• RESIDUAL STRESSES AND FRACTURE TOUGHNESS BORIDE CERAMIC COMPOSITES WITH MONOCRYSTALLINE MATRIX

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 3 (2017), Issue 3, pg(s) 115-118

    X-ray diffraction analysis studies the formation of a stress-strain state of single-crystal composites LaB6-TiB2 obtained under identical conditions by crucible-free float zone melting (FZM). The composites were obtained using monocrystalline LaB6 substrate seeds with <100>, <110> and <111> orientations. It is shown that indentation-induced deformation in the composite materials obtained by FZM is distinct from the deformation expected in their equilibrium state. This difference arises in part from residual thermal strains in both phases of the composites in a FZM -grown state. Interplay between residual thermal deformations and external mechanical deformation results in a complex distribution of dilatational strain in the LaB6 matrix and TiB2 fibers and differs in composites of different orientations. Reversal sign of the stress-strain state (e.g., alternating tensile/compressive/tensile in central part of the cross-section area) is observed predominantly in the matrix LAB6 and the TiB2 fibers of the composite with the orientation <111>. In the composite with the orientation <100>, this change in the deformation sign was not observed. The size and spread of cracks after indentation-induced deformation shows a decrease in microhardness in FZM -grown composites of <111> significantly more (40%) than in composites with a orientation of <100> (10%) compared with an equilibrium state.