Anisotropic dislocation nucleation in ZrB2 grains and deformation behaviour of constituents of ZrB2-SiC and ZrB2-B4C composites during nanoindentation

Anisotropic slip activation of ZrB2 grains and deformation behaviour of constituents of ZrB2-SiC and ZrB2-B4C composites were investigated by nanoindentation. Samples were prepared by spark plasma sintering; crystallographic orientation of grains was determined by electron backscatter diffraction and deformation around indents in constituents was studied by scanning electron microscopy. Based on the Hertzian stress analysis of the measured strain bursts, so called pop-ins, the critical resolved shear stresses for slip system families of {10 (1) over bar0}(11 (2) over bar0), {10 (1) over bar0}[0001] and {10 (1) over bar0}(11 (2) over bar3) were determined for ZrB2. Homogeneous dislocation nucleation was revealed with similar critical resolved shear stresses (similar to 35 GPa) for each slip system close to the theoretical value. Based on the analysis of the orientation dependent maximal resolved shear stress, anisotropic dislocation nucleation was inferred in ZrB2 grains with single and simultaneous activation of the investigated slip systems. Macromechanical properties of the composites were correlated to nanohardness and indentation modulus of grains and grain boundaries.