“Ductile” Fracture of Metallic Glass Nanolaminates

Abstract

strength and large elastic limit compared with their crystalline counterparts, [1][2][3] but strain (shear) localization and shear softening associated with the rapid propagation of limited shear bands curtail their ductility and hinder their applications as advanced structural materials. [4][5][6] In principle, strain localization/softening can be mitigated by generating profuse shear bands, obstructing shear band propagation, or inhibiting shear band formation by size reduction. In practice, the plasticity and toughness of MGs can be improved intrinsically by optimizing composition, inhomogeneity, and processing history, extrinsically by introducing soft crystalline phase (such as synthesizing crystalamorphous nanolaminates), or reducing sample dimension to nanoscale. [7][8][9][10][11][12] It is worth mentioning that similar to utilizing the size reduction to suppress instability of deformation of metallic glasses, higher stiffness of testing machine can also alleviate the instability. [13,14] Das et al. attributed the intercepted shear bands in CuZrAl bulk MG to structure inhomogeneity. [15] More than 10% tensile strain was achieved for ZrTi-based bulk metallic glass composites by introducing crystalline dendrites. [12] Also at nanoscale, metallic glasses can deform homogeneously without the formation of shear bands [16] and fracture by necking. [11,17] Studies show that when the sample dimension is ≈10 times of the size of STZs (shear transformation zone) or smaller than ≈100 nm, shear band formation can be inhibited in certain metallic glass systems. [14] Fracture morphology, crack path, and fracture mode, however, were not well understood especially at nanometer length scale. Fracture morphology is directly connected to the mechanism of plastic deformation and fracture toughness. Understanding the patterns of fracture surfaces can be beneficial for the selection and design of MGs with better ductility and toughness, and provides guidelines for modeling and simulations on fracture mechanisms.Thin film metallic glasses (TFMGs) are promising candidates for mirco-electromechanical systems applications, as TFMGs may have high hardness and good fatigue resistance, and can be tailored over a wide range of composition. [4,18] With the addition of crystalline phases, ductility/plasticity of TFMG composites (crystal-amorphous nanolaminates) is improved. [19][20][21][22] For instance, Cu 35 nm/amorphous CuZr 5 nm multilayers can reach ≈14% tensile ductility. [23] Due to their extraordinary mechanical properties, TFMGs can also be potentially utilized in stretchable devices in electronic industry. Therefore, tensileMost metallic glasses are brittle as deformation induces low-density sporadic shear bands and severe shear localization proceeding catastrophic failure. Here, it is demonstrated that the introduction of crystalline nanolayers with appropriate dimension can substantially suppress shear localization in metallic glasses, as manifested by ubiquitous ductile dimples in amorphous phase. Furthermore, dimple sizes c...

MXene‐Based Flexible Sensors: Materials, Preparation, and Applications

“…Aerogels are porous materials consisting of an interconnected 3D network of solids and air‐filled pores. [ 111 ] These materials usually have low density, large surface area, and high porosity, and these properties make aerogel‐based sensors characterized by large contact area, high sensitivity, and high recoverability. They have promising applications in gas sensors, biosensors, They have promising applications in gas sensors, biosensors, pressure sensors, etc.…”

Hierarchical and heterogeneous multiphase metallic nanomaterials and laminates

“…Nanolaminates consisting of metallic glasses and crystalline metals, or metal-hard phase composite systems (e.g., metal-metal nitride), exhibit strengths comparable to or less than the hard phase, and the high strain hardening can give rise to plastic codeformation and uniform distribution of plasticity resulting in suppression of shear band and/or brittle behavior of the hard phase. 8,9 As an example, Al-TiN nanolaminates with 2-nm (nominal) layer thicknesses exhibited uniform plasticity in compression to 8% plastic strain at room temperature and a maximum flow stress of approximately 4.5 GPa. 9 Nanolaminates involving immiscible elements, such as Cu and Nb, have shown high thermal, mechanical, and irradiation stability.…”

Modelling of the Influence of Tensile Test Speed on the Fracture Load

“…Engineering materials are classified in accordance to their deformation at fracture (i.e., brittle or ductile), to the form and appearance of fracture where ductile fracture produces less serious problems than brittle fracture under the same operating conditions, and to the crystallographic manner in which the fracture occurs (i.e., sliding, cleavage) (Hutiu et al, 2018). Among the various failure mechanisms introduced (Fan et al, 2017), investigating those associated with a brittle and ductile fracture in metallic alloys is important. Ductile fracture includes failure plastic instability or by cavitation.…”