Polished titanium alloy watch parts

Abstract

1. A watch or jewelry part comprising at least a portion made of a titanium alloy, one of the surfaces of which is polished.

Description

[Technical field]

[0001] The present invention relates to a watch or jewellery part comprising at least a part based on an alloy of titanium. The invention also relates to a watch comprising such a watch part. The invention finally relates to a method for producing such a watch or jewellery part. [Background technology]

[0002] The choice of material, especially of a metal or metal alloy, is very important in the design of a watch component. Indeed, the metal or metal alloy must achieve the best possible compromise between a number of constraints, including, for example: - An attractive appearance with no visible defects. For this reason, precious metals are often chosen, as they have a very fine surface finish to make them attractive. - Certain mechanical properties, in particular high resistivity and good formability, such as good resistance to fatigue and excellent resistance to corrosion. In addition, it is desirable to obtain a sufficient hardness in order to minimize the risk of deterioration of the surface condition over time. - A low density is beneficial as it minimises the overall weight of the watch.

[0003] Among the alloys that meet these constraints, titanium alloys have attracted attention because they have a much lower density than other alloys, especially steel, while having mechanical properties of global interest. However, the titanium alloys used have the disadvantage that they are inherently only mediocre in terms of polishing, which results in irregular surface conditions with defects. To prevent the existence of polishing defects on existing titanium alloy surfaces, satin or sandblasted finishes are usually applied, which limits the surface appearance that the parts can have. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] M. Morinaga, "The molecular orbital approach and its application to biomedical titanium alloy design", Titanium in Medical and Dental Applications, edited by FH Froes and M. Quian, Woodhead Publishing, 2018. Summary of the Invention [Problem to be solved by the invention]

[0005] One aim of the present invention is to define a solution that allows a wider use of titanium alloys in watch or jewellery parts, without being limited to the possibilities defined by the prior art. [Means for solving the problem]

[0006] The invention is therefore based on a watch or jewellery piece comprising at least a portion made of a titanium alloy, one of the surfaces of said titanium alloy being polished.

[0007] The invention is more particularly defined in the claims.

[0008] The objects, features and advantages of the present invention will be explained in detail in the non-limiting description of one embodiment given with reference to the accompanying drawings. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 illustrates a first view of the surface of a titanium alloy part obtained by polishing a prior art titanium alloy. [Diagram 2] FIG. 2 illustrates a second view of the surface of a titanium alloy part obtained by polishing another prior art titanium alloy. [Diagram 3]FIG. 3 shows a schematic diagram of the steps of a method for manufacturing a titanium alloy part according to one embodiment of the present invention. [Figure 4] FIG. 4 shows a schematic of the first two steps of a method for manufacturing a titanium alloy part according to a preferred embodiment of the present invention. [Diagram 5] FIG. 5 shows a schematic diagram of the last two steps of a method for manufacturing a titanium alloy part according to a preferred embodiment of the present invention. [Figure 6] FIG. 6 shows an example of a mechanical spectroscopy measurement used in this embodiment of the invention. [Figure 7] FIG. 7 shows a diagram of the surface of a titanium alloy part obtained by polishing the titanium alloy according to the present invention. [Figure 8] FIG. 8 shows measurements of HV0.2 hardness as a function of annealing time obtained from Ti-5553 titanium alloy samples obtained by a method according to one embodiment of the present invention (steps 1-4) and by an alternative method (steps 1-2+4, excluding step 3). [Figure 9] FIG. 9 shows measurements of roughness Rx according to the normalized parameters Rt, Rz, Ra obtained from a Ti-5553 titanium alloy sample obtained by a method according to one embodiment of the present invention (steps 1-4) and by two alternative methods (steps 1-2+4, excluding step 3, and steps 1-2, excluding steps 3-4, respectively). [Figure 10] FIG. 10 shows the observation results of Ti-4733 titanium alloy obtained by using a transmission electron microscope (TEM) in the method according to one embodiment of the present invention (steps 1 to 4). [Figure 11] FIG. 11 shows the observation results of Ti-4733 titanium alloy obtained using a transmission electron microscope (TEM) using the alternative method (steps 1-2+4). [Figure 12] FIG. 12 shows the results of observation of a Ti-4733 titanium alloy obtained using one embodiment of the present invention (steps 1 to 4) with a transmission electron microscope (SEM). [Figure 13]FIG. 13 shows the results of observation of Ti-4733 titanium alloy obtained using a scanning electron microscope (SEM) using the alternative method (steps 1 to 2+4). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Throughout this specification the expression "alloy-based" is used to refer to any part which contains at least 50% by weight of the alloy in question.

