Microstructure and flow stress of nanoscale Cu/Nb multilayers

Nanoscale Cu/Nb multilayers with individual layer thicknesses of 2, 5, and 15nm were prepared by d.c. magnetron sputtering. The cross-sectionalmorphologies of the multilayers were examined under transmission electron microscopy (TEM) as well as high resolution TEM, whilst the flow stresses weremeasured with nanoindentation. A unique cross-sectional microstructure comprising well-modulated and mixed regions was observed, causing length-scale-independent flow stresses not found in existing studies, and shear bandswere absent upon plastic deformation. Built upon this unique microstructure, possible mechanisms underlying the high plastic stability and length-scale-independent flow stresses of Cu/Nbmultilayers were discussed in terms of amorphous-crystalline interface and its interaction with both mixed and well-modulated regions.

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