CH712923B1 - Process for surface treatment of particles of a metal powder and particles of metal powder obtained by this process - Google Patents

Abstract

The invention relates to a process for the surface treatment of a metallic material in the powder state, this process comprising the step consisting in providing a powder formed of a plurality of particles of the metallic material to be treated, and subjecting said metal powder particles to an ion implantation process by directing to an outer surface of said particles a monocharged or multicharged ion beam (14) produced by a source of monocharged or multicharged ions, for example electron cyclotron resonance ECR, these particles having a generally spherical shape with a radius (R). The invention also relates to a powdered material formed of a plurality of particles having a ceramic outer layer (26) and a metal core (24), these particles having a generally spherical shape with a radius (R).

Description

Description

TECHNICAL FIELD OF THE INVENTION [0001] The present invention relates to a process for the surface treatment of particles of a metallic material in powder form as well as metal powder particles obtained by the implementation of such a method. . The metal powder particles obtained by the process according to the invention are intended for the manufacture of solid parts by means of powder metallurgy processes such as the injection molding process, better known by its Anglo-Saxon name Metal Injection Molding or MIM, pressing or additive manufacturing such as 3D laser printing. The present invention also relates to a particle of a metal powder with a ceramic surface and a metal core.

BACKGROUND OF THE INVENTION [0002] Ion implantation methods consist in bombarding the surface of an object to be treated, for example by means of a source of mono- or multi-charged ions of the electron cyclotron resonance type. Such an installation is still known under the name Anglo-Saxon Electron Cyclotron Resonance or ECR.

[0003] An ECR ion source makes use of the cyclotron resonance of the electrons to create a plasma. A low pressure gas volume is ionized by means of microwaves injected at a frequency corresponding to the electron cyclotron resonance defined by a magnetic field applied to a region situated inside the volume of gas to be ionized. Microwaves heat the free electrons present in the volume of gas to be ionized. These free electrons, under the effect of thermal agitation, will collide with atoms or gas molecules and cause their ionization. The ions produced correspond to the type of gas used. This gas can be pure or compound. It can also be a vapor obtained from a solid or liquid material. The ECR ion source is able to produce simply charged ions, i.e. ions with a degree of ionization equal to 1, or multicharged ions, i.e. ions whose degree of ionization is greater than 1.

[0004] A source of multicharged ions of the electron cyclotron resonance type ECR is schematically illustrated in FIG. 1 attached to this patent application. Designated as a whole by the general numerical reference 1, a multicharged ion source ECR comprises an injection stage 2 into which a volume 4 of a gas to be ionized and a microwave wave 6, a magnetic confinement stage 8 is introduced. in which a plasma 10 is created, and an extraction stage 12 which makes it possible to extract and accelerate the ions of the plasma 10 by means of an anode 12a and a cathode 12b between which a high voltage is applied. A multicharged ion beam 14 produced at the output of the multicharged ion source ECR 1 strikes a surface 16 of a workpiece 18 and penetrates more or less deeply into the volume of the workpiece 18.

[0005] The implantation of ions by bombardment of the surface of an object to be treated has numerous effects, among which the modification of the microstructure of the material in which the object to be treated is achieved, the improvement of the resistance to corrosion, improvement of the tribological properties and, more generally, improvement of the mechanical properties. Several studies have thus highlighted the increase in the hardness of copper and bronze by ion implantation of nitrogen. It has also been shown that the implantation of nitrogen or neon in the copper makes it possible to increase its resistance to fatigue. Similarly, studies have shown that even low-dose nitrogen implantation (1.1015 and 2.1015 ions.cm-2) was sufficient to significantly modify the copper shear modulus.

It is therefore understood that the implantation of ions by bombardment of the surface of an object to be treated has great interests both from a scientific point of view as technical and industrial.

However, studies conducted to date have focused only massive objects to treat. However, such massive objects are necessarily limited by the shapes and geometry that it is possible to give them through conventional machining techniques (drilling, milling, boring, etc.).

