Hvem in situ Study of High-Temperature Deformation of Ceramic and Metallic Materials

Abstract

AbstractA high-temperature straining stage was designed for the Halle HVEM. Electron bombardment is used to heat the specimen grips. At present the stage is operated at a maximum temperature of 1250 °C, but somewhat higher temperatures should also be possible. Details of the stage are described and results are presented on several materials. In yttria fully-stabilized (cubic) zirconia, the different slip behaviour on cube and octahedral planes is demonstrated at a specimen temperature of about 1150 °C. While the dislocations move very jerkily on the (primary) cube planes, their motion is more smooth on the octahedral planes suggesting the action of the Peierls mechanism. In t' zirconia, the switching of tetragonal domains was recorded during ferroelastic deformation. The same process was first observed for tetragonal precipitates in partially stabilized zirconia. In γ TiAl, at the temperature of the flow stress anomaly (about 650 °c), the so-called ordinary dislocations move in a viscous manner, in contrast to the room temperature behaviour, where glide seems to be controlled by localized obstacles. Over a wide temperature range in NiAl single crystals, moving dislocations show a discontinuous dependence of the curvature on the dislocation orientation, well agreeing with calculations of the line tension using anisotropic elasticity. Direct experimental proof of dislocation motion during plastic deformation of quasicrystals is first given for A1PdMn single quasicrystals. Dislocations smoothly move on planes orthogonal to threefold and fivefold directions.