A method for accelerating phase transformation in ti al alloys

Abstract

This invention provides a method for accelerating phase transformation in a TiAl alloy containing 43-45 at.% Al, 4-8 at.% Nb, 0.2-1 at.% Mn, 0.2-1 at.% Mo, and 0.1 at.% B. The method involves subjecting an as-cast ingot of the TiAl alloy to a strain rate of 10... ‑4 ~10 ‑2 Pre-deformation of 5% to 30% per second accelerates the microstructure evolution of TiAl alloys and shortens the heat treatment time required for the microstructure of TiAl alloys to reach equilibrium. Furthermore, this invention provides a method for preparing TiAl alloys capable of rapid phase transformation.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for phase transition of a new TiAl intermetallic compound material, in particular to a method for accelerating the phase transition of β o (ω o ) phase in TiAl alloy, and further relates to a method for preparing TiAl alloy capable of rapid phase transition. BACKGROUND

[0002] With the rapid development of aerospace industry, the requirements for the engines of aircrafts are becoming more and more stringent. Especially the turbine blades as the core components of the aerospace engines, which are often continuously in high temperature and high pressure and high speed operating environment, bear various cyclic loads such as centrifugal force, aerodynamic force, and the service environment is quite harsh. Therefore, the structural materials used must have more excellent performance characteristics to meet the research and development needs of new aircrafts.

[0003] TiAl intermetallic compound has low density, high strength, excellent high temperature oxidation resistance and creep resistance, and other excellent characteristics, and has broad application prospects as a high temperature structural material for weight reduction in the field of advanced aerospace engines.

[0004] The common room temperature phases in TiAl alloy include α2 phase, γ phase, β o phase (B2 phase) and ωo phase. The large amount of addition of β phase stabilizing elements such as Nb and Mo in the currently developed TiAl alloy will change the solidification path of the alloy, and the solid state phase transition below 1000℃ will also occur more complex changes. For example, a large amount of β phase is not completely converted to α2 phase, but is converted to β o phase through order-disorder transition and is preserved at room temperature.

[0005] Therefore, it is of great significance to study the microstructure evolution and phase transition in TiAl alloy to guide the improvement of the research and production of TiAl alloy. Generally, there are four types of microstructures commonly seen in dual-phase TiAl alloy, which are full lamellar structure, near lamellar structure, duplex structure and near γ structure. Different heat treatment processes can be used to obtain the corresponding microstructure of TiAl alloy.

[0006] However, the study of the microstructure of TiAl alloy is a very time-consuming work. This is because the evolution of the microstructure of TiAl alloy is a relatively slow process, therefore, in order to accelerate the research process and shorten the research and development cycle, researchers often need to heat treat the alloy for a long time to accelerate the phase transition process.

[0007] Moreover, since TiAl alloy is an important high-temperature structural material in the field of aerospace engines, it often needs to serve for a long time of thousands of hours, and during the service, the microstructure of TiAl alloy will also undergo a series of phase changes. In order to simulate the service temperature and time of the alloy in the laboratory, a long-term heat treatment process of thousands of hours is often carried out. Undoubtedly, such a long-term heat treatment process greatly increases the work burden of researchers and is an excessive consumption of experimental resources. For example, in recent years, more and more studies on β phase and ω o phase in TiAl alloy have been carried out. Many studies have pointed out that when TiAl alloy is kept at medium temperature for a long time, ω o phase mainly precipitates in the β o phase matrix, but sometimes it also precipitates from the α2 phase. Song et al. reported that ω o phase is widely present in TiAl alloy containing β phase, and when kept at medium temperature for a long time, ω o phase will gradually precipitate and grow, and even if the initial structure is full lamellar structure, ω o phase will also precipitate from the α2 phase after medium temperature keeping. It can be found that the experimental basis for studying ω o phase is to need long-term keeping, because the process of ω SUMMARY

[0008] In view of the above, it is necessary to develop a method capable of accelerating the microstructure evolution of TiAl alloy, so as to shorten the heat treatment time of the microstructure evolution of TiAl alloy, accelerate the microstructure of TiAl alloy to reach the equilibrium state, and thereby reduce the work burden of phase change researchers and shorten the experimental period.

