U.S. patent application number 16/395804 was filed with the patent office on 2020-10-29 for inconel nanotube composite.
This patent application is currently assigned to United States of America, as represented by the Secretary of the Navy. The applicant listed for this patent is Craig A. Gallmiore, Kahle B. Sullivan. Invention is credited to Craig A. Gallmiore, Kahle B. Sullivan.
Application Number | 20200340080 16/395804 |
Document ID | / |
Family ID | 1000004159090 |
Filed Date | 2020-10-29 |
United States Patent
Application |
20200340080 |
Kind Code |
A1 |
Sullivan; Kahle B. ; et
al. |
October 29, 2020 |
Inconel Nanotube Composite
Abstract
A metal matrix composite (MMC) material composition of nickel
alloy and carbon nanotubes is provided. The material composition
includes powdered granules of the nickel alloy; and a plurality of
the nanotubes. The granules and nanotubes are milled in a hopper
and sintered by laser to form the MMC. A method for producing the
MMC material composition is also provided. The method includes
inserting powdered granules of the nickel alloy and the nanotubes
into a hopper; rotating the hopper at 450 rpm for 120 min to mill
the granules and the nanotubes into a mixture; and sintering said
mixture by a laser at 195 W and 1100 mm/s scan speed.
Inventors: |
Sullivan; Kahle B.;
(Fredericksburg, VA) ; Gallmiore; Craig A.;
(Denver, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sullivan; Kahle B.
Gallmiore; Craig A. |
Fredericksburg
Denver |
VA
CO |
US
US |
|
|
Assignee: |
United States of America, as
represented by the Secretary of the Navy
Arlington
VA
|
Family ID: |
1000004159090 |
Appl. No.: |
16/395804 |
Filed: |
April 26, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 2201/11 20130101;
B22F 3/1007 20130101; B22F 2302/403 20130101; C22C 19/055
20130101 |
International
Class: |
C22C 19/05 20060101
C22C019/05; B22F 3/10 20060101 B22F003/10 |
Goverment Interests
STATEMENT OF GOVERNMENT INTEREST
[0001] The invention described was made in the performance of
official duties by one or more employees of the Department of the
Navy, and thus, the invention herein may be manufactured, used or
licensed by or for the Government of the United States of America
for governmental purposes without the payment of any royalties
thereon or therefor.
Claims
1. A metal matrix composite (MMC) material composition of nickel
alloy and carbon nanotubes, said material composition comprising:
powdered granules of the nickel alloy; and a plurality of the
nanotubes, wherein said granules and the nanotubes are milled in a
hopper and sintered by a laser to form the MMC.
2. The material composition according to claim Herein the nickel
alloy is Inconel 625.
3. The material composition according to claim 1, wherein the
nanotubes are multi-wall carbon nanotubes (MWCNT).
4. The material composition according to claim 1, wherein the MMC
is 99.5 wt % of Inconel 625 for the nickel alloy and 0.5 wt % of
the nanotubes.
5. A manufacturing method for producing a metal matrix composite
(MMC) material composition of nickel alloy and carbon nanotubes,
said method comprising: inserting powdered granules of the nickel
alloy into a hopper; inserting the nanotubes into said hopper;
rotating said hopper at 450 rpm for 120 min to mill said granules
and the nanotubes into a mixture; and sintering said mixture by a
laser at 195 W and 1100 mm/s scan speed.
6. The manufacturing method according to claim 5, further including
filtering said granules by an 80 .mu.m sieve prior to insertion
into said hopper;
7. The manufacturing method according to claim 5, wherein said
sintering operation is conducted within an argon (Ar) atmosphere.
Description
BACKGROUND
[0002] The invention relates generally to metal matrix composites.
In particular, the invention relates to a composite of Inconel with
nanotubes.
[0003] A metal matrix composite (MMC) represents a specialized set
of materials composed of at least two different materials, one of
which is necessarily a metal. Inconel constitutes austenitic
structure nickel-chromium alloy as an oft used metal. In any
composite, the physical, electrical, or thermal interaction between
the constituents is critical. In order to create the composite, the
two constituents must first be mixed together to form a homogenous
mixture such that the secondary constituent.
[0004] Metal matrix composites have been employed in specialized
applications since around the 1960's. The more traditional MMC
fabrication methods, such as hot isostatic pressing (HIP),
centripetal compaction, Melt infiltration, spark plasma sintering,
and thermal spraying, require expensive tooling, long lead times,
and complicated manufacturing to generate a useful metal matrix
composite.
