Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR FORMING HOLLOW PROFILE NON-CIRCULAR
EXTRUSIONS USING SHEAR ASSISTED PROCESSING AND
EXTRUSION (ShAPE)
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Patent Application Serial
No. 16/028,173 filed July 5, 2018, which is a Continuation-in-Part of
and claims priority to U.S. Patent Application Serial No. 15/898,515
filed February 17, 2018, which claims the benefit of U.S. Provisional
Application Serial No. 62/460,227 filed February 17, 2017. U.S. Patent
Application Serial No. 16/028,173 is also a Continuation-In-Part of and
claims priority to U.S. Patent Application Serial No. 15/351,201 filed
November 14, 2016, which claims the benefit of U.S. Provisional
Application Serial No. 62/313,500 filed March 25, 2016. U.S. Patent
Application Serial No. 16/028,173 is also a Continuation-In-Part of and
claims priority to U.S. Patent Application Serial No. 14/222,468 filed
March 21, 2014, which claims the benefit of U.S. Provisional Application
Serial No. 61/804,560 filed March 22, 2013, the contents of all of the
foregoing are hereby incorporated by reference.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER
FEDERALLY- SPONSORED RESEARCH AND DEVELOPMENT
This invention was made with Government support under
Contract DE- AC0576RL01830 awarded by the U.S. Department of
Energy. The Government has certain rights in the invention.
BACKGROUND
Increased needs for fuel efficiency in transportation coupled with
ever increasing needs for safety and regulatory compliance have
focused attention on the development and utilization of new materials
and processes. In many instances, impediments to entry into these
areas has been caused by the lack of effective and efficient
manufacturing methods. For example, the ability to replace steel car
parts with materials made from magnesium or aluminum or their
associated alloys is of great interest. Additionally, the ability to form
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hollow parts with equal or greater strength than solid parts is an
additional desired end. Previous attempts have failed or are subject to
limitations based upon a variety of factors, including the lack of suitable
manufacturing process, the expense of using rare earths in alloys to
impart desired characteristics, and the high energy costs for production.
What is needed is a process and device that enables the
production of items such components in automobile or aerospace
vehicles with hollow cross sections that are made from materials such
as magnesium or aluminum with or without the inclusion of rare earth
metals. What is also need is a process and system for production of
such items that is more energy efficient, capable of simpler
implementation, and produces a material having desired, grain sizes,
structure and alignment so as to preserve strength and provide
sufficient corrosion resistance. What is also needed is a simplified
process that enables the formation of such structures directly from
billets, powders or flakes of material without the need for additional
processing steps. What is also needed is a new method for forming high
entropy alloy materials that is simpler and more effective than current
processes. The present disclosure provides a description of significant
advance in meeting these needs.
Over the past several years researchers at the Pacific Northwest
National Laboratory have developed a novel Shear Assisted Processing
and Extrusion (ShAPE) technique which uses a rotating ram or die
rather than a simply axially fed ram or die used in the conventional
extrusion process. As described here after as well as in the in the
previously cited, referenced, and incorporated patent applications, this
process and its associated devices provide a number of significant
advantages including reduced power consumption, better results and
enables a whole new set of "solid phase" types of forming process and
machinery. Deployment of the advantages of these processes and
devices are envisioned in a variety of industries and applications
including but not limited to transportation, projectiles, high temperature
applications, structural applications, nuclear applications, and
corrosion resistance applications.
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Various additional advantages and novel features of the present
invention are described herein and will become further readily apparent
to those skilled in this art from the following detailed description. In the
preceding and following descriptions we have shown and described
only the preferred embodiment of the invention, by way of illustration of
the best mode contemplated for carrying out the invention. As will be
realized, the invention is capable of modification in various respects
without departing from the invention. Accordingly, the drawings and
description of the preferred embodiment set forth hereafter are to be
regarded as illustrative in nature, and not as restrictive.
SUMMARY
The present description provides examples of shear-assisted
extrusion processes for forming non-circular hollow-profile extrusions
of a desired composition from feedstock material. At a high-level this is
accomplished by simultaneously applying a rotational shearing force
and an axial extrusion force to the same location on the feedstock
material using a scroll face with a plurality of grooves defined therein.
