Dresden 2009 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 17: Mechanical Properties III

MM 17.1: Talk

Tuesday, March 24, 2009, 10:15–10:30, IFW D

Change of deformation mechanism in nanocrystalline nickel at very low temperatures — •Lutz Hollang, Suhash Ranjan Dey, and Werner Skrotzki — Institut für Strukturphysik, Technische Universität Dresden, 01062 Dresden

Pure nanocrystalline nickel was produced by pulsed electro-deposition without additives for grain refinement. The average grain size of the material is d(EBSD) = 150 nm and d(XRD) = 25 nm if determined by electron backscatter diffraction (EBSD) and X-ray diffraction (XRD), respectively. Tensile tests with constant deformation rate were performed at temperatures between 4 K and 320 K. The stress-strain curves are parabolic with the ultimate stress strongly decreasing with increasing temperature. Stress relaxation experiments reveal that dislocation interaction governs the plastic behaviour of the material at low temperatures. However, if the stress reaches the threshold of 2400 MPa, as it is the case between 4 K and 9 K, the deformation mode suddenly changes towards `catastrophic` shear. The shear events are characterized by substantial stress drops accompanied by acoustic emission. The nature of the shear events will be discussed on the basis of microstructural investigations performed by electron microscopy.