The bending strength temperature dependence of the directionally solidified eutectic LaB6-ZrB2 composite

A directionally solidified LaB6-ZrB2 eutectic was prepared by the floating zone method based on the crucible-free zone melting of compacted powders. ZrB2 and LaB6 powders were used as the initial materials. The bending strength of the composite was evaluated in the temperature range of 25-1600 degrees C and reached 950 MPa at 1600 degrees C. Using a residual stress analysis, fracture toughness, and SEM and TEM fracture investigations, the toughening mechanisms under different conditions were studied. We speculate that the strength of the LaB6-ZrB2 eutectic at 25-1200 degrees C is mainly associated with crack deflection, bridge toughening mechanisms and increasing plasticity of the ZrB2 phase; and at 1200-1600 degrees C, with the increasing plasticity of the matrix and fibers. By analyzing the dislocation structure of the fibers, the occurrence of strain hardening in the single crystalline ZrB2 during high-temperature deformation was revealed. The change from the brittle to ductile fracture mode for the directionally solidified LaB6-ZrB2 eutectic at near 1600 degrees C was determined. (C) 2011 Elsevier B.V. All rights reserved.