Assessment of the Thermal Behavior and Coefficient of Thermal Expansion of Gadolinium Zirconate-Based Thermal Barrier Coatings Using In Situ High-Temperature XRD

Understanding the coefficient of thermal expansion (CTE) of thermal barrier coatings (TBCs) used in gas turbines is essential for determining the thermal cycle life of the coatings and preventing their catastrophic failure. In this work, an attempt is made to measure CTE of TBCs using in situ high-temperature x-ray diffraction in the temperature range of 298 K to 1273 K at every 100 K increment. For this study, single-layer yttria-stabilized zirconia (YSZ), single-layer gadolinium zirconate (GZ)
coatings, YSZ/GZ bilayer coating (Bilayer YSZ/GZ), and functionally graded GZ coating (FGC) were deposited on a NiCrAlY bond coat using the atmospheric plasma spray
method with an overall coating thickness of * 300 lm. The structural and microstructural changes were studied using XRD and SEM, respectively. The linear CTEs of
YSZ, GZ, bilayer YSZ/GZ, and FGC at 1273 K were found to be 10.1 9 10-6 K-1, 9.9 9 10-6 K-1, 10.1 9 10-6 K-1, and 9.1 9 10-6 K-1, respectively. An isothermal oxidation
test (IOT), thermal cyclic fatigue test (TCT), and thermal shock resistance tests of the YSZ, GZ, YSZ/GZ, and FGC were conducted at 1273 K and analyzed using XRD and
SEM to evaluate the performance of the coatings. The bilayer YSZ/GZ TBC system has shown better isothermal oxidation resistance and thermal cyclic and thermal shock
resistance.