TIMEPIECE COMPONENT CONTAINING A HIGH-ENTROPY ALLOY

The present application is a continuation of U.S. Ser. No. 16/331,038, filed Mar. 6, 2019, pending, which is a 371 of PCT application no. PCT/EP2017/069219, filed Jul. 28, 2017, no inactive, and claims priority to European application EP16191867.7, filed Sep. 30, 2016.

The present invention concerns a timepiece component containing a high-entropy alloy, and a method for fabricating such a timepiece component. The invention also concerns the use of a high-entropy alloy for fabricating a timepiece component.

Timepiece components, and especially mainsprings, are subjected to high stresses, particularly during fabrication processes, but also during use.

They must, in particular, offer high mechanical strength and high ductility. However, at present, timepiece components rarely simultaneously offer these antagonistic features.

It is an object of the invention to overcome the drawbacks of the state of the art by proposing a timepiece component offering higher mechanical strength and higher ductility.

To achieve this, there is proposed, according to a first aspect of the invention, a timepiece component containing a high-entropy alloy, the high-entropy alloy containing between 4 and 13 main alloying elements forming a single solid solution, the high-entropy alloy having a concentration of each main alloying element comprised between 1 and 55 at. %. Indeed, such a component has higher mechanical strength and higher ductility than those of the prior art.

Advantageously, the concentration of each main alloying element is comprised between 10 and 55 at. %.

According to different preferred embodiments:

• • the high-entropy alloy may satisfy the following formula: Fe_aMn_bCo_cCr_dwhere a, b, c et d are comprised between 1 and 55 at. %;
  • the high-entropy alloy may have the following formula: Fe₅₀Mn₃₀Co₁₀Cr₁₀;
  • the high-entropy alloy may satisfy the following formula: Fe_80-xMn_xCo₁₀Cr₁₀, where x is comprised between 25 and 79 at. %, and preferably x is comprised between 25 and 45 at. %;
  • the high-entropy alloy may satisfy the following formula: Fe_aMn_bNi_eCo_cCr_dwhere a, b, c, d and e are comprised between 1 and 55 at. %;
  • the high-entropy alloy may satisfy the following formula: Fe₂₀Mn₂₀Ni₂₀Co₂₀Cr₂₀;
  • the high-entropy alloy may satisfy the following formula: Fe₄₀Mn₂₇Ni₂₆Co₅Cr₂;
  • the high-entropy alloy may satisfy the following formula: Ta_aNb_bHf_cZr_dCr_ewhere a, b, c, d and e are comprised between 1 and 55 at. %;
  • the high-entropy alloy may, in particular, satisfy the following formula: Ta₂₀Nb₂₀Hf₂₀Zr₂₀Ti₂₀;
  • the high-entropy alloy may satisfy the following formula: Al_aLi_bMg_cSc_dTi_ewhere a, b, c, d and e are comprised between 1 and 55 at. %;
  • the high-entropy alloy may, in particular, satisfy the following formula: Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀;
  • the high-entropy alloy may satisfy the following formula: Al_aCo_bCr_cCu_dFe_eNi_fwhere a, b, c, d, e and f are comprised between 1 and 55 at. %.
  • the high-entropy alloy may satisfy the following formula: Cr_18.2Fe_18.2Co_18.2Ni_18.2Cu_18.2Al_9.0.

Advantageously, the high-entropy alloy may contain one or more interstitial elements from among the following: C, N, B. These interstitial elements further increase the mechanical strength of the alloy.

Advantageously, the high-entropy alloy may contain one or more structural hardening elements from among the following: Ti, Al, Be, Nb, preferably in a mass concentration comprised between 0.1 and 3%.

According to different embodiments, the timepiece component may be one of the following: a spring, a mainspring, a jumper spring, an impulse pin, a roller, pallets, a staff, a pallet lever, a pallet fork, a wheel, an escape wheel, an arbor, a pinion, an oscillating weight, a winding stem, a crown, a watch case, a bracelet link, a watch bezel, a bracelet clasp.

A second aspect of the invention also concerns the use of a high-entropy alloy for fabricating a timepiece component, the high-entropy alloy containing between 4 and 13 main alloying elements forming a single solid solution, the alloy having a concentration of each main alloying element comprised between 1 and 55 at. %.

FIG. 1 schematically represents a mainspring 1 according to one embodiment of the invention. This mainspring 1 is made of a high-entropy alloy.

In such a high-entropy alloy, the entropy of mixing is high and makes the single phase more thermodynamically stable than the mixing of several phases.

The mainspring is preferably made from the high-entropy alloy described in the publication ‘Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off’, Zhiming Li et al, Nature 534, 227-230 (9 Jun. 2016). This high-entropy alloy has the following formula: Fe_80-xMn_xCo₁₀Cr₁₀. x is preferably comprised between 25 and 79 at. %.

More precisely, according to a first embodiment, the mainspring may be made from a Fe₃₅Mn₄₅Co₁₀Cr₁₀alloy. The mainspring produced in this manner has the advantage of combining high tensile strength and high ductility.

According to a second embodiment, the mainspring may be made from a Fe₄₀Mn₄₀Co₁₀Cr_10.alloy. The spring produced in this manner has the advantage of high tensile strength and high ductility. It also operates according to a TWIP (twinning induced plasticity) mechanism.

According to a third embodiment, the mainspring may be made from a Fe₄₅Mn₃₅Co₁₀Cr_10.alloy. The mainspring produced in this manner has the advantage of having even higher tensile strength and higher ductility. It also operates according to a TRIP (transformation induced plasticity) mechanism.

According to a fourth embodiment, the mainspring can be made from a Fe₅₀Mn₃₀Co₁₀Cr₁₀alloy. The mainspring produced in this manner has the advantage of having even higher tensile strength and higher ductility. It operates according to a TRIP mechanism with the appearance of two phases, FCC and HCP, by a twinning mechanism.

The invention is not limited to fabrication of a mainspring. Indeed, other timepiece components could be fabricated from the high-entropy Fe_80-xMn_xCo₁₀Cr₁₀alloy, such as a spring, a staff, an impulse pin, a balance, an arbor, a roller, pallets, a pallet lever, a pallet fork, an escape wheel, a shaft, a pinion, a an oscillating weight, a winding stem, a crown, a jumper spring, a watch case, a bracelet link, a watch bezel, a bracelet clasp . . . .

FIG. 2 schematically represents the steps of a method for fabricating the mainspring of FIG. 1.

This method includes a first step 101 of fabricating a high-entropy alloy ingot. To do so, the elements are mixed in pure or pre-alloy form, they are then melted, and the mixture is cast to form an ingot.

The method then includes a step 102 of hot forging the ingot.

The method then includes a hot lamination step 103.

The method then includes a cold lamination step 104.

The method then includes a wire drawing step 105.

The method then includes a cold lamination step 106.

Naturally, the invention is not limited to the embodiments described with reference to the Figures and variants could be envisaged without departing from the scope of the invention.

Thus, in the preceding examples, the Fe_80-xMn_xCo₁₀Cr₁₀alloy was used. However, other high-entropy alloys could be used, such as, for example:

• • Fe₂₀Mn₂₀Ni₂₀Co₂₀Cr₂₀,
  • Fe₄₀Mn₂₇Ni₂₆Co₅Cr₂,
  • Ta₂₀Nb₂₀Hf₂₀Zr₂₀Ti₂₀,
  • Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀,
  • Cr_18.2Fe_18.2Co_18.2Ni_18.2Cu_18.2Al_9.0.