EP4217331A1

EP4217331A1 - Ceramic article

Info

Publication number: EP4217331A1
Application number: EP21742675.8A
Authority: EP
Inventors: Bernard Bertheville; Yann Fallet
Original assignee: Swatch Group Research and Development SA
Current assignee: Swatch Group Research and Development SA
Priority date: 2020-09-25
Filing date: 2021-07-28
Publication date: 2023-08-02
Also published as: WO2022063462A1; CN115988974A; EP3974405A1; JP2023537425A; US20230295053A1

Abstract

The invention relates to an article made of a material consisting of a plurality of ceramic phases, said material comprising: - a majority-ceramic phase comprising nitrides and/or carbonitrides of one or more elements chosen among Ti, Zr, Hf, V, Nb, and Ta, the majority-ceramic phase being present in a percentage by weight of between 60 and 98%, - a single minority-ceramic phase formed from zirconium and/or aluminium silicide, the minority-ceramic phase being present in its entirety in a percentage by weight of between 2 and 40%. The present invention also relates to the method for manufacturing this article.

Description

ARTICLE IN THIS RAMIC

TECHNICAL AREA

The present invention relates to an article and in particular to a component for covering or movement in watchmaking, made of a composite material consisting solely of ceramic phases. It also relates to its manufacturing process.

PRIOR ART

Many trim components are made of composite ceramic materials which have the advantage, among other things, of having very high hardnesses which guarantee their ability not to be scratched. The literature mainly refers to composites made up mainly of an oxide such as alumina to which carbides are added. It may, for example, be composites comprising by weight 70% A^Os and 30% TiC used as reinforcement. These composites have the characteristic of presenting little or no metallic luster compared to other materials such as stainless steels or cermets, which can be a disadvantage for decorative items where this luster is sought.

Materials based on titanium nitrides or carbonitrides are also known. These materials are extremely difficult to densify due to their very high melting temperatures, e.g. of 2930°C for TiN, associated with their low diffusion coefficients. As a result, it is then necessary to use rapid sintering methods, also known as flash, such as SPS sintering (Spark Plasma Sintering) or pressure sintering methods (Sinter-HIP) or consolidation methods. under very high pressures and high temperatures after sintering such as HIP (Hot Isostatic Pressure). In addition, these sintering processes do not make it possible to obtain parts of complex shapes. A way of solving this problem consists, for example to produce cermets based on TiN or TiCN, in adding a metallic element acting as a metallic binder. Thus, an addition of a few percent of nickel or cobalt allows consolidation at lower temperatures, typically around 1500°C. However, these elements have the disadvantage of being highly allergenic, limiting their use to articles not intended to be in contact with the skin.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the aforementioned disadvantages by proposing a ceramic material, also called composite, with a composition and a manufacturing process optimized to meet the following criteria:

- avoid the use of allergenic elements such as nickel or cobalt,

- have a high metallic luster (65<L*<85),

- be able to be densified under atmospheric pressure, under vacuum or under partial gas pressure without resorting to high pressures in order to preserve the shape of the blank of the article after sintering,

- have a minimum hardness of 500 HV30, preferably minimum of 800 HV30 and more preferably minimum of 1000 HV30 for applications requiring very good scratch resistance, while having sufficient toughness with, preferably, a KiC greater than or equal to 2.5 MPa.m ^1/2 .

To this end, the present invention proposes an article made of a material consisting of several ceramic phases, said material comprising: - a majority ceramic phase comprising nitrides and/or carbonitrides of one or more elements of group IVB, namely Ti, Zr and Hf, and/or of group VB, namely V, Nb and Ta, said phase majority ceramic being present in a percentage by weight of between 60 and 98%,

- at least one minority ceramic phase, with either a single minority ceramic phase formed of zirconium and/or aluminum silicide, or several minority ceramic phases formed respectively of carbides of one or more group IVB elements (Ti, Zr, Hf), group VB (V, Nb, Ta) and group VIB (Cr, Mo, W), and zirconium oxides and/or aluminum oxides, said at least minority ceramic phase being present in its entirety in a percentage by weight of between 2 and 40%.

