A probe for the high temperature deformation of thermal barrier oxides

A probe for measuring the plastic deformation of porous thermal barrier oxides at high temperature has been designed, described and demonstrated for columnar microstructures grown by electron beam evaporation. The method involves deposition of the coating onto an alumina substrate (which is rigid at the test temperature) and impressing with a sapphire sphere, while simultaneously measuring the loads and displacements. A simulation allows de-convolution of the yield strength, as well as the inter-columnar friction. The measurements performed between 937 and 1137 °C revealed substantial differences between two grades of yttria-stabilized zirconia (7 and 20 wt%) as well as between them and Gd2Zr2O7. The anisotropy of the columnar microstructure causes the deformation to be heterogeneous, manifest as shear bands emanating from the contact zone. The exception is 7 wt% YSZ tested at 1137 °C, which exhibits a zone of homogeneous densification. The shear bands weaken the material and provide planes for preferential material removal during foreign object damage and erosion.