METHOD FOR THE SURFACE TREATMENT OF PARTICLES OF A METAL POWDER AND METAL POWDER PARTICLES OBTAINED THEREBY

Abstract

A method for surface treatment of a metal material in a powder state is provided, the method including obtaining a powder formed from a plurality of particles of the metal material to be treated; and subjecting the powder to an ion implantation process by directing a beam of singly-charged or multi-charged ions towards an outer surface of the particles, the beam being produced by a source of singly-charged or multi-charged ions, whereby the particles have an overall spherical shape with a radius (R). There is also provided a material in a powder state formed from a plurality of particles having a ceramic outer layer and a metal core, the particles having an overall spherical shape.

Claims

1. A method for surface treatment of a metal material in a powder state, the method comprising: obtaining a powder formed from a plurality of particles of the metal material to be treated; and subjecting the powder formed from the plurality of particles of the metal material to an ion implantation process by directing a beam of singly-charged or multi-charged ions towards an outer surface of the particles, the beam being produced by a source of singly-charged or multi-charged ions, whereby the particles have an overall spherical shape with a radius (R).

2. The method according to claim 1, wherein the particles are agitated throughout a duration of the ion implantation process.

3. The method according to claim 1, wherein a grain size of the particles used is such that substantially 50% of all of the particles have a diameter that lies in a range of 1 micrometre to 2 micrometres, whereby the diameter of the particles does not exceed 50 micrometres.

4. The method according to claim 1, wherein the metal material is a precious metal selected from among gold and platinum.

5. The method according to claim 1, wherein the metal material is a nonprecious metal selected from among magnesium, titanium, and aluminium.

6. The method according to claim 1, wherein the material to be ionised is selected from among carbon, nitrogen, oxygen, and argon.

7. The method according to claim 6, wherein the ion implantation process is of an electron cyclotron resonance (ECR) type.

8. The method according to claim 7, wherein the singly-charged or multi-charged ions are accelerated under a voltage in a range 15,000 volts to 35,000 volts.

9. The method according to claim 8, wherein a dose of ions implanted lies in a range from 1.10.sup.15 ions.Math.cm.sup.−2 to 1.10.sup.17 ions.Math.cm.sup.−2.

10. The method according to claim 8, wherein the singly-charged or multi-charged ions penetrate the particles up to a depth corresponding to about 10% of the radius (R) of the particles.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0027] Other characteristics and advantages of this invention will appear more clearly upon reading the following detailed description given of one example embodiment of the method according to the invention, said example being provided for illustrative purposes only and not intended to limit the scope of the invention, with reference to the accompanying drawing, wherein:

[0028] FIG. 1, mentioned hereinabove, is a diagrammatic view of a multi-charged ion source of the ECR electron cyclotron resonance type;

[0029] FIG. 2 is a sectional view of a gold particle Au whose radius is about 1 micrometre and which has been bombarded with a C.sup.+ carbon ion beam;

[0030] FIG. 3 is a diagrammatic view of a multi-charged ion source of the ECR electron cyclotron resonance type used within the scope of this invention;

[0031] FIG. 4A shows the implantation profile of the C.sup.+ carbon ions in a platinum particle Pt, the radius whereof is about 1 micrometre;

[0032] FIG. 4B is an expanded view in the plane of a substantially spherical platinum particle Pt whose radius is approximately 1 micrometre and which shows the penetration trajectory of the C.sup.+ carbon ions in the particle;

[0033] FIG. 5A shows the implantation profile of the N.sup.+ nitrogen ions in a platinum particle Pt whose radius is about 1 micrometre;

[0034] FIG. 5B is an expanded view in the plane of a platinum particle Pt whose radius is approximately 1 micrometre and which shows the penetration trajectory of the N.sup.+ nitrogen ions in the particle;

[0035] FIG. 6A shows the implantation profile of the C.sup.+ carbon ions in a gold particle Au whose radius is about 1 micrometre;

[0036] FIG. 6B is an expanded view in the plane of a substantially spherical gold particle Au whose radius is approximately 1 micrometre and which shows the penetration trajectory of the C.sup.+ carbon ions in the particle;

[0037] FIG. 7A shows the implantation profile of the N.sup.+ nitrogen ions in a gold particle Au whose radius is about 1 micrometre; and

[0038] FIG. 7B is an expanded view in the plane of a gold particle Au, the radius thereof being approximately 1 micrometre and which shows the penetration trajectory of the N.sup.+ nitrogen ions in the particle.

DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

[0039] The present invention was drawn from the general inventive idea consisting of subjecting particles of a metal powder to a treatment process for implanting ions into the surface of said particles. By bombarding the particles of a metal powder with singly- or multi-charged ions having undergone significant acceleration under electrical voltages of about 15,000 to 35,000 volts, said ions are seen to begin to fill the defects in the lattices of the crystallographic structure of the metal, then are seen to combine with the atoms of the metal material to form a ceramic. Up to a certain depth from the surface of the metal powder particles, these are transformed into a ceramic, for example into a carbide or nitride of the metal of which the particles are made. Advantageously, the mechanical and physical properties, in particular the hardness, corrosion resistance or tribological properties of said metal powder particles with a ceramic surface layer are improved. The improvement of the mechanical and physical properties of the metal powder particles provided with a ceramic surface layer is retained when said metal powders are used to produce solid parts by powder metallurgy techniques such as injection moulding, pressing, additive manufacturing or other techniques. The term “additive manufacturing technique” is understood herein as consisting of the manufacture of a solid part by the addition of material. In the case of additive manufacturing techniques, a solid part is created by gradually adding a base raw material, whereas in conventional manufacturing techniques, a raw material is used as a basis and the desired final part is obtained by gradually removing material.

[0040] FIG. 2 is a sectional view of a gold particle Au. Denoted as a whole by the general reference numeral 20, this gold particle has a substantially spherical shape with a radius R of about 1 micrometre. Said gold particle 20 has been bombarded using a C.sup.+ carbon ion beam denoted by the reference numeral 22. As shown in FIG. 2, the gold particle 20 has a core 24 made of pure gold and an outer layer or shell 26 mainly constituted from gold carbide.

[0041] The thickness e of said outer layer 26 is about one tenth of the radius R of the gold particle 20, i.e. about 100 nanometres. This outer layer 26 is mostly constituted from gold carbide, which is a ceramic material. According to the invention, the concentration of ceramic material increases from the outer surface 28 of the gold particle 20 to about 5% of the radius R of said gold particle 20, i.e. about 50 nanometres, then decreases to about one tenth of the radius R of the gold particle 20, where it is substantially zero.

[0042] Thanks to the method according to the invention, particles are obtained, for example made of gold or platinum, whose core is constituted from the original metal, whereas an outer layer that fully surrounds the core of said particles is constituted from a ceramic material, for example a carbide or nitride, which results from the combination of the metal atoms with the ions with which the particles are bombarded.

[0043] According to the invention, this method uses a powder formed from a plurality of particles of a metal material to be treated. This metal material can be, however is not limited to, a precious metal selected from the group comprising gold and platinum. It can also be a non-precious metal selected from the group comprising magnesium, titanium and aluminium.

[0044] Having chosen the metal to suit the needs, the metal powder particles 30 are subjected to an ion implantation process by directing a singly-charged or multi-charged ion beam 14 towards an outer surface of said particles, said ion beam being produced by a singly-charged or multi-charged ion source of the ECR electron cyclotron resonance type (see FIG. 3).

[0045] Preferably, however in a non-limiting manner, the material to be ionised is chosen from the group comprising carbon, nitrogen, oxygen and argon, and the singly-charged or multi-charged ions are accelerated under voltages in the range 15,000 to 35,000 volts. The dose of ions implanted lies in the range 1.10.sup.15 to 1.10.sup.17 ions.Math.cm.sup.−2.

[0046] The metal powder particles 30 have an overall spherical shape with a radius R and the grain size thereof is such that about 50% of all of said particles has a diameter that lies in the range 1 to 2 micrometres, whereby the diameter of the metal powder particles 30 does not exceed 50 micrometres. Preferably, the metal powder particles 30 are agitated throughout the duration of the ion implantation process to ensure that said particles are exposed to the ion beam 14 in a homogeneous manner over the entire outer surface thereof.

[0047] FIG. 4A shows the implantation profile of the C.sup.+ carbon ions in a platinum particle Pt, whose radius is about 1 micrometre. The abscissa extends along the radius R of the platinum particle Pt, where the origin of said abscissa corresponds to the outer surface of the platinum particle, and where the value of 2,000 Ångströms corresponds to about 20% of the length of the radius R of the platinum particle Pt. The ordinate shows the number of C.sup.+ carbon ions implanted in the platinum particle Pt at a given depth. It can be seen that the number of C.sup.+ carbon ions implanted in the platinum particle Pt increases very quickly from the outer surface of the platinum particle to reach a maximum that exceeds 14×10.sup.4 atoms.Math.cm.sup.−2 at a depth substantially corresponding to 500 Ångströms, i.e. approximately 5% of the radius R of the platinum particle. Then, the number of C.sup.+ carbon ions decreases and approaches zero at approximately 1,000 Ångströms in depth, i.e. about 10% of the radius R of the platinum particle Pt.

