ICMCTF 2012! - CD-Lab Application Oriented Coating Development

10:20am A2-1-8 New Perspectives on the Phase Stability Challenge in
Zirconia-based TBCs, J. Krogstad (jkoschmeder@engineering.ucsb.edu),
S. Krämer, University of California, Santa Barbara, US, R. Leckie, Los
Alamos National Laboratory, US, M. Lepple, Karlsruhe Institute of
Technology, Germany, Y. Gao, D. Lipkin, GE Global Research, US, C.G.
Levi, University of California, Santa Barbara, US
Zirconia-based ceramics have long been used to provide thermal protection
to the structural components of modern gas turbine engines. Economic and
environmental considerations have motivated higher engine operating
temperatures, potentially leading to more rapid degradation of thermal
barrier coating (TBC) systems dependent on a metastable phase, namely t’-
8YSZ (ZrO2+7-8wt%YO1.5) TBCs. The t’-phase was originally thought to
decay slowly into the equilibrium Y-lean tetragonal phase and Y-rich cubic
phase, the former of which may undergo further transformation to the
monoclinic phase. However, it has recently been shown that the t’-phase
destabilizes at a small fraction of the time necessary to form the deleterious
monoclinic phase. The rapid decay of t’-YSZ into a modulated
microstructure of coherent domains offers additional insight on the
importance of microstructural control in the phase evolution of YSZ TBCs.
Traditional phase stability characterization techniques have been
reevaluated in order to provide a more complete description of this process.
In particular, x-ray diffraction (XRD) techniques, both at room temperature
and elevated temperatures, have been used to quantify the changing phase
fractions and composition of each phase, with additional implications for
the equilibrium phase diagram. XRD is more powerful when used in
conjunction with microstructural observations. As such, three different
starting morphologies will be compared on the basis of phase stability.
Stemming from this comparison, potential pathways for further delaying the
onset of the monoclinic transformation will be explored. While the
effectiveness of these measures is expected to be modest, lessons can be
learned from the t’-8YSZ system. In particular, maintaining a high degree
of tetragonality over the entire range of relevant temperatures may be key to
supporting or improving the in service toughness and durability. A novel
TBC system will be introduced in which a relatively large single phase
tetragonal field with exceptional tetragonality has been stabilized and has
demonstrated comparable or improved toughness, making it a promising
alternative for next generation TBCs.
This work was partially supported with funding from the US DoE via
Cooperative Agreement DE-FC26-05NT42643 and the NSF via FRG-
GOALI Contract NSF/DMR0605700. Any opinions, findings, conclusions or
other recommendations expressed are those of the authors and do not
necessarily reflect the views of the US Department of Energy or the
National Science Foundation.
10:40am A2-1-9 Influence of the mechanical behaviour of the under
layer in coating spallation, V. Maurel (vincent.maurel@mat.ensmp.fr), A.
Koster, Mines-ParisTech, UMR CNRS 7633, France, L. Rémy, Mines-
ParisTech,UMR CNRS 7633, France INVITED
Coatings designed for high temperature protection, Aluminium rich
intermetallic coating as well as thermal barrier coatings (TBC), are prone to
damage when exposed to stages of high temperature and cooling. Coupling
thermal and mechanical loading tests provide an accurate simulation of inservice
loadings and the generation of subsequent realistic damage. Thus,
the aim of this study is to clarify the way the mechanical behaviour of the
under-layer interacts with surface damage. This point will be examined for
room temperature mechanical tests performed up to oxide or TBC
spallation. The specimens were initially subjected to high temperature
thermal loading for both isothermal and thermal cycling.
When single crystals coated with TBC are subjected to mechanical
compression, the strain localisation arising in the single crystal has been
already been shown to drive the ceramic coating to spallation. In the same
manner, when the oxide is growing on a free surface, the oxide spallation
due to mechanical compression is dependent of the local behaviour of the
coating. Indeed, for a typical CVD-NiAl coating, strain localisation is
related to the coating microstructure. Moreover, the oxide morphology will
also contribute to localisation of strain and hence oxide spallation. The
chosen experimental methodology will be explained since it offers a
complement to thermo-gravimetric analysis. It particularly includes the
intensive use of full-field analysis by surface strain field measurement. This
technique enables a quantitative characterisation of surface damage and can
be used to define intrinsic rupture material parameter. Complementary finite
element analysis of both test configuration and principal microstructural
features are performed. It allows a close view of the mechanical state
leading to rupture to be obtained. Finally, assessment of thermo-mechanical
coupling will be discussed for complex loading paths.
