Articles made of Ti-Hf or Zr-Hf binary alloys with a dark oxide layer

Abstract

Disclosed are articles having a dark surface layer on one or more surfaces, made of a Ti-Hf binary alloy containing 25 at% to 99 at% hafnium, with the remainder being titanium and together unavoidable impurities in an amount of up to 0.3 at% of the final composition, or made of a Zr-Hf binary alloy containing 10 at% to 99 at% hafnium, with the remainder being zirconium and together unavoidable impurities in an amount of up to 0.3 at% of the final composition. Furthermore, disclosed are methods for obtaining such articles by oxidative heat treatment, the use of Ti-Hf or Zr-Hf binary alloys as materials for watch case components or watch movement components, and watch case components or watch movement components that can be obtained by the methods described in the claims.

Description

Technical Field

[0001] The present invention relates to an article made of a Ti-Hf or Zr-Hf binary alloy and having a dark surface layer on one or more surfaces, and a method for obtaining said article, which is preferably a wristwatch exterior component or a wristwatch movement component. Furthermore, the present invention relates to the use of said Ti-Hf or Zr-Hf binary alloy as a material for a wristwatch exterior component or a wristwatch movement component. [Prior Art] <Hf Alloy>

[0002] JP-A-59-208080 (Toshiba - 1983) describes the heat treatment of Hf at 370 to 500 °C under steam pressure for the development of a decorative layer that is corrosion-resistant and wear-resistant (hard) and has a blue, gold or black color. <Zr Alloy>

[0003] U.S. Patent No. 5037438(A) (Richards Medical Company - 1989) and European Patent Application Publication No. 0410711(A1) (Smith and Nephew Inc. - 1989) relate to the thermal oxidation treatment of pure zirconium or zirconium alloys (> about 80 wt% Zr and Nb, Ta, or Ti, Y, and additionally Hf). U.S. Patent No. 5037438(A) discloses commercially available zirconium alloys such as Zircadyne® 702 and 705 and Zircaloy that are suitable for the oxidation treatment described in the claims. Zircadyne alloys contain up to 4.5 wt% Hf. Zircaloy refers to a zirconium alloy consisting of more than 90% Zr, and may also contain tin (about 1.5%) and other metals such as Fe, Cr, Ni, or Nb. This oxide alloy is sold by Smith & Nephew under the name Oxinium® for orthopedic applications (particularly artificial knee and hip joints). Its treatment consists of oxidation in air, steam, water, or a salt bath, for example, oxidation by heat treatment in air at 370-595°C for 6 hours. This treatment produces a bluish-black zirconium oxide layer with excellent adhesion to the substrate. <Titanium-hafnium binary alloy> Ti-Hf binary alloys are known. However, no such binary alloy with a hard, black oxide layer is known.

[0004] Ti-Hf binary alloys have been studied primarily in biomedical non-patent literature focusing on their prosthetic applications. For a wide variety of compositions, biocompatibility has been analyzed in terms of a) corrosion resistance to bodily fluids and b) mechanical properties aimed at mimicking bone tissue.

[0005] International Publication No. 2013 / 137857(A2), filed by MIT on March 12, 2012, discloses a principle for identifying binary alloys with stable nanocrystalline structures based on thermodynamic parameters. Among the numerous such alloys described, the Ti-Hf system is the subject of the claims. However, experimental preparation of Ti-Hf nanocrystalline alloys is not provided. Compositional details are not disclosed, nor is oxidation treatment mentioned.

[0006] In the paper "Development of hafnium metal and titanium-hafnium alloys having apatite-forming ability by chemical surface modification", J. Biomed. Mat. Res.: Part B - Appl. Biomat. (USA), 2018, Vol. 106, pp. 2519-2523, T. Myazaki investigated the bone-forming ability of Ti-xHf (x=20%, 40%, 60%, 80%, and 100%, atomic percentage) alloys. Pure metals or alloys were treated with NaOH and heat. It was found that anatase, sodium titanate, hafnium titanate, apatite, or hafnium oxide were formed on the alloy surface, depending on the Hf content.

[0007] In the paper "Multiple-species ion beams from titanium-hafnium alloy cathodes in vacuum arc plasmas", J. Appl. Phys., (USA), 1993, Vol. 73, pp. 7184-7187, J. Sasaki et al. experimentally studied the Ti-Hf system in detail as a target for cathode sputtering, covering the entire composition range. In particular, they have studied experiments using cathodes based on TiHf solid solutions of various chemical compositions for plasmas generated by metal vapor vacuum arcs.

