GdPO4 as a novel candidate for thermal barrier coating applications at elevated temperatures

Extensive efforts are being invested to explore alternative materials to Y2O3 partially stabilized ZrO2 (YSZ) for thermal barrier coating (TBC) applications at elevated temperatures. In this study, GdPO4 is investigated for potential use as TBCs. GdPO4 had a monazite structure, and revealed ultralow thermal conductivity, with a value of similar to 0.98 W/mK at 1000 degrees C. The toughness was measured to be 1.16 +/- 0.12 MPa.m(1/2). A nanostructured GdPO4/YSZ double-ceramic-layer (DCL) TBC was prepared by air plasma spraying. After sintering at 1400 degrees C for 50 h, some Gd3PO7 formed in the GdPO4 coating, and the coating grains underwent some growth. Thermal cycling tests of GdPO4/YSZ DCL TBCs indicated that spallation occurred in the GdPO4 coating, while the YSZ coating retained structure integrity. The failure mechanisms of the coatings are investigated, mainly attributable to the large stress produced in the coating, and the phase decomposition and low toughness of GdPO4.