U.S. patent application number 13/963197 was filed with the patent office on 2015-12-24 for joining via nano-scale reinforced bonding media: materials, procedures and applications thereof.
This patent application is currently assigned to METNA CO. The applicant listed for this patent is Anagi Manjula Balachandra, Mohammad Sayyar Bidgoli, Parviz Soroushian. Invention is credited to Anagi Manjula Balachandra, Mohammad Sayyar Bidgoli, Parviz Soroushian.
Application Number | 20150367617 13/963197 |
Document ID | / |
Family ID | 54868880 |
Filed Date | 2015-12-24 |
United States Patent
Application |
20150367617 |
Kind Code |
A1 |
Balachandra; Anagi Manjula ;
et al. |
December 24, 2015 |
Joining via Nano-Scale Reinforced Bonding Media: Materials,
Procedures and Applications Thereof
Abstract
Method of joining articles using microscale brazing alloy
particles reinforced with slender nanomaterials is described.
Surface modified graphite nanomaterials were dispersed in a medium
comprised of metal alloy particles, this dispersion was introduced
at the interface between the joining articles followed by heating
under ultra high vacuum. The nanomaterial-to-metal alloy surface
contacts were enhanced by at least one of fusion, embedment and
chemical reaction phenomena under high temperature and ultra high
vacuum yielding true nanocomposite at the interface. The fusion,
embedment and chemical reaction phenomena enhance at least one of
the mechanical, electrical, thermal, durability and functional
attributes of these contact points, which translate into improved
properties of the joined article. The enhanced contact points
enable effective use of the distinct qualities of nanomaterials
towards development of joints which offer unique balances of
strength, ductility, toughness, energy absorption, thermal
stability, weathering resistance and other characteristics.
Inventors: |
Balachandra; Anagi Manjula;
(Okemos, MI) ; Soroushian; Parviz; (Okemos,
MI) ; Sayyar Bidgoli; Mohammad; (East Lansing,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Balachandra; Anagi Manjula
Soroushian; Parviz
Sayyar Bidgoli; Mohammad |
Okemos
Okemos
East Lansing |
MI
MI
MI |
US
US
US |
|
|
Assignee: |
METNA CO
Lansing
MI
|
Family ID: |
54868880 |
Appl. No.: |
13/963197 |
Filed: |
August 9, 2013 |
Current U.S.
Class: |
156/73.1 ;
156/150; 156/60 |
Current CPC
Class: |
B23K 35/0222 20130101;
B23K 35/284 20130101; Y10T 156/10 20150115; B23K 35/327 20130101;
B23K 35/262 20130101; B23K 35/0244 20130101; B23K 35/0255 20130101;
B23K 35/286 20130101 |
International
Class: |
B32B 37/08 20060101
B32B037/08; C23C 18/16 20060101 C23C018/16; C01B 31/02 20060101
C01B031/02; B32B 37/06 20060101 B32B037/06 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH &
DEVELOPMENT
[0001] This invention was made with U.S. government support under
Contracts FA8650-07-C-3704 by the U.S. Air Force. The U.S.
government has certain rights in the invention.
Claims
1. Method of joining two or more articles through a bonding medium
reinforced by graphite nanomaterials, the method comprising: (i)
dispersion of graphite nanomaterials comprising at least one of
carbon nanotubes and carbon nanofibers within a volume which
includes a dispersant and particles which form said bonding medium
via melting during joining at elevated temperature, with weight
ratio of the nanomaterials to said particles ranging from 0.05% to
0.15%, with surfaces of said nanomaterials are modified to
facilitate dispersion of the nanomaterials and to increase their
interfacial interactions with said bonding medium; (ii) application
of said dispersion incorporating surface modified nanomaterials,
dispersant and particles on at least one joining surface of said
articles, and heating the applied dispersion in order to remove any
volatile constituents; (iii) bringing the joining surfaces of said
articles into contact; (iv) heating the contacting surfaces in
order to melt said particles in the bonding medium, with the molten
bonding medium wetting the joining surfaces of said articles, and
surfaces of said nanomaterials; and (v) cooling the contacting
surfaces to join said articles via the reinforced bonding medium
which is solidified, bonded to joining surfaces, and enhanced by
surface modified graphite nanomaterials.
