Process for manufacturing titanium-based metal compound ingots

Afterglow of the invention

The present invention relates to the general field of the manufacture of ingots of a metal compound based on titanium, such as alloys or intermetallic compounds, in particular for the manufacture of parts for an aircraft.

Ingots of titanium-based alloy, or titanium-based intermetallic compound, are typically made by melting fragments of raw material in different basins, the liquid metal then being poured into a crucible to cool and solidify the metal to form ingots.

However, the conventional manufacturing process for titanium ingots can lead to a problem of lowering the mechanical properties of the ingot obtained with respect to the desired mechanical properties.

Purpose and summary of the invention

The main aim of the present invention is therefore to overcome such a drawback by proposing, according to a first aspect of the invention, a method of manufacturing an ingot made of a titanium-based metal compound comprising the following steps:

- provide fragments of raw material;

- Melting the fragments of raw material into a liquid metal in at least one basin;

- Maintaining the molten metal in said at least one basin;

- Pouring the liquid metal from at least one basin into a crucible by overflowing from said at least one basin into said crucible;

- forming an ingot by cooling the liquid metal in the crucible; characterized in that the method comprises the following step:

- preheating the fragments of raw material before the melting of said fragments of raw material with a preheating temperature greater than or equal to 75% of the liquidus temperature of said fragments of raw material, said preheating temperature being strictly lower than the liquidus temperature.

Such a step of preheating the fragments of raw material makes it possible to improve the homogeneity of the metal in the basin, in particular by reducing the presence of unmelted in the basin.

In addition, such a preheating makes it possible to reduce the decrease in temperature in the basin when newly molten metal falls into said basin, thus also improving the homogeneity by facilitating the dissolution of the unsalted in the basin, and increasing the rate of melting of the basin. metallic compound allowing productive gains.

In addition, such preheating makes it possible to reduce the thermal shock undergone by the raw materials during the melting step, thus reducing the gaseous emissions of the raw materials. These gaseous releases can cause reactions which are liable to create inclusions, these inclusions reducing the mechanical properties of the ingots. The reactions caused by the evolution of gas can also produce elements which are deposited in the crucible, thus reducing the mechanical properties of the ingots. In addition, the thermal shock of the raw materials promotes the projections of small solid particles of raw material which can fall further downstream in the basin and thus have a reduced time to dissolve,

Such a preheating step is particularly advantageous for the manufacture of ingots made of a metal compound based on titanium because these metal compounds have a high melting point (titanium having a melting point of 1668 ° C), the metal compounds based on titanium with a higher risk of the presence of unmelted metal particles during the formation of the ingot.

The process can include the following characteristics, taken alone or in combination depending on the technical possibilities:

- the preheating temperature is greater than or equal to the solidus temperature of the raw material fragments;

- the preheating temperature is greater than or equal to 93% of the liquidus temperature;

the metal compound based on titanium comprises at least one element having a melting point higher than the melting point of titanium;

- the preheating of the raw material fragments is carried out by induction;

the preheating of the fragments of raw material by induction is configured to ensure levitation of said fragments of raw material;

- The preheating of the raw material fragments is carried out by a generator of a heating bundle;

the method comprises a step of controlling the orientation of the generator of the heating beam;

- the process comprises the following steps:

• melt fragments of raw material into a liquid metal in a first basin;

• maintain the molten metal in the first basin;

• pouring the liquid metal from the first basin into a second basin by overflowing from said first basin into said second basin;

• keep the molten metal in the second basin;

• pouring the liquid metal from the second basin into the crucible by overflowing from said second basin into said crucible.

According to a second aspect, the invention proposes a system for manufacturing an ingot made of a titanium-based metal compound comprising:

- at least one basin which is configured to receive liquid metal;

- a conveyor which is configured to convey fragments of raw material to said at least one basin;

a crucible which is fed by overflow from said at least one basin and which is configured to cool and solidify the liquid metal;

heating means which are located opposite the at least one basin and the crucible and which are configured to heat and melt fragments of raw material in said at least one basin and in said crucible;

characterized in that the system comprises a preheating device which is configured to heat the raw material fragments on the conveyor with a preheating temperature greater than or equal to 75% of the liquidus temperature of said raw material fragments, and strictly less than the liquidus temperature of said raw material fragments.

