A method for the dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current

Abstract

The present invention belongs to the field of light alloy preparation and thermal processing, and specifically relates to a method for current-assisted dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy, comprising the following steps: step 1, preparing TiAl alloy raw material; step 2, using vacuum non-consumable arc melting technology to melt the TiAl alloy ingot; step 3, after the TiAl alloy ingot is cooled, taking it out and cutting it into a rectangular alloy block; fixing both ends of the alloy block on a stretching device; connecting the alloy block to a pulse power supply; step 4, applying a pulse current to the alloy block while stretching it; the present invention cleverly utilizes a method combining micro-deformation with pulse current to couple the electric field, thermal field and force field, and can effectively promote the dynamic precipitation of ultrafine nano-carbide particles under room temperature and high temperature conditions; compared with traditional thermal deformation and heat treatment processes, the process does not require large-scale thermal processing equipment and multiple processing steps, thereby reducing energy consumption and preparation cycle.

Description

Technical Field

[0001] The invention belongs to the technical field of light alloy preparation and thermal processing, and particularly relates to a method for dynamic precipitation of ultrafine nanometer carbide particles of TiAl alloy assisted by current. Background Art

[0002] TiAl alloys are lightweight and high-temperature resistant, and are widely recognized as a promising new generation of lightweight, high-strength blade materials. For cast TiAl alloys, simply controlling the size and morphology of the reinforcing particles during solidification is insufficient. This is because the distribution of carbon becomes fixed as the temperature decreases. Even if the size and morphology of the carbides are successfully controlled, the segregation problem caused by the uneven distribution of carbon cannot be fundamentally resolved, adversely affecting the mechanical properties of the TiAl alloy. Therefore, the formation of uniform and fine carbide particles is crucial for improving microstructure and mechanical properties.

[0003] Patent CN202311534868.5 discloses "a nano-double precipitate phase reinforced low-alloy ultra-high strength steel and its preparation process". By subjecting the smelted steel ingot to multiple upsetting and forging heat treatments, the precipitation of double nanophases is promoted, thereby achieving performance enhancement of the low-alloy steel. However, these procedures require the cooperation of a variety of hot working equipment to complete, and the precise control of the precipitate phase depends to a large extent on the hot working process, which places high demands on the hot working process parameters. Patent CN202210364022.0 discloses "a high-performance nano-carbonized TiAl alloy composite material for aerospace and its extrusion molding method". By combining the addition of nano-titanium carbide powder and extrusion molding, an ultrafine and strong TiAl alloy composite material is prepared, but the cleanliness and strength of the bonding interface between the added reinforcement particles and the TiAl matrix are reduced. Through the above literature search, it can be seen that at this stage, the regulation of carbides and other reinforcement particles is mainly carried out through large plastic deformation, heat treatment and element doping. The existing TiAl alloy and composite material control process is relatively complex, the preparation and production cycle is long, and the in-situ self-reinforced particles are unevenly distributed and coarse in size, which leads to a decrease in the microstructure and mechanical properties of the TiAl alloy.

[0004] Therefore, for intermetallic compounds such as TiAl alloys with poor hot working properties and complex solid-state phase transformation, there is an urgent need to find a stable technology that can effectively control the morphology, size and distribution of reinforced particles under conditions of low plastic deformation and without changing the alloy solidification path. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a current-assisted method for the dynamic precipitation of ultrafine nano-carbide particles in TiAl alloy. By passing a pulse current of a certain amplitude through the alloy sample under room temperature or high-temperature tensile conditions, the carbon element is promoted to react with the TiAl matrix to form ultrafine nano-carbide particles. Compared with the original cast alloy, the prepared TiAl alloy has a more uniform microstructure and considerable room-temperature and high-temperature tensile properties.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for the dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current comprises the following steps:

[0008] Step 1: Prepare TiAl alloy raw materials;

[0009] Step 2: melting the TiAl alloy ingot using vacuum non-consumable arc melting technology;

[0010] Step 3: After the TiAl alloy ingot is cooled, it is taken out and cut into a rectangular alloy block; both ends of the alloy block are fixed on a stretching device; and the alloy block is connected to a pulse power supply;

[0011] Step 4: Apply a pulse current to the alloy block while stretching it.

[0012] Furthermore, in step four, the length of the alloy block is 45 mm to 55 mm, and the alloy block is stretched by clamping it at both ends with a stretching device. The stretching stroke of the alloy block is 2 mm to 10 mm, and the stretching rate is 0.1 mm / s to 1 mm / s.

[0013] Furthermore, in step 4, the pulse current to which the alloy block is subjected during stretching is 5 to 30 A, and the pulse current frequency is 50 to 3000 Hz.

