Preparation method of directional solidification TiAl-based alloy with stable mechanical properties

Abstract

The application relates to a preparation method of a directional solidification TiAl-based alloy with stable mechanical properties, comprising the following steps: ingredient preparation: using single elements and intermediate alloy raw materials to configure a molten material with an atomic percentage component of Ti-(40-50)Al-(1-10)M; fine-grain element addition: B, Y and C elements; master alloy ingot preparation: ultrasonic vibration assisted electromagnetic cold crucible suspension smelting preparation is carried out; directional solidification preparation: a material rod is cut from the master alloy ingot, ultrasonic vibration assisted electromagnetic cold crucible directional solidification preparation is carried out, and the preparation is always accompanied by ultrasonic vibration assistance; and preparation completion: the product is taken out after cooling to complete the preparation. The preparation method can simultaneously ensure that the TiAl-based alloy is pollution-free, high-flux, organization directional, and B, Y and C fine-grain element compounds are dispersedly distributed without agglomeration, can realize obtaining stable fine-grain directional solidification organization, and thus the stability of the mechanical properties of the alloy is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of special solidification of high-temperature active materials, and relates to a preparation method of directional solidification TiAl-based alloy with stable mechanical properties. BACKGROUND

[0002] TiAl-based alloy is a high-temperature structural material with light weight and high strength. At present, the TiAl-based alloy made of an aero-engine blade can realize partial replacement of a Ni-based high-temperature alloy blade, which plays an important role in improving the thrust-to-weight ratio of the aero-engine.

[0003] The columnar crystal of the TiAl-based alloy obtained by directional solidification is not a grain in the ordinary sense, and mainly consists of (alpha2 + gamma) lamellar structure in the grain, which is similar to the pearlite structure in steel. The angle between the (alpha2 + gamma) lamellar direction and the stress direction greatly affects the mechanical properties. For example, when the tensile stress and the (alpha2 + gamma) lamellar direction are 0 ° ~ 30 ° angle, the directional solidification alloy has high tensile strength and tensile elongation, and when the tensile stress direction and the (alpha2 + gamma) lamellar direction are 30 ° ~ 90 ° angle, the tensile properties are poor; for another example, when the crack propagation is along the (alpha2 + gamma) lamellar, the alloy has very small resistance to the crack, and correspondingly has very low toughness, and when the crack propagates perpendicular to the (alpha2 + gamma) lamellar, the alloy has very large resistance to the crack, and correspondingly has very high toughness. As can be seen from the above, when the prepared workpiece has a coarse columnar crystal structure, and one or several columnar crystals have an unfavorable (alpha2 + gamma) lamellar direction relative to the stress direction, the workpiece will have very low mechanical properties, even lower than the minimum performance index required by the batch workpiece, which is unacceptable especially for the aerospace field which must ensure absolute safety.

[0004] In summary, improving the stability of the mechanical properties of the directional solidification TiAl-based alloy is a difficult problem to be solved. The existing technical means still have a blank in solving this problem, which seriously affects the use safety of the alloy workpiece and limits the popularization and use of the alloy. SUMMARY

[0005] OBJECTIVE

[0006] To solve the problem of poor stability of the mechanical properties of the directional solidification TiAl-based alloy, the application provides a preparation method of directional solidification TiAl-based alloy with stable mechanical properties.

[0007] TECHNICAL SCHEME

[0008] A preparation method of directional solidification TiAl-based alloy with stable mechanical properties comprises the following steps:

[0009] Step one, ingredients: using single element and intermediate alloy raw materials to configure the molten material with atomic percentage composition of Ti-(40-50)Al-(1-10)M; wherein, Ti accounts for the balance, and M refers to alloying elements Nb, Cr, V, Mo, W, Hf, Fe and Mn; during the ingredient process, Nb, Cr, V, Mo, W, Hf and Mn are added in the form of M-Al intermediate alloy with purity ≥ 99.9%, and Ti and Fe are added in the form of single element with purity ≥ 99.9wt.%; during the ingredient process, first calculate the amount of M-Al intermediate alloy required, and the remaining Al is added in the form of single element with purity ≥ 99.9wt.%; next, add 3wt.%-5wt.% of Al in addition to the total mass of the molten material as burning loss;

