Method for preparing TiAl alloy cast ingot through vacuum induction melting

Abstract

The invention discloses a method for preparing a TiAl alloy cast ingot through vacuum induction melting, and belongs to the field of titanium-aluminum alloy smelting, metal is subjected to induction melting, the alloy cast ingot is subjected to overturning melting, in the power reduction process, the temperature of molten metal is reduced to 10 DEG C below the melting point, heat preservation is carried out for 30 min, electromagnetic stirring of a melt can last for a longer time, and the temperature of the molten metal is reduced to 10 DEG C below the melting point; therefore, the uniformity of metal components is improved. Then slowly cooling a stirring magnetic field of the alloy melt to 10 DEG C above the alpha phase transformation point at the speed of 10 kW / min, preserving heat for 30 min, performing single-phase region heat preservation heat treatment at 10 DEG C above the alpha phase transformation point without causing rapid growth of alpha crystal grains, performing furnace cooling to obtain a fine fully lamellar structure with relatively good room-temperature comprehensive mechanical property and more uniform components, and then reducing the power to the minimum at the speed of 80 kW / min, so as to obtain the high-strength alloy. And finally, the macrosegregation of the cast ingot is reduced.

Description

Technical Field

[0001] The invention belongs to the field of titanium-aluminum alloy smelting, and in particular relates to a method for preparing TiAl alloy ingots by vacuum induction melting with controllable macrosegregation and higher melting efficiency. Background Art

[0002] As a new type of lightweight and high-temperature resistant structural material, TiAl alloy has unique performance advantages in many aspects, such as lower density, higher specific strength and specific modulus, good oxidation resistance and creep performance, and excellent fatigue performance. It is a candidate high-temperature structural material in the fields of contemporary aerospace industry, civil industry, etc., and has important engineering application potential. The engineering application of TiAl alloy is directly related to the macroscopic morphology and defects of the ingot. To obtain structural parts with excellent performance, precise control of macroscopic segregation is a necessary condition.

[0003] Patent CN202310294669.5 uses a vacuum consumable electrode shell furnace with low smelting vacuum, which cannot effectively remove volatile harmful impurities in the melt. It is easily contaminated by elements such as O, N and H, and the purity of the ingot is low. The graphite crucible used is easy to introduce impurities, segregation and coarse grains. In patent CN202111039002.8, the metal melt is at a higher power, and the element loss is more serious as the smelting time progresses. In addition, the temperature of the circulating water will continue to rise until the equipment alarms during long-term high-power operation, which is easy to cause damage to the equipment itself. This significantly limits the time of electromagnetic stirring and directly affects the macroscopic uniformity of the ingot. The macroscopic segregation in the TiAl alloy will affect the use of subsequent alloys. Summary of the invention

[0004] In order to solve the macro segregation problem of titanium-aluminum alloy ingots, the purpose of the present invention is to provide a new vacuum induction melting method for TiAl alloys.

[0005] The specific technical solution adopted by the present invention is: a method for preparing TiAl alloy ingots by vacuum induction melting, which adopts vacuum induction melting under a protective atmosphere, and specifically comprises the following steps:

[0006] Step 1: Prepare ingredients according to the TiAl alloy composition;

[0007] Step 2: Slowly increase the power to the highest power, heat the metal raw material placed in the water-cooled copper crucible, and after the raw material in the crucible is completely melted, keep it warm for 10 minutes, reduce the power at a rate of 60kW / min, and let the ingot cool down along with the water-cooled copper crucible. After the power drops to the lowest, turn off the heating power supply, and take out the ingot after it cools down to obtain a primary ingot;

[0008] Step 3: turning over the primary ingot and placing it in a water-cooled copper crucible, and re-smelting it according to step 2 to obtain a secondary ingot;

[0009] Step 4: The secondary ingot is turned over again and placed in a water-cooled copper crucible for smelting again. The process is: slowly increase the power to the maximum power, and after the secondary ingot in the crucible is completely melted, keep warm for 10 minutes, reduce the power at a rate of 30 kW / min to reduce the metal liquid temperature to 10°C below the melting point, and then keep warm for 30 minutes, and then reduce the power at a rate of 10 kW / min to 10°C above the α phase transformation point, keep warm for 30 minutes, and reduce the power at a rate of 80 kW / min to allow the ingot to cool down with the water-cooled copper crucible. After the power drops to the minimum, turn off the heating power supply, and take out the ingot after it is cooled to obtain a TiAl alloy ingot with uniform structure and reduced macro-segregation.