[0014] Furthermore, in step 4, the alloy block is stretched and pulse current is applied to the alloy block at room temperature; and at the same time, the alloy block is forced to be air-cooled to maintain room temperature.

[0015] Furthermore, in step 4, the alloy block is stretched and pulsed current is applied at 700° C. to 900° C.

[0016] Furthermore, for an alloy block with a size of 50 mm×30 mm×20 mm, the stretching stroke is 2 mm to 5 mm, and the pulse current is 10 A to 20 A.

[0017] Furthermore, in step 1, the atomic percentage composition of the TiAl alloy raw material is: Al is 35-60%, Nb is 0-10%, Cr is 0-10%, Re is 0-5%, C is 0-12%, Zr is 0-5%, V is 0-3%, and the balance is Ti.

[0018] Furthermore, in step 2, a vacuum arc melting furnace is used to melt the TiAl alloy ingot; during melting, the vacuum arc melting furnace is evacuated and argon gas is introduced for atmosphere protection, the current is uniformly increased from 0 to 550-1000 A, and the current is maintained at 550-1000 A for 10-120 seconds, and then the current is reduced to 0 at a rate of 10-50 A / s; after the alloy melt solidifies, the alloy ingot is turned over, and the same process is repeated for 4-10 times, and the alloy ingot is obtained after cooling.

[0019] Furthermore, when placing the TiAl alloy raw material in the crucible, the powder in the TiAl alloy raw material is first dried, coated with aluminum foil, and placed at the bottom of the crucible; then smaller particles are placed on top of the powder, and then large pieces of sponge titanium are placed on the top of the particles.

[0020] Furthermore, before smelting, the furnace is first evacuated to negative pressure using a mechanical pump and a molecular pump, and then high-purity argon gas is introduced to purge the furnace; and then the vacuum arc melting furnace is evacuated to a vacuum degree of less than 6×10 -2 ~3×10 -4 Pa, and then argon gas is injected into the vacuum arc melting furnace as the atmosphere; the argon gas pressure is 0.05Pa.

[0021] The principle of the present invention is that, at a relatively fast solidification rate, the microstructure after casting contains (α2+γ) lamellar clusters, a small amount of B2 phase and equiaxed γ phase, and no carbide particles are precipitated, leaving the carbon element in a solid solution (low carbon content) or supersaturated (high carbon content) state. The cast alloy is then subjected to tensile micro-deformation at a temperature range of 700°C to 900°C. During this process, a pulsed current is passed through the alloy block. The coupled effects of temperature, stress, and current promote continuous lattice distortion and the accumulation of nano-defects, thereby promoting the desolvation and precipitation of the carbon element and its rapid reaction with other elements. Due to the various effects of the current itself, dislocation movement, and phase transformation, the nucleation rate of carbides increases, the size is significantly reduced, and they tend to spheroidize. These uniformly precipitated in-situ self-generated ultrafine carbide particles have a clean, well-bonded interface with the TiAl matrix; they contain a small amount of elements such as Nb and Cr, which reduces the segregation degree of these elements and the content of brittle B2 phase; they can also effectively pin dislocations during plastic deformation, promote the nucleation of mechanical twins, avoid stress concentration caused by the segregation of large-sized carbides, and thereby improve the room temperature and high-temperature mechanical properties of TiAl alloys.

[0022] The TiAl alloy prepared by the present invention contains (α2+γ) lamellar clusters, carbide particles with a size of only a dozen nanometers, a small amount of B2 phase and equiaxed γ phase. Compared with the original molten-cast TiAl alloy, after applying pulse current and tensile deformation (energized tensile deformation) to the alloy block, the tensile strength increases to varying degrees.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention cleverly utilizes a method combining micro-deformation with pulsed current to couple electric, thermal, and force fields, effectively promoting the dynamic precipitation of ultrafine nano-carbide particles at both room and high temperature conditions. Compared with traditional thermal deformation and heat treatment processes, this process does not require large-scale thermal processing equipment and multiple processing steps, reducing energy consumption and preparation cycle time.

[0025] 2. The present invention introduces a pulse current during the tensile deformation process. The Joule heating effect and pure electroplastic effect generated by the current can quickly improve the microstructure of the TiAl alloy and reduce the flow stress and energy barrier of the alloy. At room temperature, compared with the pure tensile deformation of the alloy, the pulse current acting on the TiAl alloy can effectively activate more dislocation slip systems and atomic diffusion, thereby making it easier to promote the dynamic precipitation of nanocarbides.

