U.S. patent application number 16/310855 was filed with the patent office on 2021-07-22 for high entropy alloy doped with boron and method for manufacturing the same.
The applicant listed for this patent is POSTECH ACADEMY-INDUSTRY FOUNDATION. Invention is credited to Jae Wung BAE, Jong Chan HAN, Hyoung Seop KIM, Jae Bok SEOL.
Application Number | 20210222274 16/310855 |
Document ID | / |
Family ID | 1000005533778 |
Filed Date | 2021-07-22 |
United States Patent
Application |
20210222274 |
Kind Code |
A1 |
KIM; Hyoung Seop ; et
al. |
July 22, 2021 |
HIGH ENTROPY ALLOY DOPED WITH BORON AND METHOD FOR MANUFACTURING
THE SAME
Abstract
The present invention introduces a high entropy alloy doped with
boron, comprising four or more metals selected from iron (Fe),
chromium (Cr), nickel (Ni), cobalt (Co), manganese (Mn), molybdenum
(Mo), aluminum (Al) and copper (Cu), and boron (B) which has single
phase FCC structure.
Inventors: |
KIM; Hyoung Seop;
(Pohang-si, KR) ; SEOL; Jae Bok; (Pohang-si,
KR) ; BAE; Jae Wung; (Daegu, KR) ; HAN; Jong
Chan; (Goyang-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POSTECH ACADEMY-INDUSTRY FOUNDATION |
Pohang-si |
|
KR |
|
|
Family ID: |
1000005533778 |
Appl. No.: |
16/310855 |
Filed: |
November 7, 2017 |
PCT Filed: |
November 7, 2017 |
PCT NO: |
PCT/KR2017/012543 |
371 Date: |
December 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 1/10 20130101; C22C
30/02 20130101; C22F 1/00 20130101; C22C 2202/00 20130101 |
International
Class: |
C22C 30/02 20060101
C22C030/02; C22F 1/00 20060101 C22F001/00; C22C 1/10 20060101
C22C001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 8, 2017 |
KR |
10-2017-0115407 |
Claims
1. A high entropy alloy doped with boron, comprising: four or more
metals selected from iron (Fe), chromium (Cr), nickel (Ni), cobalt
(Co), manganese (Mn), molybdenum (Mo), aluminum (Al) and copper
(Cu), and boron (B) and having single phase FCC structure.
2. The high entropy alloy doped with boron of claim 1, wherein the
content of the four or more metals is 5 to 35 at % respectively,
and the content of boron (B) is 3 at % or less (0 is not
included).
3. The high entropy alloy doped with boron of claim 1, wherein the
alloy comprises 18 to 42% of iron (Fe), 18 to 42% of manganese
(Mn), 9 to 22% of chromium (Cr), 9 to 22% of cobalt (Co), 9 to 22%
of nickel (Ni) and 0.001 to 0.01% of boron (B) on the basis of
weight %.
4. The high entropy alloy doped with boron of claim 1, wherein the
alloy comprises 18 to 42% of iron (Fe), 18 to 42% of manganese
(Mn), 9 to 22% of chromium (Cr), 9 to 22% of cobalt (Co) and 0.001
to 0.01% of boron (B) on the basis of weight %.
5. The high entropy alloy doped with boron of claim 3, wherein the
alloy comprises 0.004 to 0.005% of boron (B).
6. The high entropy alloy doped with boron of claim 1, wherein the
alloy comprises boron (B) segregated in grain boundary.
7. The high entropy alloy doped with boron of claim 6, wherein the
maximum concentration of the boron (B) segregated in the grain
boundary is 0.20 at %.
8. The high entropy alloy doped with boron of claim 6, wherein the
boron (B) segregated in the grain boundary is 95% or more of the
total boron (B).
9. The high entropy alloy doped with boron of claim 1, wherein the
average grain size of the alloy is 60 .mu.m or less.
10. The high entropy alloy doped with boron of claim 1, wherein the
yield strength of the alloy is 450 MPa or more.