SUMMARY
[0005] Conventional aspirators yield disadvantages addressed by
various exemplary embodiments of the present invention. In
particular, exemplary embodiments provide a metal matrix composite
(MMC) material composition of nickel alloy and carbon nanotubes.
The material composition includes powdered granules of the nickel
alloy; and a plurality of the nanotubes. The granules and nanotubes
are milled in a hopper and sintered by laser to form the MMC.
Further embodiments provide the nickel alloy to be Inconel 625 and
the nanotubes to be
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] These and various other features and aspects of various
exemplary embodiments will be readily understood with reference to
the following detailed description taken in conjunction with the
accompanying drawings, in which like or similar numbers are used
throughout, and in which:
[0007] FIG. 1 is a graphical view of Inconel particle size
distribution;
[0008] FIG. 2A is a diagram view of the composite fabrication
process;
[0009] FIG. 2B is a detail view of testing and analysis; and
[0010] FIG. 3 is an enlargement photographic views of the
composite.
DETAILED DESCRIPTION
[0011] In the following detailed description of exemplary
embodiments of the invention, reference is made to the accompanying
drawings that form a part hereof, and in which is shown by way of
illustration specific exemplary embodiments in which the invention
may be practiced. These embodiments are described in sufficient
detail to enable those skilled in the art to practice the
invention. Other embodiments may be utilized, and logical,
mechanical, and other changes may be made without departing from
the spirit or scope of the present invention. The following
detailed description is, therefore, not to be taken in a limiting
sense, and the scope of the present invention is defined only by
the appended claims.
[0012] The disclosure generally employs quantity units with the
following abbreviations: length in microns (.mu.m) or nanometers
(nm), mass in kilograms (kg), time in seconds (s) or minutes (min),
area in square inches (in.sup.2), strength or torque in foot-pounds
(ft-lb.sub.f), speed at millimeters-per-second (mm/s), power in
watts (W), rotation in revolutions-per-minute (rpm), pressure in
thousands of pounds-per-square-inch (ksi) or millions of
pounds-per-square-inch (Msi), specific' surface area in
square-meters-per-gram (m.sup.2/g) and density in
grams-per-milliliter (g/ml equivalent to
grams-per-cubic-centimeter).
[0013] Exemplary embodiments provide a 99.5% weight Inconel
625-0.5% weight multi-walled carbon nanotube (MWCNT) metal matrix
composite (MMC) fabricated using direct metal laser sintering
(DMLS). For exemplary embodiments, multi-wall carbon nanotubes
(MWCNT), is uniformly distributed and dispersed throughout the
matrix material The quality of the mixture controls the level of
homogeneity and isotropic nature of material properties exhibited
by the material in its useful form.
[0014] With the ramp up in additive manufacturing technology such
as three-dimensional printing, specifically direct metal laser
sintering (DMLS), it is now possible to bypass many of the
windfalls of the more traditional methods and fabricate a useful
MMC in only a short period of time, possibly even a day. The
challenge to using DMLS to fabricate a metal matrix composite using
MWCNT is to control the sufficient sintering (welding) of the
micronized metal powder to itself and around the MWCNT while not
damaging or degrading the MWCNT. DMLS employs both high temperature
and laser radiation. Both of these variables, heat flow control and
laser irradiance, must be intelligently handled to ensure the metal
matrix composite is sufficiently processed by the machine to form a
useful component, and the MWCNTs remain intact and in direct
contact with the metal matrix so their material properties can be
utilized.
[0015] Direct Metal Laser Sintering employs a laser with a maximum
output of 400 W to selectively heat micronized metal powder of a
chosen alloy such that the individual particles of metal are taken
passed their liquids point to flow and combine with adjacent
particles. The scanning path of the laser is determined from three
dimensional computer assisted design (CAD) data that are generally
"sliced" into layers with each layer being a full pass scan of the
laser. Once a single layer is complete, the build platform in the
DMLS machine (EOSint M280) is lowered, a new layer of powder is
spread across the previously sintered layer, and the laser scanning
process begins again. The current layer is sintered, or welded, to
the preceding layer until all layers are complete. At this point
the complete part, which has the same geometry as the CAD data,
within a tolerance of the machine, can be extracted from the build
plate,
[0016] The selection of the constituents of the MMC is critical.