2. The method of claim 1, wherein said articles are made of at
least one of metals, metal alloys, superalloys, metal matrix
composites, ceramics, ceramic matrix composites, carbon and carbon
composites.
3. The method of claim 1, wherein the particles of said bonding
medium are made of at least one of brazing alloys, with particle
size ranging from 1 micrometer to 1 millimeter.
4. The method of claim 3, wherein said brazing alloys comprise at
least one of silver, copper, titanium, tin, lead, gold and
nickel.
5. The method of claim 1, wherein the surfaces of said graphite
nanomaterials are modified to improve the interfacial interactions
with the said bonding medium by one of methods: (i) coating with at
least one of copper, nickel and silver via electroless deposition;
and (ii) introduction of at least one of carboxyl and hydroxyl
functional groups on to the surface of the graphite nanomaterials
via chemical functionalization.
6. The method of claim 1, wherein the dispersant of said bonding
medium comprising organic solvent and at least one of surfactants
and polyelectrolytes, wherein organic solvent is one of isopropyl
alcohol (IPA), ethanol, methanol, tetrahydrofuran (THF), dimethyl
formamide (DMF) and toluene; wherein said surfactant comprise at
least one of sodium dodecyl sulfate (SDS), Triton X-100, sodium
dodecylbenzenesulfonate (SDBS), sodium dodecyl sulfonate (SDSA),
sodium n-lauroylsarcosinate, sodium alkyl allyl sulfosuccinate,
polystyrene sulfonate (PSS), dodecyltrimethyl ammonium bromide
(DTAB), cetyltrimethyl ammonium bromide (CTAB), Tween, and
poly(vinylpyrrolidone) (PVP); and wherein said polyelectrolytes
comprise at least one of poly(acrylic acid) (PAA), polystyrene
sulfonate (PSS), poly(ethylene imine) (PEI) and polyallyl amine
hydrochloride (PAH).
7. The method of claim 1, wherein said dispersion comprising said
surface modified graphite nanomaterials and said particles in said
dispersant is achieved via at least one of sonication and mixing.
Description
FIELD OF INVENTION
[0002] The present invention relates to a method of joining through
nano-scale reinforced brazing alloy paste to enhance strength,
ductility, energy absorption capacity and toughness of the brazed
joints for high temperature aerospace applications.
BACKGROUND OF THE INVENTION
[0003] The following is a tabulation of some prior art that
presently appears relevant:
U.S. Patents
TABLE-US-00001 [0004] Patent Number Kind Code Issue Date Patentee
U.S. Pat. No. 7,416,108 B2 Aug. 26, 2008 Philip U.S. Pat. No.
5,127,969 A Jul. 7, 1992 Sekhar
U.S. Patent Application Publications
TABLE-US-00002 [0005] Application Number Kind Code Publication Date
Applicant US 2009/0186238 A1 Jul. 23, 2009 Clifford Bampton
Foreign Patent Application Publications
TABLE-US-00003 [0006] Application Number Kind Code Publication Date
Applicant EP1759806 A1 Mar. 7, 2007 Jungbluth et al.
Non Patent Literature Documents
[0007] 1. Gavens, A. J. Van Heerden, D. Mann, A. B. Reiss, M. E.
and Weihs, T. P., Effect of intermixing on self-propagating
exothermic reactions in Al/Ni nanolaminate foils. Journal of
Applied Physics 2000. 87(3): p. 1255-1263. [0008] 2. Barrena, M.,
Gomez de Salazar, J. and Matesanz, L., Interfacial microstructure
and mechanical strength of WC-Co/90MnCrV8 cold work tool steel
diffusion bonded joint with Cu/Ni electroplated interlayer.
Materials & Design, 2010. 31(7): p. 3389-3394. [0009] 3. Gain,
A. K., et al., The influence of addition of Al nano particles on
the microstructure and shear strength of eutectic Sn--Ag--Cu solder
on Au/Ni metallized Cu pads. Journal of alloys and compounds, 2010.
506(1): p. 216-223.
