Microstructural formation and evolution of near-eutectic Al2O3–ZrO2 powders prepared by a rapid cooling technique: An exploration on coupled eutectic growth range

Abstract

Regulation of eutectic compositions is a difficult challenge due to the limited formation range of this microstructure. Al2O3–ZrO2 powders were successfully prepared through a modified high-temperature melt-assisted air atomization technique. Micron-sized raw powders of α-Al2O3 and m-ZrO2 were used to regulate the temperature of system and the composition of final products. The high-temperature melt of 3500 K (3227 °C) was obtained based on the exothermic reaction between Al and O2, which was subsequently atomized and quenched to form composite powders. The phase composition and microstructure of the as-prepared powders were characterized by X-Ray diffraction and scanning electron microscopy. Eutectic colonies with nanolamellae (62–79 nm) were observed in the as-prepared Al2O3-(28–58 mol%) ZrO2 powders, with growth rates ranging from 1.9 to 2.8 mm s−1. Importantly, the powders with ZrO2 contents of 38 mol% and 42 mol% showed complete eutectic microstructures without primary dendrites, which indicated an extended coupled growth range deviating by ∼4.9 mol% from the eutectic composition (CE). The microstructural formation mechanism was discussed based on solidification behavior analysis. Furthermore, the evolution of the microstructure and phase in Al2O3-42 mol% ZrO2 powders was investigated. This work aims to develop a novel strategy for preparing oxide powders with eutectic structures and provide a reference for the composition regulation of eutectics.