• Hruby, Hynek
• Rosenthal, M.
• Mitterer, Christian
• Korsunsky, Alexander M.
• Zalesak, Jakub
• Salvati, E.
• Kopecek, J.
• Brandt, L. R.
• Meindlhumer, Michael
• Daniel, Rostislav
• Keckes, Jozef
• Todt, Juraj

Abstract

<p>In order to understand the fracture resistance of nanocrystalline thin films, it is necessary to assess nanoscopic multiaxial stress fields accompanying crack growth during irreversible deformation. Here, a clamped cantilever with dimensions of 200 × 23.7 × 40 μm³ was machined by focused ion beam milling from a thin film composed of four alternating CrN and Cr layers. The cantilever was loaded to 460 mN in two steps and multiaxial strain distributions were determined by in situ cross-sectional X-ray nanodiffraction. Characterization in as-deposited state revealed the depth variation of fibre texture and residual stress across the layers. The in situ experiment indicated a strong influence of the residual stresses on the cross-sectional stress fields evolution and crack arrest capability at the CrN-Cr interface. In detail, an effective negative stress intensity of −5.9 ± 0.4 MPa m^½ arose as a consequence of the residual stress state. Crack growth in the notched Cr layer occurred at a critical stress intensity of 2.8 ± 0.5 MPa m^½. The results were complemented by two-dimensional numerical simulation to gain further insight into the elastic-plastic deformation evolution. The quantitative experimental and modelling results elucidate the stepwise nature of fracture advancement across the alternating brittle and ductile layers and their interfaces.</p>

Topics

• impedance spectroscopy
• polymer
• experiment
• thin film
• simulation
• grinding
• crack
• milling
• focused ion beam
• texture
• two-dimensional