[0008] In the paper "Sputtered Hf-Ti nanostructures: A segregation and high-temperature stability study," Acta Materialia, (Netherlands), 2016, Vol. 108, pp. 8-16, M. Polyakov et al. investigated the preparation of Hf-Ti nanostructured alloys by sputtering. They found that when annealed at 800°C for 96 hours, the Hf-23Ti (at%) alloy exhibits segregation of Hf and Ti at the nanoscale, despite the phase diagram of bulk Hf-Ti predicting a homogeneous solid solution. <Zirconium-hafnium binary alloy>

[0009] While Zr-Hf binary alloys are generally known, they do not possess a hard, black oxide layer. U.S. Patent No. 3,373,017(A) discloses coins made of a Zr-xHf (x=8.5-20 wt%) alloy as a silver substitute and anti-counterfeiting measure.

[0010] Japanese Patent Publication No. 04-318137(A) discloses a corrosion-resistant binary alloy for nuclear material processing, comprising 1 to 50% by weight of Hf, with the remainder being one or more metals selected from the group consisting of Ti, Zr, Nb, and Ta.

[0011] European Patent Application Publication No. 0570308(A1) discloses a method for preparing Nb-Ti and Hf-Zr ingots with specific crystalline structures by co-electrodeposition of metals in a molten salt bath. An example of Zr-66.2Hf (wt%) production is provided.

[0012] Japanese Patent Publication No. 2013-054037(A) discloses reactor components made from a zirconium-hafnium alloy. The use of a Zr-Hf binary alloy is the subject of the claims, but its composition is not described in detail. Rather, it describes alloys with added Nb, Fe, Cr, Sn, and Ni.

[0013] Chinese Patent Application Publication No. 112195369(A) discloses a corrosion- and neutron-resistant Zr-xHf (x = 49-51 wt%) binary alloy and a method for manufacturing components from the alloy.

[0014] In the paper "Interdiffusion behaviors and mechanical properties of Zr-X (X = Nb, Ta, Hf) binary systems", J. Alloys Compds. (Netherlands), 2022, p.164910, J. Wang et al. studied the diffusion behavior of Zr-Hf alloys for applications in nuclear power, aerospace, and prosthetics among several zirconium binary alloys. They further measured the hardness of the above alloys by nanoindentation and found that it was approximately 4 GPa up to about 20 at% Hf and then gradually increased to about 6 GPa at 28 at%.

[0015] In the paper "The Hf-Zr (Hafnium-Zirconium) System", Bull. Alloy Phase Diagrams, (USA), 1982, p.29, Abriata et al. presented the phase diagram of the Hf-Zr system based on a literature review. They specified that the two elements are completely miscible. [Description of Technical Problems]

[0016] The inventors have previously developed a Ti-Zr-Hf ternary alloy, an article comprising a dark-colored oxide layer made from the alloy, and a method for obtaining the article, and disclosed the content in European Patent Application No. 23171553.3 in the name of the applicant of this application. This application claims the priority of the above EP prior application. This ternary alloy contains 18.4 at% - 80 at% Zr and 2 at% - 40 at% Hf, with the balance being titanium. The article has a dark-colored oxide layer and is particularly suitable for wristwatch exterior components and wristwatch movement components due to its excellent mechanical properties.

[0017] The inventors aimed, on the one hand, to develop a variable-density alloy that is paramagnetic and possesses excellent mechanical properties, enabling the realization of a dark, hard layer on the surface in order to achieve a permanent dark exterior. In particular, the inventors desired to develop an alloy having a dark layer on the surface. This material also needed to exhibit paramagnetism.

[0018] None of the binary alloys discussed above possessed the desired properties. The inventors examined the methods developed for the aforementioned ternary alloys and expanded their application to binary alloys to complete the present invention.

[0019] Therefore, the problem to be solved by the present invention is to develop a binary alloy that satisfies the above requirements. Accordingly, the inventors have developed the Ti-Hf and Zr-Hf binary alloys of the present invention that solve this problem.

[0020] The problem was solved by articles made of Ti-Hf or Zr-Hf binary alloys having the dark surface layer described in claim 1. Preferred embodiments, watch parts and / or watch movement parts, methods for obtaining the articles, and the use of the alloys are also expressed in the claims. In particular, the following embodiments are provided by the present invention:

[0021] In the Ti-Hf or Zr-Hf binary alloy according to the present invention, the density of the alloy is 7 to 12 g / cm³. 3 Therefore, the amount of Hf in each binary alloy can be adjusted as desired by appropriately selecting the amount of Hf. The binary alloy of this invention is paramagnetic.

[0022] The present invention provides articles made from the aforementioned binary alloy. The articles have a dark oxide layer on one or more surfaces. For example, the articles of the present invention are exterior components of a wristwatch or movement components of a wristwatch.

