METHOD FOR PARTICLE SURFACE TREATMENT OF A CERAMIC POWDER AND CERAMIC POWDER PARTICLES OBTAINED BY SAID METHOD

Abstract

The invention concerns a method for surface treatment of a ceramic material in powder form, wherein said method comprising the step of providing a powder formed of a plurality of particles of the ceramic material to be treated, and wherein said ceramic powder particles are subjected to an ion implantation process by directing towards an external surface of said particles a beam of singly or multiply charged ions produced by a charge of singly or multiply charged ions, for example of the electron cyclotron resonance ECR type, wherein said particles have a generally polyhedral shape.

The invention also concerns a material in powder form, formed of a plurality of particles having a ceramic external layer and a ceramic core, wherein said particles have a generally polyhedral shape.

Claims

1. A method for surface treatment of a ceramic material in powder form, the method comprising: providing a powder formed of a plurality of particles of the ceramic material to be treated; and subjecting said ceramic powder particles to an ion implantation process by directing towards an external surface of said particles a beam of singly or multiply charged ions produced by a source of singly or multiply charged ions.

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

3. The method according to claim 1, wherein the grain size of the particles of ceramic powder used is such that substantially 50% of all the particles have a dimension smaller than 2 micrometres.

4. The method according to claim 2, wherein the grain size of the particles of ceramic powder used is such that substantially 50% of all the particles have a dimension smaller than 2 micrometres.

5. The method according to claim 3, wherein the dimension of the ceramic powder particles used is comprised between 1.2 micrometres and 63 micrometres.

6. The method according to claim 4, wherein the dimension of the ceramic powder particles used is comprised between 1.2 micrometres and 63 micrometres.

7. The method according to claim 1, wherein the ceramic material is a carbide, a nitride, a boride or an oxide.

8. The method according to claim 7, wherein the carbide ceramic material is bombarded with nitrogen ions N to form a carbonitride.

9. The method according to claim 8, wherein the ceramic material is a titanium carbide TiC or a silicon carbide SiC, and wherein the product obtained after bombardment is titanium carbonitride TiCN, or silicon carbonitride SiCN respectively.

10. The method according to claim 7, wherein the nitride ceramic material is bombarded with an ion dose comprised between 1*10.sup.16 cm.sup.2 and 1*10.sup.17 cm.sup.2.

11. The method according to claim 10, wherein the ceramic material is a silicon nitride Si.sub.3N.sub.4.

12. The method according to claim 7, wherein the oxide ceramic material is bombarded with nitrogen ions to form an oxynitride.

13. The method according to claim 12, wherein the ceramic material is zirconia ZrO.sub.2 or alumina Al.sub.2O.sub.3, and in that the product obtained after bombardment is zirconia nitride Zr.sub.xO.sub.yN.sub.z, or zirconium nitride ZrN, or aluminium oxynitride Al.sub.xO.sub.yN.sub.z.

14. The method according to claim 7, wherein the oxide ceramic material is bombarded with carbon ions to form an oxycarbide.

15. The method according to claim 14, wherein the ceramic material is zirconia ZrO.sub.2 or alumina Al.sub.2O.sub.3, and in that the product obtained after bombardment is zirconia carbide ZrO.sub.2C, or zirconium carbide ZrC respectively.

16. The method according to claim 7, wherein the oxide ceramic material is bombarded with boron ions to form an oxyboride.

17. The method according to claim 16, wherein, if the ion bombardment is continued for a sufficiently long time, zirconium diboride ZrB.sub.2 is obtained.

18. The method according to claim 1, wherein the ion implantation process is of the electron cyclotron resonance ECR type.

19. The method according to claim 18, wherein the singly or multiply charged ions are accelerated at a voltage comprised between 15,000 and 35,000 volts.

20. The method according to claim 18, wherein the implanted ion dose is comprised between 1.10.sup.14 and 5.10.sup.17 ions.Math.cm.sup.2.

21. The method according to claim 19, wherein the implanted ion dose is comprised between 1.10.sup.14 and 5.10.sup.17 ions.Math.cm.sup.2.

22. The method according to claim 18, wherein the ions penetrate the particles forming the ceramic material powder to a depth corresponding to around 20% of the dimension of said particles.

23. The method according to claim 18, wherein the ions penetrate the particles forming the ceramic material powder to a depth corresponding to around 20% of the dimension of said particles.