These grooves are configured to direct plasticized material from a first
location, typically on the interface between the material and the scroll
face, through a portal defined within the scroll face to a second location,
typically upon a die bearing surface. At this location the separated
streams of plasticized material are recombined and reconfigured into a
desired shape having the preselected characteristics.
In some applications the scroll face has multiple portals, each
portal configured to direct plasticized material through the scroll face
and to recombine at a desired location either unified or separate. In the
particular application described the scroll face has two sets of grooves
one set to direct material from the outside in and another configured to
direct material from the inside out. In some instances a third set of
grooves circumvolves the scroll face to contain the material and prevent
outward flashing.
This processes provides a number of advantages including the
ability to form materials with better strength and corrosion resistance
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characteristics at lower temperatures, lower forces, and with
significantly lower energy intensity than required by other processes.
For example in on instance the extrusion of the plasticized
material is performed at a die face temperature less than 150 C. In
other instances the axial extrusion force is at or below 50 MPa. In one
particular instance a magnesium alloy in billet form was extruded into
a desired form in an arrangement wherein the axial extrusion force is
at or below 25 MPa, and the temperature is less than 100 C. While
these examples are provided for illustrative reasons, it is to be distinctly
understood that the present description also contemplates a variety of
alternative configurations and alternative embodiments.
Another advantage of the presently disclosed embodiment is the
ability to produce high quality extruded materials from a wide variety of
starting materials including, billets, flakes powders, etc. without the
need for additional pre or post processing to obtain the desired results.
In addition to the process, the present description also provides
exemplary descriptions of a device for performing shear assisted
extrusion. In one configuration this device has a scroll face configured
to apply a rotational shearing force and an axial extrusion force to the
same preselected location on material wherein a combination of the
rotational shearing force and the axial extrusion force upon the same
location cause a portion of the material to plasticize. The scroll face
further has at least one groove and a portal defined within the scroll
face. The groove is configured to direct the flow of plasticized material
from a first location (typically on the face of the scroll) through the portal
to a second location (typically on the back side of the scroll and in some
place along a mandrel that has a die bearing surface). Wherein the
plasticized material recombines after passage through the scroll face
to form an extruded material having preselected features at or near
these second locations.
This process provides for a significant number of advantages and
industrial applications. For example, this technology enables the
extrusion of metal wires, bars, and tubes used for vehicle components
with 50 to 100 percent greater ductility and energy absorption over
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conventional extrusion technologies, while dramatically reducing
manufacturing costs. This while being performed on smaller and less
expensive machinery that what is used in conventional extrusion
equipment. Furthermore, this process yields extrusions from lightweight
materials like magnesium and aluminum alloys with improved
mechanical properties that are impossible to achieve using
conventional extrusion, and can do directly from powder, flake, or billets
in just one single step, which dramatically reduces the overall energy
consumption and process time compared to conventional extrusion.
Applications of the present process and device could, for
example, be used to forming parts for the front end of an automobile
wherein it is predicted that a 30 percent weight savings can be achieved
by replacing aluminum components with lighter-weight magnesium, and
a 75 percent weight savings can be achieved by replacing steel with
magnesium. Typically processing into such embodiments have required
the use of rare earth elements into the magnesium alloys. However,
these rare earth elements are expensive and rare and in many
instances are found in areas of difficult circumstances. Making
magnesium extrusions too expensive for all but the most exotic
vehicles. As a result, less than 1 percent of the weight of a typical
passenger vehicle comes from magnesium. The processes and devices
described hereafter however enable the use of non-rare earth
magnesium alloys to achieve comparable results as those alloys that
use the rare earth materials. This results in additional cost saving in
addition to a tenfold reduction in power consumption- attributed to
significantly less force required to produce the extrusions-and smaller
machinery footprint requirements.
