EP4185726A2

EP4185726A2 - Component for a timepiece or jewellery item made of cermet

Info

Publication number: EP4185726A2
Application number: EP21733442.4A
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: 2020-07-22
Filing date: 2021-06-17
Publication date: 2023-05-31
Also published as: WO2022017697A3; CN116134170A; US20230250517A1; WO2022017697A2; JP2023533821A; EP3943630A1

Abstract

The invention concerns component for a timepiece or a jewellery item, made of a cermet material comprising a carbide phase and a metal binder phase selected from among gold, platinum, palladium rhodium, osmium, ruthenium and one of the alloys thereof, characterised in that the metal binder phase is present in a percentage by weight between 3 and 25% and in that the carbide phase is present in a percentage by weight of between 75 and 97%. The present invention also relates to the method used for producing this component

Description

COMPONENT FOR A WATCH OR JEWELRY PIECE IN

CERMET

TECHNICAL AREA

The present invention relates to a component in particular for a timepiece or piece of jewelry, made of a cermet-type material with a ceramic phase comprising carbides and with a metallic binder comprising a precious metal.

PRIOR ART

Many trim components are made of gold or a gold alloy. Gold has the advantage of possessing great ductility as well as great malleability, which allows easy shaping. It is also endowed with a very high and characteristic metallic luster. In addition, the different gold alloys can take on various hues ranging from white to red. However, gold and its alloys have the disadvantage of having a low hardness which is at most 300 HV. In this regard, various ceramic composites have been developed in order to increase the hardness of gold. The manufacturing process most often involves infiltrating a high-hardness matrix with gold and applying very high pressures. The disadvantage of this method is that the accessible shapes remain limited to simple geometries, obtaining complex shapes requiring the use of additional machining methods. Other processes as disclosed in document WO 2004/005561 consist in using gold as a metallic binder in a cermet obtained by sintering. The metallic gold binder is present in proportions well above 50% by weight. In this case, the hardness of such a precious cermet is low and inversely proportional to the percentage by weight of gold. Generally, cermets use a non-precious metal as a binder. These are often allergenic elements such as nickel or cobalt as disclosed in US 4,589,917, or iron-based alloys resulting in low corrosion resistance and high ferromagnetism.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the aforementioned disadvantages by proposing a cermet with a composition optimized to fulfill the following criteria:

- have a high metallic luster,

- have a minimum hardness of 700 HV30,

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

- not exhibit ferromagnetism and be resistant to saline corrosion.

To this end, the present invention proposes a component in particular for a timepiece or piece of jewelry made of a cermet material comprising a phase of carbides and a phase of a metallic binder chosen from silver, gold, platinum , palladium, ruthenium, osmium, rhodium and one of their alloys. The metal binder phase is present in a weight percentage between 3 and 25% and the carbides phase is present in a weight percentage between 75 and 97%.

The cermet material thus developed has, after polishing, a metallic luster which can be comparable to that observed in stainless steels, particularly when the metallic binder is palladium. These precious cermets have hardnesses between 700 and 1900 HV30 and they have sufficient tenacity for the production of trim parts. In addition, they can be shaped by conventional powder metallurgy processes such as pressing or injection in order to obtain "near-net shape" parts. The low content of precious binder makes it possible to obtain a cermet that retains the reflective and colorimetric characteristics of the carbide used, which is particularly important for trim and decorative components.

The present invention also relates to the process for manufacturing the component comprising the successive steps consisting in: a) producing a mixture comprising a powder of carbides and a powder of a metal binder chosen from silver, gold, platinum, palladium, ruthenium, osmium, rhodium and one of their alloys and optionally comprising an additive. b) Forming a blank by giving said mixture the shape of the component, c) Sintering the blank at a temperature of between 1000 and 1900°C for a period of between 30 minutes and 10 hours, the method being characterized in that the powder of carbides is present in a percentage by weight of between 75 and 97%, the powder of the metal binder in a percentage by weight of between 3 and 25% and the additive in a percentage by weight of between 0 and 4%.