There was therefore in the state of the art a need for objects whose mechanical properties are significantly improved while opposing virtually no limit as to the shape that such objects could take. SUMMARY OF THE INVENTION [0009] The object of the present invention is to meet the need mentioned above as well as others by proposing a method of surface treatment of a metallic material making it possible to produce objects whose Geometric shapes are virtually stress free while exhibiting modified and improved physical and chemical properties.

For this purpose, the present invention relates to a method of surface treatment of a metallic material, this method comprising the step of providing a powder formed of a plurality of particles of a metallic material. and directing to a surface of these particles a monocharged or multicharged ion beam produced by a source of monocharged or multicharged ions, the particles having a generally spherical shape.

According to preferred embodiments of the invention: the source of mono- or multicharged ions is of the electron cyclotron resonance type ECR; the particles of the metal powder are agitated during the entire duration of the ion implantation process; the particle size of the particles of the metal powder used is such that substantially 50% of all these particles have a diameter of between 1 and 2 micrometers, the diameter of the particles of the metal powder used not exceeding 50 microns; the metallic material is a precious metal chosen from gold and platinum; the metallic material is a non-precious metal chosen from magnesium, titanium and aluminum; the material to be ionized is chosen from carbon, nitrogen, oxygen and argon; the monocharged or multicharged ions are accelerated under a tension of between 15,000 and 35,000 volts; the dose of implanted ions is between 1.1015 and 1.1017 ions.crrf2; the maximum depth of implantation of the ions is 150 to 200 nm.

The present invention also relates to a particle of a metal powder with a ceramic surface and a metal core, and more particularly with a surface which corresponds to a metal carbide or nitride in which the particles of the powder are produced. metallic.

With these features, the present invention provides a method of treating a metal material in the powder state in which the particles forming the powder retain their original metal structure in depth, while from the surface and to a certain depth, the monocharged or multicharged ions with which the metal powder particles are bombarded come to fill the defects of the meshes of the crystallographic structure of the metal, then combine with the atoms of the metallic material to form a ceramic, c that is, a material that is solid at room temperature and is neither organic nor metallic.

Note that the particles of metal powder, after ion implantation treatment, are ready to be used in powder metallurgy processes such as injection molding process, pressing or even additive manufacturing as the three-dimensional laser printing. Moreover, since the surface of the particles of metal powder is converted into ceramic, in particular carbide and / or metal nitride constituting these particles, the mechanical and physical properties, in particular the hardness, corrosion resistance or still, the tribological properties of these metal powder particles are improved. The improvement of the mechanical and physical properties of the metal powder particles is maintained when these metal powders are used to produce massive pieces.

Preferably, the particles forming the metal powder are agitated throughout the duration of ion implantation treatment so that these particles are exposed to the ions of the implantation beam homogeneously over their entire substantially spherical surface.

Note that, in the state of the art, one of the commonly used techniques to obtain a ceramic-like material still called metal "cermet" is to mix the metal and ceramic powders in the most homogeneous manner possible to obtain ceramic particles coated with a metal layer. This technique however poses the problem of precise control of the thickness of the metal layer and the quality of the interface between the metal layer and the ceramic core.

