CH718789A2 - Electroerosion process of an amorphous metal alloy sample. - Google Patents

Abstract

The invention relates to a method for machining a sample (1) of amorphous metal alloy, comprising at least one step of spark erosion of the sample (1) with an electrode producing electric discharges along a reference trajectory for removing material from the sample (1), open-ended or not, along the reference path so as to obtain a sample (1) machined and maintained in an amorphous state, in which: the alloy amorphous metal has: – a critical diameter (Dc) less than 8 millimeters, preferably less than 6 millimeters, and even more preferably less than 4 mm, and/or – a difference (ΔTx) between the crystallization temperature (Tx) and the glass transition temperature (Tg) less than 80°C, preferably less than 70°C, and even more preferably less than 60°C, and/or – a quotient (ΔTx/(Tl-Tg)) of the difference ( ΔTx) between the crystallization temperature (Tx) and the temperature of trans vitreous ition (Tg) and the difference between the liquidus temperature (Tl) and the glass transition temperature (Tg) less than 0.16, preferably less than 0.14 and even more preferably less than 0.12.

Description

Technical area

The present invention relates to the field of metal microcomponent machining methods, in particular amorphous metal alloy parts (AMA). Indeed, amorphous alloys have particularly interesting mechanical characteristics for technical fields involving very small parts.

Prior technique

[0002] It is known to obtain amorphous metal preforms by injection into molds of specific shape. By cooling the injected metal sufficiently quickly, the crystallization of the alloy can be avoided and an amorphous type structure can be obtained. This type of amorphous alloy structure is also called metallic glass.

[0003] In order to obtain a mechanical part ready to be integrated, for example, into a clockwork mechanism, it is sometimes necessary to machine the molded preform.

[0004] In the general field of alloys, in particular crystalline alloys, numerous machining and/or shaping techniques have been developed (stamping, micro-milling, etc.). However, these techniques cannot be easily transposed to AMAs which have particular chemical compositions and generally much higher mechanical properties than crystalline alloys. Machining is therefore more complex to master (obtaining the desired precision and surface conditions, perpendicularity of the sides, tool life, production speed compatible with industrial constraints, etc.).

[0005] On the other hand, many of these techniques cause thermal heating at the level of the machined zones, thus involving a local recrystallization of the alloy and the loss of the amorphous structure of the AMA at the level of the machined zones. This is all the more true for AMAs of low thermal stability. Indeed, among the AMAs, some have a lower thermal stability than the others. This low thermal stability translates the ease/speed with which the structure of the alloy can be affected by a variation in temperature (increase in temperature beyond the glass transition temperature Tg, too slow cooling, etc.). AMAs with lower thermal stability therefore have an ability to evolve to a faster crystalline state above the glass transition temperature Tg.

[0006] Electroerosion processes are suitable for the manufacture of components, in particular microcomponents in crystalline metal alloys. Electroerosion makes it possible to overcome the mechanical characteristics of materials, the machining of hard materials is indeed possible, and makes it possible to achieve machining precision of the order of a few micrometers. However, its thermal nature, the high temperatures involved and the long machining times make electroerosion a priori a poor candidate for the machining of amorphous metal alloys. As indicated above, the latter and more particularly those with low thermal stability, are in fact much more sensitive to temperature than crystalline alloys.

[0007] Thus, the difficulty is to carry out these machining operations of the AMAs while preserving their amorphous structure, guaranteeing a quality of the surface state of the machined part and maintaining a high cycle time adapted to industrial production. Indeed, a machining operation which would lead to excessive heating of the material would cause crystallization of the heat-affected zone and would therefore cause the advantageous properties conferred by the amorphous structure of the material to be lost.

[0008] There is therefore a need to have a machining process that makes it possible to retain an amorphous microstructure while allowing an industrial-level manufacturing rate. Another requirement is to be able to obtain a surface condition with very low roughness and/or excellent perpendicularity of the flanks in the cutting zone, in order to fully exploit the intrinsic qualities of the AMA.

Summary

[0009] To this end, the invention proposes a method for machining a sample 1 of amorphous metal alloy, comprising at least one step of spark erosion of the sample 1 with an electrode 2 producing electric discharges along a reference trajectory TRef to remove material from sample 1, open-ended or not, along the reference trajectory TRef so as to obtain a sample 1 machined and maintained in the amorphous state, in which: the amorphous metal alloy has: – a critical diameter De of less than 8 millimeters, preferably less than 6 millimeters, and even more preferably less than 4 mm, and/or – a difference ΔTx between the crystallization temperature Tx and the transition temperature vitreous Tg less than 80°C, preferably less than 70°C, and even more preferably less than 60°C, and/or – a quotient ΔTx/(Tl-Tg) of the difference ΔTx between the crystallization temperature Tx and the t glass transition temperature Tg and the difference between the liquidus temperature T1 and the glass transition temperature Tg of less than 0.16, preferably less than 0.14 and even more preferably less than 0.12.

[0010]According to one embodiment, the EDM is an EDM by sinking, by sweeping, by wire or by rapid drilling with a solid or recessed electrode.

