High-Temperature Aging of Plasma Sprayed Quasi-Eutectoid LaYbZr2O7-Part I: Phase Evolution

Abstract

Phase and microstructure stability is an important issue for the durability and performance of thermal barrier coating (TBC) materials which have to work at high temperature for long time. In this work, we present a meta-stable structure LaYbZr2O7 by air plasma spraying process, which can convert into thermodynamically stable fine-grained quasi-eutectoid structure with enhanced thermal insulation properties even under high-temperature annealing. In this part, we first report on the phase composition and relationship in the LaYbZr2O7 coatings. The as-sprayed LaYbZr2O7 coatings initially exhibited a mixture of amorphous phase and a nonequilibrium fluorite phase. Then it underwent a fast crystallization and a quasi-eutectoid transformation during the first few hours of annealing at 1300°C. The phase constitution quickly reached an equilibrium state consisting of La-rich pyrochlore phase and Yb2Zr2O7 fluorite phase after 6 h annealing and kept stable ever since. Coherent phase boundaries were observed between the La-rich pyrochlore and Yb2Zr2O7 fluorite phase, indicating a lower interface energy, a lower ionic diffusion rate, a higher strength and creeping resistance of this material at high temperature, all of which could be particularly advantageous to a TBC material for high-temperature gas turbine applications.