CH719052A2 - Item in precious cermet. - Google Patents

Abstract

The invention relates to an article made of a cermet material comprising by weight between 85 and 94% of a ceramic phase and between 6 and 15% of a phase of a metal binder, the ceramic phase mainly comprising a phase of tungsten carbide and optionally one or more phases of one or more secondary carbides chosen from the elements Ti, Zr, Hf, V, Nb, Ta, Cr and Mo, the metal binder comprising Ag, Pd, Ru and Co. The invention also relates to the method of manufacturing said article.

Description

TECHNICAL AREA

The present invention relates to an article, in particular to a decorative article, and more specifically to a watch component, made of a material of the non-magnetic cermet type. This article comprises a ceramic phase with mainly tungsten carbides and a metallic binder comprising several precious elements.

PRIOR ART

[0002] Cermets generally contain a metallic binder such as nickel or cobalt, which have the disadvantage of having a non-negligible residual ferromagnetism for applications in the watchmaking field. It is becoming increasingly necessary to limit or completely eliminate this ferromagnetism in order to guarantee the most precise possible operation of watches, in particular mechanical watches. It is therefore imperative to develop new cermets free of any use of ferromagnetic or diamagnetic binders.

[0003] In addition, the cermets used for specific applications such as glasses or more generally watch cases must have very good scratch resistance, ie. a hardness greater than 1000 Vickers. This then requires reducing the amount of metallic binder while controlling the wettability between said metallic binder and the ceramic phase, poor wettability resulting in a drop in density on the final product and hence in hardness.

[0004] In addition to the absence of ferromagnetism or diamagnetism and the high hardnesses required, toughness is an important property in the watchmaking field. Added to this is aesthetics, which is crucial for watch exterior components. In particular, the metallic luster of the component is an aesthetic aspect to which particular attention is paid.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the aforementioned disadvantages by proposing an article made of a material of the cermet type, with a composition and a manufacturing process optimized to meet the following criteria: get rid of any ferromagnetism or diamagnetism, have a low magnetic susceptibility ¿m, less than 5x10-5, have a high metallic luster, i.e. a minimum luminance index L* of 65 and more preferably a minimum of 70 for watch exterior applications, be able in particular to be densified by sintering in the liquid phase, under atmospheric pressure, under vacuum or under partial gas pressure, have a minimum Vickers hardness of 500, preferably a minimum of 700 and more preferably a minimum of 1000 HV30 for an application requiring very good scratch resistance, while having sufficient toughness with, preferably, a Kic greater than or equal to 4 MPa .m1/2,

To this end, the present invention provides an article made of a cermet material comprising by weight between 85 and 94% of a ceramic phase mainly comprising tungsten carbides and between 6 and 15% of a phase of a metal binder comprising several metals including precious metals.

More specifically, said cermet material comprises the element cobalt between 0.02 and 4% by weight, the element ruthenium between 0.02 and 4% by weight, the element palladium between 0.5 and 4% by weight and the element silver between 5 and 14% by weight. In other words, said cermet material consists, except for impurities, of the element cobalt between 0.02 and 4% by weight, of the element ruthenium between 0.02 and 4% by weight, of the element palladium between 0.5 and 4% by weight and of the silver element between 5 and 14% by weight.

Preferably, said cermet material consists, except for impurities, of the element cobalt between 0.02 and 3% by weight, of the element ruthenium between 0.02 and 3% by weight, of the element palladium between 0.5 and 3 % by weight and of the silver element between 7 and 13.4% by weight.

[0009]Even more preferably, said cermet material consists, except for impurities, of the element cobalt between 0.03 and 2% by weight, of the element ruthenium between 0.03 and 2% by weight, of the element palladium between 0.5 and 2% by weight and of the silver element between 7 and 10% by weight.

[0010] Silver is mainly used in the binder given its low cost and its miscibility with the elements cobalt, ruthenium and palladium. Palladium is mainly added to prevent tarnishing or oxidation in the air of the silver while having the other advantage of not exhibiting ferromagnetism. It also increases corrosion resistance.