[0011] Machining can be cutting, drilling, engraving and/or surfacing.

[0012] According to one embodiment, the machining process is such that: the machining is a cutting, more particularly an electroerosion by wire 2a, and the discharge energy is less than 5000 μJ/mm thickness of sample 1, preferably less than 3000 μJ/mm thickness of sample 1, preferably less than 1500 μJ/mm thickness of sample 1 and even more preferably less than 800µJ/mm sample thickness 1.

Advantageously, the diameter of wire 2a is less than 200 μm, preferably less than 100 μm and even more preferably less than 75 μm.

[0014]According to one embodiment, the cut is made in several stages of electroerosion: at least one electroerosion step, called "roughing", of the sample 1 with a wire 2a along a reference trajectory TRef+n to remove material from the sample 1 along a reference trajectory TRef+n, implemented to produce a blank 5; 51 along a trajectory TRef+n, n being the total number of electroerosion steps, called „roughing; a so-called “finishing” electroerosion step of sample 1 with a wire 2a along a reference trajectory TRef to remove material from sample 1 along the reference trajectory TRef, the reference trajectory or trajectories TRef+n being translated by a given distance gn from the reference trajectory TRef; TRef+(n-1) which is directly adjacent to it and which is closest to the final part 4, in the direction opposite to that of the final part 4 cut; and the given distances (gn) between two directly adjacent reference trajectories (TRef; TRef+(n-1); TRef+n), identical or different, are such that the electric discharges along the wire (2a), removing material of the sample (1) to be machined on the reference trajectory (TRef+(n-1) or TRef+n), also remove, at least partially, material from the sample (1) to be machined on the reference trajectories (TRef; TRef+(n-1))) which is or are directly adjacent to it.

Advantageously, the finishing spark erosion step is carried out with a discharge energy along the wire 2a of less than 800 μJ/mm of sample thickness 1, preferably less than 400 μJ/mm of sample thickness. 1 and even more preferably less than 200 μJ/mm of thickness of sample 1.

[0016] According to another embodiment, the electroerosion is electroerosion by sinking or rapid drilling, and the discharge energy is less than 5000 μJ/mm<2> of surface of sample 1, preferably less than 3000 μJ/ mm<2> of sample 1 surface, preferably less than 1500 μJ/mm<2> of sample 1 surface and even more preferably less than 800 μJ/mm<2> of sample surface.

[0017] Advantageously, the current of each electrical discharge across the terminals of electrode 2 is less than 200 amps.

[0018] The voltage across the terminals of electrode 2 is preferably less than 200V.

The pulse duration during which the sample 1 is subjected to an electric discharge is advantageously less than 1000 μs, preferably less than 400 μs or even more preferably less than 100 μs.

The amorphous metal alloy with low thermal stability of sample 1 to be machined preferably comprises, in atomic percentage, more than 40% of Ni, Zr, Cu, Ti, Fe or Co, preferably more than 50% of Ni , Zr, Cu, Ti, Fe or Co. According to another embodiment, this AMA comprises, in atomic percentage, more than 50% of the elements Ni and Nb, preferably more than 60% of the elements Ni and Nb, more preferably more 70% of the elements Ni and Nb.

[0021] According to one embodiment, the machining method comprises at least one step of spark erosion of a first surface of the sample 1 with electric discharges so as to obtain a second surface whose roughness Ra is less than 800 nm, preferably less than 600 nm, more preferably less than 400 nm and even more preferably less than 300 nm.

[0022] According to an advantageous embodiment, the machining method comprises at least one step of spark erosion of a first surface P1 of the sample 1 so as to obtain a second surface P2, such that at each point of intersection of surfaces P1 and P2, said surfaces P1 and P2 form between them an angle Ad of 90° ± 1.5°, preferably 90° ± 1° and even more preferably 90° ± 0.5° between them.

The invention also relates to a method of manufacturing a part 4 of amorphous metal alloy, comprising the steps: melt a mixture of metals to obtain a piece of alloy, injecting the slug obtained into a mold and cooling the cast alloy with a cooling rate greater than a critical rate of crystallization of the alloy, to obtain a sample 1 of amorphous alloy, machining at least one surface of the sample 1 according to the machining process described above to obtain a part 4 in an amorphous alloy according to a predetermined geometry, optionally performing a finishing step on at least the machined surface of sample 1, preferably a tribofinishing step or a chemical treatment.

The invention also relates to a mechanical component in an amorphous metal alloy comprising at least one surface machined according to the machining process or according to the manufacturing process described above.

Brief description of the drawings

[0025] Other characteristics, details and advantages will appear on reading the detailed description below and on analyzing the appended drawings, in which:

[0026] [Fig 1] represents an X-ray diffraction analysis of an amorphous metal alloy.

[0027] [Fig 2] shows an X-ray diffraction analysis of a partially amorphous metal alloy.

[0028] [Fig 3] represents an X-ray diffraction analysis of a crystalline metal alloy.

