Microstructural development of porous â-si3n4 ceramics prepared by pressureless-sintering compositions in the si-re-o-n quaternary systems (re=la, nd, sm, y, yb).

M. QUINLAN,; D. HEARD; K P. PLUCKNETT; L,.B GARRIDO; L. GENOVA

(Daytona Beach-USA

Congreso; Cocoa Beach ACerS composites meeting; 2007

It has recently been demonstrated that porous ¥â-Si3N4 can be engineered to provide similar mechanical properties to dense ¥â-Si3N4, with the additional benefits of reduced mass. Porous ¥â-Si3N4 applications could potentially include filtration media, thermal shock resistant components and high-strength, lightweight structural components. Prior work in Japan has shown that flexural strengths exceeding 1 GPa can be achieved by tailoring the microstructure of the ¥â-Si3N4 grains, such that moderately high aspect ratios are obtained after sintering (up to 10:1) with considerable anisotropic grain alignment, while maintaining porosity levels of ~10-15 %. In the present study, ¥â-Si3N4 ceramics containing higher porosity levels are generated via pressureless sintering in a nitrogen atmosphere, with the addition of single rare earth oxide sintering aids. The oxide additives have been chosen from both the lanthanide (La, Nd, Sm, Yb) and Group IIIB (Y) elements. In each case, the compositions were milled for 24 hours, cold isostatically pressed and then sintered in nitrogen (0.1 MPa) at temperatures ranging from 1500 to 1750¨¬C. Post sinter microstructural characterization was performed using scanning electron microscopy and x-ray diffraction. It is noted that densification and phase transformation kinetics are both strongly influenced by the oxide chosen.