ICMCTF 2012! - CD-Lab Application Oriented Coating Development

esidual stress and to the Poisson’s ratio of the coating. This is done by
adopting a unique novel geometry for the milled trench and by means of
digital image correlation (DIC) techniques and ad hoc constitutive models.
The method consists of two sequential steps: (1) FIB milling of two parallel
slots and analysis of the consequent relaxation strain that might occur in the
central area (along the X-direction which is the direction perpendicular to
the slots); (2) milling of two additional slots along a direction perpendicular
to the previous one, so to induce a full biaxial stress relief of the central
square island. The analysis of the relaxation strain after the second milling
step is then performed along the same X-direction. The depth of all trenches
and the distance between them are kept equal to the coating’s thickness. The
relaxation strain analysis is performed by means of high-resolution in-situ
SEM-FEG imaging of the relaxing surface and a full field strain analysis by
digital image correlation (DIC).
A FE modeling approach was also used to demonstrate that, for a wide
range of isotropic materials, the ratio between the two acquired X-strains is
a unique simple function of the Poisson’s ratio of the coatings,
independently of the elastic modulus. Furthermore, the analysis of the X
and Y relaxation strains at each milling step allows the direct evaluation of
the residual stress depth profile in the coating.
The model was experimentally validated on a 3.0 µm CAE-PVD Chromium
Nitride (CrN) coating.
An equal-biaxial average stress of -5.04 ± 0.75 GPa was detected and found
to be in good agreement with that obtained by XRD (adopting the same
elastic constants). Moreover, a Poisson’s ratio of 0.23 ± 0.02 was estimated,
which is in the range reported in the literature for similar coatings.
The two situations of non-equal biaxial stress and non-isotropic in-plane
elastic behavior are analyzed and correcting equations are proposed.
Finally, the influence of coating’s texture and microstructure on the
reliability of the method is discussed.
2:10pm TS2-2-3 Low temperature deformation in complex crystals, V.
Schnabel, University of Cambridge, UK, S. Korte, Gordon Laboratory,
Department of Materials Science and Metallurgy, University of Cambridge,
UK, C. Walter, R. Stearn, W. Clegg (wjc1000@cam.ac.uk), University of
Cambridge, UK
The development of new materials for coatings has generally focussed on a
limited number of materials with relatively simple crystal structures in
which deformation occurs predominantly by the movement of dislocations.
However there are crystals with unit cells that are sufficiently large that
conventional dislocations are energetically unfavourable. Despite this, such
materials are known to be plastic above a ductile-brittle temperature,
typically 0.5 – 0.75 of the melting point.
In this paper the low temperature deformation behaviour of single crystals
of an orthorhombic Al13Co4 and a cubic Mg2Al3 has been studied at
temperatures using micropillar compression. This allows cracking to be
suppressed by making the sample sufficiently small, in this case a few
microns in diameter. The materials studied had grains of a sufficient size
that micropillars could be milled within individual grains, allowing the
single crystal flow behaviour in grains of different orientations to be
studied. It is shown that there is a very pronounced yield drop in these
materials, and that the yield stress appears to be almost independent of
temperature, similar to what has been observed in a metallic glasses. In
some orientations, the orientations of the slip traces with respect to the pillar
orientation were consistent with what would be expected from the slip
systems at higher temperatures. However, this was not observed in many
cases, suggesting that the glide bands form on or close to planes of
maximum shear stress.
2:30pm TS2-2-4 Carbon-Based Coating for Flexible Fabric Heater
Prepared by Arc Ion Plating, C.C. Hsu, C.M. Chen, J.L. He
(jlhe@fcu.edu.tw), Feng Chia University, Taiwan
Electric heating textiles have widely been used in many applications,
including clothes, furnishings and medical equipments, as well as in recent
year, the car or construction interior materials. The traditional metal wire
and carbon fiber are currently the two major types of heating element for
electric heating textiles. The former suffers non-uniform heating, easy
corrosion, uncomfortable to the user and without far infrared emission,
while the carbon fabric presents area heating, flexible and particular far
infrared emission. However, the carbonization process to prepare carbon
fiber is expensive, energy consuming and emitting environmental
unfriendly VOCs. Carbon-based coatings such as diamond-like carbon
(DLC) film presents high chemical stability and effective far infrared
emission. Therefore, in this study, an arc ion plating (AIP) technique,
capable of low temperature deposition, is used to prepare carbon-based film
on glass fiber fabric, and thus a flexible fabric heater with low processing
cost and far infrared emission capability is expected. By adjusting the
acetylene flow rate during deposition, the film composition and phase
structure are investigated to reveal how they affect the electrical properties
and far infrared emissivity. Experimental results show that the AIP carbonbased
film presents a lower electrical resistivity as well as thermal-electrical
conversion efficiency when obtained at low acetylene flow rate, but an
ultimate far infrared emissivity when obtained at high acetylene flow rate.