The use of precious binders such as platinum or palladium makes it possible to densify these carbide-based cermets from much lower temperatures than those of said carbides alone and without resorting to sintering at high temperatures and under pressure, either from 1250°C with palladium and 1400°C with platinum.

The powders of the mixture preferably have a d50 of less than 20 μm, more preferably less than 10 μm and even more preferably less than 5 μm. With a small particle size, the homogeneity of the mixture is improved and excellent coverage of the metallic binder on each carbide grain is guaranteed. In addition, by decreasing the size of the carbides, the final density is increased while increasing the mechanical properties such as hardness and toughness. after sintering. Also, reducing the particle size results in a high metallic luster, i.e. a high luminance value L*

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 drawings.

BRIEF DESCRIPTION OF THE FIGURE

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

Figure 2 represents an electron microscopy image of the cermet type material for a composition according to the invention (80% Mo2C - 15% Au and 5% Cu).

FIG. 3 represents an electron microscopy image of the cermet type material for another composition according to the invention (80% TiC - 2% SiC - 18% Pt).

DETAILED DESCRIPTION

The present invention relates to a component, in particular for a timepiece or piece of jewelry, made of a cermet-type material comprising a majority phase of carbides and a minority phase of a metallic binder comprising a precious element such as silver, gold, platinum, palladium, ruthenium, osmium, rhodium or an alloy of one of these precious elements. Preferably, the metallic binder is chosen from silver, gold, platinum, palladium or an alloy of one of these precious elements. The component according to the invention can form a decorative article such as a constituent element of watches, jewellery, bracelets, etc. In the horological field, this component can be a covering part such as a middle part, a back, a bezel, a pusher, a bracelet link, a dial, a hand, a dial index, etc. he can it can also be a component of the movement such as an oscillating weight, a plate, etc. By way of illustration, a middle part 1 made with the cermet-type material according to the invention is represented in FIG. 1.

The cermet component is made by sintering from a mixture of carbide and metal powders. The manufacturing process comprises the steps consisting of: a) Making a mixture with the different powders, possibly in a humid environment. The powders of the mixture preferably have a d50 of less than 20 μm, more preferably less than 10 μm and even more preferably less than 5 μm. The mixture can optionally be carried out in a grinder to obtain the desired d50. The particle size is measured by laser diffraction in accordance with the ISO 13320: 2020 standard.

This mixture comprises by weight between 75 and 97%, advantageously between 78 and 97%, and more advantageously between 78 and 94%, of the carbide powder and between 3 and 25%, advantageously between 3 and 22%, and more advantageously between 6 and 22% of the metal powder. The mixture may optionally comprise one or more additives in a percentage by weight for all the additives of less than or equal to 4%. In the presence of one or more additives, the latter are preferably present in a percentage for all the additives of between 1 and 3% by weight. More specifically, in the presence of one or more additives, the mixture comprises the carbide powder in a percentage by weight of between 75 and 96%, the powder of the metal binder in a percentage by weight of between 3 and 24% and the additive or additives in a percentage by weight for all the additives comprised between 1 and 3%. These additives are intended to improve densification during sintering. For example, it may be a metal disilicide such as SbTi or SbZr.

