EP2066829A2

EP2066829A2 - Gold alloy layer having nitrogen atoms inserted therein and related processing method

Info

Publication number: EP2066829A2
Application number: EP07823862A
Authority: EP
Inventors: Denis Busardo
Original assignee: Quertech Ingenierie SA
Current assignee: Ionics France SA
Priority date: 2006-09-26
Filing date: 2007-09-26
Publication date: 2009-06-10
Also published as: WO2008037927A3; FR2906261A1; WO2008037927A2; FR2906261B1

Abstract

The invention relates to a gold alloy layer having nitrogen atoms inserted to a thickness higher than or equal to 0.05 μm and a related multi-energy implantation method.

Description

GOLD ALLOY LAYER COMPRISING INSERTED NITROGEN ATOMS, PROCESSING METHOD THEREOF

The subject of the invention is a layer of gold alloy comprising inserts of nitrogen, as well as a process for treating a gold alloy, in order to obtain such a layer. The invention also relates to a part comprising at least a portion on the surface of which is disposed such a layer.

As such, it implements a device for ion implantation segregation of a gold alloy piece from a beam of nitrogen ions emitted by an ion source. The invention also relates to a method of mtruration of a gold alloy piece implementing such a device.

The invention has applications for example in the field of goldsmithery or watchmaking or it is important to treat gold alloy parts to harden the surface and thus prevent the appearance of scratches. The invention can also find applications in the field of electrical circuits and / or electronics.

Gold a noble metal like copper and silver. The peripheral electron of gold is strongly attached to its atom. Gold is very difficult to ionize, it does not oxidize and does not corrode. The cfc structure of x'or contains very romantic sliding planes. As a result, pure gold is very ductile and very malleable. gold pure is not hard enough to find applications for example in the field of tools.

Goldsmithing uses very little pure gold, which is too soft; it prefers gold alloys with better mechanical properties. In contrast, pure gold is very popular in the field of microelectronics for its good electrical conductivity and its stainless character.

The hardness of gold depends on many factors including the composition of the alloys and the manner in which the pieces are worked.

To combine the gold with other elements has the effect of reinforcing its hardness, its mechanical resistance, and to reduce in return its ductility and malleability. Silver atoms being slightly larger than gold atoms, combining gold with silver moderately improves the hardness and strength of the alloy. Copper is much smaller in size than gold. With copper, we obtain a reinforcement of the alloy more marked than that obtained with silver: copper forces the crystalline structure and thus blocks the movement of dislocations. Other atomic species such as nickel, arsenic, lead can be added but have the disadvantage of being allergenic or even dangerous to health.

The pure gold can be hardened mechanically, by Tartexant, by folding it, by rolling it. Its structure is called ecrouie. Gold thus makes it brighter and more resistant to wear. By a heating effect, for example at a temperature above about 300 ^° C., it is possible to eliminate the internal stresses, the defects crystalline and dislocations: gold regains its original malleability.

Usually, gold alloys are classified according to the amount of gold they comprise (expressed as mass%).

For example, 24 carat gold is substantially pure gold; 22 carat gold comprises substantially 91.6% of gold, between 0 and 8.4% of silver and between 0 and 8.4% of copper; 18-carat gold comprises substantially 75% gold, between 4.5 and 25% silver and between 0 and 20.5% copper; the 14 carat gold comprises substantially 58.5% of gold, between 9 and 41.5% of silver and between 8 and 32.5% of copper.

The hardness of these annealed alloys varies in general between 20 and 150 HV (Vickers hardness) depending on the silver and copper levels. These alloys can be hardened by work hardening which can substantially double their hardness and reach respectively hardnesses of the order of 50 to 300 HV. It is customary to consider that hardness greater than 300 HV can not be achieved with conventionally processed gold alloys.

In addition, chlorine or acidity from sweat may tarnish a gold alloy by reacting with some non-gold atomic species of the alloy.

More and more, particularly in the field of goldsmithery, we are seeking to strengthen strongly and superficially gold alloy parts so that they retain as long as possible their original surface state. The scratches due to shocks degrade the surface condition of the piece (watch, jewelry ...) and makes its appearance less brilliant. As we have seen, sweat can also tarnish the shine by reacting chemically with certain elements of the gold alloy.

