Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LOW COST AMORPHOUS STEEL
[0001] This application claims the priority of U.S.
Provisional Patent Application No. 60/613,780 entitled "LOW
COST AMORPHOUS STEEL" and filed September 27, 2004.
Background
[0002] This application relates to compositions of amorphous
metallic materials and bulk metallic glasses (BMGs).
[0003] Amorphous metallic materials made of multiple
components are amorphous with a non-crystalline structure and
are also known as "metallic glass" materials. Such materials
are very different in structure and behaviors from many
metallic materials with crystalline structures. Notably, an
amorphous metallic material is usually stronger than a
crystalline alloy of the same or similar composition. Bulk
metallic glasses are a specific type of amorphous materials or
metallic glass made directly from the liquid state without any
crystalline phase and exhibit slow critical cooling rates,
e.g., less than 100 K/s, high material strength and high
resistance to corrosion. Bulk metallic glasses may be
produced by various processes, e.g., rapid solidification of
molten alloys at a rate that the atoms of the multiple
components do not have sufficient time to align and form
crystalline structures. Alloys with high amorphous
formability can be cooled at slower rates and thus be made
into larger volumes. The amorphous formability of an alloy
can be described by its thermal characteristics, namely the
relationship between its glass transition temperature and its
crystallization temperature, and by the difference between its
liquidus temperature and its ideal solution melting
temperature. Amorphous formability increases when the
difference between the glass transition temperature-and
crystallization temperature increases, and when the difference
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between its liquicius temperature and ideal solution melting
temperature increases.
[0004] Various known iron-based amorphous alloy compositions
suitable for making non-bulk metallic glasses) have relatively
limited amorphous formability and are used for various
applications, such as transformers, sensor applications, and
magnetic recording heads and devices. These and other
applications have limited demands on the sizes and volumes of
the amorphous alloys, which need to be produced. By contrast,
iron-based bulk metallic glasses can be formulated to be
fabricated at slower critical cooling rates, allowing thicker
sections or more complex shapes to-be formed. These Fe-based
BMGs can have strength and hardness far exceeding conventional
high strength materials with crystalline structures and thus
can be used as structural materials in applications that
demand high strength and hardness or enhanced formability.
[0005] Some iron-based bulk metallic glasses have been made
using iron concentrations ranging from 50 to 70 atomic
percent. Metalloid elements, such as carbon, boron, or
phosphorous, have been used in combination with refractory
metals to form bulk amorphous alloys. The alloys can be
produced into volumes ranging from millimeter sized sheets or
cylinders. A reduced glass transition temperature on the
order of .6 and a supercooled liquid region greater than
approximately 20K indicates high amorphous formability in Fe-
based alloys.
Summary
This application describes compositions of and techniques
for designing and manufacturing iron-based amorphous steel
alloys with a significantly high iron content and high glass
formability that are suitable for forming bulk metallic
glasses. For example, a composition.suitable for bulk
metallic glasses described in this-application may include 59
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to /U atomic percent ot iron, 10 to 20 atomic percent of
metalloid elements, and 10 to 25 atomic percent of refractory
metals, where the iron, metalloid elements and refractory
metals are alloyed with one another to form an amorphous phase
material. One exemplary formulation for iron-based metallic
glass materials is
Fe78-a-b-cC flBeCraMObWc
where (a + b + c) <_ 17, 'a' ranges from 0 to 10 (e.g., 2 to
10), 'b' from 2 to 8, 'c' from 0 to 6, 'd' from 10 to 20, and
'e' from 3 to 10. The values of a, b, c, d, and e are
selected so that the atomic percent of iron exceeds 59 atomic
%. One specific example is Fe78-a-b-cC12B1oCraMobWc.
[0006] Bulk metallic glass materials based on the above
formulation may be designed by computing the liquidus
temperatures based upon the concentrations of alloying
elements and optimizing the compositions. This method
determines alloys with high glass formability by using
theoretical phase diagram calculations of multi component
alloys.