[0010] Furthermore, the TiAl alloy is Ti(43-48)Al(1-13)Nb.

[0011] Furthermore, the TiAl alloy is Ti45Al8Nb.

[0012] Specifically, during the mixing process, high-purity sponge Ti, high-purity Al blocks and Nb-Al master alloy particles are used as metal raw materials.

[0013] Furthermore, the protective atmosphere was high-purity argon, and the vacuum degree was maintained at 0.05 Mpa.

[0014] Furthermore, slowly increasing the power to the maximum power means slowly increasing the power to the maximum power at a rate of 60 kW / min.

[0015] Compared with the prior art, the present invention provides a TiAl alloy induction shell smelting method. In the process of vacuum induction smelting, the coupling effect of the magnetic field and the temperature field in the water-cooled copper crucible is utilized to accurately control the melt temperature during the smelting process. When the melt temperature is 10°C below the melting point, insulation is performed once. At this time, the temperature of the equipment cooling water will not continue to rise, and long-term insulation will not damage the equipment. The element burnout is low, the electromagnetic stirring time can be increased, and the macroscopic uniformity is significantly improved. Secondary insulation is performed in the single-phase region 10°C above the α phase transformation point, and then the temperature is rapidly reduced and solidified under the action of water cooling, so that a structure with more uniform composition can be obtained. The present invention combines the smelting process with the heat treatment by designing a two-step insulation process in the smelting process, and finally achieves a significant reduction in the macroscopic segregation of the ingot, thereby improving the smelting efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] Figure 1(a, b) are macroscopic morphologies of the Ti45Al8Nb alloy prepared in Example 1, and (c, d) are macroscopic morphologies of the Ti45Al8Nb alloy prepared in Example 2.

[0018] Figure 2 (a, b) are SEM-BSE microstructure diagrams of the Ti45Al8Nb alloy prepared in Example 1, and (c, d) are SEM-BSE microstructure diagrams of the Ti45Al8Nb alloy prepared in Example 2.

[0019] Figure 3 This is the ICP composition test result diagram of the Ti45Al8Nb alloy prepared in Example 2.

[0020] Figure 4 This is an optical microscope image of the Ti45Al8Nb alloy prepared in Example 1.

[0021] Figure 5 This is an optical microscope image of the Ti45Al8Nb alloy prepared in Example 3.

[0022] Figure 6 This is the ICP composition test result diagram of the Ti45Al8Nb alloy prepared in Example 3.

[0023] Figure 7 This is an optical microscope image of the Ti45Al8Nb alloy prepared in Example 4.

[0024] Figure 8 This is the ICP composition test result diagram of the Ti45Al8Nb alloy prepared in Example 5.

[0025] Fig. 9 The present invention is a process flow chart of preparing TiAl alloy ingots by vacuum induction melting. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below according to specific embodiments. The protection scope of the present invention is not limited to the following embodiments, which are listed for illustrative purposes only and are not intended to limit the present invention in any way.

[0027] The present invention uses an induction melting heating method to melt the metal raw materials, turns over the alloy ingot for melting, and uses an embedded thermocouple to measure the temperature of the melt center during the process of reducing the power of vacuum induction shell melting. The melt temperature is kept at 10°C for 30 minutes when the melt temperature is below the melting point of the TiAl alloy but does not meet the supercooling degree. At this time, the reduction of the melt temperature by cooling water and the increase of the melt temperature by electromagnetic induction reach a balance, the temperature of the equipment circulating water will not continue to increase, and the equipment can continue to operate safely. At this time, the melt is not solidified, and the electromagnetic stirring of the melt can be continued for a longer time, thereby improving the uniformity of the metal component. Then, by turning the power knob, the stirring magnetic field of the alloy melt is slowly reduced to 10°C above the α phase transformation point at a speed of 10kW / min and kept warm for 30 minutes. The single-phase zone heat treatment is performed at 10°C above the α phase transformation point because the temperature is only slightly higher than the α transformation temperature, so it will not cause the rapid growth of α grains. However, the diffusion rate of Nb in the conventional method is very slow. The electromagnetic stirring of induction melting can promote this process. The full lamellar structure is then obtained by furnace cooling. The fine full lamellar structure has good room temperature comprehensive mechanical properties and more uniform composition. Selecting a power reduction speed of 80kW / min will reduce the power to the minimum, allowing the ingot to cool with the furnace. At this time, it is most beneficial to control the macroscopic segregation of the alloy. Generally speaking, the full lamellar structure of TiAl alloy is obtained by keeping warm in the α single-phase zone and furnace cooling. When the α single-phase region is kept warm, the α single-phase structure is formed, which destroys the α2 / γ lamellar structure in the original cast structure. If the holding temperature is too high, the α grains will easily grow rapidly, resulting in a larger size of the α2 / γ lamellar clusters after cooling, thereby reducing the room temperature mechanical properties of the alloy.