As a general rule, metal nitrides are well known in metallurgy to increase the hardness, reduce the corrosive action of acids or chlorine. Among these nitrides are found nitrides of aluminum, titanium or those produced in steels.

For gold, nitriding is however more difficult, even exceptional.

A process for nitriding gold, the result of which results in a deposit of gold nitride on a silicon wafer, is described in document WO2005121395

(KRISHNAMURTY et al). The application concerns the field of microelectronics. This process consists in creating a nitrogen plasma by RF excitation, then accelerating the ions on a gold sheet put under a voltage of a few hundred volts. Sputtered gold ions mix with the nitrogen ions to give rise to gold nitride deposition on a silicon substrate. The gold nitride deposition has the advantage of preserving the electrical properties of gold and has a hardness of 50% higher than that of pure gold of origin. Thus, in the field of microelectronics, it is possible to replace connectors made of pure gold with gold nitride connectors, which are harder and therefore less thick. This reduces the amount of gold needed for manufacturing and reduces the production costs of electronic components. This process, however, is not adapted to the needs of goldsmithing because deposit adhesion problems on a gold alloy piece result, or still insufficient control of the composition of the deposit, which influences the color.

It is noted that, according to this document, nitrogen is combined with gold to form an Au ₃ N compound, and is not inserted into the gold network.

The purpose of the invention is to remedy the disadvantages and problems of the techniques described above.

It is particularly the object of the present invention to provide a gold alloy whose surface hardness is improved.

This object is achieved by a layer of gold alloy comprising nitrogen atoms inserted over a thickness greater than or equal to 0.05 μm, for example greater than or equal to 0.1 μm, even for example greater than or equal to 0.2 μm, or even greater than or equal to 0.5 μm.

According to various embodiments, which can in particular be combined:

the maximum atomic concentration, N / (Au + N), is greater than or equal to 5%, for example greater than or equal to 10%, or even greater than or equal to 20% over a thickness greater than or equal to 0.05 μm;

the atomic concentration N / (Au + N) is less than or equal to 75%, for example less than or equal to 50% over the entire depth of the alloy layer comprising insertional nitrogen atoms;

the concentration profile of the nitrogen as a function of the thickness of the layer is a curve resulting from the sum of at least two Gaussian curves; the quarter-height width of the nitrogen concentration profile is greater than or equal to 0.05 ar, for example greater than or equal to 0.1 μm, even by example greater than or equal to 0.2 μm, or even greater than or equal to 0.4 μm;

the concentration profile of the nitrogen has a plateau over a depth greater than or equal to 0.1 μm, for example greater than or equal to 0.2 μm;

the content, expressed in% by weight, of gold (Au) of the gold alloy is greater than or equal to 50%, for example greater than or equal to 75%, or even greater than or equal to 90%. It is found that the hardness is very significantly increased from 5% atomic concentration of nitrogen, that it increases substantially linearly up to 30%, then that the curve of increase of hardness is squeezed between substantially 30% and 50% atomic concentration of nitrogen.

By way of example, for 18-carat gold, it is possible to reach a nanodurete of the order of 3.5 GPa for a nitrogen atomic concentration of 15%, of the order of 4 GPa for an atomic concentration. 30% nitrogen, and can be expected a nanodurete of the order of 5 GPa for 50% atomic concentration of nitrogen.

In some cases, defects can be observed if the atomic concentration of nitrogen exceeds 75% or even 50%. In general, the implantation of mono-energy ions leads to a distribution curve of the ions as a function of the thickness, called the concentration profile, of substantially Gaussian form. It is possible to obtain concentration profiles resulting from the sum of at least two Gaussian curves by implanting ions different energies that penetrate to different depths.

The gold alloy layers having the above characteristics are remarkable in that their hardness is considerably increased in comparison with a gold alloy layer of the same alloy composition without inserting nitrogen atoms .

In addition, it can be seen that these layers are particularly resistant to corrosion. According to the invention, the term "thickness", a part of a layer located substantially perpendicular to its outer surface.

The thickness may aim a distance from said surface, as a distance from a point below said surface.

