EP2376668A1

EP2376668A1 - Method for treating a metal element with ion beam

Info

Publication number: EP2376668A1
Application number: EP09797120A
Authority: EP
Inventors: Denis Busardo
Original assignee: Quertech Ingenierie SA
Current assignee: Ionics France SA
Priority date: 2008-12-01
Filing date: 2009-11-30
Publication date: 2011-10-19
Also published as: FR2939150A1; FR2939150B1; US20110236592A1; WO2010063928A1

Abstract

The present invention relates to a method for treating a metal element subjected to an ion beam, where: - the ions of the beam are selected from among boron, carbon, nitrogen, and oxygen; - the ion acceleration voltage, greater than or equal to 10 kV, and the power of the beam, between 1 W and 10 kW, as well as the ion load per surface unit are selected so as to enable the implantation of ions onto an implantation area with a thickness eI of 0.05 µm to 5 µm, and also enable the diffusion of ions into an implantation/diffusion area with a thickness eI + eP, of 0.1 µm to 1,000 µm; the temperature TZF of the area of the metal element located under the implantation/diffusion area is less than or equal to a threshold temperature TSD. In this manner, metal surfaces having remarkable mechanical characteristics are advantageously produced.

Description

PROCESS FOR TREATING A METAL PART WITH A

ION BEAM

The invention relates to a method of treating a metal part of a part where a surface of said metal part is subjected to an ion beam so as to implant ions of the beam in an implantation zone.

The invention aims in particular to allow a treatment of the surface of said part of the part so as to increase the mechanical properties.

Several techniques are known that can improve the mechanical properties of the surface of a metal part. By way of example, mention may be made of nitriding which, by virtue of a thermochemical treatment, makes it possible to enrich the surface areas of a metal part with nitrogen.

The nitriding can be carried out by using a plasma, especially cold, generated under low pressure by radio frequency excitation, where the workpiece is kept at a high temperature in a furnace to allow the diffusion of nitrogen ions. This technique has the disadvantage of having to be implemented at a temperature where the metal of the metal part of the workpiece can experience unwanted transformations, which can sometimes, and especially in the case of aluminum alloys, to lose the mechanical qualities of the treated metal part.

Nitriding can also be carried out by ion implantation, where nitrogen ions are accelerated by voltages from a few kV to a few hundred kV and bombard the surface of the metal part to be treated. The workpiece is usually cold. We can thus implant significant amounts of nitrogen. However, the penetration depth of the nitrogen ions is generally limited to 1 μm to 1.5 μm.

Other nitriding techniques are known, such as, for example, thermal nitriding, which allows the penetration of nitrogen over fairly large thicknesses.

A part is kept at a high temperature in a nitrided atmosphere for long periods of time from which it can result in structural transformations of the metal of the part to be treated.

It is also noted that the nitriding processes where the workpiece is heated to high temperature, also have drawbacks in terms of risk of deformation of the workpiece after treatment, at the time of its cooling from these high temperatures.

The object of the invention is to remedy these drawbacks.

The invention thus proposes a method of treating a metal part, of thickness e _M , of a part where a surface of said metal part is subjected to an ion beam so as to implant ions of the beam into a implantation area (ZI), thick

the ions of the beam are selected from the ions of the elements of the list consisting of boron (B), carbon (C), nitrogen (N), oxygen (O); the ion acceleration voltage is greater than or equal to 10 kV, the beam power is between 1 W and 10 kW, and said acceleration and beam power voltages as well as the ion dose per unit area are chosen in such a way allow the implantation of ions of the beam in an implantation zone (ZI) of thickness ei, between 0.05 microns and 5 microns and to allow the diffusion of ions in an implantation-diffusion zone (ZID) ) of thickness, e _τ + e _D , greater than e _τ and between 0.1 μm and 1000 μm;

the temperature, T _ZF , of the zone (ZF) of the metal part to be treated situated below the implantation-diffusion zone (ZID) is less than or equal to a threshold temperature T _S D _Λ OÙ T _S D is a temperature at which the beam ions have a path equal to 50 nm in 100 seconds in the metal of said metal part.

It is thus possible to improve the mechanical properties of the surface of a metal part by introducing the atoms thus selected over a large depth of the metal part to be treated while avoiding that the part is heated to temperatures. high. This avoids the risks of metallurgical transformation of the workpiece during the treatment and due to a low or moderate temperature during the treatment of the room, also avoid the risk of deformation after the cooling of the room.

