Effects of Yttrium Doping α‐Alumina: I, Microstructure and Microchemistry

The influence of yttrium doping on the microstructure and microchemistry of hot‐pressed α‐alumina was investigated using a combination of electron microscopy techniques. The implications of microstructure and microchemistry on the improved creep behavior of the doped material are discussed. The samples doped only with yttrium had a bimodal grain‐size distribution that was strongly correlated to the frequency and distribution of Y 3 Al 5 O 12 (YAG) precipitates in the microstructure. Yttrium segregated to most of the grain boundaries, with a normal excess concentration of Gamma= 3.3 ± 0.9 atoms/nm 2 at random boundaries. Two types of twin boundaries (Sigma3 and Sigma7) accommodated no yttrium. None of the boundaries or triple‐point junctions contained a glassy grain‐boundary phase. Strong interaction of the grain boundaries and dislocations with YAG precipitates indicated a pinning mechanism by the precipitates. Yttrium doping did not appear to favor formation of special boundaries in α‐alumina.