Search

Owing to its unique functionalities, micro-origami has been attracting tremendous research interest recently as a novel method for micro- and nano-fabrication of 3D structures. Here, we develop a facile method to fabricate micro-origami through self-folding or -rolling of 2D metallic nanosheets (also termed as “2D metals” in the literature). Unlike in the previous works, the 2D metals used in this work are mass-produced via polymer surface buckling enabled exfoliation and have an in-plane size on the scale of 1 cm and thickness ranging from ~10 nm to ~100 nm, which enables a discovery of an intriguing geometric effect on the mechanism for the self-construction of the micro-origami that has never been reported before in the origami literature. More interestingly, we demonstrate a passive but rapid method to unfold and re-fold the micro-origami of 2D metals by surface tension. The outcome of our combined research, including experiments, modeling and simulations, indicates that the large sized 2D metals provide a unique way for the mass fabrication of 3D micro-origami structures with a great potential for novel applications.

In this study, we develop a non-equiatomic Co2CrNi1.5Al0.25Ti0.25 quinary medium-entropy alloy (MEA). The heterogeneous grain structure (HGS) (comprising residual deformed grains, micro-sized recrystallized grains and nano-sized recrystallized grains) and heterogeneous precipitation (HP) of the L12 phase corresponding to different kinds of grain structures are simultaneously introduced into the alloy by the well-designed thermomechanical processing. The alloy exhibits an ultra-high yield stress ( σ y ) of 1.73 GPa, ultimate tensile stress ( σ u ) of 1.89 GPa and remarkable total elongation ( e te ) up to 16.0% at 293 K, as well as ultra-high σ y up to 2.02 GPa, σ u up to 2.31 GPa and excellent e te up to 21.2% at 77 K. The synergy of multiple hardening mechanisms, mainly including back-stress hardening, precipitation hardening and pre-existed dislocation hardening contributes to the ultra-high σ y at 293 K and 77 K. The HGS promotes the continuously increased geometrically necessary dislocations (GNDs) density, which, combined with the nano-spaced stacking fault (SF) networks, leads to the outstanding three-stage work-hardening behaviors during tensile tests at 293 K and 77 K. The simultaneous introduction of HGS and HP into this newly-developed MEA without brittle intermetallic phase, is a new effective method in designing high-performance alloys applied at both ambient and cryogenic temperatures.

Bulk metallic glasses (BMGs) are well-known for their superb strength (1–4 GPa) (Ashby and Greer, 2006) [1] but poor/localized plasticity when deformed at low temperatures or high strain rates (Inoue and Takeuchi, 2011; Kumar et al., 2009) [ 2 , 3 ]. Therefore, processing of BMGs, such as forming and shaping for various important applications, is usually performed above their glass transition temperatures (Tg) – also known as “thermo-plastic” forming (Geer, 1995) – for which the selection of alloy composition and the protocol for thermal treatment is demanding in order to promote extensive homogeneous plastic flows while avoiding crystallization (Geer, 1995). In stark contrast, here we demonstrate that homogeneous super-plasticity can occur rapidly in different BMGs below their Tg when subjected to ultrasonic agitations. Through atomistic simulations and nanomechanical characterization, we provide the compelling evidence to show that this super-plasticity is attributed to dynamic heterogeneity and cyclic induced atomic-scale dilations in BMGs, which leads to significant rejuvenation and final collapse of the solid-like amorphous structure, thereby leading to an overall fluid-like behavior. Our finding uncovers that BMGs can undergo substantial plastic flows through unusual liquefaction near room temperature and, more importantly, it leads to the development of a facile and cost-effective “ultrasonic-plastic” forming method to process a wide range of BMGs at low temperatures.