As a result the present technology could find ready adaptation in
the making of lightweight magnesium components for automobiles such
as front end bumper beams and crush cans. In addition to the
automobile, deployments of the present invention can drive further
innovation and development in a variety of industries such as
aerospace, electric power industry, semiconductors and more. For
example, this technique could be used to produce creep-resistant steels
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for heat exchangers in the electric power industry, and high-
conductivity copper and advanced magnets for electric motors. It has
also been used to produce high-strength aluminum rods for the
aerospace industry, with the rods extruded in one single step, directly
from powder, with twice the ductility compared to conventional
extrusion. In addition, the solid-state cooling industry is investigating
the use of these methods to produce semiconducting thermoelectric
materials.
The process of the present description allow precise control over
various features such as grain size and crystallographic orientation-
characteristics that determine the mechanical properties of extrusions,
like strength, ductility and energy absorbency. The technology
produces a grain size for magnesium and aluminum alloys at an ultra-
fine regime (<1 micron), representing a 10 to 100 times reduction
compared to the starting material. In magnesium, the crystallographic
orientation can be aligned away from the extrusion direction, which is
what gives the material such high energy absorption. A shift of 45
degrees has been achieved, which is ideal for maximizing energy
absorption in magnesium alloys. Control over grain refinement and
crystallographic orientation is gained through adjustments to the
geometry of the spiral groove, the spinning speed of the die, the amount
of frictional heat generated at the material-die interface, and the
amount of force used to push the material through the die.
In addition this extrusion process allows industrial-scale
production of materials with tailored structural characteristics. Unlike
severe plastic deformation techniques that are only capable of bench-
scale products, ShAPE is scalable to industrial production rates,
lengths, and geometries. In addition to control of the grain size, an
additional layer of microstructural control has been demonstrated
where grain size and texture can be tailored through the wall thickness
of tubing-important because mechanical properties can now be
optimized for extrusions depending on whether the final application
experiences tension, compression, or hydrostatic pressure. This could
make automotive components more resistant to failure during collisions
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while using much less material.
The process's combination of linear and rotational shearing
results in 10 to 50 times lower extrusion force compared to conventional
extrusion. This means that the size of hydraulic ram, supporting
components, mechanical structure, and overall footprint can be scaled
down dramatically compared to conventional extrusion equipment -
enabling substantially smaller production machinery, lowering capital
expenditures and operations costs. This process generates all the heat
necessary for producing extrusions via friction at the interface between
the system's billet and scroll- faced die, thus not requiring the pre-
heating and external heating used by other methods. This results in
dramatically reduced power consumption; for example, the 11 kW of
electrical power used to produce a 2-inch diameter magnesium tube
takes the same amount of power to operate a residential kitchen oven
- a ten- to twenty-fold decrease in power consumption compared to
conventional extrusion. Extrusion ratios up to 200:1 have been
demonstrated for magnesium alloys using the described process
compared to 50:1 for conventional extrusion, which means fewer to no
repeat passes of the material through the machinery are needed to
achieve the final extrusion diameter - leading to lower production costs
compared to conventional extrusion.
Finally, studies have shown a 10 times decrease in corrosion rate
for extruded non-rare earth ZK60 magnesium performed under this
process compared to conventionally extruded ZK60. This is due to the
highly refined grain size and ability to break down, evenly distribute-
and even dissolve-second-phase particles that typically act as
corrosion initiation sites. The instant process has also been used to
clad magnesium extrusions with aluminum coating in order to reduce
corrosion.
Various advantages and novel features of the present disclosure
are described herein and will become further readily apparent to those
skilled in this art from the following detailed description. In
the
preceding and following descriptions exemplary embodiments of the
disclosure have been provided by way of illustration of the best mode
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contemplated for carrying out the disclosure. As will be realized, the
disclosure is capable of modification in various respects without
departing from the disclosure. Accordingly, the drawings and
description of the preferred embodiment set forth hereafter are to be
regarded as illustrative in nature, and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure la shows a ShAPE setup for extruding hollow cross
section pieces.
Figure lb shows another configuration for extruding hollow cross-
sectional pieces.
Figure 2a shows a top perspective view of a modified scroll face
tool for a portal bridge die.
Figure 2b shows a bottom perspective view of a modified scroll
face that operates like a portal bridge die.