The nitrogen concentration N / fAu + N) is chosen for example in order to obtain a desired hardness as a function of parameters related in particular to the treatment time, the cost of treatment. The width of the concentration profile measured for a nitrogen atomic concentration equal to one-quarter of the maximum value of the nitrogen concentration of said profile is denoted width to quarter of a height.

It is noted that a nitrogen concentration profile can be measured experimentally, for example by using a measurement method known by ESCA.

The invention also relates to a part comprising at least a portion on the surface of which is disposed a gold alloy layer according to the previous embodiments. According to one embodiment, the piece is made of gold alloy and the layer of gold alloy comprising nitrogen atoms is in continuity of material with the gold alloy. According to another embodiment, the part is at least partially coated with a gold alloy and the gold alloy layer comprising nitrogen atoms is in continuity of material with said gold alloy.

Such a piece may include, but not limited to, a piece of goldsmithery, a timepiece, a piece of electrical circuit and / or eiectronique.

The invention also relates to a part comprising at least one part on the surface of which is disposed a layer of gold comprising nitrogen atoms and whose surface nano-hardness is greater than or equal to 3.5 GPa, for example greater than or equal to 4 GPa, and / or the Vickers hardness is greater than or equal to 350 for a load of 50 g. Remarkably, such a hardness exceeds the known hardness values of gold alloys, even when not in use.

The invention also relates to a process for treating a gold alloy comprising a step of implantation of nitrogen ions, emitted by a source of energy greater than or equal to 10 keV (kilo electron volts) for example greater than or equal to 20 keV, even for example greater than or equal to 30 keV, or even greater than or equal to 50 keV. According to different modes of realization, which can in particular be combined: the xmplant nitrogen ions are multi-energy ions; the multi-energy nitrogen ions implants comprise nitrogen ions of at least two states of charge selected from the list comprising N +, N 2 +, N 3 +, N 4 +, N 5 +;

the source is an electron cyclotron resonance (ECR) source;

the electron cyclotron resonance source delivers accelerated ions by an extraction voltage and first adjustment means of an initial beam of ions emitted by said source into an implantation beam; the multi-energy nitrogen ions are simultaneously implanted at a depth controlled by the extraction voltage of the source.

In general, it can be seen that low energies, especially between 10 and 20 keV, can lead to an increase in the sputtering phenomena of the surface gold atoms. This phenomenon can be advantageously used to obtain a surface devoid of roughness. If it is desired to limit the spraying phenomena and / or deep implant nitrogen ions, we will tend to increase their energy and can consider energies for example of the order of 100 or 200 keV for N + ions. In the case of an ECR source, emitting Nf ⁴ - a N5 + ions, the energy of the N2τ, N3 +, N4 +, N5 + ions will be respectively double, triple, quadruple and fivefold. The invention relates loosely to the tracking of a part comprising at least a part on the surface of which is disposed a layer of gold alloy and or said layer of gold alloy is treated.

According to different embodiments.

the nitrogen ions are energy ions and are implanted in the room at a temperature less than or equal to 300 ° C .;

the ion beam, especially the energies, moves relative to the workpiece, for example at a constant speed or for example at a variable speed taking account of the angle of incidence of the ion beam, by relative to the surface of the piece or is disposed the layer of gold alloy to be treated.

The implantation of the nitrogen atoms can be carried out at a low temperature, for example at a temperature of less than or equal to 300 ^° C., which can make it possible to preserve a metallurgical structure, in particular a hardening, of the workpiece. It is even possible to treat a piece of temperatures up to 100 ⁰ C, for example between 50 and 60 ⁰ C. The invention will be described in detail below after the aid of nonlimiting examples, in particular distinguished by following figures:

FIG. 1 represents a functional diagram of a device implemented in one embodiment of the method according to the invention.

Figures 2 to 5 show examples of implant ion distribution in gold according to different embodiments of the process of the present invention. Selor jn non jjiτj.tatif embodiment, the treatment of a piece er gold alloy is done by simultaneous implantation of multi-energy ions. These latter are, for example, obtained by extracting, with the same single extraction voltage, mono- and multi-ring ions created in the plasma chamber of an electron cyclotron resonance ion source source (ECR source). In this case, each ion produced by said source has an energy that is proportional to its state of charge. It follows that the ions with the highest charge state, and therefore the highest energy, are implanted in the gold alloy part at greater depths.

