Microstructures and Properties of Sm₂(Zr_0.7Ce_0.3)₂O₇/8YSZ Double-Ceramic-Layer Thermal Barrier Coatings Deposited by Atmospheric Plasma Spraying

The properties of Sm₂(Zr_0.7Ce_0.3)₂O₇ (SZ7C3) as a novel thermal barrier coating (TBC) candidate have been evaluated. There is no evidence for a phase transformation for SZ7C3 from room temperature to 1600 °C. SZ7C3 exhibits a higher sintering resistance than the conventional yttria-stabilized zirconia (YSZ). The Vickers hardness for the SZ7C3 bulk is ca. 9.6 GPa, and the fracture toughness lies in a range of 1.5-2.5 MPa m^1/2. Single SZ7C3 coatings and SZ7C3/8YSZ double-ceramic-layer (DCL) coatings were prepared by plasma spraying. The thermal conductivities of SZ7C3 coatings range from 0.4 to 0.6 W m⁻¹ K⁻¹ (significantly lower than those of 8YSZ). SZ7C3 coatings also exhibit moderate thermal expansion coefficients (TECs), near 10.8 × 10⁻⁶ K⁻¹ at 1200 °C. The values of thermal expansion coefficients and fracture toughness are higher than those of La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3), which has been proposed as a promising high-temperature (> 1250 °C) TBC candidate material. The thermal cycling lifetime of SZ7C3/8YSZ DCL coating is much longer than that of LZ7C3/8YSZ TBC as demonstrated by the furnace thermal cycling tests, further confirming that SZ7C3 coatings have great potential as high-temperature TBCs for use in the next generation of advanced engines.