Fine-grained 3Y-TZP was known to show high superplasticity. Addition of a small amount of metal oxide influenced the superplastic behavior in 3Y-TZP. Here, 3Y-TZP doped with 1mol% of GeO2, TiO2 or BaO were fabricated, and respective grain boundary energy was systematically measured by a thermal grooving technique with atomic force microscopy. It was found that addition of Ge4+ or Ti4+ ions decreased the grain boundary energy to stabilize the grain boundaries in TZP whereas doping of Ba2+ ion increased the grain boundary energy to destabilize the grain boundaries. A change in the grain boundary energy should be due to segregation of dopant at grain boundaries. It was also found that the elongation to failure of cation-doped 3Y-TZP was directly proportional to the stability of grain boundary. Grain boundary energy was thus one of the principal factors to determine the tensile ductility of TZP. In order to reveal the effect of dopant on the grain boundary energy, lattice static calculations and first principles molecular orbital calculations were performed for super-cells and model clusters including the present dopant, respectively. A series of results showed that substitution of Ge4+ or Ti4+ ion for Zr4+ ion increased the covalency of TZP, but the covalency of TZP was reduced by addition of Ba2+ ions. The grain boundary energy was found to have a relationship with covalency nearby grain boundaries in TZP.

Grain Boundary Energy and Tensile Ductility in Superplastic Cation-doped TZP. A.Kuwabara, S.Yokota, Y.Ikuhara, T.Sakuma: Materials Transactions, 2004, 45[7], 2144-9