Assessment of stress relaxation experiments on diamond coatings analyzed by digital image correlation and micro-Raman spectroscopy

The analysis and control of residual stresses are important for understanding the fracture and delamination behavior of coatings and thin films. In this work, the stress relaxation in microcrystalline diamond coatings after focused ion beam (FIB) milling was assessed by micro-Raman spectroscopy and digital image correlation. Using the FIB, the so called H-Bar geometry was milled in the diamond coating. The cutting introduced a strain relief in the coating perpendicular to the longer sides of the bar. The relaxation strains were recorded from high resolution scanning electron microscopy images of the H-Bar before and after FIB cutting. Using finite element modeling of the milled geometry, the residual stress level in the coating is evaluated from the relaxation strains. Furthermore, μ-Raman spectroscopy was used to assess the biaxial residual stress level in the coating before and after FIB cutting. The μ-Raman signal inside the bar showed strong incidence for stress relaxation and confirmed to some extent the applicability of the FIB-DIC method.