WO2012123389A1

WO2012123389A1 - Method and device for forming metallic-glass beads

Info

Publication number: WO2012123389A1
Application number: PCT/EP2012/054207
Authority: WO
Inventors: Sébastien GRAVIER; Georges KAPELSKI; Jean-Jacques Blandin; Charles JOSSEROND
Original assignee: Universite Joseph Fourier; Institut Polytechnique De Grenoble; Centre National De La Recherche Scientifique (Cnrs)
Priority date: 2011-03-14
Filing date: 2012-03-12
Publication date: 2012-09-20
Also published as: FR2972729A1

Abstract

The invention relates to a method and a device for forming metallic-glass beads from a metal alloy. The metal alloy, heated in a crucible (7) to a temperature at least equal to the melting point thereof, is extruded through at least one extrusion hole (10) provided in the lower portion of the crucible, so as to flow downward and form a series of separate drops (G) of melted metal alloy, said drops of melted metal alloy entering a cooling liquid (L) so as to solidify, thereby forming metallic-glass beads (B).

Description

Method and device for training

of metallic glass beads

The present invention relates to the field of the manufacture of metal glasses, also called alloys or amorphous or vitreous metals.

Processes and devices are known in which metals are heated in a crucible and extruded through extrusion orifices in the form of separate and sequential melt drops which enter a cooling liquid to solidify. by forming particles or metal balls. Such methods and devices are described in FR 2,18,707, US 3,206,799, US 3,019,485, US 2,919,471, US 2,595,780 and EP 136,866.

However, these methods and devices are not at all suitable for the formation of metallic glass beads.

Metallic glasses are recent materials, which are conventionally obtained by rapid cooling of a molten metal alloy.

The amorphous structure of these metal glasses gives them interesting properties: a very high mechanical strength, a high capacity for elastic deformation, a high resistance to corrosion and abrasion. Metallic glasses based on zirconium (Zr), based on magnesium (Mg) and based on iron (Fe) are more particularly known.

It is now known to obtain metal glasses by atomization, in the form of amorphous powders, the particles of which generally have sizes of typically between 10 microns and 100 microns and which can reach a few millimeters in the case of atomization with water. However, in these techniques, a dimensional distribution of the powders obtained is observed, which requires a method to obtain a range of desired sizes.

It is also known to obtain metallic glasses by casting a liquid metal alloy on a cooled surface, for example on a cooled wheel, on a cooled plate or in a cooled mold, to cause rapid solidification of the liquid alloy.

For example, it is known to produce ribbons, wire glass or metallic glass plates. However, the manufacture of pieces of the order of one cubic millimeter (mm ³ ), from such plates, ribbons or son poses real difficulties that are due to the fact that the metal glasses are difficult to machine.

In general, obtaining pieces of determined volumes, for example of the order of one cubic millimeter (mm ³ ), poses real difficulties, particularly if one wants to avoid losses of materials from a sieving or a machining phase.

There is provided a method of forming metal glass beads from a metal alloy.

This process is such that the metal alloy, heated in a crucible at a temperature at least equal to its melting temperature, is extruded through at least one extrusion orifice arranged at the bottom of the crucible to flow. downwards and forming separate and successive drops of molten metal alloy and in which the droplets of molten metal alloy enter a cooling liquid which is contained in a container and whose surface is spaced from said orifice of extrusion, to solidify by forming metal glass beads.

The crucible and the container being disposed in a closed chamber, the coolant is introduced into the container after at least one suction of the air contained in the chamber followed by introduction into the chamber of an inert gas to the metal alloy.

Thus, it is possible to obtain high quality metallic glass beads whose volumes and shapes can be approximately calibrated by the extrusion orifice of the crucible, because the drops of the molten metal alloy are detached. under the effect of gravity and by breaking the effects of capillarity.

The extrusion can be carried out by applying an overpressure to the surface of the molten metal alloy in the crucible, relative to at the pressure above the surface of the coolant.

The coolant may be inert to the metal alloy.

The coolant can be cooled.

