Metastable Phase Formation in Rapidly Solidified ZrO_2-Al_2O_3 Powders

摘要

Rapidly solidified powders of ZrO_2/20Al_2O_3 and ZrO_2/57Al_2O_3 (eutectic) were prepared by melting fine-particle aggregates in a high enthalpy plasma flame and then rapidly quenching the molten particles in cold water or on a copper chill plate. To ensure complete melting and homogenization of all the particles prior to quenching, the water-quenching treatment was often repeated two or even three times. The resulting melt-quenched powders and splats displayed a variety of metastablc structures. The ZrO_2-rich composition formed an extended solid solution phase, whereas the eutectic composition formed a nano-fibrous or amorphous structure. Upon heat treatment, both compositions developed nanocomposite structures, comprising a uniform mixture of t-ZrO_2 + α-Al_2O_3 phases.