[0026] 3. The method proposed in the present invention allows ultrafine nano-carbide particles to precipitate in the TiAl alloy. The size of these particles is only a dozen nanometers. They have a good bonding interface with the TiAl matrix and are distributed at the phase interface and within the phase, which can effectively pin dislocation slip and grain boundary migration without causing serious stress concentration. When subjected to stress, they have the function of bearing and transmitting loads, significantly improving the room temperature and high temperature tensile properties of the TiAl alloy.

[0027] 4. The method provided by the present invention has wide adaptability and is applicable not only to TiAl alloys, but also to alloys with good plastic deformation ability or difficult to deform. This method does not require the alloy to undergo a high degree of plastic deformation, nor does it require heat treatment processes such as solid solution aging treatment, and can significantly improve the microstructure of the alloy. The process is relatively simple and easy to operate, saving preparation time and production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0029] Figure 1 These are SEM photos of the alloy of Example 1 of the present invention before and after electrical stretching at room temperature;

[0030] Among them, (a) is the SEM photo of the cast alloy; (b) is the SEM photo of the alloy after electrical stretching at room temperature.

[0031] Figure 2 The room temperature tensile properties of the alloy of Example 1 of the present invention before and after room temperature electrical stretching.

[0032] Figure 3 These are SEM photos of the alloy of Example 2 of the present invention before and after electrical stretching at 900°C;

[0033] Among them, (a) is the SEM photo of the cast alloy; (b) is the SEM photo of the alloy after electrical stretching at 900°C.

[0034] Figure 4 This is the transmission microstructure of the alloy of Example 2 of the present invention after electrical stretching at 900°C.

[0035] Figure 5 The room temperature tensile properties of the alloy of Example 2 of the present invention before and after electrical stretching at 900°C.

[0036] Figure 6 The tensile properties at 750°C of the alloy of Example 2 of the present invention before and after electrical stretching at 900°C.

[0037] Figure 7 The tensile properties of the alloy of Example 2 of the present invention at 850°C before and after electrical stretching at 900°C.

[0038] Figure 8 These are SEM photos of the alloy of Example 3 of the present invention before and after electrical stretching at 900°C;

[0039] Among them, (a) is the SEM photo of the cast alloy; (b) is the SEM photo of the alloy after electrical stretching at 900℃.

[0040] Figure 9 The tensile properties of the alloy of Example 3 of the present invention at 800°C before and after electrical stretching at room temperature.

[0041] Figure 10 This is a SEM photo of the alloy of the comparative example of the present invention;

[0042] Among them, (a) is the SEM photograph of the comparative alloy in the cast state; (b) is the SEM photograph of the comparative alloy after only pulse current was applied; (c) is the SEM photograph of the comparative alloy after only room temperature tensile micro-deformation.

[0043] Figure 11 The room temperature tensile properties of the comparative alloy after being treated by tensile deformation and pulse current respectively. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0045] To improve the uniformity of in-situ reinforcement particles, promote the nano-sizing of reinforcement particles, shorten the preparation cycle of TiAl alloys, and enhance the microstructure and mechanical properties of TiAl alloys, a current-assisted method for the dynamic precipitation of ultrafine nanocarbide particles in TiAl alloys has been proposed. The "dynamic precipitation" in the patent title refers to the precipitation of fine carbides during tensile microdeformation rather than during solidification. This method does not rely on severe plastic deformation or a specific heat treatment regime. Instead, it passes a pulsed current of a certain amplitude through the alloy block under room temperature or high temperature tensile stress, promoting the reaction of carbon with the TiAl matrix to form ultrafine nanocarbide particles. Under the guidance of the current and tensile stress, the carbide particles are uniformly distributed and finely sized. The TiAl alloy prepared by this method exhibits a more uniform microstructure and impressive room temperature and high temperature tensile properties compared to the original cast alloy, providing an ingenious approach to addressing current shortcomings of TiAl alloys and composites.

[0046] A method for the dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current comprises the following steps:

[0047] Step 1, preparing TiAl alloy raw materials; the atomic percentage composition of the TiAl alloy raw materials is: Al is 35-60%, Nb is 0-10%, Cr is 0-10%, Re is 0-5%, C is 0-12%, Zr is 0-5%, V is 0-3%, and the balance is Ti;

[0048] Weigh corresponding masses of titanium sponge particles, high-purity aluminum particles, chromium particles, aluminum-niobium master alloy particles (wherein the mass fraction of niobium is 63 wt.%), zirconium particles, vanadium particles, high-purity rhenium powder, and carbon powder; dry these particles and wrap the powder with aluminum foil;

[0049] Step 2: melting the TiAl alloy ingot using vacuum non-consumable arc melting technology;