The system can include the following characteristics, taken alone or in combination depending on the technical possibilities:

- The preheating device comprises a generator of a heating bundle;

the system comprises an image acquisition device and an image analysis device, said image acquisition device being configured to acquire images of the preheating of the raw material fragments by the generator of the heating beam, and said image analysis device being configured to control the orientation of the generator of the heating beam from the images acquired by said image acquisition device;

- The preheating device comprises an induction preheating device;

- the induction preheating device is configured to levitate the fragments of raw material.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof without any limiting nature. In the figures:

FIG. 1 schematically represents a system for manufacturing an ingot made of a titanium-based metal compound according to one embodiment of the invention;

FIG. 2 represents a first variant embodiment of a device for preheating the system for manufacturing an ingot;

- Figure 3 shows a second embodiment of the preheating device;

FIG. 4 represents a schematic view of the various steps of a process for manufacturing an ingot of a titanium-based metal compound according to one implementation of the invention;

- Figure 5 shows a schematic view of the various stages of the manufacturing process implemented with the variant of the manufacturing system of Figure 1.

Detailed description of the invention

As illustrated in FIG. 1, a system 1 for manufacturing an ingot 2 made of a titanium-based metal compound comprises a conveyor 11 on which fragments of raw material 3 are conveyed. The conveyor 11 may for example be formed by a table. vibrator, a push cylinder, a conveyor belt, or an endless screw.

The raw material fragments 3 can be master alloys, recycled material fragments, or virgin raw material of titanium-based alloy or titanium-based intermetallic compound. Typically, the fragments of raw material 3 can be formed by blocks of particles, such as chips, which are agglomerated and compacted in the press, these blocks having a length of between 20cm and 50cm for example.

The term “titanium-based metal compound” is understood here to mean either a titanium-based alloy, that is to say an alloy of which titanium is the main constituent, or an intermetallic compound based on titanium, that is to say say an intermetallic compound of which titanium is the main constituent. An alloy is a combination of different metals, while an intermetallic compound is a combination of at least one metal with at least one metalloid.

The metal compound can, for example, be an alloy from among the following alloys: Til7, TiBetalo, T121S, TÎ6242, and TΊ6246; or else an intermetallic compound from among the following intermetallic compounds: TiAl 48-2-2, and TiNMBl. The examples given are not limiting; other alloys or intermetallic compounds based on titanium can be used.

The system 1 comprises at least one basin in which the fragments of raw material 3 are melted. In the exemplary embodiment illustrated in FIG. 1, the system 1 comprises a first basin 12 and a second basin 13 located downstream of said first basin 12. The number of basins can however be greater, the system 1 thus being able to comprise three. or four basins for example, or much less, the system 1 thus being able to include a single basin.

The first basin 12 and the second basin 13 collect liquid metal 4 obtained by melting the fragments of raw material 3.

The first basin 12 and the second basin 13 are formed on the one hand by a wall which receives the liquid metal 4, said wall being for example made of copper, and on the other hand by a cooling device which makes it possible to keep the wall at a temperature below its deterioration temperature, said cooling device typically being produced by a circuit for circulating a cooling liquid.

The fragments of raw material 3 are melted in the first basin 12, then the liquid metal 4 obtained by the fusion of said fragments of raw material 3 is transferred into the second basin 13.

The melting of the fragments of raw material 3 is carried out by heating means 14 which are located opposite the first basin 12 and the second basin 13.

The heating means 14 can for example be formed by plasma torches, electron guns, electric arc generators, laser generators, or induction heating means.

In addition, the heating means 14 are configured to keep the molten metal 4 in the first and second basins 12 and 13 in order to place the liquid metal 4 in the desired metallurgical state.

