Low Thermal Conductivity Yttrium Aluminum Garnet Thermal Barrier Coatings Made by the Solution Precursor Plasma Spray: Part I—Processing and Properties

Critical properties of TBCs include low thermal conductivity (TC) and high cyclic durability. In recent years, the solution precursor plasma spray (SPPS) process has been effectively used for deposition of TBCs with enhanced cyclic durability for yttria-stabilized zirconia (YSZ) and the higher temperature yttrium aluminum garnet (YAG) TBCs. Improvements in deposition efficiency (DE) and deposition rate (DR) were identified as needed for cost-effective commercialization. In this work, SPPS YAG TBCs with low TC and high DE and DR have been produced with microstructures containing a high density of planar arrays of increased porosity called inter-pass boundaries (IPBs). The IPBs have been shown to reduce the TC of SPPS YAG TBCs by 39% to a value of 0.58 W/mK at 1300 °C. Increasing the precursor feed rates and decreasing the raster scan step heights generate high-density IPB microstructures, while simultaneously increasing the DE and DR by 53 and 190%, respectively. The SPPS YAG microstructures with high-density IPBs also exhibit improved thermal cycling and sinter resistance compared to APS YSZ.