Treatment method using a beam of singly- or multiply-charged gas ions in order to produce colored metals

Abstract

The disclosure relates to a treatment method for coloring a metal that includes a) bombardment of the metal with a beam of singly- or multiply-charged gas ions produced by an electron cyclotron resonance source; b) heat treatment in ambient air so as to color the implanted metal using a temperature between 100 C. and 400 C. and an exposure time of between 1 minute and 4 hours.

Claims

1. A treatment process for coloring a metal, comprising: a) bombarding the metal with a beam of mono- and multicharged ions of a gas produced by an electron cyclotron resonance (ECR) source, wherein: a dose of mono- and multicharged ions of the gas implanted per unit of surface area by the bombardment is in a range of between 10.sup.16 ions/cm.sup.2 and 10.sup.19 ions/cm.sup.2, a single acceleration voltage is applied, said single acceleration voltage has a value in a range of between 5 kV and 1000 kV; and b) performing a heat treatment for coloring the implanted metal, wherein: the heat treatment is performed at a temperature of between 100 C. and 600 C. for an exposure time of between 1 min and 4 hours.

2. The process as claimed in claim 1, wherein the mono- and multicharged ions of the gas of the beam of ions are ions of the elements selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr) and xenon (Xe).

3. The process as claimed in claim 1, wherein the mono- and multicharged ions of the gas of the beam of ions are ions of the gases selected from the group consisting of nitrogen (N.sub.2) and oxygen (O.sub.2).

4. The process as claimed in claim 1, wherein the mono- and multicharged ions of the gas are all ions of one and the same atomic compound.

5. The process as claimed in claim 4, wherein the atomic compound is a gas at ambient temperature.

6. The process of claim 4, wherein the mono- and multicharged ions of the gas from all ions of one and the same atom or of one and the same diatomic molecule.

7. The process as claimed in claim 1, wherein the beam of mono- and multicharged ions of the gas comprises 10% of multicharged ions or more than 10% of multicharged ions.

8. The process of claim 7, wherein the beam of mono- and multicharged ions of the gas comprises 30% of multicharged ions or more than 30% of multicharged ions.

9. The process as claimed in claim 1, wherein the heat treatment is carried out in ambient air.

10. The process as claimed in claim 1, wherein the acceleration voltage is chosen in order to obtain an implanted thickness equal to p* 100 nm, where p is an integer.

11. The process as claimed in claim 1, wherein the metal is selected from the group consisting of steels, titanium alloys, aluminum alloys, cobalt alloys, copper alloys and gold alloys.

12. The process of claim 1, wherein the metal is a bulk metal part selected from the group consisting of a watch part, a place setting and a jewel.

13. The process of claim 1, wherein the heat treatment is performed a temperature of between 100 C. and 400 C.

14. A treatment process for coloring a metal, comprising: a) bombarding the metal with a beam of mono-and multicharged ions of a gas produced by an electron cyclotron resonance (ECR) source, wherein: the dose of mono- and multicharged ions of the gas implanted per unit of surface area by the bombardment is in a range of between 10.sup.16 ions/cm.sup.2 and 10.sup.19 ions/cm.sup.2, and the dose of mono- and multicharged ions of the gas which are implanted per unit of surface area is chosen in order to achieve an atomic concentration of implanted ions of greater than or equal to 10%, and an acceleration voltage is in a range between 5 KV and 1000 kV; and b) performing a heat treatment for coloring the implanted metal, wherein: the heat treatment is performed at a temperature of between 100 C. and 600 C. for an exposure time of between 1 min and 4 hours.

15. A treatment process for coloring a metal, comprising: a) bombarding the metal with a beam of mono- and multicharged ions of a gas produced by an electron cyclotron resonance (ECR) source, wherein: the metal is movable with respect to the beam of mono- and multicharged ions of the gas at a rate, V.sub.D, of between 0.1 mm/s and 1000 mm/s a dose of mono- and multicharged ions of the gas implanted per unit of surface area by the bombardment is in a range of between 10.sup.16 ions/cm.sup.2 and 10.sup.19 ions/cm.sup.2, and an acceleration voltage is in a range of between 5 kV and 1000 kV; and b) performing a heat treatment for coloring the implanted metal, wherein: the heat treatment is performed at a temperature of between 100 C. and 600 C. for an exposure time of between 1 min and 4 hours.