Figure 2c shows a side view of the modified portal bridge die.
Figure 3 shows an illustrative view of material separated device
and process shown in Figures 1-2.
Figure 4a shows a ShAPE set up for consolidating high entropy
alloys (HEAs) from arc melted pucks into densified pucks.
Figure 4b shows an example of the scrolled face of the rotating
tool in Figure 4a.
Figure 4c shows an example of HEA arc melted samples crushed
and placed inside the chamber of the ShAPE device prior to processing.
Figure 5 shows BSE-SEM image of cross section of the HEA arc
melted samples before ShAPE processing, showing porosity,
intermetallic phases and cored, dendritic microstructure.
Figure 6a shows BSE-SEM images at the bottom of the puck
resulting from the processing of the material in Figure 4c.
Figure 6b shows BSE-SEM images halfway through the puck.
Figure 6c shows BSE-SEM images of the interface between high
shear region un-homogenized region (approximately 0.3 mm from puck
surface).
Figure 6d shows BSE-SEM images of a high shear region.
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DETAILED DESCRIPTION OF THE INVENTION
The following description including the attached pages provide
various examples of the present invention. It will be clear from this
description of the invention that the invention is not limited to these
illustrated embodiments but that the invention also includes a variety of
modifications and embodiments thereto. Therefore, the present
description should be seen as illustrative and not limiting. While the
invention is susceptible to various modifications and alternative
constructions, it should be understood, that there is no intention to limit
the invention to the specific form disclosed, but, on the contrary, the
invention is to cover all modifications, alternative constructions, and
equivalents falling within the spirit and scope of the invention as defined
in the claims.
In the previously described and related applications various
methods and techniques are described wherein the described
technique and device (referred to as ShAPE) is shown to provide a
number of significant advantages including the ability to control
microstructure such as crystallographic texture through the cross
sectional thickness, while also providing the ability to perform various
other tasks. In this description we provide information regarding the use
of the ShAPE technique to form materials with non-circular hollow
profiles as well as methods for creating high entropy alloys that are
useful in a variety of applications such as projectiles. Exemplary
applications will be discussed on more detail in the following.
Referring first now to Figure la and 1 b, examples of the ShAPE
device and arrangement are provided. In an arrangement such as the
one shown in Fig. 1 a rotating die 10 is thrust into a material 20 under
specific conditions whereby the rotating and shear forces of the die face
12 and the die plunge 16 combine to plasticize the material 20 at the
interface of the die face 12 and the material 20 and cause the
plasticized material to flow in desired direction. (In other embodiments
the material 20 may spin and the die 10 pushed axially into the material
20 so as to provide this combination of forces at the material face.) In
either instance, the combination of the axial and the rotating forces
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plasticize the material 20 at the interface with the die face 12. Flow of
the plasticized material can then be directed to another location
wherein a die bearing surface 24 of a preselected length facilitates the
recombination of the plasticized material into an arrangement wherein
.. a new and better grain size and texture control at the micro level can
take place. This then translates to an extruded product 22 with desired
characteristics. This process enables better strength and corrosion
resistance at the macro level together with increased and better
performance. This process eliminates the need for additional heating
.. and curing, and enables the functioning of the process with a variety of
forms of material including billet, powder or flake without the need for
extensive preparatory processes such as "steel canning". This
arrangement also provides for a methodology for performing other
steps such as cladding, enhanced control for through wall thickness
and other characteristics.
This arrangement is distinct from and provides a variety of
advantages over the prior art methods for extrusion. First, during the
extrusion process the force rises to a peak in the beginning and then
falls off once the extrusion starts. This is called breakthrough. In this
ShAPE process the temperature at the point of breakthrough is very
low. For example for Mg tubing, the temperature at breakthrough for
the 2" OD, 75mi1 wall thickness ZK60 tubes is <150C. This lower
temperature breakthrough is believed in part to account for the superior
configuration and performance of the resulting extrusion products.
