Shell-free large-size directional solidification titanium-aluminum alloy forming method and equipment

Abstract

The invention relates to a shell-free large-size directional solidification titanium-aluminum alloy forming method and equipment in the field of titanium-aluminum alloy casting, and the forming method comprises the following steps: preparing an alloy master ingot, and processing the alloy master ingot into a material bar; the top end of the charge bar is installed on a feeding device above directional solidification equipment, and the bottom end of the charge bar is placed in an induction coil in the directional solidification equipment; a graphite plate or a metal plate is placed below the charge bar and the induction coil at a certain interval; vacuumizing the directional solidification equipment and injecting protective gas; starting an induction coil to heat the bottom end of the charge bar, and adjusting the speed of a feeding device to enable the bottom end of the charge bar to be continuously molten and drop onto the plate; after the instillation process is finished, the alloy is naturally cooled and solidified; and the directionally solidified titanium-aluminum alloy is obtained. According to the method, by using a non-shell and instillation forming method, crucible or shell particles can be effectively prevented from being introduced into the metal melt, the high-purity directionally-solidified TiAl alloy is obtained, and the mechanical property of the directionally-solidified TiAl alloy is improved.

Description

Technical Field

[0001] The present application relates to the technical field of titanium-aluminum alloy casting, and in particular to a large-size directional solidification titanium-aluminum alloy forming method and equipment without a mold shell. Background Art

[0002] The Bridgman method is a commonly used method for directional solidification of TiAl alloys. The process of this method is: during directional solidification, the sample is placed in a ceramic crucible or mold shell. After the sample is fully melted and thermally stabilized in the heating zone, it enters the bottom liquid metal cooling medium through the gradient zone. The melt crystallizes under the action of strong cooling, and directional solidification is completed under the action of unidirectional heat flow.

[0003] In practical applications of the Bridgman method, it takes a long time to melt TiAl metal. The whole heating process of the equipment is usually more than 120 minutes. After the metal is melted, the reaction time between the melt and the crucible or shell is also long, generally more than 30 minutes. In addition, in order to melt the metal, the reaction temperature is relatively high, generally above 1600°C, which easily causes a large number of crucible or shell particles to enter the metal melt. Shell particles are mainly metal oxide particles with a maximum size of more than 50μm. Once these shell particles become crack sources, they will greatly reduce the strength and plasticity of the directionally solidified alloy. Summary of the invention

[0004] In view of the problems existing in the background technology, the present application provides a large-size directionally solidified titanium-aluminum alloy forming method and equipment without a mold shell, which can improve the mechanical properties of the directionally solidified TiAl alloy.

[0005] According to one aspect of the present invention, a method for forming a large-size directional solidification titanium-aluminum alloy without a mold shell is provided, comprising the following steps: preparing an alloy mother ingot, and processing the alloy mother ingot into a material rod; installing the top end of the material rod on a feeding device above a directional solidification device, and placing the bottom end of the material rod in an induction coil in the directional solidification device; placing a graphite plate or a metal plate at a certain distance below the material rod and the induction coil; evacuating the directional solidification device and injecting a protective gas; turning on the induction coil to heat the bottom end of the material rod, and adjusting the feeding device to move the material rod downward at a predetermined speed, so that the bottom end of the material rod is continuously melted and drips onto the graphite plate or the metal plate; after the dripping process is completed, waiting for the alloy to cool and solidify naturally; and obtaining a directionally solidified titanium-aluminum alloy.

[0006] In some embodiments of the present invention, the power of the induction coil is 15-40 kW.

[0007] In some embodiments of the present invention, the feeding device moves the material rod downward at a speed of 0.1 to 0.4 mm / s.

[0008] In some embodiments of the present invention, the distance between the upper surface of the graphite plate or metal plate and the center of the induction coil is 20 to 60 cm.

[0009] In some embodiments of the present invention, the directional solidification device is evacuated to a pressure below 10 -3 Pa, and then inject protective gas to a pressure of 0.03~0.06MPa.

