Evaluation of surface integrity for ultra-precision machined fused silica surface based on atomic point-defect density

The degree of plasticity and brittleness (DPB) of the material significantly affects the service performance of fused silica manufacturing surfaces in many frontier fields. However, there is still no effective method to quantitatively and non-destructively characterize their DPB, severely restricting the application of fused silica. Herein, atomic manufacturing-induced point defects on fused silica manufacturing surfaces were determined. Based on this, the evolution laws of various types of point defects with the DPB were discussed. Interestingly, it was found that the DPB is closely related to the densities of specific ODCII point defects, whose proportion (k) was chosen as the characteristic parameter to judge surface brittle fractures. Additionally, it was discovered that k sharply increased at the material brittle-plastic transition boundary, which was also verified based on the molecular dynamics simulation. Accordingly, whether k is >15 % was proposed as a criterion to judge whether the material has undergone brittle fractures during manufacturing processes. Furthermore, the significant increment of ODCII point defects was found to be the main cause of the obvious increment of k. Moreover, two causes of the significant increment of ODCII point defects were determined. Finally, the effectiveness of the judge criterion in six specific manufacturing cases was verified. Summarily, the study proposes a powerful nondestructive approach to judge the brittle fractures. It could quantitatively and non-destructively characterize the DPB during manufacturing processes. It is also applicable to the quantitative DPB characterization and the early warning detection of fracture breakdown for other brittle silicate materials.