[0010] Step two, adding fine-grained elements: adding B, Y and C elements in the final molten material prepared in step one, which can add one, or any two, or all three, wherein B element is added in the form of TiB2 intermediate alloy with purity ≥ 99.9wt.%, Y element is added in the form of YAl2 intermediate alloy or AlY intermediate alloy with purity ≥ 99.9wt.%, and C element is added in the form of TiC intermediate alloy with purity ≥ 99.9wt.%;

[0011] Step three, master alloy ingot preparation: using ultrasonic vibration assisted electromagnetic cold crucible suspension melting technology, the final prepared raw material in step two is melted under argon protective atmosphere, and after melting, it is cast into a master alloy ingot. Both the melting process and the casting process need to apply ultrasonic vibration, and after the ingot solidifies, the ultrasonic vibration device is turned off;

[0012] Step four, directional solidification preparation: using ultrasonic vibration assisted electromagnetic cold crucible directional solidification device technology, a material rod is cut from the master alloy ingot, and the alloy is prepared by ultrasonic vibration assisted electromagnetic cold crucible directional solidification under argon protective atmosphere; ultrasonic vibration assistance is always accompanied during the electromagnetic cold crucible directional solidification process;

[0013] Step five, preparation is completed: first, turn off the electromagnetic cold crucible directional solidification device, then turn off the ultrasonic vibration auxiliary device, and then take out the prepared product after cooling, thus completing the preparation of directional solidification TiAl-based alloy with stable mechanical properties.

[0014] Further, the single element and intermediate alloy in step one are both <30mm particles.

[0015] Further, in the step two, the B, Y, C elements are added by cold spraying method, the total atomic weight of the added B, Y, C elements is 0.05at.% to 0.3at.% of the total weight of the material to be melted in the step one, and compressed air is used as the gas in the cold spraying process, and the air pressure is 5 to 15 atmospheres.

[0016] Further, in the step two, the TiB2 intermediate alloy, YAl2 intermediate alloy, AlY intermediate alloy and TiC intermediate alloy are in powder form and need to pass through a 50-mesh sieve.

[0017] Further, in the step three, the raw materials are melted under the protection of 200Pa to 500Pa argon atmosphere, the melting temperature is 1600℃ to 1800℃, the temperature is maintained for 15min to 25min, and after melting, the alloy ingot with a diameter of 100mm to 300mm and a height of 150mm to 300mm is cast, the ultrasonic vibration is applied during the melting and casting processes, the frequency of the ultrasonic vibration is 60kHz to 80kHz, and the displacement amplitude is 30μm, and the ultrasonic vibration device is turned off after the ingot is solidified.

[0018] Further, in the step four, the material rod with a diameter of 17mm to 30mm is cut from the master alloy ingot, and the alloy is prepared by ultrasonic vibration assisted electromagnetic cold crucible directional solidification under the protection of 200Pa to 500Pa argon atmosphere, the power of the electromagnetic cold crucible directional solidification is required to be 45kW to 50kW, and the solidification rate of the electromagnetic cold crucible directional solidification is required to be 0.3mm / min to 0.7mm / min.

[0019] Further, when the solidification rate is 0.3mm / min to 0.5mm / min, the ultrasonic vibration frequency is 40kHz to 45kHz, and the displacement amplitude is 30μm, and when the solidification rate is 0.5mm / min to 0.7mm / min, the ultrasonic vibration frequency is 45kHz to 50kHz, and the displacement amplitude is 30μm.

[0020] Further, in the step five, the cooling time is 10min to 15min.

[0021] Further, in the step three and step four, the argon atmosphere refers to that the gas pressure is first extracted to ≤5Pa, and then the argon is filled to 200Pa to 500Pa, and the above process is repeated four times, and finally the argon atmosphere is maintained at 200Pa to 500Pa.

