Slow sintering in garnet-containing Y and Gd zirconate-aluminate mixtures for thermal barrier coatings

Mixtures of rare-earth zirconates and aluminates containing Y or Y + Gd that form a two-phase garnet-fluorite mixture exhibit much slower sintering than pure fluorite at 1400 degrees C. An equivalent Y-free, Gd-containing composition that forms a perovskite aluminate instead of garnet showed faster densification after the metastable garnet decomposes. At 1500 degrees C, the Y-free sample also showed the fastest initial sintering rate, whereas there was more divergence in the sintering rate for the samples containing Y + Gd. The zirconate-aluminate with equimolar Y + Gd shows the slowest densification at 1500 degrees C and retains similar to 25% porosity after 250 h. The results highlight possibilities for designing compliant thermal barrier coatings that can retain significant porosity at 1400 degrees C or higher.

Automated summary

Mixtures of rare-earth zirconates and aluminates with Y or Y + Gd exhibit slower sintering compared to pure fluorite at 1400 degrees C. A Gd-containing composition that forms a perovskite aluminate instead of garnet shows faster densification after garnet decomposition. At 1500 degrees C, the Y-free sample shows the fastest initial sintering rate, while the samples containing Y + Gd have varying sintering rates. The equimolar Y + Gd zirconate-aluminate exhibits the slowest densification and retains approximately 25% porosity after 250 h.