[0010] High-temperature exposures are encountered in many aerospace
systems, including reentry and hypersonic air vehicles, and jet
engines. Joining of dissimilar (and similar) materials which are
exposed to elevated temperature is a key step in manufacturing
aerospace components for such applications. These joints should
meet certain mechanical and thermal stability requirements, and
should also safely accommodate the thermal expansion mismatch
caused by dissimilar expansion coefficients and/or temperature
gradients of joined parts. The high-temperature joining processes,
originally developed for metals and extended to metal-to-ceramic
joining, include mechanical fastening, fusion welding, diffusion
bonding, friction welding, ultrasonic joining, and brazing.
[0011] Most of these joining techniques have drawbacks in terms of
the leakage of adhesive and the thermal stability of the joint.
Fasteners have the problem of added weight and corrosion problems.
Further, for some materials (ceramics to ceramics or ceramics to
metals), joining methods are limited due to inherent weakness of
the joining substrates that lead to poor machinability and restrict
the use of fasteners. Brazing and diffusion bonding are the most
commonly employed processes for joining of ceramics and metals.
Diffusion bonding involves application of high pressures at
elevated temperatures, which could limit their applications due to
cost constraints. Brazing is more convenient compared to diffusion
bonding as large pressure is not required in joint formation.
However, brazed joints are brittle as metal alloys are used in bond
formation. Typically, large thermal expansion mismatch between
joining articles such as ceramics and metals, caused by relatively
large difference between their coefficients of thermal expansion as
well as temperature gradients, produces residual thermal stresses
within ceramic-to-metal or dissimilar metal joints after
high-temperature joining followed by cooling. These stresses
compromise the joint strength; high-temperature service exposures
could also produce higher thermal stress levels. The effect of
residual stresses on joint strength has been demonstrated. For
example, it has been shown that alumina-to-superalloy brazed joints
provide lower strengths than alumina-to-alumina brazed joints. A
strong demand therefore exists for development of a bonding method
that can securely bond the parts for more durable strong bonds.
[0012] In U.S. Pat. No. 7,416,108 nanoparticles are used as the
interface of two articles as a constituent of the braze material,
which melt upon temperature rise to join the two articles. This
approach takes advantage of the fact that metal nanoparticles have
lower melt temperatures compared to the corresponding bulk metals.
The use of nanoparticles thus lowers the brazing temperature; after
melting, however, the nanoparticles would no more exist as
nanomaterials. The present invention employs slender nanomaterials
in lieu of nanoparticles, and such slender nanomaterials would
preserve their nanoscale geometry after joining resulting strong
conformable joint.
[0013] U.S. Pat. No. 5,127,969 discloses a method of making
reinforced composite solder, brazing or welding material through
incorporation of graphite, silicon carbide, a metal oxide, an
elemental metal or metal alloy in particulate or fibrous form. This
invention does not incorporate any nanomaterial in the brazing
media.
[0014] Patent Application No. EP1759806A1 presents a crack repair
method utilizing brazing through incorporation of same metal
nanoparticles as in brazing medium. This invention differs from the
current invention as no nano features are retained after the repair
is been done.
[0015] NanoFoil is a new class of nano-engineered material,
fabricated by vapor-depositing thousands of alternating nanoscale
layers of aluminum and nickel. When activated by a small pulse of
local energy from an electrical, optical or thermal source, the
foil reacts to precisely deliver localized heat, and then cooling
equally quickly. NanoBond is reactive joining process, utilizing
NanoFoil to act as a local heat source for room temperature
soldering of both similar and dissimilar materials (Gavens, A. J.,
et al., Journal of Applied Physics 87(3) 1255-1263 (2000)).
[0016] Barrena et. al. investigated a high temperature joining
method between a cemented carbide (WC-15% Co) and a cold work tool
steel (90MnCrV8), which involved diffusion bonding in vacuum using
a ductile interlayer of Ni--Cu. Due to the substantial difference
between thermal expansion coefficients in substrates, the
interlayer was selected as its thermal expansion occurs between
those of cemented carbides and steels. High strength of such joints
at elevated temperatures was shown in their investigation (Barrena,
M., et al., Materials & Design 31(7) 3389-3394 (2010)).