[0022] Further, the equipment used in the ultrasonic vibration assisted electromagnetic cold crucible suspension smelting technology comprises a split crucible, a water passing high frequency induction coil, an ultrasonic wave generating device and a casting crucible, the split crucible is vertically provided with a plurality of evenly distributed slits, the slits are filled with mica sheets, the bottom of the split crucible is an integrated crucible bottom, the ultrasonic wave generating device is arranged outside the split crucible, the ultrasonic wave generating device is connected with ultrasonic wave conducting parts through wires, one ultrasonic wave conducting part is connected to the split crucible through a fixing device, and the lower end of the ultrasonic wave conducting part is deep into the smelting material, the other ultrasonic wave conducting part is connected to the casting crucible through a fixing device, and the lower end of the ultrasonic wave conducting part is deep into the smelting material poured into the casting crucible subsequently;

[0023] The equipment used in the ultrasonic vibration assisted electromagnetic cold crucible directional solidification device technology comprises an ultrasonic wave generating device, an up-down penetrating cold crucible, a Ga-In-Sn liquid metal tank, a stainless steel crucible, a lower end servo motor and an upper end servo motor, the up-down penetrating cold crucible is fixed in the shell through a support, the shell is provided with a part for vacuumizing and argon filling, the upper end and the lower end of the shell are respectively provided with openings, and the upper end servo motor and the lower end servo motor are respectively fixed, the upper end servo motor and the lower end servo motor are located directly above and below the up-down penetrating cold crucible, the ultrasonic wave generating device is arranged outside the shell and connected with ultrasonic wave conducting parts on the inner side of the up-down penetrating cold crucible through wires, the ultrasonic wave conducting parts are connected to the up-down penetrating cold crucible through fixing devices, the extension end of the lower end servo motor is used for being connected to a lower feeding device, and the extension end of the upper end servo motor is used for being connected to an upper feeding device, the Ga-In-Sn liquid metal tank is arranged at the lower end of the up-down penetrating cold crucible, the lower end of the Ga-In-Sn liquid metal tank is provided with an opening through which the extension end of the lower end servo motor can pass, and the Ga-In-Sn liquid metal tank contains Ga-In-Sn liquid.

[0024] Advantages and effects

[0025] 1. The ultrasonic vibration technology is combined with the electromagnetic cold crucible suspension smelting technology and the electromagnetic cold crucible directional solidification technology to prepare the TiAl-based alloy, and B, Y and C fine-grain elements are reasonably added, so that the preparation method can ensure that the TiAl-based alloy is pollution-free, high-flux, organization directional and B, Y and C fine-grain element compounds are dispersedly distributed without agglomeration.

[0026] 2. The stable fine-grain directional solidification organization can be obtained, the organization can provide more longitudinal grain boundaries, promote the deflection of the radial crack when the radial crack expands from one grain into the next grain, avoid the fatal damage of the coarse grain with an unfavorable (alpha2+gamma) lamella direction to the mechanical properties of the alloy workpiece, and thus the stability of the alloy mechanical properties is improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] The application will be further described in conjunction with the accompanying drawings and specific embodiments. The protection scope of the application is not limited to the following content.

[0028] Figure 1 is a schematic diagram of the ultrasonic vibration assisted electromagnetic cold crucible suspension smelting technology;

[0029] Figure 2 is a schematic diagram of the ultrasonic vibration assisted electromagnetic cold crucible directional solidification technology;

[0030] Figure 3 is a macrostructure diagram of the directional solidification Ti-44Al-6Nb-1Cr-2V alloy prepared by using the conventional method in example one;

[0031] Figure 4 is a microstructure diagram of the directional solidification Ti-44Al-6Nb-1Cr-2V alloy prepared by using the conventional method in example one;

[0032] Figure 5 is a fracture toughness performance summary diagram of the directional solidification Ti-44Al-6Nb-1Cr-2V alloy prepared by using the conventional method in example one, wherein 40-0.5 in the abscissa indicates that the directional solidification power is 40 kW and the pulling speed is 0.5 mm / min, and the performance of 8 fracture toughness samples prepared under each condition is tested;

[0033] Figure 6 is a macrostructure diagram of the directional solidification Ti-44Al-6Nb-1Cr-2V-(0.1B0.15Y) alloy prepared by using the method of the application in example two;

[0034] Figure 7 is a microstructure diagram of the directional solidification Ti-44Al-6Nb-1Cr-2V-(0.1B0.15Y) alloy prepared by using the method of the application in example two;