The atmosphere in which the first basin 12 and the second basin 13 are located can be controlled. So that the liquid metal 4 does not react with the atmosphere, the controlled atmosphere can for example be produced by a vacuum atmosphere or else by an inert gas atmosphere under a controlled pressure. According to another possible variant, the controlled atmosphere is formed by a specific gas under a controlled pressure, said specific gas being adapted to react with the liquid metal 4 in order to charge said liquid metal 4, and thus the metal compound of the ingot 2, with said specific gas.

The first basin 12 and the second basin 13 can also be exposed to an uncontrolled atmosphere.

As illustrated in FIG. 1, the system 1 comprises a crucible 15 into which the liquid metal 4 from the second basin 13 is poured in order to cool said liquid metal 4, solidify it and thus form a solid metal advancing front 5 which is shaped to form the ingot 2 by semi-continuous casting.

In order to cool the liquid metal 4 which is poured into the crucible 15, said crucible 15 comprises a cooling circuit which cools the walls of said crucible 15. The walls of the crucible 15, which are cooled by the cooling circuit, are made in one piece. material with high thermal conductivity, for example copper or copper alloy.

Furthermore, as can be seen in FIG. 1, the heating means 14 are also located opposite the crucible 15 and are configured to maintain the molten metal 4 in the upper part of the crucible 15.

The liquid metal 4 is transferred from the first basin 12 to the second basin 13, and from the second basin 13 to the crucible 15 by overflow. In other words, the second basin 13 is supplied by overflow of the liquid metal 4 from the first basin 12 towards said second basin, and the crucible 15 is supplied by overflow of the liquid metal 4 from the second basin 13 towards said crucible 15. Such a characteristic makes it possible to limit the risk of an unmelted metal particle reaching the crucible 15, which would reduce the mechanical properties of the ingot 2. In fact, the still solid metal tends to fall to the bottom of the first basin 13 and of the second basin 14.

In order to improve the mechanical characteristics of the ingot 2 of the titanium-based metal compound, the system 1 comprises a preheating device 16 which is located opposite the conveyor 11 and which is configured to preheat the fragments of raw material 3 before said fragments of raw material 3 are melted in the first basin 12.

The preheating device 16 is configured to heat the fragments of raw material 3 to a preheating temperature which is greater than or equal to 75% of the liquidus temperature of said.

fragments of raw material 3, and which is strictly lower than the liquidus temperature of said fragments of raw material 3.

Such a preheating temperature makes it possible to reduce the temperature gradient at the inlet of the first basin 12. This makes it possible to facilitate the melting of the fragments of raw material 3, which reduces the presence of unmelted metal particles in the first and second basins. 12 and 13, thus limiting the risk of these unfelted metal particles reaching the crucible 15.

The preheating according to the invention makes it possible in particular to reduce the presence of the small size unmelted metal particles thanks to the facilitation of the melting of these particles, the small size particles being the most likely not to fall to the bottom of the first and second basins 12 and 13 and therefore to be poured with the liquid metal 4 into the crucible 15.

In addition, such a preheating temperature makes it possible to reduce the thermal shock undergone by the fragments of raw material 3 when they arrive in the first basin 12. The reduction of the thermal shock makes it possible to reduce the gas emissions, thus limiting the reactions caused by these gaseous releases which are liable to produce unwanted elements in the metal compound degrading the mechanical properties of the ingot.

Preferably, the preheating temperature is greater than or equal to the solidus temperature of the metal compound, which makes it possible to further accelerate the dissolution of the solid metal particles in the first and second basins 12 and 13, and makes it possible to reduce thermal shock. The preheating temperature is always strictly lower than the liquidus temperature of the alloy.

Thus, the fragments of raw material 3 are partially melted because they are at a temperature above the solidus temperature but strictly below the liquidus temperature of the metal compound.

Even more preferably, the preheating temperature is greater than or equal to 93% of the liquidus temperature of the alloy, making it possible to further accelerate the dissolution of the solid metal particles, and to further reduce the temperature difference. undergone by the fragments of raw material 3. Here again, the temperature

preheating temperature is strictly lower than the liquidus temperature of the alloy.