[0028] Example 1

[0029] Combination Fig. 9 The TiAl alloy smelting method with precisely controlled composition described in this embodiment comprises the following steps:

[0030] (1) According to the atomic ratio of Ti: 0.47, Al: 0.45, Nb: 0.08, 8022 g of high-purity sponge Ti, 3459.6 g of high-purity Al block, and 3518.4 g of Nb-Al master alloy particles were accurately weighed, with a total mass of 15,000 g of metal raw materials.

[0031] (2) Before smelting begins, place the metal raw material particles in a beaker and pour in high-purity anhydrous ethanol; place the beaker in an ultrasonic cleaner to thoroughly clean the material, and after cleaning, dry it and prepare for smelting.

[0032] (3) Before smelting, the inside of the copper crucible needs to be cleaned with alcohol to ensure that it is free of impurities. The materials are stacked according to specific requirements. According to the temperature field and magnetic field analysis of the crust furnace, the elements with low melting points are placed at the bottom of the crucible, and the elements with high melting points are placed at the top, so that the heating power can be utilized to the maximum extent.

[0033] (4) Turn on the low-pressure cooling water, dryer, mechanical pump and argon cylinder switches in sequence; cover the hatch and lock the lock; turn on the mechanical pump and the large and small Roots pumps to evacuate the air, then turn on the diffusion pump, preheat to 280°C, and evacuate the air to a vacuum degree of 5. 10 -3 Pa; turn off the diffusion pump, open the charging valve, and fill in argon to keep the vacuum degree of the melting chamber at 0.05 Mpa.

[0034] (5) Turn on the cooling water system, heat the power supply, and slowly increase the power to the maximum power (360 kW) to heat the metal raw materials placed in the water-cooled copper crucible. After the raw materials in the crucible are completely melted, keep warm for 10 min, reduce the power at a rate of 60 kW / min, and let the ingot cool down along with the water-cooled copper crucible. After the power drops to the minimum, turn off the heating power supply, and take out the ingot after it cools down to obtain a primary ingot.

[0035] (6) Turn over the ingot and place it back in the water-cooled copper crucible. Turn on the low-pressure cooling water, dryer, mechanical pump and argon bottle in turn. Close the hatch and lock the lock. Turn on the mechanical pump and the large and small Roots pumps to evacuate the air. Then turn on the diffusion pump, preheat to 280°C, and evacuate the air to a vacuum degree of 5. 10 -3 Pa; turn off the diffusion pump, open the charging valve, and fill in argon to keep the vacuum degree of the smelting chamber at 0.05 Mpa; turn on the cooling water system, heat the power supply, slowly increase the power to the maximum power, heat the primary ingot placed in the water-cooled copper crucible, and after the primary ingot in the crucible is completely melted, keep it warm for 10 min, reduce the power at a rate of 60 kW / min, let the ingot cool down with the water-cooled copper crucible, turn off the heating power supply after the power drops to the minimum, take out the ingot after it is cooled, and obtain the secondary ingot.

