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Nanostructured materials: nano-clusters, nano-foams, nano-pillars

Control of the grain-size dispersion is extremely important in the experimental design of nano-structured materials. A nano-structured material with a broad grain-size dispersion will exhibit a lower overall yield/flow stress than a material with the same average grain size but with a much smaller grain-size distribution. To control the defect content and microstructure in nano-structured metallic systems a relatively new approach was explored based on sputtering, i.e. using a so-called magnetron based nanocluster source. Interestingly, the clusters are grown in extreme non-equilibrium conditions, which allow obtaining metastable structures of metals and alloys.

Over the last couple of years a strong impetus has been given in our group to studies of nano-cluster/nano-structured thin metal layers. The appeal of these types of thin films stems from their novel magnetic and mechanical properties, which can be intrinsically different from their macrocrystalline counterparts. Nano-sized clusters are investigated with in-situ transmission electron microscopy and various scanning probe techniques. Lorentz microscopy and electron holography methodologies have been explored for the first time to characterize the magnetic structure of these clusters as a function of roughness.

Metal foams have recently become a popular topic of research interest in the materials science community although these materials have existed for over almost fifty years. The commercially available metal foams have random microstructures but here we like to manufacture nanofoams with topologies that lead to properties superior to their stochastic analogues. Selective electrolytic dissolution of the less noble element out of a binary alloy gives rise to a disordered nanoscale foam network. In particular nanoporous metals with high specific surface are suitable as surface-stress induced actuation and sensing applications.








JOURNAL OF MATERIALS RESEARCH Volume: 20 Issue: 7 Pages: 1785-1791 Published: JUL 2005
APPLIED PHYSICS LETTERS Volume: 83 Issue: 19 Pages: 3909-3911 Published: NOV 10 2003
APPLIED PHYSICS LETTERS Volume: 82 Issue: 2 Pages: 197-199 Published: JAN 13 2003
JOURNAL OF MATERIALS RESEARCH Volume: 20 Issue: 7 Pages: 1785-1791 Published: JUL 2005


nano_2We demonstrate that information about the morphological properties of the foams can be obtained from the computation of the Minkowski functionals for the 3DCT images. In this paper we outline the basic concepts of integral-geometry-based morphological image analysis. This approach yields an objective, numerical characterization of two- and three dimensional patterns in terms of geometrical and topological descriptors called Minkowski functionals. We review its mathematical foundation and show that it is easy to put the theory into practice by presenting simple computer algorithms to perform the analysis. Illustrative examples are given of applications of this approach to simple lattice structures, random point sets and minimal surfaces. As a more advanced application we show how the technique can be used to obtain a morphological characterization of computer tomography images of metal foams.

movie1 (Tensile test on aluminum foam - Adobe Flash movie) 

ACTA MATERIALIA Volume: 56 Issue: 3 Pages: 609-618 Published: FEB 2008