Effect of Pt deposition on digital image correlation analysis for residual stress measurement using FIB-DIC ringcore method

FIB-DIC ringcore milling is an attractive semi-destructive method of measuring microscopic residual stress. Ensuring the accuracy and reliability of DIC analysis of sample surface deformation is critical for correct stress quantification, and relies on achieving reliable correlation between tracking sub-windows in the initial and deformed configurations. One way to improve the correlation is by increasing the image contrast using in-chamber deposition of an array of platinum nano-dots in a specific pattern. We carried out a study of the effect of Pt deposition on the accuracy of DIC analysis by comparing the results from the analysis of an un-patterned surface, and that of a Pt-patterned ring-core milling sequence. The results show that the Pt-patterned ring-core leads to a higher quality DIC analysis compared with the non-patterned case. This is demonstrated by the small relative displacement of markers, small marker 'cleaning' ratio, and a narrow distribution and high value of the correlation coefficient. Insufficient surface contrast is therefore identified as the main reason for aberrations and errors in DIC analysis: Pt pattern deposition can be used to ensure improved quality and reliability of DIC analysis. Hence, the utilization of Pt patterning is advised for FIB-DIC ring-core method, particularly for samples with smooth surface.