[0011] The present invention relates to a watch or jewellery part at least partly made of or based on a titanium alloy, which extends over at least part of the visible surface of said part. The invention defines a method that makes it possible to obtain a titanium alloy with new properties, which allows to obtain a surface state of attractive aesthetic appearance, and in particular to advantageously obtain a polished surface, theoretically of a quality comparable to that obtained for example with other alloys, in particular with steel.

[0012] According to the present invention, it is known that prior art titanium alloys used in watch applications have a two-phase morphology, including α and β phases. The α phase corresponds to a hexagonal structure and the β phase corresponds to a cubic-centered structure. The mechanical property difference between the two phases causes problems in finishing titanium alloy surfaces that continue to have a β phase granular microstructure that remains visible after polishing attempts, resulting in an "orange peel" appearance, as shown in FIG. 1, and / or abrasives embedded in the ductile β phase that cause scratches and defects, as shown in FIG. 2. FIGS. 1, 2, and 7 were obtained by imaging the reflection of a pattern on a titanium alloy surface, including black and white areas, making it possible to show polishing defects.

[0013] For this reason, it is currently impossible to obtain a polished finish on the surface of titanium alloys that is satisfactory in terms of the high demands of watches and jewelry. This difficulty is particularly evident on enlarged surfaces (e.g. the surfaces of small watch cases, bracelet link parts, or clasps). This limits the application of titanium alloys to satin-finished or sandblasted surfaces. As a result, there is currently no way to polish the surface of a titanium alloy watch or jewelry part, and no efficient manufacturing method for carrying out the finishing of a watch or jewelry part that includes a polishing step. For this reason, there are no watches that have this kind of polished titanium alloy surface on most, or even all, of the visible surface. This places a severe restriction on the use of titanium alloys in watches and jewelry.

[0014] To this end, the invention is based, inter alia, on a method for manufacturing all or part of a titanium alloy or titanium alloy-based part, which makes it possible to use a step of polishing the titanium alloy or titanium alloy-based surface of the part in a manner compatible with the high demands of watches and jewellery.

[0015] In one embodiment of the present invention, the manufacturing method is based on a thermomechanical process, which includes the following steps, as shown diagrammatically in FIG. - heat treatment of the titanium alloy at a temperature above the α to β phase transformation temperature Tβ, followed by cooling, to obtain a structure containing essentially only β phase particles (step 1, homogenization); - a series of deformation cycles, in particular cold deformation, or at least one deformation cycle, and a recrystallization heat treatment (step 2) at a temperature slightly above the α to β phase transformation temperature in order to reduce the size of the β phase grains while maintaining a structure comprising substantially only β phase grains, - nucleation or precipitation of the metastable ω-phase by heat treatment at low temperatures (step 3), - Precipitation of the α phase (step 4) by heat treatment at an intermediate temperature, higher than the low temperature of nucleation of the ω phase and lower than the α to β phase transition temperature, to obtain the growth (or precipitation) of the α phase, which hardens the titanium alloy. In other words, the nucleation of the ω phase serves as a nucleation supply for the precipitation of the α phase.

[0016] FIG. 4 shows diagrammatically the implementation of the first two steps of the method according to one particularly advantageous embodiment.

[0017] The first, heat treatment step is advantageously carried out at a temperature between 0 and 100°C, preferably between 10 and 50°C, higher than the α to β phase transition temperature Tβ, and preferably under a protective atmosphere. This first step makes it possible to obtain a microstructure of the titanium alloy entirely composed of the β phase. The cooling by quenching TR makes it possible to fix the β phase at ambient temperature. The treatment time t is relatively short, ideally less than 30 minutes, in order to limit the growth of the grains of the β phase and to obtain a minimum grain size. This step also makes it possible to homogenize the titanium alloy.

[0018] In other words, this first homogenization step makes it possible to break down any alpha phase that may be present in the material. Rapid cooling from the full beta structure makes it possible to fix this structure at ambient temperature in alloys that do not form martensite phases. The full beta structure is sufficiently ductile to carry out a subsequent deformation step that allows recrystallization.

[0019] In this embodiment, the second step of the sequence of deformation cycles comprises a sequence of cold deformation cycles D and recrystallization heat treatment RX. The objective of this step is to obtain a microstructure with a minimum grain size that still contains a maximum of β phase, ideally 100%, and a minimum of α phase, ideally no α phase. In fact, it is very difficult to deform a material in the presence of α phase, which is the hardest and induces cracks during deformation. For this reason, it is very difficult to reduce the size of β phase grains in the presence of α phase. The selected approach overcomes this difficulty by working on an alloy that is entirely composed of β phase. Of course, the method may also be carried out in the presence of a small amount of α phase, preferably less than 10% by volume. The heat treatment advantageously involves briefly exposing the titanium alloy to a temperature slightly higher than Tβ, followed by an immediate quench TR. This temperature may be greater than or equal to Tβ and less than or equal to Tβ+20°C. The duration is preferably greater than or equal to 3 minutes and less than or equal to 10 minutes for typical dimensions of external watch parts, but must be adapted to suit the dimensions of the part to be treated. To purify the particles, it is possible to carry out several cycles in succession. Alternatively, a single cycle is sufficient. Between 2 and 10 cycles, or even between 2 and 5 cycles, are advantageously carried out.

