Hardness and elastic properties of Bi2O3-based glasses

The hardness and elastic properties of 20PbO · xBi₂O₃ · (80 – x)B₂O₃ glasses with x = 20–60 were evaluated through usual Vickers indentation and nanoindentation tests. The glass transition temperature (T _g = 295–421°C), Vickers hardness (H _v = 2.9–4.5 GPa), true hardness (H = 1.5–3.8 GPa) and Young's modulus (E = 24.4–72.6 GPa) decreased monotonously with increasing Bi₂O₃ content. This compositional trend demonstrates that the strength of Bi–O chemical bonds in these glasses is considerably weak compared with B–O bonds and plastic deformations under indentation loading occur easily. The elastic recovery after unloading was about 45% for the glasses with x = 20–50, and the Poisson's ratio was 0.27 for the glass with x = 20. The fracture toughness was evaluated to be 0.37–0.88 MPam^1/2 from the values of H _v and E, and it was proposed that not only weak Bi–O bonds but also boron coordination polyhedra (BO₃ or BO₄) and their arrangements affect on crack formation. From the temperature dependence of Vickers hardness up to the glass transition region, it was suggested that the glasses with high Bi₂O₃ contents belong to the category to fragile glass-forming liquids.