[0029] [Fig. 4] is a schematic side view of an installation capable of implementing a method for machining an amorphous metal alloy sample,

[0030] [Fig. 5] is a schematic top view illustrating one embodiment of the machining process,

[0031] [Fig.6] is a schematic side view detailing an embodiment of the machining process,

[0032] [Fig. 7] is a schematic side view detailing a method for cutting a stack of samples,

[0033] [Fig. 8] is a schematic top view illustrating a cutting process comprising roughing EDM steps and a finishing EDM step,

[0034] [Fig. 9] is a schematic side view illustrating a machining process for obtaining a part having excellent sidewall perpendicularity.

[0035] [Fig. 10] is a diagram representing the results of the bending tests of Example 1.

Description of embodiments

[0036] In order to facilitate reading of the figures, the various elements are not necessarily shown to scale. In these figures, identical elements bear the same references. Certain elements or parameters can be indexed, that is to say designated for example by first element or second element, or else first parameter and second parameter, etc. The purpose of this indexing is to differentiate between similar but not identical elements or parameters. This indexing does not imply a priority of an element, or of a parameter, compared to another and it is possible to interchange the denominations.

Within the meaning of the present description, the following definitions should be specified.

[0038] The term "one" or "one", "at least one" or "at least one", respectively.

[0039] The term "amorphous metallic alloy" or "AMA" or "metallic glass" means metals or metallic alloys which are not crystalline, that is to say whose atomic distribution is mainly random. Nevertheless, it is difficult to obtain a one hundred percent amorphous metallic glass because most often a fraction of the material remains which is crystalline in nature. This definition can therefore be generalized to metals or metal alloys which are partially crystalline and which therefore contain a fraction of crystals, as long as the amorphous fraction is predominant. Generally, the fraction of the amorphous phase is greater than 50%. The term "amorphous metallic alloy" or "AMA" or "metallic glass" is therefore understood to mean metals or metallic alloys whose fraction of the amorphous phase is greater than 50%, preferably greater than 65%, more preferably greater than 75% and more preferably still greater than 80%

It is specified here that a metallurgical structure is said to be amorphous or entirely amorphous when an X-ray diffraction analysis as described below does not reveal crystallization peaks.

[0041] The term "critical diameter" (Dc) of a specific metal alloy is understood to mean the maximum thickness limit below which the metal alloy has an entirely amorphous metallurgical structure or beyond which it is no longer possible to obtain a completely amorphous metallurgical structure, when the metal alloy is molded from a liquid state and is subjected to rapid cooling such that the transfer of heat inside the metal alloy is optimal. More specifically, the critical diameter is determined by successive molding of cylindrical bars (generally longer than 50mm) of different diameters, molded from the liquid state under the following conditions: The alloy is melted at a temperature of Tl + 150°C with Tl, the liquidus temperature of the alloy (in °C). It is molded in a CuC1 type copper mold and is cooled to a maximum temperature of approximately twenty degrees Celsius (20°C). The alloy is produced and molded under an inert, high-purity atmosphere (e.g. under argon of quality 6.0) or under a secondary vacuum (pressure < 10-4mbar). The alloy is cast with a system allowing the application of a pressure differential to facilitate the casting of the alloy and to ensure intimate contact between the alloy and the walls of the mold in order to ensure the rapid cooling of the alloy. The molding step can be carried out under a pressure of 20 MPa. This system can be mechanical (e.g. piston) or gaseous (application of an overpressure). After moulding, the bars are cut in order to obtain a slice (cross section of the cylinder preferably located towards the middle of the bar, thickness between 1 and 10 mm) and analyzed by X-ray diffraction (XRD) at a minimum to determine whether the slices exhibit an amorphous or partially crystalline structure. The critical diameter is then determined as being the maximum diameter for which the structure is amorphous (the presence of bumps characteristic of AMAs is then highlighted by X-ray diffraction). Given that there are most often defects in metallurgical structures, a 100% amorphous alloy is almost impossible to obtain and the critical diameter can be defined as the diameter above which an analysis by X-ray diffraction clearly highlights evidence of crystallinity peaks. Such an evaluation of the amorphous character of a metallic alloy is detailed in the article Cheung et al., 2007 (Cheung et al. (2007) „Thermal and mechanical properties of Cu-Zr-Al bulk metallic glasses)“ doi:10.1016 /j.jallcom.2006.08.109). It makes it possible to carry out an average analysis on a surface and to overcome the few inevitable metallurgical defects while analyzing only the crystals of significant size (greater than a few nanometers) and/or in significant quantity. Figures 1, 2 and 3 represent an XRD analysis as described previously of a metallic alloy in the amorphous state (figure 1), partially amorphous (we find the bump characteristic of AMAs but with the presence of peaks - figure 2) and crystalline (Figure 3) respectively.

[0042] “AMA with low thermal stability” means a metal alloy having: a critical diameter (Dc) less than 8 millimeters, preferably less than 6 millimeters, and even more preferably less than 4 mm, and/or a difference (ΔTx) between the crystallization temperature (Tx) and the glass transition temperature (Tg) of less than 80°C, preferably less than 70°C, and even more preferably less than 60°C, and/or a quotient (ΔTx/(Tl-Tg)) of the difference (ΔTx) between the crystallization temperature (Tx) and the glass transition temperature (Tg) and of the difference between the liquidus temperature (Tl) and the temperature of glass transition (Tg) less than 0.16, preferably less than 0.14 and even more preferably less than 0.12.

