Residual stress versus microstructural effects on the strength and toughness of phase-separated PbO-B2O3-Al2O3 glasses

A few authors have reasonably proposed that liquid-liquid phase-separated (LLPS) glasses could show improved fracture strength, S-f, and toughness, K-Ic, as the second phase could provide a barrier to crack propagation via deflection, bowing, trapping, or bridging. Due to the associated tensile or compressive residual stresses, the second phase could also act as a toughening or a weakening mechanism. In this work, we investigated five glasses of the PbO-B2O3-Al2O3 system spanning across the miscibility gap: Four of them undergo LLPS-three are binodal (two B2O3-rich and one PbO-rich) and one is spinodal-and one does not show LLPS (composition outside the miscibility gap). Their compositions were designed in such a way that the amorphous particles are under compressive residual stresses in some and under tensile residual stresses in others. The following mechanical properties were determined: the Vickers hardness, ball on three balls (B3B) strength, and toughness, KIc-SEVNB (single-edge V-notch beam [SEVNB]). The microstructures and compositions were analyzed using scanning electron microscopy with energy-dispersive X-ray spectrometry. The spinodal glass showed, by far, the best mechanical properties. Its KIc-SEVNB = 1.6 +/- 0.1 MPa m(1/2), which embodies an increase of almost 50% over the B2O3-rich binodal composition, and 90% considering the PbO-rich binodal composition. Moreover, its fracture strength, S-f = 166 +/- 7 MPa, is one of the highest ones ever reported for an LLPS glass. Fracture analyses evidenced that the spinodal composition exhibited the lowest net stress at the fracture point. Moreover, calculations indicate that the internal residual stress level is the lowest in the spinodal glass. The overall results indicate that the microstructural effect of the spinodal glass is the most significant factor for its superior mechanical properties. This work corroborates the idea that LLPS provides a feasible and stimulating solution to improve the mechanical properties of glasses.

Automated summary

In this study, the mechanical properties of different glass samples were investigated, and it was found that the spinodal glass exhibited the best performance, with a 50% increase in K-Ic and a 90% increase in S-f compared to other samples. The microstructural effect of the spinodal glass was identified as the most significant factor for its superior mechanical properties.