A novel structure design towards extremely low thermal conductivity for thermal barrier coatings – Experimental and mathematical study

In this paper, a novel structure design towards extremely low thermal conductivity for thermal barrier coatings (TBCs) has been proposed. The structure design includes layer structure design and the defects configuration design. Firstly, an experimental investigation has been performed. The La2Zr2O7 (LZ) which is one of the zirconate-based TBCs materials was chosen as the investigated material in the layer structure design. Nanostructured ZrO2–8 wt%Y2O3 (8YSZ), conventional 8YSZ TBCs and double-ceramic-layer (DCL) La2Zr2O7/nanostructured 8YSZ (LZ/n-8YSZ) were prepared by atmospheric plasma spraying (APS) on 45#steel substrates with the NiCrAlY as the bond-coat, respectively. The insulation temperatures of the three coatings were measured by oxyacetylene flame flash method and the effective thermal conductivities of the as-sprayed coatings have been obtained. Secondly, the effect of defects configuration on the effective thermal conductivity has been discussed systematically based on the strict mathematical calculation combined with finite element simulation. Based on the experimental and mathematical studies, an ideal coating structure was proposed for further decreasing the effective thermal conductivity of the TBCs. The effective thermal conductivity of the DCL LZ/n-8YSZ TBCs based on the actual morphology was calculated using computational micro-mechanics (CMM) method.