BRIEF DESCRIPTION OF THE FIGURES [0017] Other features and advantages of the present invention will emerge more clearly from the detailed description which follows of an exemplary implementation of the method according to the invention, this example being given for purely illustrative purposes and non-limiting only in connection with the accompanying drawing in which: FIG. 1 already cited, is a schematic representation of a source of multicharged ions of the electron cyclotron resonance type ECR; fig. 2 is a sectional view of an Au gold particle having a radius of about 1 micrometer and which has been bombarded with a C + carbon ion beam; fig. 3 is a schematic representation of a multicharged ion source of the electron cyclotron resonance type ECR used in the context of the present invention; fig. 4A illustrates the implantation profile of C + carbon ions in a Pt platinum particle whose radius is about 1 micrometer; fig. 4B is an expanded view in the plane of a substantially spherical Pt platinum particle having a radius of approximately 1 micrometer and showing the path of C + ion penetration into the particle; fig. 5A illustrates the implantation profile of the N + nitrogen ions in a Pt platinum particle whose radius is about 1 micrometer; fig. 5B is an in-plane view of a Pt platinum particle having a radius of approximately 1 micron and showing the path of penetration of N + nitrogen ions into the particle; fig. 6A illustrates the implantation profile of C + carbon ions in an Au gold particle whose radius is about 1 micrometer; fig. 6B is an expanded view in the plane of a substantially spherical particle of Au gold whose radius is approximately 1 micrometer and which shows the path of penetration of C + carbon ions into the particle; fig. 7A illustrates the implantation profile of the N + nitrogen ions in an Au gold particle whose radius is about 1 micrometer, and FIG. 7B is an expanded view in the plane of an Au gold particle whose radius is approximately 1 micrometer and which shows the path of penetration of the N + nitrogen ions into the particle.

DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION [0018] The present invention proceeds from the general inventive idea of subjecting particles of a metal powder to an ion implantation treatment process in the surface. of these particles. By bombarding the particles of a metal powder with highly accelerated mono- or multicharged ions under electrical voltages of the order of 15,000 to 35,000 volts, it is realized that these ions start by filling the defects of the meshes of the crystallographic structure of the metal, then combine with the atoms of the metallic material to form a ceramic. To a certain depth from the surface of the metal powder particles, they are transformed into ceramic, for example carbide or metal nitride in which the particles are made. Advantageously, the mechanical and physical properties, in particular the hardness, the resistance to corrosion or even the tri-bological properties of these metal powder particles with a ceramic surface layer are improved. The improvement of the mechanical and physical properties of metal powder particles having a surface ceramic layer is retained when these metal powders are used to make solid parts by powder metallurgy techniques such as injection molding, pressing, additive manufacturing Or other. By additive manufacturing technique is meant a technique that consists of making a massive piece by adding material. In the case of additive manufacturing techniques, a massive piece is created by progressively providing a raw base material, whereas in conventional manufacturing techniques, starting from a raw material and the final piece sought is obtained by progressive removal of material.

FIG. 2 is a sectional view of a Au gold particle. Designated as a whole by the general numeral 20, this gold particle is substantially spherical in shape with a radius R of about 1 micrometer. This gold particle 20 was bombarded by means of a carbon ion beam C + denoted by the reference numeral 22.

As can be seen from FIG. 2, the gold particle 20 has a heart or core 24 of pure gold and an outer layer or bark 26 mainly made of gold carbide.

The thickness e of this outer layer 26 is of the order of one tenth of the radius R of the gold particle 20, or about 100 nanometers. This outer layer 26 is mainly made of 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 B of this gold particle 20, that is to say about 50 nanometers, then decreasing to about one tenth of the radius R of the gold particle 20 where it is substantially zero.

With the method according to the invention, therefore, particles are obtained for example gold or platinum whose core is made of the original metal, while an outer layer that completely surrounds the core of these particles is made of a ceramic material, for example a carbide or a nitride, which results from the combination of the metal atoms with the ions with which the particles are bombarded.

According to the invention, it is provided with a powder formed of a plurality of particles of a metal material to be treated. This metallic material may be, without limitation, a precious metal chosen from gold and platinum. It may also be a non-precious metal selected from magnesium, titanium and aluminum.

Once the metal chosen according to requirements, the metal powder particles 30 are subjected to an ion implantation process by directing to an outer surface of these particles a monocharged or multicharged ion beam 14 produced by a source single-charged or multicharged ions of the electron cyclotron resonance type ECR (see FIG.

Preferably, but not exclusively, the material to be ionized is chosen from carbon, nitrogen, oxygen and argon, and the monocharged or multicharged ions are accelerated under voltages of between 15,000 and 35,000 volts. . The dose of implanted ions is between 1.1015 and 1.1017ions.cm ~ 2.

