A method for preparing a large-size ingot of an electromagnetic cold crucible directional solidification Nb-Si-based alloy

Abstract

The application relates to a mechanical power closed test platform and relates to a preparation method of an electromagnetic cold-crucible directional solidification Nb-Si-based alloy large-size ingot. In order to solve the problem that the preparation method of the existing Nb-Si-based alloy directional ingot is not conducive to the directional solidification of the alloy due to the electromagnetic force disturbance existing in the solid-liquid interface front, the convection is promoted, and the temperature gradient of the solid-liquid interface front is reduced. The application comprises the following steps: step one, ingredient preparation; step two, vacuum induction suspension smelting; step three, wire cutting round bar; step four, electromagnetic cold-crucible large-size ingot melting; step five, ultrasonic wave assisted electromagnetic cold-crucible directional solidification; and step six, directional ingot cooling. After the directional solidification process is stopped, the ultrasonic wave device is turned off, and the cooling time is 30 min. Thus, the preparation of the Nb-Si-based alloy large-size ingot is completed. The large-size directional ingot obtained through the directional coupling growth of the ductile phase and the brittle phase is beneficial to the improvement of the fracture toughness of the Nb-Si alloy. The application is used for the preparation of engine blade raw materials.

Description

TECHNICAL FIELD

[0001] The application relates to an ingot preparation method, in particular to an electromagnetic cold crucible directional solidification Nb-Si-based alloy large-size ingot preparation method, and belongs to the directional solidification technical field of refractory active materials. BACKGROUND

[0002] With the improvement of the thrust-to-weight ratio requirement of a new generation engine, increasing the engine thrust while reducing the engine weight is conducive to the improvement of the thrust-to-weight ratio. In order to meet the use requirements of high-pressure turbine blades, Nb-Si-based alloy has a high melting point, and is a material with a more extensive application prospect. The main preparation method for high-pressure turbine blades is directional solidification, and the electromagnetic cold crucible directional solidification method can better realize the preparation of large-size pollution-free blade base materials.

[0003] The electromagnetic cold crucible directional solidification method can realize the preparation of Nb-Si-based alloy directional ingots, but due to the electromagnetic cold crucible directional solidification process, the vortex flow velocity direction of the solid-liquid interface front is clockwise on the left side and counterclockwise on the right side. With the increase of the pulling rate, the maximum flow velocity position gradually moves from the skin layer to the center, and the convection in the melt increases, which is conducive to the uniform treatment of the melt. However, at the solid-liquid interface front, the convection in the melt gradually increases, and the solid-liquid interface front convection gradually increases. The solid-liquid interface front convection is enhanced, the temperature of the solid-liquid interface front is reduced, and the temperature gradient of the solid-liquid interface front is reduced, which is not conducive to the generation of the directional solidification structure, is not conducive to the unidirectional growth of the dendritic crystal, is prone to deflection, is not conducive to the unidirectional load service environment of the blade material, and meanwhile, the convection generated by the electromagnetic force disturbance is not conducive to the coupled growth of the toughness Nbss phase and the brittle silicide phase, and is not conducive to the room temperature fracture toughness.

[0004] In summary, the existing Nb-Si-based alloy directional ingot preparation method has the problem that the electromagnetic force disturbance exists at the solid-liquid interface front, promotes convection, reduces the temperature gradient of the solid-liquid interface front, and is not conducive to the directional solidification of the alloy. SUMMARY

[0005] The purpose of the present application is to solve the problem that the existing Nb-Si-based alloy directional ingot preparation method has the problem that the electromagnetic force disturbance exists at the solid-liquid interface front, promotes convection, reduces the temperature gradient of the solid-liquid interface front, and is not conducive to the directional solidification of the alloy. Furthermore, an electromagnetic cold crucible directional solidification Nb-Si-based alloy large-size ingot preparation method is provided.