[0050] (1) Check the furnace body and circulating water cooling system of the vacuum arc melting furnace, install the tungsten arc gun, place the powder wrapped in aluminum foil at the bottom of the crucible, place smaller aluminum particles, chromium particles and aluminum-niobium master alloy particles on the top of the powder, and then place the large piece of sponge titanium on the top to ensure that the raw materials will not be scattered during melting; (2) Close the furnace door, turn on the mechanical pump and molecular pump in turn to evacuate the furnace to a vacuum state, after the mechanical pump is used to evacuate the furnace to a negative pressure state, introduce high-purity argon gas to purge the furnace; then turn on the molecular pump to continue evacuating until the vacuum degree is less than 6×10-2 ~3×10 -4 Pa; stop the molecular pump and mechanical pump in turn, fill a certain volume of argon gas and prepare for arc melting; (3) turn on the power supply, increase the current from 0 to 550~1000A at a uniform speed, so that the raw materials are softened, connected and melted. When the raw materials are completely in liquid state, maintain the current at 550~1000A for 10~120s, and then quickly reduce the current to 0 at a speed of 10~50A / s; after the alloy melt solidifies, turn the alloy ingot over, and repeat the melting process 4~10 times with the same process to ensure the uniformity of the microstructure; after each melting, turn the alloy ingot over with a turning spoon.

[0051] Step 3. After the smelting is completed, wait for the alloy ingot to cool to room temperature, take out the ingot, and then cut it into a rectangular alloy block; the length of the alloy block is 45mm to 55mm; the surface of the alloy block is polished with sandpaper until it is smooth and has no cutting marks, in preparation for uniaxial room temperature and high temperature tensile micro-deformation; the polished alloy block is clamped and fixed on the stretching equipment at both ends; the clamping part of the alloy block is respectively equipped with positive and negative electrodes to ensure that the current flows from one side of the block to the other side; the positive and negative electrodes are connected to the pulse power supply through insulated wires, the working voltage of the pulse power supply is 220V, and the digital oscilloscope on the pulse power supply can display the current waveform; the clamping end of the stretching beam uses a high-temperature resistant insulating clamp to prevent a short circuit between the clamping end and the electrode, which causes the universal testing machine or power supply to overheat; a thermocouple is spot welded at the center of the alloy block, and the thermocouple is connected to the thermometer through an insulated wire to measure the temperature of the alloy block in real time;

[0052] Step 4: Set the stretching rate to 0.01mm / s~1mm / s, turn on the pulse power supply, pass the current in the range of 5~30A, then turn on the universal testing machine, and perform stretching micro-deformation while powering on; when stretching at room temperature, the Joule heat caused by the pulse current will cause the alloy block to heat up during the stretching micro-deformation at room temperature, so forced air cooling will be performed during the room temperature stretching micro-deformation to maintain the room temperature. When the displacement reaches 2~10mm, turn off the pulse power supply and then stop the universal testing machine; before high-temperature stretching, the alloy needs to be The block is placed in a high-temperature heating furnace, connected to a pulse power supply, and a current in the range of 5 to 30 A is passed. When the digital oscilloscope is stable and the Joule heat generated by the current is constant, the alloy block is heated to a specified temperature through step heating, and then high-temperature tensile micro-deformation experiments are carried out at different temperatures; when the displacement stroke reaches 2 to 10 mm, the pulse power supply is turned off, and then the universal testing machine is stopped; the high-temperature heating furnace is opened, the alloy block is taken out, and air-cooled; the stretched alloy block is cut using wire cutting to obtain the tissue to obtain observation samples and room temperature and high-temperature tensile performance test samples.

[0053] Specifically, the alloy block is 50mm long, 30mm wide, and 20mm thick. The stretching equipment uses a universal stretching machine with a load capacity of 20 to 100kN and a crossbeam stroke of 100 to 1200mm. A high-temperature heating furnace can be installed on the tensile beam of the universal testing machine, and the interior of the high-temperature heating furnace is filled with asbestos to isolate heat loss. The high-temperature heating furnace has a heating range of room temperature to 1000°C, and the heating method is stepped. The pulse power supply has an operating voltage of 220V, a maximum output voltage of 15V, a maximum output current of 50A, an output frequency of 50 to 3000Hz, and an output duty cycle of 0 to 100%.

[0054] The method provided by the present invention promotes the uniform precipitation of carbide particles during thermal deformation rather than during solidification. The size of these carbides is only a dozen nanometers, which avoids the stress concentration caused by the coarse size and segregation of carbides. The present invention can achieve uniform precipitation of ultrafine nanoparticles through micro-deformation and pulse current, which is a precise regulation of carbides without significantly changing the structure of the alloy matrix. It not only simplifies the processing steps, but also reduces the preparation cycle and energy consumption. The whole process is flexible, easy to control, and has high adjustability. In addition, the various effects introduced by the pulse current can assist the deformation of the microstructure in a short time. Compared with traditional thermal processing technology, it has more active regulation on the formation of defects such as dislocations, vacancies and nanotwins, accelerates the slidability of the slip system and the diffusion rate of atoms, thereby increasing the nucleation rate of the precipitated phase, refining the size and morphology of the precipitated phase, promoting the dispersion precipitation of the nanophase, and improving the uniformity of the microstructure.