The critical diameter De, the difference ΔTx=Tx-Tg between the crystallization temperature Tx and the glass transition temperature Tg, as well as the quotient ΔTx/(Tl-Tg) are quantities which all three define a criterion thermal stability of the metal alloy. The lower the value of each of these three quantities, the more unstable the alloy, in other words the more difficult it is to maintain the metallic alloy in an amorphous state.

[0044] The term "machining" means a removal of material from a sample 1. This may in particular be a through machining such as a cutout or a drilling, a non-through machining such as an engraving , or surfacing, for example to obtain a given roughness, or even the production of surfaces or flanks whose angle formed between them has excellent precision, for example an angle of 90° ± 1.5°, preferably of 90° ± 1° and even more preferably 90° ± 0.5°.

[0045] The term "microcomponent" means a component of small dimensions, for example a component of which at least one of the dimensions does not exceed 2 mm or even 1 mm, preferably 100 μm, more preferably 60 or even 25 μm. “Mechanical microcomponent” means a microcomponent capable of cooperating with one or more other microcomponents.

Electroerosion, ("electrical discharge machining" in English, also indicated by the acronym of "EDM"), is a machining process which consists of removing material from a part using an electrode producing electrical discharges.

[0047] Machining by electroerosion takes place in different phases: 1/ Application of a voltage between the part and the electrode; 2/ Under the action of the electric field, the dielectric is ionized, thus creating a conductive channel between the electrode and the part; 3/ The passage of current in this channel allows the formation of a spark which will generate a plasma bubble and a significant increase in temperature (breakdown of the spark). It is this electrical discharge, which occurs from the electrode to the part, which will cause the melting and vaporization of material on the part, but also on the electrode; 4/ When the current is interrupted, the gas bubble implodes and ejects the molten material. This is then found in the dielectric in the form of microparticles and is thus quickly cooled and evacuated. At the end of this discharge, a crater is left on the part and the electrode (removal of material). The material melted during the discharge but not ejected during the implosion of the gas bubble resolidifies on the part and the electrode.

[0048] EDM is recommended for machining very hard (but imperatively conductive) materials, hardened steels, or else in cases where the complexity of the part requires it.

Against all expectations, the present inventors have demonstrated that EDM could be used for the machining of samples in AMA, in particular in AMA with low thermal stability, while maintaining the amorphous structure of the alloy and its associated mechanical characteristics.

Schematically shown in Figure 4 an electroerosion installation. The installation comprises an enclosure 7 in which a sample 1 is placed, bathed in a dielectric liquid 3. An electrode 2, placed opposite the sample 1, emits electric discharges. The part to be machined of sample 1 is placed opposite the emission point of electrode 2. Sample 1 can thus be machined by electric discharges, that is to say that the Electric discharges can reach the surface to be machined of sample 1 and interact with the material of sample 1. Electrode 2 is therefore mobile along a defined machining trajectory, indicated as reference trajectory TRef in this document. The portion of sample 1 on which the electric discharges are carried out is designated by the reference sign 8.

The interaction between the electric discharges and the sample 1 makes it possible to remove material in portion8. A relative movement of the electrode 2 with respect to the sample 1 makes it possible to move the portion 8 and to carry out a removal of material along the reference trajectory TRef.

An electronic control unit 6 makes it possible to control the instants of triggering and interruption of the electric discharges, as well as the displacement movements of the electrode 2 with respect to the sample 1. The reference trajectory TRef can thus be monitored in real time.

As a variant, the sample 1 to be machined can be mobile so as to move relative to the electrode 2. For this, the sample 1 to be machined is fixed to a mobile plate along at least 2 axes.

As a variant, the electrode 2 and the sample 1 to be machined can both be mobile, successively or concomitantly, in particular to facilitate the machining of complex parts.

The sample 1 to be machined can have any shape and the sample portion 1 to be machined can also be of any shape, emerging or not.

By way of example, in one embodiment, the sample 1 to be machined is flat. In other words, sample 1 to be machined is an amorphous metal alloy plate. The thickness of sample 1 to be machined is preferably between 5 μm and 6 mm, preferably between 100 μm and 4 mm.

In another embodiment, the sample 1 to be machined is a cylinder or comprises a cylindrical part and the method aims to arrange an axis, crossing or not, within said cylinder or said cylindrical part. The diameter of the microcomponent resulting from the machining process preferably has a diameter, preferably a maximum diameter, less than or equal to 4 mm.

The sample 1 can be a sample only or a stack of several samples 1. In an advantageous embodiment, it is a stack of several samples, preferably a stack of more than three, again more preferably more than 8 samples. This embodiment makes it possible in particular to reduce the cutting time.