[0017] Gain et al. proposed introduction of Al nanoparticles into
Sn--Ag--Cu solder alloy in order to enhance shear strength of low
temperature joints. Strength of the bulk solder was enhanced by the
formation of fine Sn--Al--Ag intermetallic particles as well as the
controlled fine microstructure after long-term aging. The failure
mode of Sn--Ag--Cu solder joints containing Al nanoparticles
appeared to be ductile fracture with very rough dimpled surfaces
due to the formation of fine Sn--Al--Ag intermetallic compound
particles at the top surface of Sn--Ni--Cu intermetallic compound
layer (Gain, A. K., et al., Journal of alloys and compounds 506(1)
216-223 (2010)).
BRIEF SUMMARY OF THE INVENTION
[0018] Current invention relates to joints fabricated between
similar or dissimilar substrates through nano-scale reinforced
brazing alloy particulate medium to enhance strength, ductility,
toughness, and energy absorption capacity of the fabricated joints.
These joints have applications in aerospace and other engineered
structures where thermal stability of the joint is a consideration.
Graphite nanomaterials and brazing alloy paste (bonding medium
comprises brazing alloy particles) were used as the bonding medium
in lieu of brazing alloy sheet. Utilization of high aspect ratio
graphite nanomaterials render ductility to the joint, which in turn
helps with overcoming the adverse effects of stresses developed due
to thermal expansion mismatch of the dissimilar materials joined.
FIG. 1 schematically shows the fabrication of joint through
nano-scale reinforced bonding medium.
[0019] The present invention makes effective use of graphite
nanomaterials towards improving the performance of structural
joints for high temperature applications.
[0020] The novel approach brings about multi-faceted improvements
in the performance characteristics of a traditional braze alloy
paste through introduction of graphite nanomaterials. The addition
of graphite nanomaterials enhances the mechanical properties,
toughness, ductility and energy absorption capacity of the brazed
joints.
[0021] The present invention also brings multi-functionality into
the joint, rendering novel features to the article.
[0022] Another feature rendered by nano-scale reinforcement to
brazed joints is the rise in thermal and electrical conductivity.
This may even lower the thermal stresses, and reduce the
fabrication cost.
[0023] Addition of nanomaterials does not alter the manufacturing
process, is easy to scale-up, and is cost-effective. The newly
developed nano-braze joints transforms traditional braze joints
into tougher, stronger and more ductile joints without adding any
additional weight or carrying a significant cost penalty.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0024] Accompanying drawings help with explaining the invented
nano-scale reinforced brazed joints, materials and procedures for
making them, and their applications and performance. The
accompanying drawings are only for the purpose of illustrating the
embodiments of the invented methods, and not for the purpose of
limiting the invention.
[0025] FIG. 1 Schematic representation of joint fabrication process
through nano-scale reinforced bonding media.
[0026] FIG. 2 Preparation of different carbon nanomaterial
dispersion with brazing alloy paste.
[0027] FIG. 3 Solvent casting of nanomaterials-Ticusil
dispersion.
[0028] FIG. 4 Steps involved in processing of nano-braze joints
with different substrates.
[0029] FIG. 5 SEM microscope images (cross-sectional views) of
different locations of the nano-braze Inconel-to-Inconel joint
fabricated with 5 (CuCNT-F/Ticusil) brazing alloy (scale bar is
0.05 inches).
[0030] FIG. 6 EDS elemental maps for cross-section of the nano
braze inconel-to-inconel joint fabricated using copper-coated
carbon nanomaterials/Ticusil.RTM..
[0031] FIG. 7 Comparison of shear stress-deflection behavior of
nano braze joint and control joint fabricated similarly but without
incorporation of graphite nanomaterials in braze.
[0032] FIG. 8 Strength and deformation capacity of nano-braze
joints incorporating different graphite nanomaterials with and
without metal coating versus those of the control joint.
