Evaluation of subsurface damage layer of BK7 glass via cross-sectional surface nanoindentation

Subsurface damage (SSD) introduced from abrasive machining significantly degrades the reliability and lifetime of glass ceramics. In this work, nanoindentation tests were performed on the cross section near the lapped surface to determine the nanomechanical properties of subsurface layer of a lapped BK7. Remarkable differences were found between SSD layer and its bulk counterpart in terms of load-displacement characteristics and nanomechanical response. The nanomechanical parameters (hardness and elastic modulus) of subsurface layer follow an exponential descending trend with the shortening of distance from lapped surface, which is consistent with the increase of crack density. The ratio of hardness to elastic modulus decreases exponentially with increasing subsurface depth until it reaches bulk material, which suggests that SSD layer has lower plasticity. Furthermore, the crack distribution becomes a critical parameter for characterizing the hardness gradient in SSD layer.