HIGH ENTROPY ALLOY FOR EXTERNAL COMPONENTS

Abstract

A high entropy alloy with a composition containing between 4 and 9 major alloying elements chosen from the list including Cr, Fe, V, Al, Si, Mn, Mo, Ti and Ni with: 3 major alloying elements which are Cr, Fe and V, each having an atomic concentration include between 20 and 40%, 1 or 2 major alloying elements chosen from Al and Si each having an atomic concentration higher than or equal to 5% with a total concentration of these 2 major alloying elements of less than or equal to 25%, 0, 1, 2, 3 or 4 major alloying elements chosen from Mn, Mo, Ti and Ni, each having an atomic concentration higher than or equal to 5% with a total atomic concentration of these 4 major alloying elements of less than or equal to 35%, the total atomic concentration of the 4 to 9 major alloying elements being higher than or equal to 80%, the remainder being made up of any impurities and/or one or more minor alloying elements, each in an atomic concentration of less than 5%.

Claims

1. A high entropy alloy with a composition containing between 4 and 9 major alloying elements chosen from the list comprising Cr, Fe, V, Al, Si, Mn, Mo, Ti and Ni with: 3 major alloying elements which are Cr, Fe and V, each having an atomic concentration comprised between 20 and 40%, 1 or 2 major alloying elements chosen from Al and Si each having an atomic concentration higher than or equal to 5% with a total concentration of these 2 major alloying elements of less than or equal to 25%, 0, 1, 2, 3 or 4 major alloying elements chosen from Mn, Mo, Ti and Ni, each having an atomic concentration higher than or equal to 5% with a total atomic concentration of these 4 major alloying elements of less than or equal to 35%, the total atomic concentration of all of the 4 to 9 major alloying elements being higher than or equal to 80% and the remainder being made up of impurities and/or one or more minor alloying elements each having an atomic concentration of less than 5%.

2. The alloy according to claim 1, wherein the minor elements are chosen from the list including Si, Mn, Mo, Al, Nb, H, B, C, N, O, Mg, Sc, Ti, Cu, Ni, Zn, Ga, Ge, Sr, Y, Zr, Rh, Pd, Ag, Sn, Sb, Hf, Ta, W, Pt and Au.

3. The alloy according to claim 1, wherein the alloy contains between 0.00.5 and 0.1% atomic concentration of B as minor alloying element.

4. The alloy according to claim 1, wherein the alloy contains between 7 and 15% atomic concentration of Ni as major alloying element.

5. The alloy according to claim 1, wherein the alloy meets one of the following formulae expressed in atomic fractions: Al10Fe25Cr40V25, Al10Fe40Cr25V25, Al10Fe25Cr25V40, Al10Fe30Cr30V30, Al5Cr30Fe30Mo5V30, Al6Cr30Fe30Mo5V29, Al5Cr30Fe30Si5V30, Al5Cr30Fe30Mn5V30, Al13Cr25Fe25Ni12V25 Cr31Fe31V31Si7 or Fe25Cr25V25Al10Ni10Ti5.

6. The alloy according to claim 1, wherein the alloy includes a single-phase, body-centred cubic solid solution.

7. The alloy according to claim 1, wherein the alloy has a two-phase structure including a body-centred cubic matrix and nanoprecipitates.

8. The alloy according to claim 1, wherein the alloy exhibits non-ferromagnetic behaviour and does not exhibit signs of corrosion after being subjected to the salt spray test according to ISO standard 9227.

9. The alloy according to claim 1, wherein the alloy has a hardness HV10 higher than or equal to 400.

10. An external component for horology or jewellery, wherein the component is made from an high entropy alloy with a composition containing between 4 and 9 major alloying elements chosen from the list comprising Cr, Fe, V, Al, Si, Mn, Mo, Ti and Ni with: 3 major alloying elements which are Cr, Fe and V, each having an atomic concentration comprised between 20 and 40%, 1 or 2 major alloying elements chosen from Al and Si each having an atomic concentration higher than or equal to 5% with a total concentration of these 2 major alloying elements of less than or equal to 25%, 0, 1, 2, 3 or 4 major alloying elements chosen from Mn, Mo, Ti and Ni, each having an atomic concentration higher than or equal to 5% with a total atomic concentration of these 4 major alloying elements of less than or equal to 35%.

11. A component according to claim 10, wherein the component is chosen from the list including a case middle, a case back, a bezel, a pusher, a crown, a bracelet link, a clasp, a buckle, a prong, a dial, a hand and a how symbol.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 represents a watch case made with the alloy according to the invention.

[0011] FIG. 2 represents the diffractogram of an Al6Cr30Fe30Mo5V29 alloy after casting and heat treatment for 3 hours at 1300 C. followed by cooling in a furnace with a mean cooling speed of around 100 C./min.

[0012] FIG. 3 represents the hysteresis curve for this same alloy.

DETAILED DESCRIPTION

[0013] The present invention relates to high entropy alloys and to their use for external components for watches or pieces of jewellery, especially for components intended to be in contact with the skin. The external component can be a case middle, a case back, a bezel, a pusher, a crown, a bracelet link, a dial, a hand, a how symbol, a clasp, etc. By way of illustration, a watch case 1 made from the alloy according to the invention is represented in FIG. 1.

