Tuning Hardness of ZrO ₂ –SiO ₂ Glass‐Ceramics Through Densification

ABSTRACT Compared with homogeneous glasses, glass‐ceramics with heterogeneous microstructures enable multiscale architecture control to optimize their performance. In this work, we attempt to regulate the mechanical properties of ZrO 2 –SiO 2 glass‐ceramics through hot compression‐induced densification. The refractory glass‐ceramic is first synthesized through aerodynamic levitation (containerless) melting, with the inherent immiscibility between zirconia and silica yielding a heterogeneous microstructure upon quenching, comprising a continuous silica‐rich glass matrix embedded with discrete ZrO 2 crystalline phases. Upon subsequent hot compression, the overall microstructure is largely retained, but hardness displays a non‐monotonic dependence on pressure, that is, decreasing at an intermediate pressure (1 GPa) and increasing at a higher pressure (2 GPa). This behavior contrasts with the monotonic hardness increase typically observed in pressure‐treated oxide glasses. We attribute this distinct hardness–densification relationship to pressure‐dependent interfacial binding between the glass and crystalline phases. This involves a volume contraction of the ZrO 2 phase due to the monoclinic‐to‐tetragonal phase transition and densification of the glass matrix phase, collectively determining the interfacial binding strength and thus hardness. Overall, this work demonstrates an alternative approach for tailoring the mechanical properties of glass‐ceramics beyond conventional approaches that focus on modifying crystal phase morphology, size, or composition.