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EP-4737599-A1 - ARTICLE MADE OF A BINARY OR TERNARY ALLOY CONSISTING OF TWO OR THREE OF TI, ZR AND HF, AND HAVING A FINE MARTENSITIC CRYSTAL STRUCTURE

EP4737599A1EP 4737599 A1EP4737599 A1EP 4737599A1EP-4737599-A1

Abstract

Disclosed is an article made of an alloy consisting of two or three of Ti, Zr and Hf, along with unavoidable impurities in an amount of up to 0.3 at.%, the alloy having a martensitic crystal structure of fine plates as determined by Scanning Electron Microscopy, SEM, or by electron backscatter diffraction, EBSD, of a metallographic section. Further disclosed is a process for obtaining said article, an article having an adherent dense thick dark oxide layer, and a watch exterior component or watch movement component.

Assignees

  • Rolex S.A.

Dates

Publication Date
20260506
Application Date
20241031

Claims (20)

  1. Article made of an alloy consisting of two or three of Ti, Zr and Hf, along with unavoidable impurities in an amount of up to 0.3 at.%, the alloy having a martensitic crystal structure of fine plates as determined by Scanning Electron Microscopy, SEM, or by electron backscatter diffraction, EBSD, of a metallographic section.
  2. Article of claim 1, wherein the alloy is a) a ternary Ti-Zr-Hf alloy comprising 18.4 at.% to 80 at.% zirconium and 2 at% to 40 at.% hafnium, the balance being titanium, or b) a binary Ti-Hf alloy comprising 25 to less than 100 at.% hafnium, the balance being titanium, or c) a binary Zr-Hf alloy comprising 10 to less than 100 at.% of hafnium, the balance being zirconium, or d) a binary Ti-Zr alloy comprising 18.4 to less than 100 at.% of zirconium, the balance being titanium.
  3. Article according to claim 2a), wherein the amount of Zr in the ternary Ti-Zr-Hf alloy is 78 at.% or less, more preferably 75 at% or less, more preferably 60 at.% or less, even more preferably 50 at.% or less, most preferably 30 at.% or less, and/or 20 at.% or more, more preferably 23 at.% or more, even more preferably 25 at.% or more.
  4. Article according to claim 3, wherein the amount of Zr in the ternary Ti-Zr-Hf alloy is 18.4-78 at.%, more preferably 23-75 at%, even more preferably 23-50 at.%, most preferably 25-30 at.% Zr.
  5. Article according to any of claims 2 a) to 4, wherein the amount of Hf in the ternary Ti-Zr-Hf alloy is 35 at.% or less, more preferably 30 at.% or less, more preferably 25 at.% or less, more preferably 20 at.% or less, more preferably 10 at.% or less, most preferably 7 at.% or less, and/or 3 at.% or more.
  6. Article according to any of claims 2 a) to 5, wherein the amount of Hf in the ternary Ti-Zr-Hf alloy is 2-20 at.%, preferably 2-10 at% Hf, more preferably 3-7 at.% Hf.
  7. Article according to claim 2 b), wherein the amount of Hf in the binary Ti-Hf alloy is 99 at.% or less, 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, and/or 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 80 at.% or more.
  8. Article according to any of claims 2 b) or 7, wherein the amount of Hf in the binary Ti-Hf alloy is 20-80 at.%, more preferably 23-75 at%, even more preferably 23-50 at.%, most preferably 25-30 at.%.
  9. Article according to claim 2 c) wherein the amount of Hf in the binary Zr-Hf alloy is 99 at.% or less, 95 at.% or less, 80 at.% or less, 70 at.% or less, or 50 at.% or less, and/or 10 at.% or more, 30 at.% or more or 50 at.% or more.
  10. Article according to claim 2 c) or 9, wherein the amount of Hf in the binary Zr-Hf alloy is 10 to 60 at% Hf, more preferably 10 to 50 at.% Hf.
  11. Article according to claim 2 d), wherein the amount of Zr in the binary Ti-Zr alloy is 99 at.% or less, preferably 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 and/or 18.4 at.% or more, more preferably 23 at.% or more, even more preferably 25 at.% or more.
  12. Article according to any of claims 2 d) or 11, wherein the amount of Zr in the binary Ti-Zr alloy is 18.4 to 99 at.%, more preferably 18.4 to 80 at.%, preferably 18.4 to 60 at.%, or 20 to 80 at.%, preferably 25 to 60 at.%.