The DMLS only has fourteen different alloys to choose from such
that useful parts with predictable material properties can be
fabricated. This is largely a function of alloys that are produced
in a micronized form by either EOS or other suppliers because the
laser parameter sets on the machine are specific to the micronized
powder alloy and size distribution of particles. MWCNTs were chosen
as the secondary constituent largely because their outstanding
material properties would cause a noticeable change in material
performance, even in small weight percent of the overall composite.
MWCNTs are very stable due to their SP2 electron bond structure,
but are difficult to disperse and obtain a homogenous mixture due
to self-attraction and van der Waal forces.
[0017] When working with MWCNT (or any carbon nanotube), dispersion
is always the fundamental challenge. Inconel 625 was chosen because
nickel (Ni), the base element in the alloy, does not form stable
carbides over a wide and elevated temperature range. Additionally,
carbon nanotubes are often grown on nickel substrates due to low
reactivity between nickel and carbon. Nickel is also often used as
an intermediary between MWCNT and other metals in MMCs to reduce
carbide formation between the MWCNT and the metal matrix, aluminum
(Al) for example, which have high affinity for carbide
formation.
[0018] Any carbides formed in the MMC are a direct result of
degradation, damage, or complete destruction of the MWCNT. Thus,
carbide formation in MMC is usually undesirable. All details in the
selection process, including the thermodynamic data, used in matrix
metal selection is included in the attached technical brief. So far
as known, an Inconel 625--MWCNT MMC has not been previously
fabricated, especially with DMLS technology.
[0019] First, to fabricate an Inconel-MWCNT metal matrix composite
using DMLS, an additive manufacturing process, where change to the
material properties (yield strength, ultimate strength, elongation
to failure, modulus, electrical, and thermal) can be shown to be
materially altered from the base matrix alloy (Inconel 625) through
test data gathered in accordance with American Society for Testing
and Materials (ASTM) standards. Second, to develop or combine
processes (i.e., additive manufacturing, bulk mixing methods) to
circumvent complications or complexities arising in more
traditional methods (HIP, casting, etc.) of MMC manufacturing.
[0020] All details on material choice and selection are given in
the attached brief. As stated in the Background section, the
fundamental challenge when making a MMC using MWCNT is nanotube
dispersion throughout the matrix material. The MWCNT were supplied
by Nanostructured & Amorphous Materials, Inc. as graphitized
multi-walled carbon nanotubes, stock number 1228YJF, with the
following properties: [0021] Functionalization: --OH [0022] Purity:
99.9% [0023] Content of --OH: 1.45-1.61 wt [0024] Outside Diameter:
10-20 nm [0025] Inside Diameter: 5-10 nm [0026] Length: 10-30
micrometer [0027] Specific Surface Area: >100 m.sup.2/g [0028]
Color: Black The MWCNT were functionalized to aid in dispersion and
graphitized to reduce impurities which would promote MWCNT damage
during the rapid heating during the DMLS process.
[0029] The Inconel 625 metal matrix powder was procured through
Electrical Optical Systems (EOS) GmbH of North America and is a
stock product they offer for normal DMLS operation when processing
Inconel 625. The tested particle size distribution and published
elemental composition of the Inconel 625 is listed: [0030] Ni
(nickel #28) (balance 58 wt %) [0031] Cr (chromium #24) (20-23 wt
%) [0032] Mo (molybdenum #42) (8-10 wt %) [0033] Nb (niobium #41)
(3.15-4.15 wt %) [0034] Fe (iron #26) (.ltoreq.0.5 wt %) [0035] Ti
(titanium #22) (.ltoreq.0.4 wt %) [0036] Al (aluminum #13)
(.ltoreq.0.4 wt %) [0037] Co (cobalt #27) (.ltoreq.0.1 wt %) [0038]
Ta (tantalum #73) (.ltoreq.0.05 wt %) [0039] Si (tin #50), Mn
(manganese #25) (each .ltoreq.0.5 wt %) [0040] P (phosphorous #15),
S (sulfur #16) (each .ltoreq.0.015 wt %). The density from this
alloy is a minimum of 8.4 g/ml.
[0041] FIG. 1 shows graphical view 100 of scale plots for unmilled
Inconel 625 powder. Diameter size 110 represents the abscissa in
microns, while volume density 120 in percentage denotes the left
ordinate and cumulative volume 130 in percent denotes the right
ordinate. A legend 140 identifies a dark line for frequency and
undersize components 150, with the ideal diameter 160 at 77 .mu.m
for the left ordinate, and an S-curve 170 for the right
ordinate.