[0023] The Vickers hardness HV1 (ISO 6507, HV1) of the Ti-Hf alloy of the present invention increases with Hf content, and the maximum hardness HV1 = 323 reached corresponds to Ti-50Hf. The hardness HV1 of the Zr-Hf alloy of the present invention increases with Hf content, and the maximum value HV1 = 223 reached corresponds to Zr-50Hf.

[0024] The thickness of the dark oxide layer is at least 5 μm, preferably at least 10 μm, and typically 5 to 25 μm, preferably 7 to 20 μm, and more preferably about 15 μm. The thickness of the oxide layer depends on the duration of the heat treatment in air. A thicker oxide layer is obtained with heat treatments longer than 1 hour as shown in the examples of the present invention, but it will be obvious to those skilled in the art that the thickness does not change linearly with time. In fact, this is sqrt(D * It is proportional to t), where t is time and D is the diffusion coefficient of the oxygen species.

[0025] Hardness H of the dark oxide layer IT This measurement, performed by nanoindentation according to ISO 14577-1, 1st edition 2002, "Metallic materials -- Instrumented indentation test for hardness and materials parameters -- Part 1: Test method", shows a hardness of at least 10 GPa. IT , more preferably 13 GPa H IT Even higher.

[0026] Depending on the circumstances, the surface of the dark oxide layer may be partially or completely polished. Polishing can be carried out using conventional techniques. Alternatively, the surface may be partially or completely finished by other commonly used finishing techniques, such as sandblasting, brushing, or satin finishing. The present invention further relates to a method for obtaining an article made of a Ti-Hf and Zr-Hf binary alloy having the aforementioned dark oxide layer, the following steps:

[0027] 1) A step of producing a binary alloy containing desired amounts of Ti and Hf, or Zr and Hf, and incidental impurities, by a conventional melting method which may include several melting and cooling steps, 2) The step of forming the alloy into an article of a desired shape, 3) Depending on the case, a step of grinding, micro-machining, sandblasting, brushing and / or polishing one or more surfaces of the article,

[0028] 4) The step of oxidizing the surface of the article by heat-treating it in an oxygen-containing atmosphere at a temperature of 400 to 750°C, preferably 450 to 700°C, more preferably 450 to 650°C for an appropriate amount of time, 5) Depending on the case, the oxidized surface may be sandblasted, brushed, satin-finished, or polished. This provides a method that includes this.

[0029] The temperature range for heat treatment is selected to optimize the parameters of the hardening process by oxide layer conversion, such as the duration of the process, in relation to the nature of the process. The lower temperature limit is determined because the oxidation reaction will slow down to an unacceptable level due to insufficient reactivity. The upper temperature limit is determined because oxygen diffusion is slower in the β phase and there is a risk of the oxide layer delaminating during the β→α phase transition when cooling. The β-transformation point (β-transus) of the alloy can be determined before performing the heat treatment, for example, by DSC (differential scanning calorimetry). Furthermore, it is desirable to find an optimal temperature that uses the highest possible temperature to accelerate hardening by conversion, and the lowest possible temperature to minimize the cost of heating equipment, its operation, and thermal deformation of the parts to be treated.

[0030] In one embodiment, the oxidation heat treatment is carried out at 400-750°C, preferably 450-700°C, more preferably 450-650°C. Preferably, the oxidation heat treatment of the article is carried out for 1-420 minutes, preferably 60-400 minutes, more preferably 100-400 minutes, and most preferably about 180-360 minutes. The oxygen-containing atmosphere is air, pure oxygen gas, or an oxygen-containing environment, such as a gas mixture of oxygen and an inert gas such as argon. Most preferably, the oxidation heat treatment is carried out by heating in an oven.

[0031] The present invention provides the use of the above-mentioned Ti-Hf or Zr-Hf binary alloy as a material for watch exterior components and / or watch movement components having a dark surface layer on one or more surfaces.

[0032] The watch case components or watch movement components made from the Ti-Hf or Zr-Hf binary alloy of the present invention have a dark surface layer as described above. The watch case components or watch movement components of the present invention can be obtained by the method of the present invention. [Detailed description of the invention]

[0033] The Ti-Hf and Zr-Hf alloys of the present invention were developed by the inventors to obtain materials that can form a hard, thick, adhesive, and dark-colored layer on the surface of watch components. Such alloys are of interest for applications within the movement (e.g., shafts, spindles, or pinions), as well as for cases, bands, and even band pins. This group of alloys is further interesting in terms of density, particularly 7-12 g / cm³. 3 It is possible to adjust within this range, which could potentially increase the degree of freedom in the concept and design of watch components.

[0034] The Ti-Hf and Zr-Hf binary alloys of the present invention are particularly interesting in this respect due to their ease of alloying, the feasibility of manufacturing and finishing watch components, and the formation of oxide layers. The oxide layer formed by conversion during heat treatment is adhesive, thick, hard, and dark in color. Surprisingly, Ti and Hf, and Zr and Hf, each appear to form a complete solid solution in both the high-temperature β phase and the low-temperature α phase, which is extremely advantageous for alloying and has enabled the inventors to produce watch components for watch cases with an impeccable finish.