[0006] The technical scheme of the present application is: an electromagnetic cold crucible directional solidification Nb-Si-based alloy large-size ingot preparation method, which comprises the following steps:

[0007] Step one, ingredients: according to the atomic percentage of Nb-16Si-22Ti, take the metal elemental raw materials;

[0008] Step two, vacuum induction suspension melting:

[0009] Put the elemental raw materials into the vacuum induction suspension equipment, after vacuumizing, fill in argon, carry out vacuum induction suspension melting, and obtain Nb-16Si-22Ti suspension melting ingot after cooling;

[0010] Step three, wire cutting round bar:

[0011] Use the electric spark wire cutting to obtain a round bar with a diameter of 30mm and a length of 40mm and a round bar with a diameter of 20mm and a length of 80mm from the large size casting ingot of Nb-16Si-22Ti alloy;

[0012] Step four, electromagnetic cold crucible large size casting ingot melting:

[0013] Step four one: connect a round bar with a diameter of 30mm with the pulling rod at the bottom of the vacuum furnace;

[0014] Step four two: connect another round bar with a diameter of 20mm with the feeding rod at the top;

[0015] Step four three: after vacuumizing, fill in argon, start the melting power, and carry out the casting ingot melting at a certain pulling speed and feeding speed;

[0016] Step five, ultrasonic assisted electromagnetic cold crucible directional solidification:

[0017] Step five one: start the ultrasonic device;

[0018] Step five two: carry out the pulling and feeding movement of the melted round bar at a certain speed, and obtain a directional solidification Nb-16Si-22Ti casting ingot with a length of 200mm;

[0019] Step six, cooling of the directional casting ingot:

[0020] After the directional solidification process is stopped, the ultrasonic device is turned off, and the cooling time is 30min, thus the preparation of the large size casting ingot of Nb-Si based alloy is completed.

[0021] Further, the elemental raw materials in step one are composed of Nb, Si and Ti, with a total weight of 1kg, the Nb raw material is 793.097g, the Si raw material is 61.870g, and the Ti raw material is 145.033g, and the Nb is 4-6mm flake with a purity of 99.99%, the Si is 3-5mm particle with a purity of 99.99%, and the Ti is 3-25mm sponge titanium with a purity of 99.7%.

[0022] Further, the single-element raw material in step one is subjected to descaling and ultrasonic cleaning before vacuum induction suspension smelting.

[0023] Further, in step two, the vacuum induction suspension furnace is kept at a pressure of 5*10 -4 Pa, the frequency of the vacuum induction suspension furnace is 80 Hz, the frequency power of the vacuum induction suspension furnace is 100 kW, and the smelting time of the vacuum induction suspension furnace is 20 min.

[0024] Further, in step four, the electromagnetic cold crucible directional solidification internal pressure is 200 Pa-300 Pa, the upper end of the 30 mm diameter round bar is located at the center of the coil, the lower end of the 20 mm diameter round bar is parallel to the first turn of the coil, the frequency of the electromagnetic cold crucible coil is 50 kHz, and the power is 45 kW; the large-size ingot reaches the incandescent state, i.e., the melting is started; after the large-size ingot is melted, the power is maintained at 60 kW for 5 min.

[0025] Further, in step four, the ultrasonic wave with a frequency of 20 kHz-30 kHz and a displacement amplitude of 20 μm is applied to the prepared directional solidification sample at a low pulling rate, and the ultrasonic wave with a frequency of 30 kHz-40 kHz and a displacement amplitude of 20 μm is applied to the bottom of the directional solidification sample at a high pulling rate.

[0026] Further, in step four, the low pulling rate is less than 0.8 mm / min, and the solid-liquid interface front flow rate is less than 0.5 m / s; the high pulling rate is 0.08 mm / min-2.0 mm / min, and the solid-liquid interface front flow rate is 0.7 m / s-1.8 m / s.

[0027] Further, in step five, the ultrasonic wave frequency is 20-40 kHz, and the ultrasonic wave displacement amplitude is 20 μm.

[0028] Further, in step five, the feeding rod movement speed is 2.25 times the pulling rod movement speed.

