Thermomechanical Fatigue Damage Evolution in a Superalloy/Thermal Barrier System Containing a Circular Through Hole

Abstract

The results of an investigation of thermomechanical fatigue (TMF) on a superalloy specimen, with an applied thermal barrier coating (TBC) and a circular through hole, are presented. Tensile loads were applied in phase with increasing temperature. Damage evolution in the form of cracks develops in the TBC adjacent to the hole. These cracks run perpendicular to the loading axis. Stress mapping of the thermally grown oxide (TGO) using luminescence spectroscopy determined an increase in compressive residual stress with increasing TMF cycling. Scanning electron microscopy examination, following cross sectioning, determined the TBC cracks to be vertical separations of the columnar yttria-stabilized zirconia (YSZ) top coat. Microscopic damage mechanisms in the form of plasticity (bending of YSZ columns) and TGO cracking were observed. Imperfections in the bond coat are associated with these vertical separations. Energydispersive element mapping of these imperfections indicated a composition of alumina and mixed Cr, Co, and Ni oxides.C. Levi-contributing editor

Porous yttria‐Stabilized Zirconia Ceramics Fabricated by Nonaqueous‐Based Gelcasting Process with PMMA Microsphere as Pore‐Forming Agent

“…Porous zirconia ceramics have many advantages, such as low thermal conductivity, low density, corrosion resistance, and high‐temperature resistance, and so can be applied in many fields, namely ceramic filters, catalyst supports, solid oxide fuel cells, biological materials, and thermal barriers . For thermal isolation use, research has been recently focused on zirconia thermal barrier coatings (TBC), but few studies have reported the application of porous zirconia ceramics in bulk thermal isolators . This is mainly because porous zirconia ceramics have a critical shortcoming, low strength, which seriously limits their application.…”