The amorphous metal alloy of sample 1 to be machined may for example contain, in atomic percentage, more than 40% of Ni, Zr, Cu, Ti, Fe or Co, preferably more than 50% of Ni, Zr, Cu, Ti, Fe or Co. According to another embodiment, the amorphous metal alloy of sample 1 to be machined contains, in atomic percentage, more than 50% of the elements Ni and Nb, preferably more than 60% of the elements Ni and Nb, more preferably more than 70% of the elements Ni and Nb.

[0060] Alloys with low thermal stability as described above are particularly difficult to shape while retaining their amorphous character. The process described here is therefore particularly advantageous for forming such alloys.

The present invention proposes a method for machining a sample 1 of an amorphous metal alloy with low thermal stability using a femtosecond laser, comprising at least one step of spark erosion of the sample 1 with a electrode 2 producing electrical discharges along a reference trajectory TRef to remove material from sample 1, open or not, along the reference trajectory TRef so as to obtain a sample 1 machined and maintained in an amorphous state.

Figure 5 illustrates the notion of sample 1, machined sample 1 and/or part 4. Sample 1 forms the raw material or preform to be machined. After one or more machining operations, a machined sample 1 or part 4, also called a microcomponent, is obtained. Part 4 can be a part detached from sample 1, in particular when the process is open machining such as cutting. The sign 9 schematizes the circumference 9 of the part 4. The shape of the part 4 can be arbitrary. In the example of Figure 5, part 4 is entirely within the perimeter of sample 1. According to an example not shown, part of the perimeter 10 of sample 1 may be part of part 4 .

The reference trajectory TRef can define a part of the perimeter 9 of the part 4. In other words, the machining process can be implemented in order to form only a part of the perimeter 9 of the part 4. The rest of the periphery 9 of part 4 can be obtained by other methods or transformation processes-A part of the periphery 9 of the microcomponent 4 can also be formed by a portion of the periphery 10 of the sample 1, which then remains raw in this area.

[0064] According to an alternative embodiment compatible with the previous mode, the machined sample or the part 4 can be the sample 1 from which part of the initial material has been removed without the removal of material being emerging. Figure 6 illustrates the concept of non-opening removal.

[0065] As an example illustrated in Figure 6, sample 1 can be a cylinder and the portion to be removed 8 such that it allows a bearing to be machined in part 4.

[0066] More generally, EDM can be sinking EDM, wire EDM or rapid drilling with a solid or hollow cylindrical electrode. The solid electrode can in particular be a cylinder and the hollow electrode can be a tubular electrode.

[0067] Machining according to the method can be cutting, drilling, engraving and/or surfacing. By surfacing is meant a machining making it possible to obtain at least one new surface on the sample 1, this surface possibly being of any shape and size.

According to one embodiment of the invention, the machining is a cutting, more particularly a wire spark erosion. As illustrated in FIG. 7, electrode 2 is therefore a wire 2a which is applied along one side of sample 1 or, as illustrated in FIG. 7, along the sides of at least two samples 1 stacked. The wire 2a, traversed by successive electrical discharges, makes it possible to remove material from the samples 1. Along a reference trajectory TRef. In this embodiment, the discharge energy of the electrical discharges is less than 5000 μJ/mm of thickness of sample 1 or of the total thickness of the stack of samples 1 in the case of stacked samples, preferably less at 3000µJ/mm of thickness of sample 1 or of the total thickness of the stack of samples 1 in the case of stacked samples, preferably less than 1500µJ/mm of thickness of sample 1 or of the total thickness of the stack of samples 1 in the case of stacked samples and even more preferably less than 800 μJ/mm of thickness of sample 1 or of the total thickness of the stack of samples 1 in the case of stacked samples.

Advantageously, the diameter of wire 2a is less than 200 μm, preferably less than 100 μm and even more preferably less than 75 μm. Such a diameter in fact makes it possible to obtain an optimized cutting surface quality.

Advantageously, cutting by wire EDM 2a is carried out in several EDM steps. Thus at least one so-called "roughing" step is carried out followed by a so-called "finishing" step. The electro-erosion step or steps, called "roughing", of sample 1 with a wire 2a are carried out along a reference trajectory TRef+n to remove material from sample 1 along d a reference trajectory TRef+n, to produce one or more blanks 5; 51 along a trajectory TRef+n, n being the total number of EDM steps, called "roughing". The so-called “finishing” spark erosion step of sample 1 is carried out along a reference trajectory TRef to remove material from sample 1 along the reference trajectory TRef. The reference trajectory or trajectories TRef+n are translated by a given distance gn from the reference trajectory TRef; TRef+(n-1) which is directly adjacent to it and which is closest to the final part 4, in the direction opposite to that of the final part 4 cut. the given distances (gn) between two directly adjacent reference trajectories (TRef; TRef+(n-1) -TRef+n), identical or different, are such that the electric discharges along the wire (2a), removing material of the sample (1) to be machined on the reference trajectory (TRef+(n-1) or TRef+n), also remove, at least partially, material from the sample (1) to be machined on the reference trajectories (TRef; TRef+(n-1)) which is or are directly adjacent to it.