[0036] (7) The secondary ingot is turned over again and placed in a water-cooled copper crucible. The low-pressure cooling water, dryer, mechanical pump and argon gas bottle are turned on in sequence. The hatch is closed and the lock is locked. The mechanical pump and the large and small Roots pumps are turned on to evacuate the air. Then the diffusion pump is turned on and preheated to 280°C. The vacuum is evacuated to 5 10 -3Pa; turn off the diffusion pump, open the inflation valve, fill with argon to keep the vacuum degree of the melting chamber at 0.05 Mpa; turn on the cooling water system, heat the power supply, slowly increase the power to the maximum power, and after the secondary ingot in the crucible is completely melted, keep warm for 10 minutes, reduce the power at a rate of 30kW / min to reduce the metal liquid temperature to 10°C below the melting point, that is, 1570°C (using an embedded thermocouple for temperature measurement), then keep warm for 30 minutes, and then reduce the power at a rate of 10kW / min to 10°C above the α phase transformation point, that is, 1310°C, and keep warm for 30 minutes. In order to quickly solidify, refine the grains, and improve the surface quality of the ingot, reduce the power at a rate of 80kW / min, and let the ingot cool down with the water-cooled copper crucible. After the power drops to the minimum, turn off the heating power supply, and take out the ingot after it cools down. The TiAl alloy ingot is obtained, and its macroscopic morphology is shown in the following figure. Figure 1 As shown in (a) and (b) in the figure, the SEM-BSE organization diagram is shown in Figure 2 The average values ​​of the alloy ingot composition test results are shown in Table 1, and the optical microscope images are shown in Figure 4 shown.

[0037] Table 1 Composition of Ti45Al8Nb after secondary feeding

[0038] Alloy components Ti Al Nb At(%) 47.07 44.99 7.94 wt(%) 53.59 28.87 17.54

[0039] Example 2

[0040] The present embodiment describes a TiAl alloy smelting method with precisely controlled composition. The other steps are the same as those in the first embodiment, except that in step (1), according to the atomic ratio of Ti: 0.47, Al: 0.45, Nb: 0.08, 10696 g of high-purity sponge Ti, 4612.8 g of high-purity Al block and 4691.2 g of Nb-Al master alloy particles are accurately weighed, with a total mass of 20,000 g of metal raw materials. Finally, a TiAl alloy with precise composition is obtained, and its macroscopic morphology is shown in the following figure: Figure 1 As shown in (c) and (d) in the figure, the SEM-BSE organization diagram is shown in Figure 2 The average values ​​of the composition test results are shown in Table 2. The composition test results of aluminum and niobium at multiple locations of the alloy fluctuate as shown in (c) and (d). Figure 3 shown.

[0041] Table 2 Composition of Ti45Al8Nb after secondary feeding

[0042] Alloy components Ti Al Nb At(%) 47.17 44.91 7.92 wt(%) 53.70 28.81 17.49

[0043] Example 3

[0044] The TiAl alloy smelting method described in this embodiment is the same as that in embodiment 1 in other steps, except that: in step (7), the secondary ingot is turned over and placed back in a water-cooled copper crucible, and the low-pressure cooling water, dryer, mechanical pump and argon gas bottle are turned on in sequence; the hatch is closed and the lock is locked; the mechanical pump and the large and small Roots pumps are turned on to evacuate the vacuum, and then the diffusion pump is turned on, preheated to 280°C, and evacuated to a vacuum degree of 5 10 -3 Pa; turn off the diffusion pump, open the charging valve, and fill with argon to keep the vacuum degree of the melting chamber at 0.05 Mpa; turn on the cooling water system, heat the power supply, slowly increase the power to the maximum power, heat the secondary ingot placed in the water-cooled copper crucible, and after the secondary ingot in the crucible is completely melted, keep it warm for 10 min, reduce the power at a rate of 80 kW / min, and let the ingot cool down with the water-cooled copper crucible. After the power drops to the minimum, turn off the heating power supply, and take out the ingot after it cools down to obtain a TiAl alloy ingot. The optical microscope picture is as follows Figure 5 As shown in the figure, the composition test results of aluminum and niobium at various locations of the alloy fluctuate as follows: Figure 6 shown.

[0045] Example 4

[0046] The TiAl alloy smelting method described in this embodiment is the same as that in embodiment 1 in other steps, except that: in step (7), the secondary ingot is turned over again and placed in a water-cooled copper crucible, and the low-pressure cooling water, dryer, mechanical pump and argon gas bottle are turned on in sequence; the hatch is closed and the lock is locked; the mechanical pump and the large and small Roots pumps are turned on to evacuate the vacuum, and then the diffusion pump is turned on, preheated to 280°C, and evacuated to a vacuum degree of 5 10 -3 Pa; turn off the diffusion pump, open the charging valve, and fill in argon to keep the vacuum degree of the melting chamber at 0.05Mpa; turn on the cooling water system, heat the power supply, and slowly increase the power to the highest power. After the secondary ingot in the crucible is completely melted, keep it warm for 10 minutes, reduce the power at a rate of 30kW / min to reduce the metal liquid temperature to 10℃ below the melting point, that is, 1570℃, and then keep it warm for 30 minutes, reduce the power at a rate of 80kW / min, and let the ingot cool down with the water-cooled copper crucible. After the power drops to the lowest, turn off the heating power supply, and take out the ingot after it cools down to obtain a TiAl alloy ingot. The optical microscope picture is as follows Figure 7 shown.