[0020] In the second step, the deformation of the titanium alloy part introduces dislocations in the alloy that induce recrystallization in the form of finer grains during heat treatment. Cold deformation, such as rolling at ambient temperature or cold forging, is beneficial for the deformation. These cold deformation methods are advantageous because they are easier to control. Nevertheless, it is also possible to use hot deformation methods, such as forging or uniaxial deformation at high temperatures. In summary, the function of the second step is to reduce the microstructure, more precisely the size of the β phase grains, as much as possible.

[0021] FIG. 5 illustrates diagrammatically the last two steps of the method according to one particularly advantageous embodiment.

[0022] The third step of ω-phase nucleation advantageously comprises a heat treatment Tω at a temperature between 150° C. and 350° C. for less than 4 hours, in particular between 250° C. and 330° C. for 2 hours and 4 hours. This low-temperature heat treatment step causes the nucleation of the metastable ω-phase, which appears homogeneously in the titanium alloy. This benefit results from the fact that the ω-phase serves as a seeding site for the future growth of the α-phase.

[0023] In fact, the fourth step of precipitation of the α phase comprises a heat treatment Tα at a temperature between 350° C. and 650° C. for a period between 1 and 3 hours, or even between 500° C. and 600° C. for a period between 1 and 3 hours. This step makes it possible for the final α phase to appear in the titanium alloy. The growth (precipitation) of this α phase by seeding with the ω phase has the advantage of obtaining a homogeneous and fine distribution of the α phase in the alloy (ideally on the scale of less than one micron, and even between 1 and 10 μm in its largest dimension). For this reason, the structure obtained is advantageously not a lamellar structure. Moreover, precipitation at the grain boundaries, even if it occurs, does not constitute the majority of the α phase.

[0024] It should be noted that the third step has been described as a separate, independent step, alternatively, the third step may be included in the increase in temperature in the fourth step, i.e., may correspond to a sub-step of the fourth step.

[0025] The above-mentioned methods make it possible to obtain an alloy that optimally combines the two phases α and β, each of which provides advantages to the alloy without the drawbacks of the prior art.

[0026] In fact, the α phase allows alloys that are too soft with the β phase alone to achieve a sufficient hardness. For this reason, a good distribution of the α phase and its nanometric size favors obtaining an optimal hardness of the alloy. A minimum hardness is important, since if the material is too soft, a polishing step can be carried out that would degrade the surface. Hardness, of course, favors maintaining the quality of the surface over time. To illustrate these properties, FIG. 8 illustrates an example of HV0.2 hardness measurements obtained for samples of Ti-5553 titanium alloy obtained with the method according to one embodiment of the invention (steps 1-4) and with the alternative method (steps 1-2, 4, excluding step 3) as a function of the annealing time t at a temperature of 550° C. in step 4. For the same annealing time, a significant difference of more than 50 HV occurred between the samples according to this embodiment of the invention and those without step 3 of the method according to this embodiment of the invention. Generally speaking, the precipitation of very fine α phase induced by the method according to the invention allows to increase the typical hardness by 50 HV with respect to the alternative method. Thus, the very fine precipitation of the α phase induced by the method according to the invention makes it possible to increase the hardness to more than 450 HV, even to more than 500 HV, depending on the titanium alloy concerned and on the hardness obtained by the alternative method. By way of comparison, a titanium alloy without α phase has a hardness lower than 300 HV. By way of example, a measurement carried out on a sample, not shown, obtained using the alternative method of steps 1-2 only, corresponding to a sample quenched from the β phase and without the formation of the α phase, shows a hardness of 291 HV0.2. A titanium alloy of the prior art, containing two phases, α and β, has a hardness lower than 400 HV. The homogeneous distribution of the particles of the α phase also makes it possible to prevent the carbide particles used for polishing from being embedded in the alloy and degrading the surface, as shown in FIG. 2. The proportion of the α phase is advantageously between 35% and 55% by volume, or even between 35% and 65% by volume.

[0027] The β phase is decisive for the reflectivity of the surface. Larger dimensions of the β phase grains may have different reflectivities, which may, for example, mar the appearance of the surface obtained. In fact, if the β phase grains are too large, they form irregularities on the surface that are visible to the naked eye during the step of polishing the surface. The method makes it possible to minimize the dimensions of the β phase grains. Furthermore, the method makes it possible to homogenize the distribution of the α phase within the β phase grains.

