High-plasticity TiAl alloy and preparation method thereof

Abstract

According to the high-plasticity TiAl alloy and the preparation method thereof, firstly, the TiAl alloy containing a nanoscale Ti2AlC reinforced phase is prepared through electron beam selective melting, then twin crystals can be formed in a matrix through room-temperature stretching, meanwhile, the nanoscale Ti2AlC reinforced phase is twisted through room-temperature stretching, a twin crystal expansion path is provided, the twin crystals can continue to expand, and the high-plasticity TiAl alloy is obtained. And further, stress concentration can be quickly relieved, and finally the high-plasticity TiAl alloy is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of TiAl alloys, in particular to a high-plasticity TiAl alloy and a preparation method thereof. Background Art

[0002] TiAl alloy has become a new type of lightweight high-temperature structural material with great potential due to its low density, excellent specific strength and specific stiffness, good strength and excellent oxidation resistance in high temperature environment, and is expected to partially replace Ni-based high-temperature alloys. In recent years, with the rapid development of my country's aerospace and automobile industries, the thrust-to-weight ratio requirements for key core components such as aircraft and engines have been increasing, which undoubtedly poses more stringent challenges to the room temperature plasticity, toughness, and high temperature mechanical properties of TiAl alloys. In past studies, domestic and foreign researchers usually added alloying elements for alloying treatment to improve room temperature plasticity, high temperature strength, and high temperature creep resistance. With the continuous development of composite technology, it has become a hot topic to improve and enhance the comprehensive mechanical properties of TiAl alloys by introducing reinforcements into TiAl alloys to play a synergistic role. Ti2AlC, as a unique layered ternary carbide, has the dual excellent characteristics of metals and ceramics. Its density and thermal expansion coefficient are similar to those of TiAl alloys, which can effectively avoid the large internal stress caused by the difference in properties between the two. Therefore, the introduction of Ti2AlC significantly improves its mechanical properties and opens up a broader prospect for the application of TiAl alloys.

[0003] However, although the introduction of micron-sized Ti2AlC into TiAl alloy can significantly enhance the strength of TiAl alloy, the introduction of micron-sized Ti2AlC is often accompanied by the problem of stress concentration, thus failing to bring about a substantial improvement in the plasticity of TiAl alloy. Summary of the invention

[0004] In order to address the deficiencies in the prior art, the present invention provides a high-plasticity TiAl alloy and a preparation method thereof. First, a TiAl alloy containing a nano-scale Ti2AlC reinforcement phase is prepared by electron beam selective melting, and then twins are formed in the matrix by room temperature stretching. At the same time, the room temperature stretching causes the nano-scale Ti2AlC reinforcement phase itself to be kinked, providing a twin expansion path, so that the twins can continue to expand, thereby quickly relieving stress concentration, and finally obtaining a high-plasticity TiAl alloy.

[0005] In order to achieve the above object, the specific scheme adopted by the present invention is: On the one hand, the present invention provides a method for preparing a high plasticity TiAl alloy, which mainly comprises the following steps: Step 1: preparing TiAl alloy by electron beam selective melting method, wherein the microstructure of TiAl alloy includes matrix and nano-scale Ti2AlC reinforcement phase; Step 2: The TiAl alloy prepared in step 1 is stretched at room temperature. During the stretching process, twins can be formed in the matrix. At the same time, the stretching at room temperature can cause the nano-scale Ti2AlC reinforcement phase to twist itself, providing a twin expansion path, so that the twins can continue to expand, thereby quickly relieving stress concentration and finally obtaining a high-plasticity TiAl alloy.

[0006] Furthermore, in step 1, the raw material used is a composite powder comprising a monolayer dispersed graphene and a TiAl spherical powder, and the nominal composition of the composite powder is Ti-45Al-8Nb-0.6C at%.

[0007] Furthermore, in step 1, the matrix is ​​a full lamellar structure composed of lamellar γ-TiAl / α2-Ti3Al, the average grain size of the lamellar γ-TiAl / α2-Ti3Al is 150~250μm, and the size of the nano-scale Ti2AlC reinforcement phase is 10~40nm.

[0008] Furthermore, in step one, when electron beam selective melting is performed, the forming temperature is 1200-1300°C.

[0009] Furthermore, in step 2, during stretching at room temperature, the stretching force is 800-1200 N, the stretching rate is 0.2-0.25 mm / min, and the total stretching deformation is 0.4-0.6%.

[0010] On the other hand, the present invention provides a high plasticity TiAl alloy prepared by the above method.

