CH715620A2 - Decorative ceramic item. - Google Patents

Abstract

The invention relates to a decorative article (1) made of a ceramic material, said ceramic material comprising a carbide phase and an oxide phase, the carbide phase being present in a percentage by volume of between 50 and 95% and the oxide phase being present in a percentage by volume of between 5 and 50%. The present invention also relates to the method of manufacturing this decorative article by sintering.

Description

TECHNICAL AREA

The present invention relates to a decorative article and in particular to a clockwork trim component, made of a ceramic composite material. It also relates to its manufacturing process.

PRIOR ART

[0002] Numerous trim components are made from composite ceramic materials having, among other things, the advantage of having very high hardnesses which guarantee their ability not to be scratched. The literature mainly reports on composites consisting mainly of an oxide such as alumina to which carbides are added. They may, for example, be composites comprising by weight 70% of Al2O3 and 30% of TiC used as reinforcement. These composites have the characteristic of exhibiting little or no metallic luster compared to other materials such as stainless steels or cermets, which can be a disadvantage for decorative articles where this luster is desired.

SUMMARY OF THE INVENTION

[0003] The object of the present invention is thus to overcome the aforementioned disadvantage by providing a ceramic material with a composition suitable for exhibiting this metallic luster.

[0004] To this end, the present invention provides a decorative article made from a ceramic comprising mainly a phase of carbides and a minority of a phase of oxides. More specifically, the present invention provides a decorative article made of a ceramic material comprising by volume a phase of carbides in a percentage between 50 and 95%, preferably between 51 and 85%, and an oxide phase in a percentage of between 5 and 50%, preferably between 15 and 49%.

[0005] Preferably, the carbide phase comprises one or more carbides chosen from TiC, Mo2C and NbC and the oxide phase comprises one or more oxides chosen from Al2O3, ZrO2, Cr2O3 and Y2O3.

[0006] More preferably, the carbide phase predominantly comprises TiC or Mo2C and the oxide phase predominantly comprises Al2O3, preferably predominantly in alpha phase or a mixture of alpha phase and gamma phase, or ZrO2 ; the latter is preferably a stabilized zirconia, for example with Y2O3. According to one variant, the phase of oxides mainly comprising aluminum oxide also mainly comprises chromium oxide.

[0007] According to a preferred embodiment of the invention, the decorative article comprises a phase of carbides comprising mainly titanium carbide and said phase of carbides comprising mainly titanium carbide is present in a percentage by volume of between 55 and 90%, preferably between 60 and 85%, the oxide phase being present in a percentage by volume of between 10 and 45%, preferably between 15 and 40%. According to a variant of this embodiment, said phase of carbides may contain niobium carbide in a minority.

[0008] According to another embodiment of the decorative article of the invention, the decorative article comprises a phase of carbides comprising mainly molybdenum carbide and said phase of carbides comprising mainly molybdenum carbide is present in a percentage by volume of between 50 and 75%, preferably between 51 and 75%, the oxide phase being present in a percentage by volume of between 25 and 50%, preferably between 25 and 49%.

[0009] According to yet another embodiment of the decorative article of the invention, said phase of carbides consists of titanium carbide and said phase of oxides consists of aluminum oxide, said phase of carbides being present in a percentage by volume of between 65 and 85, preferably between 70 and 80%, and said oxide phase being present in a percentage by volume of between 15 and 35%, preferably between 20 and 30%.

[0010] According to yet another embodiment of the decorative article of the invention, said carbide phase consists of titanium carbide and said oxide phase consists predominantly of aluminum oxide and mainly of oxide. chromium, said carbide phase being present in a percentage by volume of between 55 and 75%, preferably between 60 and 70%, and said phase of oxides being present in a percentage by volume of between 25 and 45%, preferably between 30 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 metallic binder. These composites have the other advantages of being free from allergenic elements such as Ni, of being resistant to corrosion and of not being magnetic. They also have high hardnesses and sufficient toughness for the production of trim elements. In addition, they can be shaped by conventional powder metallurgy processes such as pressing or injection in order to obtain “near-net shape” parts.