[0029] Compared with the prior art, the present application has the following effects:

[0030] 1、The present application adopts the method combined with external field, utilizes the sound flow effect of the sound field generated by the ultrasonic wave under the action of the external field, the flow direction is counterclockwise on the left side and clockwise on the right side. Under the action of the ultrasonic wave, the sound flow effect makes the flow velocity direction of the melt opposite to the flow velocity direction generated by the electromagnetic force disturbance, and then slows down the convection flow velocity generated by the electromagnetic force disturbance, reduces the convection of the solid-liquid interface front, slows down the convection flow velocity and the lateral flow velocity, the solid-liquid interface front can maintain a larger temperature gradient, so that the dendritic crystal grows unidirectionally along the temperature gradient direction. The flow velocity direction of the solid-liquid interface front is opposite to the flow velocity direction of the strong ultrasonic action area of the ultrasonic treatment, and the coupling effect of the two can reduce the strong convection of the solid-liquid interface front, reduce the flow velocity, and the weaker the convection of the solid-liquid interface front, the stronger the control of the strong convection of the solid-liquid interface front. A flow opposite to the flow direction of the solid-liquid interface front is generated, which can effectively inhibit the convection of the solid-liquid interface front in the process of electromagnetic cold crucible directional solidification, so as to be more conducive to the coupled directional growth of the ductile and brittle two-phase of Nb-Si based alloy. Then, the problem of reducing the temperature gradient of the solid-liquid interface front in the process of electromagnetic cold crucible directional solidification is overcome, the convection of the solid-liquid interface front is inhibited, the temperature gradient of the solid-liquid interface front is improved, and the coupled directional growth of the ductile and brittle two-phase of Nb-Si based alloy large-size ingot is obtained. The fracture toughness is improved by 130% to 150%, which can meet the fracture toughness threshold of blade material processing, that is, greater than 20MPa·m 1 / 2 .

[0031] 2、The present application can realize the weak convection of the solid-liquid interface front of the electromagnetic cold crucible directional solidification large-size non-polluted Nb-Si based directional solidification ingot, the directional solidification process adopts a water-cooled copper crucible, a solidified shell is formed on the surface of the directional ingot, the inside ingot is protected, no impurities are introduced, and the application of ultrasonic is indirect contact, the ultrasonic probe is not inserted into the melt, and the melt is not polluted. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is the preparation flowchart of the present application;

[0033] Figure 2 is the microstructure diagram of the ultrasonic wave assisted electromagnetic cold crucible directional solidification Nb-16Si-22Ti ingot of example one of the present application;The white Nbss phase and the black silicide phase grow along the inverse temperature gradient direction, and the silicide phase wraps the white ductile phase, the white Nbss phase has good toughness, the black silicide phase is beneficial to high temperature performance, grows along a single direction, the phase boundary direction is single, can bear single direction load in the preparation of blade material, the load perpendicular to the phase boundary direction, the toughness phase and the brittle phase cooperate, the high temperature performance and the room temperature performance are matched.

[0034] Figure 3 is the room temperature fracture toughness columnar diagram of example one and example two of the present application.

[0035] Figure 4 is the preparation principle of the present application. DETAILED DESCRIPTION

[0036] Detailed implementation one: combination Figure 1 In this embodiment, the present embodiment is an electromagnetic cold crucible directional solidification Nb-Si-based alloy large-size ingot preparation method, which comprises the following steps:

[0037] Step one, batching: according to the atomic percentage of Nb-16Si-22Ti, taking the metal elemental raw material;

[0038] Step two, vacuum induction suspension melting:

[0039] Put the elemental raw material into the vacuum induction suspension equipment, after vacuumizing, fill in argon, carry out vacuum induction suspension melting, and obtain Nb-16Si-22Ti suspension melting large ingot after cooling;

[0040] Step three, wire cutting round bar:

[0041] Use wire cutting to cut the Nb-16Si-22Ti alloy large-size ingot, obtain a round bar with a diameter of 30mm and a length of 40mm, and a round bar with a diameter of 20mm and a length of 80mm;

[0042] Step four, electromagnetic cold crucible large-size ingot melting:

[0043] Step four one: connect a round bar with a diameter of 30mm with the pulling rod at the bottom of the vacuum furnace;

[0044] Step four two: connect another round bar with a diameter of 20mm with the feeding rod at the top;

