Casting ring for obtaining a product made of titanium alloy or titanium-aluminum intermetallic alloy and method of use thereof

Abstract

The invention relates to a method for obtaining, by fusion with a plasma torch, a product made of a titanium alloy or a titanium aluminum intermetallic compound, said alloy having a directional structure, said method comprising: heating said molten alloy (1) in a casting ring (2) by means of a plasma torch (3); cooling a cold zone (21) of said casting ring over a length LI, said cooling forming a semi-solid arch (12) of alloy; heating a hot zone (22) of said casting ring over a length L2, thereby forming a solidified front (13), the flatness of said solidified front (13) being less than 10° with respect to a plane perpendicular to the direction of drawing; and drawing said solidified alloy (14) in said direction of drawing at a speed higher than 10 ‑4 m / s. The invention also relates to a facility for implementing said method.

Description

Technical Field

[0001] This invention relates to the field of alloy production, particularly to aerospace alloys such as titanium alloys or TiAl intermetallic alloys, and more particularly to casting rings for obtaining ingots and methods of using such casting rings. Background Technology

[0002] In particular, the production of alloys by ingot stretching mainly involves heating the raw materials in a crucible to melt them and pouring them into a casting ring that will give the ingot its shape.

[0003] Generally, the cast ring portion is made of copper and is water-coolable. Copper is used because its high thermal conductivity allows for good heat exchange, and its good ductility promotes its use while limiting the risk of breakage in this critical part. Therefore, copper is particularly suitable for making cast rings in areas that require cooling, known as cold zones.

[0004] Regarding the area to be heated, known as the hot zone, cast ceramics (e.g., alumina, yttrium oxide, zirconium oxide, or their derivatives and complexes) are generally best suited for manufacturing alloys.

[0005] Disadvantages include the drawbacks of using these materials to manufacture titanium alloys or TiAl intermetallic alloys. In fact, these alloys in the molten state react violently with the cast ceramics, leading to corrosion of the casting rings and incorporation of solid ceramic inclusions that tear from the walls of the casting rings. Worse still, because the ceramics are oxides, the oxygen they contain contaminates and weakens the alloy.

[0006] Furthermore, since cast ceramics are non-conductive, the use of an external resistor is necessary. If induction heating is required, an additional base surrounding the casting ring is needed to prevent direct coupling with the alloy during solidification within the casting ring. In effect, this coupling creates circulating eddies in the molten alloy, thereby destabilizing the pre-solidification phase.

[0007] Refractory metals are occasionally used to create hot zones. However, the risk of chemical interactions between these metals and titanium alloys or TiAl intermetallic materials is high. Specifically, low-melting-point eutectics can form and cause critical defects in these alloys.

[0008] Recently, aluminum nitride has been used to manufacture casting crucibles, which have proven to be promising. However, this material is expensive. Summary of the Invention

[0009] This disclosure improves upon the aforementioned situation.

[0010] For this purpose, the present invention provides a casting ring for molding ingots made of titanium alloys or TiAl intermetallic alloys, the casting ring being made of a tube having a first end and a second end and comprising:

[0011] - The first section, which is made of thermally conductive material and extends from the first end, specifically exceeding the length L1 between 0.065m and 0.09m;

[0012] - The second section, which is made of the largest phase alloy material and extends from the first section, specifically exceeds a length L2 between 0.17m and 0.3m;

[0013] The largest phases selected are: Nb4Al1C3, Nb2AlC, Ti2AlC and Ti2AlN.

[0014] Thanks to the use of this cast ring, there is no risk of contaminants from the manufacturing process, as the elements constituting the cast ring are those commonly found in titanium alloys and TiAl intermetallic alloys. Therefore, there is no risk of it being weakened by the inclusion of foreign elements (e.g., oxygen from the cast ceramic). Furthermore, this cast ring exhibits good resistance to thermal shock and low thermal expansion.

[0015] Other optional and non-restrictive features are described below.

[0016] Copper can be used as the thermally conductive material.

[0017] The inner surface of the tube in the second section may be covered with one or more layers, each of which is made of a material selected from the following: Nb4Al1C3, Nb2AlC, Ti2AlC, Ti2AlN and AlN.