[0035] The binary alloy of the present invention comprises at least 25 at% to 99 at% Hf, with the remainder being titanium; or comprises at least 10 at% to 99 at% Hf, with the remainder being zirconium, and includes unavoidable impurities in amounts up to a maximum of 0.3 at% of the final composition. The upper limit of the amount of Hf in the Ti-Hf alloy and Zr-Hf alloy is preferably 95 at%, more preferably 80 at%, respectively. Desired amounts of alloying components Ti-Hf and Zr-Hf are defined in the appended claims. Specific examples of the alloys of the present invention are as follows: 25 at% Hf 27 at% Hf 30 at% Hf 50 at HF 60 at HF 75 at HF A Ti-Hf binary alloy containing 80 at% Hf, with the remainder being titanium and, together with other unavoidable impurities, in each case. 10 at% Hf 20 at% Hf 35 at% Hf 50 at HF It contains 75 at% Hf, with the remainder being zirconium and, together with other unavoidable impurities, a Zr-Hf binary alloy. That is the case.

[0036] The alloys of the present invention preferably consist of Ti and Hf, or Zr and Hf, respectively. However, unavoidable impurities can reach up to about 0.3 at% of the final composition. The impurities mainly result from the production of the alloying metals at the start, and are, for example, Fe, N, O, C and / or H.

[0037] In this invention, the amount of metal in the alloy is expressed in at%. The sum of all alloying elements is 100 at%. A Ti-Hf alloy can be expressed as Ti-yHf, where y is at% Hf and the remainder is Ti unless otherwise specified, totaling 100 at%. Similarly, a Zr-Hf alloy can be expressed as Zr-yHf, where y is at% Hf and the remainder is Zr unless otherwise specified, totaling 100 at%. The parameter y is selected according to the amount of Hf as defined in the claims.

[0038] Pure elements are weighed to ensure the precise relative atomic composition of the resulting alloy. Alternatively, the composition of the alloy can be measured using conventional metallurgical methods known in this field. X-ray fluorescence analysis (EDXRF - energy-dispersive X-ray fluorescence analysis, WDXRF - wavelength-dispersive X-ray fluorescence analysis) and emission spectroscopy (Spark OES, ICP-OES / MS - inductively coupled plasma OES / mass spectrometry, LIBS - laser-induced breakdown spectroscopy, SEM / EDX and SEM / WDX - combinations of scanning electron microscopy and energy-dispersive or wavelength-dispersive X-ray spectroscopy) are commonly used methods.

[0039] In this specification, the terms "Ti-based alloy," "Zr-based alloy," and "Hf-based alloy" are used interchangeably because they have equivalent microstructure and properties, and the same applies to the notations "Zr-Hf" and "Hf-Zr," or "Ti-Hf" and "Hf-Ti."

[0040] Ti, Zr, and Hf are transition metals belonging to Group IVb of the periodic table. The atomic weight of Hf is 178.5 g / mol, whereas that of Zr is 91.2 g / mol and that of Ti is 47.9 g / mol. The density of Hf is 13.3 g / cm 3 whereas that of Zr is 6.52 g / cm 3 and that of Ti is 4.5 g / cm 3 Thus, Hf is a heavy and dense element; the alloy can be considered an Hf alloy rather than a Ti alloy when the Hf content exceeds ~10 at%. However, as described above, in this specification, the terms Ti alloy, Zr alloy, and Hf alloy are used interchangeably.

[0041] The density of the binary alloy of the present invention is estimated according to the proportionality rule. The density can be measured using the buoyancy method. The density is preferably 7 - 12 g / cm 3 The density can be adjusted by appropriately selecting the amounts of Ti and Hf, or Zr and Hf, respectively. The density of stainless steel is approximately 8 g / cm 3 Therefore, the alloy of the present invention preferably has a density range wider than that of the stainless steel commonly used for watch components, such as austenitic 904L or 316L stainless steel, and enables the manufacture of lightweight watch components and watches, or watches and watch components having a desired weight.

[0042] The binary alloy of the present invention is obtained by a known method of melting the metal components of the starting alloy as described below. The method can include the melting step and the cooling step several times, for example, at least 5 or 10 times.

[0043] Articles of the present invention are made from the above-mentioned binary alloy by routine processes such as cold forming or hot forming, cutting, milling, casting, drawing, or any other suitable method. Articles of the present invention are preferably watch components, particularly watch case components or watch movement components. Examples of watch case components include watch cases, watch bands and / or their components (e.g., links, pins, clasps, fasteners), crowns, bezels, hands, or any other watch case components. Examples of watch movement components include balance wheels, barrels, bridges, base plates, shafts, pinions, or any other watch movement components. The articles of this invention are paramagnetic and therefore not magnetized by a magnetic field.