The metal powder particles 30 have a spherical general shape with a radius R and their particle size is such that about 50% of all these particles have a diameter of between 1 and 2 micrometers, the diameter metal powder particles not exceeding 50 microns. Preferably, the metal powder particles are agitated throughout the ion implantation process to ensure that these particles are exposed to the ion beam 14 uniformly over their entire outer surface.

FIG. 4A illustrates the implantation profile of C + carbon ions in a Pt platinum particle whose radius is about 1 micrometer. The abscissa axis extends along the radius R of the platinum particle Pt, with the origin of this axis corresponding to the outer surface of the platinum particle, and the value of 2000 Angstroms corresponding to about 20 % of the length of the radius R of the platinum particle Pt. The ordinate represents the number of C + carbon ions implanted in the platinum particle Pt at a given depth. It can be seen that the number of C + carbon ions implanted in the platinum particle Pt grows very rapidly from the outer surface of the platinum particle to reach a maximum exceeding 14 x 104 atoms.cm-2 at a depth corresponding substantially to 500 Angstroms. approximately 5% of the R radius of the platinum particle. Then the number of carbon ions C? decreases and tends to zero at about 1000 Angstroms deep, or approximately 10% of the R radius of the platinum particle Pt.

Fig. 4B is an expanded view in the plane of a substantially spherical Pt platinum particle having a radius of approximately 1 micrometer and showing the average free path of the individual C +, C ++, carbon ions, etc. when they penetrate into a particle of platinum Pt. This fig. 4B has been established for a density of the order of 14 × 10 4 atoms. On the abscissa of fig. 4B is the depth of the platinum particle Pt between the surface (0 Angstroms) and 2000 Angstroms. On the ordinate of FIG. 4B is the diameter of the carbon ion beam C +. The center of the carbon ion beam C + is at mid-height on the y-axis, between the values -1000 Angstroms and +1000 Angstroms. So we see in this fig. 4B that the approximate diameter of the carbon ion beam C + is of the order of 150 nanometers and that the depth of penetration of C + carbon ions in the platinum particle Pt hardly exceeds more than 100 nanometers.

Fig. 5A illustrates the implantation profile of N + nitrogen ions in a Pt platinum particle whose radius R is about 1 micrometer. The abscissa axis extends along the radius R of the platinum particle Pt, with the origin of this axis corresponding to the outer surface of the platinum particle Pt and the value of 2000 Angstroms corresponding to about 20 % of the length of the radius R of the platinum particle Pt. The ordinate represents the number of N + nitrogen ions implanted in the platinum particle Pt at a given depth. It can be seen that the number of N + nitrogen ions implanted in the platinum particle Pt grows very rapidly from the outer surface of the platinum particle Pt to reach a maximum exceeding 16 x 104 atoms.cm-2 at a depth substantially corresponding to 500. Angstroms, ie approximately 5% of the radius r of the platinum particle Pt. Then the number of N + nitrogen ions decreases and tends to zero to a depth of about 1000 Angstroms from the outer surface of the platinum particle Pt, approximately 10% of the radius R of this platinum particle Pt.

Comparing FIGS. 4A and 5A, it is noted that the nitrogenous ions N + penetrate less deeply into the crystallographic mesh of the platinum particle Pt than the carbon ions CL

FIG. 5B is an in-plane view of a substantially spherical platinum Pt particle having a radius of approximately 1 micrometer and showing the average free path of the individual N +, N ++, and other nitrogen ions. when they penetrate into a particle of platinum Pt. This fig. 5B was established for a density of the order of 16 x 104 atoms.cm-2. On the abscissa of fig. 4B is the depth of the platinum particle Pt between the surface (0 Angstroms) and 2000 Angstroms. On the ordinate of FIG. 4B is the diameter of the nitrogen ion beam N +. The center of the N + ion beam is at mid-height on the y-axis, between the values -1000 Angstroms and +1000 Angstroms. So we see in this fig. 5B that the approximate diameter of the N + ion beam is of the order of 150 nanometers and that the penetration depth of N + ions in the platinum particle Pt is slightly less than 100 nanometers. It is therefore found that the N + ions penetrate less deeply into the platinum particles than the CL ions.