The composite material thus developed has, after polishing, a metallic luster similar to that observed in stainless steels or cermets using nickel or cobalt as a metallic binder. These composites have other advantages of being devoid of allergenic elements such as Ni. They also have high hardnesses and sufficient tenacity for the production of trim components while being non-magnetic. In addition, they can be shaped by conventional powder metallurgy processes such as pressing or injection or by various processes dedicated to the manufacture of three-dimensional parts such as, for example, 3D printing in order to obtain near-net-shape pieces. Parts of more or less complex shape can be finally consolidated at temperatures between 1400 and 1900°C under atmospheric pressure, under vacuum or under partial gas pressure, i.e. without resorting to significant pressure.

Articles made of this ceramic material also have the advantage of having a beautiful color present in the mass with shades ranging from yellow to pink verging on red depending on the composition. Other characteristics and advantages of the present invention will appear in the following description of a preferred embodiment, presented by way of non-limiting example with reference to the appended drawing.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 represents a timepiece comprising a middle part made with the ceramic material according to the invention.

DETAILED DESCRIPTION

The present invention relates to an article made of a composite material consisting solely of ceramic phases. The article may be a decorative article such as an integral part of watches, jewellery, bracelets, etc. or more generally an external part of a portable element such as a shell of a mobile telephone. In the watchmaking field, this article can be a covering part such as a middle part, a back, a bezel, a crown, a bridge, a pusher, a bracelet link, a dial, a hand, a dial index , etc By way of illustration, a middle part made with the ceramic material according to the invention is represented in FIG. 1. It can also be a component of the movement such as a plate or an oscillating weight.

The ceramic material comprises a majority phase composed of nitrides and/or carbonitrides of one or more elements chosen from Ti, Zr, Hf, V, Nb and Ta, and one or more minority phases. The latter can be either zirconium and/or aluminum silicide, or a combination of carbides of one or more elements chosen from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W and of zirconium (Zr) and/or aluminum (Al) oxides. Preferably, the majority phase is composed of titanium nitrides and/or titanium carbonitrides. Preferably, the minority phase or phases are respectively composed either of zirconium silicide and/or aluminum or a combination of tungsten and/or vanadium carbides and zirconium and/or aluminum oxides

The majority phase is present in a percentage by weight of between 60 and 98% and all of the minority phases are present in a percentage by weight of between 2 and 40%. Preferably, the majority phase is present in a percentage by weight of between 65 and 97%, more preferably between 70 and 96% by weight, and even more preferably between 75 and 95%. In addition to the majority phase, all of the minority phases are present in a percentage by weight preferably between 3 and 35%, more preferably between 4 and 30% and even more preferably between 5 and 25%. When the majority phase comprises nitrides and carbonitrides of one or more elements chosen from Ti, Zr, Hf, V, Nb and Ta, the nitrides and carbonitrides are preferably present respectively in a percentage of between 20 and 70% by weight , more preferably between 25 and 60%, relative to the total weight of the ceramic material. When the ceramic material comprises two minority phases respectively of carbides of one element or several elements chosen from among Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W and oxides (Al2O3 and/or ZrCh), they are respectively and preferably present in a percentage of between 3 and 35% by weight, more preferably between 5 and 25%, relative to the total weight of the ceramic material.

The ceramic article is produced by sintering starting from a mixture of powders. The manufacturing process comprises the steps consisting of: a) Making a mixture with the various ceramic powders, possibly in a humid environment. The starting powders preferably have a d50 of less than 45 μm. The mixture can optionally be carried out in a grinder, which reduces the d50 of the particles of the powder to a size of the order of a few microns (<5 μm) after grinding. Powders of nitrides and/or carbonitrides of one or more elements elements chosen from Ti, Zr, Hf, V, Nb and Ta are present in a percentage by weight for all of these powders of between 60 and 98%, preferably between 65 and 97%, more preferably between 70 and 96 % and even more preferably between 75 and 95%. Powders of zirconium silicide and/or aluminum silicide or powders of carbides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W and of zirconium and/or aluminum oxides are present in a percentage by weight of between 2 and 40%, preferably between 3 and 35%, more preferably between 4 and 30%, even more preferably between 5 and 25%. By way of example, the mixture of powders may comprise by weight one of the following distributions for a total of 100%:

