Thermal diffusivity of plasma sprayed monolithic coating of alumina-3 wt.% titania produced with nanostructured powder

Nanostructured and conventional alumina-3 wt.% titania monolithic coatings were deposited by air plasma spraying (APS). The thermal diffusivity was measured by the laser flash technique. The thermal diffusivity of the nanostructured Al2O3-3 wt.% TiO2 coating was higher compared with that of the corresponding conventional coating at temperature ranging from 200 to 1000 °C. For the nanostructured coating, there was no difference in the thermal diffusivity between during heating and cooling. However, the thermal diffusivities of the conventional coating were higher during cooling than those during heating. SEM and TEM examination showed that the nanostructured coating contained equiaxed grains with sizes from 150 to 800 nm besides splat lamellae. In the nanostructured coating, most of columnar grains in splat lamellae were less than 200 nm. Splat lamellae of the nanostructured coating bonded well each other and their thickness ranged from 0.4 to 1 μm. The decrease of thermal diffusivity of the nanostructured coating was attributed to the increase of grain boundaries and defective crystal structure. The stability of thermal diffusivity of the nanostructured coating was considered to relate to the absence of narrow long micro-cracks between splat lamellae. Nanostructured and conventional alumina-3 wt.% titania monolithic coatings were deposited by air plasma spraying (APS). The thermal diffusivity was measured by the laser flash technique. The thermal diffusivity of the nanostructured Al2O3-3 wt.% TiO2 coating was higher compared with that of the corresponding conventional coating at temperature ranging from 200 to 1000 °C. For the nanostructured coating, there was no difference in the thermal diffusivity between during heating and cooling. However, the thermal diffusivities of the conventional coating were higher during cooling than those during heating. SEM and TEM examination showed that the nanostructured coating contained equiaxed grains with sizes from 150 to 800 nm besides splat lamellae. In the nanostructured coating, most of columnar grains in splat lamellae were less than 200 nm. Splat lamellae of the nanostructured coating bonded well each other and their thickness ranged from 0.4 to 1 μm. The decrease of thermal diffusivity of the nanostructured coating was attributed to the increase of grain boundaries and defective crystal structure. The stability of thermal diffusivity of the nanostructured coating was considered to relate to the absence of narrow long micro-cracks between splat lamellae.