June 22-27, 2014
The early development of an adherent, slowly-growing α-alumina film on the bond coat is a critical factor in the life of a thermal barrier coating system. This presentation will include results of recent experiments at the University of Pittsburgh and reanalysis of older data from the literature on the selective oxidation of aluminum from Ni-base alloys. The following aspects of alumina scale establishment will be addressed: • The manner by which alloy composition affects the kinetics and mechanism of the transition of alumina from the θ to the α polymorph. • The influence of the θ to α transition on the critical Al concentration for developing and maintaining a protective external alumina scale. • The manner by which SO2 and H2O affect the kinetics and mechanism of the θ to α transition. • The influence of SO2 and H2O in affecting the critical Al concentration for developing and maintaining a protective external alumina scale. This presentation will be relevant to alumina-scale forming alloys and coatings, with the latter including the more recent bond coatings based on γ′-Ni3Al.
Gerry Meier, "The effect of exposure variables on the development of alumina scales" in "Thermal Barrier Coatings IV", U. Schulz, German Aerospace Center; M. Maloney, Pratt & Whitney; R. Darolia, GE Aviation (retired) Eds, ECI Symposium Series, (2015). http://dc.engconfintl.org/thermal_barrier_iv/4