Nanolaminates Utilizing Size‐Dependent Homogeneous Plasticity of Metallic Glasses

Abstract

Homogeneous plasticity in metallic glasses is generally only observed at high temperatures or in very small structures (less than ≈100 nm), so their applications for structural performance have been very limited. Here, nanolaminates with alternating layers of Cu50Zr50 metallic glass and nanocrystalline Cu are synthesized and it is found that samples with an optimal composition of 112‐nm‐thick metallic‐glass layers and 16‐nm‐thick Cu layers demonstrate a maximum strength of 2.513 GPa, a value 33% greater than that predicted by the rule‐of‐mixtures and 25% better than that of pure Cu50Zr50 metallic glass. Furthermore, ≈4% strain at fracture is achieved, suppressing the instantaneous catastrophic failure often associated with metallic glasses. It is postulated that this favorable combination of high strength and deformability is caused by the size‐dependent deformation‐mode transition in metallic glasses, from highly localized plasticity, leading to immediate failure in larger samples to homogeneous extension in the smaller ones.

Thickness-Dependent Strain Rate Sensitivity of Nanolayers via the Nanoindentation Technique

“…Therefore, the SRS should be similar to the single layer Cu. However, when h is smaller, the and would be close to 0.5 due to the co-deformation of crystalline phase and amorphous phase (the two phases share the deformation equally) [8,13], and the SRS would be closer to the single-layer amorphous film based on Equation (6). Figure 6b is a schematic showing the different deformation mechanisms at different h. When h > 100 nm, Cu layers deform plastically due to its low strength and accommodate most of the strain, and thus Cu/a-CuNb multilayers have an apparent SRS value similar to that of the single layer Cu film.…”

“…Metallic glasses (MGs) exhibit high strength, excellent abrasion and corrosion resistance [4], but they are generally brittle due to the shear band (SB) controlled-deformation mechanisms therefore the SRS is close to zero [5]. Prior studies have shown that adding a crystalline phase to the amorphous matrix can increase the toughness/plasticity of ZrTi-based MGs [6] and crystalline/amorphous (C/A) multilayers [7][8][9][10][11][12][13][14]. For the C/A multilayer composites, their thermally-activated plastic deformation mechanisms can also be revealed by quantifying their SRS.…”

Atomistic Design of High Strength Crystalline-Amorphous Nanocomposites

“…To solve the brittle nature of both BNMs and MGs, nanolaminates with alternating layers of nanoscale MGs and crystalline metals have been recently synthesized. 7,8) The new category of nanolaminates utilize the concept that MGs demonstrate homogenous plasticity instead of catastrophic failure when their size is extremely small. 8) Therefore, they could exhibit apparent tensile ductility.…”

“…7,8) The new category of nanolaminates utilize the concept that MGs demonstrate homogenous plasticity instead of catastrophic failure when their size is extremely small. 8) Therefore, they could exhibit apparent tensile ductility. By varying the size of its compositions, the nanolaminates could demonstrate higher strength than that of both MGs and nanocrystalline metals.…”

“…The improved strength and ductility are furthermore suggested due to a transition of deformation mechanisms from localized plasticity to more homogenous extension as the size decreases. 8) Here we use atomistic modeling to optimize the mechanical responses of a kind of three-dimensional (3D) nanocomposite materials which are composed of nanoscale crystalline copper and CuZr metallic glass. It is actually a spatially extension of the experimentally synthesized 2D nanolaminates.…”