Microstructures and mechanical properties of Mg/Zr nanostructured multilayers with coherent interface

Nanostructured Mg/Zr multilayer films were fabricated by depositing magnesium and zirconium alternately onto a single-crystal Si substrate using magnetron sputtering. The Mg and Zr layers had equal individual layer thickness (h) which was varied from 2.5 to 100 nm. Epitaxial growth and coherent layer interface were identified for the as-deposited multilayers at all h using X-ray diffraction and scanning transmission electron microscopy techniques. The multilayers with relatively large h were highly textured along the c-axis. Columnar grains were detected in the h = 2.5 nm multilayer, accompanied with variations in crystallographic orientation. These multilayers exhibited impressive strength with the maximum value of 1.4 GPa. The flow strength increased with decreasing h when h ≥ 10 nm while the opposite trend was observed when h < 10 nm. The strain rate sensitivity exponent was measured to be 0.021–0.037. A comparison to other nanostructured multilayers composed of hexagonal close-packed metals is presented to understand the role of interface coherency on mechanical behavior.