Characterization and strengthening of porous alumina-20 wt% zirconia ceramic composites

Abstract

Porous alumina-20 wt% zirconia (stabilized with 3 mol.% Y2O3) ceramic composites doped with 1 wt% -niobium oxide were fabricated using sol-gel derived nano-powders. Corn starch with nominal content of 0, 10, 20, and 40 wt% was added as a pore forming agent. The porous composites were pressureless sintered and characterized for open and total porosity, and for pore size, shape, distribution and connectivity. Mechanical properties including hardness, indentation fracture toughness and compressive strength were determined and related to the porosity. The results showed that pores have near spherical morphology with uniform size and distribution and good connectivity. The 40 wt% starch sample doped with niobia retained a maximum porosity of 57%, compressive strength of ~ 60 MPa and fracture toughness of 1.60 MPa m1/2 after sintering. Although Niobium oxide destabilized the tetragonal zirconia phase significantly and reduced the tetragonal phase to about 30%. Comparison of niobia-doped and undoped samples with the equal amount of 40 wt% starch, revealed that in the niobia-doped samples the sintered density, hardness and fracture toughness increased by 22%, 16%, and 12%, respectively while compressive strength decreased by 14%. Indeed, the objective of this study was to combine the toughening and strengthening effect of tetragonal zirconia along with positive densification effect of niobium oxide, to further strengthen the porous alumina-zirconia ceramic composites.