[0009] To this end, the inventors of the present application, based on the driving force of the precipitation of βo (ωo) and the like in TiAl alloy, which can be summarized into four forms, i.e., the tendency to transform from an unbalanced state to a thermodynamic equilibrium state, the lamellar group coarsening and spheroidization to reduce the interface energy of the system, the reduction of elastic strain energy of α2 / γ and γ / γ coherent interface, and the elimination of dislocations and other defects in the crystal, proposed a technical idea of using pre-deformation, such as room temperature pre-deformation, to increase dislocations and other defects in the as-cast ingot and make the as-cast ingot in an unbalanced state, so as to provide more driving force for phase change in the heat treatment process, accelerate the microstructure evolution of TiAl alloy, and thereby shorten the time required for heat treatment.

[0010] Specifically, the technical scheme is proposed in the present application.

[0011] According to one specific embodiment of the present application, a method for accelerating phase transition in TiAl alloy is provided, which subjects the as-cast ingot of TiAl alloy to a strain rate of 10 -4 ~ 10 -2Pre-deformation: 5% to 30% deformation

[0012] According to one embodiment of the method for accelerating phase transformation in TiAl alloy, the pre-deformation is performed at room temperature. However, the present application is not limited thereto, and in another embodiment of the present application, the pre-deformation is performed at 600 to 1000°C.

[0013] According to one embodiment of the method for accelerating phase transformation in TiAl alloy, when the pre-deformation is performed at room temperature, after the pre-deformation is completed, the TiAl alloy ingot on which the pre-deformation is performed at room temperature is preferably further subjected to heat treatment by being held at 300 to 600°C and then cooled at a cooling rate of 10°C / min.

[0014] According to one embodiment of the method for accelerating phase transformation in TiAl alloy, the TiAl alloy contains 43 to 45 at.% of Al, 4 to 8 at.% of Nb, 0.2 to 1 at.% of Mn, 0.2 to 1 at.% of Mo, and 0.1 at.% of B. Further preferably, the TiAl alloy contains 43.5 at.% of Al, 4 at.% of Nb, 0.2 at.% of Mn, 0.5 at.% of Mo, and 0.1 at.% of B or contains 43.5 at.% of Al, 4 at.% of Nb, 0.5 at.% of Mn, 0.2 at.% of Mo, and 0.1 at.% of B.

[0015] According to one embodiment of the method for accelerating phase transformation in TiAl alloy, the TiAl alloy contains 43 to 45 at.% of Al, 4 to 8 at.% of Nb, 0.2 to 1 at.% of Mn, 0.2 to 1 at.% of Mo, and 0.1 at.% of B. Further preferably, the TiAl alloy contains 43.5 at.% of Al, 4 at.% of Nb, 0.2 at.% of Mn, 0.5 at.% of Mo, and 0.1 at.% of B or contains 43.5 at.% of Al, 4 at.% of Nb, 0.5 at.% of Mn, 0.2 at.% of Mo, and 0.1 at.% of B.

[0016] Step (1) : ingredient preparation

[0017] The zero-grade titanium sponge, high-purity aluminum, niobium-aluminum alloy, high-purity manganese, and high-purity molybdenum required for the ingot preparation are weighed according to the ingredient ratio and mixed uniformly. In view of the fact that Al and Mn elements may be largely volatilized during smelting, in order to ensure that the actual composition of the ingot is consistent with the nominal composition or the error is within an acceptable range, 3 wt.% of Al and 6 wt.% of Mn can be additionally added during the ingredient preparation, i.e., the actual amount of Al added is 1.03 times the nominal content, and the actual amount of Mn added is 1.06 times the nominal content, so as to compensate for the loss of elements that may occur during smelting.

[0018] Step (2) : smelting of ingot

[0019] The raw materials in step (1) are melted into button ingots by a vacuum arc melting furnace, and the melting process is repeated 3-5 times to obtain ingots with uniform composition; the vacuum degree during melting is lower than 0.1 Pa, and the melting current is controlled in the range of 0.2 kA-0.3 kA. However, the present application is not limited thereto, and other melting processes such as a vacuum skull furnace can also be used.