It will be noted at this stage of the description that this implantation is fast and inexpensive since it does not require a high extraction voltage of the ion source. Indeed, to increase the implantation energy of an ion, it is economically preferable to increase its state of charge rather than increase its extraction voltage.

Note also that this device allows processing a workpiece without altering its mechanical properties obtained by hardening (for example by treating a gold piece has a temperature below 300 ⁰ C).

Said ion implantation device in a gold alloy part comprises a source delivering accelerated ions by an extraction voltage and first adjustment means for an initial beam of ions emitted by said source into a beam implantation.

Such a device is mainly recognizable in that said source is an electron cyclotron resonance source producing multi-energy ions that are implanted in the room, for example a a temperature below 300 ^° C., the implantation of the ions of the implantation beam being carried out simultaneously at a depth controlled by the extraction voltage of the source. More particularly, an embodiment of the method according to the invention proposes to use multi-energy nitrogen ions produced by the source of RCE ions within which nitrogen has been introduced beforehand. implanting the ions produced simultaneously into the gold alloy part, which generates interstitial nitrogen ions in the gold structure, gold nitride microcrystals in turn inducing an increase in hardness. The simultaneous implantation of these nitrogen ions can be done at varying depths, depending on the needs and the shape of the room. These depths depend on the ion implantation energies of the implantation beam; they can for example vary from 0 to about 1 micron.

Given a different spray effect depending on the energy and the state of charge of the incident ion, the same implanted ion concentration profile is not obtained according to, for example, that it is implanted simultaneously. N +, N2 +, N3 +, or that is successively implanted by increasing state of charge N +, N2 +, then N3 +, or that it is successively implanted by decreasing order of charge N3 +, N2 +, then N + . According to this embodiment, the successive implantation by state of charge of increasing order gives a profile of wide thickness but low concentration. The successive implantation by decreasing order of charge gives a profile of narrow thickness but of high concentration. The simultaneous implantation is a compromise between the two previous types of implantation, we obtain a profile of average thickness and average concentration. It is expensive in terms of time to implant ions successively in ascending and descending order. One embodiment of the method of the invention recommends the simultaneous implantation of multi-energy ions with a multi-energy beam and is therefore both technically advantageous and advantageous in terms of the physical compromise obtained (concentration profile). balance). It is possible to obtain a concentration profile comprising a plate of large thickness, the height of which can be controlled. This plateau height may be below a critical concentration determined by an unacceptable color of the room.

The increase in the hardness of the gold alloy is related to the concentration of implanted nitrogen ions.

The embodiment of the method of the invention using an ECR source has an additional advantage over the implantation carried out with a mono-energy nitrogen ion beam: for the same concentration of implant ions, it is preferable to effect with a beam of multi-energy nitrogen ions the appearance of gold nitride. In addition, the simultaneous implantation of multi-energy ions can generate by collisions and cascades an efficient mixing of the different layers of gold nitride (which occur at different depths of implantation in the treated thickness; efficiency of the fragmentation processes and αe microcπstals of which are constituted the Gold foil layers can allow additional hardness increase achieved by implantation with a multi-energy nitrogen ion beam.

In an application to gold alloy parts, the method of the invention provides a surface hardness close to that of steel, while maintaining the massive mechanical properties due to the hardening.

The device used advantageously further comprises second means for adjusting the relative position of the workpiece and the ion source. It will be understood that a relative displacement between the ion source and the workpiece can be implemented to be able to process the latter. According to one embodiment of the device used in the present invention in which the part is movable relative to the source, the second adjustment means comprise a workpiece which is movable to move the workpiece during its treatment. In another embodiment of the device, it is the source of ions that is displaced relative to the workpiece; the latter embodiment can be implemented when the parts to be treated together represent a too important poes. The workpiece is for example equipped with cooling means for evacuating the heat produced in the room during the implantation of the multi-energy ions.

The first means of adjusting the ion beam also comprise a mass spectrometer for sorting the ions produced by the source as a function of their size and mass. The first means of adjusting the initial ion beam may comprise optical focusing means, a profiler, an intensity transformer and a shutter. The device can be confined in an enclosure equipped with a vacuum pump.