[0035] Figure 8 is a fracture toughness performance summary diagram of the directional solidification Ti-44Al-6Nb-1Cr-2V-(0.1B0.15Y) alloy prepared by using the method of the application in example two, wherein 40-0.5 in the abscissa indicates that the directional solidification power is 40 kW and the pulling speed is 0.5 mm / min, and the performance of 8 fracture toughness samples prepared under each condition is tested;

[0036] Ti-44Al-6Nb-1Cr-2V-(0.1B0.15Y) alloy prepared by using the method of the application in example two, wherein 40-0.5 in the abscissa indicates that the directional solidification power is 40 kW and the pulling speed is 0.5 mm / min, and the performance of 8 fracture toughness samples prepared under each condition is tested;

[0037] Explanation of reference numerals: 1 - split crucible, 2 - mica sheet, 3 - smelting material, 4 - crucible bottom, 5 - water-passing high-frequency induction coil, 6 - ultrasonic wave generating device, 7 - ultrasonic wave conducting part, 8 - casting crucible, 9 - up-and-down-through-type cold crucible, 10 - Ga-In-Sn liquid metal tank, 11 - stainless steel crucible, 12 - upper feeding, 13 - lower feeding, 14 - lower end servo motor, 15 - upper end servo motor. DETAILED DESCRIPTION

[0038] A preparation method of a directional solidification TiAl-based alloy with stable mechanical properties, comprising the following steps:

[0039] Step one, ingredient preparation: using single elements and intermediate alloy raw materials to configure the smelting material with atomic percentage composition of Ti-(40-50)Al-(1-10)M; wherein, Ti accounts for the balance, and M refers to alloying elements Nb, Cr, V, Mo, W, Hf, Fe and Mn; during the ingredient preparation process, Nb, Cr, V, Mo, W, Hf and Mn are added in the form of M-Al intermediate alloy with purity ≥ 99.9%, and Ti and Fe are added in the form of single elements with purity ≥ 99.9wt.%; during the ingredient preparation process, first calculate the amount of M-Al intermediate alloy required, and supplement Al in the form of single elements with purity ≥ 99.9wt.% to make up for the lack of Al; next, add 3wt.%-5wt.% of Al in addition to the total mass of the smelting material as burn loss; both the single elements and the intermediate alloy are granules with a size of < 30mm.

[0040] Step two, adding fine-grained elements: in the smelting material prepared in step one, B, Y and C elements are added by cold spraying method, one or any two or all three of them can be added; wherein, B element is added in the form of TiB2 intermediate alloy with purity ≥ 99.9wt.%, Y element is added in the form of YAl2 intermediate alloy or AlY intermediate alloy with purity ≥ 99.9wt.%, and C element is added in the form of TiC intermediate alloy with purity ≥ 99.9wt.%; the total atomic amount of B, Y and C elements added is 0.05at.%-0.3at.% of the total amount of the smelting material prepared in step one, which can ensure that a directional solidification structure with fine columnar crystals is obtained subsequently; compressed air is used as the gas during the cold spraying process, and the gas pressure is 5-15 atmospheres; TiB2 intermediate alloy, YAl2 intermediate alloy, AlY intermediate alloy and TiC intermediate alloy are in powder form and need to pass through a 50-mesh sieve.

[0041] Step three, master alloy ingot preparation: as Figure 1As shown, the raw material is melted under 200 Pa to 500 Pa argon protective atmosphere by using ultrasonic vibration assisted electromagnetic cold crucible suspension melting technology, the melting temperature is 1600 ℃ to 1800 ℃, and the temperature is kept for 15 min to 25 min. After melting, the mother alloy ingot with a diameter of 100 mm to 300 mm and a height of 150 mm to 300 mm is cast. The ultrasonic vibration is applied during the melting process and the casting process. The frequency of the ultrasonic vibration is 60 kHz to 80 kHz, and the displacement amplitude is 30 μm. After the ingot is solidified, the ultrasonic vibration device is turned off.