[0020] Step (3) wire cutting:

[0021] A cylinder is cut from the center of the ingot by a numerical control wire cutting machine, for example, a cylinder with a size of Φ6*9 mm or Φ4*6.

[0022] Step (4) pre-deformation:

[0023] The cylinder sample cut from the as-cast ingot is compressed at a deformation strain rate of 10 -4 ~10 -2 / s and a deformation amount of 5%-30%, and the pre-deformation can be performed at room temperature or a high temperature of 600-1000 ℃.

[0024] (5) heat treatment: when the pre-deformation is performed at room temperature, after the pre-deformation treatment is completed, the TiAl alloy ingot pre-deformed at room temperature is kept at 300-750 ℃ for 100-300 h, and then cooled to room temperature at a cooling rate of 10 ℃ / min.

[0025] According to one embodiment of the method for preparing a TiAl alloy capable of rapidly performing phase transition, the TiAl alloy contains 43-45 at.% of Al, 4-8 at.% of Nb, 0.2-1 at.% of Mn, 0.2-1 at.% of Mo, and 0.1 at.% of B. Preferably, the TiAl alloy is Ti-43.5Al-4Nb-0.5Mn-0.2Mo (i.e., containing 43.5 at.% of Al, 4 at.% of Nb, 0.5 at.% of Mn, and 0.2 at.% of Mo) or Ti-43.5Al-4Nb-0.2Mn-0.5Mo (i.e., containing 43.5 at.% of Al, 4 at.% of Nb, 0.2 at.% of Mn, and 0.5 at.% of Mo), with the balance being Ti, and a small amount of inevitable impurities such as H, O, and N.

[0026] The application accelerates the microstructure evolution of the TiAl alloy, shortens the heat treatment time required for the microstructure of the TiAl alloy to reach an equilibrium state, and makes the microstructure of the alloy reach the equilibrium state more quickly during heat treatment after the casting ingot is pre-deformed at room temperature or high temperature.

[0027] Specifically, compared with the prior art, the application has the advantages and beneficial effects that:

[0028] 1. Compared with the TiAl alloy with a relatively slow phase transition process, the method provided by the application accelerates the microstructure evolution of the TiAl alloy, greatly promotes the precipitation of the γ phase and the β o (ω o ) phase, and provides an experimental basis for the research on the phase transition and decomposition law of the β o phase, the preparation of the ω o phase with a large grain size, and the mechanical properties of the ω o phase.

[0029] 2. Compared with the existing heat treatment process which takes hundreds of hours and consumes a large amount of manpower and material resources, the experimental method greatly shortens the time required for the microstructure of the TiAl alloy to reach an equilibrium state, even to tens of hours or even hours, significantly reduces resource consumption, and reduces the work burden of researchers. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 BSE-SEM microstructure morphology of the Ti-43.5Al-4Nb-0.5Mn-0.2Mo-0.1B alloy in Example 1 after heat treatment at 750℃ for 300h, wherein (a) and (b) are samples without compression; (c), (d) and (e) are samples compressed at room temperature by 5%, 10% and 15%, respectively.

[0031] Figure 2 BSE-SEM microstructure morphology of the Ti-43.5Al-4Nb-0.5Mn-0.2Mo-0.1B alloy in Example 2 after heat treatment at 750℃ for 300h, wherein (a) and (b) are samples compressed at 1000℃ by 10% and 20%, respectively.

[0032] Figure 3BSE-SEM microstructure of Ti-43.5Al-4Nb-0.2Mn-0.5Mo-0.1B alloy in Example 3 after heat treatment at 750℃ for 300h, wherein (a) and (b) are samples without compression, (c), (d), (e) are samples compressed at room temperature by 5%, 10%, 15%, respectively.