The second means for adjusting the relative position of the part and the ion source may comprise means for calculating this position from information relating to the nature of the ion beam, to the geometry of the part, at the speed of movement of the workpiece relative to the source and the number of passes previously made.

According to one embodiment, the treatment of the gold alloy by ion implantation implements a multi-energy ion beam that moves relative to the workpiece at a constant speed.

According to another embodiment, the multi-energy ion beam moves relative to the workpiece at a variable speed taking into account the angle of incidence of the multi-energy ion beam relative to the surface of the room.

The relative speed of movement between the workpiece and the ion source may be constant or variable depending on the angle of incidence of the beam relative to the surface, for example during the treatment time. The velocity may lose beam throughput, implant ion concentration profile, and number of passes. The speed can vary according to the angle of incidence of the beam with respect to the surface, for example to compensate for the weakness of the depth of implantation by increasing the number of implant ions.

The multi-energy ion beam can be emitted with a rate and emission energies that are constant and controlled by the ion source. As explained above, the method of the invention can make it possible to act on the penetration depths of the multi-energy ions in the room. These penetration depths, which can occur in the treated thickness, may vary depending on the different ion input energies at the surface of the workpiece.

Implantation of the nitrogen ions in the crystalline structure of the part to be treated has the effect of inserting interstitial nitrogen ions and possibly creating gold nitride microcrystals (beyond a certain concentration of 'Nitrogen in gold) which are extremely hard blocking dislocation sliding planes at the origin of material deformations. In other words, the fact of implanting nitrogen ions in the part to be treated makes it possible to increase the surface hardness of the part and in particular to make it very resistant to wear.

The process according to the invention can also, by the phenomenon of superficial spraying induced by the passage of the incident ions, to erase the micro-roughness of the part, in other words to improve the surface condition and thus the room's oriance. . The process according to the invention also makes it possible to considerably reduce the corrosion of the species the atomic component of the alloy, by implanting beneath the surface a barrier of nitrogen atoms, known for their chemical inertness or their neutralizing effect acids. The process is thus likely to prevent the tarnishing of gold alloys.

It follows from these provisions that proceeds according to the invention can effectively treat gold alloy parts.

In FIG. 1, a device implemented in one embodiment of the method according to the present invention is placed in a vacuum chamber 3 by means of a vacuum pump 2. This vacuum is intended to prevent the interception of the beam by residual gases and to avoid contamination of the surface of the room by these same gases during implantation.

This device comprises an electron cyclotron resonance ion source 6, known as ECR source. This source RCE 6 delivers an initial beam fl 'ions multi-energies nitrogen for a total current of about 7.5 mΛ (all loads N +, N2 +, etc.), under an extraction voltage that can vary from 20 KV to 200 KV. The RCE source 6 emits the ion beam fl 'towards first adjustment means 7-11 which ensure the focusing and adjustment of the initial beam fl' emitted by the source RCE 6 into an ion implantation beam f1. who comes to hit a room to be treated 5.

These first adjustment means ^π -ll comprise, from the source RCE 6 to the piece 5, the following elements:

a mass spectrometer 7 capable of filtering the ions as a function of their charge and their mass. This eiement is optional; indeed, in the case where one injects a pure nitrogen gas (N2), it is possible to recover all the mono and multi-charge nitrogen ions produced by the source to obtain a multi-energy nitrogen ion beam. The mass spectrometer is a very expensive element is greatly reduced the cost of the device using a nitrogen ion beam multi energ-.es obtained from a pure nitrogen gas l _^ vre bottled.

lenses 8 whose role is to give the initial beam of ions a chosen shape, for example cylindrical, with a chosen radius. a profiler 9 whose role is to analyze the intensity of the beam in a perpendicular section plane. This analysis instrument becomes optional as long as the lenses 8 are definitively adjusted during the first implantation. an intensity transformer 10 which continuously measures the intensity of the initial beam fl 'without intercepting it. The essential function of this instrument is to detect any interruption of the initial beam f1 and to allow the recording of the intensity variations of the beam f1 during the treatment. a shutter 11 which may be a Faraday cage, whose role is to interrupt the trajectory of the ions at certain times, for example during a displacement without treatment of the part.