- between 75 and 85% TiN or TiCN and between 15 and 25% ZrS i2 ,

- between 85 and 95% TiN or TiCN and between 5 and 15% ZrS i2 ,

- between 75 and 85% TiN or TiCN, between 5 and 15% WC or VC and between 5 and 15% ZrO2 or Al2O3,

- between 40 and 55% TiN, between 25 and 35% TiCN, between 5 and 15% WC or VC and between 5 and 15% ZrO2. b) Optionally, a second mixture comprising the aforementioned mixture and an organic binder system (paraffin, polyethylene, etc.) can be produced. c) Forming a blank by giving the mixture the shape of the desired article, for example, by injection or pressing or by 3D printing. d) Sintering the blank under partial gas pressure, under vacuum or under atmospheric pressure at a temperature between 1200 and 2100°C, preferably between 1400 and 1900°C for a period between 10 minutes and 20 hours, preferably between 15 minutes and 3 hours. This step can be preceded by a debinding step in a temperature range of between 60 and 500° C. if the mixture includes a binder system. Although the compositions according to the invention allow sintering under low pressure, the present invention does not exclude that the sintering is carried out by SPS (Spark Plasma Sintering) or by sinter-HIP, followed or not by HIP (Hot Isostatic Pressure) consolidation.

The blank thus obtained is cooled and polished. It can also be machined before polishing to obtain the desired article.

The article resulting from the manufacturing process comprises the majority phase and the minority phase or phases in percentages by weight close to those of the starting powders. However, small variations in composition and percentages between the base powders and the material resulting from sintering cannot be ruled out following, for example, contamination or transformations during sintering. For example, carbides could react with nitrides to form carbonitrides.

The article has a CIELAB color space (conforms to CIE n°15, ISO 7724/1, DIN 5033 Teil 7, ASTM E-1164) with a luminance component L*, representative of how the material reflects light , between 60 and 85 and, preferably, between 65 and 80, and more preferably between 70 and 75. Advantageously, the article is yellow in color and has an a* component (red component) between +1 and +7 and a b* component (yellow component) between +20 and +35. Advantageously, the article is pink-red in color and has an a* component of between +2 and +15 and a b* component of between +2 and +10.

The ceramic material has a hardness HV30 greater than or equal to 500, preferably between 800 and 1800 depending on the types and percentages of the constituents. It has a toughness KiC greater than or equal to 2 and preferably greater than or equal to 2.5 MPa.m ^1/2 with values that can go up to 8 MPa.m ^1/2 , the toughness being determined on the basis of measurements the lengths of the cracks at the four extremities of the diagonals of the hardness impression according to the formula: with P being the applied load (N), a being the half-diagonal (m) and / being the measured crack length (m).

The examples below illustrate the process according to the invention and the material resulting therefrom.

7 mixtures of powders were prepared in a grinder in the presence of a solvent. The mixtures were made without binder. They were shaped by pressing and sintered either under vacuum or under a flow of argon or nitrogen at 60 mbar, at a temperature which depends on the composition of the powders. After sintering, the samples were polished. Table 1 below shows the compositions, the sintering parameters and the mechanical properties (HV30, Kic) as well as the Lab colorimetric values. The values in italics and bold fulfill the criteria for a hardness greater than 800 Vickers, a toughness greater than 2.5 MPa.m ^1/2 , an L* index greater than 70 or a b* index greater than 20 for a very yellow color.

HV30 hardness measurements were carried out on the surface of the samples and the toughness was determined on the basis of the hardness measurements as described previously.