[0018] When the material is Nb4Al1C3, the inner surface of the pipe in the second section can be covered from the outside inward with:

[0019] -A single layer of Nb2AlC;

[0020] - First layer Nb2AlC and second layer Ti2AlC;

[0021] - First layer Nb2AlC, second layer Ti2AlC, and third layer AlN; or

[0022] - First layer Nb2AlC, second layer Ti2AlC, third layer Ti2AlN and fourth layer AlN.

[0023] When the material is Nb2AlC, the inner surface of the pipe in the second section can be covered from the outside inward with:

[0024] -A single layer of Ti2AlC;

[0025] - First layer Ti2AlC and second layer AlN; or

[0026] - First layer Ti2AlC, second layer Ti2AlN and third layer AlN.

[0027] When the material is Ti2AlC, the inner surface of the tube in the second section can be covered from the outside inward with:

[0028] - A single-layer AlN; or

[0029] - First layer Ti2AlN and second layer AlN.

[0030] The first and second sections can be connected to each other via joints made of mechanical assemblies or welded together.

[0031] The cast ring may further include a third section extending from the second section to the second end, specifically exceeding a length of at least 0.03 m, and made of a thermally conductive material.

[0032] The cast ring may further include an extended and outwardly extending annular flange perpendicular to the first segment from the first end.

[0033] In another aspect, the present invention relates to a method for obtaining products made of titanium alloys or TiAl intermetallic alloys by plasma torch melting, the alloys having an oriented structure.

[0034] The method includes:

[0035] - Select a casting ring as described above, where length L1 is between 0.065m and 0.09m, and length L2 is between 0.17m and 0.3m. Choose the thicknesses e1 and e2 of the first and second segments according to the following inequalities: Mathematical Equation 1 and Mathematical Equation 2, where R is the inner radius of the casting ring, ΔT1 is the desired maximum thermal gradient in the first segment, ΔT2 is the desired maximum thermal gradient in the second segment, A1 equals 9℃·m, and A2 equals 60℃·m. L1 min Equal to 0.065m, L1 max Equal to 0.09m, L2 min Equal to 0.17m, and L2 max Equal to 0.3m;

[0036] - Heat the surface of the molten alloy at the casting ring;

[0037] - The first section of the cooling casting ring is formed, thereby creating a cold region, which in turn forms a semi-solid arch of the alloy.

[0038] - Heating the second section of the cast ring, thereby forming a hot zone and thus creating an alloy solidification front in this hot zone, wherein the flatness of the alloy solidification front is less than 10° relative to a plane perpendicular to the tensile direction; and

[0039] - Along the stretching direction at a value greater than 10 -4 Stretching and curing of alloys at speeds of m / s.

[0040] [Mathematics 1]

[0041]

[0042] [Mathematics 2]

[0043] Attached Figure Description

[0044] Other features, details, and advantages will be presented when reading the detailed description below and when analyzing the accompanying drawings, wherein:

[0045] Figure 1

[0046] [ Figure 1 The diagram illustrates the plasma torch melting process using the casting ring according to the invention in a cold crucible.

[0047] Figure 2

[0048] [ Figure 2 This describes a cast ring according to the invention having cold and hot zones.

[0049] Figure 3

[0050] [ Figure 3 This describes a cast ring according to the invention having a cold region, a hot region, and a second cold region.

[0051] Figure 4

[0052] [ Figure 4 The angle α formed by the cured front relative to a plane perpendicular to the stretching direction is shown as a function of the length of the cold region L1 and the length of the hot region L2 at a stretching speed of 0.00015 m / s.

[0053] Figure 5

[0054] [ Figure 5 The angle α formed by the cured front relative to a plane perpendicular to the stretching direction is shown as a function of the length of the cold region L1 and the length of the hot region L2 at a stretching speed of 0.0003 m / s.

[0055] Figure 6

[0056] [ Figure 6 The angle α formed by the cured front relative to a plane perpendicular to the stretching direction is shown as a function of the length of the cold region L1 and the length of the hot region L2 at a stretching speed of 0.00045 m / s.