Without wishing to be bound by any scientific theory, it may be suggested that the ion beam used in the conditions of the invention acts as a thermal peak and allows firstly to implant ions at the surface, and then allows their diffusion. on deeper thicknesses. It can indeed be assumed that the implementation conditions according to the invention make it possible to "recover" the heat generated by the braking of the ions of the beam in the metal part of the workpiece and thus to allow a diffusion of these ions beyond the area implantation without the need for additional heat input. This results in a particularly advantageous method in terms of energy cost. The thermal energy is thus brought very localized by the beam ions and it is no longer necessary to heat the room to allow the diffusion of ions on significant depths. It is thus possible, according to the invention, to nitride titanium, steels, alloys of aluminum or other metals and alloys to thicknesses of several micrometers and to obtain remarkable hardness over large thicknesses.

The choice of the conditions of adjustment of the ion beam in the ranges according to the invention advantageously makes it possible to choose the thicknesses of the implantation zone and the implantation-diffusion zone according to the desired results. It is thus possible to choose these conditions depending on the desired hardness, the type of workpiece, the type of metal of the metal part to be treated, the industrial conditions in which the present treatment method fits. For example, it is possible to choose the values of the acceleration voltage and the power of the beam according to the desired processing speeds. The present method of treatment can be implemented with several ions, independently or simultaneously, selected from boron, carbon, nitrogen and oxygen. In one embodiment, the beam ions are nitrogen ions. The inventors have been able to show that an acceleration voltage greater than or equal to 10 kV and a power greater than or equal to 1 W are necessary to allow an implantation of ions capable of diffusing at least in part over a thickness greater than the thickness of the implantation area. The acceleration voltage is defined as the voltage that gives the ions their kinetic energy. The power of the beam is equal to the intensity of the produced ions multiplied by the acceleration voltage.

The implantation zone may have a small thickness e _Ir of between 0.05 and 0.2 μm, a thickness ei corresponding to the most common implantation conditions, of between 0.2 and 1 μm, or even a thickness ei. important, between 1 and 5 microns if the ion beam is very energetic.

Under the conditions of the present invention, a part of the implanted ions diffuse beyond the implantation zone of thickness ei, to a depth ei + e _D , where e _D corresponds to the thickness of the zone where the ions can diffuse beyond the implantation zone of thickness ei.

The thickness, ei, of the diffusion zone may be small and between 0.1 and 0.5 μm, it may be average and between 0.5 and 10 μm, it may be large and between 10 and 100 μm, or even be very high and reach up to 1000 μm if the ion beam is very energetic.

According to one embodiment, the thickness, e _D , of the diffusion zone is greater than or equal to the thickness, ei, of the implantation zone.

By choosing a temperature of the area of the metal part of the workpiece less than the threshold temperature T _SD , it is possible to ensure that the beam ions can not diffuse beyond the thickness desired and thus precisely control the treatment thickness. It is also possible to ensure that the heart of the metal part to be treated is not brought to a temperature where unwanted metallurgical changes are likely to take place. Likewise, the fact that only the implantation and diffusion zones are heated by the energy provided by the ion beam, in a controlled manner, makes it possible to avoid disadvantageous deformations of the part during cooling.

In order to maintain the area of the metal part to be treated located below the implantation-diffusion zone at a temperature below T _S D, it is possible to cool the part by any means known to those skilled in the art.

The inventors have been able to determine that a threshold temperature T ₃ D at which the beam ions have a path equal to 50 nm in 100 seconds in the metal of the portion to be treated is such as to avoid a significant diffusion of these ions over- beyond implantation and dissemination areas.

The invention can find many applications in very diverse industrial fields, such as the automotive industry, the aeronautical industry, connectors where it is advantageous to improve the surface properties of metal parts.

According to one embodiment of the present invention, the metal of the metal part is chosen from the list of the following metals: magnesium (Mg), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc

(Zn), zirconium (Zr), silver (Ag), hafnium (Hf), tantalum (Ta), iridium (Ir), platinum (Pt), gold (Au), molybdenum

(Mo), tungsten (W), niobium (Nb) or the alloys of each of these metals. To allow the diffusion of an implanted ion, the implantation zone should be subjected to a diffusion temperature during a sufficient exposure time. The diffusion distance of the ion can be calculated by means of the following formula: (2 * D * t) ^1/2 , where D represents the diffusion coefficient of the ion in the metal at a given temperature and t the time exposure to this temperature. The diffusion coefficient of the ion in the metal increases with temperature. From a diffusion threshold temperature, the diffusion distances of the ion become significant relative to the implantation depths. For example, it is estimated at 400 ⁰ C, the threshold temperature of diffusion of nitrogen in aluminum alloys.