[0042] FIG. 2A shows a process flowchart 200 of MMC Manufacture
using DMLS. The process begins with materials 210 that include
metal powder 220 and carbon nanotubes 230 combined together in a
ball mill Attritor 240 for mixing in a hopper 245. Upon completion
the aggregation produces dispersed carbon nanotubes 250 subject to
laser sintering 260. Following this mechanical binding process, the
resulting material is subject to testing and analysis 270 with FIG.
2B providing a detail view.
[0043] A stress-strain plot with strain (dependent response) as the
abscissa and stress (driver) as the ordinate reveals a response
curve 275 for metal coupons 280. Such tests are further described
for ASTM E8. These coupons begin in the initial unstressed state
282, through elastic deformation 284, then plastic deformation 284
ending at necking, and finally fracture 288.
[0044] FIG. 3 shows enlargement photographic views 300 of MWCNT
dispersion during milling and mixing of powder prior to sintering.
The photographs show top image 310 with scale of 3 mm and, bottom
image 320 with scale of 0.5 .mu.m. The top image 310 shows spheres
330 of Inconel 625. The bottom image 320 shows nanotube bundles
340.
[0045] Material Mixing is described herein for the resulting milled
powder 250. The Inconel 625 powder 220 and MWCNT 230 were combined
in a ball mill Attritor 240 for mechanical mixing. The relative
weight percent of Inconel 625 powder 220 and MWCNT 230 were 99.5
and 0.5, respectively. The total weight of material in the Attritor
240, excluding milling media, was 30 kg. The Attritor 240 used 440C
stainless steel milling media with a Rockwell hardness of 58-65to
agitate and disperse the MWCNT 230 into the Inconel 625 powder 220.
The material and hardness (treatment) of the media were chosen to
reduce cross contamination between the milling media and Inconel
625 powder 220. The hopper 245 spun at 450 rpm for 120 min to
adequately disperse the MWCNT 230.
[0046] Laboratory experiments 270 were conducted to determine an
adequate milling time such that good MWCNT dispersion was evident
and changes in particle size distribution of Inconel 625 was kept
to a minimum. A small addition of two weight percent (2 wt %)
deionized water (H.sub.2O) was added to the mixture as a process
control agent prior to milling to inhibit cold welding of the
Inconel 625 particles when caught in between the stainless steel
milling media. This was an effort to reduce the change in particle
size distribution of the Inconel 625 powder 220 prior to direct
metal laser sintering 260.
[0047] Direct metal laser sintering 260 is described herein. The
milled powder 250 was fed through an 80 micron (or .mu.m) sieve
into the powder distribution hopper 245 of the EOS M280 DMLS
machine 240 to eliminate or filter particles that had grown too
large (due to cold welding) during the mixing process. The layer
thickness of the DMLS was set to 20 .mu.m and a high speed steel
recoating blade was used to distribute powder over the build plate.
The sample geometries were oversized versions of ASTM-E8M and
ASTM-E23 test specimens such that they could be post machined to
final size prior to testing.
[0048] The laser operated at 195 W and 1100 mm/s scan speed. These
parameters were chosen to ensure the MWCNT could handle the DMLS
laser irradiance based on prior research into laser calorimetry.
The sintering process took place in a 99.9% industrial grade argon
(Ar) atmosphere to reduce oxidation of any material.
[0049] AU parts were built on a hybrid support structure to
optimize heat transfer from the test specimens and the build plate
and reduce residual stresses in completed parts. The hybrid support
structure comprised solid Inconel 625 support at each end with an
approximate area of 0.25 in.sup.2 (per end) with latticed support
throughout the middle of each specimen. The specimens were then cut
free of the build plate and post machined to applicable ASTM test
geometry after the build was complete.
[0050] Testing performed 270 is described as follows. The specimens
were tested to ASTM-E8M and ASTM-E23 to record relevant test data.
Test data (yield strength, ultimate tensile strength, elongation to
failure (%), elastic modulus, percent shear fracture, and Charpy
impact strength) was collected and post-processed, and compared
against 100 wt % Inconel 625 specimens fabricated in the same
manner as the MMC specimens. Scanning Electron Micrographs were
taken of the materials to prove MWCNT survival.