[0044] The articles of the present invention exhibit a dark oxide layer on one or more surfaces, preferably all surfaces. The dark oxide layer can be obtained by the method of the present invention disclosed below, which includes a thermal oxidation treatment as an essential step.

[0045] Typically, after forming a dark oxide layer on an article, all surfaces of the article are covered by the oxide layer. However, if desired, the dark oxide layer can be removed from one or more surfaces of the article, for example, by polishing, machining, laser treatment, or other similar treatments. The resulting article has only one or a few surfaces, rather than all, covered by the dark oxide layer.

[0046] The thickness of the dark oxide layer is at least 3 μm, preferably at least 5 μm, preferably at least 10 μm, and typically 3 to 25 μm, preferably 5 to 20 μm, and more preferably about 15 μm. The thickness of the dark oxide layer is measured on a metallographic cross section of the article by scanning electron microscopy or optical microscopy. An example of such a cross section is shown in Figure 3. The layer thickness of up to 25 μm allows for final surface finishing treatments that would not be possible with thinner layers, such as sandblasting, satin finishing, brushing, and / or polishing.

[0047] Articles having a dark oxide layer are black or dark gray in color. These dark colors have little to no bluish tint. (CIELab color space L) * a * The color of the article of the present invention in b (EN ISO 11664-4 "Colorimetry - Part IV: CIE 1976 L * a * b * The color space (measured according to "Colorimetry - Part 4: CIE 1976 L* a* b* Colour space", 2019 edition) is preferably L * <50, |a * |<5, |b * |<10, more comfortable L * <40, |a * |<1, |b * |<1. In the CIELab color system, L * indicates perceptual brightness, a * and b * These represent the inherent colors of human vision: red, green, blue, and yellow. * Black is defined as 0 and white as 100. * The axis relates to the opposite colors red and green, with negative values ​​towards green and positive values ​​towards red. * The axis represents opposite colors, blue and yellow, with negative values ​​associated with blue and positive values ​​associated with yellow.

[0048] The hardness of the oxide layer, measured by nanoindentation according to ISO 14577-1, 1st edition 2002, "Metallic materials - Instrumented indentation hardness tests and material parameters - Part 1: Test methods", is at least 10 GPa H IT Preferably 10 GPa H IT ~13 GPa H IT More preferably, H250 ITTherefore, the surface of the article is extremely hard, making it scratch-resistant and improving its overall mechanical resistance. It should be noted that standard hardness measurement of oxide layers by indentation, such as Vickers hardness according to ISO 6507, 2nd edition 1997 cited above, is quite difficult because the optical contrast of the indentations on the dark oxide surface is very low. To overcome this problem, nanoindentation according to ISO 14577-1, 1st edition 2002 cited above can be used in this invention to measure the hardness of the oxide layer, because this technique does not require optical microscopy to analyze the shape of the indentations and measure their dimensions. The hardness of the bulk alloy material should be distinguished from the hardness of the invert oxide layer on its surface. The invert oxide layer is far harder than the unoxidized bulk alloy.

[0049] The concept of conversion arises from the gradual formation of the oxide layer from the surface inward. An oxygen concentration gradient exists between the oxide layer and the bulk material, where the oxygen concentration reaches nearly zero, and the hardness transitions from the hardness of the oxide layer to the hardness of the bulk alloy. This gradient is typically measurable by GDOES (glow discharge emission spectroscopy) and usually occurs within the range of 100-1000 nm. Because this region is relatively narrow, it is not always resolved using optical or electron microscopy in the metallographic cross-section (due to insufficient contrast or resolution).

[0050] The dark surface oxide layer exhibits very strong adhesion to the alloy core, i.e., it does not peel off. According to ISO 2409, 4th edition 2013, using a type 1a cutting tool, the test result is rated as 1 on a scale of 0 to 5. The oxide layer actually has a dense surface free of pinholes or surface defects. This is determined by the oxide formation process when the oxide layer grows inward between the initial thin natural oxide layer (several nanometers thick) and the bulk alloy, allowing the oxide to grow uniformly at the oxide-metal interface, as illustrated on the right side of Figure 2 (O 2-(Movement mechanism). The present invention provides a method for obtaining the article having a dark oxide layer. In the first step, an alloy having the desired composition is formed by a normal melting process. The amount of metal at the start is selected and weighed according to the desired composition of the alloy. Depending on the circumstances, the starting materials, such as metal chips, sponges, fragments, or slag of each alloying metal, may be cleaned, for example, by ultrasonic cleaning, before melting.