According to one embodiment of the present invention the temperature T _SD is a temperature at which the beam ions have a diffusion coefficient equal to 10 ^{~ 17} m ² , s ^"1 in the metal of said metal part.

According to one embodiment of the present invention, the temperature, T _s , of the area of the surface of the metal part bombarded by the ion beam is greater than or equal to a threshold temperature T _SID , where T _S i _D ( in Kelvin) = 1.1 x I _sD (in Kelvin). The temperature, T _s , is understood as the temperature measured at the surface of the metal part of the part to be treated in the part of this surface being treated, that is to say during the bombardment of the ion beam on this part of surface. The choice of a temperature, T ₃ , greater than or equal to a threshold temperature T _SID thus defined makes it possible to obtain conditions in which the diffusion in the implantation and diffusion zones is particularly ef f icace.

The inventors have been able to determine that a threshold value T _SID = 1.1 × T _SD , where the temperatures are expressed in Kelvin, makes it possible to obtain these advantageous conditions. It is then possible to deduce advantageous conditions of acceleration voltage and beam power.

According to one embodiment, the zone of the metal part to be treated is of restricted size and the part does not move relative to the ion beam.

According to another embodiment, the piece moves relative to the ion beam.

The part can move and the ion beam remain in a fixed position, or conversely the part can be fixed and the beam can be provided with means for moving its section interacting with the part. It is also possible to combine a displacement of the part and the ion beam. When the ion beam moves relative to the surface of the metal part of the workpiece, it can be considered that a thermal peak is created at each point of passage of the ion beam. At a given point of this surface, the thermal point leads to a rise in temperature when the beam reaches this point, then to a maximum temperature at this point followed by a lowering of the temperature to the initial temperature of said metal portion .

According to one embodiment, the section of the ion beam interacting with the metal part of the workpiece moves relative to this metal part at a constant speed, called the scanning speed V.

In such an embodiment, where the beam has a circular section, it is possible to determine, for a temperature, T ₃ , chosen, the parameters of power, P, of the scanning speed, V, of radius, R, of the ion beam so that the following equation be respected:

τ _s = (4 * p * (2 * R / V) ^1/2 ) / (ρ * c * π * R ² * (4 * π * (γ / ρ * C)) ^1/2 ) + τ _ZF

where: T ₃ is expressed in Kelvin;

T _ZF is the temperature of the metallic part of the part under the implantation-diffusion zone, less than or equal to T ₃₀ , expressed in Kelvin;

P is the power of the ion beam (in W); R is the radius of the ion beam (in m);

V is the scanning rate of the ion beam (in m s ^-1 ) p is the density of the metal of the metal part (in kg m ³ );

C is the heat capacity of the metal of the metal part (in J. kg ^-1 K ^-1 ); γ is the thermal conductivity of the metal of the metal part (in W m ^-1 K ^-1 ).

It goes without saying that the present invention is not limited to the case where the ion beam has a circular section and that any other shape of the beam can be implemented.

According to embodiments that can be combined with one another:

the ion beam has a scanning speed V of between 0.01 mm / s and 1000 mm / s, for example greater than or equal to 1 mm / s and / or less than or equal to 100 mm / s and a radius R between 0.1 mm and 100 mm, for example greater than or equal to 1 mm and / or less than or equal to 50 mm ;

the power of the ion beam is greater than or equal to 10 W and / or less than or equal to 2000 W, for example less than or equal to 1000 W;

the dose of ions per unit area is greater than or equal to 10 ¹⁸ ions / cm ² , for example greater than or equal to 2.10 ¹⁸ ions / cm ² , or even greater than or equal to 4.10 ¹⁸ ions / cm ² ;

the ion beam makes a passage or a plurality of passages on the same area of the surface of the metal part to be treated and the ion dose per unit area and per passage is greater than or equal to 0.5 × 10 ¹⁷ ions / cm ² per passage, for example greater than or equal to 1.10 ¹⁷ ions / cm ² per passage, or even greater than or equal to 2.10 ¹⁷ ions / cm ² per passage; according to one embodiment, the dose of ions per unit area and per passage is also less than or equal to 100 × 10 ¹⁷ ions / cm ² per passage, for example less than or equal to 50 × 10 ¹⁷ ions / cm ² per passage, or even example less than or equal to 20.10 ¹⁷ ions / cm ² per pass;

the thickness, ei, of the implantation zone (ZI) is greater than or equal to 0.1 μm and / or less than or equal to 1 μm;

the thickness, e _τ + e _D , of the implantation-diffusion zone (ZID) is greater than or equal to 1 μm and / or less than or equal to 100 μm, for example less than or equal to 10 μm.

