Plasma spraying of micro-composite thermal barrier coatings

Abstract

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 100 wt% ZrO 2 or Al 2O 3. 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 μm 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 Al 2O 3 can result in an increase in the transverse thermal resistivity of YSZ.