HVEM HIGH-TEMPERATURE IN-SITU STRAINING EXPERIMENTS ON CUBIC ZIRCONIASINGLE-CRYSTALS

Cubic ZrO2 single crystals fully stabilized with 9.4 mol% Y2O3 were st rained in situ in a high-temperature tensile straining stage inside a high-voltage electron microscope. Straining was usually performed at 1 150 degrees C. One experiment started at 1150 degrees C was interrupte d before it was continued at 870 degrees C. For investigating the depe ndence of the deformation process on the activated slip systems, speci mens with [112] and [100] tensile axes were used. Specimens with a [11 2] tensile axis, where sin le slip on one cube slip system is preferen tially activated, were prepared to have {111} or {110} foil surfaces. Of the specimens with a [100] tensile axis, where slip on cube planes is suppressed, {001} foil surfaces were chosen. The observed dislocati on structures and especially the dynamic behaviour of dislocations rec orded on video tape furnished information on the mode of dislocation m ultiplication and on the mechanisms controlling the flow stress. The a nalyses of the dislocation density provided a value of the long-range stress component. Estimating the local shear stress from the bowed-out dislocation segments yielded a semi-quantitative explanation of the m acroscopic flow stress for the deformation on the cube slip plane at 1 150 degrees C. In this temperature range, the athermal dislocation mot ion is in accordance with the very low strain rate sensitivity measure d in macroscopic tests. At 870 degrees C, dislocations are pinned at l ocalized obstacles. Dislocations on non-cube systems experience a latt ice friction, even at 1150 degrees C. (C) 1997 Elsevier Science S.A.