11. A method for manufacturing a high entropy alloy doped with
boron, comprising: preparing a raw material of four or more metals
selected from iron (Fe), chromium (Cr), nickel (Ni), cobalt (Co),
manganese (Mn), molybdenum (Mo), aluminum (Al) and copper (Cu), and
a raw material of boron (B); dissolving the raw materials to cast
an ingot; cold-rolling the ingot to produce an alloy material; and
annealing the alloy material; wherein the alloy material has a
single phase FCC structure.
12. The method of claim 11, further comprising: homogenizing heat
treating the ingot; and removing oxides generated on the surface of
the ingot; after the step of casting the ingot.
13. The method of claim 11, wherein in the step of annealing the
alloy material, the annealing temperature is 650 to 1100.degree.
C.
14. The method of claim 11, further comprising: forming mechanical
twinned crystal by deformation of the alloy material; after the
step of annealing the alloy material.
15. The high entropy alloy doped with boron of claim 4, wherein the
alloy comprises 0.004 to 0.005% of boron (B).
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for improving the
mechanical properties at room temperature of a high entropy alloy
through boron doping, and a high entropy alloy doped with boron
with improved mechanical properties at room temperature while
maintaining intrinsic properties of the entropy alloy by adding
boron which improves the cohesive strength of grain boundary.
BACKGROUND
[0002] The traditional alloy design, which has been ongoing for a
long time, is designed to a direction to improve the physical
properties of materials by adding a small amount of heteroatoms
based on one or two main metal elements. Commercial alloys such as
steel, nickel alloys, titanium alloys and aluminum alloys are
representative examples.
[0003] However, the newly developed high-entropy alloy (HEA), in
contrast to the existing alloy design, is an alloy consisting of
multi-component main elements that alloy five or more constituent
elements at the composition of atoms having the same or similar
ratio but without a main element. This is a metal material that
forms a single phase structure such as face-centered cubic (FCC) or
body-centered cubic (BCC) without forming an intermetallic compound
or an intermediate phase, by increasing the mixed entropy in the
alloy through the substitutional type properties of the
multiatom.
[0004] These entropy alloys should constitute of a mixture of at
least five elements, and each alloy constituent element should
contain a composition ratio of 5 to 35 at %. If an alloy element
other than the main element is added, the addition amount should be
5 at % or less.
[0005] Among the high entropy alloys designed through the above
definition, the FCC-based high entropy alloy exhibits excellent
mechanical properties, and the Fe--Mn--Cr--Co--Ni-based high
entropy alloy, which has attracted attention as a material
appliable as a structure material in an extreme environment by
having excellent cryogenic properties which have not be seen in
conventional structure materials due to the expression of
mechanical twinned crystal between cryogenic deformations, high
fracture toughness and corrosion resistance.
[0006] However, at room temperature, unlike cryogenic temperatures,
the formation of mechanical twinned crystal is not active so that
it exhibits very low mechanical properties compared to commercial
structure materials. In addition, considering the yield strength,
which is one of important factors in the application of structure
materials, the high entropy alloy also exhibits the low yield
strength which is the limit of FCC-based metals, so that limiting
the application range as structure materials and having a
limitation in replacing conventional commercial materials.
[0007] There have been many studies to solve this problem, and
among them, there is a method of improving the mechanical
properties by adding a trace amount of a heteroatom other than the
main element to the high entropy alloy to form a precipitate in the
material.
[0008] As the content of boron in the
Cu--Co--Ni--Cr--Al.sub.0.5--Fe based high entropy alloy was varied
from 3.5 to 15.4 at %, the amount of boride precipitation was
increased to improve the hardness and compressive yield strength
but it showed a limitation with low ductility and toughness due to
formation of boride.
[0009] Therefore, it is essential to increase the yield strength
and simultaneously to secure excellent mechanical properties at
room temperature while maintaining the properties to be shown by
existing high entropy alloys for application as structure materials
in various fields of high entropy alloys.