[0047] Example 5

[0048] The TiAl alloy smelting method described in this embodiment is the same as that in embodiment 1 in other steps, except that: in step (7), the secondary ingot is turned over again and placed in a water-cooled copper crucible, and the low-pressure cooling water, dryer, mechanical pump and argon gas bottle are turned on in sequence; the hatch is closed and the lock is locked; the mechanical pump and the large and small Roots pumps are turned on to evacuate the vacuum, and then the diffusion pump is turned on, preheated to 280°C, and evacuated to a vacuum degree of 5 10 -3 Pa; turn off the diffusion pump, open the inflation valve, and fill with argon to keep the vacuum degree of the smelting chamber at 0.05Mpa; turn on the cooling water system, heat the power supply, and slowly increase the power to the maximum power. After the secondary ingot in the crucible is completely melted, keep warm for 10 minutes, reduce the power at a rate of 30kW / min to 10°C above the α phase transformation point, that is, 1310°C, keep warm for 30 minutes, and reduce the power at a rate of 80kW / min. Let the ingot cool down with the water-cooled copper crucible, turn off the heating power after the power drops to the minimum, and take it out after the ingot cools down. Let the ingot cool down with the water-cooled copper crucible, turn off the heating power after the power drops to the minimum, and take it out after the ingot cools down to obtain a TiAl alloy ingot. The composition test results of aluminum and niobium at multiple locations fluctuate as shown in the following figure. Figure 8 shown.

[0049] The present invention accurately controls the melt temperature, and temperature control in a stable temperature range is more conducive to obtaining a desired grain size and uniform structure. This new and efficient vacuum induction shell melting process for TiAl alloy can reduce macrosegregation, improve the uniformity of the ingot, and improve the melting efficiency.

Claims

1. A method for preparing TiAl alloy ingots by vacuum induction melting, characterized in that: Under a protective atmosphere, vacuum induction melting is used, which specifically includes the following steps: Step 1: Prepare ingredients according to the TiAl alloy composition; Step 2: Slowly increase the power to the highest power, heat the metal raw material placed in the water-cooled copper crucible, and after the raw material in the crucible is completely melted, keep it warm for 10 minutes, reduce the power at a rate of 60kW / min, and let the ingot cool down along with the water-cooled copper crucible. After the power drops to the lowest, turn off the heating power supply, and take out the ingot after it cools down to obtain a primary ingot; Step 3: turning over the primary ingot and placing it in a water-cooled copper crucible, and re-smelting it according to step 2 to obtain a secondary ingot; Step 4: The secondary ingot is turned over again and placed in a water-cooled copper crucible for smelting again. The process is: slowly increase the power to the maximum power, and after the secondary ingot in the crucible is completely melted, keep warm for 10 minutes, reduce the power at a rate of 30 kW / min to reduce the metal liquid temperature to 10°C below the melting point, and then keep warm for 30 minutes, and then reduce the power at a rate of 10 kW / min to 10°C above the α phase transformation point, keep warm for 30 minutes, and reduce the power at a rate of 80 kW / min to allow the ingot to cool down with the water-cooled copper crucible. After the power drops to the minimum, turn off the heating power supply, and take out the ingot after it is cooled to obtain a TiAl alloy ingot with uniform structure and reduced macro-segregation.

2. The method according to claim 1, characterized in that TiAl alloy is Ti(43-48)Al(1-13)Nb.

3. The method according to claim 1 or 2, characterized in that TiAl alloy is Ti45Al8Nb.

4. The method according to claim 2, characterized in that When the TiAl alloy is Ti(43-48)Al(1-13)Nb, high-purity sponge Ti, high-purity Al blocks and Nb-Al master alloy particles are used as metal raw materials.

5. The method according to claim 1, characterized in that The protective atmosphere was high-purity argon, and the vacuum degree was maintained at 0.05Mpa.

6. The method according to claim 1, characterized in that Slowly increasing the power to the maximum power means slowly increasing the power to the maximum power at a rate of 60 kW / min.

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