24. A material in powder form formed of a plurality of particles having a ceramic external layer and a ceramic core, said particles having a generally polyhedral shape, the external layer corresponding to a boride, a carbide or a nitride of the ceramic material from which the core of the ceramic powder particles is made.

25. The material according to claim 24, wherein around 50% of the particles have a dimension smaller than 2 micrometres.

26. The material according to claim 25, wherein the dimension of the ceramic powder particles used is comprised between 1.2 micrometres and 63 micrometres.

27. The material according to claim 24, wherein the ceramic material from which the ceramic powder particles are made is a boride, a carbide, oxide or a nitride.

28. The material according to claim 25, wherein the ceramic material from which the ceramic powder particles are made is a boride, a carbide, oxide or a nitride.

29. The material according to claim 26, wherein the ceramic material from which the ceramic powder particles are made is a boride, a carbide, oxide or a nitride.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Other features and advantages of the present invention will appear more clearly from the following detailed description of an example implementation of the method according to the invention, this example being given purely by way of non-limiting illustration with reference to the annexed drawing, in which:

[0055] FIG. 1, cited above, is a schematic representation of an ECR ion source;

[0056] FIG. 2 is a cross-sectional view of an alumina particle Al.sub.2O.sub.3 whose radius is around 1 micrometre, and which has been bombarded with a nitrogen ion beam N.sup.+, and

[0057] FIG. 3 is a schematic representation of an ECR ion source used within the scope of the present invention.

DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

[0058] The present invention proceeds from the general inventive idea which consists subjecting ceramic powder particles to a process of ion implantation treatment in the surface of said particles. When bombarding the particles of a ceramic powder with highly accelerated, singly or multiply charged ions at electrical voltages on the order of 15,000 to 35,000 volts, it becomes clear that these ions combine with the atoms of the ceramic material to form a new type of ceramic. To a certain depth from the surface of the ceramic powder particles, the latter are transformed, for example, into a carbide or nitride of the ceramic material from which the particles are made. Advantageously, the mechanical and physical properties, especially the hardness, tribological properties and machinability of these ceramic powder particles are substantially improved. The improvement in the mechanical and physical properties of the ceramic powder particles provided with a boride, carbide or nitride ceramic surface layer is maintained when these ceramic powders are used to make solid parts by powder sintering techniques, such as sintering at atmospheric pressure or HIP.

[0059] FIG. 2 is a cross-sectional view of an alumina particle Al.sub.2O.sub.3. For the sake of clarity, it will be assumed for the purposes of demonstration that this alumina particle Al.sub.2O.sub.3 is substantially spherical, it being understood that, in reality, such alumina particles Al.sub.2O.sub.3 actually have a polyhedral shape. Designated as a whole by the general reference number 20, this alumina particle Al.sub.2O.sub.3 has a radius R of around 1 micrometre. This alumina particle 20 was bombarded with a nitrogen ion beam N+ designated by the reference number 22. As shown in FIG. 2, alumina particle 20 has a core 24 of pure alumina and an external layer or shell 26 mainly formed of aluminum oxynitride Al.sub.xO.sub.yN.sub.z whose stoichiometry varies as a function of depth from the surface of alumina particle 20.

[0060] The thickness e of this external layer 26 is on the order of 7% of radius R of alumina particle 20, i.e. around 70 nanometres. This external layer 26 is mostly formed of aluminum oxynitride Al.sub.xO.sub.yN.sub.z, which is a ceramic material. According to the invention, the concentration of Al.sub.xO.sub.yN.sub.z increases from external surface 28 of alumina particle 20 to around 15% of radius R of alumina particle 20, i.e. around 140 nanometres, and then decreases to a depth of around 200 nm under the surface of alumina particle 20 where it is substantially zero.

[0061] More specifically, the composition of two samples of alumina Al.sub.2O.sub.3, referred to as A and B respectively, was analysed by X-ray photoelectron spectroscopy (XPS). These two alumina samples A and B were bombarded with nitrogen ions N+, and the nitrogen concentration from the surface towards the core of these samples was then examined by XPS analysis.