[0057] Figure 7

[0058] [ Figure 7 The angle α formed by the cured front relative to the plane perpendicular to the stretching direction is shown as a function of the length of the hot region L2 and the length of the cold region L3 for a cold region length L1 of approximately 0.077 m at a stretching speed of 0.0003 m / s.

[0059] The above text Figures 4 to 7 In this diagram, lines are the junctions of equally spaced lines with the same angle value. Continuous lines indicate the boundary between regions with angle α greater than 10° and regions with angle α less than 10°. The darker the pattern, the larger the angle. Detailed Implementation

[0060] The following text is for reference only. Figure 2 and Figure 3 A casting ring according to the invention is described. This casting ring 1 is particularly suitable for molding ingots made of titanium alloys or TiAl intermetallic alloys, said casting ring being made of a tube having a first end 11 and a second end 12.

[0061] The cast ring 1 includes a first tube section 13 and a second tube section 14. The first section 13 is made of a thermally conductive material and extends from the first end 11, specifically exceeding a length L1 between 0.065 m and 0.09 m. The second section 14 is made of a maximum phase alloy and extends from the first section 13, specifically exceeding a length L2 between 0.17 m and 0.3 m; the maximum phase is selected from Nb4Al1C3, Nb2AlC, Ti2AlC, and Ti2AlN. These maximum phases are the most compatible phases with the composition of titanium alloys and TiAl intermetallic alloys. In fact, in addition to titanium and aluminum, this alloy includes other elements, the most commonly used being zirconium, molybdenum, niobium, chromium, tungsten, vanadium, carbon, and boron. Therefore, all selected maximum phases have aluminum at site A. Furthermore, these selected maximum phases are temperature-compatible with the melting temperatures of titanium alloys and TiAl intermetallic alloys, which are close to 1,500 °C.

[0062] The cast ring 1 may further include a third segment 15 extending from the second segment 14 to the second end 12, specifically exceeding a length L3 of at least 0.03 m, and made of a thermally conductive material.

[0063] Lengths L1, L2, and L3 have been determined through simulation, specifically aimed at obtaining a cured front portion perpendicular to the stretching direction (i.e., the longitudinal axis of the casting ring 1). The results of these simulations are shown in... Figures 3 to 6These figures illustrate the effect of the selection of lengths L1 and L2 on the flatness of the pre-cured portion at different stretching speeds, 0.00015 m / s, 0.0003 m / s, and 0.00045 m / s, respectively. The flatter the pre-cured portion, the lighter the corresponding region. It can be noted that the higher the stretching speed, the smaller the region corresponding to the formation of a pre-cured portion at an angle of less than 10° relative to the plane perpendicular to the stretching direction. The angle is measured at the inner surface of the casting ring in a plane including the longitudinal axis of the stretched ingot, which is collinear with the stretching direction; this angle is between the tangent of the line formed by the intersection of the plane under consideration and the plane perpendicular to the stretching axis, and the curve formed by the intersection of the plane under consideration and the pre-cured portion considered at the inner surface of the casting ring. The length intervals have been defined to achieve a good trade-off between the flatness of the pre-cured portion and the range of stretching speeds to which the method is applicable. When lengths L1 and L2 are within the aforementioned intervals, the angle is less than 10° for a wide range of stretching speeds.

[0064] The first section 13 is a cold region and specifically serves as a heat exchange surface between the alloy poured into the casting ring and the heat transfer fluid circuit, making it possible to maintain the alloy temperature at approximately 25°C in this region. Preferably, the thermally conductive material is copper, a material with high thermal conductivity and ductility.

[0065] The second section 14 is a hot zone, that is, a zone where the alloy is heated to remelt the alloy, thereby making it possible to obtain the flattest possible solidification front, specifically with an angle of less than 10°.

[0066] For alloys containing niobium and aluminum, the phases Nb4AlC3 and Nb2AlC can be used alone. In other cases, the inner surface of the tube in the second section is preferably covered with one or more layers, each of which is made of a material selected from Nb4AlC3, Nb2AlC, Ti2AlC, Ti2AlN, and AlN.

