Preparation method and device of TiAl-based alloy casting

Abstract

The invention provides a preparation method of a TiAl-based alloy casting which takes a TiAl intermetallic compound as a matrix and is added with multi-component alloy elements. The preparation method comprises the following steps: S1, carrying out suspension smelting on Ti and Al to form a TiAl alloy matrix; s2, alloy elements are subjected to suspension smelting to form an alloy element intermediate alloy; and S3, the TiAl alloy matrix and the alloy element intermediate alloy are subjected to suspension smelting to form the TiAl-based alloy casting. A step-by-step smelting method is adopted for smelting of a TiAl alloy matrix, and the process solves the problem that Ti and Al with the melting point difference of 1000 DEG C are smelted through a suspension smelting technology; a refractory metal intermediate alloy with the melting point similar to that of a TiAl alloy matrix is used as an additive, and the problem that refractory metal components with the very high melting point are added into the TiAl alloy matrix in the suspension smelting process is solved; the TiAl-based alloy casting is prepared by using a centrifugal casting technology combined with suspension smelting equipment, so that metallurgical defects formed in casting blanks are eliminated, and excellent materials can be prepared.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and in particular relates to a method and a device for preparing a TiAl-based alloy casting. Background Art

[0002] TiAl-based alloy refers to an alloy with TiAl intermetallic compound as the matrix and a certain amount of alloying elements added. TiAl-based alloy can be made of TiAl X -M (X = 0.15 ~ 0.55at.) indicates that M refers to alloying elements, which include one or more elements, such as M1, M2, M3, etc., and the content of each element is 0-10wt%. Commonly used alloying elements include Nb, W, Mo, Ta, Cr, Mn, etc.

[0003] So far, the TiAl-based alloys that have been developed include Ti-48Al-1V-0.3C, Ti-48Al-2Cr-2Nb, Ti-47Al-2(Cr,Mn)-2Nb, Ti-(45-47)Al-2Nb-2Mn-0.8TiB2, Ti-47Al-3.5(Nb,Cr,Mn)-0.8(Si,B), Ti-47Al-2W--0.5Si, Ti-47Al-5(Cr,Nb,Ta), etc. Casting alloys also include Ti-46.2Al-2Cr-3Nb-0.2W (K5) and Ti-(45-47)Al-(1-2)Cr-(1-5)Nb-(0-2)(W, Ta, Hf, Mo, Zr)-(0-0.2)B-(0.03-0.3)C-(0.03-0.2)Si-(0.1-0.25)O and other forging alloys, as well as alloys based on Ti2Al, such as Ti-22Al-24Nb-0.5Mo (atomic fraction, %). These alloys have become the best materials for the aviation industry.

[0004] Titanium metal is an active element, and suspension smelting technology is recognized as one of the best means of smelting Ti and Ti alloys. Therefore, smelting with suspension smelting technology has technical advantages. However, there are also technical difficulties in smelting TiAl-based alloys using suspension smelting technology, which is related to the large melting point difference between Ti and Al - the melting point difference is about 1000℃. When Ti and Al are placed in a crucible and heated, Al melts first to form a low-temperature molten pool, and the high-melting-point Ti bubbles are difficult to melt in the molten pool - in the suspension smelting process, after the metal melts to form a molten pool, the smelting temperature is difficult to increase, even if the heating power is increased, the overheating degree is only more than 100 degrees at most.

[0005] The alloying elements M added to TiAl-based alloys are mostly refractory metals, such as Nb, W, Mo, Ta, Cr, etc., most of which have melting points much higher than the TiAl alloy matrix, and their density is much higher than Ti and Al. Therefore, dissolving these alloying elements into the TiAl alloy matrix and forming a material with uniform composition also requires specific technical methods.

[0006] After smelting, TiAl-based alloys need to be cast into dense billets. However, this alloy shrinks significantly during solidification and is very brittle, so it is easy to form metallurgical defects such as shrinkage cavities, micropores, porosity and cracks.

[0007] Therefore, there is an urgent need for a method and device for preparing TiAl-based alloy castings that can solve the above problems. Summary of the invention

[0008] The invention provides a method for preparing a TiAl-based alloy casting which takes a TiAl intermetallic compound as a matrix and adds alloy elements.

[0009] In order to solve the problems mentioned in the background technology, the smelting of the TiAl matrix of the present invention can adopt a step-by-step smelting method, that is, first smelting a high-Ti and low-Al alloy, and then adding Al to obtain an alloy that meets the composition requirements of the TiAl matrix. Most of the alloy elements are refractory metals, so they are first smelted into an intermediate alloy with a lower melting point and then added to the TiAl matrix. In order to cast TiAl-based alloy castings without metallurgical defects, a vertical centrifugal casting device is installed in the smelting chamber, and the mold is installed on the edge of the centrifugal disk. During the casting process, the centrifugal disk is started to rotate, and after the alloy liquid is injected from the crucible into the center injection pipe of the mold, it flows into the mold and solidifies under the action of centrifugal force.