CONTENTS OF THE INVENTION
Problem to Solve
[0010] An object of the present invention to provide a high entropy
alloy which realizes a high yield strength and excellent mechanical
properties at room temperature while maintaining the properties
exhibited by the high entropy alloy by adding a trace amount of
boron, which is an interstitial element, to the conventional
FCC-based high entropy alloy.
SUMMARY OF THE INVENTION
[0011] A high entropy alloy doped with boron according to the
present invention, comprises four or more metals selected from iron
(Fe), chromium (Cr), nickel (Ni), cobalt (Co), manganese (Mn),
molybdenum (Mo), aluminum (Al) and copper (Cu), and boron (B) and
has single phase FCC structure.
[0012] The content of the four or more metals may be 5 to 35 at %
respectively, and the content of boron (B) may be 3 at % or less (0
is not included).
[0013] The alloy may comprise 18 to 42% of iron (Fe), 18 to 42% of
manganese (Mn), 9 to 22% of chromium (Cr), 9 to 22% of cobalt (Co),
9 to 22% of nickel (Ni) and 0.001 to 0.01% of boron (B) on the
basis of weight %.
[0014] The alloy may comprise 18 to 42% of iron (Fe), 18 to 42% of
manganese (Mn), 9 to 22% of chromium (Cr), 9 to 22% of cobalt (Co)
and 0.001 to 0.01% of boron (B) on the basis of weight %.
[0015] The alloy may comprise 0.004 to 0.005% of boron (B).
[0016] The alloy may comprise boron (B) segregated in grain
boundary.
[0017] The maximum concentration of the boron (B) segregated in the
grain boundary may be 0.20 at %
[0018] The boron (B) segregated in the grain boundary may be 95% or
more of the total boron (B).
[0019] The average grain size of the alloy may be 60 .mu.m or
less.
[0020] The yield strength of the alloy may be 450 MPa or more.
[0021] A method for manufacturing a high entropy alloy doped with
boron according to the present invention, comprises preparing a raw
material of four or more metals selected from iron (Fe), chromium
(Cr), nickel (Ni), cobalt (Co), manganese (Mn), molybdenum (Mo),
aluminum (Al) and copper (Cu), and a raw material of boron (B);
dissolving the raw materials to cast an ingot; cold-rolling the
ingot to produce an alloy material; and annealing the alloy
material; wherein the alloy material has a single phase FCC
structure.
[0022] The steps of homogenization heat treating the ingot; and
removing oxides generated on the surface of the ingot; after the
step of casting the ingot may be further comprised.
[0023] In the step of annealing the alloy material, the annealing
temperature may be 650 to 1100.degree. C.
[0024] The step of forming mechanical twinned crystal by
deformation of the alloy material; after the step of annealing the
alloy material may be further comprised.
Effects of the Invention
[0025] The high entropy alloy doped with boron according to the
present invention suppresses growth of grain boundary and improves
cohesive strength by adding a trace amount of boron which is an
interstitial element to segregates into a grain boundary.
[0026] In addition, it does not affect the formation of mechanical
twinned crystal, which is the main strengthening mechanism of
FCC-based high entropy alloys, and thus has excellent properties of
high elongation while obtaining high yield strength and tensile
strength.
DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a graph showing changes in average grain size when
annealing is performed for specimens 1 to 7 of Example 1 and
Specimens 1 to 7 of Comparative Example 1 at different temperature
conditions.
[0028] FIG. 2 shows boron segregated in grain boundary by atomic
probe spectroscopy analysis according to Example 2.
[0029] FIG. 3 is a graph showing tensile properties at room
temperature in Examples and Comparative Examples.
[0030] FIG. 4 shows ESBD analysis results on whether mechanical
twinned crystal is formed after tensile deformation of Example 2
and Comparative Example 2.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Hereinafter, some embodiments of the present invention will
be described in detail with reference to the accompanying drawings
so that those people who are having ordinary knowledge will easily
carry out. The present invention may be implemented in several
different forms and is not limited to the embodiments described
herein.