[0011] The cobalt and ruthenium elements are incorporated in small quantities in order in addition to improve the densification during sintering given that they are both miscible in silver while improving the wettability with the tungsten carbide grains. They therefore advantageously make it possible to improve the densification.

[0012] The cermet material thus developed has no ferromagnetic or diamagnetic component, and after polishing has a metallic luster comparable to that observed in stainless steels. These precious cermets have the further advantage of being free of nickel, which is known to be a highly allergenic element. They also have high hardnesses and sufficient tenacity for the production of trim components and functional parts. In addition, they can be produced by conventional methods of manufacturing solid materials such as by casting, or by powder metallurgy in order to obtain three-dimensional parts shaped by pressing or by injection or by extrusion or by various other manufacturing methods. additives such as 3D printing.

[0013] Pieces of more or less complex shape can therefore be finally consolidated at temperatures between 1100 and 1500° C., under atmospheric pressure, under vacuum or under partial gas pressure, ie. without resorting to significant pressure.

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 accompanying drawings.

BRIEF DESCRIPTION OF FIGURES

Figure 1 shows two optical and electron microscopy images respectively of the cermet type material according to the invention with a composition by weight of 90% WC and 10% of a valuable binder consisting of 89% Ag , 10% Pd, 0.5% Ru and 0.5% Co, i.e. relative to the total weight 8.9% Ag, 1% Pd, 0.05% Ru and 0.05% Co.

[0016] FIG. 2 represents the paramagnetic behavior of this same material of the cermet type having a magnetic susceptibility ¿mde 1.2×10<-5>.

DETAILED DESCRIPTION

The present invention relates to an article made of a cermet-type material comprising a ceramic phase consisting of carbides and a phase of a binder consisting of several metals including precious metals. The cermet comprises by weight between 85 and 94% of the ceramic phase and between 6 and 15% of the phase of the metallic binder. Preferably, the cermet comprises by weight between 86 and 93% of the ceramic phase and between 7 and 14% of the phase of the precious metallic binder. Preferably, the cermet comprises by weight between 87 and 92% of the ceramic phase and between 8 and 13% of the phase of the precious metallic binder. Even more preferably, the cermet comprises by weight between 89 and 91% of the ceramic phase and by weight between 9 and 11% of the phase of the precious metallic binder.

[0018] The metal binder comprises silver, palladium, ruthenium and cobalt. Preferably, the metal binder consists, except for impurities, of silver, palladium, ruthenium and cobalt. Based on the total weight, cobalt and ruthenium are each present in a percentage of between 0.02 and 4% by weight. Preferably, the cobalt and the ruthenium are each present in a percentage of between 0.02 and 3%, more preferably between 0.03 and 2% by weight, even more preferably between 0.03 and 1%, even more preferably between 0.03 and 0.5% and particularly preferably between 0.03 and 0.4%. Relative to the total weight, the palladium is between 0.5 and 4% and the silver between 5 and 14%. Preferably, the palladium is between 0.5 and 3%, more preferentially, the palladium is between 0.5 and 2%, and even more preferentially between 0.5 and 1.5%. Preferably, the silver is between 7 and 13.4% and more preferably between 7 and 10% by weight.

[0019] The ceramic phase comprises a majority phase of tungsten carbide and optionally one or more carbide phases of an element or of several elements chosen from Ti, Zr, Hf, V, Nb, Ta, Cr and Mo. in other words, the ceramic phase consists either of a single phase of tungsten carbide, or of a major phase of tungsten carbide with the addition of one or more phases respectively of one or more carbides of Ti, Zr , Hf, V, Nb, Ta, Cr and Mo, this or these carbide phases of Ti, Zr, Hf, V, Nb, Ta, Cr and Mo being present in a minor proportion. By majority is meant a percentage greater than 50% by weight, preferably greater than or equal to 65%, more preferably greater than or equal to 75%. In summary, within the ceramic phase, the tungsten carbide phase is present in a percentage by weight greater than 50% and less than or equal to 100% (50 < WC ¿ 100%), preferably greater than or equal to 65 % and less than or equal to 100% (65 ¿ WC ¿ 100%), more preferably greater than or equal to 75% and less than or equal to 100% (75 ¿ WC ¿ 100%) with the balance formed from the other carbides of Ti, Zr, Hf, V, Nb, Ta, Cr and Mo.