[0014] According to the invention, the alloys include between 4 and 9 major alloying elements. Major alloying elements means elements having an atomic concentration higher than or equal to 5%. The alloys include the following 3 major alloying elements: Cr, Fe, V in an atomic concentration comprised between 20 and 40%. They also include 1 or 2 major alloying elements chosen from among Al and Si with a total atomic concentration of these two elements of less than or equal to 25%. They also optionally include one or more major alloying elements chosen from among Mn, Mo, Ti and Ni with a total atomic concentration of these 4 major alloying elements of less than or equal to 35%.

[0015] According to the invention, the total atomic concentration of all the aforecited major alloying elements is greater than or equal to 80%. The remainder may, optionally, contain minor alloying elements selected from the list including Si, Mn, Mo, Al, Nb, H, B, C, N, O, Mg, Sc, Ti, Cu, Ni, Zn, Ga, Ge, Sr, Y, Zr, Rh, Pd, Ag, Sn, Sb, Hf, Ta, W, Pt and Au. Minor alloying elements means elements having an atomic concentration of less than 5%. The remainder can also contain residual impurities arising from the implementation.

[0016] To obtain the alloys according to the invention, any shaping methods can be envisaged. It is possible, in particular, to obtain these alloys by casting, by powder metallurgy processes, by additive manufacturing techniques or by layer deposition technologies. This also includes any thermomechanical treatments (heat treatment, hot deformation, cold deformation) and sintering and hot isostatic pressing steps (HIP).

[0017] After shaping and performance of any thermomechanical treatments, the alloys according to the invention mostly have a body-centred cubic structure (BCC), which may be disordered (structure A2, space group Im3m) or ordered (B2 structure, space group Pm3m). In particular, a single-phase microstructure can be obtained at ambient temperature for alloys according to the invention which contain neither Ni, nor Ti as major alloying elements, nor any minor alloying elements, which promotes corrosion resistance and polishability. Nonetheless, depending on the composition and heat treatments carried out, the alloys according to the invention may have a microstructure with a second phase in the form of precipitates, which, in some cases, can improve mechanical properties (hardness, ductility, resistance to deformation, etc.). When the precipitates are small with sizes that may be nanometric and when the matrix has a virtually unchanged composition, i.e. it has a composition that satisfies the definition of alloys according to the invention (multi-element solid-solution phases), the high polishability, high corrosion resistance and absence of ferromagnetism are maintained. In particular, the addition of Ni or of Ni and Ti is particularly interesting, since this makes it possible to obtain very hardening nanoprecipitates.

[0018] In short, after implementation, the alloys of the invention have the following properties required for external components: non-ferromagnetic behaviour, hardness higher than or equal to 400 HV, high corrosion resistance, especially with no sign of corrosion after the salt spray test according to ISO standard 9227.

[0019] A few examples of alloy compositions which meet all these criteria after fabrication are given in Table 1 below. The alloys were fabricated by arc melting with no other heat treatment. In the table, the atomic fractions have been rounded to the nearest whole number and hardness has been rounded to the nearest ten.

TABLE-US-00001 TABLE 1 Hardness Compositions (at. %) (HV10) Al10Fe25Cr40V25 450 Al10Fe40Cr25V25 410 Al10Fe25Cr25V40 500 Al10Fe30Cr30V30 410 Al5Cr30Fe30Mo5V30 480 Al6Cr30Fe30Mo5V29 480 Al5Cr30Fe30Si5V30 460 Al5Cr30Fe30Mn5V30 410 Al13Cr25Fe25Ni12V25 650 Fe25Cr25V25Al10Ni10Ti5 630 Cr31Fe31V31Si7 500

[0020] It is observed, in particular, that the addition of nickel makes it possible to significantly increase hardness, owing to the formation of nanoprecipitates of NiAl in the body-centred cubic structure matrix.

[0021] After casting and a heat treatment for 3 hours under argon at 1300 C. to homogenise the casting structure, a single phase microstructure is obtained, particularly for alloys containing only major alloying elements without Ni or Ti, such as, for example, for the alloy Al6Cr30Fe30Mo5V29.

[0022] An X ray diffraction analysis (Bragg-Brentano configuration) was performed on this alloy and confirmed that a single phase was present with three lines corresponding to the body-centred cubic structure. This diffractogram is represented in FIG. 2.

[0023] With regard to the magnetic properties of this alloy, a hysteresis curve was measured at ambient temperature with a vibrating sample magnetometer (magnetisation M according to the applied field H). Although the alloy has a relatively high volume susceptibility (4.8 10.sup.3), the alloy exhibits linear behaviour, signature of paramagnetic behaviour, as shown in FIG. 3.

[0024] It is also possible to improve the properties, particularly the mechanical properties, by adding some minor alloying elements while maintaining a major phase that meets the definition of alloys according to the invention. It is, for example, possible to add a small amount of boron as minor alloying element. Adding 0.1 at. % of boron to the alloy Al10Cr30Fe30V30 leaves the hardness unchanged relative to the same alloy without boron (410 HV), however, the addition of boron reduces grain growth after heat treatment and thereby improves ductility and polishability. The addition of interstitial atoms such as C, N and 0 as minor alloying elements also makes it possible to increase hardness.