TY - JOUR

T1 - Evolution of stress fields during crack growth and arrest in a brittle-ductile CrN-Cr clamped-cantilever analysed by X-ray nanodiffraction and modelling

AU - Meindlhumer, Michael

AU - Brandt, L.R.

AU - Zalesak, Jakub

AU - Rosenthal, M.

AU - Hruby, Hynek

AU - Kopecek, J.

AU - Salvati, E.

AU - Mitterer, Christian

AU - Daniel, Rostislav

AU - Todt, Juraj

AU - Keckes, Jozef

AU - Korsunsky, Alexander M.

PY - 2020/11/28

Y1 - 2020/11/28

N2 - 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 μm 3 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.

AB - 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 μm 3 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.

UR - http://www.scopus.com/inward/record.url?scp=85097236081&partnerID=8YFLogxK

U2 - 10.1016/j.matdes.2020.109365

DO - 10.1016/j.matdes.2020.109365

M3 - Article

VL - 2021

JO - Materials and Design

JF - Materials and Design

SN - 0264-1275

IS - 198

M1 - 109365

ER -