[0067] For example, when the material is Nb4Al1C3, the inner surface of the pipe in the second section 14 is covered from the outside in with:

[0068] -A single layer of Nb2AlC;

[0069] - First layer Nb2AlC and second layer Ti2AlC;

[0070] - First layer Nb2AlC, second layer Ti2AlC, and third layer AlN; or

[0071] - First layer Nb2AlC, second layer Ti2AlC, third layer Ti2AlN and fourth layer AlN.

[0072] In another example, the material is Nb2AlC, and the inner surface of the tube at the second section 14 is covered from the outside inward with:

[0073] -A single layer of Ti2AlC;

[0074] - First layer Ti2AlC and second layer AlN; or

[0075] - First layer Ti2AlC, second layer Ti2AlN and third layer AlN.

[0076] In another example, the material is Ti2AlC, and the inner surface of the tube in the second section 14 is covered from the outside inward with:

[0077] - A single-layer AlN; or

[0078] - First layer Ti2AlN and second layer AlN.

[0079] The order of the layers mentioned above is crucial. In fact, it makes it possible to avoid the formation of secondary phases at the interfaces between different layers; a continuous solid solution is recommended between these phases.

[0080] Configurations with AlN in the innermost layer are particularly suitable for stretching aluminum-free alloys with melting temperatures above 1,600°C.

[0081] Preferably, the layer has a thickness between 50 μm and 1,000 μm. For example, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 250 μm, 500 μm, or 750 μm.

[0082] Furthermore, the selection of the aforementioned materials also has the advantage of facilitating the manufacture of the casting ring. In fact, all of these materials are now available in powder form. Therefore, to make the casting ring, the different selected powders can be densified or deposited in the form of layers. The temperatures required to densify these different materials are relatively close, between 1,400°C and 1,700°C, which makes it possible to sinter them together. In any case, the following method can be implemented: the different materials are concentrically positioned in a mold to achieve high-temperature sintering of the powder. Where a thin layer (i.e., less than 250 μm) is required, a cold spraying process can be used to create the necessary layer on the inner surface of the casting ring. For cases involving AlN, and if a thin layer (i.e., less than 250 μm) is necessary, a high-power pulsed magnetron sputtering process (also known as HiPIMS) can be implemented on the inner surface of the casting ring.

[0083] Regarding co-sintering, the discharge plasma sintering process can be used, for example, by applying the following densification cycle:

[0084] - Maximum sintering temperature: 1,500℃ to 1,600℃;

[0085] - Holding time: 10 to 30 minutes;

[0086] -Applied pressure: 30MPa to 100MPa;

[0087] -Atmospheric pressure; vacuum.

[0088] An additional layer that does not contact the molten alloy may be added, for example, to the outer surface of the cast ring, but is typically added only in restricted areas where it should not contact the molten alloy. This additional layer is composed of a ferromagnetic material, particularly a ferromagnetic alloy. This additional layer makes it possible to promote magnetic coupling with the cast ring. Examples of materials used for this layer include pure iron, FeCo, or FeSi alloys. Preferably, the additional layer has a thickness of at least 250 μm, for example, 300 μm, 350 μm, 400 μm, 450 μm, or 500 μm. This additional layer can be obtained by thermal spraying or cold spraying.

[0089] The first segment 13 and the second segment 14 can be connected to each other via a joint 17 formed by mechanical assembly or welding. Preferably, the joint 17 is contained within a cold region of the cast ring. In effect, this avoids limiting assembly techniques and utilizes the ductility of copper to limit bending stress in the stacking of the largest phase layers.

[0090] When provided, the third section 15 is a cold zone for cooling the alloy.

[0091] The second end 12 of the casting ring may have a chamfer that facilitates insertion of the casting ring into the device for obtaining an alloy ingot by stretching. When the third section 15 is provided, a chamfer may be made in the third section 15, specifically completely covering the third section 15.