[0010] The present invention provides a method for preparing a TiAl-based alloy casting with a TiAl intermetallic compound as a matrix and a multi-component alloy element M added thereto, comprising the following steps:

[0011] S1, suspension melting Ti and Al to form a TiAl alloy matrix;

[0012] S2, smelting the alloy element M in suspension to form an alloy element master alloy;

[0013] S3, levitation melting the TiAl alloy matrix, the alloy element master alloy and the remaining alloy elements with a melting point lower than 1800° C. to form a TiAl-based alloy.

[0014] 2. The preparation method according to claim 1, characterized in that step S1 comprises the following steps:

[0015] S11, melting all the high melting point Ti and part of the low melting point Al to form a TiAl-based master alloy;

[0016] S12, adding Al once, twice or multiple times, and finally obtaining a TiAl alloy matrix meeting the composition requirements of the TiAl alloy matrix;

[0017] Among them, the volume of Al material added in each step of the smelting process is V Al Should not be greater than the volume V of the metal Ti or TiAl-based master alloy Ti , with V Al ≤1 / 2V Ti For the best.

[0018] Furthermore, the TiAl-based master alloy ingot formed in step S11 is turned over and then Al is added;

[0019] And / or, the TiAl alloy matrix ingot meeting the composition requirements obtained by smelting in step S12 is turned over and remelted once more.

[0020] Further, in step S2,

[0021] S21, if the melting point of the alloy element M is not higher than 1800°C, the alloy element M is directly added to the TiAl alloy matrix for melting;

[0022] S22, if the alloy elements M include components with a melting point higher than 1800°C, one, two or more components with higher melting points are combined with one, two or more components in the remaining alloy components, and first smelted into a master alloy with a melting point lower than 1800°C. Depending on the types and quantities of the alloy components, one, two or more master alloys may be smelted;

[0023] S23, if the alloying elements M include a component with a melting point higher than 1800°C and the combination of the alloying elements M cannot form an intermediate alloy with a melting point lower than 1800°C, then the high melting point component M h Combined with Ti and / or Al for smelting to obtain a master alloy M-Ti, M-Al or M-(Ti,Al) with a melting point below 1800°C;

[0024] Among them, in step S1, the amount of Ti material and / or Al material added when smelting the Ti-Al alloy matrix should be deducted from the amount of Ti material and / or Al material required for smelting M-Ti, M-Al or M-(Ti,Al) in S2.

[0025] Further, it is characterized in that, for the composition of the selected intermediate alloy with a suitable melting point, if the volume V of the low melting point component M1 is Ml Not less than the volume V of the high melting point component Mh Mh , then step S22 includes the following steps:

[0026] S221, combining high melting point components and part of low melting point components in the alloy element M, and smelting to obtain a primary master alloy;

[0027] S222, starting from the primary master alloy, successively adding the remaining components in the alloy element M to obtain secondary, tertiary or multiple master alloys, and finally obtaining a master alloy of alloy elements that meets the composition requirements;

[0028] Among them, in the batching method of each step of the smelting process, the volume ratio of the low melting point component to the high melting point component or the intermediate alloy is ensured to be ≤1, and ≤1 / 2 is the best.

[0029] Further, the alloy element intermediate alloy ingot in step S2 is crushed and added to a water-cooled copper crucible filled with the TiAl alloy matrix in step S1 for smelting to obtain the TiAl-based alloy casting in step S3.

[0030] The present invention also provides a preparation device for TiAl-based alloy castings, which is applied to the above preparation method, and comprises a water-cooled copper crucible installed in a vacuum melting chamber, and an induction coil arranged around the water-cooled copper crucible;

[0031] Wherein, a feeder which is in sealed communication with the vacuum melting chamber is arranged above the vacuum melting chamber, and a discharge port of the feeder is connected to a water-cooled copper crucible;

[0032] A centrifugal casting device is installed below the water-cooled copper crucible, wherein the centrifugal casting device includes a centrifugal disk installed at the bottom of the vacuum melting chamber, a mold device installed on the upper end surface of the centrifugal disk, a drive shaft passing through the bottom of the vacuum melting chamber through a vacuum dynamic seal and a bearing, and a centrifugal drive device that is transmission-connected to the drive shaft.

[0033] Furthermore, the feeder includes a feeding barrel, a feeding pipe, a spiral pushing device and a feeding drive device. The feeding barrel is installed above the vacuum melting chamber. One end of the feeding pipe is sealed and connected to the feeding barrel, and the other end extends into the interior of the vacuum melting chamber and is located above the water-cooled copper crucible. The spiral pushing device is arranged in the feeding barrel and is connected to the feeding drive device in a transmission manner.

