Cracking Behavior of Gd2Zr2O7/YSZ Multi-Layered Thermal Barrier Coatings Deposited by Suspension Plasma Spray

A new multi-layered thermal barrier coating system (TBCs) containing gadolinium zirconate (GZ, Gd2Zr2O7) and yttria-stabilized zirconia (YSZ) was developed using suspension plasma spray (SPS) to improve the overall thermal cycling performance. This study focuses on the cracking behavior of the GZ/YSZ TBC after thermal exposure to find out the key factors that limit its lifetime. Different cracking behaviors were detected depending on the thermal treatment condition (i.e., horizontal cracks within the ceramic layer and at the thermally grown oxide (TGO)/YSZ interface) which can be related to stresses developed through thermal expansion mismatch and increased TGO thickness beyond a critical value, respectively. A reduction in hardness of bond coat (BC) was measured by nanoindentation and linked with the thermally activated grain growth mechanism. The hardness and elastic modulus of ceramic layers (GZ and YSZ) showed an increased trend after treatment that contributed to the interfacial cracks.

Automated summary

A new multi-layered thermal barrier coating system was developed using suspension plasma spray to improve thermal cycling performance. Cracking behavior of the coating after thermal exposure was studied, revealing different crack types and their relationship with thermal expansion mismatch and increased thermally grown oxide thickness. The reduction in bond coat hardness was linked to thermally activated grain growth. The increased hardness and elastic modulus of the ceramic layers contributed to interfacial cracks.