[0033] Figure 4 BSE-SEM microstructure of Ti-43.5Al-4Nb-0.2Mn-0.5Mo-0.1B alloy in Example 4 after heat treatment at 750℃ for 300h, wherein (a) and (b) are samples compressed at 1000℃ by 10%, and (c) and (d) are samples compressed at 1000℃ by 20%, respectively. DETAILED DESCRIPTION

[0034] The application is further described below with reference to the preparation of button ingots and the characterization of material properties in the examples, which are presented by way of illustration and not limitation, and the application is not limited to the examples. Indeed, the devices, methods, and systems described herein can be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein can be made without departing from the spirit of the disclosure. For example, when the application is presented in a given step, alternative embodiments can perform similar functions using different steps and / or orders, and some steps can be deleted, moved, added, subdivided, combined, and / or modified. At least one of these steps can be implemented in a variety of different ways, and the order of these steps can also be changed. And any suitable combination of elements and acts of some of the following examples can be combined to provide further examples. Example 1

[0035] This example explores a method for accelerating phase transformation in TiAl alloy, and further explores a complete method for preparing TiAl alloy capable of rapid phase transformation using the method.

[0036] Specifically, the atomic percentage of the TiAl alloy in this example is: Ti-43.5Al-4Nb-0.5Mn-0.2Mo-0.1B, and the balance is Ti. The preparation of the TiAl alloy is achieved by the following steps:

[0037] Step (1) ingredient: the raw materials used for smelting and ingot casting are sponge titanium (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), niobium-aluminum alloy (containing niobium 72.63 wt.%, containing aluminum 27.3 wt.%), high-purity manganese (99.99 wt.%), high-purity molybdenum (99.95 wt.%), high-purity boron (99.99 wt.%). The above materials are mixed uniformly according to the component ratio to prepare a smelting standby material with a mass of 40 g. In order to prevent a large amount of Al and Mn from volatilizing during smelting, causing deviation of the actual composition from the nominal composition, 3 wt.% of Al and 6 wt.% of Mn are additionally added during ingredient preparation, i.e. the addition amount of Al and Mn is 1.03 times and 1.06 times of the above nominal component ratio respectively, to compensate for the possible element loss during smelting. The additional amount can be adjusted according to the actual experiment or the burning loss in production;

[0038] Step (2) smelting and ingot casting: the smelting standby material prepared in step (1) is melted into a button ingot by using a vacuum arc melting furnace (VAR), and the smelting process is repeated 3-5 times to obtain an ingot with uniform composition. The vacuum degree of the vacuum arc melting furnace during the smelting process is less than 0.1 Pa, and the smelting current is controlled in the range of 0.2 kA-0.3 kA.

[0039] Step (3) wire cutting to obtain as-cast sample: a cylinder is cut from the center part of the ingot melted in step (2) by using a numerical control wire cutting machine tool;

[0040] Step (4) room temperature pre-deformation: the as-cast sample cut is compressed at room temperature. The sample size is a cylindrical sample with a diameter of Φ4*6 mm, and the deformation amount is 5%, 10% and 15% respectively;

[0041] Step (5) heat treatment: the TiAl alloy ingot pre-deformed at room temperature is placed in a heat treatment furnace at 750℃, and is kept for 300h, and is cooled to room temperature with the furnace.

[0042] Step (6) observation of microstructure by electron microscope: the TiAl alloy sample capable of rapid phase transition can be obtained through the above steps. In order to further analyze the microstructure, this step is carried out. The sample is cut parallel to the compression direction, mechanically polished until the surface is mirror-like and free of scratches, and then observed by using a backscattered mode scanning electron microscope (BSE-SEM). The results are shown in Figure 1 .

[0043] After micro observation of the Ti-43.5Al-4Nb-0.5Mn-0.2Mo-0.1B alloy before and after room temperature compression, it is found that, as shown in Figure 1 , the microstructure of the TiAl alloy is mainly composed of lamellar groups, γ phase and β o (ω ophase composition. As can be seen from the comparison Figure 1 As can be seen from the comparison between (a), (b) and (c), (d) and (e), the un-compressed sample has a low volume fraction of γ phase and β o (ω o ) phase, and the lamellar colony is the main organization; after the sample is deformed by room temperature compression, a large amount of γ phase precipitates, and the amount of β o (ω o ) phase also increases a lot, which shows that room temperature compression can accelerate the evolution of the organization of the TiAl alloy; in addition, as the deformation amount increases from 5% to 15%, the γ phase and β o (ω o ) phase precipitates more and more, which fully shows that the increase of the deformation amount can accelerate the evolution of the organization of the TiAl alloy. Embodiment 2

[0044] This embodiment explores a method for accelerating the phase transformation in the TiAl alloy, and further explores a complete method for preparing the TiAl alloy capable of rapidly performing the phase transformation by using the method.