[0042] Step four, directional solidification preparation: as shown in Figure 2 As shown, the alloy is prepared by ultrasonic vibration assisted electromagnetic cold crucible directional solidification device technology under 200 Pa to 500 Pa argon protective atmosphere from the mother alloy ingot with a diameter of 17 mm to 30 mm. The power of the electromagnetic cold crucible directional solidification is required to be 45 kW to 50 kW. When the power is less than 45 kW, the temperature gradient is insufficient, and when the power is greater than 50 kW, the electromagnetic stirring is too strong, which are not conducive to the organization orientation. The solidification rate of the electromagnetic cold crucible directional solidification is required to be 0.3 mm / min to 0.7 mm / min. When the solidification rate is less than 0.3 mm / min, the preparation efficiency is low, and when the solidification rate is greater than 0.7 mm / min, the composition undercooling is high, which are not conducive to the organization orientation. When the solidification rate is 0.3 mm / min to 0.5 mm / min, the ultrasonic vibration frequency is 40 kHz to 45 kHz, and the displacement amplitude is 30 μm. When the solidification rate is 0.5 mm / min to 0.7 mm / min, the ultrasonic vibration frequency is 45 kHz to 50 kHz, and the displacement amplitude is 30 μm. The ultrasonic vibration is always assisted during the electromagnetic cold crucible directional solidification process.

[0043] Step five, preparation end: first, the electromagnetic cold crucible directional solidification device is turned off, and then the ultrasonic vibration assisted device is turned off. After the preparation product is cooled, it is taken out. The cooling time is 10 min to 15 min. Thus, the preparation of the directional solidification TiAl-based alloy with stable mechanical properties is completed.

[0044] In the above steps three and four, the argon protective atmosphere refers to that the gas pressure is first extracted to ≤5 Pa, and then the argon is filled to 200 Pa to 500 Pa. The above process is repeated four times, and finally the argon atmosphere is kept at 200 Pa to 500 Pa.

[0045] The equipment used in the ultrasonic vibration assisted electromagnetic cold crucible suspension melting technology is as shown in Figure 1As shown, it includes a segmented crucible 1, a water-cooled high-frequency induction coil 5, an ultrasonic generator 6, and a casting crucible 8. The segmented crucible 1 has multiple evenly distributed vertical slits filled with mica sheets 2. The bottom of the segmented crucible 1 is a single crucible bottom 4. The ultrasonic generator 6 is located outside the segmented crucible 1 and is connected to an ultrasonic wave conduction part 7 via a wire. One ultrasonic wave conduction part 7 is connected to the segmented crucible 1 via a fixing device (e.g., a clamp), and its lower end extends into the molten material 3. The other ultrasonic wave conduction part 7 is connected to the casting crucible 8 via a fixing device (e.g., a clamp), and its lower end extends into the molten material 3 that will be subsequently poured into the casting crucible 8.

[0046] The equipment used in ultrasonic vibration-assisted electromagnetic cold crucible directional solidification device technology, such as Figure 2 As shown. It includes an ultrasonic generator 6, a through-type cold crucible 9, a Ga-In-Sn liquid metal tank 10, a stainless steel crucible 11, a lower servo motor 14, and an upper servo motor 15. The through-type cold crucible 9 is fixed inside the housing by a bracket. The housing has sections for vacuuming and argon filling. Openings are provided at the upper and lower ends of the housing, and the upper servo motor 15 and lower servo motor 14 are fixed thereon, respectively. The upper servo motor 15 and lower servo motor 14 are located directly above and below the through-type cold crucible 9. The ultrasonic generator 6 is located outside the housing and is connected to the upper servo motor 11 via wires. On the inner side of the lower through-type cold crucible 9, the ultrasonic wave conduction part 7 is connected to the upper and lower through-type cold crucible 9 by a fixing device (e.g., a clamp). The telescopic end of the lower servo motor 14 is used to connect to the lower feed 13, and the telescopic end of the upper servo motor 15 is used to connect to the upper feed 12. The Ga-In-Sn liquid metal tank 10 is provided at the lower end of the upper and lower through-type cold crucible 9. The lower end of the Ga-In-Sn liquid metal tank 10 is provided with an opening that allows the telescopic end of the lower servo motor 14 to pass through. The Ga-In-Sn liquid metal tank 10 is filled with Ga-In-Sn liquid.