According to the invention, this cermet type material is non-magnetic. For the rest of this description, the mention of ¿amagnetic¿ for this cermet type material refers to a material that is only paramagnetic and has a very low magnetic susceptibility. It is well known that in a phase diagram, the Curie temperature indicates the transition temperature from a ferromagnetic state to a paramagnetic state, at a given temperature and for a fixed composition Thus, for the Cobalt-Ruthenium phase diagram, this magnetic transition occurs at room temperature for a Ruthenium mass concentration between 45% and 50%. In the same way, it is possible to determine in the Cobalt-Palladium phase diagram a paramagnetic transition located between 4% and 6% by weight of cobalt, at the same ambient temperature. By respecting the two limits stated above, it is then possible to have a paramagnetic transition in the ternary Palladium-Cobalt-Ruthenium system. The material of the cermet type with a precious binder consisting of the elements palladium, cobalt, ruthenium according to the limits of the defined compositions and of silver is therefore paramagnetic.

[0021] The article can be a constituent element of watches, jewellery, bracelets, etc. In the horological field, this article 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. It may also be a component of the movement chosen from the non-exhaustive list comprising a toothed wheel, an axis, a pinion, a spring, a bridge, a plate, a screw and a balance wheel. Advantageously, within the components of the movement, there is a balance shaft.

[0022] The cermet article can be shaped by conventional powder metallurgy processes such as pressing or injection or extrusion or by various additive manufacturing processes dedicated to the manufacture of three-dimensional parts such as fusion Selective Laser Melting (SLM), Selective Electron Beam Melting (SEBM), such as 3D Printing (3DP), Binder Jetting 3D Printing (BJAD), Gel 3D Printing (3DGP) and fused filament fabrication (FFF).

The cermet article is preferably produced by sintering starting from a mixture of ceramic and metal powders. The manufacturing process comprises the following steps: a) Making a mixture with the different powders, possibly in a humid environment. The starting powders preferably have a d50 of less than 10 μm, and more preferably between 0.8 and 5 μm. The mixture can optionally be produced in a grinder, which reduces the d50 of the particles of the powder to a size of the order of a micron, or even less than a micron after grinding. This mixture comprises by weight between 85 and 94%, preferably between 86 and 93%, more preferably between 89 and 91%, of the ceramic powder and between 6 and 15%, preferably between 7 and 14%, more preferably between 9 and 11% of the metal powder. The ceramic powder comprises tungsten carbide and optionally one or more other carbides. The metal powder consists only of the elements silver, palladium, ruthenium and cobalt. The cermet thus produced therefore comprises by total weight from 5 to 14% silver, preferably between 7 and 13.4% silver, more preferably between 7 and 10% silver. It also comprises by total weight from 0.5 to 4% palladium, preferably between 0.5 and 3% palladium, more preferably between 0.5 and 2% palladium, and even more preferably between 0.5 and 1.5% palladium. This cermet also comprises ruthenium and cobalt with a weight content for each of between 0.02 and 4%, preferably between 0.02 and 3%, more preferably between 0.03 and 2%, and even more preferably between 0.03 and 1%, between 0.03 and 0.5% and between 0.03 and 0.4%. It will be specified for this step that the metallic phase can also be manufactured by arc melting then be atomized in the form of pre-alloyed powders to finally be mixed with the carbide powders. 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 shaping the mixture into the shape of the desired article, for example, by injection, pressing, extrusion or 3D printing. d) Sintering the blank under an inert atmosphere or under nitrogen or under vacuum at a temperature between 950°C and 1600°C, preferably between 1000°C and 1500°C, and more preferably between 1100 and 1500°C, for a period of between 15 minutes and 8 hours, preferably between 30 minutes and 4 hours, and more preferably between 30 minutes and 2 hours. This stage can be preceded by a debinding stage in a temperature range of between 200 and 800° C. if the mixture comprises a system of organic binders.