16. The process as claimed in claim 15, wherein one and the same region of the metal is moved under the beam of mono- and multicharged ions of the gas according to a plurality, N, of passes at the rate V.sub.D.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other distinguishing features and advantages of the present invention will emerge in the description below of nonlimiting exemplary embodiments illustrated by the appended figures, where:

(2) FIG. 1 describes the procedure for reflection of an incident wave through the layer created in a metal by the process of the invention in order to produce a shade.

(3) FIG. 2 describes the masking procedure which makes possible the creation of distinct colored regions appearing during one and the same heat treatment operation.

DETAILED DESCRIPTION

(4) According to implementational examples of the present invention, polished samples made of 304L steel were made the subject of studies, with mono- and multicharged nitrogen ions.

(5) The inventors carried out a campaign of tests with a beam of mono- and multicharged nitrogen ions with an intensity of 5 mA comprises N.sup.+, N.sup.2+ and N.sup.3+ ions; the acceleration voltage is 35 kV; the N.sup.+ energy is 35 keV, the N.sup.2+ energy is 70 keV and the N.sup.3+ energy is 105 keV. The treatment dose is equal to 510.sup.17 ions/cm.sup.2. These energies are sufficient to create an implanted layer estimated by the inventors at approximately 100 nm.

(6) These mono- and multicharged ions of the gas were emitted by an ECR source.

(7) The samples are at ambient temperature during the treatment with the mono- and multicharged nitrogen ions.

(8) The treated samples move in a series of to-and-fro movements with respect to the beam with a diameter equal to 60 mm, with a rate of movement of 80 mm/s and at an advancement step at each to-and-fro movement corresponding to a fraction of the beam diameter equal to 20% in order to guarantee homogeneity of the treatment. Several passes were required to reach the required dose equal to 510.sup.17 ions/cm.sup.2.

(9) The samples were thus subjected, after treatment, in an ambient air oven, to different temperatures and different exposure times in order to reveal colors. The colors observed with the naked eye by the inventors are summarized in the table below:

(10) TABLE-US-00001 Dose Temperature Exposure time (10.sup.17 N ions/cm.sup.2) ( C.) (%) Color observed 0 Reference sample Silvery gray 0 300 C. 1 h Silvery gray 5 Treated sample Golden yellow 5 250 C. 1 h Purple 5 300 C. h Crimson 5 300 C. h Purple 5 300 C. 1 h Blue 5 350 C. 4 h Silvery pale pink

(11) The inventors retain from this table that the time necessary to reveal a substantially identical color (for example purple) is two times greater when the temperature is lower by 50 C. (when the temperature changes from 300 C. to 250 C.). This delay is explained by a slowing in the oxidation procedure in the implanted layer. The reference sample (304L stainless steel) exhibits an unchanged color after a heat treatment in an ambient air oven at 300 C. for 1 hour (silver color, no oxidation procedure). The treated sample promotes the appearance of a golden yellow color which is gradually converted into crimson (red/blue mixture), into purple and then into blue. For a high temperature (350 C.) and an exposure time equal to 4 h, the color tends towards a silvery pale pink color. This can be explained by the diffusion of the implanted entity (nitrogen) and, with it, the diffusion of its oxides. This has the effect of creating a deep oxidized layer in keeping with the reflecting of the large wavelengths (red). By amplifying the effect, the range of filtering of the visible waves is left behind and there is a gradual return toward the starting silvery gray color.

(12) The inventors immersed the colored samples in a sodium hydroxide solution for 15 min and observed no change in color, thus confirming that the implanted layer has indeed been oxidized until it forms a compact passivated protective layer (in contrast to the PVD deposits, which have a porous columnar structure).

(13) The inventors also treated polished samples made of 316L steel with mono- and multicharged nitrogen ions, under the following conditions:

(14) The samples are at ambient temperature during the treatment with the mono- and multicharged nitrogen ions. The beam of mono- and multicharged nitrogen ions has an intensity of 5 mA comprises N.sup.+, N.sup.2+ and N.sup.3+ ions; the acceleration voltage is 35 kV. The treatment dose is equal to 510.sup.17 ions/cm.sup.2.

