Regensburg 2013 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 49: Topical Session: Fundamentals of Fracture - Novel Experimental Techniques I

MM 49.4: Talk

Thursday, March 14, 2013, 11:15–11:30, H4

Study on the fracture properties of NiAl single crystals by in-situ micro-cantilever bending experiments — •Johannes Ast, Karsten Durst, and Mathias Göken — Institute of General Material Properties (WW1) , Erlangen, Germany

In order to to study fracture mechanical properties on a small length scale and to understand the relation between micron-scale fracture toughness and the one of the bulk materials, in-situ and ex-situ micro-cantilever fracture tests were carried out on anisotropic NiAl single crystals. This material system offers two interesting fracture systems consisting of the soft <110> and the hard <100> orientation. The macroscopically determined fracture toughness for these two orientations is around 3-4 MPa√m and 8-9 MPa√m respectively. Beams of different sizes in the micron regime were prepared by Focused-Ion-Beam (FIB) machining. An AFM-based force measurement system mounted inside a Scanning Electron Microscope (SEM) was used for the in-situ experiments and a Nanoindenter XP was chosen for the ex-situ experiments. The experiments were evaluated by means of elastic-plastic fracture mechanics using the J-Integral and the crack tip opening displacement (CTOD). The discussion is focusing on the size of the plastic zone ahead of the crack tip where strong strain-gradients are formed and size effects in the flow stresses occur due to the small sample dimensions. TEM investigations and EBSD measurements of the fractured cantilevers provide detailed insights into the processes leading to fracture.