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 ceramic phase and the metallic phase in percentages by weight close to those of the starting powders. However, small variations in compositions and percentages between the base powders and the material resulting from sintering cannot be excluded, depending in particular on the different vapor pressures of the constituent elements of the metallic binder with the temperature.

[0026] The article has a CIELAB colorimetric space (in accordance with CIE n°15, ISO 7724/1, DIN 5033 Teil 7, ASTM E-1164 standards) with a luminance component L*, representative of the way in which the material reflects light, minimum 60, preferably minimum 65 and more preferably minimum 70.

The cermet material has a Vickers hardness measured under a load of 30 kg (HV30) of between 500 and 1600, preferably between 700 and 1400, depending on the types and percentages of the constituents. Advantageously, it has a hardness greater than 1000 Vickers for trim parts requiring high scratch resistance. It has a K1C toughness of at least 3 MPa.m<1/2>, preferably at least 4.0 MPa.m<1/2>, the toughness being determined on the basis of measurements of the lengths of the cracks at the four ends of the diagonals of the indentation of hardness 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)

For the magnetic properties, the hysteresis curve M(H) was characterized at ambient temperature and by varying the field applied to the samples with a vibrating sample magnetometer (VSM) of the MicroSense EZ9 type. The magnetic susceptibility (¿m) per unit volume of the cermet according to the invention is less than 5×10<-5>, preferably less than or equal to 4×10<-5>

Table 1 below shows several examples of materials of the cermet type with a comparative example without cobalt (sample 01) and two examples according to the invention (samples 02 and 03). In the examples, the ceramic phase is a tungsten carbide phase with a weight percentage of 90%. The metal binder is therefore present in a percentage by weight of 10% with the compositions given in the table.

[0030] The samples were all manufactured by powder metallurgy. The mixtures of powders of different compositions were prepared in a mill in the presence of a solvent. The mixtures were made without adding organic binders. After drying, they were shaped by uniaxial pressure and sintered under argon and at the same temperature. After sintering, the samples were plane polished in order to precisely measure the mechanical properties and the colorimetric indices.

For sample 01, a low hardness value of less than 350 HV30 is obtained. It is attributed to the significant presence of porosity in the sample in the absence of cobalt. Adding cobalt to sample 02 makes it possible to improve the densification during sintering and thereby drastically increase the hardness with a value greater than or equal to 800 HV30. Reducing the cobalt and ruthenium contents in sample 03 makes it possible to reduce the magnetic susceptibility value per unit volume to a value of 1.2×10<-5> with the hysteresis curve visible in figure 2. This makes a cermet of choice for a horological movement component such as a balance wheel. Sample 03 is also well densified with very few porosities having sizes of about 1 micron as shown by the photos taken by optical microscopy and electron microscopy in figure 1 with on the optical microscopy the black dots which are porosities. This results in an increase in hardness with a value reaching 1208 HV30. All the samples according to the invention meet the criteria set for a watch component not exhibiting ferromagnetic properties and no diamagnetic properties, with a toughness greater than 4.0 MPa.m<1/2>, with a hardness greater than 700 HV30 and exhibiting a high metallic luster with an L* value greater than 70.