[0034] Furthermore, the mold device includes a pouring cup, a center pouring pipe, a runner and a plurality of membrane shells, wherein the pouring cup and the center pouring pipe are vertically arranged at the center of the centrifugal disk, and a plurality of membrane shells located at the end of the runner are connected to the center pouring pipe through the runner;

[0035] Or, the mold device includes a pouring cup, a center pouring pipe, a runner and a plurality of mold tubes, the plurality of mold tubes are installed near the edge of the centrifugal disk, the axes of the mold tubes are radially inclined downward and outward, the upper ends of the mold tubes are connected to the runner, and the pipe openings at the lower ends are equipped with detachable head plugs.

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] 1. The present invention adopts a step-by-step smelting method for smelting the TiAl alloy matrix, that is, firstly smelting a high-Ti and low-Al alloy, and then adding Al once or twice, to finally obtain an alloy that meets the composition requirements of the TiAl alloy matrix. This process solves the difficulty of smelting Ti and Al with a melting point difference of 1000°C using a suspension smelting technology.

[0038] 2. The present invention uses a refractory metal master alloy having a melting point close to that of the TiAl alloy matrix as an additive, thereby solving the difficulty of adding a refractory metal component having a very high melting point to the TiAl alloy matrix during suspension smelting.

[0039] 3. The present invention uses a centrifugal casting technology combined with a suspension smelting device to prepare TiAl-based alloy castings, thereby eliminating metallurgical defects formed in the casting blank and being able to prepare rods with excellent material quality.

[0040] 4. The suspension melting technology eliminates the contamination of the crucible material, can achieve very high melting temperatures, and has a strong electromagnetic stirring effect. These characteristics provide favorable conditions for melting TiAl-based alloys with high component activity, high melting temperature, large component melting point and density differences, and a large number of components. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0042] Figure 1 Schematic diagram of suspension smelting in a water-cooled copper crucible;

[0043] Figure 2 A diagram of a centrifugal casting device using a ceramic membrane shell tree as a mold device;

[0044] Figure 3 A diagram of a centrifugal casting apparatus for casting bars equipped with a tubular mold.

[0045] In the figure, 1-water-cooled copper crucible, 2-vacuum melting chamber, 3-induction coil, 4-molten pool, 5-feeder, 6-feeding barrel, 7-feeding tube, 8-screw pushing device, 9-feeding drive device, 10-centrifugal disk, 11-mold device, 12-vacuum dynamic seal and bearing, 13-drive shaft, 14-centrifugal drive device, 15-pouring cup, 16-center injection tube, 17-sprue, 18-mold, 19-motor, 20-reducer, 21-transmission device, 22-mold tube, 23-head plug, 24-clip, 25-ring. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0047] In this embodiment, the TiAl-based alloy refers to an alloy in which a certain amount of alloying elements is added to the TiAl intermetallic compound as a matrix. X -M alloy (X = 0.35 ~ 0.55at.) means that the content of Al in this alloy is about 48 ~ 68wt.%. M refers to alloying elements, which include one or more elements, such as M1, M2, M3, etc., and the content of each element is 0 ~ 10wt%. Commonly used alloying elements are mostly high melting point metals, such as Nb, W, Mo, Ta, Cr, Mn, etc.

[0048] It should be noted that suspension melting technology is the most effective means of melting TiAl-based alloys. Figure 1 The suspension smelting device includes a water-cooled copper crucible 1 with axial petals installed in a vacuum smelting chamber 2. The current input by the induction power supply generates an electromagnetic field in the induction coil 3 surrounding the water-cooled copper crucible 1. The electromagnetic field passes through the side wall of the water-cooled copper crucible 1 to heat the material in the water-cooled copper crucible 1 to form a molten pool 4, and generates a suspension force perpendicular to the axial direction of the water-cooled copper crucible 1 on the molten pool 4, so that the molten pool 4 is separated from the inner wall of the water-cooled copper crucible 1 under the action of the suspension force. In order to prevent gas contamination of the material, the smelting process is carried out in a vacuum or inert gas atmosphere.

[0049] The suspension melting technology eliminates the contamination of the molten pool 4 by the crucible material in other melting processes, and guarantees the purity of the material, which is very important for the melting of highly active Ti and Al and their alloys. The suspension melting technology also eliminates the limitation of the crucible material in terms of its ability to withstand high temperatures, so it can be used for very high melting temperatures. X The alloying element M in the -M alloy is mostly refractory metal, requiring a very high melting temperature. Suspension melting uses electromagnetic fields to heat the molten pool, which has a strong electromagnetic stirring effect, which is very suitable for TiAl with many components and very different melting points and densities between components. X The smelting of TiAl-M alloy plays a more important role. Suspension smelting has no restrictions on the shape and size of the smelted materials, and can also directly produce products of various shapes using different casting techniques after smelting. This is also the advantage of using suspension smelting technology to melt TiAl-based alloys.

