Mechanical properties of tough multiscalar microlaminates

Abstract

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 (≈ 1 or ≈5 μm) 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 ≈ 51 and ≈31 μm, respectively. Microstructure and fracture were examined using SEM. Uniaxial tensile and hardness testing were performed to measure strength and toughness; both increased with tough phase thickness. Several models were used to estimate K IC and fracture strength. Upper bound models showed ≈2- and ≈6-fold increases in K IC and fracture strength, respectively, when tough phase thickness was increased from 1 to 5 μm, while hardness decreased from ≈430 to ≈380 kg/mm 2. The results are discussed in terms of multiscalar design concepts.