[0048] FIG. 4B is an expanded view in the plane of a substantially spherical platinum particle Pt, whose radius is approximately 1 micrometre and which shows the average free trajectory of the individual C.sup.+, C.sup.++ carbon ions, etc. when they penetrate a platinum particle Pt. This FIG. 4B was drawn up for a density of about 14×10.sup.4 atoms.Math.cm.sup.−2. The abscissa in FIG. 4B shows the depth of the platinum particle Pt between the surface (0 Ångströms) and 2,000 Ångströms. The ordinate in FIG. 4B shows the diameter of the C.sup.+ carbon ion beam. The centre of the C.sup.+ carbon ion beam is located midway along the height of the ordinate, between the values −1,000 Ångströms and +1,000 Ångströms. It can thus be seen in FIG. 4B that the approximate diameter of the C.sup.+ carbon ion beam is about 150 nanometres and that the penetration depth of the C.sup.+ carbon ions in the platinum particle Pt barely exceeds more than 100 nanometres.

[0049] FIG. 5A shows the implantation profile of the N.sup.+ nitrogen ions in a platinum particle Pt, whose radius R is about 1 micrometre. The abscissa extends along the radius R of the platinum particle Pt, where the origin of said abscissa corresponds to the outer surface of the platinum particle Pt, and where the value of 2,000 Ångströms corresponds to about 20% of the length of the radius R of the platinum particle Pt. The ordinate shows the number of N.sup.+ nitrogen ions implanted in the platinum particle Pt at a given depth. It can be seen that the number of N.sup.+ nitrogen ions implanted in the platinum particle Pt increases very quickly from the outer surface of the platinum particle Pt to reach a maximum that exceeds 16×10.sup.4 atoms.Math.cm.sup.−2 at a depth substantially corresponding to 500 Ångströms, i.e. approximately 5% of the radius R of the platinum particle Pt. Then, the number of N.sup.+ nitrogen ions decreases and approaches zero at a depth of about 1,000 Ångströms from the outer surface of the platinum particle Pt, i.e. about 10% of the radius R of said platinum particle Pt.

[0050] By comparing FIGS. 4A and 5A, the N.sup.+ nitrogen ions can be seen to penetrate the crystallographic lattice of the platinum particle Pt to a lesser degree than the C.sup.+ carbon ions.

[0051] FIG. 5B is an expanded view in the plane of a substantially spherical platinum particle Pt, the radius thereof being approximately 1 micrometre and which shows the average free trajectory of the individual N.sup.+, N.sup.++ nitrogen ions, etc. when they penetrate a platinum particle Pt. This FIG. 5B was drawn up for a density of about 16×10.sup.4 atoms.Math.cm.sup.−2. The abscissa in FIG. 5B shows the depth of the platinum particle Pt between the surface (0 Ångströms) and 2,000 Ångströms. The ordinate in FIG. 5B shows the diameter of the N.sup.+ nitrogen ion beam. The centre of the N.sup.+ ion beam is located midway along the height of the ordinate, between the values −1,000 Ångströms and +1,000 Ångströms. It can thus be seen in FIG. 5B that the approximate diameter of the N.sup.+ ion beam is about 150 nanometres and that the penetration depth of the N.sup.+ ions in the platinum particle Pt is slightly less than 100 nanometres. It is thus clear that the N.sup.+ ions penetrate the platinum particles to a lesser degree than the C.sup.+ ions.

[0052] FIG. 6A shows the implantation profile of the C.sup.+ carbon ions in a gold particle Au, the radius R thereof being about 1 micrometre. The abscissa extends along a radius R of the gold particle Au, where the origin of said abscissa corresponds to the outer surface of the gold particle Au, and where the value of 2,000 Ångströms corresponds to about 20% of the radius R of the gold particle Au. The ordinate shows the number of C.sup.+ carbon ions implanted in the gold particle Au at a given depth. It can be seen that the number of C.sup.+ carbon ions implanted in the gold particle Au increases very quickly from the outer surface of the gold particle Au to reach a maximum that exceeds 12×10.sup.4 atoms.Math.cm.sup.−2 at a depth of 500 Ångströms, i.e. approximately 5% of the radius R of the gold particle Au. Then, the number of ions decreases and approaches zero at about 1,000 nm below the outer surface of the gold particle Au, i.e. about 10% of the length of the radius R of the particle.

[0053] FIG. 6B is an expanded view in the plane of a substantially spherical gold particle Au, the radius thereof being approximately 1 micrometre and which shows the average free trajectory of the individual C.sup.+, C.sup.++ carbon ions, etc. when they penetrate a gold particle Au. This FIG. 6B was drawn up for an ion density of about 12×10.sup.4 atoms.Math.cm.sup.−2. The abscissa in FIG. 6B shows the depth of the gold particle Au between the surface (0 Ångströms) and 2,000 Ångströms. The ordinate in FIG. 6B shows the diameter of the C.sup.+ carbon ion beam. The centre of the C.sup.+ ion beam is located midway along the height of the ordinate, between the values −1,000 Ångströms and +1,000 Ångströms. It can thus be seen in FIG. 6B that the approximate diameter of the C.sup.+ ion beam is about 150 nanometres and that the penetration depth of the C.sup.+ ions in the gold particle Au slightly exceeds 100 nanometres.

