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ADVANCED MATERIALS & PROCESSES •
NOVEMBER-DECEMBER 2014
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JTST HIGHL IGHTS
The
Journal of Thermal Spray Technology
(JTST),
the official journal of the ASM
Thermal Spray Society, publishes contri-
butions on all aspects—fundamental and
practical—of thermal spray science, in-
cluding processes, feedstock manufacture,
testing, and characterization. As the pri-
mary vehicle for thermal spray information
transfer, its mission is to synergize the rap-
idly advancing thermal spray industry and
related industries by presenting research
and development efforts leading to advancements in imple-
mentable engineering applications of the technology. Articles
from the October and December issues, as selected by
JTST
Editor-in-Chief Christian Moreau, are highlighted here. The
October issue is a special issue on “Nanocomposite Coatings,”
organized by guest editors Rehan Ahmed and Christopher
Berndt. The first two articles highlighted below are from this
special issue. In addition to the print publication,
JTST
is avail-
able online through
springerlink.com. For more information,
visit
asminternational.org/tss.“Nanostructural Characteristics
of Vacuum Cold-Sprayed
Hydroxyapatite/Graphene-Nanosheet
Coatings for Biomedical Applications”
Yi Liu, Jing Huang, and Hua Li
Hydroxyapatite (HA)/graphene nanosheet (GN) composite
coatings were deposited by vacuum cold spray (VCS). Signifi-
cant shape changes of HA nanograins during the coating deposi-
tion occurred. The nano-
structural features of HA
together with curvature al-
ternation of GN give rise to
dense structures. Based on
the microstructural charac-
terization, a structure model
was proposed to elucidate
the nanostructural charac-
teristics of the HA-GN
nanocomposites. Results
show that addition of GN
significantly enhances frac-
ture toughness and elastic
modulus of HA-based coatings, which is presumably accounted for
by crack bridging offered by GN in the composites. VCS HA-GN
coatings show potential for the repair or replacement of hard tissues.
“Nanocomposite Fe-Al Intermetallic
Coating Obtained by Gas Detonation
Spraying of Milled Self-Decomposing
Powder”
Cezary Senderowski
The nanocomposite structure of Fe-Al intermetallic coatings,
created in situ during gas detonation spraying (GDS) of as-milled
self-decomposing powder and containing disordered 8 nm FeAl
nanocrystals, was analyzed using scanning electron microscopy
(SEM) with energy-dispersive x-ray (EDX) spectroscopy, trans-
mission electron microscopy (TEM), selected-area electron dif-
fraction (SAED), and x-ray diffraction methods. The Fe-Al coating
is characterized by a sublayer morphology consisting of flattened
and partially melted splats containing a wide Al range from about
26 to 52 at.%, as well as Al
2
O
3
oxides, created in situ at the inter-
nal interfaces of splats
during the GDS process.
Complex oxide films,
identified as amorphous
Al
2
O
3
, which are formed
in the nanocrystalline Fe-
Al matrix of the GDS
coating, behave like a
composite reinforcement
in the intermetallic Fe-Al
coating. The combined
presence of nanosized
subgrains in the Fe-Al ma-
trix and the Al
2
O
3
nanoce-
ramic dispersoids significantly increases microhardness.
“Aircraft Skin Restoration
and Evaluation”
M. Yandouzi, S. Gaydos, D. Guo, R. Ghelichi,
and B. Jodoin
Cold spray technology
enables the deposition of
low porosity and oxide-free
coatings with good adhesion
and minimal changes in the
microstructure of coated
parts. The use of low-pres-
sure cold spray was used to
repair damaged Al-based
aircraft skin, hoping to ob-
tain dense coatings with
strong adhesion to the
Al2024-T3 alloy. In order to
prove the feasibility of using
cold spray as a repair
process for aircraft skin, se-
ries of characterization/tests
including microstructures,
microhardness, adhesion
strength, three-point bend-
ing, surface finish, fatigue
test, and corrosion resist-
ance were performed. Re-
sults reveal that cold spray
is suitable for the repair of
aircraft skin.
“Thermal Shock Resistance of Stabilized
Zirconia/Metal Coat on Polymer Matrix
Composites by Thermal Spraying Process”
Ling Zhu, Wenzhi Huang, Haifeng Cheng,
and Xueqiang Cao
Stabilized zirconia/metal coating systems were deposited on
the polymer matrix composites by a combined thermal spray
process. Effects of the thicknesses of metal layers and ceramic
layer on thermal shock resistance of the coating systems were in-
vestigated. According to the results of thermal shock lifetime, the
coating system consisting of 20 μm Zn and 125 μm 8YSZ exhib-
ited the best thermal shock resistance. Based on microstructure
evolution, failure modes and failure mechanism of the coating sys-
tems were proposed. The main failure modes were the formation
of vertical cracks and delamination in the outlayer of substrate,
Continued on page 12
Schematic illustration demonstrates the
formation mechanisms of the HA-GN
nanocomposite coating.
TEM bright-field micrographs of
grains of as-sprayed coating with
nanocrystalline particles of
aluminum oxides.
Repaired sample during the three-
point bending test and after 90°
bending, respectively (a, b). SEM
images at different magnifications
revealing the fracture nature that
took place during bending (c, d).