[0045] Step four three: after vacuumizing, fill in argon, start the melting power, and carry out ingot melting at a certain pulling speed and feeding speed;

[0046] Step five, ultrasonic assisted electromagnetic cold crucible directional solidification:

[0047] Step five one: start the ultrasonic device;

[0048] Step five two: at a certain speed, carry out pulling and feeding movement of the melted round bar, and obtain a 200mm long directional solidification Nb-16Si-22Ti ingot;

[0049] Step six, cooling of the directional ingot:

[0050] After the directional solidification process is stopped, the ultrasonic device is turned off, and the cooling time is 30min, thus the preparation of the Nb-Si-based alloy large-size ingot is completed.

[0051] The present embodiment can realize the preparation of large-size directional ingot of Nb-16Si-22Ti alloy by electromagnetic cold crucible directional solidification. Electromagnetic induction can provide a large temperature gradient, and electromagnetic force can promote the uniform mixing of each element in the molten pool during smelting, which is beneficial to the directional growth of the microstructure of Nb-16Si-22Ti alloy.

[0052] The present embodiment can inhibit the strong convection at the solid-liquid interface front by the acoustic streaming effect during ultrasonic melt processing, and the flow direction is opposite to that during electromagnetic cold crucible directional solidification. By utilizing the principle of promoting the flow in opposite directions, the strong convection at the solid-liquid interface front can be inhibited, the effect of temperature reduction of the solid-liquid interface front by strong convection can be reduced, a higher temperature gradient can be provided for the directional solidification process, and the directional growth of the tough and brittle phases can be facilitated.

[0053] Specific embodiment two: combination Figure 1 The present embodiment is described. The elemental raw materials in step one of the present embodiment are composed of Nb, Si and Ti, and the total weight is 1 kg. The Nb raw material is 793.097 g, the Si raw material is 61.870 g, and the Ti raw material is 145.033 g. The Nb has a purity of 99.99% and is in the form of 4-6 mm flakes. The Si has a purity of 99.99% and is in the form of 3-5 mm particles. The Ti has a purity of 99.7% and is in the form of 3-25 mm sponge titanium.

[0054] The Nb-16Si-22Ti alloy in the present embodiment is the main alloy matrix component of Nb-Si-based alloy, which is generally composed of tough Nbss phase and brittle Nb3Si phase. The tough Nbss phase provides room temperature performance for the alloy, and the brittle Nb3Si phase can meet the requirements of high temperature performance.

[0055] The melting point of the Nb-16Si-22Ti alloy in the present embodiment is close to 2000K, and the melting point temperature is high. Vacuum induction suspension smelting can improve the melting efficiency and ensure a certain superheat, so that the alloy can achieve the best smelting effect. Under the action of electromagnetic stirring, the elements are uniformly mixed, the composition of the obtained ingot is uniform, the segregation is less, and the ingot defects are less.

[0056] The other components and connection relationships are the same as those in specific embodiment one.

[0057] Specific embodiment three: combination Figure 1In this embodiment, the single-element raw material in step one is subjected to descaling and ultrasonic cleaning before vacuum induction suspension smelting. The ultrasonic cleaning time is 10-15 min, the frequency is 30-40 kHz, the power is 200-250 W, and the cleaning liquid is alcohol. This setting can shake off and clean the oxide scale and external impurities on the surface of the single element, remove impurities from the single-element raw material, and better preserve the purity of the raw material. The other components and connection relationships are the same as those in embodiment one or two.

[0058] Embodiment four: combination Figure 1 In this embodiment, when step two is subjected to vacuum induction suspension smelting, the vacuum induction suspension furnace maintains a pressure of 5x10 -4 Pa in the furnace; the frequency of the vacuum induction suspension furnace is 80 Hz; the frequency power of the vacuum induction suspension furnace is 100 kW; and the smelting time of the vacuum induction suspension furnace is 20 min. This setting can achieve sufficient melting and uniform mixing of the single-element raw material, and a certain smelting time can weaken the segregation of the prepared ingot. The other components and connection relationships are the same as those in embodiment one, two, or three.