[0012] Other characteristics and advantages of the present invention will become apparent from the following description of a preferred embodiment, presented by way of non-limiting example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURE

[0013] Figure 1 shows a timepiece comprising a middle part made with the ceramic material according to the invention. FIG. 2 represents an electron microscopy image of the ceramic material according to the invention.

DETAILED DESCRIPTION

The present invention relates to a decorative article made of a ceramic composite material. The decorative article can be a component of watches, jewelry, bracelets, etc. or more generally an external part of a portable element such as a mobile telephone. In the watchmaking field, this article can be a covering part such as a caseband, a back, a bezel, a push-piece, a bracelet link, a dial, a hand, a dial index, etc. By way of illustration, a caseband 1 made with the ceramic material according to the invention is shown in Figure 1.

The ceramic material comprises a carbide-type phase constituting the matrix and an oxide-type phase distributed within the matrix. The carbide phase is present in the ceramic material in a percentage by volume of between 50 and 95% and the complementary oxide phase is present in a percentage by volume of between 5 and 50%. Preferably, the carbide phase is present in the ceramic material in a percentage by volume of between 51 and 85% and the complementary phase of oxides is present in a percentage by volume of between 15 and 49%. The carbide phase comprises one or more types of carbides. By way of example, it may be one or more carbides chosen from TiC, Mo2C, NbC, WC, etc. Preferably, the carbide phase comprises one or more carbides chosen from TiC, Mo2C and NbC. More preferably, the carbide phase mainly comprises TiC or Mo2C. The oxide phase can comprise one or more oxides chosen by way of example from Al2O3, ZrO2, Cr2O3, Y2O3, etc. Preferably, the oxide phase comprises one or more oxides chosen from Al2O3, ZrO2 and Cr2O3. More preferably, the oxide phase predominantly comprises Al2O3 or ZrO2.

The ceramic article is produced by sintering starting from a mixture of powders of carbides and oxides. The present invention therefore does not relate to a composite material with a ceramic matrix reinforced with a directional load such as ceramic fibers. The manufacturing process comprises the steps of: a) Mixing with the various ceramic powders, possibly in a humid environment. The starting powders preferably have an d50 of less than 45 μm. The mixing can optionally be carried out in a mill or ball mill, which reduces the d50 of the particles of the powder to a size of the order of a few microns (<5 μm) after milling. This mixture comprises by volume between 50 and 95% of a carbide powder and between 5 and 50% of an oxide powders, each powder respectively comprising one or more carbides and one or more oxides as indicated above. Preferably, the carbide powder mainly comprises titanium carbide (TiC) or molybdenum carbide (Mo2C). It can, except for impurities, consist entirely of TiC or Mo2C. Alternatively, it can include TiC or Mo2C and other carbides such as NbC and WC; the latter being present in a minority in the carbide powder when the powders are mixed in a mill using WC balls with a cobalt binder. The purpose of adding additional carbides is to modify the process parameters, such as the sintering temperature and / or to modify the properties obtained. Preferably, the oxide powder mainly comprises aluminum oxide (Al2O3) or zirconium oxide (ZrO2). It can, except for impurities, consist entirely of Al2O3 or ZrO2. As a variant, it may comprise Al2O3 or ZrO2 and another oxide such as Cr2O3, the latter being present in a minority in the oxide powder and having the object of modifying the properties obtained. By way of example, the mixture of powders can comprise by volume one of the following distributions for a total of 100%: - between 65 and 85% of TiC and between 15 and 35% of Al2O3, - between 60 and 80% of TiC, between 2 and 10% of NbC and between 15 and 35% of Al2O3, - between 55 and 75% of TiC, between 2 and 10% of Cr2O3 and between 20 and 40% of Al2O3, - between 70 and 90% of TiC and between 10 and 30% of ZrO2, - between 60 and 80% of Mo2C and between 20 and 40% of Al2O3, - between 50 and 60%, preferably between 51 and 60%, of Mo2C and between 40 and 50%, preferably between 40 and 59%, of Al2O3, - between 65 and 85% of TiC, between 1 and 5% of Cr2O3 and between 10 and 30% of Al2O3. b) Optionally, a second mixture comprising the above mixture and an organic binder system (paraffin, polyethylene, etc.) can be produced. c) Form a blank by shaping the mixture into the shape of the desired article, for example, by injection or pressing. d) Sinter the blank under an inert atmosphere at a temperature between 1300 and 2100 ° C for a period of between 15 minutes and 20 hours. This step can be preceded by a step of dewaxing the organic binders in a temperature range of between 200 and 800 ° C. if the mixture comprises a binder system.

