Porous alumina coating with tailored fracture resistance for alumina composites

A porous Al2O3 coating for Al2O3 composites was prepared by aerosol-spray d eposition of submicrometer-sized Al2O3 powder. A model composite specimen w as hot-pressed to change the coating's porosity and, thereby, change the in terphase fracture resistance. The mixed-mode fracture resistance of the int erphase ranged from 0.5 to 14.8 J/m(2). The interphase fracture was charact erized using electron and acoustic microscopy, Finite-element analysis (FEA ) showed that the testing method possessed a short transient behavior and w as immune to asymmetrical cracks. This approach provided a fundamental inve stigation 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.