Another feature is the low extrusion coefficient kf which describes
the resistance to extrusion (i.e. lower kf means lower extrusion
force/pressure). Kf is calculated to be 2.55 MPa and 2.43 MPa for the
extrusions made from ZK60-T5 bar and ZK60 cast respectively (2" OD,
75mi1 wall thickness). The ram force and kf are remarkably low
compared to conventionally extruded magnesium where kf ranges from
68.9-137.9 MPa. As such, the ShAPE process achieved a 20-50 times
reduction in kf (as thus ram force) compared to conventional extrusion.
This assists not only with regard to the performance of the resulting
materials but also reduced energy consumption required for fabrication.
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For example, the electrical power required to extrude the ZK60-T5 bar
and ZK60 cast (2" OD, 750mi1 wall thickness) tubes is 11.5 kW during
the process. This is much lower than a conventional approach that uses
heated containers/billets.
The ShAPE process is significantly different than Friction Stir
Back Extrusion (FSBE). In FSBE, a spinning mandrel is rammed into a
contained billet, much like a drilling operation. Scrolled grooves force
material outward and material back extrudes around the mandrel to
form a tube, not having been forced through a die. As a result, only very
small extrusion ratios are possible, the tube is not fully processed
through the wall thickness, the extrudate is not able to push off of the
mandrel, and the tube length is limited to the length of the mandrel. In
contrast, ShAPE utilizes spiral grooves on a die face to feed material
inward through a die and around a mandrel that is traveling in the same
direction as the extrudate. As such, a much larger outer diameter and
extrusion ratio are possible, the material is uniformly process through
the wall thickness, the extrudate is free to push off the mandrel as in
conventional extrusion, and the extrudate length is only limited only by
the starting volume of the billet.
An example of an arrangement using a ShAPE device and a
mandrel 18 is shown in Figure lb. This device and associated
processes have the potential to be a low-cost, manufacturing technique
to fabricate variety of materials. As will be described below in more
detail, in addition to modifying various parameters such as feed rate,
heat, pressure and spin rates of the process, various mechanical
elements of the tool assist to achieve various desired results. For
example, varying scroll patterns 14 on the face of extrusion dies 12 can
be used to affect/control a variety of features of the resulting materials.
This can include control of grain size and crystallographic texture along
the length of the extrusion and through-wall thickness of extruded
tubing and other features. Alteration of parameters can be used to
advantageously alter bulk material properties such as ductility and
strength and allow tailoring for specific engineering applications
including altering the resistance to crush, pressure or bending.
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The ShAPE process has been utilized to form various structures
from a variety of materials including the arrangement as described in
the following table.
Table 1
PUCKS
Alloy Material Class Precursor Form
BbTe3 Thermoelectric Powder
Fe-Si Magnet Powder
Nd2Fe11B/Fe MaQnet Powder
MA956 ODS Steel Powder
Nb 0.95 Ti 0.05 Fe 1 Sb 1 Thermoelectric Powder
Mn-Bi Magnet Powder
AlCuFe(Mg)Ti High Entropy Alloy Chunks
TUBES
Alloy Material Class Precursor Form
ZK60 Magnesium Alloy Barstock, As-Cast Ingot
AZ31 Magnesium Alloy Barstock
AZ91 MaQnesium Alloy Flake, Barstock, As-Cast
InQot
Mg2Si Magnesium Alloy As-Cast Ingot
Mg1Si Magnesium Alloy As-Cast Ingot
AZ91- 1, 5 and 10 wt.%Ab03 Magnesium MMC Mechanically Alloyed
Flake
AZ91- 1, 5 and 10 wt.% Y203 Magnesium MMC Mechanically Alloyed
Flake
AZ91- 1, 5 and 10 and 5 wt. %SiC Magnesium MMC Mechanically Alloyed
Flake
RODS
Alloy Material Class Precursor Form
Aluminum Manganese
Al-Mn wt. 15% Alloy As-Cast
Al-Mg Mg Al Co-extrusion Barstock
Mg-Dy-Nd-Zn-Zr Magnesium Rare Barstock
Earth
Cu Pure Copper Barstock
Mg Pure Magnesium Barstock
AA6061 Aluminum Barstock
High Strength
AA7075 Aluminum Barstock
Al-Ti-Mg-Cu-Fe High Entropy Alloy As-Cast
Al- 1,5,10 at.% Mg Magnesium Alloy As-Cast
High Strength
A-12.4TM Aluminum Powder
Rhodium Pure Rhodium Barstock
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In addition, to the pucks, rods and tubes described above, the
present disclosure also provides a description of the use of a specially
configured scroll component referred by the inventors as a portal bridge
die head which allows for the fabrication of ShAPE extrusions with non-
circular hollow profiles. This configuration allows for making extrusion
with non-circular, and multi-zoned, hollow profiles using a specially
formed portal bridge die and related tooling.