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

The article resulting from the manufacturing process comprises the phase comprising the carbides and the phase comprising the oxides in percentages by volume close to those of the starting powders. Indeed, a priori, the phases of carbides and oxides coexist without the formation of new phases during sintering. However, small variations in composition and in percentages between the base powders and the material resulting from the sintering cannot be ruled out as a result, for example, of contamination.

The article has a CIELAB color space (in accordance with CIE No. 15, ISO 7724/1, DIN 5033 Teil 7, ASTM E-1164) with a luminance component L *, representative of the way in which the material reflects light, between 60 and 85 and, preferably, between 65 and 80. The a * (red component) and b * (yellow component) components can be modulated as desired depending on the choice of oxides. Advantageously, the components a * and b * are respectively between -1 and 5 and between -2 and 5. Preferably, the component a * is between -0.5 and 2 and the component b * is between -0.5 and 3. A ceramic material with a white metallic appearance may be preferred. In this case, the components a * and b * are equal to 0.

The ceramic material has a hardness HV30 of between 1200 and 1950 depending on the types and percentages of the constituents. It has a Kic tenacity of between 2 and 8.5 MPa.m <1/2>, the tenacity being determined on the basis of the measurements of the lengths of the cracks at the four ends of the diagonals of the hardness indentation according to the formula: with P which is the applied load (N), a which is the half-diagonal (m) and / which is the length of the measured crack (m).

In particular, the ceramic material comprising a carbide phase consisting of TiC and an oxide phase consisting of Al2O3, except for impurities, has a very good compromise between toughness and hardness. Thus, when this carbide phase is present in a percentage by volume of between 65 and 85, preferably between 70 and 80%, with the complementary phase of Al2O3, the HV30 values are greater than or equal to 1800, or even to 1900, and the Kic values are greater than or equal to 3.5 MPa.m <1/2>.

Likewise, the ceramic material comprising a carbide phase consisting of TiC and an oxide phase consisting of Al2O3 and Cr2O3, except for impurities, has a very good compromise between toughness and hardness. Thus, when this carbide phase is present in a percentage by volume of between 55 and 75%, preferably between 60 and 70%, with the complementary phase of Al2O3 and Cr2O3, the HV30 values are greater than or equal to 1800 and the values Kic are greater than or equal to 4.5, or even 5 MPa.m <1/2>.

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

Examples

Seven mixtures of powders were prepared in a mill in the presence of a solvent. The mixtures were made without a binder. They were shaped by pressing and sintered under a flow of argon at 60 mbar at a temperature which depends on the composition of the powders. After sintering, the samples were coated and plane polished.

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 above.

The 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 °, measurement area MAV 8 mm in diameter.

Example 1 (80% TiC and 20% Al2O3 by weight)

The mixture of powders comprises by weight 80% TiC and 20% Al2O3 (in alpha phase) or by volume respectively 76% and 24%. The blank was sintered at 2000 ° C for 20 minutes. The sample has an average hardness of 1932 HV30 and a tenacity of 4 MPa.m <1/2>. The Lab components are respectively equal to 66.3, 0.44 and 0.73.

Example 2 (70% TiC, 10% NbC and 20% Al2O3 by weight).

The mixture of powders comprises by weight 70% TiC, 10% NbC and 20% Al2O3 (in alpha phase) or by volume respectively 69%, 6% and 25%. The blank was sintered at 1800 ° C for 30 minutes. The sample has an average hardness of 1255 HV30 and a toughness of 3.8 MPa.m <1/2>. The Lab components are respectively equal to 63.3, 0.00 and 0.09. The addition of NbC makes it possible to lower the sintering temperature by 200 ° C. but has the effect of reducing the hardness.