[0059] Embodiment five: combination Figure 1 In this embodiment, when the ingot in step four three is subjected to melting, the electromagnetic cold crucible directional solidification internal pressure is 200-300 Pa; the upper end of the 30 mm diameter round bar is at the center of the coil, and the lower end of the 20 mm diameter round bar is parallel to the first turn of the coil; the coil frequency of the electromagnetic cold crucible is 50 kHz, and the power is 45 kW; the large-size ingot reaches the incandescent state, i.e., melting; after the large-size ingot is melted, the power is maintained at 60 kW for 5 min. This setting can make the ingot melt, the temperature is more uniform, the melt is kept at a certain superheat, the temperature gradient is constant, a certain temperature gradient is reached, and the melt convection is stable. The other components and connection relationships are the same as those in embodiment one, two, three, or four.

[0060] Embodiment six: combination Figure 1In the step four three of the embodiment, the ultrasonic wave with the frequency of 20-30 kHz and the displacement amplitude of 20 μm is applied in the preparation of the directional solidification sample at the low pulling rate. The ultrasonic wave with the frequency of 30-40 kHz and the displacement amplitude of 20 μm is applied at the bottom of the directional solidification sample at the high pulling rate. In this way, the flow velocity of the solid-liquid interface front is low at the low pulling rate, and the flow range is small. The corresponding flow range of the applied ultrasonic wave is set to suppress the flow. The frequency of 20-30 kHz is applied at the bottom at the high pulling rate. The flow velocity of the solid-liquid interface front is high, and the flow range is large. In order to expand the flow range of the ultrasonic wave and better suppress the flow of the solid-liquid interface front, the frequency of 30-40 kHz is applied at the bottom. The other components and connection relationships are the same as those in the first, second, third, fourth or fifth embodiment.

[0061] The seventh embodiment is combined with the first embodiment. Figure 1 In the step four three of the embodiment, the low pulling rate is less than 0.8 mm / min, and the flow velocity of the solid-liquid interface front is less than 0.5 m / s. The high pulling rate is 0.8-2.0 mm / min, and the flow velocity of the solid-liquid interface front is 0.7-1.8 m / s. In this way, the directional solidification ingot with different solidification speeds can be prepared. Since the solidification speeds are different, the flow velocities of the solid-liquid interface front are different. The flow range is determined to provide a basis for the subsequent application of the ultrasonic wave. The other components and connection relationships are the same as those in the first, second, third, fourth, fifth or sixth embodiment.

[0062] The eighth embodiment is combined with the first embodiment. Figure 1 In the step five one of the embodiment, the ultrasonic wave frequency is 20-40 kHz, and the ultrasonic wave displacement amplitude is 20 μm. In this way, the flow of the solid-liquid interface front can be suppressed by adjusting the frequency of the ultrasonic wave to change the flow range. Different frequencies are suitable for the flow of the solid-liquid interface front corresponding to different pulling rates. The other components and connection relationships are the same as those in the first, second, third, fourth, fifth, sixth or seventh embodiment.

[0063] The ninth embodiment is combined with the first embodiment. Figure 1 In the step five two of the embodiment, the movement speed of the feeding rod is 2.25 times the movement speed of the pulling rod, which is determined by the cross-sectional area of the connected round bar and the feeding rod. In this way, the movement speed of the feeding rod and the pulling rod is matched to realize the material supplement in the directional solidification process, so as to ensure the surface quality and the ingot quality of the prepared ingot and avoid the lack of meat. The other components and connection relationships are the same as those in any one of the first to eighth embodiments.