According to one embodiment of the present invention, it is possible to adjust the beam diameter and the relative speed of movement of the beam relative to the workpiece so as to produce during a desired exposure time a thermal peak that exceeds a diffusion threshold temperature without ever exceeding the melting temperature of the metal. Thus at a given point of the metal part, the implanted ion is allowed to diffuse to the desired depth. If the duration of exposure is not sufficient one can repeat the operation several times by proceeding in several passes. Between two successive passes the surface temperature of the room falls back to its initial value.

Note that the angle of incidence of the beam may vary depending on the geometry of the metal part to be treated. When the beam presents at a given point an angle of incidence different from 0 °, it is possible to compensate the decrease of its power per unit area by proportionally reducing the speed of the beam.

According to one embodiment of the invention, the source of ions is an electron cyclotron resonance (ECR) source which has the particularity of being compact, light, and low in energy consumption and of producing a stable and reproducible beam in the duration. The stability of the ion beam thus generated is an advantageous quality for producing the thermal peak. Filament sources are generally less reliable. In addition, the ECR type sources produce multicharged ions which are, at equivalent acceleration voltage, much more energetic. The ions thus produced penetrate significant depths with little surface spraying effect. This results in significant treatment thicknesses.

It is noted that it is possible to modify certain characteristics of the beam as needed. As for example, when the initial ion beam is not strong enough to create the desired thermal peak, a magnetic lens may allow the reduction of the ion beam diameter to concentrate more power per unit area. The minimum diameter can be determined by the advancement step of a relative displacement system. The relative displacement system piece / beam can be controlled in position and speed so as to create a peak of sufficient heat to diffuse the implanted ion without exceeding the melting temperature of the metal.

The advancing step of the beam can be calculated so as to have a coverage of the superficial diffusion zones of the ion. For example, if it is estimated that the diffusion circle of the ion is centered around the axis of the beam with a radius corresponding to half of that of the beam, it is possible to take as the no beam advancement the radius of this beam. diffusion circle, which is half the radius of the beam. By way of example, it is possible to multiply the number of passes so as not to exceed in the implanted and diffused thickness a desired maximum atomic concentration. By way of example, it can be considered that it is advantageous not to exceed an atomic concentration of 50% in the case of nitrogen.

To implement the invention, it is advantageous to control the various parameters through a computerized system. The control of the displacement system can be done with a postprocessor produced on a CAD / CAM system that relies on the digital model of the metal part to be treated. With the digital model, it is possible to know the angle of incidence of the beam at each point of passage on the surface of the metal part. This information can be used to weight the beam speed so as to produce an optimal thermal peak on the surface of the part.

According to one embodiment of the present invention the metal of the metal part is titanium (Ti) or a titanium alloy and where:

T _ZF <773 K and T ₃ ≥ 973 K.

By way of examples, the following treatment conditions can advantageously be implemented by a titanium alloy:

P = 300 W, V = 1 mm. s ^"1 , R ≤ 10 mm;

P = 30 W, V = 1 mm. s ^"1 , R ≤ 2, 5 mm;

P = 300 W, V = 10 mm. s ^"1 , R ≤ 5 mm, P = 30 W, V = 10 mm, s ^{" 1} , R ≤ 1 mm.

According to another embodiment, the metal of the metal part is iron (Fe) or an iron alloy, especially a stainless steel, and where:

T _ZF ≤ 393 K and T ₃ ≥ 473 K.

By way of examples, the following treatment conditions can advantageously be implemented by a steel alloy:

P = 300 W, V = 1 mm. s ^"1 , R ≤ 22 mm, P = 30 W, V = 1 mm, s ^{" 1} , R ≤ 5.5 mm;

P = 300 W, V = 10 mm. s ^"1 , R ≤ 10 mm;

P = 30 W, V = 10 mm. s ^"1 , R ≤ 2.25 mm.