FIG. 6A illustrates the implantation profile of C + carbon ions in an Au gold particle whose radius R is about 1 micrometer. The x-axis extends along a radius R of the Au gold particle, with the origin of this axis corresponding to the outer surface of the Au gold particle and the value of 2000 Angstroms which corresponds to about 20% of the radius R of the Au gold particle. On the ordinate, we represent the number of C + carbon ions implanted in the Au gold particle at a given depth. It can be seen that the number of C + carbon ions implanted in the Au gold particle grows very rapidly from the outer surface of the Au gold particle to reach a maximum exceeding 12 x 104 atoms.cm-2 at a depth of 500 Angstroms, approximately 5% of the radius R of the Au gold particle. Then the number of ions decreases and tends to zero at about 1000 nm below the outer surface of the Au gold particle, about 10% of the length of the particle's radius.

FIG. 6B is an expanded view in the plane of a substantially spherical particle of Au gold whose radius is approximately 1 micrometer and which shows the average free path of the individual carbon ions CL C ++ etc. when they enter a gold Au particle.

This fig. 6B has been established for an ion density of the order of 12 x 104 atoms.cm-2. On the abscissa of fig. 6B is the depth of the Au gold particle between the surface (0 Angstroms) and 2000 Angstroms. On the ordinate of FIG. 6B shows the diameter of the carbon ion beam CL The center of the ion beam C + is at mid-height on the ordinate axis, between the values -1000 Angstroms and +1000 Angstroms. So we see in this fig. 6B that the approximate diameter of the C + ion beam is of the order of 150 nanometers and that the depth of penetration of C + ions in the Au gold particle slightly exceeds 100 nanometers.

FIG. 7A illustrates the implantation profile of N + nitrogen ions in an Au gold particle whose radius is about 1 micrometer. The x-axis extends along a radius R of the Au gold particle, with the origin of this axis corresponding to the outer surface of the Au gold particle and the value of 2000 Angstroms which corresponds to about 20% of the radius R of the Au gold particle. The ordinate represents the number of N + nitrogen ions implanted in the Au gold particle at a given depth. It can be seen that the number of N + nitrogen ions implanted in the gold particle Au grows very rapidly from the outer surface of the Au gold particle to reach a maximum exceeding 14 x 104 atoms.cm-2 at a depth of 500. Angstroms, or approximately 5% of the length of the radius R of the Au gold particle. Then the number of N + nitrogen ions decreases and tends to zero at about 1000 nm below the outer surface of the Au gold particle, which is about 10% of the length of the particle's radius R.

FIG. 7B is an expanded view in the plane of a substantially spherical particle of Au gold whose radius is approximately 1 micrometer and which shows the average free path of the individual nitrogen ions N +, N ++ etc. when they enter a gold Au particle.

This fig. 7B has been established for an ion density of the order of 14 x 104 atoms.cm-2. On the abscissa of fig. 7B is the depth of the Au gold particle between the surface (0 Angstroms) and 2000 Angstroms. On the ordinate of FIG. 7B is the diameter of the N + carbon ion beam. The center of the nitrogen ion beam N + is at mid-height on the ordinate axis, between the values -1000 Angstroms and +1000 Angstroms. So we see in this fig. 7B that the approximate diameter of the nitrogen ion beam N + is of the order of 150 nanometers and that the penetration depth of N + ions in the platinum particle Pt is of the order of 100 nanometers. It can thus be seen that the N + nitrogen ions penetrate less deeply into the Au gold particles than the C + ions.