[0007] As another example, this application describes a
composite material that includes 59 to 70 atomic percent of
iron, 10 to 20 atomic percent of a plurality metalloid
elements, and 10 to 25 atomic percent of a plurality of
refractory metals. The iron, metalloid elements and
refractory metals are alloyed with one another to form an
amorphous phase material.
[0008] A process for producing a bulk metallic glass based on
a composition disclosed here is described as an example.
First, a mixture of the components including iron, refractory
metals, carbon and boron is melted into an ingot (e.g., using
an arc melting process). The molten final ingot is solidified
to form a bulk amorphous metallic material. The
solidification may be conducted rapidly using a chill casting
technique. This fabrication process can be used to make Fe-
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based alloys into amorphous samples with 0.5 mm in thickness
in its minimum dimension. This process can also be used to
produce, among other compositions, a steel of Fe68C12B3Cr5Mo1oW2
with a high iron content and a large supercooled liquid region
greater than about 50K.
[0009] These and other compositions and their properties and
fabrications are described in the attached drawings, the
detailed description, and the claims.
Brief Description of the Drawings
[0010] FIG. 1 shows measured X-ray diffraction patterns
showing amorphous structures of a) Fe60C15B6MoloCryW3r b)
Fe60Ci8B5MoioCr4W3, c) Fe59Ci2BioMoiiCr5W3, d) Fe6iCi2BioMoioCr4W3, e)
Fe6iCi2B7MoiiCr3W3. Fe68Ci2B3MoioCr5W2. f) Fe68CioBioC4Mo6WZ, and g)
Fe69C1oB8Mo11Cr4W3, Fe68C1oB8Mo11W3, where the vertical axis is the
measured strength of the diffraction signal and the horizontal
axis is the measured angle which is twice of the diffraction
angle.
[ooii] FIG. 2 shows the measured'X-ray diffraction pattern
showing the amorphous structure of ( Fe68C1oB1oCr4Mo6W2 ) 98Y2.
[00121 FIG. 3 shows the measured X-ray diffraction pattern
showing the amorphous structure of (Fe57C1oB1oCr13Mo7W3) 98Y2.
[0013] FIG. 4 shows the measured X-ray diffraction pattern
showing the amorphous structure of Fe61C12B1oCr4Mo1oW3225 [0014] FIG. 5 shows
the measured X-ray diffraction pattern
showing the amorphous structure of Fe68C12B3Cr5Mo1oW2.
[0015] FIG. 6 shows thermal mechanical analysis (TMA)
results for Fe68C12B3CrSMo1oWZ where the glass transition
temperature Tg is indicated by an arrow.
[0016] FIG. 7 shows differential thermal analysis (DTA)
results for Fe68C12B3Cr5Mo1oW2 where glass transition and
crystallization temperatures are indicated by arrows.
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Lezailed Description
[0017] Designing of bulk metallic glass compositions having
multiple elements with desired material properties is
technically difficult in part because the complexities of the
interactions and effects of the different elements. In such a
complex material, a change in any aspect of the composition,
such as the quantity of one element or a substitution of one
element with another element, may significantly affect the
property of the final metallic glass material. Due to such
complexity, many known metallic glass compositions are results
of trial and error. The Fe-based metallic glass compositions
described in this application were designed based on a
systematic approach to selection of metalloid elements and
refractory metal elements in combinations with iron to search
for compositions with high glass formability represented by a
large difference between a low glass transition temperature
and a high crystallization temperature and a large difference
between the liquidus temperature and the ideal solution
melting temperature which the weighted average of the melting
temperatures of different elements-in the mixture.
