Crystallographic characterization and indentation mechanical properties of LaB6-ZrB2 directionally solidified eutectics

LaB6-ZrB2 eutectics were directionally solidified by a zone melting process. The microstructure and crystallography were characterized by X-ray diffraction, optical microscopy and transmission electron microscopy. The anisotropies of hardness and indentation fracture toughness were assessed by making measurements along different crystallographic directions on both transverse and longitudinal sections. While the hardness did not vary appreciably between the two orientations, the fracture toughness was observed to be highly anisotropic. Toughening behavior was observed on longitudinal sections with crack deflection and bridging mechanisms apparent. Cracks were difficult to initiate on transverse sections along directions perpendicular to the growth direction, but for 20 N loads an indentation fracture toughness of 11 MPa could be measured.