LOW-TEMPERATURE SUPERPLASTIC FLOW OF YTTRIA-STABILIZED TETRAGONAL ZIRCONIA POLYCRYSTALS

Very fine-grained (0.2 mum), dense Y-TZP ceramics have been produced b y free sintering at 1150-degrees-C. The superplastic deformation of th ese materials is studied in compression at low temperatures (1100-1300 -degrees-C). A significant enhancement in initial strain rates was obs erved compared to a coarser-grained (0.4 mum) commercially available m aterial (Tosoh, Japan). Doping with small amounts of Fe2O3 led to a fu rther enhancement of strain rate. Deformation occurred via interface r eaction controlled grain boundary sliding. Prior to deformation a cont inuous glassy silicate film was observed at the grain boundaries. The applicability of interface reaction controlled solution-precipitation creep models is discussed. The absence of a steady-state during deform ation at low stresses is attributed to dewetting of the silicate film.