[0045] Specifically, the atomic percentage of the TiAl alloy in this embodiment is: Ti-43.5Al-4Nb-0.5Mn-0.2Mo-0.1B, and the balance is Ti. The preparation of the TiAl alloy is realized by the following steps:

[0046] Step (1) batching: the raw materials used for melting and ingot casting are titanium sponge (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), niobium-aluminum alloy (containing niobium 72.63 wt.%, containing aluminum 27.3 wt.%), high-purity manganese (99.99 wt.%), high-purity molybdenum (99.95 wt.%), and high-purity boron (99.99 wt.%). The above materials are mixed uniformly according to the component ratio to prepare a melting standby material with a mass of 40 g. In order to prevent a large amount of Al and Mn from volatilizing during melting, causing a deviation between the actual composition and the nominal composition, 3 wt.% of Al and 6 wt.% of Mn are additionally added during batching, i.e., the addition amount of Al and Mn is 1.03 times and 1.06 times of the above nominal component ratio, respectively, to compensate for the possible element loss during melting. The additional amount can be adjusted according to the actual experiment or the burning loss in production;

[0047] Step (2) melting and ingot casting: a vacuum arc melting furnace (VAR) is used to melt the melting standby material obtained in step (1) into a button ingot, and the melting process is repeated 3-5 times to obtain an ingot with uniform composition. The vacuum degree of the vacuum arc melting furnace during the melting process is less than 0.1 Pa, and the melting current is controlled within the range of 0.2 kA-0.3 kA;

[0048] Step (3) Wire cutting: cutting a cylindrical sample with a size of Φ6*9mm from the center of the ingot melted in step (2) by a numerical control wire cutting machine tool;

[0049] Step (4) High temperature pre-deformation: high temperature compression of the cut as-cast sample at 1000℃, with deformation amounts of 10%, 20% respectively;

[0050] Step (5) Heat treatment: placing the TiAl alloy ingot pre-deformed at room temperature in a heat treatment furnace at 750℃, holding for 300h, and cooling to room temperature in the furnace;

[0051] Step (6) Electron microscope observation of microstructure: the TiAl alloy sample capable of rapid phase transition can be obtained through the above steps. In order to further analyze the microstructure, the heat-treated sample is cut parallel to the compression direction, mechanically polished until the surface is mirror-like and free of scratches, and then observed by backscattered mode scanning electron microscope (BSE-SEM), and the results are shown in Figure 2 .

[0052] Microscopic observation of the Ti-43.5Al-4Nb-0.5Mn-0.2Mo-0.1B alloy after high temperature compression shows that, as shown in Figure 1 and Figure 2 : under the same deformation amount, the γ phase and β o (ω o ) phase content of the high temperature compression sample is higher than that of the room temperature compression sample, and under the same deformation temperature, the γ phase and β o (ω o ) phase precipitates more in the sample with larger deformation amount, indicating that increasing the deformation temperature or increasing the deformation amount can accelerate the microstructure evolution of TiAl alloy. Example 3

[0053] This example explores a method for accelerating phase transition in TiAl alloy, and further explores a complete method for preparing TiAl alloy capable of rapid phase transition by using the method.

[0054] Specifically, the atomic percentage of the TiAl alloy in this example is Ti-43.5Al-4Nb-0.2Mn-0.5Mo-0.1B, and the balance is Ti. The preparation of the TiAl alloy is realized by the following steps:

[0055] Step (1) : ingredients: the raw materials used for smelting and ingot casting are sponge titanium (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), niobium-aluminum alloy (containing niobium 72.63 wt.%, containing aluminum 27.3 wt.%), high-purity manganese (99.99 wt.%), high-purity molybdenum (99.95 wt.%), high-purity boron (99.99 wt.%). The above materials are mixed uniformly according to the component ratio to prepare a smelting standby material with a mass of 40 g. In order to prevent a large amount of Al and Mn from volatilizing during smelting, causing deviation between the actual composition and the nominal composition, 3 wt.% of Al and 6 wt.% of Mn are additionally added during batching, i.e. the addition amount of Al and Mn is 1.03 times and 1.06 times of the above nominal component ratio respectively, to compensate for the possible element loss during smelting. The additional amount can be adjusted according to the actual experiment or the burning loss in production;