[0051] Results are presented as follows. The MMC specimens showed
the following average increase/(decrease) in material properties
over the 100 wt % Inconel 625 specimens. [0052] Yield Strength:
34.5% (144.1 ksi versus 107.1 ksi) [0053] Ultimate Tensile
Strength: 26.8% (187 ksi versus 147.5 ksi) [0054] Elongation to
failure: (58.5%) (15.7% versus 37.8%) [0055] Elastic Modulus: 5.9%
(28.5 Msi versus 26.9 Msi) [0056] Resilience: 57.8% (710
in-lb.sub.f/in.sup.3 versus 450 in-lb.sub.f/in.sup.3) [0057] Charpy
Impact Strength: (74.7%) (26.2 ft-lb.sub.f versus 103.6
ft-lb.sub.f) [0058] Hardness: 19.9% (30.7 RHC versus 25.6 RHC) Note
that resilience is area under the stress-strain curve from zero
load to yield.
[0059] As can be observed, the MMC possesses higher values over the
pure Inconel 625 in yield strength, ultimate tensile strength,
elastic modulus, resilience, and hardness, along with less
elongation to failure. Charpy impact strength is constitutes the
primary tradeoff.
[0060] Commercial Potential can be introduced as follows. As stated
in the background section, MMCs have been employed in high
performance applications for about the last half century. However,
the ability to fabricate MMCs using Direct Metal Laser Sintering
affords significant time and cost savings over more traditional
methods of MMC manufacture. DMLS circumvents the necessity for mold
design, mold fabrication, and mold reconditions, which are required
in MMC fabrication using HIP, for example.
[0061] Multiple components can be fabricated at the same time using
DMLS with little machine oversight. Additionally, many MMCs are not
100% solid. Due to traditional manufacture, with the exception of
melt infiltration or melt casting of MMC, which are very expensive,
there are often voids which create stress concentrations in the
material causing premature or unpredictable failure. DMLS
processing produces a 100% solid part with predictable material
properties and dynamics under load.
[0062] Purpose for the exemplary embodiments are described herein.
In the 30-year Department of the Navy (DON) Research and
Development (R&D) plan, there is emphasis on developing
processes and technology to further additive manufacturing and
nanotechnology. The primary objective for these efforts is to
utilize additive manufacturing processes to produce production
representative hardware.
[0063] Up until recently, most additive manufacturing efforts have
been geared towards making prototypes quickly (rapid prototyping)
for design verification rather than deployment. MMCs are typically
used in applications where a combination of material properties
from each constituent is desired (thermal and strength, electrical
and ductility, etc). Utilizing DMLS to fabricate MMCs with known
material properties (through testing) is a large step towards
producing parts composed of advanced materials which can satisfy a
Navy need in a very short period of time compared to historic MMC
development.
[0064] The advantages of exemplary embodiments include: Using DMLS
to fabricate MMCs creates significant time and cost savings, where
much of the design normally used to construct molds or fine tune
expensive and lengthy processes can now be circumvented. MMCs that
would traditionally take weeks or even months to fabricate can now
be made in as little as a day if all the equipment and material is
readily available. The MMC parts made with DMLS are also 100% solid
and have predictable and repeatable material properties and load
characteristics so long as the parts with that material formulation
have been previously tested.
[0065] Alternatives to the exemplary embodiments possess distinct
disadvantages. Refinements to the powder mixing process to achieve
better dispersion of MWCNT (or other nanorod, nanotube, or
nanopowder) would be a critical improvement to the process. This
author believes (through research) that employing a large sonic
acoustic resonant mixing machine with a higher content of deionized
water as a process control agent (PCA) and resonant frequency of
>60 Hz would create enough shear energy and lubrication to
disperse the secondary constituent into the metal powder. This
process also alleviates the concern of MWCNT damage and cold
welding of the metal particles due to collision of milling
media.
[0066] This mixing process requires an inert, preferably argon
(Ar), atmosphere to reduce reactivity. Upon mixing completion, the
powder mixture can be dried in an oven (also inert) at an
intermediate temperature to evaporate any left over PCA. Another
possible alternative to producing a homogenously mixed powder would
be to incorporate the nanoparticle or nanotube into the powder
manufacturing, process. Chemical vapor deposition (CVD) or
introduction of a secondary constituent into the powder
micronization process encapsulates the secondary constituent into
the inner volume of metal particles and create a more homogenous
mixture. Alternatives to the DMLS process would be selective laser
sintering (SLS) or spark plasma sintering (SPS) without much
practical distinction.
[0067] While certain features of the embodiments of the invention
have been illustrated as described herein, many modifications,
substitutions, changes and equivalents will now occur to those
skilled in the art. It is, therefore, to be understood that the
appended claims are intended to cover all such modifications and
changes as fall within the true spirit of the embodiments.
* * * * *