[0033] FIG. 9 High-temperature single-lap shear test set-up and
comparison of the shear strength obtained at elevated temperature
for nano-braze joint incorporation nickel-coated carbon nanotubes
and control joints without any graphite nanomaterials.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Current invention relates to a method of joining two or more
articles through a bonding medium enhanced by graphite
nanomaterials, the method comprising:
(i) dispersion of graphite nanomaterials comprising at least one of
carbon nanotubes and carbon nanofibers within a volume which
includes a dispersant and at least one of particles of said bonding
medium, with the weight ratio of the nanomaterials to said
particles ranging from 0.05% to 0.15%, with surfaces of said
nanomaterials modified in order to facilitate dispersion of the
nanomaterials and their interfacial interactions with said bonding
medium; (ii) application of said dispersion incorporating
nanomaterials and particles on at least one joining surface of said
articles, and heating the applied dispersion in order to remove any
volatile constituents; (iii) bringing the joining surfaces of said
articles into contact; (iv) heating the contacting surfaces under
reduced pressure in order to melt said particles, with the molten
medium wetting the joining surfaces and the nanomaterial surfaces;
and (v) cooling the contacting surfaces to join said articles via
the medium which is solidified, bonded to joining surfaces, and
enhanced by nanomaterials.
[0035] This joining of two or more articles via nano-scale
reinforced bonding media is schematically shown in FIG. 1.
[0036] The term "dispersion" means uniformly, individually
distributed particles in a dispersant. Dispersion comprising
graphite nanomaterials and bonding medium in a dispersant,
preferably graphite nanomaterials are carbon nanotubes or carbon
nanofibers. Carbon anofibers, vapor grown highly graphitic, low
cost, tubular carbon structures. Carbon nanofibers are commercially
available as Pyrograf.RTM.-III with diameters ranging from 70 and
200 nanometers and a length of the as-produced fiber estimated to
be 50-200 microns. CNF are much smaller in diameter than
conventional continuous or milled carbon fibers (5-10 microns) but
significantly larger than carbon nanotubes. Carbon nanotubes are
single-walled, multi-walled with hollow or bamboo structure.
[0037] Surfaces of said carbon nanomaterials are modified to
improve the interfacial interactions with bonding medium through
following one of the methods: (i) coating with at least one of
copper, nickel and silver via electroless deposition; and (ii)
introduction of at least one of carboxyl and hydroxyl functional
groups on the surface of carbon nanomaterials via chemical
functionalization. Coating or metallization of carbon nanomaterials
with metals has been done using a two-step process comprising of
surface activation with noble metals such as Pd or Pt, which serves
as a catalyst for the second step, followed by the electroless
deposition of respective metal.
[0038] Dispersion of nanomaterials, and said bonding medium in a
dispersant is achieved via sonication. Typically sonication can be
achieved using bath sonicator, such as those by Branson, or using
sonicating horn design from companies such as Hielscher Inc or
Misonix, Inc. Dispersant allows uniform distribution of
nanomaterials these include at least one of surfactants,
polyelectrolytes and organic solvents. Surfactants are at least one
of the following sodium dodecyl sulfate (SDS), Triton X-100, sodium
dodecylbenzenesulfonate (SDBS), sodium dodecyl sulfonate (SDSA),
sodium n-lauroylsarcosinate, sodium alkyl allyl sulfosuccinate,
polystyrene sulfonate (PSS), dodecyltrimethylammonium bromide
(DTAB), cetyltrimethyl ammonium bromide (CTAB), Tween, and
poly(vinylpyrrolidone) (PVP). Polyelectrolytes are at least one of
the following poly (acrylic acid) (PAA), polystyrene sulfonate
(PSS), poly(ethylene imine) (PEI) and polyallyl amine hydrochloride
(PAH). Organic solvents are one of the following isopropyl alcohol
(IPA), ethanol, methanol, tetrahydrofuran (THF), dimethyl
formmamide (DMF) and toluene.
[0039] The term "bonding medium" means a material that allows
linking, binding, fastening, or holding two surfaces permanently
through melting upon heating and consolidating upon cooling.
Bonding medium comprising particles of brazing alloys of at least
one of the metals silver, copper, titanium, tin, gold and nickel
with particle size ranging from 1 micron to 1 millimeter.
[0040] The term "joining surfaces" meaning any material composed of
metallic or inorganic or organic or combination with a surface
allowing linking of nano-reinforced bonding media. Preferably
joining surfaces are made of at least one of metals, metal alloys,
super alloys, metal matrix composites, ceramics, ceramic matrix
composites, carbon and carbon composites.