Example 3 (70% TiC, 25% Al2O3 and 5% Cr2O3 by weight)

The mixture of powders comprises by weight 70% TiC, 25% Al2O3 (in alpha phase) and 5% Cr2O3, ie by volume respectively 66%, 29.5% and 4.5%. The blank was sintered at 1750 ° C for 90 minutes. The sample has an average hardness of 1830 HV30 and a toughness of 5.2 MPa.m <1/2>. The Lab components are respectively equal to 64.5, 0.34 and 0.92. Adding 5% Cr2O3 results in high hardness and increased toughness. An electron microscopy image of this sample is shown in Figure 2, the gray phase represents the TiC matrix and the white phase represents the phase formed by oxides.

Example 4 (80% TiC and 20% ZrO2 by weight)

The mixture of powders comprises by weight 80% TiC and 20% ZrO2 (stabilized zirconia containing 3 mol% of Y2O3), or by volume respectively 82% and 18%. The blank was sintered at 1750 ° C for 90 minutes. The sample has an average hardness of 1617 HV30 and a toughness of 2.5 MPa.m <1/2>. The Lab components are respectively equal to 66.5, -0.39 and -1.14. Replacing aluminum oxide with zirconia makes it possible to reduce the a * and b * components but also has the effect of reducing the toughness.

Example 5 (85% Mo2C and 15% Al2O3 by weight)

The mixture of powders comprises 85% Mo2C and 15% Al2O3 by weight (in alpha phase), ie 72% and 28% by volume, respectively. The blank was sintered at 1450 ° C for 90 minutes. The sample has an average hardness of 1319 HV30 and a toughness of 5.3 MPa.m <1/2>. The Lab components are respectively equal to 72.5, 0.21 and 2. The replacement of titanium carbide by molybdenum carbide makes it possible to greatly reduce the sintering temperature while increasing the value of the luminance index L *.

Example 6 (70% Mo2C and 30% Al2O3 by weight)

The mixture of powders comprises by weight 70% Mo2C and 30% Al2O3 (in alpha phase), ie by volume respectively 51% and 49%. The blank was sintered at 1450 ° C for 90 minutes. The sample has an average hardness of 1417 HV30 and a tenacity of 5.0 MPa.m <1/2>. The Lab components are respectively equal to 63.8, 0.13 and 1.49. The increase in the proportion of aluminum oxide makes it possible to increase the hardness but leads to a drop in the luminance index L *.

Example 7 (80% TiC, 18% Al2O3 and 2% Cr2O3 by weight)

The mixture of powders comprises by weight 80% TiC, 18% Al2O3 (in alpha phase) and 2% Cr2O3, ie by volume respectively 76.5%, 21.5 and 2%. The blank was sintered at 1650 ° C for 90 minutes. The sample has an average hardness of 1219 HV30 and a toughness of 7.8 MPa.m <1/2>. The Lab components are respectively equal to 65, 0.06 and 0.4. The addition of a small proportion of chromium oxide improves the toughness.

In summary, it is observed that samples 1 and 3 exhibit a very good toughness-hardness compromise with values of hardness and toughness higher respectively than 1800 HV30 and 3.5 MPa.m <1/2> and that sample 7 exhibits very good toughness with a value greater than 7 MPa.m <1/2>.

