Determination of Ductile Fracture Parameters of a Dual‐Phase Steel by Optical Measurements

Marciniak–Kuczynski and Nakajima tests of the dual‐phase steel Docol 600DL ( www.ssab.com/ ) have been carried out for a range of stress‐states spanning from uniaxial tension to equi‐biaxial tension. The deformation histories of the specimens have been recorded by digital images, and the displacement and strain fields have been determined by post‐processing the images with digital image correlation software. The fracture characteristics of the material are presented by means of the stress triaxiality, the Lode parameter and the equivalent strain. These parameters are evaluated on the surface of the specimens based on the optical field measurements and assumptions regarding the mechanical behaviour of the material. Additionally the minor versus major principal strains up to fracture are presented. It is found that the material displays a significantly lower ductility in plane‐strain tension than in uniaxial tension and equi‐biaxial tension, and that it, in the tests exposed to local necking, undergoes large strains between the onset of necking and fracture. Fractographs of selected specimens reveal that fracture is due to growth and coalescence of voids that occur in localised areas governed by shear‐band instability.     

Dual‐Phase Separation in a Semiconfined System: Monodispersed Heterogeneous Block‐Copolymer Membranes for Cell Encoding and Patterning

Block copolymers (BCPs) have the capacity to self‐assemble into a myriad of well‐defined aggregate structures, offering great promise for the construction of drug delivery, photolithographic templates, and complex nanoscale assemblies. A uniqueness of these materials is their propensity to become kinetically frozen in non‐equilibrium states, implying that the process of self‐assembly can be utilized to remodel the resulting structures. Here, a new semiconfined system for processing the BCP self‐assembly is constructed, in which an unusual dual‐phase separation occurs, including nonsolvent‐induced microphase separation and osmotically driven macrophase separation, ultimately yielding heterogeneous BCP membranes. These membranes with cellular dimensions show unique anisotropy that can be used for cell encoding and patterning, which are highly relevant to biology and medicine. This processing method not only provides new levels of tailorability to the structures and encapsulated contents of BCP assemblies, but can also be generalized to other block polymers, particularly those with attractive electronic and/or optical properties.     

Using Post‐Deformation Annealing to Optimize the Properties of a ZK60 Magnesium Alloy Processed by High‐Pressure Torsion

A ZK60 magnesium alloy with an initial grain size of ≈10 µm is processed by high‐pressure torsion (HPT) through 5 revolutions under a constant compressive pressure of 2.0 GPa with a rotation speed of 1 rpm. An average grain size of ≈700 nm is achieved after HPT with a high fraction of high‐angle grain boundaries. Tensile experiments at room temperature show poor ductility. However, a combination of reasonable ductility and good strength is achieved with post‐HPT annealing by subjecting samples to high temperatures in the range of 473–548 K for 10 or 20 min. The grain size and texture changes are also examined by electron back scattered diffraction (EBSD) and the results compared to long‐term annealing for 2500 min at 450 K. The results of this study suggest that a post‐HPT annealing for a short period of time may be effective in achieving a reasonable combination of strength and ductility.

     

Effect of Isothermal Annealing on Microstructural Morphology of Martensite in a Super-Martensitic Stainless Steel Subjected to Different Prior Conditions

A super-martensitic stainless steel of the Fe–Cr–Ni family was investigated for morphological changes during isothermal annealing after subjecting it to different prior conditions. The key issues during thermomechanical treatment included determination of conditions for austenite stability and reversibility and deciding the appropriate prior treatments for the cold worked alloy before subjecting it to isothermal annealing. The study evaluated the effect of isothermal annealing on the recrystallization kinetics, phase reversion, and microstructural changes in the alloy. Intercritical isothermal annealing was carried out on samples in the range 750–900 °C for short time periods in the range of 1–2.5 min. The recrystallization behavior and microstructural changes were studied by electron backscatter diffraction, X-ray diffraction, and Vickers's hardness measurements. Martensite morphology showed significant changes during the isothermal annealing process with dependence on prior matrix substrate. The tensile properties were also evaluated. The cold rolled (CR) and isothermally annealed samples provided an improved combination of strength and ductility at the optimum heat treatment parameters.     

