J. Liu, Y. Sohn, University of Central Florida, Orlando, FL; K. Murphy, Howmet Research Corporation, Whitehall, MI
Thermal cyclic lifetime and microstructural degradation of thermal barrier coatings (TBCs) with (Ni,Pt)Al bond coat and Hf- and/or Y-modified CMSX-4 superalloy substrates were examined. Thermal cycling consisted of 10-minute heat-up, 50-minute dwell at 1135?C, and 10-minute forced-air-quench. TBC lifetime was observed to improve from 600 cycles to over 3200 cycles with appropriate Hf- and/or Y-alloying of CMSX-4 superalloys. Mechanisms of degradation and failure for TBCs were examined by scanning and transmission electron microscopy (SEM and TEM/STEM). While rumpling and racheting of the TGO/bond coat interface were observed to be the main damage mechanisms for TBCs on baseline CMSX-4, the same interface remained relatively flat for durable TBCs with Hf- and/or Y-modified CMSX-4. The parabolic growth constant of the TGO scale was slightly lower for TBCs with modified CMSX-4. In addition, TEM/STEM revealed the development of monoclinic HfO2 decorating the grain boundaries of Al2O3 TGO scale.
Summary: Thermal cyclic lifetime and microstructural degradation of thermal barrier coatings (TBCs) with (Ni,Pt)Al bond coat and Hf- and/or Y-modified CMSX-4 superalloy substrates were examined. Thermal cycling consisted of 10-minute heat-up, 50-minute dwell at 1135°C, and 10-minute forced-air-quench. TBC lifetime was observed to improve from 600 cycles to over 3200 cycles with appropriate Hf- and/or Y-alloying of CMSX-4 superalloys. Mechanisms of degradation and failure for TBCs were examined by scanning and transmission electron microscopy (SEM and TEM/STEM). While rumpling and racheting of the TGO/bond coat interface were observed to be the main damage mechanisms for TBCs on baseline CMSX-4, the same interface remained relatively flat for durable TBCs with Hf- and/or Y-modified CMSX-4. The parabolic growth constant of the TGO scale was slightly lower for TBCs with modified CMSX-4. In addition, TEM/STEM revealed the development of monoclinic HfO2 decorating the grain boundaries of Al2O3 TGO scale.
