Three-dimensional Visualization of Scratch-Induced Subsurface Damage in TiSiN/TiN Multilayer Coating Using Focused Ion Beam-Scanning Electron Microscopic Tomography Technique

Abstract

It is a common practice to study crack patterns in brittle solids for strength analysis. Observations based on cracks visible on surfaces or randomly chosen cross‐sectional planes may be ambiguous and lead to an inaccurate interpretation of deformation behavior. In this study, three‐dimensional reconstruction obtained using a focused ion beam–scanning electron microscopic tomography technique was applied, for the first time, to observe the site‐specific deformation created by a scratching load on a TiSiN/TiN multilayer hard coating. This technique was demonstrated to be a powerful tool in providing detailed morphology of cracks that formed in coatings with complex structures, which would be difficult to obtain by conventional experimental methods. The cracks observed in the TiSiN/TiN multilayer coating are similar in morphology to cone cracks, which are commonly observed in homogeneous brittle solids; however, they are slightly different in this work due to the presence of sublayers in the coating with differing moduli. By locating the first crack visible on the scratched surface, in conjunction with scratch data obtained from the nanoindenter, the critical tensile stress for the formation of the cracks observed in this TiSiN/TiN multilayer coating was estimated to be ∼2.6 GPa.