The invention is particularly advantageous for metal compounds based on titanium which comprise elements having a melting point higher than the melting point of titanium, such as, for example, molybdenum, vanadium or tantalum. Indeed, the elements present in the metallic compound which have a melting point higher than the melting point of titanium, such as for example molybdenum, vanadium and tantalum, are elements which tend to form unmelted particles in the liquid metal 4 which can reach the crucible 15.

According to a first possible variant illustrated in FIG. 2, the preheating device 16 comprises an induction preheating device 16a. The induction preheating device 16a can be formed by a solenoid as illustrated in FIG. 2, or else by an induction plate parallel to the conveyor 11.

According to an advantageous characteristic making it possible to limit the pollution of the fragments of raw material 3 by contact with the conveyor 11, the induction preheating device 16a is configured to ensure levitation of said fragments of raw material 3 above the conveyor 11.

The configuration of the induction preheating device 16a to ensure the gradual rise in temperature and the levitation of the fragments of raw material is carried out by adapting the intensity and the frequency of the electric current flowing through said induction preheating device 16a.

According to a second variant embodiment illustrated in FIG. 3, the preheating device 16 comprises a generator 16b of a heating beam F, such as for example a light focus, an electron beam generator, a plasma torch, or even a generator. laser.

Advantageously, in order to improve the efficiency of the preheating of the fragments of raw material 3, the preheating device comprises an image acquisition device 16c, such as for example a camera, and an image analysis device. 16d, such as for example a processor and a memory on which is recorded an image processing program. The image acquisition device 16c is configured to acquire images of the preheating of the fragments of raw material 3 by the generator 16b of the heating beam F.

The image acquisition device 16c is also configured to transmit the acquired images to the image analysis device 16d. The image analysis device 16d is for its part configured to analyze the images transmitted by the image acquisition device 16c and to check the orientation of the generator 16b of the heating beam F by checking that the heating beam F is indeed directed towards the fragments of raw material 3, and not directed next to said fragments of raw material 3, directly towards the conveyor 11.

When the image analysis device 16d detects that the heating beam F is not directed correctly, said image analysis device 16d can issue an alert so that an operator or an automaton corrects the orientation of the generator. 16b of the heating beam F. The image analysis device 16d can also be configured to control the orientation of the generator 16b of the heating beam F so that when said image analysis device 16d detects that the heating beam F n 'is not directed correctly, said image analysis device 16d automatically corrects the orientation of said generator 16b of the heating beam F.

The system 1 for manufacturing the ingot 2 made of a titanium-based metal compound is configured to implement the manufacturing process illustrated in FIG. 4.

As illustrated in Figure 4, the manufacturing process of ingot 2 comprises the following steps:

- E1: supply the fragments of raw material 3. This step E1 is carried out with the conveyor 11.

- E2: preheat the fragments of raw material 3 with a preheating temperature greater than or equal to 75% of the liquidus temperature of said fragments of raw material 3, and strictly lower than the liquidus temperature of said fragments of raw material 3. This step preheating E2 is carried out with the preheating device 16.

- E3: melt the fragments of raw material 3 into a liquid metal 4 in at least one basin. This melting step is carried out after the preheating step E2. This melting step E3 is carried out with the heating means 14.

- E4: maintain molten liquid metal 4 in said at least one basin. This molten maintenance step makes it possible to place the liquid metal 4 in the desired metallurgical state, and also makes it possible to ensure good dissolution of the unmelted metal particles. This step of maintaining melt E4 is carried out with the heating means 14.

- E5: pour the liquid metal 4 from at least one basin into the crucible 15 by overflowing from said at least one basin into said crucible 15.

- E6: form ingot 2 by cooling liquid metal 4 in crucible 15.

With the embodiment of the system 1 illustrated in figure 1, the method comprises the following steps, as illustrated in figure 5:

- E31: melting the fragments of raw material 3 into a liquid metal 4 in the first basin 12. This step E31 of melting in the first basin 12 is a variant of the step E3 of melting in at least one basin.

- E41: maintaining molten metal 4 in the first basin 12. This step E41 of maintaining molten in the first basin 12 is a variant of step E4 of maintaining molten in at least one basin.