An inert gas vis-à-vis the metal alloy can flow in the space between the crucible and the surface of the coolant.

There is also provided a device for the formation of metallic glass beads from a metal alloy.

This device may comprise an enclosure that can be closed; a crucible adapted to receive the metal alloy and whose bottom has at least one through-extrusion orifice; heating means for heating the alloy in the crucible at a temperature at least equal to its melting temperature; and a container disposed in the chamber, adapted to contain a cooling liquid placed below and at a distance from said crucible through orifice, means for introducing a gas which is inert with respect to the metal alloy in the enclosure; and means for introducing coolant into the container (11).

The distance between the extrusion through hole of the crucible and the surface of the coolant may be such that the liquid alloy flowing downward from the crucible orifice forms separate and successive alloy drops and that these drops of alloy, in the liquid state, enter the coolant and are cooled in this liquid to form metallic glass beads.

An extrusion means may be provided for extruding the liquid alloy through said crucible through hole.

The extrusion means may comprise a source of inert gas capable of creating an overpressure on the surface of the molten metal alloy in the crucible, relative to the pressure prevailing above the surface of the coolant.

The device may comprise a lower chamber and an upper chamber separated by a partition wall carrying the crucible and provided with a through passage opening said orifice, the container being in the lower chamber and being placed below the bottom of the crucible.

A vacuum pump can be connected to the lower chamber and the upper chamber.

Means may be provided for circulating the inert gas into the lower chamber.

A gas source can be connected to the upper chamber. The device may comprise a shutter movable between a shut - off position in which it structs said extrusion through hole and a spaced apart position in which said extrusion through orifice is released and in which it is laterally spaced from the way drops of alloy.

A device for the formation of metallic glass beads will now be described by way of nonlimiting example, illustrated in the single appended figure.

A device 1, for the formation of metal glass beads from a metal alloy, shown in this figure, comprises a vertical enclosure 2, for example parallelepipedal or cylindrical, which is preferably provided with a waterproof band, of a horizontal inner wall 3 which divides it into a lower chamber 4 and an upper chamber 5, this inner wall having a passage 6, for example central. The enclosure 2 may comprise an upper cover 2a for access to the upper chamber 5.

The device 1 comprises a crucible 7, open in the upper chamber 5, for example sposed along the vertical axis of the chamber 2 and which has a vertical peripheral wall 8, for example cylindrical, and a bottom 9, for example flat and di spossed horizontally. According to the example shown, the periphery of the bottom 9 is laid and preferably fixed sealingly on the edge of the inner wall 3 surrounding the passage 6. Thus, the lower chamber 4 and the upper chamber 5 are separated by the inner wall 3 and the bottom 9 of the crucible 7, the vertical peripheral wall 8 extending into the chamber According to a variant of embodiment, the vertical peripheral wall 8 of the crucible 7 could pass through the passage 6 of the horizontal inner wall 3 and be fixed, preferably in a sealed manner, to the edge of this passage 6.

The crucible 7 may be for example quartz, graphite or boron nitride.

The bottom 9 of the crucible 7 has for example a plurality of calibrated through orifices 10, for example cylindrical.

The device 1 also comprises a heating element 7a, for example by induction, which is placed near the peripheral wall 8 of the crucible 7 and therefore in the upper chamber 5.

The crucible 7 is intended to receive a metal alloy M which, under the effect of the heating member 7a, can be heated. The upper part of the chamber 2 is adapted to be able to charge continuously or discontinuously the crucible 7 of solid metal alloy.

The device 1 comprises a container 11 which is installed in the lower part of the lower chamber 4 and which is open in this lower chamber 4, below and at a distance from the bottom 9 of the crucible 7.

The container 1 1 is intended to receive a cooling liquid L, which can be regulated in temperature by a cooling member 12. This regulating member 12 may comprise a coil placed near or in contact with the peripheral wall of the container 1 1, inside or outside this wall, this coil being connected to a source of a control fluid by conduits (not shown).

