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 °C and reached 950 MPa at 1600 °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 °C is mainly associated with crack deflection, bridge toughening mechanisms and increasing plasticity of the ZrB2 phase; and at 1200–1600 °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 °C was determined.

► We prepare the directionally solidified LaB6–ZrB2 eutectic by the floating zone method. ► The bending strength of the composite reached 950 MPa at 1600 °C. ► The mechanical behavior of the eutectic at low temperatures is associated with crack deflection and bridge toughening mechanisms. ► At high temperature, the increasing plasticity of the matrix and fibers is observed.