Preferably, the carbide powder comprises one or more carbides chosen from TiC, SiC, Mo2C, WC and NbC. More in particular, the carbide powder mainly comprises titanium carbide (TiC), tungsten carbide (WC) or molybdenum carbide (Mo2C). By predominantly we mean that, when there are several types of carbides in the powder, titanium carbide (TiC), tungsten carbide (WC) or molybdenum carbide (Mo2C) are present in a greater percentage than the others. carbides. It may thus comprise Mo2C and TiC with the majority of Mo2C present. It may also comprise Mo2C and TiC with the TiC predominantly present. It may also comprise TiC and SiC with the TiC predominantly present. As a variant, it can, except for impurities, consist entirely of TiC, WC or Mo2C. The metal powder mainly comprises palladium, platinum, silver, gold, ruthenium, osmium, rhodium or an alloy of one of these elements. It can, except for impurities, consist entirely of platinum, palladium, ruthenium, osmium, rhodium or silver. The gold is preferentially present in alloyed form with at least one element chosen from Cu, Ag, Pd, In. More preferentially, the gold alloy comprises gold alloyed with silver and copper (gold 3N yellow, 5N red gold) or palladium (white gold). The metal powder can also comprise carbon in a percentage by weight of between 0.1 and 5% relative to the total weight of the mixture of powders. Indeed, during sintering, part of the Mo2C can be transformed into Mo resulting in a reduction in hardness. The addition of carbon makes it possible to limit the formation of Mo and therefore to maintain the level of hardness. Alternatively, the addition of carbon can be carried out in the carbide powder. The carbide powder thus comprises carbon in a percentage by weight of between 0.1 and 5% relative to the total weight of the mixture of powders.

By way of example, the mixture of powders may comprise by weight one of the following distributions: between 80 and 95% of TiC and between 5 and 20% of Pd or Pt, - between 75 and 95% of TiC and between 5 and 25% of an Au alloy,

- between 50 and 70% TiC, between 5 and 30% Mo2C, and between 5 and 30% of an Au alloy, preferably between 55 and 65% TiC, between 10 and 25% Mo2C, and between 5 and 25% of an Au alloy,

- between 70 and 85% TiC, between 5 and 10% Mo2C, and between 5 and 20% Pd or Pt,

- between 75 and 85% TiC, between 2 and 10% SiC, and between 5 and 23% Pd or Pt,

- between 80 and 97% Mo2C and between 3 and 20% Pd, Pt, Ag or an alloy of Ag,

- between 75 and 95% Mo2C and between 5 and 25% of an Au alloy,

- between 75 and 95% of WC and between 5 and 25% of Pd or Pt,

- between 80 and 95% WC and between 5 and 20% of an Au alloy. Optionally, a second mixture comprising the aforementioned mixture and an organic binder system (paraffin, polyethylene, etc.) can be produced. b) Forming a parison by shaping the mixture into the shape of the desired component, for example, by injection or pressing into a mould. c) Sinter the blank under an inert atmosphere or under vacuum at a temperature between 1000 and 1900°C for a period of between 30 minutes and 10 hours, preferably between 30 minutes and 5 hours. This step can be preceded by one or more debinding steps in a temperature range between 60 and 800°C if the mixture includes an organic binder system.

The blank thus obtained is cooled and polished. It can also be machined before polishing to obtain the desired component. The component, which can also be described as an article, resulting from the manufacturing process comprises the carbide phase and the metallic phase 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, of Mo2C into Mo. Therefore, in the final product resulting from the process, the mass percentages for the different phases must be understood as follows. A distinction is made between the carbide phase and the metallic phase, also called the metallic binder phase. The carbide phase comprises the carbides as well as any elements derived from the basic carbide powder such as Mo for the example above. Similarly, for the metallic phase, it comprises the compounds of the starting metallic powder as well as a possible compound resulting from a decomposition or reaction of the metallic base powder. In the presence of additives in the mixture of powders, the latter can be found in the phase of carbides and/or in the metallic phase.

The component has a CIELAB colorimetric space (compliant with CIE n°15, ISO 7724/1, DIN 5033 Teil 7, ASTM E-1164) with a luminance component L*, representative of the way the material reflects light, between 60 and 90, preferably between 65 and 85 and, more preferably between 70 and 85.

The ceramic material has an HV30 hardness of between 700 and 1900 depending on the types and percentages of the constituents. More specifically, it has an HV30 hardness of between 700 and 1300 when the carbide phase mainly comprises molybdenum carbide. An HV30 hardness of between 900 and 1600 when the carbide phase mainly comprises tungsten carbide and an HV30 hardness of between 700 and 1900 when the carbide phase mainly comprises titanium carbide. The ceramic material has a KiC toughness of at least 2 MPa.m ^1/2 with values possibly exceeding 20 MPa.m ^1/2 . The toughness is determined on the basis of measurements of the lengths of the cracks at the four extremities of the diagonals of the Vickers hardness indentation according to the formula: with P being the applied load (N), a being the half-diagonal (m) and / being the measured crack length (m).