[0028] Finally, the resulting titanium alloy structure allows for the formation of a high quality polished surface using conventional polishing techniques, as shown in FIG.

[0029] As mentioned above, the various steps of the method are carried out under specific temperature conditions selected to control the structure of the titanium alloy. It should be noted that these temperature values ​​depend on the composition of the titanium alloy used. Therefore, it is not optimal to pre-specify fixed temperature values, and it is advantageous to select the optimal temperature for each alloy in order to carry out the method according to the embodiment in an optimal manner.

[0030] The method according to this embodiment of the invention therefore comprises one or more sub-steps of determining the optimized temperatures to be considered, in particular the transition temperatures such as seeding of the ω and α phases, and the recrystallization temperatures.

[0031] For this reason, an advantageous embodiment is based on the use of mechanical spectroscopy or internal friction. The measurement of internal friction makes it possible to measure the energy dissipation associated with the migration of defects, such as dislocations, grain boundaries or localized defects in the microstructure. If the mobility of such defects is temperature dependent, it is possible to detect the temperature at which they start to migrate in the alloy. Assuming that both nucleation and recrystallization phases require a microstructural transformation, mechanical spectroscopy can be used to detect the temperature at which both occur. The internal friction curve as a function of temperature makes it possible to identify the phenomena of phase nucleation and / or reconstitution of the alloy, as illustrated by way of example in FIG. 6 for an undeformed sample of Ti-4733 titanium alloy. It should be noted that the various structural changes used in the method according to the embodiment of the invention correspond to various peaks or shoulders of the curve. For example, the curve makes it possible to determine the temperatures allowing the nucleation of the ω-phase and the α-phase, which appear as a shoulder and a peak in FIG. 6, respectively. The position of the various peaks is obtained, for example, by deconvolution. More specifically, the deconvolution of the mechanical spectroscopy measurements may be performed using a constant baseline, the base of which varies based on an exponential function of temperature and an Arrhenius-type function applied to at least one apex, ultimately extracting the temperature. Thus, the measurement of the internal friction phenomenon in the alloy using mechanical spectroscopy allows for a precise definition of the temperatures associated with the various phenomena used in the various steps of the present invention.

[0032] In particular, the nucleation of the ω-phase in titanium alloys can be detected by mechanical spectroscopy, which is very difficult to identify by other methods. Furthermore, mechanical spectroscopy has the advantage that it can be used in real time, allowing for "in situ" observation of the alloy.

[0033] Thus, the research carried out by the inventors shows that mechanical spectroscopy is a suitable technique for determining the transition temperatures of titanium alloys, which, to the best of the inventors' knowledge, has not been considered before. Surprisingly, it is possible to identify the seeding apex in titanium alloys, which allows the practical use of the method according to the invention and allows the titanium alloy parts according to the invention to be obtained. More generally, for any titanium alloy having a type α+β microstructure at the temperature of use, it is advantageous to carry out a step of determining the transition and / or recrystallization temperatures of said titanium alloys by mechanical spectroscopy, in particular to determine the temperature of said nucleation of the ω phase, and also of the nucleation of the α phase, and also of the recrystallization temperature. This optimized embodiment of the method according to the invention makes it possible to obtain a first effect consisting of maximum surface hardness, as illustrated in FIG. 8.

[0034] Alternatively, the nucleation of the ω-phase can be demonstrated by transmission electron microscopy, particularly electron diffraction, which shows the appearance of specific features of the ω-phase crystal structure. Another technique that can be used is the measurement of electrical resistance, which varies slightly as the ω-phase is precipitated. Other detection techniques are more complicated to implement and / or less accurate.

[0035] Finally, the mechanical spectroscopy measurements make it easy to optimize the duration and temperature of the treatment for each given alloy and for each step of the method according to this embodiment of the invention, with the caveat that the duration and temperature values ​​remain comparable for one alloy to another for a particular step of the method.

[0036] The following table illustrates some complete or partial test runs of the method with some titanium alloys. The table shows, firstly, the important effect of the third step of the method. In fact, some tests carried out with the third step removed, gave poor results, more precisely surfaces that no longer react in a satisfactory manner to the polishing step. On the contrary, the use of the invention as described above allows the achievement of very good results, in particular very good polishing.