[0018] Under this approach to designing a specific bulk
metallic glass, the liquidus temperatures are calculated based
upon the concentrations of different.alloying elements
selected as the constituents of the bulk metallic glass. The
compositions are then optimized based on the respective
resulting liquidus temperatures. The concentrations of
refractory metal elements such as molybdenum and chromium
added to the Fe-based alloy can also be optimized such that
the final alloy has 1) a high or maximum viscosity due to high
concentrations of added refractory metals, and 2) a low or
minimum liquidus temperature. The compositions are selected
to achieve low liquidus temperatures and high ideal solution
melting temperatures so that a candidate composition has a
large difference between the liquidus temperature and the
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ideal solution melting temperature. Such candidate
compositions can maintain their liquidus phase over a large
temperature range within which a relatively slow cooling
process can be used to achieve the amorphous phase in a bulk
material. Among the candidate compositions with a large
difference between the liquidus temperature and the ideal
solution melting temperature, compositions with a large
difference between a low glass transition temperature and a
- high crystallization temperature are further identified and
selected as candidates for the final metallic glass
composition. This numerical and systematic design approach
works well in predicting the compositions of existing
amorphous alloys and was used to design the compositions of
the examples described below.
[0019] One application of the above design approach is
metallic glass compositions based on the metal iron, which is
relatively inexpensive and widely available. Such iron-based
metallic glass materials can be designed to achieve good glass
formability at a reasonably low price to allow for mass
production and uses in a wide variety of applications. The
compositions of iron-rich amorphous alloys described here can
be used to reach an amorphous state under a modest cooling
rate, thus forming bulk metallic glass materials. Several
examples of such bulk metallic glasses described here have a
content of iron of approximately from 59 to 70 atomic percent
and are also referred to as amorphous steels. In these
examples, the iron is further alloyed with 10 to 20 atomic
percent metalloid elements and 10 to 25 percent refractory
metals. The compositions are chosen using theoretical
calculations of the liquidus tempe"rature. The alloys are
designed to have a sufficient amount of refractory metals to
stabilize the amorphous structure, while still maintaining a
depressed liquidus temperature. In some implementations, the
principal alloying elements may be*molybdenum, tungsten,
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chromium, boron, and carbon. Some of the resulting alloys are
ferromagnetic at the room temperature, while others are non-
ferromagnetic. These amorphous steels have increased specific
strengths and corrosion resistance compared to conventional
high strength steels. The amorphous structure of these alloys
imparts unique physical and mechanical properties to these
alloys, which are not obtained in their crystalline alloy
forms.
[0020] Notably, the compositions described here have a higher
Fe content than other Fe-based bulk metallic glass materials
and do not use expensive alloying elements found in other Fe-
based bulk metallic glass materials'to make the material
amorphous under slow cooling conditions. The compositions of
the present amorphous steels are significantly closer to
standard steel alloy compositions than other Fe-based bulk
metallic glasses and thus are much more attractive to scale up
production by using various steel production techniques,
processes and equipment including existing techniques,
processes and equipment. In comparison, various commercial
bulk metallic glasses use Zr-based materials and therefore are
expensive to produce. The present compositions use iron, one
of the cheapest and widely available metallic elements, as a
major component and thus significantly reduce the cost of the
materials.
[0021] One formulation of the present compositions can be
expressed as
Fe78-a-b-cCdBeCraMObWc,
where the subscript parameters represent the relative atomic %
of the different elements. Based on the above described
systematic design approach, the relative quantities of the
elements are limited by the following conditions: (a + b + c)
17; 'a' ranges from 0 to 10; 'b' from 2 to 8; 'c' from 0 to
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b; 'ct' trom lu to Zu; ancd "e' from 3 to 10. In addition, the
values of a, b, c, d, and e are selected so that the atomic
percent of iron exceeds 59 atomic %. One amorphous material
based on this composition is Fe78-a-b-,C12B1oCraMobWc: for d = 12
and e = 10.
[0022] The alloys based on the above compositions may be
produced by melting mixtures of high purity elements. For
example, the melting may be performed in an arc furnace under
an argon atmosphere. The alloy ingot is fabricated from iron
as the main metal element, refractory elements such as Cr, W,
and Mo, and metalloid elements such as carbon and boron.
Specific quantities of these elements are selected based on
the above prescription. The mixture of these elements with
predetermined relative quantities may be melted together to
form an ingot by, e.g., using arc melting and other meting
methods. The ingot is re-melted several times to ensure
homogeneity of the ingot and then cast into a chilled casting
mold to produce a desired shape in an amorphous structure.
