TOUGHENING OF GLASS-CERAMICS BY BOTH TRANSFORMABLE AND TRANSFORMED ZIRCONIA

Zirconia-containing baria-silica system glass-ceramics were prepared by sintering and crystallizing cold-pressed mixtures of a barium silicate glass powder and 10 vol.% of a pre-heat-treated partially stabilized zirconia powder. At room temperature, all zirconia remained as tetragonal zirconia in glass-ceramics. Upon cooling to sub-zero temperatures, tetragonal zirconia in glass-ceramics transformed to monoclinic zirconia, the amount of the transformed zirconia increasing with decreasing temperature. It was found that the room-temperature fracture toughness, K-IC, of glass-ceramics, evaluated by the single-edge-precracked-beam method, increased both with increasing grain size of transformable tetragonal zirconia and with increasing amount of transformed monoclinic zirconia. The former is attributed to zirconia transformation toughening, while the latter is largely due to crack deflection toughening.