According to another embodiment, the metal of the metal part is aluminum (Al) or an alloy of aluminum and where: T _ZF <543 K and T _s > 597 K.

By way of examples, the following treatment conditions can advantageously be implemented by an aluminum alloy:

P = 300 W, V = 1 mm. s ^"1 , R <10 mm;

P = 30 W, V = 1 mm. s ^"1 , R <2.5 mm;

P = 300 W, V = 10 mm. s ^"1 , R <4.8 mm, P = 30 W, V = 10 mm, s ^{" 1} , R <1 mm.

Other features and advantages of the present invention in the following description of nonlimiting exemplary embodiments, in particular with reference to the accompanying drawings in which: - Figure 1 is a schematic sectional view of a workpiece according to the invention; Figure 2 is a schematic view of a device for implementing the method according to the invention; FIGS. 3 to 4 show curves of variation of the hardness as a function of the thickness of titanium samples, in particular treated under different conditions according to the invention;

FIGS. 5 and 7 show curves of variation of the hardness as a function of the thickness of steel samples, in particular treated under different conditions according to the invention;

FIGS. 6 and 8 show nitrogen concentration curves as a function of the thickness corresponding to the treatment conditions of FIGS. 5 and 7; FIG. 9 represents temperature profiles related to implantation-diffusion of nitrogen in an aluminum alloy for treatments according to the invention. For the sake of clarity, the dimensions of the various elements shown in these figures are not necessarily in proportion to their actual dimensions.

Figure 1 shows a part of a part 50 comprising a metal part 20, of thickness e _M. In the example shown, this metal part 20 is located on another part 30 of the part 50. It goes without saying that the part 50 can be composed solely of metal of the metal part 20. The metal part 20 is the object The ion beam is adjusted according to the invention so as to allow the creation of an implantation zone ZI, of thickness ei and of a diffusion zone ZD. , of thickness e _D. Subsequently, the ZID zone consisting of ZI implantation zones and ZD diffusion zones is called the "implantation-diffusion zone".

The zone ZF of the metal part, of thickness e _ZF and situated under the implantation-diffusion zone, is maintained according to the invention at a temperature T _ZF , less than or equal to a threshold temperature T _SD -

The ions of the beam 10 are directed in an area of the surface 21 of the metal part 20 to be treated. These ions are implanted in the zone ZI under the impact surface of the ion beam, in a region 22. Thanks to the thermal contribution of these ions interacting with the metal, a phenomenon of diffusion of a part of these ions is activated which allows their movement in a region 23 ZF region 24 is maintained at a temperature such that the ions can not diffuse significantly there.

FIG. 2 is a schematic view of a device for implementing the method according to the invention, in which an RCE source 60 delivers an ion beam 10 with a power and a given diameter. The part 50 is disposed on displacement means 80 which allow the part to move at a speed V with respect to the beam 10. It is possible to have cooling means between the displacement means and the part 50 to be treated in order to to maintain the temperature T _ZF in the desired zone ZF.

A magnetic lens 70 may be implemented to adjust the diameter of the ion beam 10 according to the desired power per unit area on the metal portion of the workpiece.

The displacement means 80 may be activated to allow several passes of the ion beam on the same area of the surface to be treated.

FIGS. 3, 4, 5 and 7 represent hardness curves, expressed in GPa as a function of the depth, expressed in nanometer, in the metal part 20 of the part to be treated starting from the treatment surface 21. These measurements are made by nano-indentation with a nano-durometer, thanks to a diamond tip whose advancement under the effect of a charge is spotted at the nanoscale.

Curves 3 and 4 report hardness measurement results made on samples where the treated alloy is titanium alloy Ti-6% A1-4% V, known under the trade reference TA6V. The curve 100 corresponds to the measurement of the hardness profile of an untreated TA6V part. Its hardness is less than 9 GPa over the entire thickness and substantially between 6 and 8 GPa. Curve 101 corresponds to the measurement of the hardness profile of a TA6V part treated by a nitrogen implantation process under known conditions of implantation; under these conditions the acceleration voltage of the ions is 46 000 V, the power of the beam is 315 kW, the scanning speed of the beam V is fast (40 mm / s) with a large number of passages (72 passages) in a same area of the surface of the metal part to be treated and the ion dose per unit area is 5, 4.10 ¹⁷ ions / cm ² . This results in a dose of ions per unit area and per passage equal to 0.07 × 10 ¹⁷ ions / cm ² per pass. The hardness of the sample thus obtained has a maximum of about 30 GPa at a depth of about 50 nm. It can be seen that the improvement in hardness fades rapidly as a function of depth and that the hardness profile of this sample reaches that of an untreated sample at around 200 nm.

