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0977-FF07-06-EE07-06

Microstructure and Mechanical Strength Evolution With Scale Refinement in Metallic Multilayers Marc M Verdier1, Muriel VERON1, and Florence ROBAUT2 1 LTPCM INPG, CNRS, Domaine Univ., BP75, F-38402 Cedex, St Martin d'Heres, France, Metropolitan 2 CMTC-INPG, St Martin d'Heres, France, Metropolitan Various processing routes are used to obtain submicronic grains in structural materials and also the integration effort of thin film technology for interconnects in semiconductor industry constitute. Metallic composite in layered structures are therefore model geometries to study the role of scale and interface in the mechanical strength of composites. For dislocation mediated plasticity, current modellings interpret the important increase of strength from a Hall-Petch like behaviour to single dislocation glide controlled by interfacial strength and reactions. In this work, we will review and compare experimental observations obtained with two different processing routes to achieve scale refinement, namely thin film depositions techniques (PVD) and intense plastic co-deformation by cold rolling stacks of thick layers. In the first part we characterize the small strain plasticity of films and multilayers. In recent analysis on tensile tests of Cu/Ag films [1,2], we show that an important initial stress increase with strain takes place and therefore conventional yield limit can not be applied to fine structure materials. A scale dependant latent hardening term can be introduced. The same conclusions can also be applied to stress–temperature experiments used for polycrystalline thin films [1]. In a second part, intense plastic cold rolling of layers is used to process multilayers over a larger range of internal scale [3]. Although the individual layer thickness is less well controlled than in PVD processed films, some relevant observations can be drawn. In particular, a distinct evolution of the crystallographic texture from the bulk is noticed on several systems we studied. The deformation mechanisms involving interface mechanics and layer confinement lead to some specific crystallographic texture reinforcement. To provide experimental data for future modelling, we present some recent local texture characterizations obtained on Pt layers in the Fe/Pt system, using EBSP in scanning microscopy and a novel orientation mapping technique in TEM [4].

Fe/Pt stack cold rolled, (Pt white,Fe black) 4th reduction stage

Pt layers microtexture (Fe layers:black) 3rd reduction stage

REFERENCES 1. G.Saada, M.Verdier, G.Dirras, submitted to Phil Mag (2006) 2. M.Verdier, H.Huang, F.Spaepen, J.D.Embury, H. Kung, Phil.Mag. 86, 5009 (2006) 3. M.Verdier,M.Veron,F.Bley,F.Ingwiller,N.Dempsey,D.Givord, Phil.Mag 85,3157 (2005) 4. E.Rauch , ACOM/TEM: an Automated Crystal Orientaton Mapping