Combining high strength and ductility is an old-known, but still unsolved problem of materials science. Nanolamellar structures consisting of alternating amorphous and crystalline layers contain a large amount of interfaces at which the shear-transformation-zone-based deformation in metallic glasses and the dislocation-based deformation of crystalline alloys can be combined. The nanometer-scaled structure might result in high strength of such materials, whereas the interfaces may impede catastrophic failure and provide some ductility.
In this work, electrodeposition was used to prepare such multilayer structures with a lamella thickness ranging from several hundred down to a few nanometers in the Fe-P system. The structures were investigated using x-ray diffraction, scanning electron microscopy as well as transmission electron microscopy. Indentation experiments were used to investigate the mechanical properties. Microhardness was found to depend on the lamella thickness according to the Hall-Petch equation as long as the lamellae were thicker than 15 nm. For finer structures a hardness plateau was observed. Nanoindentation, which was performed in different loading directions with respect to the lamella orientation, confirmed these results qualitatively. To obtain further information about the deformation behavior of these materials, bending beams with a size in the micrometer regime were produced using focused ion beam technique and in-situ micro-bending tests were performed in a scanning electron microscope.