ICMCTF 2012! - CD-Lab Application Oriented Coating Development

in the mechanical properties indicate bad adhesive properties for one
coating. For quantitative measurement of the interfacial fracture strength
and fracture toughness, micro-cantilevers with a length of about 1.5 µm and
a thickness of about 0.5 µm were prepared by focused ion beam so that the
highest bending stress or stress intensity occurs right at the interface. Using
a force measurement systems, the micro-cantilevers were loaded inside the
SEM and the fracture properties were evaluated. The interfacial fracture
strength of the different interfaces is discussed in terms of the
microstructure, the local mechanical properties and the chemical gradients
in the adhesion layer. It is found that a reduction in the bending strength of
the interface of ~40% results on a macroscopic scale in a change from good
to bad adhesion properties. Furthermore the results of fracture toughness
and bending strength of the interface are compared to the properties of pure
a-c:H.
Using these different approaches, a better understanding on the damage
behavior of thin brittle coatings on ductile substrates is achieved and the
local adhesion strength is correlated to the coating microstructure and
chemical composition.
Funding by DFG Cluster of Excellence Engineering of Advanced Materials
(EAM)
9:20am E2-1-5 Study of adhesion and cracking of TiO2 coatings on a
Ti alloy using an impact-sliding testing instrument, X. Nie
(xnie@uwindsor.ca), University of Windsor, Canada
Different thickness and surface porosity of TiO2 coatings on Ti alloys
appear to have a different combination of bioactivity and chemical stability.
For bio-implants of dentals, the coating thickness and surface morphology
would also influence mechanical integrity. There is a need in further study
on fatigue cracks and wear property of the coatings under simulated load
conditions of dental surgery operations and implant applications. In this
paper, a newly-developed impact-sliding testing instrument is used to
simulate those dental applications under a variety of forces where impacts,
scratch, fretting, and other relevant wear behaviour occur. The research
result showed that the wear behaviour was significantly affected by the
coating thickness and surface porosity. The impact-sliding instrument can
be used as a tool in study of coating adhesion and cracking for dental
implant applications.
9:40am E2-1-6 Influence of oxide film properties on the adhesion
performance of epoxy-coated aluminium, Ö Özkanat
(o.ozkanat@tudelft.nl), Delft University of Technology, Netherlands;
Materials innovation institute (M2i), Netherlands, J.M.C. Mol, J.H.W. de
Wit, Delft University of Technology, Netherlands, H. Terryn, Vrije
Universiteit Brussel, Materials innovation institute (M2i), Belgium
Adhesion of organic coatings and corrosion resistance of
polymer/(hydr)oxide/aluminium interfaces plays pivotal role in the
engineering of lightweight components. Interfacial bonds at the
polymer/metal joints have to withstand high mechanical forces and
corrosive attack to protect the functional properties of coated metals.
Therefore, it is crucial to understand and to control the delamination of
organic coatings and the molecular adhesion forces originating at the
interface in order to achieve the long-term stability of these composites.
Adhesion strength is both influenced by the functionality of the organic
molecules at the interface and the surface properties of thin oxide film e.g.
hydroxyl content, oxide thickness and surface morphology. In this work, we
present how the surface properties affect the adhesion performance of
coated systems. First, different pretreatments (acid, alkaline and immersion
in boiling water) were given in order to create variations in the surface
properties of aluminium substrate. Then differently pretreated bare surfaces
were characterized by means of surface sensitive techniques [1] in which
Scanning Kelvin Probe (SKP), X-Ray Photoelectron Spectroscopy (XPS),
Visible Spectroscopic Ellipsometry (VISSE) and Fourier Transform
Infrared Spectroscopy (FTIR) were utilized in order to evaluate Volta
Potential, hydroxyl fraction, oxide thickness and chemical composition,
respectively. Since the oxide properties of aluminium might be extremely
sensitive to the small changes in the environmental conditions, effect of
ambient humidity (40% RH or 90% RH) and aging (40min vs 240min) on
the oxide film properties was also revealed. Results showed [1] that
pseudoboehmite oxide exhibited the highest hydroxyl fraction and oxide
thickness; it was also shown that all differently pretreated surfaces along
with the reference surface were influenced by both ageing and humidity.
This was followed by the molecular bonding of functional groups -
representative interfacial adhesive molecules- on differently pretreated
surfaces by means of Volta potential shift [2] (SKP) and affinity (XPS).
Finally, the influence of the oxide film properties on macroscopic adhesion
of epoxy-coatings was investigated by means of mechanical testing to
evaluate the performance of coated systems. It was observed from Shear
testing and Bell Peel testing that variations in the thin oxide film properties
resulted in different adhesion performance. This research presents a relation
Thursday Morning, April 26, 2012 78
between the adhesion performance and the oxide film properties of the
aluminium substrates.