The other curves, 102 to 104, represented in FIGS. 3 and 4, result from measurements on TA6V samples treated according to the invention with nitrogen ions under the following conditions:

Acceleration voltage: 46,000 V Beam power: 315 kW Temperature T _ZF : 300 K The following parameters have been subject to variations:

In FIG. 3, the number of passages is varied in the same area of the surface of the metal part to be treated under the following conditions:

As a result of these treatment conditions ion doses per unit area and per passage of 15.10 ¹⁷ ions / cm ² per pass.

In FIG. 4, the scanning speed V is varied under the following conditions:

As a result of these treatment conditions ion doses per unit area and per passage between 7.10 ¹⁷ and 15.10 ¹⁷ ions / cm ² per pass. Under these conditions, it is observed that diffusion-implantation phenomena take place and that the nitrogen ions make it possible to obtain a temperature, T _s , of the zone of the surface of the metal part bombarded by the ion beam. greater than a threshold temperature T _SIDΛ estimated at 973 K for a titanium alloy.

Indeed, for all the curves, 102 to 104, relative to samples of TA6V treated according to the invention, there is a very significant increase in hardness in an area close to the surface, between about 80 and 300 nm; remarkably it is found that the increase in hardness compared to an untreated sample remains at very large depths, greater than 1000 nm, or even greater than several microns. The increase in hardness at such thicknesses results from the diffusion of the nitrogen ions implanted at the surface towards the core of the metal part. It is thus possible to harden a titanium alloy to a great depth and give it remarkable surface properties.

Curves 5 and 7 report hardness measurement results made on samples where the treated alloy is a 304L commercial reference steel.

Curve 200 corresponds to the measurement of the hardness profile of an untreated 304L steel part. Its hardness is of the order of 5 GPa.

The other curves, 201 to 206, represented in FIGS. 5 and 7, result from measurements on 304L samples treated according to the invention with nitrogen ions under the following conditions:

Acceleration voltage: 46,000 V Beam power: 315 kW Temperature T _ZF : 300 K

The following parameters have been subject to variations:

In FIG. 5, the number of passages in the same zone of the surface of the metal part to be treated in the same zone is varied under the following conditions:

As a result of these treatment conditions ion doses per unit area and passage of 3.10 ions / cm per pass.

In FIG. 7, the scanning speed V is varied under the following conditions:

As a result of these treatment conditions ion doses per unit area and per passage are between 1.5, 5.10 ¹⁷ and 6.10 ¹⁷ ions / cm ² per pass.

Under these conditions, it is observed that diffusion-implantation phenomena take place and that the nitrogen ions make it possible to obtain a temperature, T ₃ , of the area of the surface of the metal part bombarded by the ion beam. greater than a threshold temperature T _SID , estimated at 473 K for a steel. Indeed, for all the curves, 202 to 206, relating to steel samples treated according to the invention, there is a very significant increase in the hardness in a first zone from the surface, between about 100 and 800 nm; remarkably it is found that the increase in hardness compared to an untreated sample remains at very large depths, greater than 1000 nm, or even greater than several microns. The increase in hardness at such thicknesses results from the diffusion of the nitrogen ions implanted at the surface towards the core of the metal part. It is thus possible to harden a steel to a great depth and to give it remarkable surface properties.

These observations are corroborated by the nitrogen concentration profiles (expressed in atom% as a function of the depth expressed in μm) presented in FIGS. 6 and 8, where the nitrogen concentration profiles are measured by EDS on slices of the samples. The profiles 301 to 306 respectively corresponding to the samples for which the hardnesses have been reported in FIGS. 5 and 7 under the numbers 201 to 206. It can be seen that for all these curves, at least 5% of nitrogen has been introduced up to at more than 5 μm, thus allowing an increase in hardness over very large depths. It should be noted that a nitrogen implantation process performed under known conditions leads to a concentration profile where the nitrogen does not penetrate deeper than about 0.2 μm.