[0032] In order to clearly illustrate the present invention, parts
that are not related to the description are omitted, and the same
or similar components are denoted by the same reference numerals
throughout the description.
[0033] In addition, the size and thickness of each component shown
in the drawings are arbitrarily shown for convenience of
explanation, and thus the present invention is not necessarily
limited to those shown in the drawings. In the drawings, the
thicknesses are enlarged to clearly indicate layers and regions. In
the drawings, for the convenience of explanation, the thicknesses
of some layers and regions are exaggerated.
[0034] Also, when a portion of a layer, film, region, plate, etc.
is referred to as being "on" or "above" another portion, it
includes not only the case where it is "directly on" another part
but also the case where there is another part in the middle.
Conversely, when a part is "directly on" another part, it means
that there is no other part in the middle. In addition, to be "on"
or "above" the reference portion is located above or below the
reference portion and does not necessarily mean "on" or "above"
toward the opposite direction of gravity.
[0035] Also, throughout the specification, when referring that a
certain part "comprises" a certain component, it means that it may
comprise other components as well, rather than excluding other
components, unless specifically stated otherwise.
A High Entropy Alloy Doped with Boron
[0036] A high entropy alloy doped with boron according to the
present invention comprises four or more metals selected from iron
(Fe), chromium (Cr), nickel (Ni), cobalt (Co), manganese (Mn),
molybdenum (Mo), aluminum (Al) and copper (Cu), and boron (B) and
has single phase FCC structure.
[0037] The content of the four or more metals may be 5 to 35 at %
respectively, and the content of boron (B) may be 3 at % or less (0
is not included),
[0038] The high entropy alloy has excellent mechanical properties
in a cryogenic environment. On the other hand, it was studied to
improve low yield strength and mechanical properties at room
temperature which are pointed out as limit of high entropy
alloy.
[0039] As a result, it was found that when boron which is an
interstitial element is added in a trace amount, not only the grain
boundary cohesion stress is improved but also the grain growth
resistance is improved, so that a high yield strength and excellent
mechanical properties at room temperature can be obtained due to
grain refining effect.
[0040] In particular, when boron was added, it was found and
reached the present invention that the mechanical properties at
room temperature could be further improved due to effect of the
segregation of boron into grain boundary while maintaining the
characteristics of the FCC-based high entropy alloy having the
expression of mechanical twinned crystal as the main enhancement
mechanism.
[0041] There is no particular limitation on the composition of high
entropy alloy doped with boron according to the present
invention.
[0042] However, since the FCC single phase is realized, and the
cryogenic mechanical properties are excellent so that it is high
possibility of application to cryogenic structure materials.
[0043] But it has low yield strength and mechanical properties at
room temperature, so it is sufficient that the high entropy alloy
is required improvement.
[0044] For example, it comprises four or more metals selected from
iron (Fe), chromium (Cr), nickel (Ni), cobalt (Co), manganese (Mn),
molybdenum (Mo), aluminum (Al) and copper (Cu), wherein content of
metal is from 5 to 35 at % respectively, so it may be the
composition of atoms having the same or similar ratio.
[0045] Accordingly, this may be a alloy forming FCC structure
without forming an intermetallic compound or an intermediate phase,
by increasing the mixed entropy in the alloy through the
substitutional type properties of the metal elements.
[0046] Boron is added to alloys and it serves to improve grain
boundary cohesion stress and grain growth resistance. Boron may be
added at 3 at % or less. Accordingly, the grains become refiner and
the low yield strength and insufficient mechanical properties at
room temperature of the conventional high entropy alloy may be
improved.
[0047] However, if the amount of boron to be added is excessive, a
boron compound having a weak brittleness is formed in the alloy,
which may cause a serious effect on the mechanical properties.
[0048] Specifically, the high entropy alloy doped with boron
according to the present invention may comprises 18 to 42% of iron
(Fe), 18 to 42% of manganese (Mn), 9 to 22% of chromium (Cr), 9 to
22% of cobalt (Co), 9 to 22% of nickel (Ni) and 0.001 to 0.01% of
boron (B) on the basis of wt % and it may be expressed as the
following composition formula 1.
