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 z irconia polycrystals (Y-TZP) as a function of grain size, strain rate, stre ss, and temperature will be presented in this paper. Data have been analyze d using the standard creep equation incorporating a threshold stress. Micro structural observations of deformed samples indicated that deformation was achieved primarily by grain boundary sliding (GBS). This microscopic charac teristic was used to join pieces of these materials. When two pieces of cer amics are compressed in the superplastic regime, GBS will produce a junctio n 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 inter faces were as strong as the matrix. This joining technique allows the const ruction of a complex shape or a functional gradient material. (C) 2001 Else vier Science B.V. All rights reserved.