Phase Separation and Mechanical Properties in Si‐Poor Sodium‐Borosilicate Glasses

ABSTRACT

Phase separation is a well‐known approach to increase the damage tolerance of oxide glasses. Here, we report the separation of a silicon‐ and boron‐rich phase in a Si‐poor sodium‐borosilicate glass. This phase separation follows initially a strongly suppressed growth‐law, shows a droplet to needle morphology phase evolution, and exhibits a phase inversion. We discuss the phase separation and inversion in terms of structural mobility constraints and internal stresses. Once a needle‐dominated phase morphology is established, a marked increase of of the indentation fracture toughness and an enhanced crack resistance by more than a factor of 5 is observed.