Tables 1 to 3 below show various examples of cermets according to the invention.

27 mixtures of powders were prepared in a grinder in the presence of a solvent. The mixtures were made without binder. They were compacted in the form of pellets by uniaxial pressure and sintered under vacuum or under a partial pressure of argon between 5 and 100 mbar at a temperature which depends on the composition of the powders. After sintering, the samples were plane polished mechanically.

In Table 1, there are tests Nos. 1 to 9 with a carbide phase comprising TiC, Mo2C or TiC and Mo2C and with a binder phase comprising Pd, Au or an alloy of 'At. For test 7, 0.5% of C is added to limit the formation of Mo.

In Table 2, there are tests Nos. 11 to 18 with a carbide phase comprising TiC, TiC and SiC or TiC and Mo2C and with a binder phase comprising Pt or Pd. In test 16, the mixture of powders includes an additive to improve the densification. This additive is Si2Ti _p resent in a weight percentage of 2%.

In table 3, there are tests n°19 to 27 with a phase of carbides comprising Mo2C or WC and with a phase of binder comprising Pd, Pt, Ag, an alloy of Ag or an Au alloy. 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.

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.

It emerges from these tests that the cermets with a carbide phase mainly comprising TiC generally have a higher hardness than that of the cermets with a carbide phase mainly comprising Mo2C. The hardnesses are thus comprised between 750 and 1800 HV30 for the cermets comprising TiC compared with values comprised in the range 750-1200 HV30 for the cermets comprising mainly Mo2C. Sample 4 comprising TiC and an Au alloy has a lower hardness (761 HV30) attributed to a lower sintering time compared to sample 3 comprising TiC and an Au alloy (1209 HV30). Sample 4 also has a lower toughness compared to sample 3.

Cermets comprising Mo2C and Pd have extremely high toughness values which are greater than 10 MPa.m ^1/2 for Pd contents greater than or equal to 8% (tests 6, 20, 21). For certain compositions, there is no crack propagation during the HV30 hardness measurements, a toughness value could therefore not be measured.

Cermets mainly comprising Mo2C have high L* luminance indices regardless of the type of precious binder used (Pt, Pd, Ag, Au-Cu) with values of around 80 against values in the 70 range. -75 for cermets mainly comprising TiC. A cermet composed solely of tungsten carbides, up to 80% by weight, and 20% palladium as the precious metal binder, has a high hardness (1472 HV30) and good toughness (6.3 MPa.m ^1/2 ) which makes it a good candidate for the production of functional parts such as an oscillating weight, also given its high density.

In terms of microstructures, figure 2 represents an electron microscopy of a sample sintered from the mixture of powders comprising by weight 80% Mo2C, 15% Au and 5% Cu. The carbide phase is formed of the dark gray zone composed of Mo2C and the medium gray zone rich in Mo. Part of the Mo2C is transformed into Mo during sintering with a consequent decrease in hardness. The metallic AuCu phase is the white phase.

Figure 3 represents an electron microscopy of a sample sintered from the mixture of powders comprising by weight 80% TiC, 2% SiC and 18% Pt. There is the phase of carbides formed from the black and gray zones with the black zone rich in TiC and the gray zone comprising TiC and Pt. In white, there is the metallic phase.

As explained above, the invention relates to the component made of a cermet material. This component has been designed for applications in particular in the field of watchmaking and jewelery such as for example trim elements or the movement of a timepiece. Of course, the component according to the invention cannot be limited to watchmaking. Thus, in no way limiting, one can also imagine that this component can be applied in the field of tableware, cutlery, leather goods, jewelry or jewelry. lO

HE

Claims

1. Non-ferromagnetic component free of nickel and cobalt, in particular for a timepiece or piece of jewelery made of a cermet material comprising a phase of carbides and a phase of a binder formed from platinum, characterized in that the phase of the metallic binder is present in a percentage by weight of between 3 and 25% and in that the carbide phase is present in a percentage by weight of between 75 and 97%.

