Effect of B2O3 content on crack initiation under Vickers indentation test

Abstract

Effect of B 2 O 3 content on crack resistance was investigated by indentation tests of glass samples with various compositions of B 2 O 3 . The ternary SiO 2 B 2 O 3 Na 2 O glass system (SBN series) and non-alkaline aluminoborosilicate glass system (SAB series). When B 2 O 3 is substituted with SiO 2 in the SBN system ("SBN1" series), crack resistance has a relationship with density. In a series of the SBN system where density did not change with B 2 O 3 content ("SBN2" series), crack resistance decreased with increasing B 2 O 3 content. On the other hand, crack resistance increased with increasing B 2 O 3 content in the SAB series, where density did not change. According to the results of NMR measurement, boron in 4-cordination state ([4] B) increased in the SBN2 series while boron in 3-cordination state ([3] B) increased in the SAB series with increasing B 2 O 3 content. Therefore, crack resistance increases with increasing [3] B and decreases with increasing[4] B. The difference in structure between [3] B and [4] B containing glasses leads to different effect on residual stress around the indentation, resulting in difference in crack resistance.

Influence of Cooling Rate on Cracking and Plastic Deformation during Impact and Indentation of Borosilicate Glasses

“…However, neither E, H, and m seem to change for different cooling rates. The amount of energy dissipated by densification reduces the amount of shear taking place, which reduces the probability for cracking as a smaller amount of residual stresses is introduced and maintained in the deformed volume (Kato et al, 2010;Gross, 2012;Sellappan et al, 2013;Bruns et al, 2017). This correlation is observed for impact and quasi-static indentation testing, both showing a larger threshold load for the activation of cracks for samples that were quenched than for annealed ones.…”

Vickers Indentation Cracking of Ion-Exchanged Glasses: Quasi-Static vs. Dynamic Contact

“…Both the normal and damage-resistant glasses exhibit normal free volume and density dependence on fictive temperature (Bruckner, 1970), so the higher fictive temperature state has higher free volume and lower density. The damage-resistant glass also has approximately 7 mol% B2O3 and when added to a glass with R2O approximately equal to Al2O3, the boron exists primarily in a trigonal coordination state (Kato et al, 2010;Gross, 2017). The incorporation of trigonal units into the glass structure reduces the average coordination number of glass-forming cations and the increased ease of rearrangement of the connected, low-NBO glass network allows greater ease of densification under a sharp contact.…”

“…When comparing a glass with many NBOs like soda-lime to a glass with few NBOs like silica, the glass with few NBOs has more free volume and this contributes greatly to its ability to densify. However, since some degree of shear aids in the densification process, the substitution of a low coordination number glass former like trigonal boron oxide in the place of tetrahedral silica has been shown to increase the crack resistance (Kato et al, 2010) despite increasing the packing density (Gross, 2017). For a glass with limited NBOs, reducing the average number of constraints on the network forming cations apparently aids in the densification process even as free volume is reduced (Gross, 2017).…”

Load dependence of densification in glass during Vickers indentation test

“…Therefore, it is thought that the contribution of densification of glasses with a low threshold pressure does not decrease significantly with increasing load. Our previous study 19) showed that RID increases with increasing amount of 3-coordinated boron and that almost all the boron in Glass C is 3-coordinated boron. The 3-coordinated boron in Glass C may be the origin of its low threshold pressure and the small slope of its load dependence of densification.…”