Strengthening porous ceramics by molten metal infiltration

Interpenetrating phase composites with ceramic matrix were fabricated by infiltration with a molten hypoeutectic Al-Si alloy (A-356) of two porous sintered alumina samples, APC-2011SG ALCOA-BR and EPUSP-BR, using a pressurised inert gas furnace (PIC process). The resulting CMCs showed a 4 to 5 fold increase in strength over the porous ceramic, as measured in the three point bending test. A maximum strength of 550 MPa was achieved. Infiltrated samples were cut, polished and microstructurally characterised by optical and scanning electron microscopy. Fracture surfaces of the three point bending test samples were examined under the scanning electron microscope. The microstructural analysis showed that the metal filled most of the pores, the aluminium alloy also filling small flaws and tiny cracks already present in the sintered ceramic, showing that the infiltration had a ″healing″ effect, that can benefit structural ceramics.