[0055] The core of this patent is to provide a technical means to improve the microstructure of TiAl alloy, which has a good optimization effect on TiAl alloy. The examples of this invention are based on laboratory scenarios. If it is to be applied to actual production, since TiAl alloy needs to be processed later, the size of TiAl alloy in actual production is larger, and accordingly, the size of the pulse current and the model of the universal testing machine need to be adjusted.

[0056] The present invention will be described in detail below with reference to the accompanying drawings in combination with embodiments and comparative examples.

[0057] Example 1

[0058] A method for the dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current comprises the following steps:

[0059] Step 1: Prepare TiAl alloy raw material; the atomic percentage composition of the TiAl alloy raw material is: Al is 42%, Nb is 5%, Cr is 2%, Re is 0.6%, C is 0.1%, and the balance is Ti; record it as Ti-42Al-2Cr-5Nb-0.6Re-0.1C;

[0060] Weigh corresponding masses of titanium sponge particles, high-purity aluminum particles, chromium particles, aluminum-niobium master alloy particles (wherein the mass fraction of niobium is 63 wt.%), zirconium particles, vanadium particles, high-purity rhenium powder, and carbon powder; dry these particles and wrap the powder with aluminum foil;

[0061] Step 2: Use vacuum non-consumable arc melting technology to melt TiAl alloy ingots; put aluminum foil-wrapped powder, smaller granular raw materials and large pieces of sponge titanium into the crucible in turn to ensure that the raw materials will not scatter during melting; then close the furnace door, pump the furnace to negative pressure, wash the furnace with high-purity argon gas, and then pump the furnace to a vacuum degree of less than 3×10 -3 Pa, fill a certain volume of argon gas and prepare for arc melting; after fine-tuning the position of the arc gun, turn on the power of the vacuum arc melting furnace and increase the current from 0 to 600A at a uniform speed, so that the raw materials are softened, connected and melted under the action of the arc; when the raw materials are completely in a liquid state, maintain the current at 600A for about 15 seconds, then quickly reduce the current to 0 at a rate of 50A / s and turn off the power; after the alloy melt solidifies, turn the alloy ingot over with a turning spoon, turn on the power again, and repeat the melting of the alloy ingot 5 times with the same process to ensure the uniformity of the microstructure; after each melting, turn the alloy ingot over with a turning spoon;

[0062] Step 3: After the 6 meltings are completed, wait for the alloy to cool to room temperature and start preparing for the power-on tensile micro-deformation experiment; use a digital electric spark wire cutting machine to cut the prepared alloy ingot into a rectangular alloy block with a size of 50mm×30mm×20mm; use sandpaper to polish the surface of the alloy block until it is smooth and there are no cutting marks; adjust the height of the tensile beam in the universal testing machine, and clamp the polished TiAl alloy block on the tensile beam along the length direction. A high-temperature heating furnace is installed on the tensile beam of the universal testing machine; positive and negative electrodes are respectively installed at the clamping parts on both sides of the TiAl alloy block, and the positive and negative electrodes are connected to an external pulse power supply through high-temperature resistant insulated wires; a thermocouple is spot-welded at the center of the alloy block, and the thermocouple is connected to a thermometer through an insulated wire to measure the temperature of the alloy block in real time;

[0063] Step 4. Turn on the universal testing machine, set the stretching rate to 0.5 mm / s, connect the pulse power supply, pass a current of 10 A, and start room temperature stretching micro-deformation of the TiAl alloy block; at room temperature, turn on the forced air cooling device, and when the displacement stroke of the alloy block reaches the specified stroke of 2 mm, turn off the pulse power supply and then stop the universal testing machine; use wire cutting to cut the stretched alloy block into tissue observation samples and room temperature and high temperature tensile performance test samples.