Tuesday Morning, April 24, 2012 24
11:20am A2-1-11 Inhibiting High Temperature Densification Through
Multi-Phase TBCs, J.S. Van Sluytman
(jason.vans@engineering.ucsb.edu), C.G. Levi, University of California,
Santa Barbara, US, V.K. Tolpygo, Honeywell Aerospace, Pheonix, AZ, US
Thermal barrier coatings (TBCs) are essential for the effective operation of
turbine blades in high temperature gas environments. The drive for next
generation TBCs, however, poses new demands that the current TBC, 7.6
mol% YO1.5 stabilized zirconia (7YSZ) is unlikely to satisfy. At issue is the
phase stability of the coating and its resistance to sintering, both of which
are explored in the YO1.5 - TaO2.5 - ZrO2 (Y-Ta-Zr) system. This research
addresses the issue of high temperature densification and its mitigation
using multi-phase compositions within this ternary system. In addition to
the baseline 7YSZ, four compositions were selected for investigation
representing four different phase constitutions: 16Y-16Ta-Zr (stable
tetragonal, t); 20Y-20Ta-Zr (two-phase tetragonal zirconia solid solution, t,
and monoclinic yttrium tantalate, m-YTaO4); 22Y-13Ta-Zr (two-phase non
transformable tetragonal, t, and fluorite, c); and finally 18Y-28Ta-Zr
(three-phase mixture of t, m-YTaO4, and orthorhombic Zr3TaO8 phases).
Densification studies were performed at 1250 °C with dwell times of 1, 4, 9,
and 300 h. Pore size distributions have been quantified at each sintering
time using BET analysis. Remarkably, the 18Y-28Ta-Zr composition
increased only to 55% of its theoretical density from a green body density
of 49% after 300 h. Pore size analysis indicates that the pores are relatively
stable from 1 to 300 h at 1250°C. This compares with 22Y-13Ta-Zr and
7.6YSZ, which reached 70% and 85% of their theoretical densities,
respectively, after the same exposure. The 22Y-13Ta-Zr, along with 18Y-
28Ta-Zr, which are also phase stable and offer lower thermal conductivity
than 7YSZ, suggests alternate regions within the Y-Ta-Zr system offering
promise for future development.
Hard Coatings and Vapor Deposition Technology
Room: Royal Palm 4-6 - Session B1-3
PVD Coatings and Technologies
Moderator: P. Eklund, Linköping University, Sweden, J.H.
Huang, National Tsing Hua University, Taiwan, J. Vetter,
Sulzer Metaplas GmbH, Germany
8:00am B1-3-1 Preparation and characterization of anti-wear and
anti-bacteria TaN-Cu, TaN-Ag, TaN(Ag,Cu) nanocomposite thin films,
J.H. Hsieh (jhhsieh@mail.mcut.edu.tw), Ming Chi University of
Technology, Taiwan INVITED
The processes and functions of MeN-(soft metal) nanocomposite films were
first reviewed. Following that, the processing, structure, and multifunctional
properties of TaN-Cu, TaN-Ag, and TaN-(Cu,Ag)
nanocomposite films were discussed and compared. The TaN-(soft metal)
films were prepared by a hybrid process that combines co-sputtering
deposition and rapid thermal annealing. After the surface morphologies as
well as the microstructures were analyzed and compared, the samples were
examined for their tribological properties. It is found that the tribological
properties could be improved when the soft metals were smeared out and
functioned as solid lubricants. All TaN-(soft metal) nanocomposite thin
films showed similar behaviors. However, it is found further that Cuincorporated
films could behave better under low load or low contact
temperature while Ag-incorporated films could do better under high load or
high temperature. For TaN-(Cu,Ag), the films might behave more like Agincorporated
films. The samples were also tested for their anti-bacterial
behaviors against Gram-negative (E. coli) and Gram-positive ( S. Aureus )
bacteria. It is found that the antibacteria efficiency against either E.coli or S.
aureus can be much improved for TaN-(Cu,Ag), comparing with TaN-Ag or
TaN-Cu films. The annealing temperature for TaN-(Cu,Ag) can be as low
as 200 o C. Being annealed at this temperature, the film still shows good
antibacterial behaviors against either bacterium. The synergistic effect due
to the co-existence of Ag and Cu would be discussed.
8:40am B1-3-3 Effects of sputtering gas for the preparation of CNx
films by RF reactive sputtering, T.S. Shiroya (s0721171KH@itchiba.ac.jp),
Graduate School, Chiba Institute of Technology, Japan, Y.
Sakamoto, Chiba Institute of Technology, Japan
CNx is nitrogen contained Diamond-Like Carbon (DLC) and it has
excellent mechanical properties such as high hardness and low friction
coefficient especially in nitrogen gas atmosphere. These properties may be
controlled by controlling of nitrogen content. In addition, CNx is capable of
preparation by using thin film deposition techniques both Physical Vapor
Deposition (PVD) and Chemical Vapor Deposition (CVD) and expected to
apply for mechanical parts. On the other hand, reactive sputtering is one of
method prepared oxide and nitride easily by chemical reaction with the