The previous embodiment is illustrated in FIG. 8. The illustrated mode represents cutting by electroerosion comprising two roughing steps along reference trajectories TRef1 and TRef2 and a finishing step along trajectory TRef. The first step of roughing according to the reference path TRef2 makes it possible to produce the roughing 51. The second step of roughing according to the reference path TRef1 makes it possible to produce the roughing 5. The finishing step according to the reference path TRef makes it possible to obtain the final part 4. The reference trajectory TRef2 is distant from the reference trajectory TRef1 by a given distance g2 while the reference trajectory TRef1 is distant from the reference trajectory TRef by a given distance g1. The distances g1 and g2 can be identical or different. This embodiment makes it possible to obtain cutouts with complex trajectories with excellent surface finishes.

Advantageously, the finishing electroerosion step is carried out with a discharge energy along the wire 2a of less than 800 μJ/mm of thickness of sample 1 (or of the total thickness of the stack of samples 1), preferably less than 400 μJ/mm of thickness of sample 1 (or of the total thickness of the stack of samples 1) and even more preferably less than 200 μJ/mm of thickness of sample 1 ( or the total thickness of the sample stack 1).

[0073] According to another embodiment, the EDM is an EDM by sinking, by sweeping or by rapid drilling. The discharge energy traveling through the electrode is then less than 5000µJ/mm<2> of sample surface 1, preferably less than 3000µJ/mm<2> of sample surface 1, preferably less than 1500µJ/mm<2 > of sample surface 1 and even more preferably less than 800 μJ/mm<2> of sample surface. This embodiment makes it possible in particular to pierce, engrave and/or surface a sample 1 or pierce a stack of samples 1.

The current of each electrical discharge across the terminals of electrode 2 is preferably less than 200 amps.

The voltage across electrode 2 is advantageously less than 200V.

Advantageously, the pulse duration during which sample 1 is subjected to an electric discharge is less than 1000 μs, preferably less than 400 μs or even more preferably less than 100 μs. Such a pulse duration is adapted to the AMA of sample 1 in order to avoid any recrystallization of the AMA during the machining process.

The machining method according to the invention can advantageously comprise or can be able to carry out a surfacing of the sample 1. The machining then comprises at least one step of spark erosion of a first surface of the sample 1 with electrical discharges so as to obtain a second surface whose roughness Ra is less than 800 nm, preferably less than 600 nm, more preferably less than 400 nm and even more preferably less than 300 nm. Such roughness makes it possible in particular to obtain microcomponents having excellent surface states, suitable in particular for the fields of watchmaking and/or implantology, in particular dental implantology.

According to one embodiment illustrated in Figure 9, the machining process makes it possible to obtain a part 4 whose surfaces or flanks have between them an angle of excellent precision, for example an angle of 90° ± 1.5°, preferably 90°±1° and even more preferably 90°±0.5°. According to this embodiment, the machining method comprises at least one step of spark erosion of a first surface P1 of the sample 1 so as to obtain a second surface P2, such that at each point of intersection of the surfaces P1 and P2, said surfaces P1 and P2 form between them an angle Ad of 90° ± 1.5°, preferably 90° ± 1° and even more preferably 90° ± 0.5° between them.

The invention also relates to a method of manufacturing a part 4 of amorphous metal alloy, comprising the steps: melt a mixture of metals to obtain a piece of alloy, injecting the slug obtained into a mold and cooling the cast alloy with a cooling rate greater than a critical rate of crystallization of the alloy, to obtain a sample 1 of amorphous alloy, machining at least one surface of the sample 1 according to the machining process described above to obtain a part 4 in an amorphous alloy according to a predetermined geometry, optionally performing a finishing step on at least the machined surface of sample 1, preferably a tribofinishing step or a chemical treatment, in particular a surface deoxidation treatment.

Finally, the invention relates to a mechanical component, in particular an AMA mechanical microcomponent comprising at least one surface machined according to the preceding methods.

The mechanical component can for example be an element of a timepiece mechanism for a mechanical watch, such as a date finger, a toothed wheel, or even an axis. The combination of the intrinsic mechanical properties of amorphous alloys and the precision of the cutting produced by the process makes it possible to provide components, in particular micromechanical components, particularly suited to this application. It can also be a component for medical purposes, such as an implant.

List of reference signs

[0082] 1: Sample to be machined 2: Electrode 2a: Wire electrode 3: Dielectric 4. Machined part 5, 51. Blank 6. Control unit 7. Enclosure 8. Irradiated portion 9. Outline of the part 10. Periphery of sample 1

Examples

Example 1 - Conservation of the amorphous structure

[0083] Ni(57-67)Nb(28-38)Zr(0-10) alloy samples (atomic %) were cut with different sets of parameters detailed in Table 1 to validate the maintenance of the amorphous structure of the alloy of the samples machined according to the process of the invention. The Ni(57-67)Nb(28-38)Zr(0-10) alloy has low thermal stability within the meaning of the invention. Indeed, its critical diameter De is only 3mm, its stability coefficient, i.e. its quotient (ΔTx/(Tl-Tg)) is 0.07 and its ΔTx is equal to 40.

The samples were cut by wire spark erosion in preforms 500 μm thick and two assemblies were made: Assembly 1: Cutting of a single sample, Assembly 2: Cutting of a stack of 9 samples.