Such a newly developed flexible fabric heater has been a great potential for
usage in the electric heating products.
2:50pm TS2-2-5 Kinetics of Thin Film Growth and Gas-Solid
Reactions using in situ High-Temperature Scanning Tunneling
Microscopy, S. Kodambaka (kodambaka@ucla.edu), Y. Murata,
University of California, Los Angeles, US, V. Petrova, I. Petrov, University
of Illinois at Urbana-Champaign, US INVITED
In situ microscopy is a powerful method that enables direct visualization of
surface morphological, structural, compositional evolution, and often
reveals surprising and previously unknown aspects. Since the observations
are carried out at the processing conditions (for example, during growth or
annealing in vacuum or in a reactive ambient), the phenomena can be
quantitatively described with minimal uncertainties in kinetic rate
measurements. In this talk, I will showcase the capabilities of in situ
variable-temperature scanning tunneling microscopy (VT-STM) using two
examples: 1) growth of graphene thin films on SiC(0001) and 2) gas-solid
reactions on TiO2(110).
In order to follow graphene growth on SiC surfaces, we used hightemperature
(~ 1400 K) STM and observed for changes occurring on the
SiC(0001) during annealing in ultra-high vacuum. From the time-lapsed
STM images, we identify three distinct modes of bilayer graphene growth.
We used VT-STM at temperatures between 700 K and 1000 K and studied
the influence of ethylene (C2H4) on the surface dynamics of rutile-structured
TiO2(110). STM images were acquired as a function of time, oxygen and
ethylene partial pressure, and temperature. From the STM images, we
determined the role of gas chemistry on the oxide surface composition.
3:30pm TS2-2-7 In-situ AFM studies of crack initiation in ultra-thin
SiOx films on polymer substrates., B. Ozkaya (oezkaya@tc.unipaderborn.de),
University of Paderborn, Germany, S. Steves, Ruhr
Universität Bochum, Germany, C.N. Liu, O. Ozcan, University of
Paderborn, Germany, P. Awakowicz, Ruhr Universität Bochum, Germany,
G. Grundmeier, University of Paderborn, Germany
Barrier properties of thin films with respect to the diffusion of oxygen and
water are of crucial importance in assessing their protection performance.
Thin SiOx plasma polymer films have been intensively researched for their
possible application as barrier coatings on engineering metals. Their high
formability makes them suitable for applications involving forming
processes; whereas their superior barrier properties prevent corrosive
electrolytes from reaching the film-metal interface. The key step in the
development of these films is the simultaneous optimisation of the
mechanical and barrier properties to achieve coatings which can hinder the
ingress of electrolyte to the interface and at the same time sustain a high
resistance to crack formation during forming processes.
This paper focuses on crack initiation of SiOx plasma polymer films.
Various films are deposited in a low pressure microwave plasma to study
the effect of process parameters (plasma gas composition, substrate bias and
adhesion promoting pre-treatments) on film properties. For the investigation
of deformation at various strain values, plasma polymer films were applied
on PET-foils and the crack formation was studied in-situ by means of
atomic force microscopy (AFM). A custom build AFM-stage was used to
apply the desired strain in a perfectly controlled manner. Moreover, the
evaluation of water up-take in barrier films was performed on films
deposited on gold electrodes by means of discrete polarisation modulation
Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS)
and by collection of cyclic voltammetry data, in atmospheres with
controlled humidity and in corrosive electrolytes, respectively. Presented
results will demonstrate the correlation between the deposition parameters
and crack formation mechanisms. The understanding of the interplay
between the plasma parameters and the observed barrier properties will
enable the design of high performance thin film coatings.
The authors gratefully acknowledge the support provided by the Deutsche
Forschungsgemeinschaft (DFG) within the framework of the SFB-TR 87.
3:50pm TS2-2-8 High Frequency Characterization of Screen-printed
Silver Circuits with an Environmental Reliability Test, K.S. Kim, W.R.
Myung, S.B. Jung (sbjung@skku.ac.kr), Sungkyunkwan University,
Republic of Korea
Printed electronics is a developing alternative to conventional
photolithography as “green technology”. Direct printing techniques such as
inkjet, screen, and gravure printing are adopted to deposit thin films. They
are based on an additive manufacturing, which conductive nanoinks or
nanopastes are printed on the designated positions, thereby are an
21 Monday Afternoon, April 23, 2012