[1] Ö. Özkanat, B. Salgin, M. Rohwerder, J. M. C. Mol, J. H. W. de Wit ,
H. Terryn, Journal of Physical Chemistry C 2012, 116, 1805.
[2] Ö. Özkanat, B. Salgin, M. Rohwerder, J. H. W. de Wit , J. M. C. Mol,
H. Terryn, Surface and Interface Analysis 2012, Accepted.
10:00am E2-1-7 Adhesion and fatigue properties of TiB2-MoS2
composite coatings deposited by closed-field unbalanced magnetron
sputtering, F.B. Bidev, Ö. Baran (obaran@erzincan.edu.tr), E. Arslan, Y.
Totik, İ. Efeoglu, Ataturk University, Turkey
In this work, TiB2-MoS2 composite coatings deposited by closed-field
unbalanced magnetron sputtering (CFUBMS) technique using Taguchi
L9(3 4 ) experimental method.The structural properties of TiB2-MoS2
composite coatings were analyzed SEM and XRD.The hardness of coatings
were measured using microhardness tester.Adhesion and fatique properties
of coatings have been scratch tested in two modes. A multi-mode operation
was used as sliding-fatigue, like multi-pass scratching in the same track at
different fractions of critical load (unidirectional sliding) and a standard
mode using progressive load operation. Failure mechanisms were discussed
according to SEM examinations of the scratch tracks.
Key Words:TiB2-MoS2 ,Taguchi method, Adhesion, Multi-pass scratch
10:20am E2-1-8 Coating thickness and interlayer effects on CVDdiamond
film adhesion to cobalt-cemented tungsten carbides, P. Lu,
The University of Alabama, US, H. Gomez, University of South Florida,
US, X. Xiao, M.J. Lukitsch, A. Sachdev, General Motors, US, D. Durham,
A. Kumar, University of South Florida, US, K. Chou (kchou@eng.ua.edu),
The University of Alabama, US
In this study, diamond coating adhesion on cobalt-cemented tungstencarbide
(WC-Co) substrates was investigated using scratch testing. In
particular, the methodology was applied to evaluate the effects of the
coating thickness and interlayer on coating delaminations. In the coating
thickness effect study, substrate surface preparations, to remove the surface
cobalt, prior to diamond depositions was common chemical etching using
Murakami solutions . On the other hand, to study the interlayer effect, by
halting the catalytic effect of the cobalt binder, two different interlayers,
Cr/CrN/Cr and Ti/TiN/Ti, were deposited to WC-Co substrate surfaces (no
chemical etching) by using a commercial physical vapor deposition (PVD)
system in a thickness architecture of 200nm/1.5µ m/1.5µ m, respectively.
Diamond films were synthesized by using a hot-filament chemical vapor
deposition (HFCVD) reactor at a gas mixture of 6 sccm of CH4 and 60 sccm
of H2, with varied deposition times.
Scratch testing was conducted on the fabricated specimens using a
commercial machine, at a maximum normal load of 20 N and a speed of 2
mm/min. It is noted that the onset of coating delamination can be clearly
identified by high-intensity acoustic emission (AE) signals when such
events occur, which can be used to determine the critical load. Scratched
track geometry was also characterized by white-light interferometry and
scanning electron microscopy.
The results show that the adhesion of the diamond coating increases with
the increased coating thickness, with a nearly linear relation, in the range
tested. In a previous investigation, finite element (FE) simulations of
scratching on a diamond-coated carbide were developed, using a cohesive
zone model, to evaluate coating delaminations related to interface
characteristics. The FE model was applied in this study to investigate the
coating thickness effect on delamination critical loads and the results
suggest a linear relation too. For the two types of interlayer materials tested,
either of them seems to be effective and the diamond coating with Tiinterlayer
shows poorer adhesion comparing to the Cr-interlayer coating.
10:40am E2-1-9 On the effect of pressure induced change of Young's
modulus, hardness and yield strength, N. Schwarzer
(n.schwarzer@siomec.de), Saxonian Institute of Surface Mechanics,
Germany
It will be shown how relatively simple models simulating the bond
interaction in solids applying effective potentials like Lennard-Jones and
Morse can be used to investigate the effect of pressure induced changes of
Young's modulus and yield strength of these solids. Relatively simple
dependencies of the bulk-modulus B on the pressure P being completely
free of microscopic material parameters are derived wherever the solid bond
interaction can be described or at least partially described by Lennard-Jones
potentials. Instead of bond energies and length only specific integral
constants like Young's modulus and Poisson's ratio are of need. The
influence of the pressure induced Young's modulus change B(P) is
discussed especially with respect to mechanical contact experiments.
Thereby it is also shown how the extraction of critical decomposition