Thermal and mechanical properties of sintered bodies and EB-PVD layers of Y2O3 added Gd2Zr2O7 ceramics for thermal barrier coatings

In this study, the sintered bodies and EB-PVD coatings of gadolinium zirconate (Gd2Zr2O7) ceramics with thermal and elastic resistance are prepared by the addition of yttrium oxide (Y2O3) to the composition of Gd2Zr2O7 for thermal barrier coatings. XRD analysis reveals that the Y2O3-doped Gd2Zr2O7 thermal barrier material has a thermally stable pyrochlore structure. The Y2O3-doped Gd2Zr2O7 shows lower thermal conductivity than Y2O3-doped stabilized zirconia (YSZ), from 2.12 W/m K to 0.82–1.32 W/m K, and greater hardness than pure Gd2Zr2O7, from 6 GPa to 10 GPa as measured by Vickers indentation and more than 20 GPa by nano-indentation, mainly owing to changes in the microstructure. The indentation stress–strain curves and load–penetration depth curves obtained by Hertzian and nano-indentation measurements indicate that the behavior of the curve is crucially influenced by the addition of Y2O3 to the pure Gd2Zr2O7. The results suggest that Y2O3-doped Gd2Zr2O7 may be expected to yield hardness and thermal insulation properties superior to those of commercial YSZ coatings for thermal barrier coatings on high temperature alloys.

Research highlights▶ In this study, Y2O3 from 2.3 wt% to 8.25 wt% was added to Gd2Zr2O7, to improve the thermal and elastic properties of a pure Gd2Zr2O7 thermal barrier material. Mechanical properties such as the hardness, stress–strain curves and load–penetration curve as measured by indentation tests were evaluated. Thermal properties such as the thermal expansion coefficient and thermal conductivity were evaluated for pure Gd2Zr2O7 and Y2O3-doped sintered Gd2Zr2O7 materials. The results of phase analysis of the Y2O3-doped Gd2Zr2O7 confirmed the thermally stable pyrochlore structure of the material. ▶ Mechanical properties such as the hardness and elastic properties were enhanced in Gd2Zr2O7 by Y2O3 addition mainly because of microstructural change that resulted from change in the densification behavior. The hardness was improved from 6 GPa to 10 GPa as measured by Vickers test and more than 20 GPa as measured by nano-indentation test with the addition of 3.52 wt% Y2O3 (4.56 mol% of YSZ to Gd2O3) to Gd2Zr2O7. ▶ The Y2O3-doped Gd2Zr2O7 showed lower thermal conductivity than YSZ, from 2.12 W/m K to 0.82–1.32 W/m K and the increase of Y2O3 content in the Gd2Zr2O7 composition enhanced the thermal expansion coefficient of the pure Gd2Zr2O7, 10–10.5 × 10−6/°C.