Unusually thick shear-softening surface of micrometer-size metallic glasses

Abstract

Unusually thick shear-softening surface of micrometer-size metallic glasses. The Innovation 2(2), 100106.The surface of glass is crucial for understanding many fundamental processes in glassy solids. A common notion is that a glass surface is a thin layer with liquid-like atomic dynamics and a thickness of a few tens of nanometers. Here, we measured the shear modulus at the surface of both millimeter-size and micrometer-size metallic glasses (MGs) through high-sensitivity torsion techniques. We found a pronounced shear-modulus softening at the surface of MGs. Compared with the bulk, the maximum decrease in the surface shear modulus (G) for the micro-scale MGs reaches~27%, which is close to the decrease in the G upon glass transition, yet it still behaves solid-like. Strikingly, the surface thickness estimated from the shear-modulus softening is at least 400 nm, which is approximately one order of magnitude larger than that revealed from the glass dynamics. The unusually thick surface is also confirmed by measurements using X-ray nano-computed tomography, and this may account for the brittle-to-ductile transition of the MGs with size reductions. The unique and unusual properties at the surface of the micrometer-size MGs are physically related to the negative pressure effect during the thermoplastic formation process, which can dramatically reduce the density of the proximate surface region in the supercooled liquid state.

Strong yet Ductile High Entropy Alloy Derived Nanostructured Cermet

“…As shown in Figure g, there are large compressive atomic stresses, indicating strong elastic confinements against the flowing amorphous interphase from sideways when the model cermet is pulled. A similar phenomenon was observed when viscous metallic liquids were pulled through narrow confinements . Based on the atomistic simulations, we conclude that plasticity in our cermet is mainly accommodated by the amorphous interphase, and the atomic reshuffles around the nanocrystal boundaries as well as the elastic confinements in the unique nanostructure contribute to strain hardening, which is required for the uniform strain, or the ductility measured for our cermet (Figure d).…”

Exceptionally shear-stable and ultra-strong Ir-Ni-Ta high-temperature metallic glasses at micro/nano scales

“…As a new class of disordered materials, metallic glasses exhibit superb high strength (close to the ideal strength in some cases) and large elastic strain [8], yet the strength-ductility trade-off still persists in MGs [9]. Unlike crystalline alloys, the plastic deformation of MGs is highly localized into nanoscale shear bands, which is prone to become runaway with the assistance of strain softening [10,11]. As a result, MGs display a propensity for catastrophic and instantaneous brittle failure [12], which has become the Achilles' heel for their structural applications.…”

Dynamic mechanical relaxation and thermal creep of high-entropy La30Ce30Ni10Al20Co10 bulk metallic glass

“…Metallic glasses (MGs) and high-entropy alloys (HEAs) have attracted much attention to researchers worldwide over various disciplines. MGs possess unique mechanical and physical properties such as superior compressive/tensile strength, high elastic limit, ultrahigh hardness, and excellent anti-corrosion behavior [1][2][3][4][5][6]. HEAs are multicomponent alloys containing at least five elements in equiatomic/near-equiatomic concentrations.…”