プラズマ溶射遮熱コーティングシステムのクリープおよび疲労損傷挙動のその場観察(<小特集>ガスタービン用遮熱/耐環境コーティング技術)

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In order to investigate crack initiation sites and the crack propagation behavior in connection with the microstructure of thermal barrier coating (TBC) systems under creep and fatigue loadings, the failure behavior was observed in situ for plasma-sprayed TBC systems by optical microscopy, as a first step for elucidating the thermo-mechanical failure mechanism. Two types of TBC systems with differing top-coat (TC) microstructures were prepared by changing the processing conditions. The mechanical failure behavior of TBC system was found to depend strongly on the loading conditions. Under static creep loading, many segmentation cracks in the TC widened with increasing creep strain in the substrate. However, the propagation of these cracks into the bond-coat (BC) and alloy substrate was prevented due to the stress relief induced by plastic flow in the BC layer at elevated temperatures. As a result, the TBC system exhibited typical creep rupture behavior with nucleation and coalescence of microcracks in the alloy substrate interior regardless of the TC microstructure. Under dynamic fatigue loading, on the other hand, many fatigue cracks initiated not only from the tips of segmentation cracks in the TC layer but also from the TC/BC interface. Furthermore, it was found that the fatigue cracks propagated into the BC and alloy substrate even at elevated temperatures above the ductile-brittle transition temperature of the BC; the fatigue failure behavior under dynamic fatigue loading was dependent on the TC microstructure and the properties of the TC/BC interface.
2010-07-25

プラズマ溶射遮熱コーティングシステムのクリープおよび疲労損傷挙動のその場観察(<小特集>ガスタービン用遮熱/耐環境コーティング技術)

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