FIG. 9 illustrates temperature profiles related to implantation-diffusion of nitrogen in an aluminum alloy for treatments according to the invention. The results shown were obtained by calculation and simulate the thermal peak caused by the passage of a beam 400 W, a radius of 15 mm, at a speed of 1 mm / s on a metal part made of aluminum alloy. The threshold temperature T _SD is estimated at 543 K and the melting temperature is 66O ⁰ C. The thermal peak is here calculated from the Fourier equation in its one-dimensional form. This equation takes into account the diffusivity of heat, which is a metal-specific datum. For an aluminum alloy the thermal diffusivity is estimated at 5.4 * 10 ^{~ 5} m. s ² . On the abscissa we find the axis of time expressed in seconds and corresponding to the passage of the beam in given point. In ordinate the temperature is represented this point and expressed in degree Celsius.

For a beam whose profile would be Gaussian, one would observe the temperature profile 401, for a beam whose profile would be constant, one would observe the temperature profile 402. It is estimated that a profile of a current beam is between the two previous configurations and one draws accordingly an estimated temperature profile 403.

It is noted that in a first zone I, for a time of up to about 10 seconds, the temperature is below T _SD . In a second zone II, for a time ranging from about 10 seconds to about 22 seconds, the temperature is higher than T _SD . Then in a third zone III, for a time beyond about 22 seconds, the temperature is below T _SD . The nitrogen atoms can not significantly diffuse in zones I and III, while they can in zone I.

It is further noted that the temperature remains below the melting point of an aluminum alloy estimated at about 66O ⁰ C. For temperatures of 400 ^° C. and 500 ^° C. and different exposure times, the distances traveled by the nitrogen in an aluminum alloy were calculated. At 400 ^° C., the nitrogen diffusion exceeds the half-micron for a duration of 100 seconds. At 500 ^° C., values of the order of one micron are reached for a few tens of seconds. The diffusion distance is added to the implantation thickness.

For example, for an acceleration voltage of 60 kV, three states of charge N + (2.4 mAe), N2 + (3 mAe), N3 + (1 mAe), for a duration of exposure of 15 seconds, one ion implantation nitride about 0.7 micron thick with a mean atomic concentration of nitrogen of 9.37%. If the conditions of displacement of the beam are such that a thermal peak is created between 400 and 500 ^° C. for 15 seconds, the nitrogen must be diffused over a distance whose value is between 0.25 and 0, 85 micron. The total thickness treated, which takes into account the diffusion distance, thus varies between approximately 0.95 and 1.55 micron. The average atomic concentration of nitrogen that dilutes in this thickness varies between about 6.9% and 4.2%. If the operation is repeated 5 times, a nitrided thickness is created in 90 seconds, the minimum thickness of which is 2.3 microns and the maximum thickness is 5.8 microns. Multiplying the operations increases the depth of the nitride thickness and the average concentration of nitrogen in the same thickness. It can further be thought that the average nitrogen concentration may tend towards a surface limiting concentration which depends on the diffusion of the nitrogen produced at each operation from the sputtering due to implantation.

The invention is not limited to the types of embodiment exemplified and must be interpreted in a non-limiting manner and encompasses any equivalent embodiment. It should be noted that if examples of treatment of titanium, steel, aluminum have been presented, the method according to the invention can be implemented with very many metals in order to improve their surface properties. .

Claims

A method of treating a metal part (20), of thickness e _M , of a part (50) where a surface (21) of said metal part (20) is subjected to an ion beam (10). ) so as to implant ions of the beam in an implantation zone (ZI), of thickness ei, characterized in that:

the ions of the beam (10) are selected from the ions of the elements of the list consisting of boron (B), carbon (C), nitrogen (N), oxygen (O);

the ion acceleration voltage is greater than or equal to 10 kV, the beam power is between 1 W and 10 kW, and said acceleration and beam power voltages as well as the ion dose per unit area are chosen so as to allow the implantation of ions of the beam in an implantation zone (ZI) of thickness ei, between 0.05 μm and 5 μm and to allow the diffusion of ions in a zone of implantation-diffusion (ZID) of thickness, e _τ + e _D , greater than e _Ir and between 0.1 μm and 1000 μm;

the temperature, T _ZF , of the zone (ZF) of the metal part (20) to be treated located beneath the implantation-diffusion zone (ZID) is less than or equal to a threshold temperature T _S Ό, OÙ T _S D is a temperature at which the beam ions have a path equal to 50 nm in 100 seconds in the metal of said metal portion (20).