The machining process comprises a first roughing step then two finishing steps. The first so-called roughing pass makes it possible to cross the material and defines the first reference geometry, the intensity of the machining parameters for this pass is therefore the most important. The other so-called finishing passes are less energetic and make it possible to improve the surface finish created by the roughing pass.

Table 1 below summarizes the range of parameters tested:

[Table 1]

[0087] Roughing E < 5000µJ/mm E < 5000µJ/mm Roughing E < 2000µJ/mm E < 2000µJ/mm Finishing E < 200µJ/mm E < 200µJ/mm

Two sets of parameters making it possible to obtain two levels of roughness have been defined using the passes defined in table 1 above. Table 2 below summarizes the sets of parameters defined for the cutting tests.

[Table 2]

[0089] Set 1 Rough Rough Rough Finish - - - Set 2 Rough Rough Rough Rough Rough Rough Finish

Table 3 below summarizes the structural state of the samples after cutting.

[Table 3]

[0091] Amorphous Amorphous Amorphous Amorphous

The microstructural analyzes as well as the XRD analyzes clearly showed conservation of the amorphous microstructure for all the gaps tested.

In addition to the microstructural analyses, mechanical tests were carried out with the aim this time of quantifying the influence of electroerosion on the properties of the material. Bars 500µm wide in Ni(57-67)Nb(28-38)Zr(0-10) (atomic %) alloy were machined by EDM cutting and by micro-cutting machine (controlled cutting means which does not does not affect the material, equivalent to the same sample from the casting step or so-called „as-cast“ sample).

The mechanical tests carried out are 3-point bending tests. The machine used is the Shimadzu MMT-101NV-10 in bending mode. The test parameters were as follows: Length between supports L0=5mm Crosshead speed v=0.005mm/s Total sample length l=10mm Sample width L=500µm Sample thickness e=500µm The dimensions of the samples are presented in table 4.

[Table 4]

[0095] 1:Game 1_Montage 1 0.5 0.5 10 2:Game 1_Montage 2 0.5 0.5 10 3:Game 2_Montage 1 0.5 0.5 10 4:Game 2_Montage 2 0.5 0.5 10 5:As cast cut out 0.53 0.5 10

The results are shown in figure 10.

By comparison, a conservation of the properties of the AMA before and after EDM cutting is indeed observed for all the samples tested in bending. There is no dispersion in the results and the value of elastic limit in bending is indeed equal to that obtained for the as-cast sample.

Similarly, a conservation of the properties in the plastic zone is observed. The elastic limit and plastic deformation values are consistent with the values observed on directly molded parts and for which no cutting step or other treatment has been carried out.

Example 2- Obtaining the desired quality (dimensional and geometric) and influence on the rates

This example aims to evaluate the states of the surfaces, of the edges as well as the roughness and the state of the flanks after cutting. Indeed, for the type of application targeted, for example parts of watch movements, a low Ra and good perpendicularity are essential to control the tribological contacts and to obtain coefficients of friction and low wear rates, which allow optimize the performance of mechanical systems (energy conservation) and their lifespan

[0100] Yes The quality criteria therefore include here the roughness of the cut surfaces, the obtaining of straight sides (perpendicularity between the cutting zone and the upper and lower surfaces and the obtaining of parts that are not oxidized and without redeposition of particles ( burrs)

The quality analyzes were therefore carried out in table 5.

[Table 5]

[0102] Conicity < 0.5° Between 0.5° and 1° >1° Roughness <N5 = N5 >N5 Surface quality (qualitative analysis) No Redeposition of particles and no oxidation Little Redeposition of particles and little oxidation Redeposition excessive particles Or oxidation

[0103] Table 6 below summarizes the results obtained after carrying out the test plan:

[Table 6]

[0104] 1:Game 1_Montage 1, Level 1 Level 1 2:Game 1_Montage 2 Level 1 Level 2 3:Game 2_Montage 1: Level 1 Level 3 4:Game 2_Montage 2 Level 1 Level 3

[0105] All the tests made it possible to obtain roughnesses after machining lower than N5, overall the surface states are homogeneous

Claims (16)

