Controlling strength and toughness of multilayer films: A new multiscalar approach

Multiscalar films are produced in order to combine both toughness and strength into a multilayer film. These structures incorporate both a strengthening phase and a toughening phase in a compositionally modulated microcomposite. The mechanical properties and microstructure for thick (∼50 μm) Mo/W multiscalar films have been characterized. A detailed microstructural analysis (including transmission electron microscopy, scanning electron microscopy, and x-ray techniques) of Mo/W multiscalar films has shown that large single-crystal columns of Mo interspersed with epitaxial layers of W extend for the entire film thickness. The microstructure is a zone-II-type microstructure, yet the temperatures during deposition are well below the lower limit (0.3 T/Tm) previously reported for such microstructures. Hardness and tensile tests have shown that a multiscalar approach is capable of tailoring a desired strength and toughness into a multilayered film.