Fe.sub.18-42Mn.sub.18-42Cr.sub.9-22Co.sub.9-22Ni.sub.9-22B.sub.0.001-0.0-
1(wt %) [Composition Formula 1]
[0049] In addition, specifically, the high entropy alloy doped with
boron according to the present invention may comprises 18 to 42% of
iron (Fe), 18 to 42% of manganese (Mn), 9 to 22% of chromium (Cr),
9 to 22% of cobalt (Co), and 0.001 to 0.01% of boron (B) on the
basis of wt % and it may be expressed as the following composition
formula 2.
Fe.sub.18-42Mn.sub.18-42Cr.sub.9-22Co.sub.9-22B.sub.0.001-0.01(wt
%) [Composition Formula 2]
[0050] As in the composition formula 1 and the composition formula
2, 0.001 to 0.01% of boron may be added.
[0051] When boron is added in an amount less than 0.001%, the grain
refining effect is not large, and when it is added in excess of
0.01%, boron compounds having weak brittleness can be formed in the
alloy.
[0052] More specifically, 0.004 to 0.005% of boron may be added in
order to prevent the formation of the boron compound as much as
possible and to maximize the grain refining effect.
[0053] The high entropy alloy doped with boron according to the
present invention may comprise boron segregated in grain
boundary.
[0054] Boron is segregated into grain boundary by the addition of
boron, which is an interstitial element, to suppress growth of
grain boundary and improve cohesion strength.
[0055] Specifically, as can be seen in FIG. 2, the concentration of
boron in the grain boundary between the FCC grains and the FCC
grains may be 0.20 at % maximum. In addition, boron (B) segregated
in the grain boundary may be 95% or more of the total boron.
[0056] On the other hand, the boron concentration of FCC grains may
be confirmed to be 0.075 at % maximum. More than 95% of the boron
added is concentrated in the grain boundary to suppress the growth
of the grains.
[0057] In addition, it does not affect the formation of mechanical
twinned crystal, which is the main enhancement mechanism of
FCC-based high entropy alloys, and thus has excellent properties of
high elongation while obtaining high yield strength and tensile
strength.
[0058] The average grain size of the high entropy alloy doped with
boron according to the present invention by addition of boron may
be 60 .mu.m or less. Specifically, it may be 8 .mu.m or less, and
more specifically may be 4 .mu.m or less.
[0059] As mentioned above, excellent yield strength and mechanical
properties at room temperature may be expected as the grain becomes
refiner.
[0060] The yield strength of the high entropy alloy doped with
boron according to the present invention may be 440 MPa or more.
Specifically, it may be 650 MPa or more.
Method for Manufacturing High Entropy Alloy Doped with Boron
[0061] A method for manufacturing a high entropy alloy doped with
boron according to the present invention, comprises preparing a raw
material of four or more metals selected from iron (Fe), chromium
(Cr), nickel (Ni), cobalt (Co), manganese (Mn), molybdenum (Mo),
aluminum (Al) and copper (Cu), and a raw material of boron (B),
dissolving the raw materials to cast an ingot, cold-rolling the
ingot to produce an alloy material, and annealing the alloy
material.
[0062] First, in the step of preparing a raw material of four or
more metals selected from, iron (Fe), chromium (Cr), nickel (Ni),
cobalt (Co), manganese (Mn), molybdenum (Mo), Aluminum (Al) and
copper (Cu) having a purity of 99.9% or more are prepared, and then
boron (B) raw materials are prepared, and then it may be weighed so
as to have a mixing ratio single phase FCC structure.
[0063] Next, in the step of casting the ingot, the raw materials
prepared are charged into the crucible, and then melted by heating
at 1400 to 1800.degree. C., and then the ingot may cast using the
mold.
[0064] Thereafter, the ingot is cold-rolled so as to have a
reduction ratio of 50 to 80% to produce an alloy material, and the
alloy material produced through cold rolling be annealed.
