INFLUENCE OF YTTRIUM DOPING ON GRAIN MISORIENTATION IN ALUMINUM-OXIDE

Oversized dopant ions such as yttrium and lanthanum segregate to grain boundaries and reduce the tensile creep rate of alpha-Al2O3 by 2-3 or ders of magnitude. One explanation for this behavior is that the overs ized segregants give rise to a ''site-blocking'' effect for grain boun dary diffusion. It has also been speculated that the dopant ions modif y the grain boundary structure in alumina and reduce the creep rate by promoting the formation of special (e.g., coincidence site lattice (C SL)) grain boundaries. In order to test the latter hypothesis, we have used electron backscattered Kikuchi diffraction to characterize the m isorientation and special grain boundary distribution for undoped and 1000-ppm-yttrium-doped alumina. The results show that the grain bounda ry structure in alumina las characterized by the frequency of selected CSLs and misorientation distribution) was not significantly changed b y the addition of yttrium, indicating that creep retardation results m ainly from site-blocking.