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| Hauptseite > Publikationsdatenbank > Entwicklung neuer Wärmedämmschichten für thermisch hochbelastete Komponenten in Gasturbinen |
| Dissertation / PhD Thesis/Book | PreJuSER-37413 |
2003
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/295
Report No.: Juel-4042
Abstract: Hot parts of modern gas turbines with high thermal loads are covered by thermal barrier coatings which protect the metallic substrates against the steadily increasing gas entry temperatures. Further increase of the turbine entry temperatures which is necessary for the enhancement of the degree of efficiency can only be achieved with the application of new materials für thermal barrier coatings. The state-of-the-art material yttria stabilized zirconia (YSZ) can only withstand temperatures of about 1200°C during long time exposure. The present thesis investigates the group of rare-earth-zirconates, crystallizing in a pyrochlore structure, in regard to their applicability as thermal barrier coatings. Starting from lanthanum zirconate suitable substitutions of cations will be done, whereas the Substitution elements are selected according to theoretical interrelations between the thermal conductivity as well as the coefficient of thermal expansion and atomistic parameters. The thermophysical properties thermal conductivity, specific heat, and coefficient of thermal expansion as well as the Young's modulus of these new substances where La is partial or complete substituted by Nd, Eu, Gd, Dy, and Ca and Zr is partial substituted by Ta, are measured and compared to each other and with those of YSZ. This comparison Shows that some of the new materials have much better properties than the conventional YSZ. Especially neodymium zirconate and Gd containing substances exhibit notedly lower thermal conductivities than YSZ or lanthanum zirconate. Lanthanum-europium zirconate Shows a clearly higher coefficient ofthermal expansion than lanthanum zirconate. Two of the materials investigated have been choosen for further investigation because of their extraordinary promising thermophysical properties. The focus of these further evaluations are an the test of the thermal shock behavior of plasma-sprayed coatings. Neodymium zirconate and lanthanum-europium zirconate are deposited as plasma sprayed layers onto substrates which are coated with a metallic bond coat. Beside single layers of the new materials also double layer systems consisting of the new materials and an underlaying YSZ tier are produced. The life time of these coatings under sequences of rapid heating and cooling is investigated in thermal cycling experiments. As a result the YSZ-neodymium zirconate layers Show for temperatures above 1320°C much longer life times than conventional YSZ coatings. The lanthanum-europium zirconate layers failed after a very short period of time. This failure is led back to a change in volume of the material that is caused by a change of the oxydation state (valency) of the Eu which occurs between 200 and 300°C.
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