Preparation of Rare-Earth Doped Thermal Barrier Coatings via Suspension Plasma Spray

Thermal barrier coatings (TBCs) are ceramic coatings that are used in the hot sections of gas turbine engines to protect the underlying superalloys during service. TBCs with lower thermal conductivity allow engines to operate at higher temperature and therefore increases the engine efficiency. Recent research has shown that the addition of paired rare-earth oxides with equal ratio can reduce the thermal conductivity of the yttria-stabilized zirconia (YSZ) coatings. In this work, suspension plasma spray (SPS) is used to fabricate rare-earth doped coatings by dissolving rare-earth nitrates into 8 wt% YSZ powder-ethanol suspensions prior to spraying. Five coatings with different amount or type of rare-earth dopants were prepared. The incorporation of rare-earth dopants was confirmed utilizing energy dispersive X-ray spectroscopy (EDS). The majority of coatings were ~300 to 350 μm thick. The Archimedes’ density of the as-sprayed coatings ranges from 3.45±0.14 to 4.62±0.44 g/cm³ with the most dense being the undoped coatings and the least dense being the coatings with highest dopant concentration. Two different heat treatment conditions (1200  ̊C for 50 hr and 1300  ̊C for 50 hr) have been applied to samples from each coating type to investigate the effect of dopant on thermal conductivity after heat treatment.