[0050] In this embodiment, TiAl is melted using the suspension melting technique. X The preparation method of the TiAl-M alloy casting comprises the following steps: S1, smelting a TiAl alloy matrix, that is, an alloy of Ti and Al; S2, adding an alloy element M or a master alloy containing M to the TiAl alloy matrix.

[0051] It is understandable that the suspension smelting technology has a characteristic: in the suspension smelting equipment, as the power increases, the solid material can reach a very high temperature until the material melts. However, when the power is increased after the material melts, it is difficult for the temperature of the molten pool to continue to rise, and the superheat of the molten pool generally does not exceed 100°C.

[0052] Therefore, when melting an alloy composed of a high-melting-point component A and a low-melting-point component B, if the melting points of the two components differ greatly, for example, greater than 300°C, and the volume of component B is significantly greater than that of component A, during the heating process, component B first melts to form a large molten pool, while the smaller high-melting-point component A remains in a solid state. In this case, due to the presence of a large molten pool of component B, further increasing the heating power cannot significantly increase the temperature of the material, so the solid component A bubbles in the low-temperature molten pool of component B are difficult to melt.

[0053] In order to solve the above problems, this embodiment adopts a step-by-step smelting method to smelt the AB alloy in a suspension smelting device: first, all the A components and part of the B components are used to smelt the master alloy, and then the remaining component B is added to the master alloy to obtain an AB alloy that meets the composition requirements. When smelting the master alloy, the amount of the added B component should ensure that its volume V B Obviously smaller than the volume V of all A components A , for example, V B / V A ≤1, and V B / V A ≤1 / 2 is the best. In this way, even if the B component melts first, the volume of the liquid it forms is not large, and it does not affect the temperature rise process of the solid A component when the power is increased. Therefore, the temperature of the material can continue to rise until the A component is completely melted, so that the two liquid components can be fused into a uniform alloy.

[0054] Therefore, the present invention adopts the step-by-step smelting technology for smelting the TiAl alloy matrix and the intermediate alloy of alloy elements.

[0055] In the TiAl alloy matrix, Ti and Al have a large difference in melting points - the melting point of Ti is 1670°C, while the melting point of Al is only 660°C, with a melting point difference of about 1010°C. For the phase diagram of Ti-Al binary alloy, please refer to "China Nonferrous Metals Industry Association, Tang Renzheng, Tian Rongzhang, Binary Alloy Phase Diagram and Intermediate Phase Crystal Structure, Central South University Press, 2009.4, P81". The process of smelting the TiAl alloy matrix by the step-by-step smelting method, that is, in step S1, all the high-melting-point Ti and part of the low-melting-point Al are first smelted to form an intermediate alloy; then Al is added once or twice, and finally an alloy that meets the composition requirements of the TiAl alloy matrix is ​​obtained. It should be noted that the composition of the TiAl alloy matrix designed in this embodiment is centered on the γ-TiAl phase, and the melting point is in the range of 1500±200°C.

[0056] Specifically, for the composition of TiAl X (X = 0.35 ~ 0.55at.) TiAl alloy, i.e., TiAl alloy with Al content of 48 ~ 68wt.%, Ti-Al binary alloy phase diagram see "China Nonferrous Metals Industry Association, Tang Renzheng, Tian Rongzhang, Binary Alloy Phase Diagram and Intermediate Phase Crystal Structure, Central South University Press, 2009.4, P81". First, melt Ti-(20 ± 5wt.%)Al alloy (referred to as intermediate alloy 1), and then turn the ingot of intermediate alloy 1 over and mix it with the remaining Al material 1, and melt to obtain a TiAl alloy matrix that meets the composition requirements.

[0057] Alternatively, the second step is to flip the ingot of the master alloy 1 and mix it with part of the Al material 2 in the remaining Al material 1, and smelt to obtain a Ti-Al alloy with an Al content of 40±5wt.% (referred to as the master alloy 2), and then, in the third step, flip the ingot of the master alloy 2 and mix it with the remaining Al material (i.e., the material of Al material 1 minus Al material 2), and smelt to obtain a TiAl alloy matrix that meets the composition requirements. In this embodiment, in order to ensure the uniformity of the composition, the ingot of the TiAl alloy matrix that meets the composition requirements obtained by the last step of smelting can be flipped and remelted again.

[0058] It should be noted that the so-called remaining Al material 1 refers to the amount of Al material required for the target composition of the TiAl alloy matrix minus the amount of Al material required for smelting the master alloy 1. The principle for determining the composition of the master alloy smelted in the first and second steps is that the volume V of the Al material added in each smelting process is Al It should be significantly smaller than the volume V of the high melting point material (metal Ti or Ti-Al master alloy) h , for example V Al / V h ≤1, V Al / Vh ≤1 / 2 is the best.

