In situ microscopy of crack healing in borosilicate glass

In situ environmental scanning electron microscopy studies of semi-macro indent cracks in borosilicate glass indicate that crack healing occurred at humidities as low as 8% relative humidity and at temperatures as low as about 400 degree C. The crack morphology changes observed in situ include slow crack regression (at low temperatures) and multiple crack pinch-off (at higher temperatures). Subsurface crack morphology changes were observed using conventional scanning electron microscopy of the fractured healed specimens. Subsurface healing included pinch-off into voids which appear quasi-circular in cross-section. In addition, crack debris were observed to hinder the crack healing process, which has important implications for fatigue of ceramic materials, where debris generation is frequently reported in the literature.