[0064] The alloy obtained in Example 1 is Ti-42Al-2Cr-5Nb-0.6Re-0.1C; it is stretched at room temperature with a stretching rate of 0.5 mm / s and a stretching stroke of 2 mm; the pulse current is 10 A. Figure 1 The microstructure of the Ti-42Al-2Cr-5Nb-0.6Re-0.1C alloy in (a) shows that the as-cast structure consists of (α2+γ) lamellar clusters and a network B2 phase on the boundary, without carbide particles. However, after the 10A pulse current and tensile deformation, the as-cast structure is composed of (α2+γ) lamellar clusters and a network B2 phase on the boundary, without carbide particles. Figure 1 As shown in (b), the content of B2 phase in the microstructure is significantly reduced, and a small amount of nano-carbide particles are precipitated from the boundaries and interiors of the lamellar clusters; driven by the electric field and stress field, the dispersed precipitation of fine second phase and the reduction of the content of hard and brittle B2 phase improve the cast microstructure. Figure 2 The room temperature tensile properties of the alloy in the cast state and after room temperature electrical stretching. It can be seen that after room temperature electrical stretching, the room temperature tensile strength of the Ti-42Al-2Cr-5Nb-0.6Re-0.1C alloy increases from 401 MPa (cast state) to 437 MPa, an increase of 8.98%, without losing plasticity, and the tensile properties are significantly improved.

[0065] Example 2

[0066] The preparation process of the alloy of Example 2 is similar to that of Example 1, and the stretching stroke and stretching rate remain the same. The difference is that compared with Example 1, the raw material composition of Example 2 is: Al is 45%, Nb is 5%, Cr is 2%, Re is 0.3%, C is 0.3%, and the balance is Ti; a high-temperature heating furnace is used to stretch the alloy of Example 2 at 900°C; the pulse current is increased to 15A, and finally a Ti-45Al-2Cr-5Nb-0.6Re-0.3C alloy is obtained.

[0067] from Figure 3 The SEM photo of the Ti-45Al-2Cr-5Nb-0.6Re-0.3C alloy in (a) shows that there are no carbide particles in the cast structure, and the C element is in a solid solution or supersaturated state; after a 15A current is passed during tensile deformation at 900℃, Figure 3 (b) It can be seen that nano-carbide particles appear in the microstructure of the modified alloy, and these particles precipitate along the lamellar interfaces and lamellar cluster boundaries; in addition to the significant refinement of the lamellar clusters, the content of B2 phase is also significantly reduced. This is because elements such as Nb and Cr can be dissolved in small amounts in the precipitated carbide particles, thereby reducing the segregation of these β-phase stabilizing elements.

[0068] Figure 4This is the transmissive microstructure of a Ti-45Al-2Cr-5Nb-0.6Re-0.3C alloy subjected to tension and electrical conduction at 900°C. Brightfield images show that nanocarbides tend to precipitate at dislocation entanglements. This is because external field coupling not only activates more slip systems and nanotwins in the γ phase, but also activates slip systems in the harder α2 phase, leading to the formation of a high density of dislocations and abundant nanotwins in the TiAl matrix. These defect-concentrated regions possess higher energy, serving as rapid atomic diffusion channels, accelerating the reaction of carbon atoms with the matrix and leading to the dynamic precipitation of carbides. Impeded by the surrounding phase interfaces, these carbides form nanospheres, further stabilizing the system.

[0069] Figure 5 The room-temperature tensile properties of the Ti-45Al-2Cr-5Nb-0.6Re-0.3C alloy are shown in the as-cast state and after being stretched at 900°C and energized. In the as-cast state, the room-temperature tensile strength of the Ti-45Al-2Cr-5Nb-0.6Re-0.3C alloy is 375 MPa, and the elongation is 0.98%. After energized stretching at 900°C, the room-temperature tensile strength of the Ti-45Al-2Cr-5Nb-0.6Re-0.3C alloy increases from 385 MPa (as-cast) to 433 MPa, and the elongation increases from 0.9% to 1.50%, for a 12.47% increase in room-temperature tensile strength. This indicates that energized stretching can effectively improve the room-temperature tensile properties of Ti-45Al-2Cr-5Nb-0.6Re-0.3C by improving the microstructure and promoting the dynamic precipitation of ultrafine nano-carbide particles.

[0070] Figure 6 、 Figure 7 High temperature tensile properties of Ti-45Al-2Cr-5Nb-0.6Re-0.3C alloy at 750℃ and 850℃ respectively, in the as-cast state and after electrical stretching at 900℃. Figure 6 As shown in the figure, at 750℃, the tensile strength and engineering strain of the cast state are 497MPa and 2.12% respectively; while after 900℃ electric stretching, the tensile strength and engineering strain of the TiAl alloy are 569MPa and 3.06% respectively, and the tensile strength of the TiAl alloy stretched at 750℃ increases by 14.49%. Figure 7 As shown in the figure, at 850°C, the as-cast tensile strength and engineering strain were 421 MPa and 11.07%, respectively. However, after electrical stretching at 900°C, the tensile strength and engineering strain increased to 537 MPa and 9.56%, respectively. The tensile strength increased by 27.56% at 850°C, with virtually no loss in engineering strain. This indicates that the high-temperature tensile properties of the TiAl alloy significantly improve with increasing temperature after electrical stretching, demonstrating a good match between strength and ductility.

