Critical zirconia amount to enhance the strength of alumina

A small amount of zirconia particles (≤5 vol.%) is added into alumina in the present study. The grain size of alumina is reduced; the strength of alumina is therefore enhanced. Though the theoretical analysis demonstrates that an addition of 1 vol.% of fine zirconia particles is sufficient to prohibit the coarsening of alumina grains; the experimental measurements indicate that a minimum amount of 2 vol.% is required to reduce the coarsening of alumina matrix and its size distribution. This discrepancy is due to the separation between the zirconia particles and alumina grain boundaries, which takes place when the alumina grain size increases above a critical value.