[0059] The above-mentioned step-by-step smelting method can be replaced by a method of adding Al with a feeder. In this method, the method of melting the master alloy 1 in the first step is the same as the first step of the above-mentioned step-by-step smelting method, except that the remaining Al material 1 is all loaded into the feeder 5, and after the smelting process of the material in the water-cooled copper crucible 1 is completed and a molten pool of the master alloy 1 is formed, the remaining Al material is gradually added from the feeder 5 to the water-cooled copper crucible 1 until the Al material in the feeder 5 is all added to the water-cooled copper crucible 1, and all melted in the water-cooled copper crucible 1 to form a molten pool 4 with uniform composition.

[0060] It should be noted that the process of adding Al material from the feeder 5 to the water-cooled copper crucible 1 must be sufficiently slow to prevent Al from forming a large-area low-temperature molten pool in the water-cooled copper crucible 1, causing the melted material to precipitate and solidify, and the temperature cannot be raised again.

[0061] In the above method, see Figure 1 The feeder 5 is arranged to be in sealed communication with the vacuum melting chamber 2 so that the feeding process does not destroy the vacuum condition or the inert gas atmosphere condition of the melting process. The structural design of the feeder 5 should ensure that the feeding process is smooth and does not get stuck, and should ensure that the feeding speed can be controlled. It can be understood that any structure that meets the above requirements can be used as the feeder 5 of this embodiment. For example, Figure 1 As shown, the spiral feeder 5 includes a feeding barrel 6, a feeding pipe 7, a spiral pushing device 8 and a feeding drive device 9. When using the spiral feeder 5, it is required that the Al material loaded into the feeder 5 has a small and uniform particle size and a smooth surface, otherwise the material will get stuck during the feeding process.

[0062] After smelting the Ti-Al alloy matrix, alloying elements M need to be added. M can be one, two or more alloying elements M1, M2, M3, M4, etc. Methods for adding alloying elements M include:

[0063] The components with lower melting points in the alloy elements M, for example, components with melting points below 1800°C, can be directly added to the Ti-Al alloy matrix. If there are components with higher melting points in the alloy elements M, for example, components with melting points above 1800°C, the components above 1800°C can be combined with other alloy components and first smelted into a master alloy with a lower melting point, for example, master alloys M1-M2, M1-M2-M3 or M1-M2-M3-M4 with melting points ≤ 1800°C, and then TiAl with the required composition can be obtained by adding such master alloys to the Ti-Al alloy matrix. X -M alloy. It is worth noting that most of the intermediate alloys with a melting point of ≤1800℃ are very brittle and can be easily pounded or smashed into small particles or powders, so they are relatively easy to melt into the TiAl alloy matrix.

[0064] The composition of the intermediate alloy with a suitable melting point can be determined from the liquidus-composition curve of the alloy phase diagram. Ml Not significantly less than the volume V of the high melting point component Mh Mh , for example V Ml / V Mh >1 / 2, even V Ml / V Mh >1, then the melting of this master alloy needs to adopt a step-by-step melting method, that is, all high melting point components Mh and part of low melting point components Ml are melted into a primary master alloy, and then the remaining components are added again or gradually until a master alloy with the required composition is obtained. In this process, the volume of each added low melting point component Ml should be significantly smaller than the volume V of the matrix G (high melting point components or primary master alloy, secondary master alloy, etc.) G , for example V Ml / V G ≤1, V Ml / V G ≤1 / 2 is the best.

[0065] If the combination of the alloy components M cannot form an intermediate alloy with a lower melting point, the high melting point component M h Combined with Ti and / or Al, the intermediate alloy M-Ti, M-Al or M-(Ti,Al) with a lower melting point is obtained by melting. By adding such intermediate alloy into the Ti-Al alloy matrix, a TiAl alloy with the required composition is obtained. X -M alloy. If this method is used to add the alloying element M, the amount of Ti material and / or Al material added when smelting the Ti-Al alloy matrix should be deducted from the amount of Ti material and / or Al material required for smelting M-Ti, M-Al or M-(Ti,Al).

[0066] The TiAl obtained by these methods is also smelted by suspension melting technology. X -M alloy is best turned over and remelted once or more to improve the uniformity of the alloy composition.

[0067] Taking Ti-48Al-2Cr-2Nb alloy as an example, in order to add the alloying elements Nb and Cr, it can be achieved by adding 50wt.% Nb-50wt.% Cr intermediate alloy; the melting point of Nb is 2460℃, the melting point of Cr is 1863℃, and the melting point of 50wt.% Nb-50wt.% Cr is about 1700℃, which is close to the melting point of TiAl alloy matrix. For the phase diagram of Cr-Nb binary alloy, please refer to "China Nonferrous Metals Industry Association, Tang Renzheng, Tian Rongzhang, Binary Alloy Phase Diagram and Intermediate Phase Crystal Structure, Central South University Press, 2009.4, P400". For other TiAl X -M alloy, the optional intermediate alloys include: 50wt.% Nb-50wt.% Mn (melting point of about 1500°C), 50wt.% W-50wt.% Al (melting point of about 1400°C, smelting in three times), 30wt.% V-70wt.% Cr (melting point of about 1750°C), 50wt.% W-50wt.% Cr (melting point of about 2200°C), 35wt.% Ta-65wt.% Cr (melting point of about 1700°C), 50wt.% Mo-50wt.% Al (melting point of about 1570°C, smelting in three times).

