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@PHDTHESIS{Mutter:826748,
author = {Mutter, Markus Gerhard},
title = {{H}erstellung thermisch gespritzter {S}chichten mit
optimierten {S}pannungseigenschaften},
volume = {354},
school = {Universität Bochum},
type = {Dr.},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
reportid = {FZJ-2017-00966},
isbn = {978-3-95806-200-9},
series = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
Umwelt / Energy $\&$ Environment},
pages = {198 S.},
year = {2016},
note = {Universität Bochum, Diss., 2016},
abstract = {Gasturbines are widely used in stationary applications for
power generation as well as in aero applications due to
their high efficiency. The use of ceramic thermal barrier
coatings (TBC) on the thermally high loaded turbine
components allows either to increase the gas inlet
temperature and therefore the efficiency of the system or to
increase the lifetime of the system while maintaining the
gas inlet temperature on it´s initial level. The ceramic
thermal barrier coatings are typically deposited by
atmospheric plasma spraying (APS) or electron beam –
physical vapor deposition (EB-PVD). While the latter leads
to microstructures with beneficial strain tolerance, the APS
scores with it´s high deposition rates and the lower
thermal conductivity due to the lamellar structure of these
coatings perpendicular to the loading direction. Several
factors occur during high temperature operation of the
gasturbines that can increase the stiffness of the thermal
barrier coating, influence the stresses within the thermal
barrier coating, and finally may lead to delamination of the
coating. The residual stress state of the as-sprayed coating
can have an important effect on the behavior of the coating
in operation. The in situ measurement of the sample´s
curvature during the atmospheric plasma spraying process
allows the evaluation of the residual stress evolution
during the process and the determination of the residual
stress depth profiles in the as-sprayed coatings. However,
determination of the change of the stress depth profile in
operation is not possible by this technique. The incremental
hole-drilling method on the other hand is a widely used
technique to determine residual stress depth profiles in the
near surface region of components. By a comparison of the
two measurement techniques for as-sprayed coatings the
enhancement of the incremental hole-drilling method on
coating systems is aspired. This finally enables the
determination of the change of the residual stress states
within the coating, the substrate and especially at the
interface between the coating and the substrate by the
thermo-mechanical loadings occuring in operation. A
fundamental understanding of the interaction between the
coating microstructure and the stress evolution is required
to enable specific fabrication of coatings with well defined
residual stress states. The investigation of these
interrelations is aim of the present work. For this purpose,
the different particle conditions in the plasma plume were
evaluated in this work. Therefore, measurements of the
temperature and velocity of single particles along the
plasma plume were performed and combined with a simulation
of the particle trajectories and the heat transfer between
plasma and particles. Experimental studies of single splats
deposited on mirror-polished substrates showed a high
variety of splat morphologies that were classified into four
basic splat-types to allow a systematic evaluation. The
formation of these splat-types was linked to distinct
particle and substrate conditions. The introduced particle
melting degrees enabled the quantification of the relative
fractions of the different particle conditions and,
consequently, the relative fractions of the splat-types
based on the particle temperature measurements. The
formation of the coating and the connected properties was
interpreted as the statistical distribution of the impact of
single particles with various conditions. It was further
shown that the properties of the deposited coating exhibit a
distinct correlation to the distributions of the particle
conditions. This is in particular the case for the coating
porosity, which influences the Young´s modulus and the
stress evolution. While the Young´s modulus of the coating
is well defined by the porosity and the bonding between the
single splats, the stress evolution exhibits more complex
relations. The stress evolution in a single splat is
dominated by the occurrence of various plastic effects
(stress relaxation factors) depending on statistical
factors, and therefore an exact prediction is hardly
possible. An exemplary description was conducted based on
existing analytical models and own finite element and
analytical calculations. The layering of the single splats
during the coating formation process was interpreted in the
context of the statistic distribution of the different
splat-types. However, it was not possible to completely
describe the stress evolution by the influencing parameters
used in this investigation. Since the impact frequency of
the splats showed an effect on the stress evolution, the
influence of the interface temperature between the single
splats during deposition on the stress relaxation factors is
supposed to play a key role. The outcome of this work can be
used as starting point for the fabrication of atmospheric
plasma sprayed coatings with well defined residual stress
states. This offers the possibility to optimize the residual
stress states in terms of the operation conditions as well
as the fabrication of suitable samples for the enhancement
of the incremental hole-drilling method on coating systems.},
cin = {IEK-1},
cid = {I:(DE-Juel1)IEK-1-20101013},
pnm = {113 - Methods and Concepts for Material Development
(POF3-113) / HITEC - Helmholtz Interdisciplinary Doctoral
Training in Energy and Climate Research (HITEC)
(HITEC-20170406)},
pid = {G:(DE-HGF)POF3-113 / G:(DE-Juel1)HITEC-20170406},
typ = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
url = {https://juser.fz-juelich.de/record/826748},
}