[0011] Beneficial effects: (1) Starting from the disadvantage of TiAl alloy - intrinsic brittleness, the present invention first prepares TiAl alloy by electron beam selective melting, and introduces nano-scale Ti2AlC reinforcing phase into TiAl alloy, and then stretches the TiAl alloy at room temperature. The room temperature stretching not only promotes the formation of twins, but also causes the nano-scale Ti2AlC reinforcing phase itself to twist. This twist provides a path for the expansion of twins, allowing the twins to continue to expand. Large-scale twins can quickly relieve stress concentration, thereby improving the plasticity of the alloy. In other words, the plasticity of TiAl alloy is effectively improved by utilizing the twin formation and the twisting effect of nano-scale Ti2AlC during room temperature stretching, which makes it possible for TiAl alloys to be widely used.

[0012] (2) The present invention can obtain a high-plasticity TiAl alloy by combining electron beam selective melting with room temperature stretching. The entire preparation process is simple and easy to operate, without the need for complex equipment or cumbersome steps. More importantly, compared with the traditional heat treatment process, the method of the present invention can obtain a high-plasticity TiAl alloy with excellent performance without further heat treatment. This innovation not only reduces production costs, but also improves production efficiency, opening up a new path for the widespread application of TiAl alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a process flow chart of the present invention.

[0014] Figure 2 It is a schematic diagram of the preparation process of the present invention.

[0015] Figure 3 is a transmission image of the alloy prepared in Example 1. DETAILED DESCRIPTION

[0016] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the protection scope of the present invention.

[0017] The present invention provides a high-plasticity TiAl alloy and a preparation method thereof. The present invention successfully improves the intrinsic brittleness of the TiAl alloy and improves its plasticity by introducing a nano-scale Ti2AlC reinforcement phase and performing a room temperature stretching treatment. Figure 1 and Figure 2 , and its preparation method mainly comprises the following steps: Step 1, ultrasonic dispersion: placing graphene nanosheets with a thickness of 3 to 10 nm and a sheet size of 10 μm in deionized water, and performing ultrasonic dispersion treatment for 30 to 50 minutes to obtain a monolayer dispersed graphene nanosheet solution; vacuum drying the solution in a vacuum drying oven at a temperature of 50 to 80° C. for 8 to 10 hours, and wait for the deionized water to completely evaporate to obtain a monolayer dispersed graphene; Step 2, low-energy ball milling: put TiAl pre-alloyed spherical powder (Ti-45Al-8Nb) with a purity of 99.99% and a ball diameter of 150-250 μm and the monolayer dispersed graphene obtained in step 1 into a ball mill filled with argon (atomic ratio: Ti-45Al-8Nb-0.6C), and obtain a composite powder by low-energy ball milling; during ball milling, 5mm-10mm zirconia balls are used as ball milling media, the ball-to-material ratio is 10:1, the ball milling speed is 100r / min, and the ball milling time is 10-15h; anhydrous ethanol is added as a process control agent during low-energy ball milling to avoid mechanical alloying during low-energy ball milling; Step 3, electron beam selective melting: The composite powder prepared in step 2 is used for electron beam selective melting (SEBM) to prepare TiAl alloy, wherein the matrix of the TiAl alloy is a full lamellar structure composed of lamellar γ-TiAl / α2-Ti3Al, and nano-scale Ti2AlC reinforcement phase is precipitated in situ in the matrix; the forming temperature is selected to be 1200-1300°C, and a lower preheating current is selected to improve efficiency and prevent current surge from causing powder blowing defects, and then powder preheating-solid melting-solid preheating are performed in sequence; under high temperature conditions, the monolayer dispersed graphene is fully diffused and dissolved in the TiAl matrix in the form of carbon atoms, and when cooling with the furnace, the carbon atoms are driven by thermodynamics and kinetics, and are transformed from disordered solid solution to ordered structured nano-Ti2AlC (10-40nm) existing in the matrix; Step 4, room temperature stretching: The prepared TiAl alloy is stretched at room temperature, the stretching force is 800~1200N, the stretching rate is 0.2~0.25mm / min, and the total stretching deformation is 0.4~0.6%; twins can be formed in the matrix during the room temperature stretching process. Twins are a special crystal defect that can disperse stress during plastic deformation, thereby improving the plasticity of the alloy; at the same time, Ti2AlC is a typical flexible ceramic. During the room temperature stretching process, the nano-Ti2AlC itself can provide a twin expansion path through the twisting, so that the twins can continue to expand, and then quickly relieve stress concentration, and ultimately improve the plasticity of the TiAl alloy.

[0018] Example 1 This embodiment provides a high plasticity TiAl alloy and a preparation method thereof, and the specific steps are as follows: Step 1: Electron beam selective melting: A selective electron beam melting (SEBM) experiment is performed on the composite powder, and the forming temperature is selected to be 1250°C to prepare a TiAl alloy containing a nano-scale Ti2AlC reinforcement phase; Step 2: Room temperature stretching: The TiAl alloy prepared in step 1 is stretched at room temperature, with a stretching force of 1000 N, a stretching rate of 0.2 mm / min, and a total stretching deformation of 0.4%.