[0037] [Table 1]

[0038] FIG. 9 represents the Rt, Rz and Ra roughness measurements (Ra values ​​are multiplied by 10 in the bar graphs) obtained from samples of Ti-5553 alloy obtained using the method according to an embodiment of the invention (steps 1-4) and two alternative methods (using only steps 1-2+4, excluding step 3, and using only steps 1-2, excluding steps 3 and 4, respectively). The three roughness parameters considered are measured and calculated according to the ISO 21920 standard, where Rt, referred to as total height: the distance between the deepest and highest points of all the profiles considered; Rz, referred to as maximum height: the average value over all the profiles of the maximum distance between the deepest and highest points; Ra, referred to as the arithmetic mean value; and the length of the profile considered is 0.8 mm. The samples used with the alternative method ("steps 1-2") correspond to samples quenched from the β phase without the formation of α phase and having a low hardness, lower than 300 HV0.2. The samples used in the other alternative method ("Steps 1-2+4") are samples quenched from the β phase and then subjected to a high temperature annealing at 550°C, resulting in the precipitation of the α phase in the β phase grains at the grain boundaries, and show a clear increase in hardness. The samples according to the invention ("Steps 1-4") are samples quenched from the β phase and then subjected to a first annealing at a moderate temperature of 290°C to precipitate the ω phase and a second annealing at a high temperature of 550°C to form the α phase in the β grains, and show the maximum hardness. For the three roughness parameters considered, the roughness is much lower in the samples according to the invention compared to the samples obtained using the alternative method. Thus, an optimized use of the method according to the invention makes it possible to obtain the second effect of minimal surface roughness.

[0039] More specifically, when the third step of the present invention is omitted, a microstructure is obtained with a maximum height difference of about 100 nm, measured between the various β-phase grains across the polished surface, as shown by the measurement of the roughness parameter Rz (the measurement area is typically 1.5×1.5 cm2 ), so that the polishability is judged by the specialist to be very average, as evident by the visible "orange peel" areas. When the third step is used, the α-phase areas are of very small dimensions and a hardness of 472 HV is achieved. Furthermore, the measurement of the roughness parameter Rz shows that the maximum difference in the average height measured between the various β-phase particles over the polished surface is about 50 nm, which is the height difference obtained without the third step divided by 2, allowing a significant improvement in the polishability of the surface, allowing a particularly satisfactory polished appearance, in particular the absence of the orange peel effect and the absence of embedded abrasive particles.

[0040] Figure 10 shows a selection of the beams diffracted by the α phase. <110> Figure 11 illustrates the observation of a Ti-4733 titanium alloy sample obtained by the method according to the present invention using a dark-vision transmission electron microscopy (TEM) with the sample aligned to the area axis. The sample obtained by the alternative method (steps 1-2+4) in which step 4 was performed at a lower temperature within the recommended range (390°C for 1 hour), as illustrated in Figure 11, shows a very extensive growth of alpha grains in a given preferred direction with a very non-uniform distribution. Thus, when the alpha seeding and growth heat treatment is performed in a single step, the alpha phase becomes very non-uniform and very elongated grains with a length of more than 500 nm in the largest dimension, as shown in Figure 11. The sample according to the present invention (steps 1-4) with a step of omega seeding at 240°C for 1 hour before annealing at 390°C for 1 hour in step 4 shows very fine alpha phase grains distributed in a homogeneous manner. It should be noted that the TEM observation made after step 3 but before step 4 shows the presence of the omega phase but not the alpha phase.

[0041] FIG. 12 illustrates the observation of a Ti-4733 titanium alloy sample obtained with the method according to the invention using a scanning electron microscope (SEM). The sample obtained with the alternative method (steps 1-2+4), in which step 4 is performed at a temperature of 600° C., shown in FIG. 13, again shows a very extensive growth of α particles with a very non-homogeneous distribution. This sample can be seen as a logical outgrowth of the sample of FIG. 11, since the high temperature of step 4 favors the growth of the α phase. The sample according to the invention (steps 1-4), which has an ω-phase seeding step at 240° C. for 1 hour before the annealing at 600° C. in step 4, clearly shows finer, homogeneously distributed α-phase particles. These TEM and SEM observations clearly show the importance of the ω-phase (and therefore of step 3 according to the invention) to obtain homogeneously distributed, very fine particles of α-phase.

[0042] The above table shows that some alloys, such as Ti-4733 and Ti-5553, are particularly suitable for obtaining a satisfactory polished appearance. Other alloys, such as Ti-15-3 or Ti-15.9V-3Cr-3.6Al-3Sn, are less suitable.

[0043] The above table also indicates various conditions for certain steps that yield comparable results. Thus, for the third step of the method, conditions (temperature, time) between (300° C., 1 hour) and (350° C., 3 hours) have been successfully tested.

[0044] More generally, the time and temperature parameters of the method are interchangeable to a certain extent, for example applying a higher temperature for a shorter time will give results equivalent to those of applying a lower temperature for a longer time. Thus, a person skilled in the art can find advantageous conditions by selecting a temperature / time pair from the following generalized ranges: To obtain the precipitation of the ω phase (third step of the method), a low temperature between 150° C. and 350° C. for up to 4 hours may be appropriate, and a low temperature between 250° C. and 330° C. for a time between 2 hours and 4 hours may be even more appropriate. To obtain the precipitation of the α phase (fourth step of the method), the temperature / time pair may be fixed between (500° C., 1 hour) and (600° C., 3 hours). Thus, the above conditions are adjustable and are not fixed and absolute limits.