[0041] Having described the invention, the following examples are
given to illustrate specific applications of and provide a better
understanding of the invention. These specific examples are not
intended to limit the scope of the invention described in this
application.
Example 1
[0042] Nano-brazed joints were fabricated using copper-coated
carbon nanotube (CuCNT) or copper-coated carbon nanofiber (CuCNF)
and brazing alloy bonding medium. Brazing alloy (TiCusil.RTM.)
paste comprising of particles ranging from 1 micrometer to 1
millimeter. Ticusil.RTM. paste was made of copper, silver and
titanium. Copper coating on carbon nanotubes or carbon nanofibers
was carried out through electroless deposition method. The
concentration of carbon nanomaterial in brazing alloy was 0.5-1 wt.
%. Carbon nanotubes were copper-coated and functionalized. Carbon
nanofibers were used in the following forms: (i) functionalized
(CNF--F); (ii) copper-coated and functionalized (CuCNF--F); (iii)
functionalized, copper-coated and functionalized (Cu--F--CNF--F).
Hybrid coatings of modified graphite nanomaterils/TiCusil.RTM. were
introduced on to the faying surfaces of ceramic matrix composites
(CMC), supper alloy inconel prior to fabrication of brazed joints.
The desired structure of nano-brazed inconel-to-inconel joints
provided the basis to undertake mechanical evaluation of these
nano-brazed joints by performing single-lap shear tests.
Dispersion of Graphite Nanomaterials in Ticusil Brazing Alloy
Paste
[0043] 0.1 g of Ticusil.RTM. paste was mixed with 1 mL of
copper-coated graphite nanomaterial (either CuCNT or CuCNF) or
functionalized copper-coated graphite nanomaterials (either CuCNT-F
or CuCNF--F), noting that 0.02 g of CNT or CNF was originally
dispersed in 20 mL of isopropyl alcohol (IPA). The mixture was
diluted to 5 mL with isopropyl alcohol (IPA). The dispersion was
prepared by 10 minutes of homogenization followed by 10 minutes of
sonication (sonic probe), with procedure was repeated two more
times FIG. 2 shows the dispersion of CuCNT (or CuCNF) in
Ticusil.RTM. paste.
Functionalization of Copper-Coated Carbon Nanomaterials
[0044] In our approach to functionalization of CuCNT (or CuCNF),
0.02 g of 11-Mercapto-1-undecnol (MUD) was added to 20 ml of
ethanol, and the mixture was bath-sonicated for 5 minutes; 0.02 g
of CuCNT (or CuCNF) was then added, and stirred overnight. The
dispersion was centrifuged with ethanol twice to remove the excess
MUD.
Deposition on Surfaces
[0045] Solvent-casting or spraying was employed for deposition of
graphite nanomaterials in Ticusil.RTM. paste. FIG. 3 shows the
solvent-casting process, this process comprised of: (i)
introduction of a layer of CuCNT/Ticusil.RTM. or CuCNF/Ticusil.RTM.
dispersion in IPA; and (ii) evaporation of solvent through heating
at 60.degree. C. Two steps were repeated until the required amount
of nano-reinforced bonding medium was deposited.
Nano-Brazed Joint Fabrication
[0046] Joints were made either between CMC and inconel or CMC and
CMC or inconel to inconel. The steps involved in forming the
high-temperature nano-engineered joints are presented in FIG. 4.
The joining plates were assembled with the coated surfaces (hybrid
coatings of CuCNT/TiCusil.RTM. or CuCNF/TiCusil.RTM.) placed
against each other; the assembly was pressed within a stainless
steel clamp, and heated in a vacuum furnace.
Microscopic Evaluation of Nano-Brazed Joints
[0047] Fabricated joints were sectioned and characterized through
microscopy. Scanning electron microscopy (SEM) and Energy
Dispersive X-ray Spectroscopy (EDS) analysis were undertaken to
provide insight into the structure and composition of the
nano-brazed joints. FIG. 5 shows SEM micrographs of cross-sections
of nano-brazed joints. FIG. 6 shows EDS elemental mapping of
cross-sections nano-brazed joints. These EDS elemental maps
indicated that carbon is well distributed on the joint area. In
addition, Cu, Ag and Ti, which were constituents of Ticusil.RTM.,
were distributed uniformly in the joining interface. These findings
indicate that graphite nanomaterials interact well with the
Ticusil.RTM. brazing alloy medium forming and metal matrix
nanocomposite at the joining interface.
