Effects of platinum additions and sulfur impurities on the microstructure and scale adhesion behavior of single-phase CVD aluminide bond coatings

摘要

The adhesion of alumina scales to aluminide bond coats is a life-limiting factor for some advanced thermal barrier coating systems. This study investigated the effects of aluminide bond coat sulfur and platinum contents on alumina scale adhesion and coating microstructural evolution during isothermal and cyclic oxidation testing at 1150 °C. Low-sulfur NiAl and NiPtAl bond coats were fabricated by chemical vapor deposition (CVD). Lowering the sulfur contents of CVD NiAl bond coatings significantly improved scale adhesion, but localized scale spallation eventually initiated along coating grain boundaries. Further improvements in scale adhesion were obtained with Pt additions. The observed influences of Pt additions included: (1) mitigation of the detrimental effects of high sulfur levels, (2) drastic reductions in void growth along the scale-metal interface, (3) alteration of the oxide-metal interface morphology, and (4) elimination of Ta-rich oxides in the Al{sub}2O{sub}3 scales during thermal cycling. The results of this study also suggested that the microstructure (especially the grain size) of CVD aluminide bond coatings plays a significant role in scale adhesion.