[0056] Step (2) : smelting and ingot casting: the smelting standby material obtained in step (1) is melted into a button ingot by using a vacuum arc melting furnace (VAR), and the smelting process is repeated 3-5 times to obtain a cast ingot with uniform composition. The vacuum degree of the vacuum arc melting furnace during smelting is less than 0.1 Pa, and the smelting current is controlled within the range of 0.2 kA-0.3 kA;

[0057] Step (3) : wire cutting: a cylindrical sample with a size of Φ4*6 mm is cut from the center part of the ingot melted in step (2) by using a numerical control wire cutting machine tool;

[0058] Step (4) : room temperature pre-deformation: the cut cast sample is compressed at room temperature, and the deformation amount is 5%, 10% and 15%;

[0059] Step (5) : heat treatment: the TiAl alloy ingot pre-deformed at room temperature is placed in a heat treatment furnace at 750℃, and is kept for 300h, and is cooled to room temperature in the furnace;

[0060] Step (6) : electron microscope observation of microstructure: the TiAl alloy sample capable of rapidly phase transition can be obtained through the above steps. In order to further analyze the microstructure, the heat-treated sample is cut parallel to the compression direction, mechanically polished until the surface is mirror-like and free of scratches, and then observed by using a backscattered mode scanning electron microscope (BSE-SEM), and the results are shown in Figure 3

[0061] After microscopically observing the Ti-43.5Al-4Nb-0.2Mn-0.5Mo-0.1B alloy before and after room temperature compression, it is found that, as shown in Figure 3 , the alloy mainly contains a large number of lamellar groups, γ phase and β o (ω o ) phase. As shown in comparison Figure 3 ​From (a), (b) and (c), (d) and (e), it can be seen that the flake layer content ratio is large before compression, β o (ω o ) volume fraction is low; after room temperature compression deformation, the γ phase and β o (ω o ) phase in the sample precipitate significantly under the same heat treatment conditions; in addition, when the deformation increases from 5% to 15%, the γ phase and β o (ω o ) phase also correspondingly increases, which shows that the pre-deformation at room temperature or the increase of deformation can promote the microstructure evolution of TiAl alloy. Example 4

[0062] This example explores a method for accelerating phase transformation in TiAl alloy, and further explores a complete method for preparing TiAl alloy capable of rapid phase transformation by using the method.

[0063] Specifically, the atomic percentage of the TiAl alloy in this example is: Ti-43.5Al-4Nb-0.2Mn-0.5Mo-0.1B, with the balance being Ti. The preparation of the TiAl alloy is realized by the following steps:

[0064] Step (1) batching: the raw materials used for melting and ingot casting are sponge titanium (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), niobium-aluminum alloy (containing niobium 72.63 wt.%, containing aluminum 27.3 wt.%), high-purity manganese (99.99 wt.%), high-purity molybdenum (99.95 wt.%), and high-purity boron (99.99 wt.%). The above materials are mixed uniformly according to the component ratio to prepare a sample with a mass of 40g. In order to prevent a large amount of Al and Mn from volatilizing during melting, causing a deviation between the actual composition and the nominal composition, 3 wt.% of Al and 6 wt.% of Mn are additionally added during batching, i.e. the addition amount of Al and Mn is 1.03 times and 1.06 times of the above nominal component ratio, respectively, to compensate for the possible element loss during melting. The additional amount can be adjusted according to the actual experiment or production loss;

[0065] Step (2) melting and ingot casting: a vacuum arc melting furnace (VAR) is used to melt the raw materials in step (1) into a button ingot, and the melting process is repeated 3-5 times to obtain an ingot with uniform composition. The melting vacuum degree is controlled to be less than 0.1 Pa during the melting process, and the melting current is controlled in the range of 0.2kA~0.3kA;

[0066] Step (3) wire cutting: a cylindrical sample with a size of Φ6*9mm is cut from the center of the ingot melted in step two by a numerical control wire cutting machine tool;

[0067] Step (4) high temperature pre-deformation: the cut as-cast sample was compressed at 1000℃, and the deformation was 10%, 20%, respectively;