[0068] At the same time, as a multi-component alloy, TiAl-based alloy shrinks greatly during solidification, and the material is very brittle, and has a serious tendency to form metallurgical defects such as shrinkage cavities, micropores, looseness and cracks during the casting process.

[0069] This embodiment uses centrifugal casting technology to eliminate the above casting defects. Figure 2 A centrifugal casting device is installed below the suspension smelting equipment, wherein the centrifugal casting device includes a centrifugal disk 10 installed at the bottom of the vacuum melting chamber 2, a mold device 11 installed on the upper end surface of the centrifugal disk 10, a drive shaft 13 passing through the bottom of the vacuum melting chamber 2 through a vacuum dynamic seal and a bearing 12, and a centrifugal drive device 14.

[0070] Among them, the mold device 11 includes a pouring cup 15, a center injection tube 16, a runner 17 and a mold 18, wherein the pouring cup 15 and the center injection tube 16 are vertically arranged at the center of the centrifugal disk 10, and a plurality of molds 18 located at the end of the runner 17 are connected to the center injection tube 16 through the runner 17. The centrifugal drive device 14 includes a motor 19, a reducer 20 and a transmission mechanism 21, and the speed and rotation direction of the centrifugal disk 10 can be adjusted by a controller. After starting the motor 19, the centrifugal drive device 14 drives the centrifugal disk 10 to rotate through the drive shaft. At this time, the alloy liquid in the water-cooled copper crucible 1 is injected into the pouring cup 15 and the center injection tube 16. Under the action of centrifugal force, the alloy liquid enters the mold 18 through the runner 17 at a high speed and solidifies to form a dense billet.

[0071] like Figure 2As shown, the mold device 11 can be composed of a membrane shell component made of ceramic material, that is, the membrane shell component includes a pouring cup 15, a center pouring tube 16, a runner tube 17 and a plurality of membrane shells 18, which are prepared into components by a lost wax method from a ceramic slurry, and the components are sintered together to form a membrane shell tree, and the mold shell tree is firmly installed on the centrifugal disk 10. This mold device 11 is suitable for casting precision castings with smaller sizes and more complex shapes. The mold device 11 can also be made of metal materials. When the casting process starts, its pouring cup 15, center pouring tube 16, runner 17 and mold 18 can be made of cast iron, carbon steel and other materials. This mold device 11 is suitable for casting castings with larger sizes and simpler shapes.

[0072] TiAl-based alloy rods are often used in powder making technology and coating technology. The centrifugal casting method of this embodiment can also produce rods with no casting defects and excellent material quality. Figure 3 As shown, the mold device 11 used for casting TiAl-based alloy rods includes a pouring cup 15, a center pouring pipe 16, a runner 17 and a plurality of mold tubes 22. The plurality of mold tubes 22 are firmly installed near the edge of the centrifugal disk 10. The axis of the mold tube 22 is radially inclined downward and outward. The angle α between the axis of the mold tube 22 and the axis of the centrifugal disk 10 is 0-90°. The upper end of the mold tube 22 is connected to the runner 17, and the pipe mouth at the lower end is detachably equipped with a head plug 23.

[0073] In order to facilitate the removal of the billet from the mold tube 22, the mold tube 22 can be designed to be a structure that is split in half along the length direction, and the split structure is connected by a clip 24 or other structure. One or more rings 25 are arranged below the centrifugal disk 10 to fix the mold tube 22, and the rings 25 are connected to each other and to the centrifugal disk 10. When the casting process starts, the alloy liquid flows into the mold tube 22 through the pouring cup 15, the center injection pipe 16 and the runner 17. The centrifugal force forms pressure on the solidification process of the alloy liquid in the mold tube 22, and the alloy liquid in the runner 17 can also provide shrinkage liquid for the solidification process, thereby eliminating casting defects, including shrinkage holes, micropores, looseness and cracks.

[0074] The present invention provides some specific embodiments to better understand the present implementation mode:

[0075] Example 1

[0076] In this embodiment, it is planned to melt 35kg of Ti-48Al-2Cr-2Nb alloy (4822 alloy), and the melting equipment is a suspension melting furnace ( Figure 1), equipped with a water-cooled copper crucible with an inner diameter of 200mm, a height of 440mm, and axially split. The crucible is installed in a vacuum melting chamber 2, and a 1000kW induction power supply is used. The current input by it generates an electromagnetic field in the induction coil 3 surrounding the crucible, and the electromagnetic field passes through the side wall of the crucible to heat the material in the crucible. The smelting process is carried out under argon filling conditions.

