Design and Characterization of Porosity Gradient for the Laminated Alumina Tubes

Abstract

Based on the FGM concept, laminated alumina tube with a tailored porosity gradient along the radial direction has been successfully fabricated by the lamination method in the centrifugal molding technique. Experiments were performed with colloidally processed alumina powder and pore-former agent. The powder mixture was made into slurry in water media and the tubes were cast using a stainless steel mold. The porosity profile was designed with the presence of PMMA particles as pore-former agent and the nature of porosity was investigated by microstructure observations. The bimodal pore structure of the tubes was constructed from large spherical pores about 10 μm formed by burning-out the pore-former agent and small sub-micron pores caused by the lower sintering temperature. The fracture behavior of porous tubes with tailored porosity gradient was investigated using the O-ring compression testing. The failure behavior was divided into two types depending on the pore-former agent. The air permeability and fracture behavior were independent of the lamination process. The influence of the porosity gradient on the fracture strength was investigated and the results showed there was a reduction in fracture strength with increase in the laminate number, and the minimum strength was found in continuous graded tubes.