Immiscibility, nucleation and mechanical properties in the lithia-baria-silica system

The current work investigates the effects of nucleation heat treatments, on the microstructure and mechanical properties of a novel silicate glass in Li2O-BaO-SiO2 system with 1 mol% P2O5 as nucleating agent. As-cast glass was exposed to nucleation heat treatments at 490-550 degrees C for 1-3 h. The microstructural examination was performed by SEM/EDS. The highest Vickers microhardness was determined to be 650 Hv for the sample heat treated at 550 degrees C for 1 h. The increase in the nucleation time also affected Vickers microhardness and the highest one was determined to be 600 Hv after nucleation for 3 h. The fracture toughness, K-IC reached 2.51 MPa.m(1/2) after nucleation at 550 degrees C for 1 h. The nucleation temperatures had a more pronounced effect on the fracture toughnesses in comparison to nucleation times. The indentation toughness data was used to determine Weibull parameters from Ln ln [1/(1-P)]-lnK(IC) plots. Weibull modulus, m of the samples nucleated at 500, 510, 530, 550 degrees C for 1h. and 540 degrees C for 2 h. were determined similarly to be 3.8, 3.5, 4.7 and 3.9, respectively. The rest of the samples indicated higher Weibull moduli, which may be attributed to the formations of microcracks due to the mismatch in between newly formed crystals and remaining glassy matrix.