Evolution of mechanical properties of porous alumina during free sintering and hot pressing

This comparative study addresses the influence of microstructural evolution on mechanical properties of porous alumina sintered with and without the application of uni-axial pressure. A complete set of data on Young's modulus, long-crack fracture toughness, and fracture strength for two alumina powders as a function of density was obtained. The evolution of fracture strength with increased density was modeled using a porosity-dependent crack-tip fracture toughness, linked to the contact area of grains and a porosity-dependent size of the largest defect. The defect shape factor was found independent of porosity. A uniaxial pressure of 13 MPa during densification had negligible effect on the relation of strength to porosity.