[0045] There are alternatives to the above steps 1 and 2 in order to obtain a microstructure formed with small-sized β-phase grains. In particular, it is possible to carry out forging and hot deformation at temperatures below Tβ or above Tβ. In said alternatives, α-phase grains may already be present and the aim is to refine the β-phase grains as much as possible by deformation. Steps 3 and 4, in particular the ω-phase seeding step 3, remain unchanged. In another alternative, the ω-phase seeding step 3 may include forging and deformation in order to combine mechanical refinement of the grains with the formation of homogeneously distributed, very fine ω-grains.

[0046] Finally, the invention also consists of a method for manufacturing a watch or jewellery part, including a finishing step of polishing the titanium alloy surface of the part.

[0047] The embodiment of the manufacturing method can be carried out with any titanium alloy. However, certain titanium alloys have a more favorable structure than others, which allows optimal results to be obtained, especially in terms of grindability. To enable the method according to the invention, these alloys contain alloying elements that stabilize the beta phase at ambient temperature. By way of example, Ti-5553 or Ti-4733 alloys, or even Ti-5553 or Ti-4733 or Ti-10-2-3 or Beta-C or VT22 or Ti-1-8-5 or Ti-8823 alloys, or even Ti-5553 or Ti-4733 or Ti-10-2-3 or Beta-C or VT22 or Ti-1-8-5 or Ti-8823 or Beta21S or Timetal21S or BetaIII or TMA alloys, give very good results.

[0048] More generally, titanium alloys conforming to the ranges 8≦MoE≦11, and even 8.3≦MoE≦10.0, where MoE is the molybdenum equivalent, appear to be particularly responsive during the practice of the methods according to embodiments of the present invention. The molybdenum equivalent (MoE) is weighted using the formula MoE=1.0 (wt% Mo) + 0.67 (wt% V) + 0.44 (wt% W) + 0.28 (wt% Nb) + 0.22 (wt% Ta) + 2.86 (wt% Fe) + 1.67 (wt% Cr) + 1.25 (wt% Ni) + 1.70 (wt% Mn) + 1.70 (wt% Co) + 0.77 (wt% Cu) + 0.78 (wt% Sn) - 0.17 (wt% Zr) - 1.0 (wt% Al) to take into account the β-phase stabilizing effect of various elements.

[0049] Additionally or alternatively, the titanium alloy may be characterized by the parameters of the bonding order and Bo and Md, which are the average d-orbital energy levels defined by Molinaga (Non-Patent Document 1), respectively, and may be calculated by the following formulas. Md = 2.447 (atomic % of Ti) + 1.961 (atomic % of Mo) + 1.872 (atomic % of V) + 2.072 (atomic % of W) + 2.424 (atomic % of Nb) + 2.531 (atomic % of Ta) + 0.969 (atomic % of Fe) + 1.478 (atomic % of Cr) + 0.724 (atomic % of Ni) + 1.194 (atomic % of Mn) + 0.807 (atomic % of Co) + 0.567 (atomic % of Cu) + 2.100 (atomic % of Sn) + 2.934 (atomic % of Zr) + 2.200 (atomic % of Al); Bo = 2.79 (atomic % of Ti) + 3.063 (atomic % of Mo) + 2.805 (atomic % of V) + 3.125 (atomic % of W) + 3.099 (atomic % of Nb) + 3.144 (atomic % of Ta) + 2.651 (atomic % of Fe) + 2.779 (atomic % of Cr) + 2.412 (atomic % of Ni) + 2.723 (atomic % of Mn) + 2.529 (atomic % of Co) + 2.114 (atomic % of Cu) + 2.283 (atomic % of Sn) + 3.086 (atomic % of Zr) + 2.426 (atomic % of Al). Therefore, titanium alloys that follow the ranges of 2.755 < Bo < 2.810 and 2.33 < Md < 2.44, further 2.758 < Bo < 2.788 and 2.330 < Md < 2.385, and further 2.765 < Bo < 2.775 and 2.36 < Md < 2.38 seem to react particularly well during the implementation of the method according to this embodiment of the present invention.

[0050]

Table 2

[0051] The method according to the invention makes it possible to obtain both high hardness and a fine microstructure, and therefore good polishability and low roughness after polishing. The seeding and growth of the α phase is controlled by two annealing steps (steps 3 and 4), preferably based on a small β-grained microstructure. The size of the β-phase grains is determined by the recrystallization and deformation steps, and the size of the α-phase grains is determined first by seeding of the ω-phase (annealing step 3) and then a second time by additional annealing (step 4). Characterization of the alloy by mechanical spectroscopy makes it possible to identify the temperature and duration of the various annealing steps. The controlled growth of the ω-phase causes the presence of homogeneously distributed ω-phase grains of very small size, without the simultaneous growth or seeding of the α-phase. For this reason, the α-phase nucleated and grown during the subsequent annealing is also extremely fine and homogenized, as the observations in figures 10 and 12 show.

