Many traditional approaches for strengthening steels typically come at the expense of useful ductility, a dilemma known as strength-ductility trade-off. New metallurgical processing might offer the possibility of overcoming this. Here we report that austenitic 316L stainless steels additively manufactured via a laser powder-bed-fusion technique exhibit a combination of yield strength and tensile ductility that surpasses that of conventional 316L steels. High strength is attributed to solidification-enabled cellular structures, low-angle grain boundaries, and dislocations formed during manufacturing, while high uniform elongation correlates to a steady and progressive work-hardening mechanism regulated by a hierarchically heterogeneous microstructure, with length scales spanning nearly six orders of magnitude. In addition, solute segregation along cellular walls and low-angle grain boundaries can enhance dislocation pinning and promote twinning. This work demonstrates the potential of additive manufacturing to create alloys with unique microstructures and high performance for structural applications.
Perfect graphene is believed to be the strongest material. However, the useful strength of large-area graphene with engineering relevance is usually determined by its fracture toughness, rather than the intrinsic strength that governs a uniform breaking of atomic bonds in perfect graphene. To date, the fracture toughness of graphene has not been measured. Here we report an in situ tensile testing of suspended graphene using a nanomechanical device in a scanning electron microscope. During tensile loading, the pre-cracked graphene sample fractures in a brittle manner with sharp edges, at a breaking stress substantially lower than the intrinsic strength of graphene. Our combined experiment and modelling verify the applicability of the classic Griffith theory of brittle fracture to graphene. The fracture toughness of graphene is measured as the critical stress intensity factor of 4:0 AE 0:6 MPa ffiffiffiffi m p and the equivalent critical strain energy release rate of 15.9 J m À 2 . Our work quantifies the essential fracture properties of graphene and provides mechanistic insights into the mechanical failure of graphene.
Twinning is a fundamental deformation mode that competes against dislocation slip in crystalline solids. In metallic nanostructures, plastic deformation requires higher stresses than those needed in their bulk counterparts, resulting in the 'smaller is stronger' phenomenon. Such high stresses are thought to favour twinning over dislocation slip. Deformation twinning has been well documented in face-centred cubic (FCC) nanoscale crystals. However, it remains unexplored in body-centred cubic (BCC) nanoscale crystals. Here, by using in situ high-resolution transmission electron microscopy and atomistic simulations, we show that twinning is the dominant deformation mechanism in nanoscale crystals of BCC tungsten. Such deformation twinning is pseudoelastic, manifested through reversible detwinning during unloading. We find that the competition between twinning and dislocation slip can be mediated by loading orientation, which is attributed to the competing nucleation mechanism of defects in nanoscale BCC crystals. Our work provides direct observations of deformation twinning as well as new insights into the deformation mechanism in BCC nanostructures.
Metallic nanowires usually exhibit ultrahigh strength but low tensile ductility owing to their limited strain hardening capability. Here we study the unique strain hardening behavior of the five-fold twinned Ag nanowires by nanomechanical testing and atomistic modeling. In situ tensile tests within a scanning electron microscope revealed strong strain hardening behavior of the five-fold twinned Ag nanowires. Molecular dynamics simulations showed that such strain hardening was critically controlled by twin boundaries and pre-existing defects. Strain hardening was size dependent; thinner nanowires achieved more hardening and higher ductility. The size-dependent strain hardening was found to be caused by the obstruction of surface-nucleated dislocations by twin boundaries. Our work provides mechanistic insights into enhancing the tensile ductility of metallic nanostructures by engineering the internal interfaces and defects.
A vertically aligned ZnO/ZnS core/shell nanowire array with type II band alignment was directly synthesized on an indium-tin-oxide glass substrate and the photovoltaic effect of the nanowire array was investigated. The epitaxial relationship, wurtzite (0001) matching zinc-blende (111), was observed in the ZnO/ZnS nano-heterostructure. ZnS coating is found to quench the photoluminescence of ZnO nanowires but enhance the photocurrent with faster response in the photovoltaic device, indicating improvement in charge separation and collection in the type II core/shell nanowire.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.