(15) The samples were subsequently treated in an ambient air oven at 300 C. and for different exposure times in order to reveal colors. The colors observed with the naked eye by the inventors are summarized in the table below:

(16) TABLE-US-00002 Exposure time at 300 C. Color 10 min Dark red 30 min Dark red-purple 32.5 min Dark purple 37.5 min Midnight blue 40 min Blue 45 min Light blue 60 min Pale light blue

(17) The inventors also treated polished samples made of 316L steel with mono- and multicharged nitrogen ions, under the following conditions:

(18) The samples are at a temperature of 340 C. during the treatment with the mono- and multicharged nitrogen ions (implantation/diffusion conditions). The beam of mono- and multicharged nitrogen ions has an intensity of 5 mA comprises N.sup.+, N.sup.2+ and N.sup.3+ ions; the acceleration voltage is 35 kV. The treatment dose is equal to 3.310.sup.18 ions/cm.sup.2.

(19) The samples were subsequently treated in an ambient air oven at 300 C. and for different exposure times in order to reveal colors. The colors observed with the naked eye by the inventors are summarized in the table below:

(20) TABLE-US-00003 Exposure time at 300 C. Color 60 min Dark gray 90 min Blue-dark gray 240 min Gray-blue

(21) The inventors also treated polished samples made of titanium alloy (TiAl.sub.6V.sub.4) with mono- and multicharged nitrogen ions, under the following conditions:

(22) The samples are at ambient temperature during the treatment with the mono- and multicharged nitrogen ions. The beam of mono- and multicharged nitrogen ions has an intensity of 5 mA comprises N.sup.+, N.sup.2+ and N.sup.3+ ions; the acceleration voltage is 35 kV. The treatment dose is equal to 510.sup.17 ions/cm.sup.2.

(23) The samples were subsequently treated in an ambient air oven at 500 C. and for different exposure times in order to reveal colors. The colors observed with the naked eye by the inventors are summarized in the table below:

(24) TABLE-US-00004 Exposure time at 500 C. Color 3 min Brown 5 min Midnight blue 20 min Green-blue 50 min Green-golden yellow 120 min Olive green

(25) The inventors also treated polished samples made of titanium alloy (TiAl6V4) with mono- and multicharged nitrogen ions, under the following conditions:

(26) The samples are at a temperature of 370 C. during the treatment with the mono- and multicharged nitrogen ions (implantation/diffusion conditions). The beam of mono- and multicharged nitrogen ions has an intensity of 5 mA comprises N.sup.+, N.sup.2+ and N.sup.3+ ions; the acceleration voltage is 37.5 kV. The treatment dose is equal to 4.510.sup.18 ions/cm.sup.2.

(27) The samples were subsequently treated in an ambient air oven at 500 C. and for different exposure times in order to reveal colors. The colors observed with the naked eye by the inventors are summarized in the table below:

(28) TABLE-US-00005 Exposure time at 500 C. Color 2 min 30 Dark brown 5 min Midnight purple-blue 30 min Blue-gray 60 min Dark green 300 min Olive green

(29) The inventors treated, by the process of the invention, samples made of aluminum alloy (AU4G) with the beam mentioned above for steel, using different doses, respectively equal to 4, 6 and 810.sup.17 ions/cm.sup.2. The samples are at ambient temperature during the treatment with the mono- and multicharged nitrogen ions.

(30) TABLE-US-00006 Dose Temperature Exposure time (10.sup.17 N ions/cm.sup.2) ( C.) (%) Color observed 0 Reference sample Silvery gray 4 100 C. 2 h Blue 6 100 C. 2 h Yellow 8 100 C. 2 h Red

(31) The aluminum alloys differ from steel in so far as the implanted entities cannot diffuse in the temperature range for appearance of the colors (preferably less than 150 C. in order to retain the mechanical properties).

(32) From this table, it appears that the dose acts in the direction of a widening of the implantation profile promoting, during the oxidation procedure, the reflection of the short (blue) wavelengths toward long (yellow then red) wavelengths. Hence the appearance of the red, yellow and blue shades.