[0019] In the TiAl alloy obtained in this embodiment, the size of the nano-scale Ti2AlC reinforcement phase is between 10 and 30 nm, the tensile strength is 516 MPa, and the elongation is 0.97%.

[0020] Figure 3 is a transmission image of the alloy prepared in the example, Figure 3 a is the TEM morphology of the interaction between nano-Ti2AlC and twins. From the figure, it can be seen that when the twins encounter nano-Ti2AlC during the expansion process, the expansion path is not hindered, and they continue to expand after passing through the nano-Ti2AlC. Figure 3 b is Figure 3 Energy spectrum of a. Figure 3 c is Figure 3 HRTEM image of the corresponding area in a. It can be seen from the figure that the twins present a mirror-symmetric crystal orientation relationship. Figure 3 d is Figure 3 The SAED diagram of the corresponding area in a shows that the nano-Ti2AlC has a kink phenomenon with an angle of about 20°. Figure 3 e~f Figure 3 HRTEM image of the corresponding area in a. Based on the above research results, it can be considered that when the twins encounter nano-Ti2AlC during the expansion process, the nano-Ti2AlC produces a kink phenomenon, providing a twin expansion path, allowing the twins to continue to expand, and then quickly relieve stress concentration, and finally obtain a high-plasticity TiAl alloy.

[0021] Example 2 The difference between Example 2 and Example 1 is that in step 2, the total tensile deformation is 0.6%.

[0022] In the TiAl alloy obtained in this embodiment, the size of the nano-scale Ti2AlC reinforcement phase is between 10 and 30 nm, the tensile strength is 531 MPa, and the elongation is 0.89%.

[0023] Comparative Example 1 This comparative example differs from Example 1 in that step 2 is not included.

[0024] The tensile strength of the TiAl alloy obtained in this comparative example is 491 MPa, and the elongation is 0.72%.

[0025] Comparative Example 2 The difference between this comparative example and Example 1 is that in step 1, the TiAl alloy is prepared by vacuum arc melting.

[0026] The tensile strength of the TiAl alloy obtained in this comparative example is 459 MPa, and the elongation is 0.51%.

[0027] By comparing the performance of the products obtained in Examples 1-2 and Comparative Examples 1-2, it can be seen that the elongation of the alloy prepared by the method of the present invention is higher than 0.97%; in Comparative Example 1, no room temperature stretching is performed, and the elongation of the obtained alloy is only 0.72%; in Comparative Example 2, although room temperature stretching is performed, since the TiAl alloy is prepared by vacuum arc melting, the full lamellar structure of the obtained TiAl alloy has no nano-Ti2AlC precipitation in the crystal compared with Example 1, and the elongation and tensile strength of the obtained alloy are lower.

[0028] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any equivalent changes or modifications made according to the essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high plasticity TiAl alloy, characterized in that: The main steps are as follows: Step 1: Prepare TiAl alloy by electron beam selective melting method, wherein the microstructure of TiAl alloy includes matrix and nano-scale Ti2AlC reinforcement phase; Step 2: The TiAl alloy prepared in step 1 is stretched at room temperature. During the stretching process, twins can be formed in the matrix. At the same time, the stretching at room temperature can cause the nano-scale Ti2AlC reinforcement phase to twist itself, providing a twin expansion path, so that the twins can continue to expand, thereby quickly relieving stress concentration and finally obtaining a high-plasticity TiAl alloy.

2. The method for preparing a high plasticity TiAl alloy according to claim 1, characterized in that: In step 1, the raw material used is a composite powder comprising a monolayer dispersed graphene and a TiAl spherical powder, and the nominal composition of the composite powder is Ti-45Al-8Nb-0.6C at%.

3. The method for preparing a high plasticity TiAl alloy according to claim 1, characterized in that: In step 1, the matrix is ​​a full lamellar structure composed of lamellar γ-TiAl / α2-Ti3Al, the average grain size of the lamellar γ-TiAl / α2-Ti3Al is 150~250μm, and the size of the nano-scale Ti2AlC reinforcement phase is 10~40nm.

4. The method for preparing a high plasticity TiAl alloy according to claim 1, characterized in that: In step 1, when electron beam selective melting is performed, the forming temperature is 1200~1300℃.

5. The method for preparing a high plasticity TiAl alloy according to claim 1, characterized in that: In step 2, when stretching at room temperature, the stretching force is 800~1200N, the stretching rate is 0.2~0.25mm / min, and the total stretching deformation is 0.4~0.6%.

6. A high plasticity TiAl alloy prepared by the method according to any one of claims 1 to 5.

Images