Figures 2a-2c show various views of a portal bridge die design
with a modified scroll face that unique to operation in the ShAPE
process. Figure 2a shows an isometric view of the scroll face on top of
the a portal bridge die and Figure 2b) shows an isometric view of the
bottom of the portal bridge die with the mandrel visible.
In the present embodiment grooves 13, 15 on the face 12 of the
die 10 direct plasticized material toward the aperture ports 17.
Plasticized material then passes through the aperture ports 12 wherein
it is directed to a die bearing surface 24 within a weld chamber similar
to conventional portal bridge die extrusion. In this illustrative example,
material flow is separated into four distinct streams using four ports 17
as the billet and the die are forced against one another while rotating.
While the outer grooves 15 on the die face feed material inward
toward the ports 17, inner grooves 13 on the die face feed material
radially outward toward the ports 17. In this illustrative example, one
groove 13 is feeding material radially outward toward each port 17 for
a total of four outward flowing grooves. The outer grooves 15 on the die
surface 12 feed material radially inward toward the port 17. In this
illustrative example, two grooves are feeding material radially inward
toward each port 17 for a total of eight inward feeding grooves 15. In
addition to these two sets of grooves, a perimeter groove 19 on the
outer perimeter of the die, shown in Figure 2c, is oriented counter to
the die rotation so as to provide back pressure thereby minimizing
material flash between the container and die during extrusion.
Figure 2b shows a bottom perspective view of the portal bridge
die 12. In this view, the die shows a series of full penetration of ports
17. In use, streams of plasticized material funneled by the inward 15
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and outward 13 directed grooves described above pass through these
penetration portions 17 and then are recombined in a weld chamber 21
and then flow around a mandrel 18 to create a desired cross section.
The use of scrolled grooves 13, 15, 19 to feed the ports 17 during
rotation - as a means to separate material flow of the feedstock (e.g.
powder, flake, billet, etc....) into distinct flow streams has never been
done to our knowledge. This arrangement enables the formation of
items with noncircular hollow cross sections.
Figure 3 show a separation of magnesium alloy ZK60 into multiple
streams using the portal bridge die approach during ShAPE processing.
(In this case the material was allowed to separate for effect and
illustration of the separation features and not passed over a die bearing
surface for combination). Conventional extrusion does not rotate and
the addition of grooves would greatly impede material flow. But when
.. rotation is present, such as in ShAPE or friction extrusion, the scrolls
not only assist flow, but significantly assist the functioning of a portal
bridge die extrusion 17 and the subsequent formation of non-circular
hollow profile extrusions. Without scrolled grooves feeding the portals,
extrusion via the portal bridge die approach using a process where
rotation is involved, such as ShAPE, would be ineffective for making
items with such a configuration. The prior art conventional linear
extrusion process teach away from the use of surface features to guide
material into the portals 17 during extrusion.
In the previously described and related applications various
methods and techniques are described wherein the ShAPE technique
and device is shown to provide a number of significant advantages
including the ability to control microstructure such as crystallographic
texture through the cross sectional thickness, while also providing the
ability to perform various other tasks. In this description we provide
.. information regarding the use of the ShAPE technique to form materials
with non-circular hollow profiles as well as methods for creating high
entropy alloys that are useful in a variety of applications such as
projectiles. These two exemplary applications will be discussed on
more detail in the following.