[0065] During the annealing treatment, boron is preferentially
segregated in grain boundary having high energy, so that the yield
strength and the room temperature mechanical properties may be
improved.
[0066] The annealing temperature may be a temperature of 650 to
1100.degree. C. Specifically, it may be a temperature of 700 to
800.degree. C. The annealing time may be 10 to 100 minutes.
[0067] Generally, as the temperature during the annealing process
increases, the grain size grows, but boron is segregated into grain
boundary due to the addition of boron, thereby suppressing the
growth of grains. As a result, excellent yield strength and
mechanical properties at room temperature may be exhibited due to
grain refining.
[0068] It may include a step of homogenizing heat treating the
ingot and a step of removing oxides generated on the surface of the
ingot after the step of casting the ingot.
[0069] In a step of homogenizing heat treating, the ingot from
which the oxide has been removed may be subjected to homogenizing
heat treating at a temperature of 1000 to 1200.degree. C. for 4 to
8 hours to homogenize the structure.
[0070] In the step of removing the oxide, the oxide formed on the
surface of the ingot may be removed by grinding the surface of the
cast ingot.
[0071] On the other hand, step of forming mechanical twinned
crystal by deformation of the alloy material after the step of
annealing the alloy material may be further comprised.
[0072] The alloy material may be intentionally deformed or may be
deformed naturally in the environment of use after application to
the product. It does not depend on the method of
transformation.
Despite the addition of boron, it is possible to maintain the
characteristics of the FCC-based high entropy alloy having the
expression of mechanical twinned crystal as the main enhancement
mechanism.
[0073] Hereinafter, specific examples of the present invention will
be described. However, the following examples are only specific
examples of the present invention, and the present invention is not
limited to the following examples.
Producing High Entropy Alloys According to Examples and Comparative
Examples
Example 1
[0074] Raw material of iron (Fe), manganese (Mn), chromium (Cr),
cobalt (Co), nickel (Ni) and boron (B) having a purity of 99.9% or
more was prepared so as to have the mixing ratio shown in Table 1
below.
[0075] The metal prepared as above was charged into a crucible and
then melted by heating at 1550.degree. C., a plurality of ingots
which are rectangular parallelepiped shapes having a thickness of
7.8 mm, 150 g, a width of 33 mm, and a length of 80 mm, were cast
using a mold.
[0076] The surface of the cast ingot was subjected to surface
grinding to remove the oxide generated on the surface, and the
thickness of the ground ingot became 7 mm.
[0077] The ingot which had been subjected to surface grinding and
has a thickness of 7 mm was subjected to homogenizing heat
treatment at a temperature of 1100.degree. C. for 6 hours, followed
by cold rolling from a thickness of 7 mm to 1.5 mm to prepare a
plurality of alloy plates (specimens 1 to 7 of Example 1).
[0078] Next, each alloy sheet was subjected to annealing under the
conditions shown in Table 2 below.
Example 2
[0079] Raw material of iron (Fe), manganese (Mn), chromium (Cr),
cobalt (Co), and boron (B) having a purity of 99.9% or more was
prepared so as to have the mixing ratio shown in Table 1 below.
[0080] The metal prepared as above was charged into a crucible and
then melted by heating at 1550.degree. C., a ingot which is a
rectangular parallelepiped shape having a thickness of 7.8 mm, 150
g, a width of 33 mm, and a length of 80 mm, was cast using a
mold.
[0081] The surface of the cast ingot was subjected to surface
grinding to remove the oxide generated on the surface, and the
thickness of the ground ingot became 7 mm.
[0082] The ingot which had been subjected to surface grinding and
has a thickness of 7 mm was subjected to homogenizing heat
treatment at a temperature of 1100.degree. C. for 6 hours, followed
by cold rolling from a thickness of 7 mm to 1.5 mm to prepare an
alloy plate. Next, the alloy sheet material was subjected to
annealing at 800.degree. C. for 60 minutes.
