Influence of CaO-SiO2 ratio on the chemistry of intergranular films in liquid-phase sintered alumina and implications for rate of erosive wear

Polycrystalline aluminas sintered with 10 wt% additions of calcium oxide (C aO) and silica (SiO2) in varying molar ratios were fabricated via precipita tion, calcination, and hot pressing. Alumina microstructures were analyzed by scanning electron microscopy in terms of their mean grain size, grain si ze distribution, and grain aspect ratios. High-resolution transmission elec tron microscopy (HRTEM) showed the presence of an amorphous intergranular g lassy phase at two- and three-grain boundaries. The intergranular film widt h at two-grain boundaries, determined by HRTEM, appeared to vary with the [ CaO]:[SiO2] ratio of the additive as did the chemical composition and local chemistry, determined by high-resolution analytical transmission electron microscopy and scanning transmission electron microscopy (using both energy dispersive x-ray and electron energy loss spectroscopy). The factors influ encing the erosive wear rate are discussed including the chemistry and asso ciated fracture energy of the intergranular glassy film. Wet erosive wear r ates of the densified materials were determined and had a strong dependence on the [CaO]:[SiO2] ratio in the additive.