The Reactive Element Effect

Abstract

Rationalizing the reactive element effect operative in alumina- and chromia-forming alloys upon oxidation under oxidizing hot gas atmospheres, referring to investigations on zirconium oxide-coated test samples for gas turbine alloys. This retrospective study uses the results of cyclic furnace lifetime tests conducted at 1100 °C on ZrO2-coated Ni-base alloys with Y− or Y+ Hf-doped bond coats and correlates them with the parabolic oxidation rate constant at 1100 °C of binary NiAl alloys doped with Y, Zr, or Hf. Parallel results at higher temperatures allow the respective oxidation processes during the cyclic lifetimes to be assigned to cation-dominated or anion-dominated transport processes. The correlations document the close interrelationship between the refractory element content (Mo, Re, Ta, W) in the substrate alloy the total content of the two reactive elements Y and Zr in the mixed zone of the scale, representing a Me3+ iso-valence value individual relative lifetime parameters in pct for EBPVD thermal barrier coating systems associated with cation-dominated transport processes.