2. Component according to claim 1, characterized in that the phase of the metal binder is present in a percentage by weight of between 3 and 22% and in that the phase of carbides is present in a percentage by weight of between 78 and 97 %.

3. Component according to claim 1 or 2, characterized in that the metal binder phase is present in a percentage by weight of between 6 and 22% and in that the carbide phase is present in a percentage by weight of between 78 and 94%.

4. Component according to one of the preceding claims, characterized in that the carbide phase comprises one or more carbides chosen from titanium carbide, molybdenum carbide, silicon carbide and tungsten carbide and niobium carbide .

5. Component according to one of the preceding claims, characterized in that the carbide phase mainly comprises titanium carbide or molybdenum carbide or tungsten carbide.

6. Component according to claims 4 or 5, characterized in that the carbide phase mainly comprises titanium carbide and a minority of molybdenum carbide.

7. Component according to claims 4 or 5, characterized in that the carbide phase mainly comprises titanium carbide and a minority of silicon carbide.

8. Component according to claims 4 or 5, characterized in that the carbide phase mainly comprises molybdenum carbide.

9. Component according to one of the preceding claims, characterized in that it has an HV30 hardness of between 700 and 1900.

10. Component according to claim 5, characterized in that it has an HV30 hardness of between 700 and 1300 when the carbide phase mainly comprises molybdenum carbide.

11. Component according to claim 5, characterized in that it has an HV30 hardness of between 1000 and 1900 when the carbide phase mainly comprises titanium carbide and a minority of silicon carbide.

12. Component according to claim 5, characterized in that it has an HV30 hardness of between 900 and 1600 when the carbide phase mainly comprises tungsten carbide.

13. Component according to one of the preceding claims, characterized in that it has a toughness Kic greater than or equal to 4 MPa.m1/2 when the carbide phase mainly comprises molybdenum carbide and a phase of a binder comprising gold and copper.

14. Component according to one of the preceding claims, characterized in that it has a toughness KiC greater than or equal to 8 MPa.m1/2 when the carbide phase mainly comprises molybdenum carbide and a phase of a binder comprising palladium.

15. Component according to one of the preceding claims, characterized in that it has, in a CIELAB colorimetric space, an L* component of between 60 and 90 and, preferably, between 65 and 85, and more preferably between 70 and 85.

16. Component according to one of the preceding claims, characterized in that it has, in a CIELAB colorimetric space, a L* component between 77 and 85 when the carbide phase mainly comprises molybdenum carbide.

17. Component according to one of the preceding claims, characterized in that it is a covering component or the watch movement.

18. Non-ferromagnetic component free of nickel and cobalt, in particular for a timepiece or piece of jewelery made of a cermet material comprising a phase of carbides and a phase of a metallic binder chosen from silver, gold, platinum , palladium, rhodium, osmium, ruthenium and one of their alloys, characterized in that the metal binder phase is present in a percentage by weight of between 6 and 25% and in that the carbide phase is molybdenum carbide and is present in a percentage by weight of between 75 and 94%.

19. Component according to claim 15, characterized in that the metal binder phase is present in a percentage by weight of between 6 and 22% and in that the carbide phase is present in a percentage by weight of between 78 and 94 %.

20. Component according to one of the preceding claims, characterized in that it has an HV30 hardness of between 700 and 1900.

21. Component according to one of the preceding claims, characterized in that it has a KiC toughness greater than or equal to 2 MPa.m1/2

22. Component according to one of the preceding claims, characterized in that it has, in a CIELAB colorimetric space, an L* component of between 60 and 90 and, preferably, between 65 and 85, and more preferably between 70 and 85.

23. Component according to one of the preceding claims, characterized in that it is a casing component or a watch movement.