A. K. Kronenberg S. H. Kirby T. E. Mitchell J. Castaing 2000 <p><span>Hydrogen impurities in alumina have been introduced by hydrothermal annealing (see part I). In this paper, we report on reductions in the flow strength of&nbsp;</span><i>α</i><span>-Al</span>₂<span>O</span>₃<span>&nbsp;single crystals and polycrystals associated with hydrogen incorporation. Prior to deformation,&nbsp;</span><i>α</i><span>-Al</span>₂<span>O</span>₃<span>&nbsp;single crystal and ceramic specimens were annealed in the presence of supercritical water at 850° or 900°C, under 1500 MPa pressure. Sapphire and alumina ceramics were plastically deformed between 600° and 1000°C under 1500 MPa pressure, by the addition of a uniaxial stress. Flow stresses are reduced by a factor of two, due to the presence of water, for sapphire and large grain (30–50&nbsp;μm) polycrystals, as a result of enhanced dislocation mobility. Flow stresses of fine-grained (3–5&nbsp;μm) polycrystals are reduced by water by a factor of six. This large reduction in strength is attributed to a change in mechanism from dislocation glide under dry conditions to grain boundary sliding under hydrothermal conditions.</span></p> application/pdf 10.1016/S1359-6454(99)00449-8 en Elsevier Hydrogen defects in α-Al2O3 and water weakening of sapphire and alumina ceramics between 600°C and 1000°C: II. Mechanical properties article