[0047] Two examples are provided below. Example 1 uses a conventional method to prepare a directionally solidified Ti-44Al-6Nb-1Cr-2V alloy, while Example 2 uses the method of this patent to prepare a Ti-44Al-6Nb-1Cr-2V-(0.1B0.15Y) alloy. Example 1 is used for comparison to demonstrate the advantages of the method of this patent in Example 2.

[0048] Example 1

[0049] Combination Figures 3-5 This embodiment describes the preparation of a directionally solidified Ti-44Al-6Nb-1Cr-2V alloy using conventional methods, including the following steps:

[0050] Step one, using Ti, Al single element with purity ≥ 99.9wt.% and AlNb, AlCr, AlV intermediate alloy with purity ≥ 99.9wt.% to configure the Ti-44Al-6Nb-1Cr-2V alloy to be melted, and then adding 4wt.% of Al as burning loss, the single element and intermediate alloy are all <30mm particles;

[0051] Step two, using vacuum consumable method to melt and cast into a master alloy ingot with diameter of 150mm and height of 250mm under the protection of 300Pa argon gas atmosphere;

[0052] Step three, cutting a 20mm diameter rod from the master alloy ingot, and using electromagnetic cold crucible directional solidification to prepare under the protection of 300Pa argon gas atmosphere, the power of the electromagnetic cold crucible directional solidification is 45kW, and the solidification rate is 0.5mm / min; after the experiment, the electromagnetic cold crucible directional solidification device is turned off, and the sample is taken out after cooling for 10min, and the directional solidification of the TiAl-based alloy is completed;

[0053] The macro / microstructure and fracture toughness of the directional solidification Ti-44Al-6Nb-1Cr-2V alloy are investigated, and the pressure stress direction is perpendicular to the directional solidification columnar crystal during the fracture toughness test. As shown in the macrostructure of Figure 3 , it can be seen that the columnar crystal of the directional solidification is relatively thick; as shown in the microstructure of Figure 4 , it can be seen that the longitudinal grain boundary content in the microstructure is relatively small; as shown in the fracture toughness of Figure 5 , the average fracture toughness of the directional structure is improved, but the performance fluctuation is too large, the mechanical property stability is poor, and the lowest performance is only 10.1MPa·mm 1 / 2 , which is lower than the fracture toughness of the original cast alloy and is at a very low level.

[0054] Example 2

[0055] In combination with Figures 6-8 , it is illustrated that the present example uses the method of the present application to prepare Ti-44Al-6Nb-1Cr-2V-(0.1B0.15Y) alloy, which includes the following steps:

[0056] Step one, using Ti, Al single element with purity ≥ 99.9wt.% and AlNb, AlCr, AlV, AlY, TiB2 intermediate alloy with purity ≥ 99.9wt.% to configure the Ti-44Al-6Nb-1Cr-2V-(0.1B0.15Y) alloy to be melted, the Ti, Al single element and AlNb, AlCr, AlV intermediate alloy are all <30mm particles, while the AlY, TiB2 intermediate alloy is a powder passing through a 50 mesh sieve, and 10atm compressed air cold spraying is used to uniformly mix into the ingredients;

[0057] Step Two, as follows Figure 1 As shown, the above-mentioned material to be melted was melted under a 300Pa argon atmosphere using ultrasonic vibration-assisted electromagnetic cold crucible suspension melting technology. After the raw material melted, the melting temperature was controlled at 1600℃~1650℃ and maintained at this melting temperature for 20 minutes. After the holding temperature was completed, the molten material was cast into a master alloy ingot with a diameter of 150mm and a height of 250mm. Ultrasonic vibration was required during both the melting and casting processes. The frequency of the ultrasonic vibration was 80kHz and the displacement amplitude was 30μm. The ultrasonic vibration device was turned off after the ingot solidified.

