Grain Boundary Chemistry and Creep Resistance of Oxide Ceramics

Oversized dopant ions such as yttrium, lanthanum, and neodymium segregate to grain boundaries and reduce the tensile creep rate of α-Al₂O₃ by 2 or more orders of magnitude. One explanation for this behavior is that the oversized dopant segregants give rise to a 'site-blocking' effect for grain boundary diffusion. Another mechanism that has been speculated involves the change in grain boundary structure caused by dopant ion segregation, producing more abundant special boundaries. In addition, further reduction of creep rate can be obtained by selective co-doping. In this case, grain boundary diffusion is suppressed to such a degree that creep may now be controlled by lattice diffusion. The details of this behavior can be understood by careful tailoring of the alumina grain boundary chemistry as well as characterizing the grain boundary structure. This paper includes the results from analytical techniques such as SIMS, STEM, EBKD analyses along with computer modeling of segregation behavior.