1. Method for machining a sample (1) of amorphous metal alloy, comprising at least one step of spark erosion of the sample (1) with an electrode (2) producing electric discharges along a reference trajectory (TRef) to remove material from the sample (1), open-ended or not, along the reference trajectory (TRef) so as to obtain a sample (1) machined and maintained in the amorphous state, in which : the amorphous metal alloy has: – a critical diameter (Dc) less than 8 millimeters, preferably less than 6 millimeters, and even more preferably less than 4 mm, and/or – a difference (ΔTx) between the crystallization temperature (Tx) and the glass transition temperature (Tg) of less than 80°C, preferably less than 70°C, and even more preferably less than 60°C, and/or – a quotient (ΔTx/(Tl-Tg)) of the difference (ΔTx) between the crystallization temperature (Tx) and the glass transition temperature (Tg) and the difference between the liquidus temperature (Tl) and the temperature glass transition (Tg) less than 0.16, preferably less than 0.14 and even more preferably less than 0.12. 2. Method according to claim 1, characterized in that the electroerosion is electroerosion by sinking, by scanning, by wire or by rapid drilling with a solid or hollow electrode. 3. Method according to claim 1 or 2 characterized in that the machining is cutting, drilling, engraving and / or surfacing. 4. Method according to any one of the preceding claims, characterized in that: – the machining is a cutting, more particularly a wire spark erosion (2a), and – the discharge energy is less than 5000µJ/mm sample thickness (1), preferably less than 3000µJ/mm sample thickness (1), preferably less than 1500µJ/mm sample thickness sample (1) and even more preferably less than 800 μJ/mm of thickness of sample (1). 5. Method according to claim 4, characterized in that the diameter of the wire (2a) is less than 200 μm, preferably less than 100 μm and even more preferably less than 75 μm. 6. Method according to claim 4 or 5 characterized in that the cutting is carried out in several stages of electroerosion: – at least one stage of electroerosion, called "roughing", of the sample (1) with a wire (2a) along a reference trajectory (TRef+n) to remove material from the sample (1) along a reference trajectory (TRef+n), implemented to produce a blank (5; 51) along a trajectory (TRef+n), n being the total number of spark erosion steps , say „draft; – an electroerosion step, called "finishing", of the sample (1) with a wire (2a) along a reference trajectory (TRef) to remove material from the sample (1) the along the reference trajectory (TRef), – the reference trajectory(s) (TRef+n) being translated by a given distance (gn) from the reference trajectory (TRef; TRef+(n-1)) which is directly adjacent to it and which is closest to the final piece (4), in the direction opposite to that of the final piece (4) cut; and – the given distances (gn) between two directly adjacent reference trajectories (TRef; TRef+(n-1); TRef+n), identical or different, are such that the electric discharges along the wire (2a), removing material of the sample (1) to be machined on the reference path (TRef+(n-1) or TRef+n), also remove, at least partially, material from the sample (1) to be machined on the the reference trajectories (TRef; TRef+(n-1))) which is or are directly adjacent to it. 7. Method according to claim 6, characterized in that the finishing electroerosion step is carried out with a discharge energy along the wire (2a) of less than 800 μJ/mm of sample thickness (1), preferably less at 400 μJ/mm of sample thickness (1) and even more preferably less than 200 μJ/mm of sample thickness (1). 8. Method according to claims 1 to 3, characterized in that: – EDM is die-sinking, sweeping or rapid drilling, and – the discharge energy is less than 5000µJ/mm<2>of sample surface (1), preferably less than 3000µJ/mm<2>of sample surface (1), preferably less than 1500µJ/mm<2 > of sample surface (1) and even more preferably less than 800 μJ/mm<2> of sample surface. 9. Method according to any one of the preceding claims, characterized in that the current of each electrical discharge across the terminals of the electrode (2) is less than 200 amperes. 10. Method according to any one of the preceding claims, characterized in that the voltage across the terminals of the electrode (2) is less than 200V. 11. Method according to any one of the preceding claims, characterized in that the pulse duration during which the sample (1) is subjected to an electric discharge is less than 1000 µs, preferably less than 400 µs or even preferably less at 100 µs. 12. Method according to any one of the preceding claims, in which the amorphous metal alloy of the sample (1) to be machined comprises, in atomic percentage, more than 40% of Ni, Zr, Cu, Ti, Fe or Co preferably more than 50% of Ni, Zr, Cu, Ti, Fe or Co or in which the amorphous metal alloy of the sample (1) to be machined comprises, in atomic percentage, more than 50% of the elements Ni and Nb , preferably more than 60% of Ni and Nb elements, more preferably more than 70% of Ni and Nb elements. 13. Method according to any one of the preceding claims, characterized in that the machining comprises at least one step of spark erosion of a first surface of the sample (1) with electric discharges so as to obtain a second surface whose the roughness Ra is less than 800 nm, preferably less than 600 nm, more preferably less than 400 nm and even more preferably less than 300 nm. 14. Method according to any one of the preceding claims, characterized in that it comprises at least one step of spark erosion of a first surface P1 of the sample 1 so as to obtain a second surface P2, such that in each point of intersection of surfaces P1 and P2, said surfaces P1 and P2 form between them an angle Ad of 90° ± 1.5°, preferably 90° ± 1° and even more preferably 90° ± 0.5° between them. 15. Method for manufacturing a part (4) of amorphous metal alloy, comprising the steps: – melt a mixture of metals to obtain a piece of alloy, – inject the slug obtained into a mold and cool the cast alloy with a cooling rate greater than a critical rate of crystallization of the alloy, to obtain a sample (1) of amorphous alloy, – machining at least one surface of the sample (1) according to the machining method of one of claims 1 to 14 to obtain a part (4) of amorphous alloy according to a predetermined geometry, – optionally perform a finishing step on at least the machined surface of the sample (1), preferably a tribofinishing step or a chemical treatment. 16. Amorphous metal alloy component comprising at least one surface machined according to the machining method of one of claims 1 to 14 or according to the manufacturing method according to claim 15