MECHANICAL-PROPERTIES OF TOUGH MULTISCALAR MICROLAMINATES

Strength and toughness were produced concurrently and optimized in two Mo/W multilayers by using a multi-scale approach which intersperses a tough phase, thick (approximate to 1 or approximate to 5 mu m) layers of one component (Mo), with a strong phase, 29 layer stacks of Mo/W ( layer thickness = 4.0 nm). Specimens were sputtered onto 76 mm dia Si wafers, and had overall thicknesses of approximate to 51 and approxima te to 31 mu m, respectively. Microstructure and fracture were examined using SEM. Uniaxial tensile and hardness testing were performed to me asure strength and toughness; both increased with tough phase thicknes s. Several models were used to estimate K-lC and fracture strength. Up per bound models showed approximate to 2- and approximate to 6-fold in creases in K-lC and fracture strength, respectively, when tough phase thickness was increased from 1 to 5 mu m, while hardness decreased fro m approximate to 430 to approximate to 380 kg/mm(2). The results are d iscussed in terms of multiscalar design concepts.