The device 1 may also comprise a conduit 13 connected to the enclosure, which connects the lower chamber 4 and the upper chamber 5 and on which a solenoid valve 14 is installed.

The device 1 may comprise an external conduit 1 5 connected to the enclosure 2, connected to the lower chamber 4 and on which are installed a solenoid valve 16 and a vacuum pump 16a.

The device 1 may comprise an outer conduit 17 connected to the enclosure 2, connected to the lower chamber 4 and on which a solenoid valve 18 is installed, this duct 17 being connected to a source of gas under pressure.

The device 1 may comprise an outer conduit 19 connected to the enclosure 2, connected to the lower chamber 4 and on which are installed a solenoid valve 20 and a discharge pump 20a.

The ducts 17 and 19 can open in the vicinity of the upper part of the container 11.

The device 1 may comprise an outer conduit 21 connected to the enclosure 2, connected to the upper chamber 5 and on which is installed a solenoid valve 22, this conduit being connected to a source of a gas.

The device 1 may comprise a conduit 23 for filling the container 11 of the liquid L, connected to a source of liquid and on which is installed a solenoid valve 23a.

The device 1 may comprise, in the lower chamber 4, a movable shutter 24, for example, in the form of a plate movable between a closed position, in which it bears against the underside of the bottom 9 crucible 7 and obstructs the extrusion orifices 10, and a spaced position, in which it is located laterally to the space between the bottom 9 of the crucible 7 and the surface of the liquid L. For example, the shutter 24 is worn by an arm 25 fixed on a horizontal axis 26 connected to a drive motor 27.

The device 1 can operate and be used in the following manner.

Having opened the lid 2a of the chamber 2, a solid metal alloy M is deposited in the crucible 7. The device 1 could comprise a charger for this purpose.

This metal alloy M may be based on zirconium, for example an alloy Zr _52, 5Cu ₂₇ AlioNi ₈ Ti _{2; 5} (in atomic percentages), based on magnesium, for example an alloy Mg ₆ 5Cu ₂₅ Gdio (in atomic percentages or based on other compositions suitable for the manufacture of metallic glasses. Having replaced the lid 2a of the chamber 2 in the closed position, the solenoid valve 14 is opened so as to connect the chambers 4 and 5.

Then, the solenoid valve 16 being open, it operates the vacuum pump 16a so as to extract at least partly the air contained in the chamber 2. The vacuum created may be of the order of one to 10 ^"7 milli- Bar, then the solenoid valve 16 is closed. Then, by actuating the solenoid valve 18, an inert gas is introduced or sufficiently inert with respect to the alloy in the chamber 2, until a pressure is restored by example equal to or close to the atmospheric pressure and the solenoid valve 18 is closed.

The above steps can be repeated if necessary to improve the purity of the inert gas in the chamber 2.

The inert gas may, for example, be argon.

Then, the solenoid valve 23a is opened so as to fill, at least partially, the container 11 with a cooling liquid L, to a suitable level situated at a distance from the bottom 9 of the crucible 7. Means could be provided to compensate for the increase in the pressure in the chamber 4, or the chamber 2 in the case where the solenoid valve 14 is closed later, due to the volume of coolant L introduced.

The above procedure avoids the vaporization of the coolant in case it was introduced into the container 11 before the evacuation of the enclosure.

The coolant L can be a liquid that is inert or sufficiently inert with respect to the metal alloy M. For example, the cooling liquid L can be liquid nitrogen, water, liquid-based glycol or oil.

Then, the induction heating member 7a is activated so as to heat the metal alloy M to cause its complete melting in the crucible 7 and to maintain this fusion. The temperature of the molten metal alloy M may be approximately equal to its melting temperature plus a few tens of degrees, for example about 20 degrees. For the above zirconium alloy, the temperature to be reached and maintained can be 850 ° C.

Then, the solenoid valve 14 is eventually closed to isolate chambers 4 and 5 between them.

Depending on the viscosity of the molten metal alloy M, its wettability on the crucible material 7 and the dimensions and shape of the extrusion orifices 10 of the bottom 9 of the crucible 7, the following different cases can be envisaged. .

