Enhancing Thermal Cycling Resistance in MultiLayered Thermal Barrier Coatings: A Focus on Functionally Graded Designs

This study focuses on enhancing the thermal cycling resistance of multi-layered thermal barrier coatings (TBCs) developed using the atmospheric plasma spraying (APS) method with YSZ/Sm 2 Zr 2 O 7 compositions. Two distinct coating architectures were analyzed: a double-layer system comprising a YSZ intermediate layer sandwiched between a Sm 2 Zr 2 O 7 top coat and a NiCrAlY bond coat, and a functionally graded coating with a gradually varying YSZ/Sm 2 Zr 2 O 7 composition across its thickness. Thermal cycling tests revealed significant delamination, oxide discontinuities, and crack formation in the double-layered systems, which were notably absent in the functionally graded coatings, indicating superior resistance to cyclic thermal fatigue. SEM and EDAX analyses highlighted the formation of craters and a discontinuous oxide scale in the double-layered coatings, while the graded systems exhibited enhanced structural integrity and minimal defect formation. Thermal shock tests further emphasized the advantages of the graded design, revealing prominent phase transformations in all systems. Single-layer Sm 2 Zr 2 O 7 coatings predominantly transformed into cubic Sm 2 Zr 2 O 7 and Sm 2 O 3 , while double-layered systems showed increased monoclinic ZrO 2 and Sm 2 O 3 . In contrast, the graded coatings maintained a high intensity of tetragonal ZrO 2 , coupled with cubic Sm 2 O 3 and monoclinic ZrO 2 , reflecting improved phase stability under thermal shock conditions. These results underscore the potential of functionally graded coatings to outperform conventional designs by mitigating thermal stresses and maintaining structural integrity. Future work will extend these findings by investigating the behavior of these coatings under diverse extreme conditions, including salt spray corrosion, isothermal oxidation, and hot corrosion, to further validate their applicability in high-performance thermal barrier systems.