Performance of plasma-sprayed thermal barrier coating with engineered unmelted nano-particle contents

This paper provides an insight into the effect of unmelted nano-particle content (UNC) on the thermal cycling property and thermal insulation performance of plasma sprayed nanostructured yttria stabilized zirconia thermal barrier coatings. The results suggested that the as-sprayed nanostructured coating displayed a multi-modal microstructure, including the nano-grains (30–90 nm in size), submicron grains (110–900 nm in size) and unmelted nano-particles (20–60 nm in size). These unmelted nano-particles were loosely distributed among the nano-grains or submicron-grains. When the UNC increased from 11% to 34%, the bond strength of coating decreased from 28.1 MPa to 6.3 MPa and the thermal insulation temperature of coating increased from 135 °C to 170 °C. The coating with 22% UNC showed the highest thermal cycling life at 1250 °C since the unmelted nano-particles significantly reduced the residual stress and effectively prevented the propagation of cracks. The thermal insulation temperature of coating increased with the increase of thermal cycles and reached its maximum after approximately 600 cycles due to the coalescence of cracks located at the unmelted nano-particles/crystalline region interface. The performance of nanostructured coating can be tailored by modulating the UNC.