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Figure 4a shows a schematic of the ShAPE process which utilizes
a rotating tool to apply load/ pressure and at the same time the rotation
helps in applying torsional/ shear forces, to generate heat at the
interface between the tool and the feedstock, thus helping to
consolidate the material. In this particular embodiment the arrangement
of the ShAPE setup is configured so as to consolidate high entropy alloy
(HEA) arc-melted pucks into densified pucks. In this arrangement the
rotating ram tool is made from an Inconel alloy and has an outer
diameter (OD) of 25.4 mm, and the scrolls on the ram face were 0.5
mm in depth and had a pitch of 4 mm with a total of
2.25 turns. In this instance the ram surface incorporated a
thermocouple to record the temperature at the interface during
processing. (see Fig. 4b) The setup enables the ram to spin at speeds
from 25 to 1500 RPM.
In use, both an axial force and a rotational force are applied to a
material of interest causing the material to plasticize. In extrusion
applications, the plasticized material then flows over a die bearing
surface dimensioned so as to allow recombination of the plasticized
materials in an arrangement with superior grain size distribution and
alignment than what is possible in traditional extrusion processing. As
described in the prior related applications this process provides a
number of advantages and features that conventional prior art extrusion
processing is simply unable to achieve.
High entropy alloys are generally solid-solution alloys made of
five or more principal elements in equal or near equal molar (or atomic)
ratios. While this arrangement can provide various advantages, it also
provides various challenges particularly in forming. While a
conventional alloys is typically comprise one principal element that
largely governs the basic metallurgy of that alloy system (e.g. nickel-
base alloys, titanium- base alloys, aluminum-base alloys, etc.) in an
HEA each of the five (or more) constituents of HEAs can be considered
as the principal element. Advances in production of such materials may
open the doors to their eventual deployment in various applications.
However, standard forming processes have demonstrated significant
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limitations in this regard. Utilization of the ShAPE type of process
demonstrates promise in obtaining such a result.
In one example a "low-density" AlCuFe(Mg)Ti HEA was formed.
Beginning with arc-melted alloy buttons as a pre-cursor, the ShAPE
process was used to simultaneously heat, homogenize, and consolidate
the HEA resulting in a material that overcame a variety of problems
associated with prior art applications and provided a variety of
advantages. In this specific example, HEA buttons were arc-melted in
a furnace under 10-6 Torr vacuum using commercially pure aluminum,
magnesium, titanium, copper and iron. Owing to the high vapor
pressure of magnesium, a majority of magnesium vaporized and formed
All Mg0.1Cu2.5Fe1Ti1.5 instead of the intended All Mg1Cu1Fe1Ti1
alloy. The arc melted buttons described in the paragraph above were
easily crushed with hammer and used to fill the die cavity/ powder
chamber (Figure 4c), and the shear assisted extrusion process initiated.
The volume fraction of the material filled was less than 75%, but was
consolidated when the tool was rotated at 500 RPM under load control
with a maximum load set at 85 MPa and at 175 MPa.
Comparison of the arc-fused material and the materials
developed under the ShAPE process demonstrated various
distinctions. The arc melted buttons of the LWHEA exhibited a cored
dendritic microstructure along with regions containing intermetallic
particles and porosity. Using the ShAPE process these microstructural
defects were eliminated to form a single phase, refined grain and no
porosity LWHEA sample.
Figure 5a shows the backscattered SEM (BSE-SEM) image of the
as-cast/ arc-melted sample. The arc melted samples had a cored
dendritic microstructure with the dendrites rich in iron, aluminum and
titanium and were 15-30 pm in diameter, whereas the inter-dendritic
regions were rich in copper, aluminum and magnesium. Aluminum was
uniformly distributed throughout the entire microstructure. Such
microstructures are typical of HEA alloys. The inter-dendritic regions
appeared to be rich in Al-Cu-Ti intermetallic and was verified by XRD
as AlCu2Ti. XRD also confirmed a Cu2Mg phase which was not
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determined by the EDS analysis and the overall matrix was BCC phase.
The intermetallics formed a eutectic structure in the inter-dendritic
regions and were approximately 5-10 lim in length and width. The inter-
dendritic regions also had roughly 1-2 vol% porosity between them and
hence was difficult to measure the density of the same.
