2O3/GdAlO3 eutectic ceramic by laser floating zone melting with high temperature gradient]]>

摘要

Directionally solidified Al_2O_3/GdAlO_3 eutectic ceramic rods with high densities and low solidification defects are prepared by laser floating zone melting at solidification rate from 2 to 200μm/s. The microstructure evolution, eutectic growth behavior and mechanical properties are investigated. At low solidification rates (<30 μm/s), the eutectic rods present a homogeneous irregular eutectic microstruc-ture, whereas cellular microstructure containing regular lamella/rod structure is developed at higher solidification rates. The relationship is established between the eutectic interphase spacing and solidifica-tion rate, which follows the Magnin-Kurz eutectic model. The Vickers hardness (15.9-17.3 GPa) increases slightly with decreasing interphase spacing, but the fracture toughness (4.08 MPam~(1/2)) shows little dependence with the solidification rate. Different crack propagation mechanisms are revealed among the indentation cracks. The flexural strength at ambient temperature reaches up to 1.14 GPa for the eutectic grown at 100 μm/s. The fracture surface analysis indicates that the surface defects are the main crack source.