Synergies between simulations and experiments in nanocrystalline metals

Helena Van Swygenhoven 

ASQ division- Materials and Reasearch, Paul Scherrer Institute (ASQ-PSI), PSI-Villigen, Villigen 5232, Switzerland

Abstract

Atomistic simulations have provided unprecedented insight into the structural and mechanical properties of nanocrystalline materials, highlighting the role of the non-equilibrium grain boundary structure in both inter- and intra-grain deformation processes. One of the most important results is the capability of the nanosized grain boundary to act as source and sink for dislocations, in other words a deformation mechanism that does not leave behind dislocation debris. The dislocation activity suggested by molecular dynamics for four different nc-fcc metals, Al, Cu, Ni and Au are discussed in terms of the inherent restrictions and caveats of the simulation technique and in terms of material properties such as the generalized stacking fault energy curves. Details about the nucleation and propagation mechanism and their relation to grain boundary structures and grain boundary misorientations will be presented.
Simulations should however be taken as a guidance for experiments and therefore have to be validated. In the second part of this talk, several experimental investigations will be presented that are designed to validate the results of the simulations, such as stress relaxation testing at different temperatures and a new type of in-situ X-ray diffraction experiment recently developed at the Swiss Light Source. This in-situ experiment allows following in a time-resolved way the peak shift and the peak broadening during deformation. Measurements show that for electrodeposited Ni with a mean grain size of 30nm, peak broadening is reversible upon unloading, demonstrating the absence of remaining dislocation debris. However in ultra-fine grained Ni synthesized by High Pressure Torsion the peak broadening is irreversible, similar to what is observed for coarse grained metals and is to be expected when a dislocation network is built up during deformation.

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Presentation: invited oral at E-MRS Fall Meeting 2005, Symposium I, by Helena Van Swygenhoven
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-04-27 13:26
Revised:   2009-06-07 00:44
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