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The thermal durability of thermal barrier coating systems (TBCs) obtained using feedstock powders with different purity and phase content was investigated by thermal shock testing with different cycle times, including the effects on the sintering and phase transformation behaviors. Four 8 wt.% yttria-stabilized zirconia powders, with regular purity (TC1), high purity (TC2 and TC3), and without monoclinic phase (TC4), were employed to prepare the topcoat of TBC by atmospheric plasma spray on a NiCoCrAlY bondcoat deposited by high velocity oxy-fuel. The microstructure and phase stability of the topcoats affected the TBCs' lifetime in the short-term (1 h) and long-term (24 h) furnace cyclic test (FCT) at 1100 °C and jet engine thermal shock (JETS) test. In the short-term FCT and JETS tests, in which coatings are severely subjected to thermal stress, the TBCs' lifetime is most affected by the microstructure of the topcoat. The coating layer with the lowest monoclinic phase in the as-sprayed state showed the lowest phase-transformation characteristics in the isothermal oxidation test (1400 °C). These properties resulted in the best lifetime in the long-term FCT. Therefore, the coating material and evaluating methods of TBCs' life should be selected depending on the usage environment. [ABSTRACT FROM AUTHOR]

The thermal durability of thermal barrier coatings (TBCs) obtained using feedstock powders with different purity and phase content was investigated by cyclic thermal testing, including the effects on the sintering and phase transformation behaviors. Three kinds of 8 wt.% yttria-stabilized zirconia, namely regular purity (8YSZ), high purity (HP), and no monoclinic phase (nMP), were employed to prepare top coats by atmospheric plasma spraying on a NiCoCrAlY bond coat using a high-velocity oxy-fuel system. Use of 8YSZ, HP, and nMP for plasma spraying affected the microstructure and lifetime of the TBC in furnace cyclic testing (FCT) at 1100 °C and the sintering rate during annealing at 1400 °C for 50, 100, 200, and 400 h. In FCT, the TBC formed from nMP showed the longest durability, while that formed from HP showed lifetime performance similar to that obtained with regular-purity 8YSZ. The TBC obtained with nMP also exhibited the lowest monoclinic phase transition rate, followed by those obtained using HP and 8YSZ. [ABSTRACT FROM AUTHOR]