In the case where the molten metal alloy M does not flow naturally through the extrusion orifices 10, the shutter 24 can be held in its remote position. For safety reasons, the shutter 24 can nevertheless be brought and maintained in its closed position during the melting phase.

The extrusion operation can occur as follows.

The shutter 24 being in its remote position and the solenoid valve 14 being closed, the solenoid valve 22 is actuated so as to introduce an inert gas into the upper chamber 5 and cause an overpressure in this upper chamber 5.

This overpressure in the upper chamber 5, with respect to the pressure in the lower chamber 4, acts on the surface of the molten alloy M in the crucible 7 and causes its evacuation by extrusion and its flow down through the orifices. extrusion 10 of the bottom 9 of the crucible 7.

In order to obtain a constant or almost constant flow of the molten alloy M through the extrusion orifices 10, it is possible, for example, to regulate the flow rate of the gas introduced into the upper chamber 5 at a constant value.

In the case where the molten metal alloy M is capable of flowing naturally through the extrusion orifices 10, the shutter 24 is brought and held in its closed position during the melting phase.

The extrusion operation can then occur as follows. The shutter 24 is passed from its closed position to its spaced apart position and the molten alloy M is allowed to flow downwardly through the extrusion orifices 10 of the bottom 9 of the crucible 7, of course. Nevertheless, for example to obtain a constant or almost constant flow, it is also possible to introduce an overpressure into the upper chamber 5 as described above.

During the extrusion operation, the pressure in the lower chamber 4 can be maintained at a constant value.

The extrusion through the extrusion orifices 10 of the bottom 9 of the crucible 7 generates in the lower chamber 4, by beading, the formation of drops G of molten metal alloy M, separated and successive, which are detached under the effect of the gravity and by breaking the effects of capillarity, at the outlet of the orifices 10 of the crucible 7 or following the formation of molten alloy threads.

The drops G thus formed fall and penetrate into the coolant L.

The distance between the surface of the coolant L and the bottom 9 of the crucible 7 is adapted so that the drops of metal alloy are effectively melted when they enter the cooling liquid L, without the temperature prevailing in the chamber lower 4 does not change this state.

This distance can also be adapted so that the drops G take a spherical shape or close to a sphere before entering the coolant L. For example, this distance, depending on the size and shape to obtain drops G, can be between one centimeter and one meter.

The choice of coolant L and its temperature are adapted so that, by rapid cooling, the drops G transform into solid beads B of metal glass or amorphous metal alloy, these balls B being deposited on the bottom of the container 11 For example, depending on the chosen coolant L, its temperature may range from -200 ° C to 200 ° C.

The drop height in the coolant L is preferably adapted for this transformation to occur before the balls B n 'reach the bottom of the container 1 1. Since the drops G have a spherical or near-sphere shape when they enter the cooling liquid L, the resulting metallic glass beads B may be spherical or close to a sphere.

The diameter of the orifices 10 arranged through the bottom 9 of the crucible 7 may be between one tenth of a millimeter and five millimeters. This diameter determines the diameter of the droplets G of molten alloy to obtain, which itself determines the diameter of the beads B of metal glass to obtain. The diameter of the balls B to obtain metallic glass can be compri s between l / ^10th of a millimeter and 5 millimeters.

During the operation of forming the drops G and the balls B 2, it may be advantageous to open the solenoid valves 1 8 and 20 and to activate the pump 20a so as to introduce the aforementioned gas into the lower chamber 4 and to the to evacuate, in order to evacuate the vapors produced during the cooling of the drops G in the coolant L. This circulation of gas in the lower chamber 4 can be adapted to maintain a constant pressure in this lower chamber 4.

In addition, the temperature regulator 12 may be activated to control the temperature of the coolant L, for example at a constant value.

For example, when the crucible 7 is emptied, it is possible to recover the metallic glass beads B obtained in the container 11.

The structural and functional means described above may make it possible to obtain metallic glass beads B which may have a homogeneity of volume and shape between them, which may facilitate their subsequent use.