[0077] The first stage of the smelting process is to smelt 33.6 kg of a TiAl alloy matrix having a composition of 50 wt.% Ti-50 wt.% Al. According to this composition requirement, 16.8 kg of Ti and 16.8 kg of Al are required.

[0078] The first step in the first stage requires the melting of an 80wt.% Ti-20wt.% Al master alloy. The ingredients are 16.8kg of Ti and 4.2kg of Al, a total of 21kg. In the solid state, their volumes are 3733 and 1555cm 3 , meeting the requirement that the volume ratio of Al to Ti is ≤ 1 / 2. The second step requires the smelting of the intermediate alloy II with a composition of 60wt.%Ti-40wt.%Al. The process is to turn over the ingot of the intermediate alloy I and add 7kg of Al for smelting to obtain a 28kg alloy ingot. In the solid state, the volumes of the two materials are approximately 5122 and 2667cm 3 , which basically meets the requirement of Al to Ti volume ratio ≤ 1 / 2. The third step requires smelting to reach the target composition of 50wt.%Ti-50wt.%Al alloy. The process is to turn over the ingot of intermediate alloy 2 and add the remaining 5.6kg of Al for smelting to obtain 33.6kg alloy ingot. In the solid state, the volumes of the two materials are approximately 7368 and 2074cm 3 , still meeting the requirement that the volume ratio of Al to Ti is ≤ 1 / 2. Finally, the alloy ingot obtained in the third step is turned over and remelted in a crucible to further homogenize the composition.

[0079] The second stage still uses the same suspension melting equipment as the first stage, but uses a small cold crucible with an inner diameter of 60 mm. The purpose of this stage is to add a total of 1.4 kg of alloying elements Nb and Cr to the TiAl alloy matrix obtained in the first stage. The method to achieve this requirement is to melt the Nb material and the Cr material to obtain a 50wt.%Nb-50wt.%Cr master alloy, and then add this Nb-Cr master alloy to the TiAl alloy matrix.

[0080] The second stage of smelting process is carried out in several steps. The first step is to melt 0.7kg of Nb and 0.27kg of Cr to obtain 0.97kg of 72wt.%Nb-28wt.%Cr intermediate alloy. The second step is to turn the alloy ingot and add 0.43kg of Cr for melting. Then the alloy ingot is turned over and remelted to obtain an intermediate alloy with a composition of 50wt.%Nb-50wt.%Cr. Finally, the Nb-Cr alloy ingot is crushed and added to a water-cooled copper crucible with an inner diameter of 200mm containing a Ti-Al alloy matrix of 50wt.%Ti-50wt.%Al for melting. After turning over and remelting, 35kg of Ti-48Al-2Cr-2Nb alloy with uniform composition is obtained.

[0081] Example 2

[0082] The materials and methods of smelting in this embodiment are the same as those in Embodiment 1. However, at the end of the smelting process, the Ti-48Al-2Cr-2Nb alloy is cast into rods using centrifugal casting technology.

[0083] The suspension smelting equipment of this embodiment is provided with a centrifugal casting device ( Figure 3 ), the device consists of a centrifugal disk with a diameter of 1000mm installed at the bottom of the vacuum chamber, a mold device installed on the centrifugal disk, a drive shaft that is combined with the centrifugal disk and passes through the bottom of the vacuum chamber through a vacuum dynamic seal and a bearing, and a drive device. The mold device consists of a pouring cup, a center pouring pipe, three runners and three mold tubes. The inner diameter of the mold tube is 82mm and the length is 700mm. The mold tube is firmly installed near the edge of the centrifugal disk, and the end of the tube is radially downward and tilted outward. The angle between the tube axis and the centrifugal disk axis is α=60°. The upper end of the mold tube is connected to the runner, and the lower end of the pipe mouth is equipped with a detachable head. The mold tube is cut along the length direction and combined with a clip. Two rings are set to fix the lower end and the middle part of the mold tube, and there is a firm combination between the rings and between the rings and the centrifugal disk.

[0084] After the last melting process of the Ti-48Al-2Cr-2Nb alloy weighing 35kg, the centrifugal casting device was started, and the speed of the centrifugal disk was set to 150rpm. Then, the alloy liquid flowed into the mold tube through the pouring cup, the center pouring pipe and the runner, forming three bar blanks with a diameter of 80mm, a length of about 600mm, and a weight of about 10kg each. There were no shrinkage cavities, micropores, looseness and cracks in the blanks.

[0085] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a TiAl-based alloy casting with a TiAl intermetallic compound as a matrix and a multi-component alloy element M added, characterized in that: The steps include: S1, suspension melting Ti and Al to form a TiAl alloy matrix; S2, smelting the alloy element M in suspension to form an alloy element master alloy; S3, levitation melting the TiAl alloy matrix, the alloy element master alloy and the remaining alloy elements with a melting point lower than 1800° C. to form a TiAl-based alloy.

