Cu/Fe Nanolayered Composites for High Strength Applications
It is important to have a good understanding for the factors that play role in the mechanical properties of thin multilayered materials, like the resolved stresses in the layers and the nature and formation of interfaces.
The main focus of the work is to produce nanolayered Cu/Fe composites by both ARB and PVD and characterize their mechanical properties. For each production process, the size effect on the strength of the individual layer thickness will be investigated, and both production processes will be compared. For this purpose different imaging and testing methods - according to the production process - will be used.
The Cu/Fe system is very attractive, as it relies on inexpensive materials which can be easily processed by ARB due to their non-miscibility up to ~ 800 K and therefore such multilayers have incoherent interfaces. It was shown during the bachelor thesis of M. Schwab at the University of Erlangen-Nürnberg that both metals adhere well to each other and that ARB results in relatively homogenous layer thicknesses.
The Accumulative Roll Bonding (ARB) process is a severe plastic deformation process where two sheets are cleaned and wire brushed on one side and then roll-bonded at a 50% reduction and the process can be repeated many times. By joining two sheets, the ARB process is ideally suited for making laminate materials from different materials where the sequence of layers can be varied. Thus, sheet metal materials with tailored properties can be produced.
By repeating the process plastic deformation is accumulated in the material, which forms an ultrafine grain structure with grain sizes in the Nanometer range. This process creates extraordinary mechanical properties of the materials such as the increase in strength by two to three times compared to the starting material of conventional grain size.
By Thermal Evaporation Physical Vapor Deposition (PVD), a material is heated in a vacuum chamber until its surface atoms have sufficient energy to leave the surface and coat a substrate positioned above the evaporating material. For this work and in order to deposit the thin multilayered films of Cu and Fe we have updated our PVD device so it have two sources instead of one.
Testing methods that will be used include: Tensile testing, Nanoindentation, Strain-rate Testing, Micropillar Compression and Bulge Testing.
Imaging methods include: Optical Microscopy, different modes of Scanning Electron Microscopy (SEM, BSE, EBSD), and Atom Probe Tomography.