- E5 ': pour the liquid metal 4 from the first basin 12 into the second basin 13 by overflowing from said first basin 12 into said second basin 13.

- E42: maintaining molten metal 4 in the second basin 13. This step E42 of maintaining molten in the second basin 13 is a variant of step E4 of maintaining molten in at least one basin.

- E51: pour the liquid metal 4 from the second basin 13 into the crucible 15 by overflowing from said second basin 13 into said crucible 15. This step E51 of pouring into the crucible 15 by overflowing from the second basin 13 is a variant of step E5 pouring into crucible 15 by overflow of at least one basin.

Moreover, when the preheating of the fragments of raw material 3 is carried out with a generator 16b of a heating bundle F, the process for manufacturing the ingot 2 made of a titanium-based metal compound can comprise a step of controlling the orientation of the metal. heating beam F carried out during the preheating step E2 of the fragments of raw material 3. This step of controlling the orientation of the heating beam F is carried out by the image analysis device 16d from the images acquired by the device image acquisition 16c.

CLAIMS

1. A method of manufacturing an ingot (2) made of a titanium-based metal compound comprising the following steps:

- (E1) provide fragments of raw material (3);

- (E3) melting the fragments of raw material (3) into a liquid metal (4) in at least one basin;

- (E4) maintaining the molten metal (4) in said at least one basin;

- (E5) pouring the liquid metal (4) from at least one basin into a crucible (15) by overflowing from said at least one basin into said crucible (15);

- (E6) forming an ingot (2) by cooling the liquid metal (4) in the crucible (15);

characterized in that the method comprises the following step:

- (E2) preheating the fragments of raw material (3) before the melting of said fragments of raw material (3) with a preheating temperature greater than or equal to 75% of the liquidus temperature of said fragments of raw material (3), and strictly below the liquidus temperature of said raw material fragments (3).

2. The method of claim 1, wherein the preheating temperature is greater than or equal to the solidus temperature of the raw material fragments (3).

3. The method of claim 2, wherein the preheating temperature is greater than or equal to 93% of the liquidus temperature.

4. Method according to any one of claims 1 to 3, wherein the titanium-based metal compound comprises at least one element having a melting point higher than the melting temperature of titanium.

5. Method according to any one of claims 1 to 4, wherein the preheating of the raw material fragments (3) is carried out by induction.

6. Method according to any one of claims 1 to 4, wherein the preheating of the raw material fragments (3) is carried out by a generator (16b) of a heating bundle (F).

7. The method of claim 6, wherein said method comprises a step of controlling the orientation of the generator (16b) of the heating beam (F).

8. A method according to any one of claims 1 to 7, wherein the method comprises the following steps:

- (E31): melting fragments of raw material (3) into a liquid metal (4) in a first basin (12);

- (E41): keep molten metal (4) in the first basin

(12);

- (E5: pouring the liquid metal (4) from the first basin (12) into a second basin (13) by overflowing from said first basin (12) into said second basin (13);

- (E42): keep the liquid metal (4) molten in the second basin (13);

- (E51): pour the liquid metal (4) from the second basin (13) into the crucible (15) by overflowing from said second basin (13) into said crucible (15).

9. System (1) for manufacturing an ingot (2) made of a titanium-based metal compound comprising:

- at least one basin which is configured to receive liquid metal (4);

- a conveyor (11) which is configured to convey fragments of raw material (3) to said at least one basin;

- a crucible (15) which is fed by overflow from said at least one basin and which is configured to cool and solidify the liquid metal (4); - heating means (14) which are located opposite the at least one basin and the crucible (15) and which are configured to melt and keep molten fragments of raw material (3) in said at least one basin and in said crucible (15);

characterized in that the system (1) comprises a preheating device (16) which is configured to heat on the conveyor (11) said fragments of raw material (3) with a preheating temperature greater than or equal to 75% of the temperature liquidus of said raw material fragments (3), and strictly below the liquidus temperature of said raw material fragments (3).

10. System (1) according to claim 9, wherein the preheating device (16) comprises a generator (16b) of a heating bundle (F).

11. The system of claim 9, wherein the preheating device (16) comprises an induction preheating device.