Effect of B2O3 content on crack initiation under Vickers indentation test

概要

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Effect of B2O3 content on crack resistance was investigated by indentation tests of glass samples with various compositions of B2O3. The ternary SiO2–B2O3–Na2O glass system (SBN series) and non-alkaline aluminoborosilicate glass system (SAB series). When B2O3 is substituted with SiO2 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 B2O3 content (“SBN2” series), crack resistance decreased with increasing B2O3 content. On the other hand, crack resistance increased with increasing B2O3 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 B2O3 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.