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CN-116615295-B - Method for obtaining a product made of a titanium alloy or a titanium-aluminium intermetallic compound

CN116615295BCN 116615295 BCN116615295 BCN 116615295BCN-116615295-B

Abstract

The invention relates to a method for obtaining a product made of a titanium alloy or a titanium-aluminium intermetallic compound by means of plasma torch melting, the alloy having an oriented structure, the method comprising heating the molten alloy (1) in a casting ring (2) by means of a plasma torch (3), cooling a cold zone (21) of the length L1 of the casting ring, the cooling forming a semi-solid crown (12) of the alloy, heating a hot zone (22) of the length L2 of the casting ring, thereby forming a solidification front (13) having a flatness of less than 10 DEG with respect to a plane perpendicular to the drawing direction, and drawing the solidified alloy (14) in the drawing direction at a speed of more than 10 ‑4 m/s. The invention also relates to a device for carrying out said method.

Inventors

  • Pierre king Sarot

Assignees

  • 赛峰公司

Dates

Publication Date
20260505
Application Date
20211202
Priority Date
20201203

Claims (16)

  1. 1. A method for obtaining a product made of a titanium alloy or TiAl intermetallic compound by plasma torch melting, the alloy having an oriented structure, the method comprising: -a plasma torch (3) heating the surface (11) of the molten alloy (1) at the casting ring (2); -cooling a cold zone (21) of length L1 just below the surface of the molten alloy at the casting ring, thereby forming a semi-solid crown (12) of alloy; -a hot zone (22) of length L2, downstream of the cold zone, so as to achieve control of the solidification front (13) of the alloy at the outlet of the hot zone, with a flatness of less than 10 ° with respect to a plane perpendicular to the drawing direction, and Drawing a solidified alloy (14) along the drawing direction at a speed higher than 10 -4 m/s, wherein the cold zone is maintained at a temperature between 0 ℃ and 50 ℃, wherein the hot zone is maintained at a temperature between T f x 0.8 and T f x 1.25, T f representing the melting temperature of the alloy in question.
  2. 2. The method for obtaining a product made of titanium alloy or TiAl intermetallic compound by plasma torch melting according to claim 1, characterized in that the length L1 is comprised between 0.065 m and 0.09 m.
  3. 3. The method according to any one of claims 1 to 2, characterized in that the length L2 is between 0.17 m and 0.3 m, for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting.
  4. 4. Process for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any one of claims 1 to 2, characterized in that the ratio L2/L1 is between 4 and 6.
  5. 5. Process for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any of claims 1 to 2, characterized in that the ratio L2/L1 is 5.
  6. 6. Method for obtaining a product made of titanium alloy or TiAl intermetallic compound by plasma torch melting according to any one of claims 1 to 2, characterized in that the selection of the power of the plasma torch depends on the drawing speed and is governed by a control law expressed by the following equation, where V is the drawing speed (m/S), S is the section of the drawn ingot (m 2), R is the radius of the drawn ingot (m), η is the efficiency of the plasma torch, Q is the power of the plasma torch (W), σ is the radius of action of the plasma torch (m), P is the perimeter of the casting ring (m), L is the total length of the casting ring (m), ρ is the volumetric mass of the casting alloy (kg.m -3 ), h is the exchange coefficient of the casting ring (W.m -2 .℃ -1 ）,C P is the specific heat (j.kg -1 .℃ -1 ）,L M is the latent heat of fusion of the casting alloy (j.kg -1 ）,ΔT 2 ) is the thermal gradient between the inlet and outlet of the ring (° C), and where Δt 1 is the thermal gradient between the temperature of the metal at the region and the preheating temperature thereof: 。
  7. 7. The method for obtaining a product made of titanium alloy or TiAl intermetallic compound by plasma torch melting according to any one of claims 1 to 2, further comprising a second cold zone of cooling length L3 downstream of the hot zone.
  8. 8. The method for obtaining a product made of titanium alloy or TiAl intermetallic compound by plasma torch melting according to claim 7, characterized in that the length L3 is greater than 0.03 m.
  9. 9. Method for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any one of claims 1 to 2, characterized in that the cold zone is maintained at a temperature between 10 ℃ and 40 ℃ while solidifying alloy (14) is stretched at a speed higher than 10 -4 m/s along the stretching direction.
  10. 10. Method for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any one of claims 1 to 2, characterized in that the cold zone is maintained at a temperature between 25 ℃ and 35 ℃ while solidifying alloy (14) is stretched at a speed higher than 10 -4 m/s along the stretching direction.
  11. 11. Method for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any one of claims 1 to 2, characterized in that the cold zone is maintained at a temperature between 20 ℃ and 30 ℃ while solidifying alloy (14) is stretched at a speed higher than 10 -4 m/s along the stretching direction.
  12. 12. Method for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any one of claims 1 to 2, characterized in that the cold zone is maintained at a temperature of 25 ℃ while solidifying alloy (14) at a speed higher than 10 -4 m/s along the drawing direction.
  13. 13. Method for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any of claims 1 to 2, characterized in that the hot zone is maintained at a temperature comprised between T f x 0.85 and T f x 1.20 while solidifying alloy (14) at a speed higher than 10 -4 m/s along the drawing direction.
  14. 14. Method for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any one of claims 1 to 2, characterized in that the hot zone is maintained at a temperature comprised between T f x 0.9 and T f x 1.15 while solidifying alloy (14) at a speed higher than 10 -4 m/s along the drawing direction.
  15. 15. Method for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any one of claims 1 to 2, characterized in that the hot zone is maintained at a temperature comprised between T f and T f x 1.10 while solidifying alloy (14) is stretched at a speed higher than 10 -4 m/s along the stretching direction.
  16. 16. Method for obtaining a product made of titanium alloy or TiAl intermetallic compound by means of plasma torch melting according to any of claims 1 to 2, characterized in that the hot zone is maintained at a temperature of T f x 1.05 while solidifying alloy (14) is stretched at a speed higher than 10 -4 m/s along the stretching direction.