According to one embodiment of the device used in the frame of the method according to the invention and shown in Figure 1, the part 5 is movable relative to the source RCE 6. The part 5 is mounted on a movable workpiece 12 αont the displacement esc command by a numerically controlled machine 4, itself driven by a postprocessor calculated by a CAD / CAM system (computer-aided design and manufacturing) 1.

The displacement of the part 5 takes into account the radius of the beam fl, the external and internal contours of the zones α deal with the part 5, a constant speed of displacement, or variable depending on the angle of the beam fl relative to the surface and a number of passes previously made. Control information (mfl) is transmitted from the RCE source 6 to the digital control machine 4. This control information relates to the state of the beam. In particular, the RCE source 6 informs the machine 4 when the ion beam is ready to be sent. Other control information (inf2) is transmitted by the machine 4 to the shutter 11, to the source RCE 6 and possibly to one or more machines outside the device. This control information may be the values of the ion beam radius, its αebit and any other known values of the machine 4.

Furthermore, the workpiece holder 12 is equipped with a cooling circuit 13 for evacuating the heat produced in the workpiece 5 during the implantation of the multi-energy ions.

The operation of said device is as follows: wave the workpiece 5 on the workpiece carrier 12,

the enclosure 3 enclosing the device is closed, the cooling circuit 13 of the workpiece carrier 12 is optionally turned on, the vacuum pump 2 is started up so as to obtain a vacuum in the chamber 3,

as soon as the vacuum conditions are reached, the production and adjustment of the ion beam is carried out by means of adjustment means 7-11, when the beam is adjusted, the shutter 11 is raised and the numerically controlled machine 4 σui then executes the displacement in position and speed of the part 5 in front of the beam in one or more passes,

- When the required number of passes is reached, the shutter 11 is lowered to cut the beam fl, the production of the beam fl 'is stopped, the vacuum is broken by opening the chamber 3 to the ambient air, it is eventually stopped. the cooling circuit 13 and the treated part 5 is taken out of the enclosure 3.

There are two ways to reduce the peak in temperature associated with the passage of the beam fl at a given point of the room 5: increase the radius of the beam (thus reduce the power per cm ² ) or increase the speed of displacement.

If the room is too small to evacuate by radiation the heat related treatment can either reduce the power of the beam fl (thus increase the treatment time), or turn on the cooling circuit 13 housed in the door piece 12,

Figure 2 shows an example of distribution of N-ions implanted in gold. In this example, the ion source is an ECR source and delivers N +, N2 +, N3 +, N4 + and N5 + ions which are all extracted with a single extraction voltage, for example. example, of 200 KV. Thus the N + ions emitted by the ion source have an energy of 200 KeV, the N2 + ions have an energy of 400 KeV, the N3 + ions have an energy of 600 KeV, the N4 + ions have an energy of 800 KeV and the ions N5 ^ have an energy of 1000 KeV.

In these examples, no account is taken of the spray which has the effect of sliding these distributions to the extreme surface. In the present case, these distributions have the appearance of Gaussian characterized by average implantation depths (relative to the ion implantation energy) and a standard deviation specific to the statistical nature of the path of the ions in the material.

The N + ions reach a depth of 0.16 μm +/- 0.075 μm. The N2 + ions reach a depth of about 0.3 μm +/- 0.11 μm, the N3 + ions a depth of about 0.4 μm +/- 0.15 μm, the N4 + ions a depth of about 0.48 μm + / - 0.17 μm and the N5 + ions a depth of approximately 0.58 μm +/- 0.18 μm. The maximum distance reached by ions in this example is about 1 μm.

The specificity of an RCE 6 ion source lies in the fact that it delivers mono- and multi-charge ions, which makes it possible to simultaneously implant multi-energy ions with the same extraction voltage. It is thus possible to obtain simultaneously, over the entire thickness treated, an implantation profile more or less well distributed.

For the implantation profile, an optimal distribution is obtained by adjusting the frequencies of the source 6 so as to have an even distribution. charge states of the ions of the same standard source of N +, N2 +, N3 +, N4 +, N5 + ions per cm ² and per second).

