Evolution of the crack initiation resistance and hardness of low silica aluminate glasses with varying the Al2O3/CaO ratio

The hardness ( H v ) and crack initiation resistance ( C R ) of oxide glasses are crucial properties for various applications, such as in vehicles, display devices, and buildings. However, these properties are still limited for many special applications. Here, we studied the evolution of the H v and C R with varying the ratio R = [Al 2 O 3 ]/[CaO] in the low silica (0 and 17 mol% SiO 2 ) aluminate glasses, i.e., so called silico-aluminate glasses, and thereby identified a composition that exhibits the highest C R and H v . The results showed that the H v decreased with increasing R within the peraluminous region. Furthermore, a significant increase in C R value with increasing R was detected in the range of R = 1.0–1.18. In contrast, the glass series containing 50 mol % SiO 2 content exhibited only a slight increase in C R value, but pronounced increases in both T g and H v with increasing R in the peraluminous region. The Raman spectroscopy revealed that [5]Al and oxygen tri-cluster ([3]O) are the controlling factors for C R and H v of the studied glasses. Moreover, the impact of [3]O and [5]Al on H v and C R is highly dependent on the SiO 2 content in the studied glasses.