Typically such microstructures are homogenized by sustained
heating for several hours to maintain a temperature near the melting
point of the alloy. In the absence of thermodynamic data and diffusion
kinetics for such new alloy systems the exact points of various phase
formations or precipitation is difficult to predict particularly as related
to various temperatures and cooling rates. Furthermore,
unpredictability with regard to the persistence of intermetallic phases
even after the heat treatment and the retention of their morphology
causes further complications. A typical lamellar and long intermetallic
phase is troublesome to deal with conventional processing such as
extrusion and rolling and is also detrimental to the mechanical
properties (elongation).
The use of the ShAPE process enabled refinement of the
microstructure without performing homogenization heat treatment and
provides solutions to the aforementioned complications. The arc melted
buttons, because of the presence of their respective porosity and the
intermetallic phases, were easily fractured into small pieces to fill in the
die cavity of the ShAPE apparatus. Two separate runs were performed
as described in Table 1 with both the processes' yielding a puck with
diameter of 25.4 mm and approximately 6 mm in height. The pucks were
later sectioned at the center to evaluate the microstructure
development as a function of its depth. Typically in the ShAPE
consolidation process; the shearing action is responsible for deforming
the structure at interface and increasing the interface temperature;
which is proportional to the rpm and the torque; while at the same time
the linear motion and the heat generated by the shearing causes
consolidation. Depending on the time of operation and force applied
near through thickness consolidation can also be attained.
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Table 2: Consolidation processing conditions utilized for LWHEA
Run# Pressure Tool RPM Process Dwell Time
(MPa) Temperature
1 175 500 180s
2 85 500 600 C 180s
Figures 6a-6d show a series of BSE-SEM images ranging from
the essentially unprocessed bottom of the puck to the fully consolidated
region at the tool billet interface. There appears to be a gradual change
in microstructure from the bottom of the puck to the interface. The
bottom of the puck had the microstructure similar to one described in
Figure 5. But as the puck is examined moving towards the interface the
size of these dendrites become closely spaced (Figure 6b). The
.. intermetallic phases are still present in the inter-dendritic regions but
the porosity is completely eliminated. On the macro scale the puck
appears more contiguous and without any porosity from the top to the
bottom 3/4th section. Figure 6c shows the interface where the shearing
action is more prominent. This region clearly demarcates the as-cast
.. cast dendritic structure to the mixing and plastic deformation caused by
the shearing action. A helical pattern is observed from this region to the
top of the puck. This is indicative of the stirring action and due to the
scroll pattern on the surface of the tool. This shearing action also
resulted in the comminution of the intermetallic particles and also
assisted in the homogenizing the material as shown in Figure 6c and
6d. It should be noted that this entire process lasted only 180 seconds
to homogenize and uniformly disperse and comminute the intermetallic
particles. The probability that some of these getting intermetallic
particles re- dissolved into the matrix is very high. The homogenized
.. region was nearly 0.3 mm from the surface of the puck.
The use of the ShAPE device and technique demonstrated a
novel single step method to process without preheating of the billets.
The time required to homogenize the material was significantly reduced
using this novel process. Based on the earlier work, the shearing action
and the presence of the scrolls helped in comminution of the secondary
phases and resulted in a helical pattern. All this provides significant
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opportunities towards cost reduction of the end product without
compromising the properties and at the same time tailoring the
microstructure to the desired properties.
In as much as types of alloys exhibit high strength at room
temperature and at elevated temperature, good machinability, high
wear and corrosion resistance. Such materials could be seen as a
replacement in a variety of applications. A refractory HE-alloy could
replace expensive super-alloys used in applications such as gas
turbines and the expensive Inconel alloys used in coal gasification heat
exchanger. A light-weight HE-alloy could replace Aluminum and
Magnesium alloys for vehicle and airplanes. Use of the ShAPE process
to perform extrusions would enable these types of deployments.
While various preferred embodiments of the invention are shown
and described, it is to be distinctly understood that this invention is not
limited thereto but may be variously embodied to practice within the
scope of the following claims. From the foregoing description, it will be
apparent that various changes may be made without departing from the
spirit and scope of the invention as defined by the following claims.
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