic stirring is used to promote uniform mixing of the components of the melt. The alloy melt is protected by a high-purity argon atmosphere during the melting process. After melting and casting, the TiAl alloy ingots are cooled to room temperature with the furnace to obtain TiAl alloy ingots.

[0050] S2: Using TiAl alloy ingots as rotating electrodes, spherical TiAl alloy powders were prepared by plasma rotating electrode atomization technology in an argon protective atmosphere (electrode rotation speed was 18000 rpm, current was 1500 A, electrode melting speed was 2 mm / s, and positive pressure of argon protective atmosphere was 0.05 MPa), resulting in TiAl alloy powders with a particle size not exceeding 80 μm.

[0051] S3: Weigh the TiAl alloy powder and high-purity In powder according to the components in Table 1. Add the TiAl alloy powder and In powder to the stainless steel ball mill jar, lock the ball mill jar, and evacuate the ball mill jar using a vacuum pump. When the air pressure inside the ball mill jar is less than 10... -2 At MPa, stop evacuation and fill with argon gas to make the pressure inside the container equal to the external atmospheric pressure. Repeat the above evacuation and venting process 2-3 times to ensure that the mixed powder is in an argon atmosphere. Then, place the ball mill jar in a ball mill for high-energy ball milling (milling speed 250 rpm, ball-to-material ratio 1:1, milling time 5 h) to obtain the mixed powder.

[0052] S4: The mixed powder is loaded into a graphite mold. Then, the graphite mold containing the mixed powder is placed in a spark plasma sintering furnace to sinter and densify the TiAl alloy billet. First, the temperature is raised to 800°C at a heating rate of 60°C / min and held at this temperature for 10 min. The sintering pressure is 20 MPa. Then, the temperature is raised to the final sintering temperature at a heating rate of 60°C / min. The final sintering temperature is 1250°C, the sintering pressure is 20 MPa, and the holding time is 15 min. After sintering, the alloy is cooled to room temperature with the furnace, and the TiAl alloy is taken out of the furnace.

[0053] The TiAl alloy prepared in this embodiment has similar properties to that in Example 1.

[0054] Example 4 This embodiment prepares the TiAl alloy according to the following steps: S1: Weigh sponge titanium, industrial pure aluminum and niobium scrap according to the components in Table 1, and add the raw materials to a suspension furnace to melt and cast TiAl alloy ingots. The melting temperature is 1600℃ and the holding time is 40min. During the holding process, electromagnetic stirring is used to promote uniform mixing of the components of the melt. The alloy melt is protected by a high-purity argon atmosphere during the melting process. After melting and casting, the TiAl alloy ingots are cooled to room temperature with the furnace to obtain TiAl alloy ingots.

[0055] S2: Using TiAl alloy ingots as rotating electrodes, spherical TiAl alloy powders were prepared by plasma rotating electrode atomization technology in an argon protective atmosphere (electrode rotation speed was 18000 rpm, current was 1500 A, electrode melting speed was 2 mm / s, and positive pressure of argon protective atmosphere was 0.05 MPa), resulting in TiAl alloy powders with a particle size not exceeding 80 μm.

[0056] S3: Weigh the TiAl alloy powder and high-purity In powder according to the components in Table 1. Add the TiAl alloy powder and In powder to the stainless steel ball mill jar, lock the ball mill jar, and evacuate the ball mill jar using a vacuum pump. When the air pressure inside the ball mill jar is less than 10... -2 At MPa, stop evacuation and fill with argon gas to make the pressure inside the container equal to the external atmospheric pressure. Repeat the above evacuation and venting process 2-3 times to ensure that the mixed powder is in an argon atmosphere. Then, place the ball mill jar in a ball mill for high-energy ball milling (milling speed 300 rpm, ball-to-material ratio 4:1, milling time 10 h) to obtain the mixed powder.

[0057] S4: The mixed powder is loaded into a graphite mold. Then, the graphite mold containing the mixed powder is placed in a spark plasma sintering furnace to sinter and densify the TiAl alloy billet. First, the temperature is raised to 400°C at a heating rate of 100°C / min and held at this temperature for 15 min. The sintering pressure is 18 MPa. Then, the temperature is raised to the final sintering temperature at a heating rate of 100°C / min. The final sintering temperature is 1000°C and the sintering pressure is 18 MPa. The holding time is 5 min. After sintering, the alloy is cooled to room temperature with the furnace. The furnace is then opened and the TiAl alloy is obtained.

[0058] The TiAl alloy prepared in this embodiment has similar properties to that in Example 2.

[0059] Comparative Example 1 This comparative example uses the same method as Example 1 to prepare TiAl alloy, except that In is not added in this comparative example.

[0060] The microstructure of the TiAl alloy prepared in this embodiment is as follows: Figure 6 As shown, through Figure 6It can be seen that the comparative alloy contains large pores, and the number of pores is relatively large.

[0061] When the alloy obtained in Comparative Example 1 was subjected to tensile strength testing, the material fractured under the preload of the fixture, and the corresponding mechanical property test results could not be obtained.

[0062] The TiAl alloys prepared in Examples 1 and 2 of this invention were subjected to performance tests, and the results are as follows: Figure 7 As shown, through Figure 7 The quantitative results are shown in Table 2.

[0063] Table 2 As can be seen from Table 2, the TiAl alloy prepared by this invention has a significantly improved density compared to Comparative Example 1. Furthermore, the average grain size of the TiAl alloy prepared by this invention is no higher than 6 μm, and the grain size is maintained at a relatively fine level. This truly achieves the preparation of a high-density, fine-grained TiAl alloy. While achieving high density, it effectively improves the room temperature mechanical properties of the TiAl alloy, making the TiAl alloy components more suitable for assembly, processing, and application.