Table 1

[0032] 01 Comp 87.1 10.0 2.9 - 4.0 × 10<-5> Para 309 4.8 68.6 02 Inv 85.0 10.0 2.5 2.5 3.4 × 10<-5> Para 830 5.4 72.6 03 Inv 89.0 10.0 0.5 0. 5 1.2 × 10<-5> Para 1208 4.8 74.5

Claims (17)

1. Article made of a cermet material comprising by weight between 85 and 94% of a ceramic phase and between 6 and 15% of a metal binder phase, the ceramic phase mainly comprising a tungsten carbide phase and optionally one or more phases of one or more carbides selected from the elements Ti, Zr, Hf, V, Nb, Ta, Cr and Mo, the metal binder comprising Ag, Pd, Ru and Co. 2. Article according to claim 1, characterized in that the phase of the metallic binder is present in a percentage by weight of between 7 and 14% and in that the ceramic phase is present in a percentage by weight of between 86 and 93% . 3. Article according to claim 1 or 2, characterized in that the phase of the metal binder is present in a percentage by weight of between 9 and 11% and in that the ceramic phase is present in a percentage by weight of between 89 and 91%. 4. Article according to one of the preceding claims, characterized in that the carbide phase comprises only tungsten carbide. 5. Article according to one of the preceding claims, characterized in that the phase of the metallic binder consists, apart from the impurities, of Ag, Pd, Ru and Co. 6. Article according to one of the preceding claims, characterized in that the Ag has a content of between 5 and 14%, preferably between 7 and 13.4% and more preferably between 7 and 10% by weight. 7. Article according to one of the preceding claims, characterized in that the Pd has a content of between 0.5 and 4% by weight, preferably between 0.5 and 3% by weight, more preferably between 0.5 and 2%, and even more preferably between 0.5 and 1.5%. 8. Article according to one of the preceding claims, characterized in that the Co and the Ru are each present in a percentage of between 0.02 and 4%, preferably between 0.02 and 3%, more preferably between 0.03 and 2%, even more preferably between 0.03 and 0.5% and even more preferably between 0.03 and 0.4%. 9. Article according to one of the preceding claims, characterized in that it has a Vickers hardness, HV30, of between 500 and 1600, preferably between 700 and 1400. 10. Article according to one of the preceding claims, characterized in that it has a KiC toughness greater than or equal to 3.0 MPa.m1/2, preferably greater than or equal to 4.0 MPa.m1/2. 11. Article according to one of the preceding claims, characterized in that it has, in a CIELAB colorimetric space, an L* component of minimum 60, preferably of minimum 65 and more preferably of minimum 70. 12. Article according to one of the preceding claims, characterized in that the cermet material is non-magnetic with a magnetic susceptibility ¿m per unit volume of less than 5x10-5. 13. Article according to one of the preceding claims, characterized in that it is a horological covering component chosen from the list comprising a case middle, a back, a bezel, a pusher, a bracelet link, a dial, a hand and a dial index. 14. Article according to one of the claims, characterized in that it is a horological component of the movement chosen from the list comprising a toothed wheel, an axis, a pinion, a spring, a bridge, a plate, a screw and a pendulum. 15. Article according to one of the preceding claims, characterized in that it is an axis of the balance. 16. Method for manufacturing an article comprising the following successive steps: a) Making a mixture with a ceramic powder mainly comprising tungsten carbide and a powder of a metal binder consisting, except for the impurities, of silver, palladium, ruthenium and cobalt, b) Forming a blank by giving said mixture the shape of the article, c) Sintering the blank at a temperature of between 950 and 1600°C, preferably between 1100 and 1500°C, for a period of between 15 minutes and 8 hours, preferably between 30 minutes and 4 hours, the method being characterized in that the ceramic powder is present in a percentage by weight of between 85 and 94%, preferably between 86 and 93%, more preferably between 89 and 91% and in that the powder of the metal binder is present in a percentage by weight between 6 and 15%, preferably between 7 and 14%, more preferably between 9 and 11%. 17. Method according to claim 16, characterized in that step b) is carried out by pressing, by injection, by extrusion or by additive manufacturing processes.