Plasma spraying of micro-composite thermal barrier coatings

The thermal barrier coatings (TBCs) by gas tunnel-type plasma spraying exhibited ceramic-composite features consisting of a host oxide matrix ceramic with an embedded second phase material. The densities of the composite TBC were found to be higher than those sprayed with 100wt% ZrO2 or Al2O3, In the coatings produced with powder mixtures of 50 wt%, the embedded splats are found to have a relatively uniform thickness between 1 and 10 pm and they exhibited clear and pore-free interfaces with the host material. The micro-composite coatings also exhibited thickness-dependent functionally gradient Vickers hardness values by the hardness measurements across the coating thickness. A one-dimensional series heat transfer model was developed to estimate upper and lower bounds of the transverse thermal resistance as a function of alumina-zirconia weight ratio. The model shows that the addition of higher thermally conducting Al2O3 can result in an increase in the transverse thermal resistivity of YSZ. (C) 2002 Elsevier Science Ltd. All rights reserved.