Non-stoichiometry and defect structures in rapidly solidified MgO–Al 2O 3–ZrO 2 ternary eutectics

Abstract

Rapid solidification of the two MgO–Al 2O 3–ZrO 2 ternary eutectics was accomplished by inductive heating followed by quenching with a twin roller device. The as-quenched materials exhibited diverse compositional and structural phase assemblages. A metastable binary eutectic between a spinel and zirconia phase was found in the Al 2O 3-rich eutectic composition and had the same composition of the Al 2O 3-rich ternary eutectic. Heat treatment of the samples yielded nucleation of γ-Al 2O 3 and then tetragonal zirconia (t-ZrO 2) at high temperatures as magnesium and oxygen ions diffused from the zirconia phase to the spinel phase. For the as-quenched MgO-rich eutectic, a spinel with nearly the stoichiometric composition formed with cubic-ZrO 2 and MgO. Close to the maximum amount of MgO was dissolved in the spinel and zirconia phases. Heat treatment resulted in diffusion of magnesium and oxygen ions out of the ZrO 2 phase and promoted the formation of tetragonal and monoclinic ZrO 2.