Example 3
[0083] Raw material of iron (Fe), manganese (Mn), chromium (Cr),
cobalt (Co), nickel (Ni), and boron (B) having a purity of 99.9% or
more was prepared so as to have the mixing ratio shown in Table 1
below.
[0084] Thereafter, the alloy plate was prepared in the same manner
as in Example 2.
Example 4
[0085] Raw material of iron (Fe), manganese (Mn), chromium (Cr),
cobalt (Co), nickel (Ni), and boron (B) having a purity of 99.9% or
more was prepared so as to have the mixing ratio shown in Table 1
below.
[0086] Thereafter, the alloy plate was prepared in the same manner
as in Example 2.
Comparative Example 1
[0087] Raw material of iron (Fe), manganese (Mn), chromium (Cr),
cobalt (Co), and nickel (Ni) having a purity of 99.9% or more was
prepared so as to have the mixing ratio shown in Table 1 below.
[0088] Thereafter, a plurality of alloy plates (specimens 1 to 7 of
Comparative Example 1) was prepared in the same manner as in
Example 1.
[0089] Next, each alloy sheet was subjected to annealing under the
conditions shown in Table 2 below.
Comparative Example 2
[0090] Raw material of iron (Fe), manganese (Mn), chromium (Cr),
and cobalt (Co) having a purity of 99.9% or more was prepared so as
to have the mixing ratio shown in Table 1 below.
[0091] Thereafter, the alloy plate was prepared in the same manner
as in Example 2.
TABLE-US-00001 TABLE 1 Mixing Ratio of the Raw Material (wt %) Fe
Mn Cr Co Ni B Example 1 19.915 19.591 18.542 21.016 20.931 0.005
Example 2 40.318 39.663 9.381 10.633 -- 0.004 Example 3 19.914
19.59 18.541 21.015 20.93 0.02 Example 4 19.91 19.586 18.537 21.011
20.926 0.03 Comparative 19.916 19.592 18.543 21.017 20.932 --
Example 1 Comparative 40.317 39.662 9.385 10.637 -- -- Example
2
TABLE-US-00002 TABLE 2 Annealing conditions Classification
Annealing Annealing Species Specimen No. Temperature (.degree. C.)
Time (min) Example 1/ Specimen 1 650 60 Comparative Specimen 2 700
60 Example 1 Specimen 3 750 60 Specimen 4 800 60 Specimen 5 900 60
Specimen 6 1000 60 Specimen 7 1100 60
1. Results of Grain Boundary Size Analysis
[0092] FIG. 1 shows grain size changes with annealing temperature
through electron backscatter diffraction (EBSD) analysis of alloys
of specimens 1 to 7 of Example 1 and specimens 1 to 7 of
Comparative Example 1 which are subjected to annealing.
[0093] As can be seen from FIG. 1, in both of Example 1 and
Comparative Example 1, the grain size grows as the annealing
temperature increases, in the case of Example 1, however, since
boron is further added, the grain size is relatively small as
compared with Comparative Example 1. In addition, it can be seen
that the difference in grain size between Example 1 and Comparative
Example 1 is gradually increased as annealing temperature is
increased.
[0094] That is, in the Fe--Mn--Cr--Co--Ni alloy system, by keeping
the composition of the other elements constant while adding 0.005
wt % of boron to suppress grain growth during the annealing, it can
be seen that it finally has relatively fine grains as compared with
Comparative Example 1.
2. Results of Atomic Probe Spectroscopy Analysis
[0095] FIG. 2 shows the result of the atomic probe spectroscopy
analysis of the annealed Example 2. Atomic probe spectroscopy
analysis is a method to identify atomic images by element, which is
a method to analyze atomic distribution through ionization of
material and detection using electric field by applying electrical
pulses to atomic probe samples (.about.50 nm) manufactured in
conical shape.
[0096] As can be seen from FIG. 2, iron (Fe), manganese (Mn),
chromium (Cr), cobalt (Co), and nickel (Ni) are randomly
distributed uniformly over the whole area, while it can be seen
that the boron added of 0.004 wt % is segregated in a specific
region, and this region corresponds to grain boundary.
