Depth-Resolved Porosity Investigation of EB-PVD Thermal Barrier Coatings Using High-Energy X-rays

2004 ◽  
Vol 87 (2) ◽  
pp. 268-274 ◽  
Author(s):  
Anand A. Kulkarni ◽  
Herbert Herman ◽  
Jon Almer ◽  
Ulrich Lienert ◽  
Dean Haeffner ◽  
...  
Keyword(s):  
Thermal Barrier Coatings ◽  
High Energy ◽  
Thermal Barrier ◽  
X Rays ◽  
Barrier Coatings

Spalling Stress in Oxidized Thermal Barrier Coatings Evaluated by X-Ray Diffraction Method

2005 ◽  
Vol 490-491 ◽  
pp. 631-636 ◽  
Author(s):  
Kenji Suzuki ◽  
Keisuke Tanaka
Keyword(s):  
Thermal Barrier Coatings ◽  
Plane Stress ◽  
Stress Measurement ◽  
Diffraction Method ◽  
High Energy ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
X Rays ◽  
Barrier Coatings ◽  
X Ray

The spallation of thermal barrier coatings (TBCs) is promoted by thermally grown oxide (TGO). To improve TBCs, it is very important to understand the influence of TGO on the spalling stress. In this study ,the TBCs were oxidized at 1373 K for four diferent periods: 0, 500,1000 and 2000 h. The distribution of the in-plane stress in oxidized TBCs, s1, was obtained by repeating the X-ray stress measurement with low energy X-rays after successive removal of the surface layer. The distribution of the out-of-plane stress, s1− s3, was measured with hard synchrotron X-rays, because high energry X-rays have a large penetration depth. From the results by the low and high energy Xrays, the spalling stress in the oxidized TBCs, s3, was evaluated. The evaluated value of the spalling stress for the oxidized TBC was a small tension beneath the surface, but steeply increased near the interface between the top and bond coating. This large tensile stress near the interface is responsible for the spalling of the top coating.

Characterization of thermal barrier coatings formed by electon-beam physical vapor deposition (EB-PVD)

1989 ◽  
Vol 47 ◽  
pp. 426-427
Author(s):  
Ozer Unal
Keyword(s):  
Thermal Barrier Coatings ◽  
Physical Vapor Deposition ◽  
Ceramic Coating ◽  
High Vacuum ◽  
Ceramic Coatings ◽  
High Energy ◽  
Thermal Barrier ◽  
Protective Oxide ◽  
Barrier Coatings ◽  
Energy Beam

Interest in ceramics as thermal barrier coatings for hot components of turbine engines has increased rapidly over the last decade. The primary reason for this is the significant reduction in heat load and increased chemical inertness against corrosive species with the ceramic coating materials. Among other candidates, partially-stabilized zirconia is the focus of attention mainly because ot its low thermal conductivity and high thermal expansion coefficient.The coatings were made by Garrett Turbine Engine Company. Ni-base super-alloy was used as the substrate and later a bond-coating with high Al activity was formed over it. The ceramic coatings, with a thickness of about 50 μm, were formed by EB-PVD in a high-vacuum chamber by heating the target material (ZrO2-20 w/0 Y2O3) above its evaporation temperaturef >3500 °C) with a high-energy beam and condensing the resulting vapor onto a rotating heated substrate. A heat treatment in an oxidizing environment was performed later on to form a protective oxide layer to improve the adhesion between the ceramic coating and substrate. Bulk samples were studied by utilizing a Scintag diffractometer and a JEOL JXA-840 SEM; examinations of cross-sectional thin-films of the interface region were performed in a Philips CM 30 TEM operating at 300 kV and for chemical analysis a KEVEX X-ray spectrometer (EDS) was used.

Synchrotron XRD Measurements Mapping Internal Strains of Thermal Barrier Coatings During Thermal Gradient Mechanical Fatigue Loading

2014 ◽  
Author(s):  
Kevin Knipe ◽  
Albert C. Manero ◽  
Stephen Sofronsky ◽  
John Okasinski ◽  
Jonathan Almer ◽  
...  
Keyword(s):  
High Temperature ◽  
Thermal Barrier Coatings ◽  
Mechanical Loading ◽  
Bond Coat ◽  
Thermal Gradient ◽  
Room Temperature ◽  
Material Behavior ◽  
Thermal Barrier ◽  
X Rays ◽  
Barrier Coatings

An understanding of the high temperature mechanics experienced in Thermal Barrier Coatings (TBC) during cycling conditions would be highly beneficial to extending the lifespan of the coatings. This study will present results obtained using synchrotron x-rays to measure depth resolved strains in the various layers of TBCs under thermal mechanical loading and a superposed thermal gradient. Tubular specimens, coated with Yttria Stabilized Zirconia (YSZ) and an aluminum containing nickel alloy as a bond coat both through Electron Beam - Physical Vapor Deposition (EBPVD), were subjected to external heating and controlled internal cooling generating a thermal gradient across the specimen’s wall. Temperatures at the external surface were in excess of 1000 °C. Throughout high temperature testing, 2-D high-resolution XRD strain measurements are taken at various locations through the entire depth of the coating layers. Across the YSZ a strain gradient was observed showing higher compressive strain at the interface to the bond coat than towards the surface. This behavior can be attributed to the specific microstructure of the EB-PVD-coating, which reveals higher porosity at the outer surface than at the interface to the bond coat, resulting in a lower in plane modulus near the surface. This location at the interface displays the most significant variation due to applied load at room temperature with this effect diminishing at elevated uniform temperatures. During thermal cycling with a thermal gradient and mechanical loading, the bond coat strain moves from a highly tensile state at room temperature to an initially compressive state at high temperature before relaxing to zero during the high temperature hold. The results of these experiments give insight into previously unseen material behavior at high temperature which can be used to develop an increased understanding of various failure modes and their causes.

scholarly journals Oxidization of Thermal Barrier Coatings and Spalling Stress Analyzed with Synchrotron X-Rays

2004 ◽  
Vol 53 (7) ◽  
pp. 734-739 ◽  
Author(s):  
Kenji SUZUKI ◽  
Takahiro KUBO ◽  
Keisuke TANAKA ◽  
Yoshiaki AKINIWA ◽  
Hideki OKADO
Keyword(s):  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
X Rays ◽  
Barrier Coatings
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