FIG. 3 represents the atomic concentration profile obtained with a beam having the following characteristics: N + (2.5mA), N2 + (2.8mA _/ , N3 + (1.2mA), N4 + (0.25mA), N5 + (0, Q4miU , an extraction voltage of 35 K. The beam is concentrated on a surface of 1 cm ² for 15 seconds, this profile represents, on the ordinate, the atomic concentration NΛAu + N), in%, of implanted nitrogen ions as a function of the implantation depth expressed in Angstrom The maximum atomic concentration is 33% (1 nitrogen atom for 2 gold atoms) and is observed on the surface of the material This distribution is the result of a sum of atomic concentrations relative to N +, N2 + and to a lesser extent to N3 + The spraying of the surface produced by the N +, N2 +, N3 + ions causes a shift of the global concentration towards the surface, explaining on the one hand its asymmetry, on the other hand the maximum atomic concentration of 33%. maximum is about 0.17 μm. The quarter-height width is of the order of 0.08 μm, for a nitrogen atomic concentration of about 8%. FIG. 4 represents an atomic concentration profile N / (N + Au), in%, as a function of Angstrorr depth of implantation, obtained with a beam where the intensities are the same as those of the preceding beam, but where Extraction voltage is 200 KV, and the beam is concentrated on a surface of 1 cm for 70 seconds. The spraying being less strong, they will reach a maximum atomic concentration of 5OO (a nitrogen atom for a hydrogen atom or ^r). The implantation depth is approximately 0.72 μm, ie 4 to 5 times that obtained at 35 KV. The width at quarter height is of the order of 0.43 microns, for a nitrogen atomic concentration of about 12.5%.

FIG. 5 represents an atomic concentration profile, N / (N + Au), in%, which can lead to particularly advantageous properties, as a function of the implantation depth in Angstrom, obtained with a multicharge ion beam and equidistributed where: NMO, 5mA), N2 + (lmA), N3 + (1.5mA), N4 + (2mA), N5 + (2.5mA), the extraction voltage is 200 KV, and the beam is concentrated on a surface 1 cii \ ^Z for 210 seconds. The equipartition of the states of charge of the nitrogen makes it possible to obtain a broad plateau with a maximum concentration of approximately 48% (approximately 1 nitrogen atom for a gold atom) over a thickness of approximately 5000 Angstroms. The maximum implantation depth is of the order of 1 μm. The quarter-height width is of the order of 0.73 μm, for a nitrogen atomic concentration of about 12%.

By way of example, samples have been made where 18 carat gold has been treated according to one embodiment of the invention, by inserting nitrogen ions emitted by a source ECR so as to obtain the profile of concentration of Figure 3.

A treated air sample was subjected to Vickers hardness measurement according to a procedure according to ISO 4516. The applied load is 50 grams.

Five measurement points were made on one surface treated and cxnq points on an untreated surface, characteristic of the state of the sample before treatment.

The Vickers hardness, for a load of 50 g, of a treated surface was measured at 3 ^ηn HV (with a dispersion of +/- 13 HV) compared to the Vickers hardness of an untreated surface measured at 212 HV. (with a dispersion of +/- 10 HV).

There is therefore an increase of more than 50% in the Vickers hardness between an untreated gold alloy and a gold alloy treated according to the present invention.

Other samples treated as previously indicated were subjected to microhardness measurements. Microhardness measurement is understood to mean measurements made with a microdurometer according to a methodology known to those skilled in the art. In this case, a Vickers tip was used, the measurement was performed at room temperature, a 10 gram load was applied and the tip remained in contact for 15 seconds on the surface of the sample. Ten measurement points were made on the same area. An average value of 4.21 GPa is obtained for areas where nitrogen has been implanted compared to an average value of 2.53 GPa for untreated areas. In addition, samples thus treated are subjected to corrosion tests.

The test consists of immersing the gold alloy in a millet containing potassium cyanide and ammonium persulfate. an untreated part of the sample is rapidly ossified while a treated part remains free from corrosion and remains clear, of color and shine unchanged.

The invention is not limited to these types of embodiments and must be interpreted in a nonlimiting manner, encompassing any gold alloy having the characteristics and / or properties described.

Similarly, the method according to the invention is not limited to the use of a source ECR, and although it may be thought that other sources would be less advantageous, it is possible to implement the method according to the invention. , and obtain samples comprising a remarkable gold alloy layer, with monozone sources or other multi-ion sources.