[0092] The cast ring 1 may further include an extended and outwardly extending annular flange 16 perpendicular to the first segment 13 from the first end 11. Preferably, the collar 16 is circular, but it does not necessarily have to be circular. It may have a square, rectangular, or triangular shape, and optionally have rounded corners.

[0093] The aperture within the casting ring supplies the alloy ingot. Given the necessity of being able to stretch the ingot from the first end toward the second end, the inner wall of the casting ring is a mathematical cylinder, i.e., a surface created by generatrices parallel to each other around a closed curve and extending between the first end 11 and the second end 12. Although the closed curve is preferably circular (the stretched ingot is therefore a right-hand cylinder with a circular base), the invention is not limited to this shape. Specifically, the closed curve can be square, rectangular, or triangular. The angles can also be rounded.

[0094] Preferably, the wall thicknesses at the first segment 13, the second segment 14, and the third segment 15 are selected based on the maximum temperature gradient that the cast ring 1 must withstand between its inner surface in contact with the alloy and its outer surface. Specifically, the thicknesses are selected according to Mathematics 1 and 2 above.

[0095] Generally, the thickness e1 of the first segment 13 is less than the thickness e2 of the segment 14. Therefore, a shoulder is formed between the first segment and the second segment. Preferably, this shoulder is greater than 90° and preferably corresponds to the junction of the materials of the two segments.

[0096] Advantageously, the aforementioned casting ring 1 can be obtained using a method for obtaining products made of titanium alloys or TiAl intermetallic alloys by plasma torch melting to obtain an alloy with a directional structure.

[0097] The method is in Figure 1 The symbol schematically represents and includes:

[0098] - Select a casting ring 1 as described above, wherein the length L1 is between 0.065m and 0.09m, and the length L2 is between 0.17m and 0.3m, and select the thickness e1 and thickness e2 of its first and second segments according to the following:

[0099]

[0100]

[0101] Where R is the inner radius of the casting ring, ΔT1 is the maximum thermal gradient required in the first section, ΔT2 is the maximum thermal gradient required in the second section, A1 equals 9℃·m, and A2 equals 60℃·m, L1 min Equal to 0.065m, L1 max Equal to 0.09m, L2 min Equal to 0.17m, and L2 max Equal to 0.3m;

[0102] -At the casting ring, specifically the surface of the molten alloy is heated by plasma torch 3;

[0103] - The first section 13 of the cooling casting ring 1 is cooled to form a cold region, specifically through the cooling member 4, thereby forming a semi-solid arch of the alloy;

[0104] Specifically, a hot zone is formed by heating the second section 14 of the casting ring 1 with heater 5, thereby creating an alloy solidification front in this hot zone, with a flatness of less than 10° relative to a plane perpendicular to its stretching direction; and

[0105] - Along the stretching direction at a value greater than 10-4 Stretching and curing of alloys at speeds of m / s.

[0106] The method may further include cooling a third section 15 of the casting ring to form a second cold region, specifically via a second cooling member 6.

[0107] Upstream of the above steps, the method may include providing raw material MP (specifically, in the form of scrap, briquettes, rods, sponge / master alloy mixtures, etc.); heating the raw material MP (e.g., by a plasma torch 8, by an electric arc, by induction, by electron bombardment, etc.); melting the raw material MP into a primary molten alloy; refining the molten primary alloy (including, for example, stabilizing the alloy temperature and removing impurities); and casting the refined molten alloy 2 into a casting ring 1. These steps are known from the prior art and do not constitute the core of the present invention.

Claims

1. A casting ring for molding an ingot made of a titanium alloy, said casting ring being made of a tube having a first end and a second end, and comprising: - A first section having a length L1 and a thickness e1, and made of a thermally conductive material and extending from the first end; - The second section has a length L2 and a thickness e2, and is made of the largest phase alloy material and extends from the first section; The largest phase is selected from: Nb4Al1C3, Nb2AlC, Ti2AlC and Ti2AlN; Wherein, length L1 is between 0.065 m and 0.09 m, and length L2 is between 0.17 m and 0.3 m, and the thicknesses e1 and e2 of the first and second segments are selected according to the following: Where R is the inner radius of the casting ring, ΔT1 is the desired maximum thermal gradient in the first section, ΔT2 is the desired maximum thermal gradient in the second section, A1 equals 9℃·m, and A2 equals 60℃·m, L1 min Equal to 0.065 m, L1 max Equal to 0.09 m, L2 min Equal to 0.17 m, and L2 max It equals 0.3 m.