[0071] Example 3

[0072] The preparation process of the alloy of Example 3 is similar to that of Example 1, and the stretching rate remains the same. The difference is that compared with Example 1, the raw material composition of Example 3 is: Al is 48%, Nb is 5%, Cr is 2%, Re is 0.6%, C is 0.5%, and the balance is Ti; it is recorded as Ti48Al-2Cr-5Nb-0.6Re-0.5C; the vacuum arc melting furnace of this embodiment uses a high-temperature heating furnace for melting, so that the alloy of Example 2 is stretched at 900°C with a stretching stroke of 5 mm; the pulse current is increased to 20 A, and finally the Ti48Al-2Cr-5Nb-0.6Re-0.5C alloy is obtained.

[0073] Figure 8 (a) is the as-cast structure of the prepared Ti-48Al-2Cr-5Nb-0.6Re-0.5C alloy. Figure 8 (b) is the microstructure of the prepared Ti-48Al-2Cr-5Nb-0.6Re-0.5C alloy after high temperature stretching and power application. Figure 8 As shown in (a), due to the increase in the content of C element in the alloy, needle-shaped carbides are precipitated in the as-cast structure. These carbides have a high aspect ratio and are unevenly distributed inside the lamellar clusters and on the boundaries of the lamellar clusters. Figure 8 As shown in (b), after a 20A pulse current is continuously passed through the alloy and micro-stretched for 5mm at 900℃, the original large-sized needle-shaped carbides decompose under the action of electric-thermal-stress coupling. The current and stress drive the diffusion of dissolved C elements in multiple directions at the same time, causing the carbide size to change from micrometers to nanometers, and its morphology to change from needle-shaped to spherical, with a significant reduction in the aspect ratio. Figure 9 The tensile properties of the alloy before and after micro-stretching at 900℃ and when stretched at 800℃ are shown. It can be seen that after tensile deformation at 900℃, the tensile strength and elongation of the alloy at 800℃ are significantly improved, among which the tensile strength increases from 414MPa to 468MPa, and the tensile strength at 800℃ increases by 13.04%, and the tensile properties are significantly improved; the elongation increases from 2.10% to 5.61%.

[0074] Comparative Example

[0075] In this comparative example, the composition of the alloy block is the same as that in Example 1, which is Ti-42Al-2Cr-5Nb-0.6Re-0.1C;

[0076] In this comparative example, after obtaining the cast alloy, several alloy blocks were cut out; some of the alloy blocks were treated with only a 10A pulse current at room temperature, while the other alloy blocks were treated with only a stretching process at room temperature, with a stretching rate of 0.5 mm / s and a stretching stroke of 2 mm.

[0077] Figure 10(a), 10(b), and 10(c) are SEM photos of the as-cast alloy, the alloy block that has only been treated with room temperature pulse current, and the alloy block that has only been treated with room temperature stretching, respectively. Figure 10 (a) It can be seen that there are large-sized lamellar clusters, bright white B2 phase and dark gray massive γ phase in the microstructure. When only 10A pulse current is applied to the alloy at room temperature, the content of B2 phase decreases, the original large-sized lamellar clusters are transformed into several lamellar clusters with different orientations, and the microstructure is refined, such as Figure 10 (b) When the alloy is stretched for 2 mm at room temperature, a small amount of carbides are formed at the boundaries of the lamellar clusters, and almost no carbides are observed inside the lamellar clusters, as shown in Figure 2. Figure 10 (c) As shown. Comparing Comparative Example 1 and Example 1, it can be seen that applying current or stretching alone contributes to the precipitation of carbides, but the driving force for precipitation is insufficient. Applying tensile micro-deformation is a simple and effective way for TiAl alloys. For alloys such as TiAl alloys that are difficult to plastically deform, micro-deformation not only does not destroy the microstructure and cause macroscopic cracking of the alloy, but also can store the deformation energy in the alloy, providing a driving force for the precipitation of fine carbides. Therefore, only applying pulse current or only performing tensile micro-deformation has limited effects on the improvement of the microstructure. Simultaneously applying pulse current and stretching for deformation is a better way to promote the dynamic precipitation of ultrafine nano-carbide particles in TiAl alloys.

[0078] Figure 2 The black curve in the figure is the room temperature tensile properties of Ti-42Al-2Cr-5Nb-0.6Re-0.1C cast alloy. Figure 11 Figure 3 shows the room-temperature tensile properties of the alloy after two treatments. Compared to the as-cast room-temperature tensile properties, the room-temperature tensile strength did not significantly improve after micro-deformation alone, but the elongation increased from 1.51% to 1.99%. After pulse current treatment alone, both the room-temperature tensile strength and elongation increased, from 401 MPa and 1.51% to 415 MPa and 2.16%, respectively, for a 3.49% increase in tensile strength.