[0097] That is, boron is preferentially segregated in the grain
boundary having a relatively higher energy than the matrix in the
annealing.
3. Tensile Test Results
[0098] FIG. 3 and Table 3 show the results of the room temperature
tensile test of the specimens 1 and 4 of Example 1, Example 2, the
specimens 1 and 4 of Comparative Example 1, and Comparative Example
2, respectively.
TABLE-US-00003 TABLE 3 Yield Strength Tensile Strength Elongation
Specimen (MPa) (MPa) (%) Specimen 1 of 800 1035 51 Example 1
Specimen 1 of 652 854 50 Comparative Example 1 Specimen 4 of 650
910 55 Example 1 Specimen 4 of 275 635 65 Comparative Example 1
Example 2 441 858 73 Comparative Example 2 380 773 67 Example 3 451
734 47 Example 4 476 716 48
[0099] As can be seen from FIG. 3 and Table 3, the specimen 4 of
Example 1, Example 2, Example 3, Example 4, the specimen 4 of
Comparative Example 1 and Comparative Example 2 of the high entropy
alloy doped with boron according to the present invention are which
are all subjected to annealing at 800.degree. C. and the specimen 4
of Comparative Example 1 In Example 2, the annealing was carried
out at 800.degree. C. so when comparing the physical properties,
the tensile strength of the examples were improved compared to the
specimens 1 and 4 of Comparative Example 1 and Comparative Example
2 in which boron was not added, showing excellent mechanical
properties.
[0100] Comparing the specimen 1 of Example 1 with the specimen 1 of
Comparative Example 1, it can be seen that the tensile strength is
greatly improved due to the influence of boron.
[0101] Particularly, comparing the specimen 4 of Example 1 with the
specimen 4 of Comparative Example 1, it has been confirmed that the
yield strength and the tensile strength are improved remarkably by
adding boron (yield strength: 275 MPa.fwdarw.650 MPa, tensile
strength: 635 MPa 910 MPa), while the elongation shows similar
results to the case where boron was not added.
[0102] In addition, in the alloy of Example 2, the result has been
confirmed that the yield strength and tensile strength were
improved and at the same time, the elongation was also slightly
increased by the effect of adding boron compared to the alloy of
Comparative Example 2.
[0103] Comparing the specimen 4 of Example 1 and Example 2 in which
boron is added to 0.01% or less with Example 3 and Example 4 in
which boron is added in excess of 0.01%, it has been confirmed that
in Example 3 and Example 4, the boron is added in excess to lower
all of the yield strength, the tensile strength and the elongation,
thereby deteriorating the mechanical properties.
[0104] Therefore, it has been confirmed that the method of adding
boron, which is an interstitial element, to the optimum range as a
means for solving the low yield strength of the FCC-based high
entropy alloy is more effective as an improving method for
mechanical properties than other means.
4. The Expression of the Mechanical Twinned Crystal
[0105] FIG. 4 shows the transmission-electron backscatter
diffraction (t-EBSD) analysis results of the expression of
mechanical twinned crystal during tensile deformation of the high
entropy alloys according to Example 2 and Comparative Example
2.
[0106] As shown in FIG. 4, it has been confirmed that the
mechanical twinned crystal between deformations was also expressed
at the same level as in Comparative Example 2 in which boron was
not added even in the Example 2 alloy in which boron was added.
[0107] Therefore, it can be seen that the mechanical properties at
room temperature is further improved due to boron segregated in
grain boundary while retaining the properties of FCC-based high
entropy alloys having the expression of mechanical twinned crystal
as the main enhancement mechanism.
[0108] The present invention is not limited to the above-mentioned
embodiments and/or examples and may be manufactured in various
forms, those who have ordinary knowledge of the technical field to
which the present invention belongs may understand that it may be
carried out in different and concrete forms without changing the
technical idea or fundamental feature of the present invention.
Therefore, the aforementioned embodiments and/or examples are
exemplary in all the ways but not limited thereto.
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