2. Treatment method according to the preceding claim characterized in that the metal of the metal part (20) is selected from the list of metals magnesium (Mg), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn ), zirconium (Zr), silver (Ag), hafnium (Hf), tantalum (Ta), iridium (Ir), platinum (Pt), gold (Au), molybdenum (Mo), tungsten (W), niobium (Nb) ) or the alloys of each of these metals.

3. Treatment process according to any one of the preceding claims, characterized in that T _SD is a temperature at which the beam ions have a diffusion coefficient equal to ICT ¹⁷ m ² . s ^"1 in the metal of said metal part.

4. Treatment process according to any one of the preceding claims, characterized in that the temperature, T ₃ , of the zone (21) of the surface of the metal part bombarded by the ion beam is greater than or equal to a temperature. threshold T _S IΌ, where T _SID (in Kelvin) = 1.1 x T _SD (in Kelvin).

5. Treatment method according to the preceding claim characterized in that the ion beam (10) moves relatively to the surface of the metal part (20) at a scanning speed V, with a radius R and a power P, a temperature, T _s , of the area of said surface bombarded by the ion beam, greater than or equal to a threshold temperature T _SID , is chosen and P, V, R is determined in such a way as to respect the equation: τ _s = (4 * p * (2 * R / V) ^1/2 ) / (ρ * c * π * R ² * (4 * π * (γ / ρ * C)) ^1/2 ) + τ _ZF where:

T ₃ is expressed in Kelvin; T _ZF is the temperature of the metallic part (20) of the part (50) under the implantation-diffusion zone, less than or equal to T _SD , expressed in Kelvin; P is the power of the ion beam (in W); R is the radius of the ion beam (in m);

6. Treatment method according to the preceding claim characterized in that the ion beam (10) has a scanning speed V between 0.01 mm / s and 1000 mm / s, for example greater than or equal to 1 mm / s and / or less than or equal to 100 mm / s and a radius R between 0.1 mm and 100 mm, for example greater than or equal to 1 mm and / or less than or equal to 50 mm.

7. Treatment method according to any one of the preceding claims, characterized in that the power of the ion beam (10) is greater than or equal to 10 W and / or less than or equal to 2000 W, for example less than or equal to 1000 W.

8. Treatment process according to any one of the preceding claims, characterized in that the dose of ions per unit area is greater than or equal to 10 ¹⁸ ions / cm ² , for example greater than or equal to 2.10 ¹⁸ ions / cm ² , even for example greater than or equal to 4.10 ¹⁸ ions / cm ² .

9. Treatment method according to any one of the preceding claims, characterized in that the ion beam (10) makes a passage or a plurality of passages on the same area (21) of the surface of the metal part to be treated and that the dose of ions per unit area and per passage is greater than or equal to 0.5 × 10 ¹⁷ ions / cm ² per pass, for example greater than or equal to 1.10 ¹⁷ ions / cm ² per pass, or even greater than or equal to 2.10 ¹⁷ ions / cm ² per pass.

10. Treatment process according to the preceding claim characterized in that the ion beam (10) performs a passage or a plurality of passages on the same area (21) of the surface of the metal part to be treated and that the dose of ions per unit area and per passage is less than or equal to 100 × 10 ¹⁷ ions / cm ² per pass, for example less than or equal to 50 × 10 ¹⁷ ions / cm ² per pass, or even less than or equal to 20 × 10 ¹⁷ ions / cm; ² per pass.

11. Treatment process according to any one of the preceding claims, characterized in that the thickness e _rr of the implantation zone (ZI) is greater than or equal to 0.1 μm and / or less than or equal to 1 μm. .

12. Treatment process according to any one of the preceding claims, characterized in that the thickness, ei + e _D , of the implantation-diffusion zone (ZID) is greater than or equal to 1 μm and / or less than or equal to at 100 μm, for example less than or equal to 10 μm.

13. The method of treatment according to any one of the preceding claims characterized in that the metal of the metal part is titanium (Ti) or a titanium alloy and where:

-ZF <773 K and T _s > 9 73 K.

14. Treatment process according to any one of claims 1 to 8 characterized in that the metal of the metal part is iron (Fe) or an iron alloy, especially a stainless steel, and wherein:

T _ZF <393 K and T _s > 473 K.

15. Processing method according to any one of claims 1 to 8 characterized in that the metal of the metal part is aluminum (Al) or an aluminum alloy and where:

T _ZF <543 K and T _s > 597 K.