Porous Alumina Coating with Tailored Fracture Resistance for Alumina Composites

A porous Al₂O₃ coating for Al₂O₃ composites was prepared by aerosol-spray deposition of submicrometer-sized Al₂O₃ powder. A model composite specimen was hot-pressed to change the coating's porosity and, thereby, change the interphase fracture resistance. The mixed-mode fracture resistance of the interphase ranged from 0.5 to 14.8 J/m². The interphase fracture was characterized using electron and acoustic microscopy. Finite-element analysis (FEA) showed that the testing method possessed a short transient behavior and was immune to asymmetrical cracks. This approach provided a fundamental investigation of the relationships among interphase microstructure, processing, and fracture resistance. The results also provided a detailed test of the He-Hutchinson criterion for crack deflection.