Experimental and Numerical Study of the Thermo-Mechanical Behavior of Plasma-Sprayed Gadolinium and Yitria Zirconate-Based Thermal Barrier Coatings

The current study aims to analyze the thermal and residual stress distributions in both duplex and functionally-graded thermal barrier coatings (TBCs) of yttria-stabilized zirconia (YSZ) and gadolinium zirconate (GZ) during a realistic heating regime. To this end, finite element model was employed to model the effects of thermal loading on the thermomechanical response and stress distribution. In addition, three different YSZ-based TBC systems, one duplex, and two FG-TBCs were fabricated using the APS method. The coatings were characterized based on SEM/EDS, map analysis, and XRD. The residual stress, elastic modulus, microhardness, and fracture toughness of the coatings were determined using nanoindentation method. The obtained results revealed that the microstructure, porosity, and chemical composition changed gradually due to the functionally-graded coating. Examination of the surface of the samples after the application of thermal shock showed that the separation of the layers occurred more frequently in the cases of two-layer coatings than in the graded ones. The contours of the heat flux and nodal temperatures confirmed that most of the damaging thermal residual stresses were concentrated in the ceramic top coat, thus resulting in less damage and life-shortening of the substrate. The magnitude of the residual stress in the FG-TBC was lower than that in the duplex TBC, and the stress distribution was more uniform, hence improvement in the performance and extention of the life of the thermal barrier system. According to the findings, the YSZ-based TBC outperformed the gadolinium zirconate-based TBC in terms of thermal shock resistance and residual stress.