[0010] In some embodiments of the present invention, the composition of the alloy mother ingot ranges from Ti-(40-50)Al-(0-10)Nb-(0-1)C-(W, B, Y) in atomic percentage.

[0011] In some embodiments of the present invention, the bottom end of the material rod is processed into a cone shape as an initial shape.

[0012] In some embodiments of the present invention, the graphite plate or metal plate is placed in a furnace body with a heating device in a directional solidification device. Before turning on the induction coil to heat the bottom end of the material rod, the heating device is first turned on to make the furnace body reach a predetermined temperature.

[0013] In some embodiments of the present invention, while the bottom end of the material rod is continuously melted and drips onto the graphite plate or the metal plate, the graphite plate or the metal plate is continuously moved downward at a set rate.

[0014] According to another aspect of the present invention, there is provided a directional solidification device, comprising an outer shell, a feeding device for mounting a material rod is provided on the top of the outer shell, an induction coil and a graphite plate or a metal plate are sequentially provided in the outer shell below the feeding device; the directional solidification device adopts the above-mentioned large-size directional solidification titanium-aluminum alloy forming method without a mold shell to prepare a directional solidification titanium-aluminum alloy.

[0015] Compared with the prior art, the present invention achieves the following technical effects:

[0016] 1. The present invention greatly improves the inclusion of shell particles in the structure and improves the mechanical properties of the directionally solidified titanium aluminum alloy. The present invention avoids the use of traditional metal oxide shells, so there are no shell particle inclusions in the structure, reducing the crack source, and increasing the tensile strength and plasticity of the alloy. The room temperature tensile strength of the directionally solidified TiAl alloy sample prepared by this method is ≥500Mpa, and the room temperature elongation is ≥2%.

[0017] 2. The present invention can effectively reduce the equipment cost and the cost of preparing directional solidification samples. Compared with other methods, such as the optical floating zone method and the electromagnetic confinement directional solidification method, the present invention does not require lenses or large electromagnetic confinement structures, greatly reducing equipment costs, simplifying equipment structure, reducing energy consumption, and thus reducing the cost of preparing directional solidification samples. Compared with the electromagnetic cold crucible directional solidification method, the technology has greatly reduced equipment requirements.

[0018] 3. The present invention can effectively improve the efficiency of directional solidification sample preparation. The present invention omits the longest time-consuming steps of furnace heating and directional solidification pulling in directional solidification, and only retains the equipment vacuuming, argon filling and sample solidification process. The duration of the entire directional solidification process is reduced from 4 to 8 hours to 1 to 2 hours, which is conducive to improving the production efficiency of directional solidification samples.

[0019] 4. The present invention greatly reduces the difficulty of preparing large-sized directional solidification specimens. The present invention can prepare a relatively regular cylindrical directional solidification test bar with a diameter of 20 to 50 mm and a length of 0 to 200 mm, and the required parts can be cut out by machining later. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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 application. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0021] Figure 1 It is a process diagram of a large-size directional solidification titanium-aluminum alloy forming method without a mold shell according to the present invention;

[0022] Figure 2 It is a schematic diagram of the appearance of the material bar of the present invention;

[0023] Figure 3 It is a schematic structural diagram of the directional solidification equipment of the present invention;

[0024] Figure 4 This is a diagram of a directional solidification test bar with a diameter of 32 mm after dripping according to the molding method of the present invention;

[0025] Figure 5 This is a typical columnar crystal organization diagram at the center of the longitudinal section of the directional solidification test rod of the present invention.

[0026] The reference numerals in the accompanying drawings represent the following: 1. feeding device; 2. metal sleeve; 3. material rod; 4. induction coil; 5. heating device; 6. graphite plate or metal plate; 7. furnace body; 8. stretching rod; 9. outer shell. DETAILED DESCRIPTION

[0027] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0028] When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Instead, they are only examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims.

[0029] In the description of the present application, it should be understood that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances. In addition, in the description of the present application, unless otherwise specified, "multiple" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the objects associated before and after are in an "or" relationship.