Description

Method for obtaining a product made of a titanium alloy or a titanium-aluminium intermetallic compound Technical Field The present invention relates to the field of methods for manufacturing alloys, in particular aeronautical alloys such as titanium-based alloys or TiAl intermetallic compounds, and devices for implementing these methods. Background There are several processes for manufacturing alloys, in particular aerospace alloys such as nickel-based alloys, titanium-based alloys or TiAl intermetallic alloys. The latter is mainly made of virgin raw materials which are compacted in the form of cylindrical electrodes and then melted in a vacuum arc remelting process (more commonly referred to as VAR), or by recycling scrap, the vacuum induction melting method (more commonly referred to as VIM) most commonly used to recycle scrap (either in cold or in hot crucibles). However, with respect to intermetallic alloys containing about 50% aluminum atoms, these methods have the disadvantage of being carried out under vacuum. Considering the vapor pressure of aluminum in the molten titanium bath, a large amount of aluminum element may evaporate during melting, which makes control of the entire alloying element composition difficult. For these alloys, and typically for titanium-based alloys, there is and is still developing an alternative method, plasma torch melting (or PAM-CHR, representing plasma arc melting/cold hearth refining) in a cold crucible. This method is shown in fig. 1. This method uses helium and/or argon at atmospheric pressure to feed the plasma torch. The neutral gas pressure can limit the evaporation of the reactive elements comprising aluminum to 3 to 5 orders of magnitude, thereby making it possible to melt such alloys. More particularly, in this method, raw material MP (which may be in the form of scrap, briquettes, bars, or sponge/master alloy mixtures) is pushed into a cold crucible CR and melted by one or more plasma torches TC scanning the surface of the crucible. As the melting proceeds, the liquid metal AF moves towards the refining zone where the temperature is stable and some impurities are removed. Then, the liquid metal AF discontinuously flows into a cooling casting ring AM, which is made of copper, from which the ingot L is gradually extracted. From an economic point of view, the PAM-CHR process is the cheapest one of the titanium remelting processes (20% to 60% reduction in cost) which also allows easy recovery of the scrap without having to compact the scrap beforehand, and the use of a plasma torch to concentrate the energy where it is needed makes the process more energy efficient. In some cases, the material health of the resulting ingot makes it possible to use this material without any additional thermo-mechanical conversion treatment, and to cut parts directly from its bulk. However, for some alloys, such as titanium-based alloys and TiAl intermetallic alloys, the microstructure, and in particular the orientation thereof, can directly affect the mechanical properties of the resulting alloy. Thus, microstructure control during solidification of these alloys is a major area requiring improvement. In the case of PAM-CHR solidification occurs essentially at the casting ring, which nowadays is made of cooled copper. The PAM-CHR process approximates the continuous casting technique well known in the art. However, there are solutions that make it possible to orient the microstructure during solidification of these continuous casting processes. Most solutions are based on the use of two zones, a hot zone where the metal remains in the liquid state and a cold zone where the metal cools in sequence. However, these solutions cannot be directly applied to PAM-CHR methods. Indeed, the latter has unique features with respect to casting rings, including heating the liquid metal surface above the casting ring using a plasma torch, which is generally centered with respect to the casting ring. This configuration will generate a heat flux at the surface of the liquid bath, which can be modeled according to equation 1 for casting a cylindrical ingot with a circular base, where η is the efficiency of the torch, Q is its power (W), σ is the radius of action (m) of the torch, and r is the distance (m) from the center of the ingot: [ equation 1] Such a heat flux profile associated with the drawing speed of the ingot is not compatible with directional solidification because it causes a non-planar solidification front at the cast ring, deeper at the center of the ring than at the edges of the ring. Fig. 2 is a cross-section of an ingot cast using such a process. Fig. 3 schematically shows an example of a solidification front obtained using a method of this type. The authors of document FR 3090430 have attempted to solve these heterogeneities. In this document, the mixing of the liquid alloy in the casting ring is carried out by electromagnetic induction, making it possible to homogenize and optimize t