  13. Process for obtaining an article made of an alloy consisting of two or more of Ti, Zr and Hf along with unavoidable impurities in an amount of up to 0.3 at.% according to any of claims 1 to 12, the article optionally having a dark oxide layer, the process comprising the following steps: 1) manufacturing the alloy comprising the desired amounts of two or more of Ti, Zr and Hf and accidental impurities by a usual melting process, 2) forming the alloy to the shape of a pre-form, 3) carrying out a grain refinement treatment through the thickness using no or a small mechanical stress for example heat treatment in an inert atmosphere or oxygen-containing atmosphere and subsequent rapid cooling, 4) forming the pre-form to the desired shape of the article, 5) optionally grinding, fine machining, sandblasting, brushing and/or polishing one or more surfaces of the article either before or after step 3) , 6) optionally oxidizing the surface of the article by carrying out a heat treatment in an oxygen-containing atmosphere at a temperature of 400 to 750 °C, but below the beta-transus temperature depending on the alloy, for an appropriate time, and 7) optionally sandblasting, brushing, satin finishing, matte finishing or polishing the oxidized surface(s), or 1) manufacturing the alloy comprising the desired amounts of two or more of Ti, Zr and Hf and accidental impurities by a usual melting process, 2) forming the alloy to the desired shape of the article, 3) carrying out a grain refinement treatment: a) through the thickness in an inert atmosphere or an oxygen-containing atmosphere by a process using no or a small mechanical stress like heat treatment, and subsequent rapid cooling, or b) using mechanical stress selected from shot peening, ultrasonic shot peening, surface mechanical attrition treatment, microcavitation, surface mechanical attrition treatment, surface rolling, laser shot peening and ultra-fast machining 4) optionally grinding, fine machining, sandblasting, brushing and/or polishing one or more surfaces of the article, either before or after step 3), 5) optionally oxidizing the surface of the article by carrying out a heat treatment in an oxygen-containing atmosphere at a temperature of 400 to 750 °C, but blow the beta-transus temperature depending on the alloy, for an appropriate time, and 6) optionally sandblasting, brushing, satin finishing, matte finishing or polishing the oxidized surface(s).
  14. Process according to claim 13, wherein the grain refinement treatment in step 3) is carried out by a treatment using no mechanical stress.
  15. Process according to any of claims 13 or 14, wherein the grain refinement treatment in step 3) is carried out by heating in an oven to a temperature above the β transus temperature of the alloy for an appropriate time and then quenching with a cooling rate of 100 °C/s or more, preferably 200 °C or more, most preferably 300 °C/s or more.
  16. Process according to any of claims 13 to 15 wherein the grain refinement treatment in step 3) is carried out an oxygen-containg atmosphere, oxygen containing solution, and/or by quenching in water.
  17. Process according to any of claims 13 to 16, wherein the oxidizing heat treatment of the article in step 5) is carried out for 1 to 420 min, preferably 60 to 400 min, more preferably 100 to 400 min, most preferably 180 to 360 min.
  18. Process according to any of claims 13 to 17, wherein the oxygen-containing atmosphere in step 3) and/or 5) is air, pure oxygen gas or oxygen containing environment.
  19. Process according to any of claims 13 to 18, wherein the oxidizing treatment in step 5) is carried out by thermal heating in an oven or by plasma-electrolytic oxidation.
  20. Use of the alloy specified in any of claims 1 to 12 as a material for watch exterior components and/or watch movement components.

