Beneficial effects of magnetron-sputtered Al–Y seal layers on porous thermal barrier coatings

Abstract

An aluminum-yttrium (Al–Y) layer was deposited on porous thermal barrier coatings using a magnetron sputtering technique. The excellent mechanical properties of the resulting composite coating can be attributed to the dense Al–Y layer, which completely sealed the surface of a ZrO2-8%Y2O3 (YSZ) coating on NiCoCrAlY while providing a relatively smooth surface and good adhesion. This double-layer design ensured that the as-sprayed YSZ coating's porous interior texture retained a low level of thermal conductivity. In addition, the oxidation penetration channels caused by open voids in the YSZ coating were effectively eliminated. According to the X-ray powder diffraction pattern, the added Y element from the Al–Y layer compensated for the loss of yttrium oxide in the YSZ coating thus constantly stabilizing the cubic ZrO2 phase. As a result, thermal oxide growth at the YSZ and MCrAlY interface was prevented by the protective layer of Al–Y and associated oxides.