[0051] Next, the elements are melted in an inert atmosphere or under vacuum using any alloy ingot manufacturing method based on melting and solidification, such as vacuum induction melting (VIM) or vacuum arc melting (VAR). Typically, the method involves several melting and cooling steps to ensure homogeneity in order to produce an alloy ingot, which is then solidified in an inert chamber and cooled to room temperature. Subsequently, in steps that may be performed, the alloy is subjected to annealing and quenching to adjust the mechanical properties of the material. The resulting alloy is formed into the desired article shape by conventional methods known in the art, such as hot forming and / or cold forming, cutting, milling, casting, etc.

[0052] One or more surfaces of the resulting article may, if necessary, be subjected to surface treatments such as grinding, micro-machining, sandblasting, and / or polishing.

[0053] Subsequently, in the next step, the surface of the article is oxidized to obtain the desired dark surface layer. In one embodiment, the oxidation of the surface can be carried out by heat treatment in an oxygen-containing atmosphere at a temperature of 400 to 750°C, preferably 450 to 700°C, more preferably 450 to 650°C, for an appropriate time, preferably 1 to 420 minutes, more preferably 30 to 300 minutes, more preferably 40 to 240 minutes, and most preferably 50 to 70 minutes. In another embodiment, the oxidation treatment is carried out for 1 to 30 minutes, preferably 5 to 20 minutes, typically about 10 minutes. The temperature is kept below the transition temperature from the α phase to the β phase.

[0054] Experimental studies have shown that the oxidation time and adhesion of the black surface layer for Ti-Hf and Zr-Hf alloys vary depending on the surface finish. Specifically, sandblasted samples of these alloys required an oxidation time of 1–10 minutes at the maximum temperature before cooling to obtain an oxide layer approximately 5 μm thick without delamination. Longer oxidation times resulted in delamination of the formed oxide layer.

[0055] In contrast, polished or micro-ground samples required more than one hour to achieve the same oxide layer thickness. No peeling was observed in the polished or micro-ground samples. The oxidation heat treatment is preferably carried out by heating in an oven, preferably by an electric heating oven. Alternatively, plasma electrolytic oxidation treatment can be used as the oxidation process. The oxygen-containing atmosphere may be air, pure oxygen gas, or an oxygen-containing environment, such as a mixture of oxygen and an inert gas like argon.

[0056] If desired, the surface of the surface-oxidized article obtained as described above can be subjected to conventional finishing treatments, such as sandblasting, brushing, satin finishing, or polishing.

[0057] The present invention provides the use of the Ti-Hf or Zr-Hf binary alloy as a material for watch exterior components and / or watch movement components as described above. Preferably, and usually, the alloy is formed to obtain watch components and then surface-oxidized as disclosed above. Preferred watch components include watch cases and bands, mechanical watch components such as pins for bands, or watch movement shafts or pinions such as balance wheel shafts.

[0058] Finally, the present invention provides a watch component having a dark-colored surface layer. The alloy of the present invention has applications not only to watch exterior components but also to movable components of a watch, such as band pins and movement pins, such as balance shafts or pinions. Excellent wear resistance is obtained due to the hard oxide layer. Furthermore, the component is paramagnetic. [Brief explanation of the drawing]

[0059] [Figure 1] Binary phase diagrams for Hf-Ti (top diagram) and Zr-Hf (bottom diagram). Phases "rt" and "ht" represent "room temperature" (α phase) and "high temperature" (β phase), respectively. [Figure 2] A diagram showing the hypothetical oxidation mechanisms of Ti-Hf type alloys for different Hf content. [Figure 3] The image shows two samples of Zr-35Hf alloy: A on the left is untreated (polished), and B on the right is polished after oxidation in air. [Figure 4] Scanning electron microscope image of a metallographic cross-section showing the inversion layer of a Zr-75Hf alloy sample oxidized in air at 750°C for 1 hour. <Crystal structure, properties>

[0060] For oxide layers to adhere well to the surface of a metal or alloy, it is desirable to avoid oxidation at temperatures where a phase transition involving modification of the crystal structure may occur, which can cause undesirable stress on the oxide layer and increase the risk of delamination. All three alloying elements, Ti, Zr, and Hf, exhibit a well-known phase transition at temperatures above 800°C from an α-phase with a hexagonal close-packed (hcp) structure to a body-centered cubic (bcc) structure known as the β-phase. <Mechanism of Oxidation> Figure 2 schematically shows the oxidation mechanisms of Ti-Hf alloys with different Hf content.