[0064] The TiAl alloy prepared in Comparative Example 1 showed a significant decrease in density under the same conditions (lower sintering temperature and pressure). Due to the significant decrease in density (although the low temperature made the grain size of Comparative Example 1 relatively small to some extent, the excessive decrease in density caused cracks to initiate from the pores under load, and its negative impact exceeded the strengthening effect of grain refinement, becoming the main factor affecting the deterioration of room temperature performance), it had almost no tensile strength. Therefore, when the tensile strength of Comparative Example 1 alloy was tested using the same method, the material fractured under the preload of the fixture, and the corresponding mechanical property test results could not be obtained.

[0065] A comparison of Examples 1 and 2 shows that when the atomic percentage of In increases from 1% to 1.5%, both the density and room temperature tensile strength of the TiAl alloy decrease. The decrease in density is smaller, while the decrease in room temperature tensile strength is larger. This is because a higher In content increases the risk of In flowing under gravity, leading to poorer uniformity of distribution, increased porosity between TiAl alloy powders, and loss of the In liquid phase, resulting in a decrease in density. However, some In-containing liquid phase does promote the formation of sintering necks and densification. Therefore, the density of the alloy in Example 2 is slightly lower than that in Example 1, but still higher than that in Comparative Example 1. On the other hand, In has a solid solution limit in TiAl alloys; its solid solution strengthening effect can only occur within this limit. When its content exceeds the solid solution limit, it forms a metastable phase. Within a certain content range, the metastable phase can improve the strength of the alloy. However, when its content is too high, it will aggregate and precipitate, causing stress concentration and crack initiation under load, which is detrimental to the room temperature mechanical properties of the alloy. Although the alloy performance decreases to some extent when the atomic percentage of In increases from 1% to 1.5%, the In content can still play a role in densification and strengthening when it is below 5%. However, when the atomic percentage of In exceeds 5%, the negative impact increases sharply, which will cause the alloy performance to be weaker than that of alloys without In. Therefore, the present invention controls the atomic percentage of In at 0.1% to 5%.

[0066] In summary, this invention introduces In into TiAl alloy powder to form a transient liquid phase. By utilizing the wetting effect of the transient liquid phase on the surface of TiAl alloy powder particles at a lower temperature, rapid bonding between TiAl alloy powder particles is achieved, promoting the formation and growth of sintering necks and improving the sintering performance of TiAl alloy powder. At the same time, combined with the strengthening effect of In and the rapid sintering technology of spark plasma, a high-density fine-grained TiAl alloy is successfully prepared under low temperature and low pressure conditions, significantly improving the room temperature mechanical properties of TiAl alloy.

[0067] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and in detail without departing from the scope defined by the claims of the present invention.

Claims

1. A high-density, fine-grained TiAl alloy, characterized in that: The alloy comprises, by atomic percentage, 41%~48% Al, 1%~8% Nb, 0.1%~5% In, with the balance being Ti.

2. The method for preparing the alloy according to claim 1, characterized in that: The preparation method includes the following steps: S1: Under an inert gas protective atmosphere, Ti, Al and Nb raw materials are melted and cast to obtain TiAl alloy ingots; S2: Using the TiAl alloy ingot obtained in step S1 as a rotating electrode, spherical TiAl alloy powder is prepared by plasma rotating electrode atomization powder preparation method in an inert gas protective atmosphere. S3: In an inert gas protective atmosphere, the TiAl alloy powder obtained in step S2 is mixed and ball-milled with In powder to obtain a mixed powder; S4: In an inert gas protective atmosphere, the mixed powder obtained in step S3 is subjected to spark plasma segmented sintering, and after being cooled to room temperature in the furnace, a high-density fine-grained TiAl alloy is obtained.

3. The preparation method according to claim 2, characterized in that: In step S1, the melting temperature is 1560~1600℃ and the holding time is 30~40min.

4. The preparation method according to claim 2, characterized in that: In step S2, the electrode rotation speed is 16000~20000rpm, the current is 1200~1800A, the electrode melting rate is 1.5~3.0mm / s, and the inert gas protective atmosphere positive pressure is ≥0.05MPa.

5. The preparation method according to claim 2, characterized in that: In step S3, the ball-to-material ratio is 1:1 to 4:1, the ball milling speed is ≥240 rpm, and the ball milling time is 3.5 to 10 h.

6. The preparation method according to claim 2, characterized in that: In step S4, the specific process of spark plasma segmented sintering includes: first, raising the sintering temperature to an intermediate temperature of 400-800℃ at a heating rate of 60-100℃ / min, holding at that temperature for 5-15 minutes; then, raising the temperature to a sintering temperature of 1000-1250℃ at a heating rate of 60-100℃ / min, holding at that temperature for 5-15 minutes. During the segmented sintering process, the sintering pressure does not exceed 20MPa.

7. The preparation method according to any one of claims 2-6, characterized in that: In step S1, the Ti raw material is sponge titanium powder with a particle size ≤3mm and a purity ≥99.9%; the Al raw material is industrial pure aluminum block with a purity ≥99.99% and length, width and height dimensions ≤5×5×5mm; the Nb raw material is high-purity niobium shavings with a particle size of 3~6mm and a purity ≥99.95%.

8. The preparation method according to any one of claims 2-6, characterized in that: In step S3, the particle size of the In element powder is ≤65μm and the purity of the In element powder is ≥99.99%.

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