INFLUENCE OF AMORPHOUS GRAIN-BOUNDARY PHASES ON THE SUPERPLASTIC BEHAVIOR OF 3-MOL-PERCENT-YTTRIA-STABILIZED TETRAGONAL ZIRCONIA POLYCRYSTALS (3Y-TZP)

Amorphous silicate grain boundary phases of varying chemistry and amou nts were added to 3Y-TZP in order to determine their influence on the superplastic behavior between 1200-degrees and 1300-degrees-C and on t he room-temperature mechanical properties. Strain rate enhancement at high temperatures was observed in 3Y-TZP containing a glassy grain bou ndary phase, even with as little as 0.1 wt% glass. Strain rate enhance ment was greatest in 3Y-TZP with 5 wt% glass, but the room-temperature hardness, elastic modulus, and fracture toughness were degraded. The addition of glassy grain boundary phases did not significantly affect the stress exponent of 3Y-TZP, but did lower the activation energy for superplastic How. Strain rate enhancement was highest in samples cont aining the grain boundary phase with the highest solubility for Y2O3 a nd ZrO2, but the strain rate did not scale inversely with the viscosit y of the silicate phases. Grain boundary sliding accommodated by diffu sional creep controlled by an interface reaction is proposed as the me chanism for superplastic deformation in 3Y-TZP with and without glassy grain boundary phases.