Role of segregating dopants on the improved creep resistance of aluminum oxide

Recent studies have demonstrated that p.p.m. levels of rare-earth dopant io ns (e.g. Y, La, Nd) wield a beneficial and highly potent influence on the c reep properties of alumina. In addition, codoping with ions of disparate si zes (Nd, Zr) resulted in even further enhancement of the creep behavior. In all cases, the dopant ions were found to strongly segregate to grain bound aries. Creep rates were not influenced by the presence of second phase prec ipitates, verifying that the creep improvement is a solid solution effect. Ln an attempt to clarify the exact mechanism(s) that controls creep behavio r of the doped aluminas, various advanced characterization techniques have been applied including: secondary ion mass spectrometry, scanning transmiss ion electron microscopy, orientation image microscopy, and extended X-ray a bsorption fine structure as well as atomistic computer simulation and studi es of the creep kinetics. Although no definitive mechanism has been establi shed, a logical explanation is that outsize ions segregate to more energeti cally favorable grain boundary sites, and improve creep resistance by block ing a few critical diffusive pathways. This mechanism is sufficiently gener al that it may be applicable to other ceramic systems. (C) 1999 Acta Metall urgica Inc. Published by Elsevier Science Ltd. All rights reserved.