According to a variant embodiment, with a view to continuous operation, it may be advantageous to equip the device 1 with means (not shown) for continuously introducing the metal alloy M into the crucible 7 and means ( not shown) continuous recovery of the balls B, without the need to renew the pumping and filling operations by an inert gas or reducing the number of such operations. Depending on the needs, the order of the steps described above could be different.

Thanks to the device 1 described above and to its mode of operation, the decrease in volume of the drops can be continuous while the alloy remains viscous, so as to obtain metal balls of good sphericity, pure and homogeneous, while by producing the sudden cooling of the metal alloy necessary for the production of such a metallic glass.

The present invention is not limited to the examples described above. Many other embodiments are possible, without departing from the scope of the invention.

Claims

A method of forming metal glass beads from a metal alloy, wherein the metal alloy, heated in a crucible (7) at a temperature at least equal to its melting temperature, is extruded through at least one extrusion orifice (10) arranged at the bottom of the crucible to flow downwards and form separate and successive drops (G) of molten metal alloy and in which the drops of metal alloy in fusion penetrate into a cooling liquid (L) which is contained in a container and whose surface is spaced from said extrusion orifice (10), to solidify by forming metal glass beads (B); process in which the crucible (7) and the container (11) are arranged in a closed chamber (2) and in which the cooling liquid (L) is introduced into the container (11) after at least one air suction contained in the enclosure followed by introduction into the enclosure of a gas inert vis-à-vis the metal alloy.

2. Method according to claim 1, wherein the extrusion is carried out by applying an overpressure on the surface of the molten metal alloy in the crucible (7), with respect to the pressure prevailing above the surface of the liquid. cooling (L).

3. Method according to one of claims 1 and 2, wherein the coolant is inert vis-à-vis the metal alloy.

4. Method according to one of the preceding claims, wherein the coolant is cooled.

5. A method according to any one of the preceding claims, wherein the inert gas is circulated with respect to the metal alloy in the space between the crucible and the surface of the coolant.

Apparatus for forming metallic glass beads from a metal alloy, comprising:

an enclosure (2) capable of being closed; a crucible (7) disposed in the chamber, adapted to receive the metal alloy and whose bottom has at least one through-extrusion orifice (10);

a heating means (7a) for heating the alloy in the crucible to a temperature at least equal to its melting temperature, a container (11) disposed in the chamber, adapted to contain a coolant placed underneath and remote from said through-hole of the crucible,

means for introducing a gas which is inert with respect to the metal alloy in the enclosure;

means for introducing the coolant into the container (11);

the distance between the extrusion through orifice of the crucible and the surface of the coolant being such that the liquid alloy flowing downwards from the orifice (10) of the crucible forms drops (G) of alloy separated and successive and that these drops of alloy, in the liquid state, enter the coolant and are, in this liquid, cooled to form balls (B) of metal glass.

7. Device according to claim 6, comprising an extrusion means (22) for extruding the liquid alloy through said crucible through hole.

8. Device according to claim 7, wherein the extrusion means (22) comprises a source of inert gas capable of creating an overpressure on the surface of the molten metal alloy in the crucible (7), relative to the pressure prevailing above the surface of the coolant (L).

9. Device according to any one of claims 6 to 8, comprising a lower chamber (4) and an upper chamber (5) separated by a partition wall (3) carrying the crucible (7) and provided with a through passage (6) exposing said orifice, the container (11) being in the lower chamber (4) and being located below the bottom of the crucible.

10. Device according to claim 9, comprising a vacuum pump (16) connected to the lower chamber and the upper chamber.

11. Device according to claim 9, comprising means (18, 20) for circulating the inert gas in the lower chamber.

12. Device according to any one of claims 6 to 11, comprising a source of inert gas (22) connected to the upper chamber.

13. Device according to any one of claims 6 to 12, comprising a shutter movable between a closed position in which it obstructs said through-extrusion orifice and a spaced apart position in which said extrusion through orifice is released and in which is laterally spaced from the path of the drops (G) of alloy.