Description

The present invention concerns articles made of an alloy consisting of two or three of Ti, Zr and Hf, the alloy having a martensitic crystal structure comprising thin plates. Said structure preferably has fine martensite plates of an average length of 20 µm or less and a thickness of 1.5 µm or less, estimated by SEM or by EBSD of a metallographic section. The article optionally comprises a dark oxide layer. The invention further provides a process for obtaining said article comprising a grain refinement treatment step as essential step. The article of the invention is preferably a watch exterior component or a watch movement component. Prior art Hf alloys JPS59208080A (Toshiba - 1983) mentions a heat treatment of Hf at 370-500°C under water vapor (steam) pressure to develop a decorative layer that is resistant to corrosion and wear (hard), and of blue, gold, or black color. Zr alloys US5037438A (Richards Medical Company - 1989) and EP0410711A1 (Smith & Nephew Inc. - 1989) relate to a thermal oxidation treatment of pure zirconium or zirconium alloys (> about 80%wt Zr with Nb, Ta, or Ti, Y, and additionally Hf). US5037438A discloses commercially available Zirconium alloys such as Zircadyne 702 and 705 and Zircalloy which are suitable for the claimed oxidation treatment. Zircadyne alloys contain 4.5 wt.% of Hf as a maximum corresponding to 2.4 at.%. Zircalloy designates zirconium alloys consisting of more than 90 wt% Zr corresponding to more than 95 at.%, and may contain other metals such as tin (about 1.5 wt%) and Fe, Cr, Ni or Nb (about 2.5 wt%). The oxidized alloy is marketed by Smith & Nephew under the name Oxinium for orthopaedic applications (notably knee and hip prostheses). The treatment consists of an oxidation in air, steam, water, or a salt bath, for example, by a thermal treatment in air at 370-595°C for 6 hours. This treatment produces a bluish-black zirconium oxide layer with good adhesion to the substrate. Ti-Hf binary alloys Ti-Hf binary alloys are known. However, such binary alloys are not known having a hard and black oxide layer and/or a a martensitic crystal structure comprising thin plates. Ti-Hf binary alloys are mainly considered in non-patent bio-medical literature focused on their prosthesis application. The full range of composition has been analysed for biocompatibility with respect to: a) corrosion resistance to body liquids; b) mechanical properties targeted to be close to those of bone tissue. In WO2013137857A2 principles of identifying binary alloys having stable nanocrystalline structure are disclosed based on thermodynamic parameters. Among many such alloys listed, a Ti-Hf system is especially claimed. However, no experimental preparation of Ti-Hf nanocrystalline alloy was provided. No composition details are disclosed, and no oxidation treatment is mentioned. In the article "Development of hafnium metal and titanium-hafnium alloys having apatite-forming ability by chemical surface modification", J. Biomed. Mat. Res.: Part B - Appl. Biomat. 106, p. 2519-2523, 2018, T. Myazaki et al. investigated the bone-bonding ability of Ti-xHf, x=20%, 40%, 60%, 80% and 100%at, alloys. The pure metals or the alloys were treated with NaOH and heat. It was found that anatase, sodium titanate, hafnium titanate, apatite or hafnium oxide, respectively, are formed on the surface of the alloys depending on the Hf content. In the article "Multiple-species ion beams from titanium-hafnium alloy cathodes in vacuum arc plasmas", J. Appl. Phys. 73, 7184-7187, 1993, J. Sasaki et al. have studied in detail experimentally the system Ti-Hf as a cathode sputtering target, covering the entire compositional range. In particular, a plasma produced by the metal vapor vacuum arc, for the case when the cathode material is a solid solution TiHf alloy of variable composition ratio, was studied. In the article "Sputtered Hf-Ti nanostructures: A segregation and high-temperature stability study", Acta Materialia 108, p. 8-16, 2016, M. Polyakov et al. investigated preparation of Hf-Ti nanostructured alloy by sputtering. They found that upon annealing at 800 °C for 96 h, the Hf-23Ti (%at) alloy shows segregation of Hf and Ti at the nanoscale even though the bulk Hf-Ti phase diagram predicts a homogeneous solid solution. Zirconium-Hafnium binary alloys In general, Zr-Hf binary alloys are also known, but not with a hard and black oxide layer and/or a a martensitic crystal structure comprising thin plates. US3373017A discloses coins made of Zr-xHf, x = 8.5 - 20 %wt, alloy as a replacement of silver and as a counterfeiter measure. In JPH04318137A corrosion-resistant binary alloys for nuclear materials processing are disclosed which comprise 1-50%wt of Hf with the balance comprising one or more selected from the group consisting of Ti, Zr, Nb and Ta. EP0570308A1 discloses a process for preparation of Nb-Ti and Hf-Zr ingots with a particular crystalline structure by co-electrodeposition of the metals in a molten salt bath. The e