Anomalous slip of ZrB2 ceramic grains during in-situ micropillar compression up to 500 °C

The anisotropic deformation behaviour of ZrB2 grains of basal and prismatic orientations in a polycrystalline ZrB2 sample was studied during in-situ micropillar compression at room temperature (RT), 350 degrees C and 500 degrees C. Micropillars were milled out of large grains by focused ion beam machining; the basal and prismatic orientations were previously identified using electron backscatter diffraction maps. The basal pillars showed brittle behaviour and cracking on the {10 (1) over bar0} and {2 (1) over bar(1) over bar0} type prismatic planes that lead to their collapse. For this orientation, the yield/rupture stress ranged between 8 and 14 GPa and it exceeded 12 GPa even at 500 degrees C. In the prismatic orientation, considerable plasticity was observed, showing a temperature dependent yield stress from 6 to 8 GPa at room temperature to similar to 2GPa at 500 degrees C. The activated slip system family was identified as {10 (1) over bar 01}< 11 (2) over bar3 > type for all of the test temperatures (RT, 350 degrees C and 500 degrees C). Analysis of the Schmid-factors revealed that the plasticity of the prismatic micropillars is controlled by the temperature dependence of the critical resolved shear stress of the {10 (1) over bar0}< 11 (2) over bar3 > slip systems. The brittleness of the basal micropillars was influenced by their defect structure (e.g. microcracks) and it was temperature independent due to the absence of slip activation.