[0030] Directional solidification technology is an important means to prepare directional columnar crystals and single crystal alloys. Directional solidification of TiAl alloys by the Bridgman method not only takes a long time for the metal to melt, but also takes a long time for the melt to react with the crucible or shell after the metal melts, and the reaction temperature is high. As a result, a large number of crucible or shell particles enter the metal melt, which can easily cause the performance of the directionally solidified TiAl alloy to deteriorate.

[0031] Although the optical floating zone method or electromagnetic confinement directional solidification method can be used to prepare directionally solidified TiAl alloys, the sample size that can be formed by directionally solidification by these two methods is small, and it is not conducive to the precise control of the sample shape. In addition, the equipment is relatively complex and the overall cost is high.

[0032] Based on this, the present application proposes a shellless large-size directional solidification titanium-aluminum alloy forming method and equipment. By using a shellless, dripping forming method, the introduction of crucible or shell particles into the metal melt can be effectively avoided to obtain a high-purity directional solidification TiAl alloy, thereby improving the mechanical properties of the directional solidification TiAl alloy.

[0033] The present application discloses a method for forming a large-sized directional solidification titanium aluminum alloy without a mold shell. Figure 1 As shown, the large-size directional solidification titanium aluminum alloy forming method without a shell comprises the following steps:

[0034] 1) Prepare alloy mother ingots and process them into material bars.

[0035] In some embodiments of the present invention, first, the alloy composition can be selected according to the Ti-Al binary phase diagram, and the alloy composition range is Ti-(40-50)Al-(0-10)Nb-(0-1)C-(W, B, Y) in terms of atomic percentage.

[0036] The alloy mother ingot with the alloy composition range can obtain (α 2 +γ) lamellar cluster structure, and there is no precipitation of a large number of equiaxed grains and γ grains.

[0037] Furthermore, in the present invention, adding C in an atomic fraction of less than 1% to the alloy can promote the formation of columnar crystals.

[0038] In some embodiments of the present invention, the alloy mother ingot can be processed into a cylindrical material rod 3 with a diameter of 40 to 60 mm and a length of 200 to 500 mm, which is beneficial to subsequent processes, such as improving the dripping efficiency and dripping quality.

[0039] It should be noted that the diameter and length of the material rod 3 are not particularly limited, and those skilled in the art can make reasonable choices based on actual needs. As some specific examples, the diameter of the material rod 3 can be 40mm, 45mm, 50mm, 55mm, 60mm, etc., and the length of the material rod 3 can be 200mm, 250mm, 300mm, 350mm, 400mm, 450mm, 500mm, etc.

[0040] In some embodiments of the present invention, Figure 2 As shown, the outer periphery of the material rod 3 near the upper end has an annular groove structure, and the groove depth is 3 to 6 mm. The arrangement of the groove can facilitate the subsequent process to install and stably and accurately position the material rod 3.

[0041] In some embodiments of the present invention, a conical surface is cut at the lower end of the material rod 3, that is, the initial shape of the bottom end of the material rod 3 is processed into a cone. The design of the conical surface of the material rod 3 can facilitate the start of the subsequent dripping process, such as improving the efficiency and uniformity of the initial heating of the bottom end of the material rod 3 and the subsequent continuous dripping.

[0042] In some embodiments of the present invention, the length of the conical surface in the vertical direction is 20 to 40 mm.

[0043] It should be noted that the length of the conical surface in the vertical direction is not particularly limited. Those skilled in the art can make a reasonable choice based on actual needs, such as designing according to the diameter of the material rod 3. As some specific examples, the length of the conical surface in the vertical direction can be 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, etc.

[0044] 2) Install the material rod on the directional solidification equipment.

[0045] like Figure 3 As shown, the top end of the material rod 3 is mounted on the feeding device 1 above the directional solidification equipment, and the bottom end of the material rod 3 is placed in the induction coil 4 in the directional solidification equipment.