[0058] Step 3: In accordance with the requirements of electromagnetic cold crucible directional solidification technology, a 20mm diameter bar is cut from the master alloy ingot. Electromagnetic cold crucible directional solidification is then performed under a 300Pa argon atmosphere and with ultrasonic vibration assistance. Figure 2 As shown; the power supply for electromagnetic cold crucible directional solidification was 45kW, the solidification rate was 0.5mm / min, the ultrasonic vibration frequency was 45kHz, and the displacement amplitude was 30μm; ultrasonic vibration was always used to assist in the electromagnetic cold crucible directional solidification process; after the preparation was completed, the electromagnetic cold crucible directional solidification device was turned off first, and then the ultrasonic vibration assist device was turned off. The sample was taken out after cooling for 10min, thus completing the preparation of a directional solidified TiAl-based alloy with stable mechanical properties;

[0059] The macro / microstructure and fracture toughness of the directionally solidified Ti-44Al-6Nb-1Cr-2V-(0.1B0.15Y) alloy were investigated. During the fracture toughness test, the compressive stress direction was perpendicular to the directionally solidified columnar crystals. The macrostructure is as follows: Figure 6 As shown, the directionally solidified columnar crystals are clearly refined; the microstructure is as follows: Figure 7 As shown, the content of longitudinal grain boundaries in the microstructure is significantly increased; the fracture toughness is as... Figure 8 As shown, the average fracture toughness of this alloy is improved after the microstructure is oriented, especially the stability of its mechanical properties is significantly improved, with the difference between the maximum and minimum fracture toughness being only 1 MPa·mm. 1 / 2 ~5MPa·mm 1 / 2 .

[0060] The lower servo motor used in this patent's specific embodiment is a Siemens model: SIMOTICSS-1FK2 HD; the upper servo motor is a Siemens model: SIMOTICSS S-1FK2 CT. The ultrasonic generator is a Hangzhou Haoda Ultrasonic Equipment Co., Ltd. model: HDR-2000.

[0061] Obviously, the above embodiments of the present application are merely example for clearly explaining the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made, and here all the embodiments cannot be exhausted, and any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.

Claims

1. A method for preparing a directionally solidified TiAl-based alloy with stable mechanical properties, characterized in that: Comprising the following steps: Step one, batching: using single element and intermediate alloy raw materials to configure the molten material with atomic percentage composition of Ti-(40-50)Al-(1-10)M; wherein Ti accounts for the balance, and M refers to alloying elements Nb, Cr, V, Mo, W, Hf, Fe and Mn; in the batching process, Nb, Cr, V, Mo, W, Hf and Mn are added in the form of M-Al intermediate alloy with purity ≥99.9%, Ti and Fe are added in the form of single element with purity ≥99.9wt.%; in the batching process, first calculate the amount of M-Al intermediate alloy required, and the remaining Al is supplemented in the form of single element with purity ≥99.9wt.%; next, add 3wt.%-5wt.% of Al in addition to the total mass of the molten material as burn loss; Step two, adding fine-grained elements: adding one or more than one of B, Y and C elements in the final molten material prepared in step one, wherein the B element is added in the form of TiB2 intermediate alloy with purity ≥99.9wt.%, the Y element is added in the form of YAl2 intermediate alloy or AlY intermediate alloy with purity ≥99.9wt.%, and the C element is added in the form of TiC intermediate alloy with purity ≥99.9wt.%; Step three, master alloy ingot preparation: using ultrasonic vibration assisted electromagnetic cold crucible suspension melting technology, the raw material prepared in step two is melted under 200Pa-500Pa argon protective atmosphere, the melting temperature is 1600℃-1800℃, and the temperature is maintained for 15min-25min, after melting, it is poured into a master alloy ingot with a diameter of 100mm-300mm and a height of 150mm-300mm, ultrasonic vibration needs to be applied during the melting process and the pouring process, the frequency of ultrasonic vibration is 60kHz-80kHz, and the displacement amplitude is 30μm, after the ingot solidifies, the ultrasonic vibration device is turned off; Step four, directional solidification preparation: using ultrasonic vibration assisted electromagnetic cold crucible directional solidification device technology, a material rod with a diameter of 17mm-30mm is cut from the master alloy ingot, and the alloy is prepared by ultrasonic vibration assisted electromagnetic cold crucible directional solidification under the protection of 200Pa-500Pa argon protective atmosphere; ultrasonic vibration assistance is always accompanied during the electromagnetic cold crucible directional solidification process, the power of the electromagnetic cold crucible directional solidification is required to be 45kW-50kW, and the solidification rate of the electromagnetic cold crucible directional solidification is required to be 0.3mm / min-0.7mm / min; when the solidification rate is 0.3mm / min-0.5mm / min, the ultrasonic vibration frequency is 40kHz-45kHz, and the displacement amplitude is 30μm; when the solidification rate is 0.5mm / min-0.7mm / min, the ultrasonic vibration frequency is 45kHz-50kHz, and the displacement amplitude is 30μm; Step five, preparation is completed: first, turn off the electromagnetic cold crucible directional solidification device, then turn off the ultrasonic vibration auxiliary device, and then take out the prepared product after cooling, thus the preparation of directional solidification TiAl-based alloy with stable mechanical properties is completed.