[0052] The invention also relates to a watch or jewellery part comprising at least a part made of or based on a titanium alloy, the surface of which is polished. Indeed, as mentioned above, the invention makes it possible to manufacture such titanium alloys, making them compatible with the high demands of polishing, notably in the watch and jewellery industry.

[0053] The polishing may be defined by the difference between the average heights of the β-phase grains of the polished titanium alloy surface, which may be, for example, less than 150 nm, or even less than 120 nm, or even less than 100 nm. Additionally or alternatively, the polishing may also be defined by a roughness parameter Rz, which corresponds to the maximum distance between the deepest and highest points observed over the entire measured profile, and which may be less than 90 nm, or even less than 80 nm, or even less than 60 nm. Additionally or alternatively, the polishing may be defined by a roughness parameter Ra defined in the above-mentioned standard, the value of which may be less than 15 nm, or even less than 12 nm, or even less than 10 nm. The invention is not limited to a polishing defined by the specific values ​​of roughness.

[0054] In other words, a watch or jewellery part according to the invention may comprise at least a part made of a titanium alloy containing grains, in particular grains of the β phase, the surface of which is polished and the difference between the average height of the grains, in particular of the β phase grains, of the polished surface of the titanium alloy is less than 150 nm and / or the average total roughness Rz of the polished surface is less than 90 nm and / or the arithmetic mean roughness Ra of the polished surface is less than 15 nm; furthermore the difference between the average height of the grains, in particular of the β phase grains, of the polished titanium alloy surface is less than 120 nm and / or the average total roughness Rz of the polished surface is less than 80 nm and / or the arithmetic mean roughness Ra of the polished surface is less than 12 nm; furthermore the difference between the average height of the grains, in particular of the β phase grains, of the polished titanium alloy surface is less than 100 nm and / or the average total roughness Rz of the polished surface is less than 60 nm and / or the arithmetic mean roughness Ra of the polished surface is less than 10 nm.

[0055] The titanium alloy of the part may advantageously be chosen from the list above. More generally, the titanium alloy obtained achieves a very good compromise between all the constraints mentioned at the beginning of this specification. In addition to its polishability, the titanium alloy is hard, strong and light in weight.

[0056] The titanium alloy of the invention advantageously comprises β-phase grains with an average size of less than or equal to 50 μm, or even less than or equal to 45 μm or 40 μm, said size optionally being less than or equal to 25 μm or even more than or equal to 35 μm.

[0057] The titanium alloy advantageously comprises alpha phase homogeneously distributed within the beta phase grains.

[0058] The part also comprises a titanium alloy, advantageously having a hardness of 400HV or more, even 450HV or more, even 470HV or more, which may be 400 to 600HV, even 450HV to 550HV, even 470HV to 500HV.

[0059] The invention applies to a watch or jewellery part entirely made of a titanium alloy as defined above. Alternatively, the part may only comprise a part made of said titanium alloy. Alternatively, the part may be based entirely or partly on said titanium alloy. For example, in one example, said titanium alloy occupies at least 75% of the volume of said part. In another example, the part comprises at least a part including said polished surface entirely made of said titanium alloy and / or having a thickness of 0.1 mm or more, i.e. said part forms a real volume and not just a thin surface coating.

[0060] On the other hand, a timepiece part according to the invention is advantageously an external part of a timepiece, in particular a wristwatch, and in particular a part of the casing of the wristwatch, such as a small watch case, a back, a bezel, a crown or a crown cover. A timepiece part may also be a part of a bracelet or a clasp, such as a link part, an end link part, a central link part, a link, a clasp blade, a clasp cover or a clasp link part.

[0061] The invention also relates to a timepiece, in particular a wristwatch, comprising at least one timepiece part as defined above.

Claims

1. A watch or jewelry component, The aforementioned watch or jewelry component includes at least a portion made of titanium alloy. The surface of the titanium alloy is polished. Watch or jewelry parts.

2. The arithmetic mean roughness Ra of the polished surface is less than 15 nm. A watch or jewelry component according to claim 1.

3. The average total roughness Rz of the polished surface is less than 90 nm. A watch or jewelry component according to claim 1.

4. The titanium alloy contains particles, and the difference in average height between the particles on the polished surface is less than 150 nm. A watch or jewelry component according to claim 1.

5. The titanium alloy conforms to the range 8 ≤ MoE ≤ 11 and / or the ranges 2.755 < Bo < 2.810 and 2.33 < Md < 2.44, where MoE is the molybdenum equivalent, and Bo and Md are the bond order and mean d-orbital energy level, respectively. A watch or jewelry component according to claim 1.