[0061] For titanium alloys that contain little to no hafnium, the atmosphere / oxide interface is ≪Ti 4+ The diffusion of cations allows for the growth of a porous TiO2 layer during oxidation treatment in air. This layer has poor adhesion and is not very mechanically resistant. In contrast, in Ti-Hf alloys containing a "sufficient" amount of hafnium (approximately >55.4%, >25 at% by mass ratio according to the inventors' experiments), the diffusion of oxygen anions through the oxide layer causes the surface to be converted and condensed into a hard, adhesive oxide. The amount of Hf described in the claims ensures that sufficient hafnium is present in the alloy because it has an oxidation mechanism due to the diffusion of oxygen into the substrate, and because hafnium has a hardening effect, resulting in excellent mechanical properties.

[0062] The oxidation mechanism of titanium alloys is described in the book: C. Leyens and M. Peters, "Titanium and titanium alloys: fundamentals and applications", 2003, (USA), John Wiley and Sons, C. Leyens, "Oxidation and Protection of Titanium Alloys and Titanium Aluminides", p. 187 - 230. However, this reference does not disclose the criteria for defining the oxidation mechanism of Ti alloys according to the Hf content.

[0063] It is the finding of the inventors that the minimum content of Hf for binary alloys of Zr or Ti should be about 10 at% and 25 at% respectively in order to enable the formation of a dark and adherent oxide layer. The oxidation heat treatment temperature in the method of the present invention must be maintained lower than the α→β transition temperature for two reasons: ● Oxygen diffusion is faster in the α - phase than in the β - phase, thus promoting the growth of oxides;

[0064] ● When the α - phase partially transforms to the β - phase during thermal oxidation treatment, changes in the microstructure (e.g., grain growth) occur, and this microstructure becomes visible on the surface of the oxide layer, creating a topography that is incompatible with a uniform aesthetic appearance (orange peel effect). That is.

[0065] In summary, for the Ti - Hf and Zr - Hf alloys of the present invention, the oxidation heat treatment can be carried out on the compositions claimed and at a temperature below the alpha - beta transition. <Ti - Hf alloy> Various Ti - Hf alloy compositions were prepared and characterized by HV1 hardness measurement before oxidation. This measurement was carried out using a Knoop / Vickers hardness tester with a load of 1 kgf in accordance with ISO 6507 - 1, 2nd edition 1997. The following is shown from this measurement (Table 1): ● The hardness changes with the Hf content and reaches a maximum in Ti-50Hf of equiatomic composition.

[0066] ● The hardening effect of Hf has been shown by Imgram for Ti-(5-40 wt%)Hf binary alloys (A. Imgram, D. Williams, and H. Ogden, ”Tensile properties of binary titanium-zirconium and titanium-hafnium alloys,” Journal of the Less Common Metals, (Netherlands), 1962, Vol. 4, p. 217-225).

[0067] [Table 1] <Zr-Hf alloy>[[]]

[0068] Several Zr-Hf binary alloys with different compositions were prepared and characterized by HV1 hardness as described above (Table 2). As is clear from Table 2, the hardness of the Zr-Hf alloy increases with the Hf content, and the maximum value HV1 = 223 reached corresponds to Zr-50Hf.

[0069] [Table 2] <Oxidation heat treatment in air>[[]] Samples of Zr-Hf alloy and Ti-Hf alloy were then subjected to oxidation heat treatment in air for 60 minutes under various temperature conditions shown in Table 3.

[0070] [Table 3] Table 3 shows the layer thickness of the oxide layer for various samples. <Maximum Zr content>[[]]

[0071] Thermal oxidation tests in air conducted by the inventors using 90Zr-10Hf, 80Zr-20Hf, and pure Zr (which is not an alloy and therefore outside the scope of this invention) all demonstrated the possibility of obtaining a condensed dark layer on the surface. The high Zr content has already been verified by the above tests, which were disclosed in the priority application. [Examples] The present invention will be illustrated below by examples. All samples of the alloys listed in Table 3 above were prepared and their characteristics were evaluated using the same method. [Example 1]

[0072] Approximately 8 cm of the desired alloy having the composition shown in Table 3 3 The sample (button-shaped object) was prepared in an inert atmosphere and in a cooled copper crucible using an arc melting furnace equipped with a non-consumable tungsten electrode.

[0073] Pure elements of Ti, Zr, and Hf are obtained from private suppliers in the form of slag, sponge, or chips. The pure elements are weighed and ultrasonically cleaned. These metals are mixed and melted in an arc melting furnace. To homogenize the chemical composition of the button-like material, it is inverted and remelted 10 times. After cooling, the button-like material is then cut into sections 2-4 mm thick. The flat surfaces of the sections are polished by hand using P320 abrasive paper.

