Modulation-dependent deformation behavior and strengthening response in nanostructured Ti/Zr multilayers

Nanostructured Ti/Zr multilayers, with different layer thicknesses h and modulation ratios ŋ (ratio of the thickness between Zr and Ti layers), were deposited on Si (1 0 0) substrate by using magnetron sputtering. Transmission electron microscopy observations suggested that the heterophase interfaces kept semi-coherent or coherent in all the multilayers. Hardness of the Ti/Zr multilayers was evaluated by nanoindentation experiments. In contrast with the general trend of “smaller is stronger”, the hardness of present Ti/Zr multilayers with equal layer thickness increased as increasing the layer thickness h, which can be explained by the IBS model extended to large h. For the Ti/Zr multilayers with a constant bilayer thickness but various ŋ, the hardness displayed a maximum as increasing ŋ, which should be related to the deformation heterogeneity in Ti/Zr multilayers with non-uniform layer thickness. Furthermore, the high strength achieved in the Ti/Zr multilayers superior to the constituent layers was discussed.