Dresden 2020 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 60: Mechanical Properties: Plasticity, fracture, fatigue, wear - I

MM 60.5: Talk

Thursday, March 19, 2020, 16:45–17:00, IFW B

Size effect in bi-crystalline Cu micropillars with a coherent twin boundary — •Reza Hosseinabadi, Gerhard Dehm, and Christoph Kirchlechner — Max-Planck-Institut für Eisenforschung GmbH

It was recently shown by micropillar compression that the stress for ideal dislocation slip transmission through a Coherent Twin Boundary (CTB) is similar to the stress required for dislocation cross-slip. The difference in shear stress of a single and bi-crystalline micropillar (Δ*2%) can be as low as 7 MPa. A double-hump dislocation shape was proposed to explain the unexpectedly low difference, where an additional curvature of dislocations in bi-crystalline micropillars is necessary to form a perfect screw dislocation required for the cross-slip-like slip transmission.

Aim of this study is to study the size scaling of CTB containing micropillars to validate or revise the double-hump theory. We employ Focused Ion Beam (FIB) machining to mill more than 120 micron-sized single and bi-crystalline pillars with a single vertical Σ3(111) CTB. Subsequently, in situ microcompression experiments inside a scanning electron microscope (SEM) as well as post-mortem imaging using SEM were performed.

Bi-crystalline pillars follow the same size scaling laws as typically observed in micro-pillars, i.e. smaller are substantially stronger. Furthermore, Δ*2% tends to increase with reduced pillar diameters. This effect can be explained by the double-hump theory and will be quantitatively compared to model predictions.