[0046] Specifically, in this embodiment, the position of the material rod 3 can be adjusted so that the lower tip of the material rod 3 is located at the center of the induction coil 4 .

[0047] 3) Place a graphite plate or metal plate at a certain distance below the material rod and the induction coil.

[0048] In some embodiments of the present invention, the material rod 3, the induction coil 4 and the graphite plate or the metal plate 6 may be arranged with a vertical coaxial axis.

[0049] In some embodiments of the present invention, the distance between the upper surface of the graphite plate or metal plate 6 and the center of the induction coil 4 is 20 to 60 cm.

[0050] 4) Evacuate the directional solidification equipment and inject protective gas.

[0051] In some embodiments of the present invention, the directional solidification equipment may be evacuated by a vacuum system, and a protective gas may be filled into the directional solidification equipment after evacuation.

[0052] In some embodiments of the present invention, the directional solidification apparatus is evacuated to a pressure below 10 -3 Pa, and then inject protective gas to a pressure of 0.03~0.06MPa.

[0053] In some embodiments of the present invention, the protective gas includes but is not limited to inert gases such as argon and helium or mixed gases thereof, and argon is preferably used.

[0054] By evacuating the directional solidification equipment and injecting protective gas, it is not only beneficial to the subsequent directional solidification titanium aluminum alloy forming process, but also can prevent the induction coil 4 from discharging.

[0055] 5) Melt the rod and drip.

[0056] In this embodiment, the induction coil 4 is turned on to heat the bottom end of the material rod 3, and the feeding device 1 is adjusted to move the material rod 3 downward at a predetermined speed, so that the bottom end of the material rod 3 is continuously melted and drips onto the graphite plate or metal plate 6.

[0057] In some embodiments of the present invention, the power of the induction coil 4 may be 15-40 kW.

[0058] It should be noted that the heating power of the induction coil 4 is not particularly limited, and those skilled in the art can make a reasonable selection according to actual needs. As some specific examples, the power of the induction coil 4 can be 15kW, 20kW, 25kW, 30kW, 35kW, 40kW, etc.

[0059] In some embodiments of the present invention, the feeding device 1 can move the material rod 3 downward at a speed of 0.1 to 0.4 mm / s.

[0060] By selecting an appropriate power and maintaining the power constant, the material rod 3 can be melted stably and continuously and drip onto the graphite plate or metal plate 6 .

[0061] It should be understood that the feeding length can be reasonably set according to the required metal amount of the directionally solidified titanium aluminum alloy to be formed.

[0062] In some embodiments of the present invention, the graphite plate or metal plate 6 is placed in a furnace body 7 having a heating device 5 in a directional solidification device. Before turning on the induction coil 4 to heat the bottom end of the material rod 3, the heating device 5 is first turned on to make the furnace body 7 reach a predetermined temperature.

[0063] After the protective gas is filled, the temperature inside the directional solidification equipment is first raised to a specific temperature, and then the dripping operation is performed. By controlling the insulation temperature in the furnace, the solidification rate during the directional solidification process can be controlled, and then the lamellar orientation of the columnar crystals can be controlled.

[0064] In some embodiments of the present invention, while the bottom end of the material rod 3 continuously melts and drips onto the graphite plate or metal plate 6, the graphite plate or metal plate 6 is continuously moved downward at a set rate.

[0065] By pulling and moving the graphite plate or metal plate 6 at a specific rate while dripping, the solidification rate of the melt can be changed, thereby controlling the continuity of the columnar crystals and the lamellar orientation within the crystals.

[0066] 6) After the dripping process is completed, wait for the alloy to cool and solidify naturally.

[0067] 7) Obtain directionally solidified titanium aluminum alloy.