(33) As recommended by the process of the invention, the regulating of the acceleration voltage of the ions is calculated so that the implanted thickness is equal to a multiple of approximately 100 nm. It is possible to more finely regulate these values (acceleration voltage, dose, temperature, exposure time) during an experimental adjustment phase using the naked eye. Reference may be made, for this, to a preliminary calibration stage described above.

(34) For all of the results given above, the surface of the treated metal is perpendicular to the direction of the beam of ions (incidence of 0).

(35) The inventors have been able to find that the incidence of the ion beam can have an influence on the color obtained. It may thus be timely to take into consideration the incidence of the beam of ions when it is desired to treat a nonplanar surface.

(36) By way of example, for a 316L steel treated at ambient temperature with a beam of mono- and multicharged nitrogen ions which comprises N.sup.+, N.sup.2+ and N.sup.3+ ions, with an intensity of 5 mA, with an acceleration voltage of 35 kV and a treatment dose equal to 510.sup.17 ions/cm.sup.2, followed by a heat treatment of 30 min at 300 C. in ambient air, it is found that the color is dark red/purple for an angle of incidence of zero and golden yellow for an angle of incidence of 45.

(37) Consequently, the inventors recommend, in order to have a homogeneous color over a curved surface, a treatment which consists in moving the part and/or the beam so that the implanted thickness and the ion dose are substantially identical to within +/10%. By way of example, it is possible to rotate a cylindrical surface under a static beam so as to retain a substantially constant angle of incidence. For a static beam, it is considered possible to obtain a homogeneous color over a curved surface provided that the angle of incidence of the beam does not vary by more than 22.5 with respect to the perpendicular at each point of this surface. If the surface does not make it possible to abide by this rule, it is advisable to treat it with a beam oriented along several angles of incidence each associated with the different portions of the surface, so as to observe said rule. By way of example, it is possible to polyhedrize a sphere into a sufficient number of facets to observe this rule.

(38) As a general rule and independently of the nature of the metal (steels, titanium, and the like), the inventors recommend using the lowest possible temperatures to oxidize the implanted layer and to prevent as much as possible the diffusion of the implanted entities which fix the oxidation procedure. This is particularly true in order to produce colors tending toward the red with a low implantation depth, this is because the temperature can easily act in the direction of a widening of the implantation profile favorable to the appearance of a blue color.

(39) The inventors recommend the use of the present invention with other metal alloys, for example with a colorimetric display temperature corresponding to approximately M.p. (M.p. being the melting point expressed in K), in particular: cobalt alloy treated by a beam of mono- and multicharged ions of a gas and then displayed by heat treatment at approximately 500 C.; copper alloy treated by a beam of mono- and multicharged ions of a gas and then displayed by heat treatment at approximately 300 C.; gold-based alloy treated by a beam of mono- and multicharged ions of a gas and then displayed by heat treatment at approximately 300 C.

(40) FIG. 1 describes the building of the color by constructive/destructive filtering of incident waves (I) reflected (R) through the implanted layer (C) created superficially in a metal part (P). This layer exhibits an oxidation gradient controlled by the process of the invention with a semi-empirical development, the method and the rules of which are described above, for example for steels and aluminum alloys. The adjusting of the thickness (e) of the implanted layer and of its degree of oxidation relative to the temperature and to the exposure time of the heat treatment makes it possible to create a very precise color among a whole range of possible shades for the hue of the metal chosen (steel, titanium alloy, aluminum alloy or other).

(41) FIG. 2 describes the example of building a pattern corresponding to a circle (with the outline MC) inscribed within a square (with the outline MR) on a metal surface S1. A first square mask (hollowed out at its center along the outline MR) is applied to the metal surface S1, through which a dose d1 is implanted in a square region with the outline MR. Subsequently, in addition, a portion of the square region is masked with a circular mask (hollowed out at its center along the outline MC) in order to treat, through the latter, a circular region within the outline MC with a dose d2. After one and the same heat treatment operation according to the process of the invention to reveal the colors, the region accumulating a dose (d1+d2) appears under a first color, the region treated with the dose d1 appears with a separate color and, finally, the masked metal surface (thus not treated and located outside the outline MR) appears under its starting color.