[0064] The tenth embodiment is combined with the first embodiment. Figures 1 to 4Embodiments of the present application are described:

[0065] Embodiment one: the ultrasonic wave assisted electromagnetic cold crucible directional solidification Nb-Si based alloy large size ingot preparation method in this embodiment is completed according to the following steps:

[0066] Step one, batching: taking metal elemental raw materials according to the atomic percentage of Nb-16Si-22Ti; the metal elemental raw materials are composed of Nb, Si and Ti, the total weight is 1 kg, the Nb raw material is 793.097 g, the Si raw material is 61.870 g, and the Ti raw material is 145.033 g, and the Nb is 4-6 mm flaky with a purity of 99.99%, the Si is 3-5 mm granular with a purity of 99.99%, and the Ti is 3-25 mm sponge titanium with a purity of 99.7%;

[0067] The metal elemental raw materials are subjected to descaling treatment and ultrasonic cleaning treatment; the ultrasonic cleaning treatment time is 10-15 min, the frequency is 30 kHz-40 kHz, the power is 200 W-250 W, and the cleaning liquid is alcohol;

[0068] Step two, vacuum induction suspension melting: the metal elemental raw materials are placed into a vacuum induction suspension device, vacuum is drawn after argon is filled, vacuum induction suspension melting is carried out, and Nb-16Si-22Ti suspension melting large ingot is obtained after cooling; the vacuum induction suspension furnace keeps the pressure in the furnace at 5*10 -4 Pa; the frequency of the vacuum induction suspension furnace is 80 Hz; the frequency power of the vacuum induction suspension furnace is 100 kW, and the melting time of the vacuum induction suspension furnace is 20 min.

[0069] Step three, using the vacuum induction suspension melting to prepare a large size ingot of Nb-16Si-22Ti alloy, using the electric spark wire cutting to obtain a round bar with a diameter of 30 mm and a length of 40 mm and a round bar with a diameter of 20 mm and a length of 80 mm;

[0070] Step four, electromagnetic cold crucible large size ingot melting: one round bar with a diameter of 30 mm is connected with the pulling rod at the bottom of the vacuum furnace, and the other round bar with a diameter of 20 mm is connected with the feeding rod at the top, vacuum is drawn after argon is filled, and the power is turned on. The internal pressure of the electromagnetic cold crucible directional solidification is 200 Pa-300 Pa; the upper end of the round bar with a diameter of 30 mm is at the center position of the coil, the lower end of the round bar with a diameter of 20 mm is parallel to the first turn of the coil, the frequency of the coil of the electromagnetic cold crucible is 50 kHz, and the power is 45 kW; the large size ingot reaches the incandescent state, which is the melting; after the large size ingot is melted, the power is maintained at 60 kW for 5 min.

[0071] Step five, ultrasonic assisted electromagnetic cold crucible directional solidification: open the ultrasonic device, the ultrasonic frequency is 25 kHz, the ultrasonic displacement amplitude is 20 μm, the round bar after melting is drawn and fed to obtain a 200 mm long directional solidification Nb-16Si-22Ti ingot; the drawing rod movement speed is 0.6 mm / min, the solid-liquid interface front flow rate is 0.35 m / s; the feeding rod movement speed is 1.35 mm / min; the drawing movement time is 5.56 h;

[0072] Step six, after the solidification process is stopped, the ultrasonic device is closed, and the cooling time is 30 min.

[0073] Example two: the ultrasonic assisted electromagnetic cold crucible directional solidification Nb-Si based alloy large size ingot preparation method of the embodiment is completed according to the following steps:

[0074] Step one, ingredient: taking metal elemental raw materials according to the atomic percentage of Nb-16Si-22Ti; the metal elemental raw materials are composed of Nb, Si and Ti, and the total weight is 2 kg, the Nb raw material is 1586.194 g, the Si raw material is 123.74 g, and the Ti raw material is 290.066 g, and the Nb is 4-6 mm flaky with a purity of 99.99%, the Si is 3-5 mm granular with a purity of 99.99%, and the Ti is 3-25 mm sponge titanium with a purity of 99.7%;

[0075] The elemental raw materials are subjected to descaling treatment and ultrasonic cleaning treatment; the ultrasonic cleaning treatment time is 10-15 min, the frequency is 30 kHz-40 kHz, the power is 200 W-250 W, and the cleaning liquid is alcohol;

[0076] Step two, vacuum induction suspension melting: the metal elemental raw materials are put into the vacuum induction suspension equipment, after vacuumizing, argon is filled, vacuum induction suspension melting is carried out, and after cooling, a Nb-16Si-22Ti suspension melting large ingot is obtained; the vacuum induction suspension furnace keeps the pressure in the furnace at 5×10 -4 Pa; the vacuum induction suspension furnace frequency is 80 Hz; the vacuum induction suspension furnace frequency power is 100 kW, and the vacuum induction suspension furnace melting time is 20 min.