[0068] By using the method for forming large-sized directionally solidified titanium aluminide without a mold shell and by drip feeding of the present invention, it is possible to effectively avoid the introduction of crucible or mold shell particles into the molten metal, obtain a directionally solidified TiAl alloy with high purity, thereby improving the mechanical properties of the directionally solidified TiAl alloy. Moreover, the present invention eliminates the heating inside the furnace body and the drawing step during directional solidification, which are the most time-consuming steps in traditional directional solidification. The total duration of the directional solidification process is reduced from 4 - 8 hours to 1 - 2 hours, greatly improving the production efficiency of the directionally solidified titanium aluminide.

[0069] Compared with the optical floating zone method and the electromagnetic confinement directional solidification method, the forming method of the present invention does not require a lens or a large electromagnetic confinement structure, greatly reducing the equipment cost, simplifying the equipment structure, reducing energy consumption, and thus reducing the cost of preparing directionally solidified specimens. Moreover, compared with the electromagnetic cold crucible directional solidification method, the requirements for the equipment of this technology are significantly reduced.

[0070] By using the forming method of the present invention, the difficulty of preparing large-sized directionally solidified aluminum-titanium alloy is greatly reduced. It is possible to obtain cylindrical directionally solidified titanium aluminide rods with controllable sizes of 20 - 50 mm in diameter and 0 - 200 mm in length and relatively large maximum sizes and regular shapes. Subsequently, only the required parts can be cut out by machining.

[0071] As Figure 4 shown, for the directionally solidified test rod with a diameter of 32 mm obtained by using the forming method of the present invention, when the test rod is longitudinally sectioned, as Figure 5 shown, its longitudinal section core has a good directionally solidified columnar crystal structure; and the directionally solidified TiAl alloy specimen prepared by using the forming method of the present invention has a room temperature tensile strength ≥ 500 Mpa and a room temperature elongation ≥ 2%, having excellent mechanical properties.

[0072] The embodiment of the present application also discloses a directional solidification device, which uses the above-mentioned method for forming large-sized directionally solidified titanium aluminide without a mold shell to prepare the directionally solidified titanium aluminide.

[0073] As Figure 3 shown, the directional solidification device includes an outer shell 9. At the top of the outer shell 9, there is a feeding device 1 for installing a feed rod 3. Inside the outer shell 9 and below the feeding device 1, there are sequentially an induction coil 4 and a graphite plate or a metal plate 6.

[0074] In some embodiments of the present invention, the directional solidification device further includes a heating device 5, and the heating device 5 is arranged around the graphite plate or the metal plate 6.

[0075] Furthermore, the furnace body 7 of the directional solidification device is arranged inside the outer shell 9, the graphite plate or the metal plate 6 is arranged inside the furnace body 7, and a through hole is left at the top of the furnace body 7 for the molten feed rod 3 to drip onto the graphite plate or the metal plate 6.

[0076] Furthermore, the heating device 5 is installed on the side wall of the furnace body 7 to heat the space inside the furnace body 7 .

[0077] In some embodiments of the present invention, the directional solidification equipment also includes a vertically arranged stretching rod 8, one end of the stretching rod 8 is connected to the bottom of the graphite plate or metal plate 6, and the other end passes through the bottom of the furnace body 7. By controlling the up and down movement of the stretching rod 8, the up and down movement of the graphite plate or metal plate 6 can be controlled.

[0078] In some embodiments of the present invention, the directional solidification equipment further includes a water cooling device, which is disposed at the bottom of the graphite plate or the metal plate 6. The solidification rate of the titanium aluminum alloy can be further improved by the water cooling device.

[0079] Furthermore, the water cooling device may adopt a water cooling plate.

[0080] In some embodiments of the present invention, the feeding device 1 includes a feeding rod, one end of which is connected to a metal sleeve 2, and the metal sleeve 2 is provided with a protrusion that can be adapted to the outer peripheral groove of the material rod 3. The material rod 3 is connected to the feeding rod by inserting the end of the material rod 3 with the groove into the metal sleeve 2 and engaging the groove with the protrusion.

[0081] In some embodiments of the present invention, a linear drive mechanism such as a linear motor or a hydraulic rod may be used to drive the feed rod and the stretching rod 8 to control the pulling rate of the graphite plate or metal plate 6, thereby controlling the downward movement rate of the material rod 3.