Claims

1 - Gold alloy layer comprising α 'nitrogen atoms inserted over a thickness greater than or equal to 0.05 μm, for example greater than or equal to 0.1 μm, even for example greater than or equal to 0.2 μm or even greater than or equal to 0.5 μm.

2 - Gold alloy layer according to the preceding claim characterized in that the maximum atomic concentration, N / (Au + N), is greater than or equal to 5%, for example greater than or equal to 10%, or greater than or equal to equal to 20% over a thickness greater than or equal to 0.05 μm.

3 - α'or alloy layer according to any one of the preceding claims characterized in that the atomic concentration N / Αu + N) is less than or equal to 75%, for example less than or equal to 50% on the whole the depth of the alloy layer comprising inset nitrogen atoms.

4 - gold alloy layer according to any one of the preceding claims characterized in that the profile αe concentration of nitrogen as a function of the thickness of the layer is a curve resulting from the sum of at least two Gaussian curves.

5 - layer of gold alloy according to any one of claims preceαentes characterized in that the width a height αuart of the concentration profile of nitrogen is greater than or equal to 0.05 microns, for example greater than or equal to 0.1 μm, even for example greater than or equal to 0.2 μm, or even greater than or equal to 0.4 μm.

6 - layer of gold alloy according to any one of the preceding claims characterized in that the profile αe concentration of nitrogen has a plateau to a depth greater than or equal to 0.1 microns, for example greater than or equal to 0.2 μm.

7 - gold alloy layer according to any one of the preceding claims, characterized in that the content, expressed in% by weight, gold (Au) of the gold alloy is greater than or equal to 50%, example greater than or equal to 75%, or even greater than or equal to 90%.

8 - part comprising at least a portion on the surface of which is disposed a layer of gold alloy according to any one of the preceding claims.

9 - Part according to the preceding claim characterized in that the piece is made of gold alloy and the gold alloy layer comprising nitrogen atoms is in continuity of material with the gold alloy.

10 - part according to claim 8 characterized in that the part is at least partially coated with a gold alloy and the gold alloy layer comprising nitrogen atoms is in continuity of material with said alloy of gold.

11 - part according to any one of claims 8 to 10 characterized in that the piece is selected from the list comprising a goldsmithery piece, a timepiece α ', a piece of electrical circuit and / or electronic. 12 - Part comprising at least a portion on the surface of which is disposed a gold layer comprising nitrogen atoms and whose surface nano-hardness is greater than or equal to 3.5 GPa, for example greater than or equal to 4 GPa, and / or the Vickers hardness is greater than or equal to 350 for a load of 50 g.

13 - Process for treating a gold alloy comprising a step of implantation of nitrogen ions, emitted by an energy source greater than or equal to 10 keV, for example greater than or equal to 20 keV, for example even greater than or equal to 30 keV, or even greater than or equal to 50 keV.

14 - Process according to the preceding claim characterized in that the implanted nitrogen ions are multi-energy ions.

15 - Process according to the preceding claim characterized in that the multi-energy nitrogen ions implants comprise nitrogen ions of at least two states of charge selected from the list comprising N +, N2 +, N3 +, N4 +, N5 +.

16 - Process according to the preceding claim characterized in that the source is an electron cyclotron resonance source (RCE /.

17 - Process according to the preceding claim characterized in that the electronic cyclotron resonance source delivers accelerated iors by an extraction voltage and first adjustment means of an initial beam of ions emitted by said source in ur beam and implantation. 18 - Process according to any one of claims 14 to 1? characterized in that the ions multi-energy nitrogen are implanted simultaneously at a depth controlled by the extraction voltage of the source.

19 - Process for treating a part comprising at least one part on the surface of which is disposed a layer of gold alloy and wherein said layer of gold alloy is treated according to any one of claims 13 to 18.

20 - Process according to the preceding claim characterized in that the nitrogen ions are multi-energy ions and are implanted in the room at a temperature less than or equal to 300 ° C.

21 - Method according to any one of claims 19 or 20 characterized in that the ion beam, especially multi-energy, moves relative to the workpiece, for example at constant speed or for example at a variable speed taking into account the angle of incidence of the ion beam, relative to the surface of the workpiece or is disposed the gold alloy layer to be treated.