It goes without saying that the present invention is not limited to the embodiment which has just been described and that various modifications and simple variants can be envisaged by the skilled person without departing from the scope of the invention. as defined by the appended claims. In particular, it will be understood that the ECR electron cyclotron resonance type ion implantation process is indicated by way of a preferred but nonlimiting example, and that other processes for generating a hot plasma for example by induction or at using an intense magnetic field produced by a microwave generator can be envisaged. It will also be noted that additional measurements carried out by transmission electron microscopy on sapphire particles with an average diameter of 2.0 micrometers implanted by nitrogen confirm that the sapphire particles, after ion implantation, have a ceramic bark of a thickness of the order from 150 to 200 nanometers. It will also be noted that the ratio between the volume of the particles which is irradiated and the total volume of the particles is of the order of 14%. From the point of view of the Applicant, the powder obtained by the ion implantation process according to the invention is not really a composite material. Indeed, in the sense that is usually understood, a composite material results from the combination of two different materials, namely a matrix and a reinforcement. In the present case, there is only a single material in which ion bombardment causes a modification of the surface chemical structure. We can therefore preferentially speak of heterogeneous material.

Claims (16)

[0038] Nomenclature A method of surface treatment of a metallic material in powder form, which method comprises the step of providing a powder (30) formed of a plurality of particles of the metallic material to be treated, and subjecting said metal powder particles (30) to an ion implantation process by directing to an outer surface of said particles a monocharged or multicharged ion beam (14) produced by a source of single-charged or multicharged ions, these particles having a generally spherical shape with a radius R. 1. ECR multicharged ion source 2. Method according to claim 1, characterized in that one agitates the particles of the metal powder (30) throughout the duration of the ion implantation process. 2. Injection stage 3. Method according to one of claims 1 and 2, characterized in that the particle size of the particles of the metal powder (30) used is such that substantially 50% of all of these particles has a diameter between 1 and 2 micrometers, the particle diameter of the metal powder (30) not exceeding 50 micrometers. 4. Method according to one of claims 1 to 3, characterized in that the metallic material is a precious metal selected from gold and platinum. 4. Volume of a gas to be ionized 5. Method according to one of claims 1 to 3, characterized in that the metallic material is a non-precious metal selected from magnesium, titanium and aluminum. 6. Method according to one of claims 1 to 5, characterized in that the material to be ionized is selected from carbon, nitrogen, oxygen and argon. 6. Microwave wave 7. Process according to claim 6, characterized in that the ion implantation process is of the ECR electron cyclotron resonance type. 8. The method of claim 7, characterized in that the single-charged or multicharged ions are accelerated at a voltage between 15 000 and 35 000 volts. 8. Magnetic confinement floor 9. Method according to claim 8, characterized in that the dose of implanted ions is between 1.1015 and 1.1017 ions.crrf2. 10. Method according to one of claims 8 and 9, characterized in that the ions penetrate into the particles forming the powder of metallic material to a depth corresponding to about 10% of the radius R of these particles. 10. Plasma 11. Powdered material formed from a plurality of particles having an outer ceramic layer (26) and a metal core (24), these particles having a generally spherical shape with a radius R. 12. Material according to claim 11, characterized in that the ceramic surface corresponds to a carbide or nitride of the metal in which the particles of the metal powder are produced. 12. Extraction stage 12a. Anode 12b. Cathode 13. Material according to one of claims 11 or 12, characterized in that about 50% of the particles have a diameter of between 1 and 2 microns, the particle diameter not exceeding 50 microns. 14. Material according to one of claims 11 to 13, characterized in that the metallic material in which are formed particles of the metal powder (30) is a precious metal selected from gold and platinum. 14. Multi-charged ion beam 16. Surface 18. Room to be treated 20. Gold particle in R. Rayon 22. C + carbon ion beam 24. Heart or core 26. Outer layer or bark e. Thickness 28. Outside surface 30. Particles of metal powder Claims 15. Material according to one of claims 11 to 13, characterized in that the metallic material in which are formed the particles of the metal powder (30) is a non-precious metal selected from magnesium, titanium and aluminum. 16. Material according to one of claims 11 to 15, characterized in that the concentration of ceramic material increases from the outer surface to about 5% of the length of the radius R of the particles, then decreases until at about 10% of the length of the radius R of the particles where it is substantially zero.