[0062] With regard to the XPS analysis of alumina sample A, tests show that the nitrogen atoms that bombard and penetrate the original alumina particle Al.sub.2O.sub.3 bond, on the one hand, to the aluminium atoms that form part of the composition of aluminium oxynitride Al.sub.xO.sub.yN.sub.z, and, on the other hand, do not bond to the aluminium atoms. More specifically, XPS analyses show that the atomic weight concentration of nitrogen bonded in the aluminium oxynitride particles Al.sub.xO.sub.yN.sub.z has two levels from the surface towards the core of the alumina particles Al.sub.xO.sub.yN.sub.z: [0063] the first nitrogen concentration level appears at a depth of approximately 70 nm from the external surface of the particles. The average atomic percent concentration of nitrogen bonded to the aluminium of the aluminium oxynitride Al.sub.xO.sub.yN.sub.z is on the order of 6.3%. Further, the average stoichiometry of the oxynitride layer at this level is close to AlO.sub.1.2N.sub.0.16. [0064] the second nitrogen concentration level appears at a depth of around 140 nm. The average atomic percent concentration of nitrogen bonded to aluminium is on the order of 3.6%, i.e. almost half less than the concentration of nitrogen bonded to aluminium observed at a depth of 70 nm. The average stoichiometry of the aluminium oxynitride layer at this level is close to AlO.sub.1.3N.sub.0.08. [0065] Finally, beyond a depth in excess of 140 nm, there is an exponential drop in the concentration of nitrogen bonded to the aluminium that forms part of the composition of aluminium oxynitride Al.sub.xO.sub.yN.sub.z. At a considered depth of more than 200 nm from the surface of the alumina Al.sub.2O.sub.3 particles, there is a stoichiometric ratio between oxygen and aluminium that is very close to that of alumina Al.sub.2O.sub.3.

[0066] With regard to alumina sample B, XPS analysis shows that, in this case too, the nitrogen atoms that bombard and penetrate the original alumina particle Al.sub.2O.sub.3 bond, on the one hand, to the aluminium atoms that form part of the composition of aluminium oxynitride Al.sub.xO.sub.yN.sub.z, and, on the other hand, do not bond to the aluminium atoms. More specifically, XPS analyses show that the atomic weight concentration of nitrogen bonded in the aluminium oxynitride particles Al.sub.xO.sub.yN.sub.z has two levels from the surface towards the core of the alumina particles Al.sub.xO.sub.yN.sub.z: [0067] the first nitrogen concentration level appears at a depth of approximately 25 nm from the external surface of the particles. The average atomic percent concentration of nitrogen bonded to aluminium is on the order of 3.6%. Further, the average stoichiometry of the aluminium oxynitride layer at this level is close to AlO.sub.1.3N.sub.0.09. [0068] the second nitrogen concentration level appears at a depth of around 120 nm. The average atomic percent concentration of nitrogen bonded to aluminium is on the order of 4.7%, i.e. slightly more than at a depth of 25 nm. The average stoichiometry of the aluminium oxynitride layer at this level is close to AlO.sub.1.3N.sub.0.11. [0069] Finally, beyond a depth in excess of 120 nm, there is an exponential drop in the concentration of nitrogen bonded to the aluminium that forms part of the composition of aluminium oxynitride Al.sub.xO.sub.yN.sub.z. At a considered depth of more than 200 nm from the surface of the alumina Al.sub.2O.sub.3 particles, there is a stoichiometric ratio between oxygen and aluminium that is very close to that of alumina Al.sub.2O.sub.3.

[0070] It is evident that the present invention is not limited to the preceding description and that various simple modifications and variants can be envisaged by those skilled in the art without departing from the scope of the invention as defined by the annexed claims. It will be understood, in particular, that given that the ceramic particles envisaged here have a general polyhedral shape, the dimension of such particles means the largest external dimension of such a particle. It will be noted finally that, according to the invention, the ECR ion source is capable of producing singly or multiply charged ions, i.e. ions whose degree of ionisation is higher than or equal to 1, wherein the ion beam can include ions that all have the same degree of ionisation or can result from a mixture of ions having different degrees of ionisation.

Nomenclature

[0071] 1. ECR ion source

[0072] 2. Injection stage

[0073] 4. Volume of gas to be ionised

[0074] 6. Hyperfrequency wave

[0075] 8. Magnetic confinement stage

[0076] 10. Plasma

[0077] 12. Extraction stage

[0078] 12a Anode

[0079] 12b. Cathode

[0080] 14. Ion beam

[0081] 16. Surface

[0082] 18. Part to be treated

[0083] 20. Alumina particle Al.sub.2O.sub.3

[0084] R. Radius

[0085] 22. Nitrogen ion beam N.sup.+

[0086] 24. Core or centre

[0087] 26. External layer or shell

[0088] e. Thickness

[0089] 28. External surface

[0090] 30. Ceramic powder particles