Phase relations and thermomechanical properties of (Gd2Zr2O7)1-x(YbSZ)x based thermal barrier coatings (0 ≤x≤ 0.98)

Abstract

Doped Gd2Zr2O7 materials have interesting properties as thermal barrier coatings (TBC) to replace the YSZ topcoats traditionally used. Here we investigate the thermomechanical properties and phase relations of Gd2Zr2O7 (GZO) alloyed with 5 mol% Yb2O3 stabilized ZrO2 (YbSZ) in the composition range (Gd2Zr2O7)1-x(YbSZ)x, 0 ≤x≤ 0.98. With increasing YbSZ content, phase transformations from ordered to disordered pyrochlore to fluorite and tetragonal structures were observed. The thermal expansion coefficient (TEC) and Vickers hardness were correlated showing a maximum hardness (~11.5 GPa) and minimum TEC at x=0.82. At 1000 °C, the TEC for the end members, x=0 and 0.98, were 11.4 and 11.3.10-6 K-1, respectively. The fracture toughness, KIC, showed an average value around 1.5 MPa.m0.5 for x≤ 0.93 and increased significantly at x=0.98 reaching 5.4 MPa.m0.5 due to the presence of a ferroelastic phase. For TBC applications, compounds with x=0.98 show promise due to high TEC and high KIC.