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| 1 | Unusually thick shear-softening surface of micrometer-size metallic glasses显示文摘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. | J.Dong Y.Huan B.Huang J.Yi Y.H.Liu B.A.Sun W.H.Wang H.Y.Bai | 2021 | The Innovation2021，2，2： | 1 |
| 2 | Composition and size dependent torsion fracture of metallic glasses显示文摘The fracture of metallic glasses(MGs)of different compositions and sizes down to micrometers under torsion loading were systematically investigated.Contrary to the flat shear fracture along the circumferential plane as commonly supposed under torsion,we find that the torsion fracture of metallic glasses can deviate from flat shear plane,and the fracture angle is closely dependent on the composition and the size of MG samples.With a conversion method,we show that the torsion fracture of both millimeterand micrometer-sized MGs can be described by the ellipse fracture criterion as originally proposed for the tension fracture.The deviation from the circumferential shear plane under torsion is further shown to intrinsically relate to the fracture toughness of MGs.The tougher MG tends to have a smaller fracture angle with respect to the maximum shear plane,and vice versa,indicating a correlation between the fracture toughness and pressure/normal stress sensitivity in MGs.Our results provide new insights on the fracture mechanism and are helpful to design and control the deformation and fracture behavior of MGs under torsion loading. | J.Dong J.Shen Y.H.Sun H.B.Ke B.A.Sun W.H.Wang H.Y.Bai | 2021 | Journal of Materials Science & Technology2021，，23： | 1 |
| 3 | Hardening and toughening effects of intermediate nanosized structures in a confined amorphous alloy film显示文摘The plastic deformation of amorphous alloys is well known to be localized into shear bands(SBs),which are believed to stem from the atomic-scale flow defects,i.e.,shear transformation zones(STZs).Yet,the bridge between the mesoscopic SBs and the atomic-scale STZs remains poorly understood.In this work,through thermally activating pronouncedβrelaxations in the well-designed crystalline-layer confined amorphous(CLCA)Ni W alloy films,we experimentally captured and observed an intermediate nanosized structure termed as“nano shear bands”(NSBs)with a typical size of 1–2 nm in thickness and5–10 nm in length.The influences of such NSB structures on the macroscale deformation behavior were systematically investigated.It was found that NSBs lead to both hardening and toughening effects for the CLCA films,as they promote multiple and controlled shear banding deformation,which results in enhanced crystallization.The intermediate NSB structure could connect the microstructural characteristics and macroscopic plasticity in amorphous alloys and may provide new insights for understanding the microscopic deformation mechanism of amorphous alloys as well as tuning/designing their properties. | Z.Q.Chen M.C.Li X.Tong Y.Zhao J.Y.Xie S.W.Guo P.Huang F.Wang H.B.Ke B.A.Sun W.H.Wang | 2022 | Journal of Materials Science & Technology2022，，23： | 0 |
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