Research Papers

Microstructural Evolution of GdZ and DySZ Based EB-PVD TBC Systems After Thermal Cycling at High Temperature

[+] Author and Article Information
Ahmed Umar Munawar

German Aerospace Center (DLR)
Linder Hoehe,
Cologne 51147, Germany,
University of Roma Tre
Via Della Vasca Navale 79,
Rome 00146, Italy
e-mail: Ahmedumar.munawar@uniroma3.it

Uwe Schulz

German Aerospace Center (DLR)
Linder Hoehe,
Cologne 51147, Germany
e-mail: uwe.schulz@dlr.de

Giovanni Cerri

University of Roma Tre
Via Della Vasca Navale 79,
Rome 00146, Italy
e-mail: cerri@uniroma3.it

Contributed by the Manufacturing Materials and Metallurgy Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 28, 2013; final manuscript received July 12, 2013; published online August 27, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(10), 102101 (Aug 27, 2013) (6 pages) Paper No: GTP-13-1203; doi: 10.1115/1.4025006 History: Received June 28, 2013; Revised July 12, 2013

Lower thermal conductivity and high temperature stability are the two properties which are highly desired from ceramic top coat materials in thermal barrier coating (TBC) systems. Gadolinium zirconate, Gd2Zr2O7 (GdZ) and dyprosia stabilized zirconia (DySZ) are two of the candidate materials with such properties and consequently the TBC system would be able to work at higher turbine inlet temperature (TIT) or the lifetime can be increased. In the present study, lifetime measurements are done for single and double layered electron beam physical vapor deposition (EB-PVD) GdZ and DySZ samples by thermal-cycling tests. The double layered TBCs consisted of a thin 7YSZ layer and, on top, the new candidate material. Both single and double layered samples of GdZ and DySZ have shown similar or better lifetimes than the standard 7YSZ samples. However, single layered TBCs showed better lifetime results than the respective double layers. In this study, changes in the microstructure, diffusion of elements and sintering of the TBC materials with aging are observed.

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Grahic Jump Location
Fig. 4

The TGO–TBC interface of (a) single layer GdZ sample after more than 5000 h and (b) single layer DySZ sample after more than 4000 h

Grahic Jump Location
Fig. 3

Normalized lifetime of various TBC systems used in this study

Grahic Jump Location
Fig. 2

SEM microstructure of a double-layered GdZ–7YSZ TBC in the as-coated condition

Grahic Jump Location
Fig. 1

A columnar microstructure of single layered TBCs in the as-coated condition (a) standard 7YSZ and (b) GdZ

Grahic Jump Location
Fig. 5

The GdZ–7YSZ interface (a) in the as-coated condition, (b) after thermal cycling for 2000 h, and (c) DySZ–7YSZ interface after thermal cycling for 700 h

Grahic Jump Location
Fig. 6

The sintering effect in GdZ TBCs: (a) top view of as-coated columns and (b) top view after 5000 h




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