The melting may be performed in an electric furnace, an
induction-melting furnace, or any other melting technique that
allows the elements in the above-described compositions to be
melted together. The heat for the melting may generate from
various processes such as induction heating, furnace heating,
or arc melting.
[0023] For example, the arc melting method was used to
successfully produce the following bulk metallic glass
material samples with dimensions of at least of 0.635 mm:
Fe68CioBioCr9Mo6W2Y2, Fe57CioBioCri3Mo7W3Yz, Fe6iCi2BioCr4MoioW3.
Fe68C12B3Cr5M010W2, Fe6oCi5B8MoioCr9W3, Fe6oCi8B5MoioCr4W3,
Fe61C12B7Mo11Cr5Wa, Fe61C12B1oMo11Cr3W3, Fe64C1oB$Mo11Cr9W3, and
Fe68C10B$Mo11W3, The samples were suction cast into a copper
sleeve. Two sleeves of different thicknesses of 0.025" and
0.050" were used. The amorphous nature of the cast alloys was
verified using X-ray diffraction. Thermal properties were
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obtained using a differential thermal analyzer (DTA), a'
differential scanning calorimeter (DSC), and a thermal
mechanical analyzer (TMA). Two classes of iron-rich amorphous
steels were produced; one class contains yttrium, and the
other lacks yttrium. The alloys produced without the use of
yttrium represent the optimum alloys in terms of their low
cost manufacturability. In addition, these alloys are
composed of elements that are relatively resistant to
oxidation, further increasing their manufacture potential.
[0024] FIGS. 1 through 7 show various measured results of
these samples. FIGS. 1 through 5 are measured X-ray
diffraction patterns showing amorphous structures of the
samples. FIG. 6 is measured TMA data for the sample with a
composition of Fe68C12B3Cr5Mo10W2 where the vertical axis is the
TMA probe position and the location where the probe falls down
is used as a measure of the glass transition temperature Tg.
FIG. 7 shows differential thermal analysis (DTA) results for
Fe68C12B3Cr5Mo10W2 where the vertical axis. is the heat flow used
during the measurement. The sharp transitions in DTA indicate
when reactions occur, either endotherms or exotherms,
indicative of crystallization, or melting, and even the very
small transition at the start reflecting the glass transition.
The specific DTA measurement in FIG. 7 shows the difference
between the glass transition temperature (Tg) and the
crystallization temperature (Txl) to be in excess of 50K,
which is an indicator of a good glass forming ability.
[0025] The compositions of amorphous steel described here have
higher levels of iron in combination with low cost refractory
metals and metalloid elements than various amorphous steels
made by others. Therefore, the applications of such high iron
content amorphous steels are more favorable to replace
conventional high strength structural steels than other
amorphous steels. In particular, the composition of
Fe68C12B3Cr5Mo10W2 has a high iron content of 68 atomic % and
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uses low cost alloying eiements of-C, B, Cr, Mo and W to
exhibit a large supercooled liquid region, greater than
approximately 50K. Therefore, this composition is suitable
for bulk production for industrial applications.
[0026] The Fe-rich materials based on the present compositions
may be used in a wide range of applications. The relatively
high amorphous formability of these materials makes them
desirable materials for a wide range of applications including
but not limited to sporting goods such as tennis rackets
reinforcements, skis, baseball bats, golf club heads, consumer
and other electronics such as device cases, antennas, and
thermal solutions for high-strength, light-weight, components
and parts used in mobile devices such as notebook computers,
cell phones, portable PDA's, MP3 players, portable memory
devices, multimedia players, components and parts used in
avionics devices, and automotive parts and devices. The Fe-
rich materials based on the present compositions may also be
used as low cost alternatives to titanium and other specialty
alloys in various aerospace, industrial, and automotive
applications such as springs and actuators, and various
corrosion resistant applications. In addition, the
compositions may also be used to form non-ferromagnetic
structural materials in military applications for avoiding
magnetic triggering of mines. Furthermore, the present
compositions may be used for biomedical implants, transformer
cores, etc. Many other structural material applications are
certainly possible.
[0027] In summary, only a few implementations are disclosed.
However, it is understood that variations and enhancements may
be made.
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