[0068] Step (5) heat treatment: the high temperature pre-deformed TiAl alloy ingot was placed in a heat treatment furnace at 750℃, and was kept for 300h, and was cooled to room temperature in the furnace;

[0069] Step (6) electron microscope observation of microstructure: the TiAl alloy sample capable of rapid phase transformation was obtained through the above steps, in order to further analyze the microstructure, the heat treated sample was cut parallel to the compression direction, and was mechanically polished until the surface was mirror-like and had no scratches, and then was observed by backscattered mode scanning electron microscope (BSE-SEM), and the results are shown in Figure 4

[0070] Microscopic observation of the Ti-43.5Al-4Nb-0.2Mn-0.5Mo-0.1B alloy after high temperature compression found that, as compared with Figure 3 and Figure 4 : under the same deformation amount, the content of γ phase and β o (ω o ) phase of the high temperature compression sample was higher than that of the room temperature compression sample, and the same deformation temperature and the larger deformation amount resulted in more γ phase and β o (ω o ) phase, which indicated that increasing the deformation temperature or increasing the deformation amount could accelerate the microstructure evolution of TiAl alloy.​

Claims

1. A method for accelerating phase transformation in a TiAl alloy, characterized in that, The as-cast ingot of TiAl alloy is pre-deformed at a strain rate of 10 -4 / s and a deformation of 5% to 30%. The pre-deformation is performed at room temperature or at a high temperature of 600-1000℃, After the pre-deformation, the TiAl alloy ingot subjected to the pre-deformation is kept at 300-750℃ for 100-300h, and then cooled to room temperature at a cooling rate of 10℃ / min. The TiAl alloy contains, in atomic percentage, 43-45at.% of Al, 4-8at.% of Nb, 0.2-1at.% of Mn, 0.2-1at.% of Mo, and 0.1at.% of B, with the balance being Ti.

2. The method of accelerating phase transformation in TiAl alloys according to claim 1, characterized in that, The TiAl alloy composition is Ti-43.5Al-4Nb-0.5Mn-0.2Mo-0.1B or Ti-43.5Al-4Nb-0.2Mn-0.5Mo-0.1B.

3. A method for producing a TiAl alloy capable of rapid phase transition, characterized by, The method comprises the following steps: Step (1) batching: According to the composition of the TiAl alloy, the zero-grade titanium sponge, high-purity aluminum, niobium-aluminum alloy, high-purity manganese, and high-purity molybdenum required for smelting and ingot casting are weighed and mixed uniformly, and the TiAl alloy contains, in atomic percentage, 43-45at.% of Al, 4-8at.% of Nb, 0.2-1at.% of Mn, 0.2-1at.% of Mo, and 0.1at.% of B, with the balance being Ti; Step (2) smelting and ingot casting: A vacuum arc smelting furnace or a vacuum skull furnace is used for smelting, and when a vacuum arc smelting furnace is used to melt the raw materials in step (1) into button ingots, the smelting process is repeated 3-5 times to obtain an ingot with uniform composition; Step (3) wire cutting: A cylindrical sample is cut from the center of the ingot by a numerical control wire cutting machine tool; Step (4) pre-deformation: The cylindrical test sample in as-cast state obtained by cutting is subjected to compression or tension at a deformation strain rate of 10 -4 / s at room temperature or at a high temperature of 600 to 1000°C with a deformation of 5 to 30%. Step (5) heat treatment: The TiAl alloy ingot subjected to the pre-deformation is kept at 300-750℃ for 100-300h, and then cooled to room temperature at a cooling rate of 10℃ / min.

4. The method for producing a TiAl alloy capable of rapidly undergoing phase transition according to claim 3, characterized by, The smelting vacuum is controlled to be lower than 0.1Pa during smelting, and the smelting current is controlled to be in the range of 0.2kA-0.3kA.

5. The method for preparing a TiAl alloy capable of rapidly undergoing phase transition according to claim 4, wherein the TiAl alloy composition is Ti-43.5Al-4Nb-0.5Mn-0.2Mo-0.1B or Ti-43.5Al-4Nb-0.2Mn-0.5Mo-0.1B.

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