U.S. patent application number 16/271925 was filed with the patent office on 2019-09-26 for high entropy alloy for external components.
This patent application is currently assigned to The Swatch Group Research and Development Ltd. The applicant listed for this patent is The Swatch Group Research and Development Ltd. Invention is credited to Joel PORRET.
Application Number | 20190292633 16/271925 |
Document ID | / |
Family ID | 61691839 |
Filed Date | 2019-09-26 |
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United States Patent
Application |
20190292633 |
Kind Code |
A1 |
PORRET; Joel |
September 26, 2019 |
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%.
Inventors: |
PORRET; Joel; (Neuchatel,
CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Swatch Group Research and Development Ltd |
Marin |
|
CH |
|
|
Assignee: |
The Swatch Group Research and
Development Ltd
Marin
CH
|
Family ID: |
61691839 |
Appl. No.: |
16/271925 |
Filed: |
February 11, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 45/08 20130101;
C22C 45/008 20130101; C22C 30/00 20130101; C22C 38/24 20130101;
C22C 45/006 20130101; C22C 38/18 20130101 |
International
Class: |
C22C 30/00 20060101
C22C030/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 2018 |
EP |
18162716.7 |
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
FIELD OF THE INVENTION
[0001] The present invention concerns a high entropy alloy and an
external component for a watch or piece of jewellery made from this
alloy.
PRIOR ART
[0002] Various alloys are commonly used nowadays for the
fabrication of external watch components which are components
generally exposed to the external environment that may be in
contact with the skin. These are, for example, austenitic stainless
steels, titanium alloys or precious metals. Indeed, these alloys
have certain important properties for this type of parts, namely
high corrosion resistance, high polishability for aesthetic
purposes, and no ferromagnetism. In addition to these
characteristics, other properties are currently highly sought-after
in horology. These characteristics are high biocompatibility,
especially by reducing or eliminating potential allergens, such as
nickel or cobalt, and a high hardness and scratch resistance.
Alloys that meet all these criteria are rare. Precious metals have
low hardness (<200 HV in annealed condition). Austenitic
stainless steels generally contain nickel and also have limited
hardness (<300 HV in annealed condition). Martensitic stainless
steels are hard (>600 HV) but ferromagnetic. Finally, titanium
alloys, like grade 5 titanium (Ti6Al4V), certainly represent the
best compromise among the properties set out above, but they have a
particular colour and a hardness (around 350 HV for grade 5
titanium) that is not significantly higher than some austenitic
stainless steels, for example. For comparison, amorphous metals,
which are also very advantageous for external components, can have
a hardness of more than 500 HV. However, very specific
implementations are required to obtain amorphous metal components,
which further limits their use as external components.
[0003] In the field of external timepiece components, there
therefore remains a strong interest in obtaining hard, crystalline
ferromagnetic alloys (>400 HV in annealed condition), which are
corrosion resistant and highly polishable. In this context, high
entropy alloys, currently the subject of much research and which
form a new class of alloys, are particularly promising. According
to the initial definition, alloys containing at least 5 major
alloying elements with an atomic fraction of between 5 and 35% were
considered high entropy alloys and elements having an atomic
fraction of less than 5% were considered minor. These days, it is
accepted that alloys containing 4 major alloying elements can be
considered high entropy alloys. As regards thermodynamics, the high
entropy resulting from mixing various major alloying elements
should stabilise solid-solution phases relative to the formation of
potentially embrittling intermetallic phases. Consequently, unique
properties, seldom seen in traditional alloys based on one or two
major alloying elements are obtained. For external timepiece
components, obtaining simple solid-solution phases is very
advantageous, since it promotes high polishability and high
corrosion resistance. Further, the mixture of various elements
produces solid-solution hardening. Among single-phase high entropy
alloys, high hardnesses have therefore already been demonstrated,
particularly for those that have a body-centred cubic structure.
These single-phase, body-centred cubic structure, high entropy
alloys, such as, for example, NbTiVZr, AlNbTiV, Al0.4Hf0.6NbTaTiZr
or Hf0.5Nb0.5Ta0.5Ti1.5Zr, are more specifically intended for high
temperature applications, especially for aeronautics. However, they
contain many elements that are expensive, very reactive or have
high melting temperatures, such as Nb, Zr, Hf, Ta. To facilitate
the implementation of external timepiece components, it is
important to avoid or limit the quantity of these elements, since
high temperature resistance is not a desired property.
SUMMARY OF THE INVENTION
[0004] It is an object of the invention to propose a high entropy
alloy with a composition specifically adapted to the needs of
external components. The present invention more particularly aims
to develop an alloy which, after implementation, has a hardness
higher than or equal to 400 HV, non-ferromagnetic behaviour and
high corrosion resistance.
[0005] To this end, the alloy contains 3 major alloying elements
which are Cr, Fe and V, each having atomic compositions comprised
between 20 and 40%. It also contains Al and/or Si as major alloying
element, which has the effect of eliminating the ferromagnetic
behaviour of the alloy. These elements each have an atomic
concentration higher than or equal to 5% with a total atomic
concentration of Al and Si of less than or equal to 25%.
[0006] The alloy may also optionally contain one or more major
alloying elements chosen from Mn, Mo, Ti and Ni, each in an atomic
concentration higher than or equal to 5% with a total atomic
concentration of all 4 major alloying elements of less than or
equal to 35%. According to the invention, the Ni content is
specifically maintained at a value of less than 20% to avoid,
during implementation and especially during heat treatments, the
formation of undesirable phases which embrittle the material and
reduce corrosion resistance. Some grades are also free of Ni to
ensure high biocompatibility.
[0007] The remainder can be made up of any impurities and/or one or
more minor alloying elements, each in an atomic concentration of
less than 5%.
[0008] Depending on the composition and thermomechanical
treatments, the material obtained after implementation has a
single-phase with a body-centred cubic structure, which promotes
good corrosion resistance and high polishability for a better
surface finish or, in the case of multi-phase alloys, a matrix
(main phase) with a body-centred cubic structure reinforced by
nanoprecipitates. It also has the advantage of having a colour
close to that of austenitic stainless steels.
[0009] Other advantages will appear from the features set out in
the claims, and from the detailed description of the invention
illustrated hereinafter with reference to the annexed drawings,
given as non-limiting examples.
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.degree.
C. followed by cooling in a furnace with a mean cooling speed of
around 100.degree. 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.degree. 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.
* * * * *