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of PZT coatings were evaluated by various
techniques, while the phases and microstruc-
tures of coatings were investigated by XRD,
SEM, and TEM, respectively. Results show
that coatings deposited on steel substrates have
a dense microstructure, and there was no phase
transformation during spraying. Additionally, the Curie tempera-
ture of PZT coatings was roughly 370°C by the investigation of di-
electric constant.
Milestones in Functional Titanium Dioxide
Thermal Spray Coatings: A Review
M. Gardon and J.M. Guilemany
The relationship between titanium dioxide and TS technolo-
gies is explored with a goal to provide detailed information related
to the most significant achievements, lack of knowhow, and per-
formance of thermal spray TiO
2
functional coatings in photocat-
alytic, biomedical, and other applications. The influence of
thermally activated techniques such as atmospheric plasma spray
and high-velocity oxygen fuel spray on TiO
2
feedstock based on
powders and suspensions is revised; the influence of spraying pa-
rameters on the microstructural and compositional changes and
the final active behavior of the coating were analyzed. Recent find-
ings on titanium dioxide coatings de-
posited by cold gas spray and the
capacity of this technology to prevent
loss of the nanostructured anatase
metastable phase are also reviewed.
Schematic of an APS gun, interaction
between TiO
2
particles and the plasma
jet, and a representative obtained coating.
Impact Behavior of Intrinsically Brittle
Nanoparticles: A Molecular Dynamics
Perspective
B. Daneshian and H. Assadi
Impact behavior
of intrinsically brit-
tle materials at the
nanoscale is a topic
of growing interest
in aerosol deposition
and cold spraying of
ceramic materials,
for instance. The be-
havior of single-
crystalline brittle
nanoparticles upon
impact on a rigid
substrate, within the
framework of a mo-
lecular
dynamics
model was exam-
ined. The model is
based
on
the
Lennard-Jones for-
mulation, where brittleness is brought about by using a relatively
small cut-off interaction distance. Simulations were carried out for
different values of particle size and velocity. Results show that de-
spite induced brittleness, particles start to deform without break-
ing into fragments, as particle size falls below a critical value.
Deformation of particles can be accompanied by poly-crystalliza-
tion and bonding to the substrate. Results are summarized into a
parameter selection map, providing an overview of the conditions
for successful deposition of intrinsically brittle materials.
CMAS-Resistant Plasma Sprayed Thermal
Barrier Coatings Based on Y
2
O
3
-Stabilized
ZrO
2
with Al
3
+ and Ti4+ Solute Additions
Bilge S. Senturk, Hector F. Garces,
Angel L. Ortiz, Gopal Dwivedi, Sanjay Sampath,
and Nitin P. Padture
Higher operating temperatures in gas-turbine engines made pos-
sible by thermal barrier coatings (TBCs) have a new problem: Environ-
mentally ingested airborne silicate particles (sand, ash) melt on hot
TBC surfaces, forming calcium-magnesium-alumino-silicate (CMAS)
glass deposits. Molten CMAS glass degrades TBCs, leading to pre-
mature failure. Use of a commercially manufactured feedstock pow-
der, in conjunction with the air plasma spray process, deposits
CMAS-resistant yttria-stabilized zirconia-basedTBCs containingAl
3
+
and Ti
4
+ in solid solution. Results from the characterization of these
new TBCs and CMAS/TBCs interaction experiments are presented.
The ubiquity of airborne sand/ash particles and demand for higher op-
erating temperatures in future high efficiency gas-turbine engines ne-
cessitates CMAS resistance in all hot-section components. The
versatility, ease of processing, and low
cost offered by the process could bene-
fit the development of these new
CMAS-resistant TBCs.
(
a) Cross-sectional SEM image of
APS 7YSZ TBC heat treated with
CMAS (1200°C, 24 h, in air) and
(b) corresponding EDS Ca elemental
map. Horizontal dashed lines indicate
position of the TBC top surface
before CMAS interaction.
ADVANCED MATERIALS & PROCESSES •
MAY 2014
54
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JTST HIGHL IGHTS
SEM micrograph of PZT
powder prepared by
solid-state reaction.
Snapshot of the atomic positions and its
respective Fourier transform (calculated
diffraction pattern) for a 34.5-nm brittle
particle impacting a rigid substrate at a
velocity of 375 m/s. Formation of
sub-grains, labeled by letters, and
dislocations are evident. Grain structure is
clearer in the inset showing the inverse
Fourier transform of the filtered diffraction
pattern.