Mechanical Evaluation of Nano-Brazed Joints
[0048] The strength and ductility of these nano-brazed joints
fabricated with graphite nanomaterials in Ticusil.RTM. brazing
alloy paste were evaluated by room temperature single-lap shear
tests. FIG. 7 shows comparison of shear stress-deflection behavior
of nano-brazed and control joints. When compared with control
joints, nano-brazed joints provided about 25% higher shear strength
as well as improved ductility and energy absorption capacity. For
the evaluation of the high-temperature stability joints were tested
by high temperature single-lap shear exposing the samples to
elevated temperature (>480.degree. C.). Nano-engineered joints
fabricated with CNF and Ticusil.RTM. bazing alloy paste were
evaluated at 480.degree. C. showed that nano-brazed joints were
about 25-30% stronger than that of control joints fabricated
similarly without use of graphite nanomaterials.
Example 2
[0049] Joints were fabricated with as produced graphite
nanomaterials these include; single-walled carbon nanotubes,
multi-walled carbon nanotubes and carbon nanofibers. Two different
graphite nanomaterial dispersions were prepared: (1) dispersion 1
comprising graphite nanomaterials; and (2) dispersion 2, comprising
nanomaterials and poly(acrylic acid) (PAA, a polymer with uniformly
distributed carboxylic acid groups (negative charge moieties along
the polymer chain) to facilitate thorough dispersion of
nanotubes.
[0050] Dispersion 1 was made with 0.02 g of graphite nanomaterials
in 10 mL of IPA. Sonication was employed over three hours (in a
sonicator bath) to disperse the nanotubes. The dispersion was then
centrifuged over 30 minutes in order to separate the supernatant,
which was then used in solvent-casting to form the nanotube mat on
joining surfaces. Between depositions, the dispersion was kept in
the sonicator bath to avoid any agglomeration.
[0051] Dispersion 2 used a mixture of 0.02 g of the graphite
nanomaterials and 0.02 g of PAA (PAA: nano ratio of 1:1), in 100 mL
of IPA. The dispersion was sonicated using a sonic probe at
different amplitudes, followed by pulsing at 70% amplitude for two
10-minute intervals, with the whole cycle repeated one more time.
The resulting dispersion was centrifuged over 30 minutes, and the
supernatant was separated for use in solvent-casting.
[0052] Hybrid coating of graphite nanomaterials/TiCusil.RTM. was
introduced on to the faying surfaces of superalloy (inconel) prior
to fabrication of brazed joints. Brazed inconel-to-inconel joints
fabrication was carried out as described in EXAMPLE 1. Mechanical
performances of the fabricated nano-engineered joints were
evaluated in single-lap shear, and results are presented in FIG.
8.
Example 3
[0053] Brazed inconel-to-inconel joints were prepared with
Ticusil.RTM. paste and nickel coated carbon nanofiber (NiCNF), and
were subjected to high-temperature single-lap shear tests at
480.degree. C. The mean values in test results were compared
between control and nano-engineered joints.
[0054] Preparation of the CNF dispersion and its deposition on
joining surfaces followed the procedures described in EXAMPLE 1.
Briefly, the brazed inconel-to-inconel joints were prepared by
application of CNF and Ticusil.RTM. paste. These surfaces were
pressed against each other, and the assembly was heated above the
liquidous temperature of the brazing alloy. During heating molten
alloy wet the inconel surfaces and CNF surfaces, upon cooling
forming an integrated joint. Control joints were fabricated
similarly without the introduction of nanomaterials.
Nano-engineered joints, when compared with control joints, provide
30% higher shear strength at room temperature, and 25% greater
shear strength at 480.degree. C. High-temperature single-lap shear
test set-up and comparison of the shear strength obtained at
elevated temperature for nano-braze joint incorporating
nickel-coated carbon nanotubes and control joints without any
graphite nanomaterials is shown in FIG. 9. Further nano-brazed
joints provide more consistent performance characteristics when
compared with control joints.
* * * * *