Current understanding of superplastic deformation of Y-TZP and its application to joining

A review of the high-temperature, steady-state creep of yttria tetragonal zirconia polycrystals (Y-TZP) as a function of grain size, strain rate, stress, and temperature will be presented in this paper. Data have been analyzed using the standard creep equation incorporating a threshold stress. Microstructural observations of deformed samples indicated that deformation was achieved primarily by grain boundary sliding (GBS). This microscopic characteristic was used to join pieces of these materials. When two pieces of ceramics are compressed in the superplastic regime, GBS will produce a junction between the pieces. Several types of strong junctions have been produced, i.e. between pieces of the same material having different grain sizes, and between pieces of different materials. Scanning electron microscopy of the interfaces showed that each interface was cavity- and crack-free. Vickers indentations and high-temperature mechanical tests indicated that the interfaces were as strong as the matrix. This joining technique allows the construction of a complex shape or a functional gradient material.