[0077] Step three, using the vacuum induction suspension melting to prepare a large size ingot of Nb-16Si-22Ti alloy, using the electric spark wire cutting to obtain a round bar with a diameter of 30 mm and a length of 40 mm and a round bar with a diameter of 20 mm and a length of 80 mm;

[0078] Step four, electromagnetic cold crucible large size ingot melting: a diameter of 30mm round bar is connected with the pulling rod at the bottom of the vacuum furnace, another diameter of 20mm round bar is connected with the feeding rod at the top, after vacuumizing, argon is filled, and the power is started; the electromagnetic cold crucible directional solidification internal pressure is 200Pa-300Pa; the upper end of the diameter of 30mm round bar is at the center position of the coil, the lower end of the diameter of 20mm round bar is parallel to the first turn of the coil; the coil frequency of the electromagnetic cold crucible is 50kHz, and the power is 50kW; the large size ingot reaches the incandescent state, that is, the melting is started; after the large size ingot is melted, the power is maintained at 60kW for 5min.

[0079] Step five, ultrasonic assisted electromagnetic cold crucible directional solidification: the ultrasonic device is started, the ultrasonic frequency is 30kHz, the ultrasonic displacement amplitude is 20μm, the round bar after melting is subjected to pulling and feeding movement, and a 200mm long directional solidification Nb-16Si-22Ti ingot is obtained; the pulling rod movement speed is 1.5mm / min, the solid-liquid interface front flow rate is 1.2m / s; the feeding rod movement speed is 3.375mm / min; the pulling movement time is 0.99h;

[0080] Step six, after the directional solidification process is stopped, the ultrasonic device is turned off, and the cooling time is 30min.

[0081] The present application can solve the problem of strong convection at the solid-liquid interface front of the electromagnetic cold crucible directional solidification, thereby reducing the temperature gradient at the solid-liquid interface front, the axial temperature gradient is maintained at 63K / mm-65K / mm, the large temperature gradient directional solidification can be realized, the directional growth of the structure is promoted, the large size directional ingot of the ductile phase and the brittle phase directional coupling growth is obtained, and the fracture toughness of the Nb-Si alloy is improved.

[0082] The embodiment one and the embodiment two respectively select low pulling rate and high pulling rate to respectively illustrate the specific process of the preparation method of the directional solidification ingot prepared by introducing ultrasonic treatment under different pulling rates. By introducing ultrasonic assisted preparation, the convection at the solid-liquid interface front under different pulling rates is inhibited, the white Nbss phase and the black silicide phase are coupled to grow, the coupling growth of the ductile and brittle phases is realized, the phase interface is along a single direction, and the growth direction inclination degree is weakened. Under the condition of ultrasonic assisted preparation, the fracture toughness of the directional solidification ingot prepared by low pulling rate is 30MPa·m 1 / 2 , which is improved by 150%, and the fracture toughness of the directional solidification ingot prepared by low pulling rate is 28MPa·m 1 / 2 , which is improved by 133%.

[0083] Although the present application has been described in connection with the preferred embodiment thereof with reference to the drawings, it will be apparent to those skilled in the art that variations and modifications of the application can be effected thereto without departing from the spirit and scope of the application. Therefore, the scope of the application should be limited only by the appended claims.