[0082] In some embodiments of the present invention, the graphite plate or metal plate 6 can be made of high temperature resistant materials such as graphite plate, metal molybdenum plate, metal niobium plate, etc.; among them, graphite plate is very easy to obtain and has low cost; compared with graphite plate, metal molybdenum plate can improve thermal conductivity and alloy solidification rate; compared with graphite plate, metal niobium plate, niobium is one of the important components of titanium aluminum alloy. A small amount of niobium element diffuses into the melt, which has almost no effect on the microstructure and properties of the formed titanium aluminum alloy, thereby further reducing the impurity elements entering the metal melt and improving the quality of the formed titanium aluminum alloy.

[0083] 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 subject to the protection scope of the claims.

Claims

1. A large-size directionally solidified titanium-aluminum alloy forming method without a mold shell, characterized in that: The following steps are involved: preparing alloy mother ingots and processing the alloy mother ingots into material bars; The top end of the material rod is mounted on a feeding device above the directional solidification device, and the bottom end of the material rod is placed in an induction coil in the directional solidification device; A graphite plate or a metal plate is placed at a certain distance below the material rod and the induction coil; Evacuate the directional solidification equipment and inject protective gas; Turn on the induction coil to heat the bottom of the material rod, adjust the feeding device to move the material rod downward at a predetermined speed, so that the bottom of the material rod continuously melts and drips onto the graphite plate or metal plate; After the dripping process is completed, wait for the alloy to cool and solidify naturally; Directionally solidified titanium-aluminum alloy is obtained.

2. The method for forming a large-size directional solidification titanium aluminum alloy without a mold shell according to claim 1, characterized in that: The power of the induction coil is 15-40 kW.

3. The large-size directionally solidified titanium-aluminum alloy forming method without a mold shell according to claim 1, characterized in that: The feeding device moves the material rod downward at a speed of 0.1 to 0.4 mm / s.

4. The large-size directionally solidified titanium-aluminum alloy forming method without a mold shell according to claim 1, characterized in that: The distance between the upper surface of the graphite plate or metal plate and the center of the induction coil is 20 to 60 cm.

5. The large-size directionally solidified titanium-aluminum alloy forming method without a mold shell according to claim 1, characterized in that: The directional solidification equipment is evacuated to a pressure below 10 -3 Pa, and then inject protective gas to a pressure of 0.03~0.06MPa.

6. The large-size directionally solidified titanium-aluminum alloy forming method without a mold shell according to claim 1, characterized in that: In terms of atomic percentage, the composition range of the alloy mother ingot is Ti-(40-50)Al-(0-10)Nb-(0-1)C-(W, B, Y).

7. The large-size directionally solidified titanium-aluminum alloy forming method without a mold shell according to claim 1, characterized in that: The bottom end of the material rod is processed into a conical shape as an initial shape.

8. The large-size directionally solidified titanium-aluminum alloy forming method without a mold shell according to claim 1, characterized in that: The graphite plate or metal plate is placed in a furnace body with a heating device in the directional solidification equipment. Before the induction coil is turned on to heat the bottom end of the material rod, the heating device is first turned on to make the furnace body reach a predetermined temperature.

9. The large-size directionally solidified titanium-aluminum alloy forming method without a mold shell according to claim 1, characterized in that: The bottom end of the material rod continuously melts and drips onto the graphite plate or the metal plate, while the graphite plate or the metal plate is continuously moved downward at a set rate.

10. A directional solidification device, characterized in that: It comprises an outer shell, a feeding device for mounting a material rod is provided on the top of the outer shell, and an induction coil and a graphite plate or a metal plate are sequentially provided inside the outer shell and below the feeding device; The directional solidification equipment adopts the large-size directional solidification titanium-aluminum alloy forming method without a mold shell as described in any one of claims 1 to 9 to prepare the directionally solidified titanium-aluminum alloy.

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