[0079] The test results of this comparative example were compared with the tensile properties of Ti-42Al-2Cr-5Nb-0.6Re-0.1C alloy subjected to room temperature electrical stretching in Example 1. The increase in tensile strength of the Ti-42Al-2Cr-5Nb-0.6Re-0.1C alloy after pulse current and synchronous room temperature stretching was greater than the sum of the tensile strength increase rates after the two treatment methods in Comparative Example 1, indicating that the simultaneous application of tensile microdeformation and pulse current can more effectively improve the room temperature tensile properties of the alloy.

[0080] Table 1 Processing parameters and mechanical properties test table of Examples 1-3 and Comparative Examples

[0081]

[0082] It can be seen from Examples 1-3 and Table 1 that with the increase of pulse current during micro-deformation stretching of the alloy, the tensile strength increases and the elongation also increases accordingly. In addition, compared with the traditional processing technology, the improvement rate of tensile strength is greatly increased. From the comparative example, it can be seen that compared with a single tensile micro-deformation or current treatment, the simultaneous application of tensile micro-deformation and current treatment has a faster and more efficient effect on the precipitation of ultrafine nano-carbides in TiAl alloys, matrix improvement and mechanical properties.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for the dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current, characterized in that: The following steps are involved: Step 1: Prepare TiAl alloy raw materials; Step 2: melting the TiAl alloy ingot using vacuum non-consumable arc melting technology; Step 3: After the TiAl alloy ingot is cooled, it is taken out and cut into a rectangular alloy block; both ends of the alloy block are fixed on a stretching device; and the alloy block is connected to a pulse power supply; Step 4: Apply a pulse current to the alloy block while stretching it.

2. The method for dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current according to claim 1, characterized in that: In step 4, the length of the alloy block is 45 mm to 55 mm, the stretching stroke of the alloy block is 2 mm to 10 mm, and the stretching rate is 0.1 mm / s to 1 mm / s.

3. The method for dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current according to claim 1, characterized in that: In step 4, the alloy block is subjected to a pulse current of 5 to 30 A during stretching, and the pulse current frequency is 50 to 3000 Hz.

4. The method for dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current according to claim 1, characterized in that: In step 4, the alloy block is stretched and pulsed current is applied to the alloy block at room temperature; at the same time, forced air cooling is performed on the alloy block to maintain room temperature.

5. The method for dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current according to claim 1, characterized in that: In step 4, the alloy block is stretched and a pulse current is applied at a temperature of 700° C. to 900° C.

6. The method for dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current according to claim 1, characterized in that: For an alloy block with a size of 50 mm × 30 mm × 20 mm, the stretching stroke is 2 mm to 5 mm, and the pulse current is 10 A to 20 A.

7. The method for dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current according to claim 1, characterized in that: In step 1, the atomic percentage composition of the TiAl alloy raw material is: Al is 35-60%, Nb is 0-10%, Cr is 0-10%, Re is 0-5%, C is 0-12%, Zr is 0-5%, V is 0-3%, and the balance is Ti.

8. The method for dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current according to claim 1, characterized in that: In step 2, a vacuum arc melting furnace is used to melt the TiAl alloy ingot; during melting, the vacuum arc melting furnace is evacuated and argon gas is introduced for atmosphere protection, the current is uniformly increased from 0 to 550-1000A, and the current is maintained at 550-1000A for 10-120s, and then the current is reduced to 0 at a rate of 10-50A / s; after the alloy melt solidifies, the alloy ingot is turned over, and the same melting process is repeated 4-10 times, and the alloy ingot is obtained after cooling.

9. The method for dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current according to claim 8, characterized in that: When placing TiAl alloy raw materials in a crucible, first dry the powder in the TiAl alloy raw materials, wrap it with aluminum foil, and place it at the bottom of the crucible; then place smaller particles on top of the powder, and then place large pieces of sponge titanium on top of the particles.

10. The method for dynamic precipitation of ultrafine nano-carbide particles of TiAl alloy assisted by current according to claim 8, characterized in that: Before smelting, the furnace is first pumped to negative pressure with a mechanical pump and a molecular pump, and then high-purity argon is introduced to wash the furnace; then the vacuum arc melting furnace is pumped to a vacuum degree of less than 6×10 -2 ~3×10 -4 Pa, and then argon gas is flushed into the vacuum arc melting furnace as the atmosphere; The argon pressure is 0.05Pa.

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