Lab colorimetric values were measured on the polished samples with a KONICA MINOLTA CM-5 spectrophotometer under the following conditions: SCI (specular reflection included) and SCE (specular reflection excluded) measurements, inclination of 8°, MAV measurement area of 8 mm in diameter.

Example 1

This is a ceramic composite comprising titanium nitride (TiN) as the majority phase and zirconium silicide (ZrSi2) as the minority phase up to 20% by weight. According to the invention and by way of comparison with conventional sintering, this composite was densified by Spark Plasma Sintering (SPS). The hardness measured is 1328 Vickers (HV30) and the toughness 4.3 MPa.m ^1/2 .

Example 2

This is a ceramic composite comprising titanium nitride (TiN) as the majority phase and zirconium silicide (ZrSi2) as the minority phase up to 10% by weight. This 90TiN-10ZrSi2 composite was densified by both SPS and conventional sintering. When it is sintered by conventional sintering, a drop in hardness is observed compared to SPS sintering, going from 1302 to 863 Vickers but retaining good toughness (4.2 versus 4.4 MPa.m ^1/2 ). On the other hand, by conventional sintering, a much better luster is obtained with a higher luminance index (L*) (74.5 versus 66.2). Conventional sintering also makes it possible to obtain a more yellow tint with a slightly higher value of the yellow component b*.

Example 3

It is a ceramic composite comprising titanium carbonitride (TiCN) as the majority phase and zirconium silicide (ZrSi2) as the minority phase up to 10% by weight. This 90TiCN-10ZrSi2 composite has a lower hardness of 590 Vickers but shows the strongest yellow coloration with a b* value reaching 27.29.

Example 4

It is a ceramic composite based on titanium nitride (TiN) as the majority phase, and with tungsten carbides (WC) and aluminum oxide (Al2O3) as minority phases, according to the proportions by weight 80TiN-10WC-10Al203. Such a composite, densified by conventional sintering and without adding pressure, has a hardness of 938 Vickers, a toughness of 3.6 MPam ^1/2 and a deep yellow color with values of 1.7 for a* and 26.2 for b* while retaining a beautiful metallic luster (L*= 72.8).

Example 5

It is a ceramic composite based on titanium nitride (TiN) as the majority phase and with tungsten carbide (WC) and zirconium dioxide (ZrC) as minority phases, according to the proportions by weight 80TiN-10WC -10Zr02. This composite has a maximum hardness of 1187 Vickers and a measured luminance L* of 72.9. The color of such a ceramic composite is yellow, with a* and b* index values of 1.48 and 26.0 respectively. Replacing aluminum oxide (example 4) with zirconium dioxide therefore increases the hardness by 249 Vickers.

Example 6

It is a ceramic composite based on titanium nitride (TiN) as the majority phase and with vanadium carbide (VC) and zirconium dioxide (ZrC) as minority phases, according to the proportions by weight 80TiN-10VC -10Zr02. This composite has a hardness of 1275 Vickers and a measured luminance L* of 71.8. The color of such a ceramic composite is yellow, with a* and b* values of 2.9 and 23.4 respectively. Replacing tungsten carbide (example 5) with vanadium carbide therefore increases the hardness by about 7%.

Example 7

It is a ceramic composite comprising titanium nitride (TiN) and titanium carbonitride (TiCN) as the majority phase, and as minority phases tungsten carbide (WC) and zirconium dioxide (ZrCh), according to the proportions by weight 48TiN-32TiCN-10WC-10ZrO2. Such a composite has a pink-red coloring with indices a* and b* of values 7.52 and 8.02 respectively. The hardness measured is very high, ie 1727 Vickers, and almost identical to that obtained by SPS sintering. This increase results directly from the addition of tungsten carbide.

Table 1

Claims

1. Article made of a material consisting of several ceramic phases, said material comprising:

- a majority ceramic phase comprising nitrides and/or carbonitrides of one or more elements chosen from Ti, Zr, Hf, V, Nb, and Ta, said majority ceramic phase being present in a percentage by weight of between 60 and 98%,

- a single minority ceramic phase formed of zirconium and/or aluminum silicide, said minority ceramic phase being present in its entirety in a percentage by weight of between 2 and 40%.

