The effect of grain boundary phase on contact damage behavior is investigated in alumina
ceramics. Four types of aluminas doped with MgO, anorthite (CaO·Al2O3·2SiO2), silica, and
with both MgO and anorthite are prepared such that they have similar average grain size by
adjusting sintering conditions. MgO-doped alumina composed of equiaxed grains shows
brittle fracture behavior, and anorthite-doped alumina composed of elongated grains
shows a quasi-plastic response under Hertzian sphere indentation. The co-doped alumina
with MgO and anorthite, however, is damage tolerant even with its rounded grains, while
silica-doped alumina with similar grain size and shape to anorthite-doped alumina shows
abrupt strength degradation with low critical load for cone cracking. The damage behavior
is discussed from the viewpoint of residual stress induced by thermal expansion mismatch
between the grains and grain boundary phases. The damage tolerant behavior of alumina
ceramics is significantly affected by the composition of grain boundary phase.