Claims (21)

1. Decorative article made of a ceramic material, said ceramic material comprising a carbide phase and an oxide phase, the carbide phase being present in a percentage by volume of between 50 and 95% and the oxide phase being present in a percentage by volume of between 5 and 50%. 2. Article according to claim 1, characterized in that the carbide phase is in the majority and present in a volume percentage of between 51 and 85% and in that the oxide phase is in the minority and present in a volume percentage included between 15 and 49%. 3. Article according to claim 1 or 2, characterized in that the carbide phase comprises one or more carbides chosen from titanium carbide, molybdenum carbide, tungsten carbide and niobium carbide. 4. Article according to any one of the preceding claims, characterized in that the carbide phase mainly comprises titanium carbide or molybdenum carbide. 5. Article according to claim 4, characterized in that said phase of carbides predominantly comprising titanium carbide is present in a percentage by volume of between 55 and 90%, preferably between 60 and 85%, the oxide phase being present in a percentage by volume of between 10 and 45%, preferably between 15 and 40%. 6. Article according to claim 5, characterized in that said phase of carbides comprises predominantly niobium carbide. 7. Article according to claim 4, characterized in that said phase of carbides predominantly comprising molybdenum carbide is present in a percentage by volume of between 50 and 75%, preferably between 51 and 75%, the oxide phase being present in a percentage by volume of between 25 and 50%, preferably between 25 and 49%. 8. Article according to any one of the preceding claims, characterized in that the oxide phase comprises one or more oxides chosen from aluminum oxide, chromium oxide, zirconium oxide and oxide yttrium. 9. Article according to claim 8, characterized in that the oxide phase mainly comprises aluminum oxide or zirconium oxide. 10. Article according to claim 9, characterized in that said oxide phase comprising predominantly aluminum oxide also comprises predominantly chromium oxide. 11. Article according to claims 5 and 9, characterized in that said carbide phase consists of titanium carbide and in that said oxide phase consists of aluminum oxide. 12. Article according to claim 11, characterized in that said carbide phase is present in a percentage by volume of between 65 and 85, preferably between 70 and 80%, and in that said oxide phase is present in a percentage by volume of between 15 and 35%, preferably between 20 and 30%. 13. Article according to claims 5 and 10, characterized in that said carbide phase consists of titanium carbide and in that said oxide phase consists mainly of aluminum oxide and mainly of chromium oxide. 14. Article according to claim 13, characterized in that said carbide phase is present in a percentage by volume of between 55 and 75%, preferably between 60 and 70%, and in that said oxide phase is present in a percentage by volume of between 25 and 45%, preferably between 30 and 40%. 15. Article according to any one of claims 11 to 14, characterized in that it has a hardness HV30supérieur 1800, preferably 1900, and in that it has a tenacity KiCsupérieur or equal to 3.5 MPa.m < 1/2>, preferably at 5 MPa.m <1/2>. 16. Article according to any one of the preceding claims, characterized in that it has, in a CIELAB color space, an L * component between 60 and 85 and, preferably, between 65 and 80. 17. Article according to claim 16, characterized in that it has a component a * between -1 and 5, preferably between -0.5 and 2, and in that it has a component b * between -2 and 5, preferably between - 0.5 and 3. 18. Article according to claim 17, characterized in that the components a * and b * are equal to 0. 19. Article according to any one of the preceding claims, characterized in that it is a component for covering watchmaking chosen from the list comprising a middle part, a back, a bezel, a push-piece, a link of bracelet, dial, hand and dial index. 20. Method for manufacturing a decorative article comprising the successive steps consisting in: a) Prepare a mixture comprising a carbide powder in a percentage by volume of between 50 and 95% and an oxide powders in a percentage by volume of between 5 and 50%, b) Form a blank by giving the mixture the shape of the article, c) Sinter the blank at a temperature between 1300 and 2100 ° C for a period between 15 minutes and 20 hours. 21. The manufacturing method according to claim 20, characterized in that the mixture of step a) comprises, for a total of 100%, one of the following distributions by volume: - between 65 and 85% of TiC and between 15 and 35% of Al2O3, - between 60 and 80% of TiC, between 2 and 10% of NbC and between 15 and 35% of Al2O3, - between 55 and 75% of TiC, between 2 and 10% of Cr2O3 and between 20 and 40% of Al2O3 - between 70 and 90% of TiC and between 10 and 30% of ZrO2, - between 60 and 80% of Mo2C and between 20 and 40% of Al2O3 - between 50 and 60% of Mo2C and between 40 and 50% of Al2O3 - between 65 and 85% of TiC, between 1 and 5% of Cr2O3 and between 10 and 30% of Al2O3.