2. Article according to claim 1, characterized in that the majority ceramic phase is present in a percentage by weight of between 65 and 97% and in that said minority ceramic phase is present in its entirety in a percentage by weight of between 3 and 35%.

3. Article according to claim 1 or 2, characterized in that the majority ceramic phase is present in a percentage by weight of between 70 and 96% and in that said minority ceramic phase is present in its entirety in a percentage by weight of between between 4 and 30%.

4. Article according to any one of the preceding claims, characterized in that the majority ceramic phase is present in a percentage by weight of between 75 and 95% and in that said minority ceramic phase is present in its entirety in a percentage by weight between 5 and 25%.

5. Article according to any one of the preceding claims, characterized in that when the majority ceramic phase comprises nitrides and carbonitrides of one or more elements chosen from Ti, Zr, Hf, V, Nb and Ta, said nitrides and carbonitrides are present respectively in a percentage of between 20 and 70% by weight relative to the total weight of the ceramic material.

6. Article according to the preceding claim, characterized in that said nitrides and carbonitrides are present respectively in a percentage of between 25 and 60% by weight relative to the total weight of the ceramic material.

7. Article according to any one of the preceding claims, characterized in that the majority ceramic phase comprises titanium nitrides and/or titanium carbonitrides.

8. Article according to any one of the preceding claims, characterized in that it has, in a CIELAB colorimetric space, an L* component of between 60 and 85 and, preferably, between 65 and 80.

9. Article according to any one of the preceding claims, characterized in that it is yellow in color and has, in a CIELAB colorimetric space, an a* component comprised between +1 and +7 and a b* component comprised between + 20 and +35.

10. Article according to any one of claims 1 to 8, characterized in that it is pink-red in color and has, in a CIELAB colorimetric space, an a* component between +2 and +15 and a b component. * between +2 and +10.

11. Article according to any one of the preceding claims, characterized in that it has an HV30 hardness greater than or equal to 500.

12. Article according to any one of the preceding claims, characterized in that it has an HV30 hardness of between 800 and 1800.

13. Article according to any one of the preceding claims, characterized in that it has a toughness Kic greater than or equal to 2 and preferably greater than or equal to 2.5 MPa.m1/2. 15

14. Article according to any one of the preceding claims, characterized in that the material comprises for a total of 100% one of the following distributions:

- a majority ceramic phase comprising between 75 and 85% TiN or TiCN and a minority ceramic phase comprising between 15 and 25% ZrSi2,

- a majority ceramic phase comprising between 85 and 95% TiN or TiCN and a minority ceramic phase comprising between 5 and 15% ZrSi2,

15. Article according to any one of the preceding claims, characterized in that it is a watch component.

16. Article according to the preceding claim, characterized in that it is a covering component chosen from the list comprising a middle part, a back, a bezel, a pusher, a crown, a bracelet link, a dial, a hand and a dial index or a component of the movement chosen from the list comprising a plate, a bridge and an oscillating weight.

17. Process for manufacturing an article comprising the successive steps consisting in: a) producing a mixture comprising a powder of nitrides and/or carbonitrides of one or more elements chosen from Ti, Zr, Hf, V, Nb and Ta, in a percentage by weight of between 60 and 98% and comprising at least one powder:

- either made of zirconium and/or aluminum silicide,

- said at least powder being present in its entirety in a percentage by weight of between 2 and 40%, b) Forming a blank by giving said mixture the shape of the article, c) Sintering the blank at a temperature of between 1200 and 2100°C, preferably between 1400 and 1900°C, for a period of between 30 minutes and 20 hours, preferably between 15 minutes and 3 hours.

18. Manufacturing process according to claim 20, characterized in that the mixture of powders from step a) comprises for a total of 100% one of the following distributions:

- between 75 and 85% TiN or TiCN and between 15 and 25% ZrS i2,

- between 85 and 95% TiN or TiCN and between 5 and 15% ZrS i2 ,