2. The preparation method according to claim 1, characterized in that: Step S1 includes the following steps: S11, melting all the high melting point Ti and part of the low melting point Al to form a TiAl-based master alloy; S12, adding Al once, twice or multiple times, and finally obtaining a TiAl alloy matrix meeting the composition requirements of the TiAl alloy matrix; Among them, the volume of Al material added in each step of the smelting process is V Al Should not be greater than the volume V of the metal Ti or TiAl-based master alloy Ti , with V Al ≤1 / 2V Ti For the best.

3. The preparation method according to claim 2, characterized in that: The TiAl-based master alloy ingot formed in step S11 is turned over and then Al is added; And / or, the TiAl alloy matrix ingot meeting the composition requirements obtained by smelting in step S12 is turned over and remelted once more.

4. The preparation method according to claim 1, characterized in that: In step S2, S21, if the melting point of the alloy element M is not higher than 1800°C, the alloy element M is directly added to the TiAl alloy matrix for melting; S22, if the alloy elements M include components with a melting point higher than 1800°C, one, two or more components with higher melting points are combined with one, two or more components in the remaining alloy components, and first smelted into a master alloy with a melting point lower than 1800°C. Depending on the types and quantities of the alloy components, one, two or more master alloys may be smelted; S23, if the alloying elements M include a component with a melting point higher than 1800°C and the combination of the alloying elements M cannot form an intermediate alloy with a melting point lower than 1800°C, then the high melting point component M h Combined with Ti and / or Al for smelting to obtain a master alloy M-Ti, M-Al or M-(Ti,Al) with a melting point below 1800°C; Among them, in step S1, the amount of Ti material and / or Al material added when smelting the Ti-Al alloy matrix should be deducted from the amount of Ti material and / or Al material required for smelting M-Ti, M-Al or M-(Ti,Al) in S2.

5. The preparation method according to claim 4, characterized in that: For the composition of the intermediate alloy with a suitable melting point, if the volume V of the low melting point component M1 is Ml Not less than the volume V of the high melting point component Mh Mh , then step S22 includes the following steps: S221, combining high melting point components and part of low melting point components in the alloy element M, and smelting to obtain a primary master alloy; S222, starting from the primary master alloy, successively adding the remaining components in the alloy element M to obtain secondary, tertiary or multiple master alloys, and finally obtaining a master alloy of alloy elements that meets the composition requirements; Among them, in the batching method of each step of the smelting process, the volume ratio of the low melting point component to the high melting point component or the intermediate alloy is ensured to be ≤1, and ≤1 / 2 is the best.

6. The preparation method according to claim 1, characterized in that: The alloy element master alloy ingot in step S2 is crushed and added into a water-cooled copper crucible filled with the TiAl alloy matrix in step S1 for smelting to obtain the TiAl-based alloy casting in step S3.

7. A preparation device for TiAl-based alloy castings, applied to the preparation method according to any one of claims 1 to 6, characterized in that: It includes a water-cooled copper crucible installed in a vacuum melting chamber, and an induction coil arranged around the water-cooled copper crucible; Wherein, a feeder which is in sealed communication with the vacuum melting chamber is arranged above the vacuum melting chamber, and a discharge port of the feeder is connected to a water-cooled copper crucible; A centrifugal casting device is installed below the water-cooled copper crucible, wherein the centrifugal casting device includes a centrifugal disk installed at the bottom of the vacuum melting chamber, a mold device installed on the upper end surface of the centrifugal disk, a drive shaft passing through the bottom of the vacuum melting chamber through a vacuum dynamic seal and a bearing, and a centrifugal drive device that is transmission-connected to the drive shaft.

8. The preparation device according to claim 7, characterized in that: The feeder comprises a feeding barrel, a feeding pipe, a spiral pushing device and a feeding drive device. The feeding barrel is installed above the vacuum melting chamber. One end of the feeding pipe is sealed and connected to the feeding barrel, and the other end extends into the interior of the vacuum melting chamber and is located above the water-cooled copper crucible. The spiral pushing device is arranged in the feeding barrel and is transmission-connected to the feeding drive device.

9. The preparation device according to claim 7, characterized in that: The mold device includes a pouring cup, a center pouring pipe, a runner and a plurality of membrane shells, wherein the pouring cup and the center pouring pipe are vertically arranged at the center of the centrifugal disk, and a plurality of membrane shells located at the end of the runner are connected to the center pouring pipe through the runner; Or, the mold device includes a pouring cup, a center pouring pipe, a runner and a plurality of mold tubes, the plurality of mold tubes are installed near the edge of the centrifugal disk, the axes of the mold tubes are radially inclined downward and outward, the upper ends of the mold tubes are connected to the runner, and the pipe openings at the lower ends are equipped with detachable head plugs.

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