2. The method of producing a directionally solidified TiAl-based alloy having stable mechanical properties according to claim 1, characterized in that: The elemental substance and the intermediate alloy in step one are both < 30 mm particles.

3. The method of producing a directionally solidified TiAl-based alloy having stable mechanical properties according to claim 1, characterized in that: In step two, the B, Y and C elements are added by cold spraying, and the total atomic weight of the added B, Y and C elements is 0.05 at.% to 0.3 at.% of the total weight of the final prepared material in step one. Compressed air is used as the gas in the cold spraying process, and the gas pressure is 5 to 15 atmospheres.

4. The method of producing a directionally solidified TiAl-based alloy having stable mechanical properties according to claim 1 or 3, characterized in that: In step two, the TiB2 intermediate alloy, YAl2 intermediate alloy, AlY intermediate alloy and TiC intermediate alloy are in powder form and need to pass through a 50 mesh sieve.

5. The method of producing a directionally solidified TiAl-based alloy having stable mechanical properties according to claim 1, characterized in that: In step five, the cooling time is 10 to 15 minutes.

6. The method of producing a directionally solidified TiAl-based alloy having stable mechanical properties according to claim 1, characterized in that: In steps three and four, the argon protective atmosphere refers to first pumping the gas pressure to ≤ 5 Pa, and then repeatedly pumping and filling argon four times to maintain an argon atmosphere of 200 to 500 Pa.

7. The method of producing a directionally solidified TiAl-based alloy having stable mechanical properties according to claim 1, characterized in that: The equipment used in the ultrasonic vibration assisted electromagnetic cold crucible suspension melting technology includes a split crucible, a water-cooled high-frequency induction coil, an ultrasonic generator and a casting crucible. The split crucible has multiple evenly distributed slits in the vertical direction, and the slits are filled with mica sheets. The bottom of the split crucible is an integrated crucible bottom. The ultrasonic generator is arranged outside the split crucible and is connected to ultrasonic conductors through wires. One ultrasonic conductor is connected to the split crucible through a fixing device and its lower end is immersed in the molten material. The other ultrasonic conductor is connected to the casting crucible through a fixing device and its lower end is immersed in the molten material poured into the casting crucible. The equipment used in the ultrasonic vibration assisted electromagnetic cold crucible directional solidification device technology includes an ultrasonic generator, an up-down through type cold crucible, a Ga-In-Sn liquid metal tank, a stainless steel crucible, a lower servo motor and an upper servo motor. The up-down through type cold crucible is fixed inside a shell through a support. The shell is provided with a vacuum pumping and argon filling part. The upper and lower ends of the shell are provided with openings and are respectively fixed with an upper servo motor and a lower servo motor. The upper and lower servo motors are located directly above and below the up-down through type cold crucible. The ultrasonic generator is arranged outside the shell and is connected to ultrasonic conductors inside the up-down through type cold crucible through wires. The ultrasonic conductors are connected to the up-down through type cold crucible through a fixing device. The extension end of the lower servo motor is connected to a lower feeder, and the extension end of the upper servo motor is connected to an upper feeder. The Ga-In-Sn liquid metal tank is arranged at the lower end of the up-down through type cold crucible. The lower end of the Ga-In-Sn liquid metal tank is provided with an opening through which the extension end of the lower servo motor passes. The Ga-In-Sn liquid metal tank contains Ga-In-Sn liquid.

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