¡NANOEUTECTICS!

Rods of the ternary eutectics Al2O3-Y3Al5O12-YSZ (20 mol% Y2O3-doped ZrO2), Al2O3-SmAlO3-SmSZ and Al2O3-GdAlO3-GdSZ were manufactured by directional solidification from the melt at high growth rates in an inert atmosphere using the laser-heated floating zone method. Under conditions of cooperative growth, the ternary eutectics presented a homogeneous and very fine microstructure, formed by bundles of single-crystal c-oriented Al2O3 and garnet or perovskite whiskers of ≈ 100 nm in width with smaller cubic zirconia whiskers between them (see figure). The thermo-elastic residual stresses of the Al2O3 phase were measured using the piezo-spectroscopic method indicating that the interfaces were free from amorphous phases and very strong. The nanofibrous microstructure results in outstanding mechanical strength values . In the case of the Al2O3-Y3Al5O12-YSZ nanoeutectic very fast cooling rates leaves the system in a metastable state where YAlO3 phase instead of garnet phase are obtained and the material is brittle.

             TEM image of the longitudinal                 

cross-section of a AYZ nanoeutectic.    

P. B. Oliete, J. I. Peña, A. Larrea, V. M. Orera, J. LLorca, J. Y Pastor, A. Martín, and J. Segurado, Adv. Mat. 19, 2313 (2007)