6. The titanium alloy contains β-phase particles with an average size of 50 nm or less. A watch or jewelry component according to claim 1.

7. The titanium alloy comprises β-phase particles and α-phase particles, wherein the α-phase particles are homogeneously distributed within the β-phase particles. A watch or jewelry component according to claim 1.

8. The titanium alloy contains β-phase particles and α-phase particles, and the amount of α-phase particles is 35% by volume or more and 55% by volume or less. A watch or jewelry component according to claim 1.

9. The titanium alloy includes at least one alloy selected from the group consisting of Ti-5553, Ti-4733, Ti-10-2-3, Beta-C, VT22, Ti-1-8-5, Ti-8823, Beta21S, Timetal21S, BetaIII, and TMA alloy. A watch or jewelry component according to claim 1.

10. The aforementioned titanium alloy has a hardness of 400 HV or more. A watch or jewelry component according to claim 1.

11. The titanium alloy accounts for at least 75% of the volume of the watch or jewelry component, and / or The watch or jewelry component includes at least a portion having a thickness of 0.1 mm or more, including the polished surface made entirely of the titanium alloy, and / or The aforementioned watch or jewelry component is made entirely of the aforementioned titanium alloy. A watch or jewelry component according to claim 1.

12. The aforementioned watch or jewelry component is an external part of the watch. A watch or jewelry component according to claim 1.

13. A clock, the clock comprising at least one clock component which is a clock or jewelry component as described in Claim 1.

14. A method for manufacturing watch or jewelry components, A step of processing at least a portion of the titanium alloy of the watch or jewelry component, wherein the processing step includes performing a processing heat treatment step of the titanium alloy, and the heat processing step includes a step of nucleating a metastable ω phase which serves as a nucleation source for the precipitation of the α phase, A method for manufacturing watch or jewelry components.

15. The step of nucleating the metastable ω phase includes heat treatment at a temperature of 150°C to 350°C. The method then includes a step of precipitating the α phase by heat treatment at a temperature higher than the nucleation temperature of the ω phase and lower than the transition temperature from the α phase to the β phase. A method for manufacturing watch or jewelry components according to claim 14.

16. The aforementioned heat treatment process is The process includes a preliminary step of forming a microstructure of the titanium alloy containing β-phase particles having an average size of 50 μm or less. A method for manufacturing watch or jewelry components according to claim 14.

17. The preliminary step of forming the microstructure is: Heat treatment of the titanium alloy at a temperature higher than the transition temperature from the α phase to the β phase, A continuous deformation period or at least one deformation period, and a recrystallization heat treatment at a temperature slightly higher than the transition temperature from the α phase to the β phase of the titanium alloy. The steps include, The method for manufacturing watch or jewelry components according to claim 16.

18. The preliminary step of forming the microstructure is: A heat treatment at a temperature higher than the transition temperature from the α phase to the β phase, in the range of 10 to 100°C higher than the said temperature, in order to obtain a structure containing substantially only β phase particles, followed by cooling. In order to reduce the size of the β-phase particles while maintaining a structure that substantially consists only of β-phase particles, a continuous or at least one deformation period is performed, including a recrystallization heat treatment at a temperature up to 20°C higher than the transition temperature from the α-phase to the β-phase. Subsequently, nucleation of the metastable ω phase occurs by heat treatment at a low temperature of 150°C to 350°C for a shorter period than 4 hours. Subsequently, in order to precipitate the α phase that hardens the titanium alloy, the α phase is precipitated by heat treatment at an intermediate temperature, in the range of 350°C to 650°C, for 1 to 3 hours, which is higher than the nucleation temperature of the ω phase and lower than the transition temperature from the α phase to the β phase. The steps include, A method for manufacturing watch or jewelry components according to claim 17.

19. The titanium alloy conforms to the range 8 ≤ MoE ≤ 11 and / or the ranges 2.755 < Bo < 2.810 and 2.33 < Md < 2.44, where MoE is the molybdenum equivalent, and Bo and Md are the bond order and mean d-orbital energy level, respectively. A method for manufacturing watch or jewelry components according to claim 14.

20. A step of determining the transition temperature and / or recrystallization temperature of the titanium alloy by mechanical spectroscopy. A method for manufacturing watch or jewelry components according to claim 14.

21. All of the cooling substeps of the aforementioned heat treatment are carried out by rapid cooling. A method for manufacturing watch or jewelry components according to claim 14.

22. The method includes a finishing step of polishing the titanium alloy surface of the part to produce a polished surface having a total average roughness Rz less than 90 μm and / or an arithmetic mean roughness Ra less than 15 μm. A method for manufacturing watch or jewelry components according to claim 14.

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