Claims

1. A method for preparing large-size Nb-Si based alloy ingots by electromagnetic cold crucible directional solidification, characterized in that: It includes the following steps: Step 1, Ingredient Preparation: Take the elemental metal raw materials according to the atomic percentage of Nb-16Si-22Ti; The elemental raw materials in step one consist of Nb, Si, and Ti, with a total weight of 1 kg. The Nb raw material is 793.097 g, the Si raw material is 61.870 g, and the Ti raw material is 145.033 g. The Nb is 4-6 mm flakes with a purity of 99.99%, the Si is 3-5 mm particles with a purity of 99.99%, and the Ti is 3-25 mm sponge titanium with a purity of 99.7%. Step 2: Vacuum induction levitation melting: The elemental raw material is placed in a vacuum induction suspension device, vacuumed, and then filled with argon gas for vacuum induction suspension melting. After cooling, Nb-16Si-22Ti suspension melting ingot is obtained. Step 3: Wire cutting of round bars: By using electrical discharge wire cutting of a large-sized Nb-16Si-22Ti alloy ingot, a round bar with a diameter of 30mm and a length of 40mm and a round bar with a diameter of 20mm and a length of 80mm were obtained. Step 4: Initiation of melting large-size ingots in electromagnetic cold crucible: Step 41: Connect a 30mm diameter round rod to the pull rod at the bottom of the vacuum furnace; Step 42: Connect another round bar with a diameter of 20mm to the top feed bar; Step 43: After vacuuming, argon gas is introduced, the melting power is turned on, and the ingot melting is started at a certain pulling speed and feeding speed. At low pulling speed, ultrasonic waves with a frequency of 20kHz-30kHz and a displacement amplitude of 20μm are applied during the preparation of the directional solidification sample; at high pulling speed, ultrasonic waves with a frequency of 30kHz-40kHz and a displacement amplitude of 20μm are applied to the bottom of the directional solidification sample. Low pulling rate is defined as a pulling rate less than 0.8 mm / min and a flow velocity at the solid-liquid interface front less than 0.5 m / s; high pulling rate is defined as a pulling rate of 0.8 mm / min to 2.0 mm / min and a flow velocity at the solid-liquid interface front of 0.7 m / s to 1.8 m / s. Step 5: Ultrasonic-assisted electromagnetic cold crucible directional solidification: Step 51: Turn on the ultrasonic device; Step 52: At a certain speed, the round bar after melting is pulled and fed to obtain a 200mm long directional solidification Nb-16Si-22Ti ingot; Step Six: Cooling of the Directional Casting Ingot: After the directional solidification process is stopped, the ultrasonic device is turned off, and the cooling time is 30 minutes. At this point, the preparation of the large-size Nb-Si based alloy ingot is completed.

2. The method for preparing large-size Nb-Si based alloy ingots by electromagnetic cold crucible directional solidification according to claim 1, characterized in that: Before vacuum induction suspension melting, the elemental raw materials in step one are subjected to descaling and ultrasonic cleaning.

3. The method for preparing large-size Nb-Si based alloy ingots by electromagnetic cold crucible directional solidification according to claim 2, characterized in that: During step two, when performing vacuum induction levitation melting: The vacuum induction levitation furnace maintains an internal pressure of 5×10⁻⁶. -4 Pa; The vacuum induction levitation furnace has a frequency of 80Hz; The vacuum induction suspension furnace has a frequency power of 100kW; The melting time in the vacuum induction levitation furnace is 20 minutes.

4. The method for preparing large-size Nb-Si based alloy ingots by electromagnetic cold crucible directional solidification according to claim 3, characterized in that: When the ingot melting begins in step four-three: The internal pressure of the electromagnetic cold crucible during directional solidification is 200Pa-300Pa; The upper end of a 30mm diameter rod is located at the center of the coil, and the lower end of a 20mm diameter rod is parallel to the first turn of the coil. The coil frequency of the electromagnetic cold crucible is 50kHz and the power is 45kW. The melting of large-sized ingots is initiated when they reach incandescence. After the melting of large-sized ingots is initiated, the power supply is maintained at 60kW for 5 minutes.

5. The method for preparing large-size Nb-Si based alloy ingots by electromagnetic cold crucible directional solidification according to claim 4, characterized in that: When turning on the ultrasonic device in step 5: the ultrasonic frequency is 20-40kHz and the ultrasonic displacement amplitude is 20μm.

6. The method for preparing large-size Nb-Si based alloy ingots by electromagnetic cold crucible directional solidification according to claim 5, characterized in that: In step 52, the speed of the feeding rod is 2.25 times the speed of the pull rod.

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