SUPERPLASTICITY OF CERAMIC MATERIALS .2. EFFECT OF INITIAL POROSITY AND DOPING ON THE SUPERPLASTIC BEHAVIOR OF ALUMINA

The present work has demonstrated the ability of fine grained alumina containing small additions of copper oxide or nickel oxide to undergo superplastic tensile flow. The effect of small levels of porosity on s uperplastic behaviour has been examined using specimens subjected to H IP. This provides an effective way of controlling the density of ceram ic materials while avoiding appreciable grain growth. Results showed t hat low density specimens tended to have higher superplastic elongatio ns to failure than higher density specimens. In the latter case, long cracks developed during deformation and grew perpendicular to the tens ile axis; this led to premature failure. The uniformly distributed por es in the lower density specimens provided sites for both crack, initi ation and crack arrest, leading to a large number of short cracks, and to higher failure strains. TEM observations gave evidence of signific ant dislocation activity in grain boundary regions of the deformed mat erials and this is tentatively interpreted in terms of the electronic contributions of the dopants to dislocation mobility. Copyright (C) 19 96 Acta Metallurgica Inc.