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Glasses and glass–ceramics from the BaO–TiO2–SiO2 systems have potential applications in piezoelectric and photonic devices. However, more studies on their crystallization and mechanical properties are needed to put the materials into service. In this work, seven grades of glasses with 30BaO–xTiO2–(70-x)SiO2 (mol%) were prepared. The crystallization behavior and mechanical properties were investigated. The 30BaO–20TiO2–50SiO2 glass composition, possessing a glass transition temperature of 759 °C and a crystallization onset temperature of 877 °C, shows a prominent surface nanocrystallization. Heat treatments at 800 °C for different durations result in various depths for the crystalline phase layer. Depths of about 1 µm and 200 µm were obtained by heat treatments for 3 h and 70 h, respectively. The nucleation rate is found to be around 1016 to 1018 m−3 s−1, which is comparable to that of the fresnoite stoichiometric composition (Ba2TiSi2O8). The hardness and Young's modulus of the crystalline layer are about 100% and 50%, respectively, higher than those of the parent glass. The fracture behavior of this layer is highly anisotropic, as a result of the crystallization texture. [ABSTRACT FROM AUTHOR]

The apparent relationship between Poisson's ratio and fracture energy has been used to guide the discovery of ductile glasses with a brittle-to-ductile (BTD) transition at Poisson's ratio around 0.32. Most organic and metallic glasses possess Poisson's ratio above 0.32, and thus, feature fracture energy that is around three orders of magnitude higher than that of oxide glasses, which feature Poisson's ratio typically below 0.30. However, whether the BTD transition can also be observed in oxide glasses remains unknown due to the lack of fracture energy measurements on oxide glasses with high Poisson's ratio. In this work, we measure the fracture energy of six oxide glasses with high Poisson's ratio between 0.30 and 0.34. We find no clear relationship between the two parameters even in those that possess the same Poisson's ratio as ductile metallic glasses. This suggests that Poisson's ratio is not the main property to enhance the fracture energy of oxide glasses. To this end, we instead find a positive relation between fracture energy and Young's modulus of oxide glasses, and even for some metallic glasses, which could explain their absence of ductility. [ABSTRACT FROM AUTHOR]

Due to an increasing demand for oxide glasses with a better mechanical performance, there is a need to improve our understanding of the composition‐structure‐mechanical property relations in these brittle materials. At present, some properties such as Young's modulus can to a large extent be predicted based on the chemical composition, while others—in particular fracture‐related properties—are typically optimized based on a trial‐and‐error approach. In this work, we study the mechanical properties of a series of 20 glasses in the quartenary Na2O–Al2O3–B2O3–SiO2 system with fixed soda content, thus accessing different structural domains. Ultrasonic echography is used to determine the elastic moduli and Poisson's ratio, while Vickers indentation is used to determine hardness. Furthermore, the single‐edge precracked beam method is used to estimate the fracture toughness (KIc) for some compositions of interest. The compositional evolutions of Vickers hardness and Young's modulus are in good agreement with those predicted from models based on bond constraint density and strength. Although there is a larger deviation, the overall compositional trend in KIc can also be predicted by a model based on the strength of the bonds assumed to be involved in the fracture process. [ABSTRACT FROM AUTHOR]

• We show the environment dependence of K Ic for seven different glasses. • Brittle-to-ductile transition temperature is around T g. • Viscoplasticity zone is for the first time observed in experiment. • SEPB, both precracking and fracturing should be performed in inert environment. • Post-fractography in SEPB can be used to analyze the indentation cracking pattern. The role of temperature (T) and moisture on fracture toughness (K Ic) of glasses, as measured by the single-edge precracked beam method (SEPB), is investigated. The brittle to ductile temperature, shown by an increase of K Ic , is ~ T g. At T below 0.9 T g , the decrease of the bond strength with T results in the decrease of both the fracture surface energy and Young's modulus, so that K Ic decreases with T. From above T g to below 1.1 T g , the work of fracture increases because of dissipative processes, including confined viscoplasticity and blunting at the crack front. From 1.1 T g , viscous flow extends to the whole specimen and becomes more uniform, resulting in the macroscopic deformation of the specimen, eventually preventing against fracture. The results on humidity sensitive glasses show that both precracking and final fracture steps need to be performed in inert environment to meet the intrinsic K Ic value, unless the test is fast enough. [ABSTRACT FROM AUTHOR]

Poisson's ratio (ν) defines a material's propensity to laterally expand upon compression, or laterally shrink upon tension for non-auxetic materials. This fundamental metric has traditionally, in some fields, been assumed to be a material-independent constant, but it is clear that it varies with composition across glasses, ceramics, metals, and polymers. The intrinsically elastic metric has also been suggested to control a range of properties, even beyond the linear-elastic regime. Notably, metallic glasses show a striking brittle-to-ductile (BTD) transition for ν-values above ~0.32. The BTD transition has also been suggested to be valid for oxide glasses, but, unfortunately, direct prediction of Poisson's ratio from chemical composition remains challenging. With the long-term goal to discover such high-ν oxide glasses, we here revisit whether previously proposed relationships between Poisson's ratio and liquid fragility (m) and atomic packing density (Cg) hold for oxide glasses, since this would enable m and Cg to be used as surrogates for ν. To do so, we have performed an extensive literature review and synthesized new oxide glasses within the zinc borate and aluminoborate families that are found to exhibit high Poisson's ratio values up to ~0.34. We are not able to unequivocally confirm the universality of the Novikov-Sokolov correlation between ν and m and that between ν and Cg for oxide glass-formers, nor for the organic, ionic, chalcogenide, halogenide, or metallic glasses. Despite significant scatter, we do, however, observe an overall increase in ν with increasing m and Cg, but it is clear that additional structural details besides m or Cg are needed to predict and understand the composition dependence of Poisson's ratio. Finally, we also infer from literature data that, in addition to high ν, high Young's modulus is also needed to obtain glasses with high fracture toughness. [ABSTRACT FROM AUTHOR]

The effect of spherulitic crystallization on the elastic moduli and fracture toughness of a barium aluminum silicate glass was investigated. The crystallization process results in Ba 2 Si 3 O 8 phase and is initiated from Ba rich nuclei. Nucleation is optimal in the 690-720 °C interval. Young's modulus is increased by 12.5% when the glass-ceramic conversion is nearly complete. Nevertheless, as the size and the volume fraction of crystals are increased, some microcracking shows up upon cooling from the crystallization temperature. An optimal improvement of the fracture toughness (SEPB method) by 27 % is observed for a 49 % volume fraction of 5 to 10 μm large spherulites. [ABSTRACT FROM AUTHOR]