2. The casting ring for molding ingots made of titanium alloys according to claim 1, characterized in that, The thermally conductive material is copper.

3. The casting ring for molding ingots made of titanium alloys according to claim 1 or claim 2, characterized in that, The inner surface of the tube in the second section is covered with one or more layers, each of which is made of a material selected from Nb4Al1C3, Nb2AlC, Ti2AlC, Ti2AlN and AlN.

4. The casting ring for molding ingots made of titanium alloys according to claim 3, characterized in that, When the maximum phase alloy material is Nb4Al1C3, the inner surface of the tube in the second section is covered from the outside inward with: -A single layer of Nb2AlC; - First layer Nb2AlC and second layer Ti2AlC; - First layer Nb2AlC, second layer Ti2AlC, and third layer AlN; or - First layer Nb2AlC, second layer Ti2AlC, third layer Ti2AlN and fourth layer AlN; When the maximum phase alloy material is Nb2AlC, the inner surface of the tube in the second section is covered from the outside inward with: -A single layer of Ti2AlC; - First layer Ti2AlC and second layer AlN; or - First layer Ti2AlC, second layer Ti2AlN and third layer AlN; When the maximum phase alloy material is Ti2AlC, the inner surface of the tube in the second section is covered from the outside inward with: - A single-layer AlN; or - First layer Ti2AlN and second layer AlN.

5. The casting ring for molding ingots made of titanium alloys according to claim 1 or 2, characterized in that, The tube further includes an additional ferromagnetic material layer.

6. The casting ring for molding ingots made of titanium alloys according to claim 1 or 2, characterized in that, The first section and the second section are connected to each other by a joint made of mechanical assembly or welding.

7. The casting ring for molding an ingot made of a titanium alloy according to claim 1 or 2, further comprising a third section and a thermally conductive material, said third section extending from the second section to the second end.

8. The casting ring for molding an ingot made of a titanium alloy according to claim 7, wherein the third section extends from the second section to a length exceeding the second end by at least 0.03 m.

9. The casting ring for molding an ingot made of a titanium alloy as described in claim 1 or 2, further comprising an extended and outwardly extending annular flange perpendicular to the first section from the first end.

10. A method for obtaining a product made of a titanium alloy by plasma torch melting, the alloy having an oriented structure, the method comprising: - Select a casting ring, said casting ring being made of a tube having a first end and a second end, and comprising: - A first section having a length L1 and a thickness e1, which is made of a thermally conductive material and extends from the first end; - A second section having a length L2 and a thickness e2, which is made of the maximum phase alloy material and extends from the first section; The largest phase is selected from: Nb4Al1C3, Nb2AlC, Ti2AlC, and Ti2AlN. The length L1 is between 0.065 m and 0.09 m, and the length L2 is between 0.17 m and 0.3 m. The thicknesses e1 and e2 of the first and second segments are selected according to the following: Where R is the inner radius of the casting ring, ΔT1 is the desired maximum thermal gradient in the first section, ΔT2 is the desired maximum thermal gradient in the second section, A1 equals 9℃·m, and A2 equals 60℃·m, L1 min Equal to 0.065 m, L1 max Equal to 0.09 m, L2 min Equal to 0.17 m, and L2 max Equal to 0.3 m; -The surface of the alloy heated at the casting ring; - Cooling the first section of the casting ring to form a cold region, cooling to form a semi-solid arch of the alloy; - Heating the second section of the casting ring, thereby forming a hot zone and thus creating an alloy solidification front portion and a solidified alloy located below the hot zone, wherein the flatness of the alloy solidification front portion is less than 10° relative to a plane perpendicular to the stretching direction; and - Along the stretching direction at a value greater than 10 -4 The solidified alloy is stretched at a speed of m / s.

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