[0054] FIG. 7A shows the implantation profile of the N.sup.+ nitrogen ions in a gold particle Au, whose radius is about 1 micrometre. The abscissa extends along a radius R of the gold particle Au, where the origin of said abscissa corresponds to the outer surface of the gold particle Au, and where the value of 2,000 Ångströms corresponds to about 20% of the radius R of the gold particle Au. The ordinate shows the number of N.sup.+ nitrogen ions implanted in the gold particle Au at a given depth. It can be seen that the number of N.sup.+ nitrogen ions implanted in the gold particle Au increases very quickly from the outer surface of the gold particle Au to reach a maximum that exceeds 14×10.sup.4 atoms.Math.cm.sup.−2 at a depth of 500 Ångströms, i.e. approximately 5% of the length of the radius R of the gold particle Au. Then, the number of N.sup.+ nitrogen ions decreases and approaches zero at about 1,000 nm below the outer surface of the gold particle Au, i.e. about 10% of the length of the radius R of the particle.

[0055] FIG. 7B is an expanded view in the plane of a substantially spherical gold particle Au, the radius whereof is approximately 1 micrometre and which shows the average free trajectory of the individual N.sup.+, N.sup.++ nitrogen ions, etc. when they penetrate a gold particle Au. This FIG. 7B was drawn up for an ion density of about 14×10.sup.4 atoms.Math.cm.sup.−2. The abscissa in FIG. 7B shows the depth of the gold particle Au between the surface (0 Ångströms) and 2,000 Ångströms. The ordinate in FIG. 7B shows the diameter of the N.sup.+ azote ion beam. The centre of the N.sup.+ nitrogen ion beam is located midway along the height of the ordinate, between the values −1,000 Ångströms and +1,000 Ångströms. It can thus be seen in FIG. 7B that the approximate diameter of the N.sup.+ nitrogen ion beam is about 150 nanometres and that the penetration depth of the N.sup.+ ions in the platinum particle Pt gold particle Au is about 100 nanometres. It is thus clear that the N.sup.+ nitrogen ions penetrate the gold particles Au to a lesser degree than the C.sup.+ ions.

[0056] It is evident that this invention is not limited to the embodiment described above and that various simple alternatives and modifications can be considered by one of ordinary skill in the art without leaving the scope of the invention as defined by the accompanying claims. In particular, it is understood that the ion implantation process of the ECR electron cyclotron resonance type is stipulated in the form of a preferred example but in no way limiting the scope of the invention, and that other hot plasma generation processes, for example by induction or using a strong magnetic field produced by a microwave generator can be considered. It should also be noted that additional measurements performed by transmission electron microscopy on sapphire particles with an average diameter of 2.0 micrometres implanted by nitrogen confirm that the sapphire particles, after ion implantation, have a ceramic shell with a thickness of about 150 to 200 nanometres. It should also be noted that the ratio between the volume of the particles that is irradiated and the total volume of the particles is equal to about 14%. From the perspective of the Applicant, the powder obtained by the ion implantation method according to the invention is not a real composite material. More specifically, with regard to the widely-accepted meaning thereof, a composite material is the result of the combination of two different materials, namely a matrix and a reinforcement. In this case, the description only concerns a single material in which ion bombardment results in a modification to the chemical structure at the surface. This could therefore preferably be referred to as a heterogeneous material. Finally, it should be noted that, according to the invention, the ECR ion source is capable of producing singly-charged ions, i.e. ions with a degree of ionisation equal to 1, or multi-charged ions, i.e. ions with a degree of ionisation greater than 1. It should also be noted that the ion beam can comprise ions all having the same degree of ionisation, or can result from a mixture of ions having different degrees of ionisation.

NOMENCLATURE

[0057] 1. ECR multi-charged ion source [0058] 2. Injection stage [0059] 4. Volume of a gas to be ionised [0060] 6. Microwave [0061] 8. Magnetic confinement stage [0062] 10. Plasma [0063] 12. Extraction stage [0064] 12a. Anode [0065] 12b. Cathode [0066] 14. Multi-charged ion beam [0067] 16. Surface [0068] 18. Part to be treated [0069] 20. Gold particle Au [0070] R. Radius [0071] 22. C.sup.+ carbon ion beam [0072] 24. Core [0073] 26. Outer layer or shell [0074] e. Thickness [0075] 28. Outer surface [0076] 30. Metal powder particles