Microstructure of rapidly‐quenched ZrO 2 ‐SiO 2 glass‐ceramics fabricated by container‐less aerodynamic levitation technology

Abstract In this work, an aerodynamic levitation technology (ALT) was utilized to prepare ZrO 2 ‐SiO 2 glass‐ceramics with two different ZrO 2 contents, that is, 35 mol% and 50 mol%. The glass‐ceramics were partially melted at ∼2000°C or fully melted at ∼3000°C by ALT, followed by rapid quenching to obtain spherical glass‐ceramic beads. The phase compositions and microstructures of the glass‐ceramics were characterized. Crystallization of ZrO 2 occurred during the solidification process and ZrO 2 content, processing temperature, and the addition of yttrium (3 mol%) affected the crystalline phase of ZrO 2 . No ZrSiO 4 or crystalline SiO 2 were formed during the solidification process and the glass‐ceramics were away from thermodynamic equilibrium due to rapid quenching. The glass‐ceramics showed a microstructure of irregular‐shaped ZrO 2 micro‐aggregates embedded in an amorphous SiO 2 matrix, with lamellar twins and lattice defects formed within ZrO 2 crystals. For samples prepared at ∼3000°C, a liquid‐liquid phase separation occurred in the melt, which eventually resulted in the formation of large and irregular‐shaped ZrO 2 aggregates. In comparison, for samples prepared at ∼2000°C, pre‐existed ZrO 2 crystals formed during heating acted as nucleation sites during the cooling process, followed by grain growth to form large ZrO 2 aggregates. Solidification and microstructure formation mechanisms were proposed to elucidate the solidification process during rapid cooling and the microstructure of the glass‐ceramics obtained.