[0074] Following the preparation steps described above for the sample alloy, an oxidation heat treatment in air is performed using a furnace at the temperatures shown in Table 3 for 60 minutes. This treatment, at 750°C, produces a dark layer approximately 1.7 μm thick for the Zr-75Hf alloy. The metallographic cross-section of this oxidized sample is shown in Figure 4. Figure 3 shows two Zr-35Hf samples: one in a non-oxidized state (A) and one oxidized in air at 550°C for 1 hour (B). After heat treatment, CIE L as described above * a * b * The color values ​​obtained according to the system are shown in Table 4.

[0075] Table 4

Claims

1. A Ti-Hf binary alloy containing 25 at% to 99 at% hafnium, with the remainder being titanium and, together, unavoidable impurities in amounts up to a maximum of 0.3 at% of the final composition. or A Zr-Hf binary alloy containing 10 at% to 99 at% hafnium, with the remainder being zirconium and, together, unavoidable impurities in amounts up to a maximum of 0.3 at% of the final composition. Articles made of An article having a dark-colored surface layer on one or more surfaces.

2. An article made of a Ti-Hf binary alloy according to claim 1, wherein the amount of Hf is 95 at% or less, 80 at% or less, more preferably 75 at% or less, more preferably 60 at% or less, even more preferably 50 at% or less, or 30 at% or less.

3. An article made of a Ti-Hf binary alloy according to claim 1 or 2, wherein the amount of Hf is 25 at% or more, preferably 27 at% or more, more preferably 30 at% or more, more preferably 50 at% or more, 60 at% or more, 75 at% or more, or 80 at% of Hf.

4. An article made of a Ti-Hf binary alloy according to any one of claims 1 to 3, wherein the amount of Hf is 20 to 80 at%, more preferably 23 to 75 at%, even more preferably 23 to 50 at%, and most preferably 25 to 30 at%.

5. An article made of a Zr-Hf binary alloy according to claim 1, wherein the amount of Hf is 99 at% or less, 95 at% or less, 80 at% or less, 70 at% or less, or 50 at% or less.

6. An article made of a Zr-Hf binary alloy according to any one of claims 1 or 5, wherein the amount of Hf is 20 at% or more, 30 at% or more, or 50 at% or more.

7. An article made of a Zr-Hf binary alloy according to any one of claims 1, 5, or 6, wherein the amount of Hf is 10 to 60 at%, more preferably 10 to 50 at%, of Hf.

8. The density of the alloy is 7–12 g / cm³. ３ An article made of a Ti-Hf or Zr-Hf binary alloy as described in any one of claims 1 to 7.

9. A method for obtaining an article made of a Ti-Hf binary alloy or Zr-Hf binary alloy according to any one of claims 1 to 8, having a dark oxide layer on at least one surface, the method comprising the following steps: 1) A step of producing an alloy containing desired amounts of Ti and Hf, or Zr and Hf, and incidental impurities, by a normal melting process, 2) The step of forming the alloy into a desired article, 3) Depending on the case, a step of grinding, micro-machining, sandblasting, brushing and / or polishing one or more surfaces of the article, 4) The step of oxidizing the surface of the article by heat-treating it in an oxygen-containing atmosphere at a temperature of 400 to 750°C, preferably 450 to 700°C, more preferably 450 to 650°C for an appropriate amount of time, 5) Depending on the case, the oxidized surface may be sandblasted, brushed, satin-finished, or polished. A method that includes this.

10. The method according to claim 9, wherein the heat treatment for oxidation of the article is carried out for 1 to 420 minutes, preferably 60 to 400 minutes, more preferably 100 to 400 minutes, and most preferably 180 to 360 minutes.

11. The method according to any one of claims 9 or 10, wherein the oxygen-containing atmosphere is air, pure oxygen gas, or an environment containing oxygen.

12. The method according to any one of claims 9 to 11, wherein the heat treatment for oxidation is carried out by heating in an oven or by plasma electrolytic oxidation treatment.

13. Use of a Ti-Hf or Zr-Hf binary alloy specified in any one of claims 1 to 8 as a material for watch exterior components and / or watch movement components.

14. An article which is a watch exterior component or a watch movement component, as described in any one of claims 1 to 8, or obtained in accordance with claims 9 to 12.

15. An article obtained according to any one of claims 1 to 8, or according to claims 9 to 12, wherein the thickness of the oxide layer is 5 to 25 μm, preferably 7 to 20 μm.

16. The hardness H of the oxide layer measured by nanoindentation in accordance with ISO 14577, 1st edition 2002, "Metallic materials - Instrumented indentation hardness tests and material parameters - Part 1: Test methods". ＩＴ An article obtained according to any one of claims 1 to 8, 14 or 15, or according to claims 9 to 12, wherein the pressure is at least 10 GPa, preferably 10 GPa to 13 GPa, and more preferably greater than 13 GPa.

17. A watch exterior component or watch movement component that can be obtained by the method described in any one of claims 9 to 12.

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