Temperature‐Enhanced Solvent Vapor Annealing of a C3 Symmetric Hexa‐peri‐Hexabenzocoronene: Controlling the Self‐Assembly from Nano‐ to Macroscale

Temperature‐enhanced solvent vapor annealing (TESVA) is used to self‐assemble functionalized polycyclic aromatic hydrocarbon molecules into ordered macroscopic layers and crystals on solid surfaces. A novel C₃ symmetric hexa‐peri‐hexabenzocoronene functionalized with alternating hydrophilic and hydrophobic side chains is used as a model system since its multivalent character can be expected to offer unique self‐assembly properties and behavior in different solvents. TESVA promotes the molecule's long‐range mobility, as proven by their diffusion on a Si/SiO_x surface on a scale of hundreds of micrometers. This leads to self‐assembly into large, ordered crystals featuring an edge‐on columnar type of arrangement, which differs from the morphologies obtained using conventional solution‐processing methods such as spin‐coating or drop‐casting. The temperature modulation in the TESVA makes it possible to achieve an additional control over the role of hydrodynamic forces in the self‐assembly at surfaces, leading to a macroscopic self‐healing within the adsorbed film notably improved as compared to conventional solvent vapor annealing. This surface re‐organization can be monitored in real time by optical and atomic force microscopy.     

Bioinspired Mechanically Robust Metal‐Based Water Repellent Surface Enabled by Scalable Construction of a Flexible Coral‐Reef‐Like Architecture

Mechanical robustness is a central concern for moving artificial superhydrophobic surfaces to application practices. It is believed that bulk hydrophilic materials cannot be use to construct micro/nanoarchitectures for superhydrophobicity since abrasion‐induced exposure of hydrophilic surfaces leads to remarkable degradation of water repellency. To address this challenge, the robust mechanical durability of a superhydrophobic surface with metal (hydrophilic) textures, through scalable construction of a flexible coral‐reef‐like hierarchical architecture on various substrates including metals, glasses, and ceramics, is demonstrated. Discontinuous coral‐reef‐like Cu architecture is built by solid‐state spraying commercial electrolytic Cu particles (15–65 µm) at supersonic particle velocities. Subsequent flame oxidation is applied to introduce a porous hard surface oxide layer. Owing to the unique combination of the flexible coral‐reef‐like architecture and self‐similar manner of the fluorinated hard oxide surface layer, the coating surface retains its water repellency with an extremely low roll‐off angle (<2°) after cyclic sand‐paper abrasion, mechanical bending, sand‐grit erosion, knife‐scratching, and heavy loading of simulated acid rain droplets. Strong adhesion to glass, ceramics, and metals up to 34 MPa can be achieved without using adhesive. The results show that the present superhydrophobic coating can have wide outdoor applications for self‐cleaning and corrosion protection of metal parts.     

Surface Micro‐ and Nanoengineering: Applications of Layer‐by‐Layer Technology as a Versatile Tool to Control Cellular Behavior

Extracellular matrix (ECM) cues have been widely investigated for their impact on cellular behavior. Among mechanics, physics, chemistry, and topography, different ECM properties have been discovered as important parameters to modulate cell functions, activating mechanotransduction pathways that can influence gene expression, proliferation or even differentiation. Particularly, ECM topography has been gaining more and more interest based on the evidence that these physical cues can tailor cell behavior. Here, an overview of bottom‐up and top‐down approaches reported to produce materials capable of mimicking the ECM topography and being applied for biomedical purposes is provided. Moreover, the increasing motivation of using the layer‐by‐layer (LbL) technique to reproduce these topographical cues is highlighted. LbL assembly is a versatile methodology used to coat materials with a nanoscale fidelity to the geometry of the template or to produce multilayer thin films composed of polymers, proteins, colloids, or even cells. Different geometries, sizes, or shapes on surface topography can imply different behaviors: effects on the cell adhesion, proliferation, morphology, alignment, migration, gene expression, and even differentiation are considered. Finally, the importance of LbL assembly to produce defined topographical cues on materials is discussed, highlighting the potential of micro‐ and nanoengineered materials to modulate cell function and fate.     

Synergizing Phase and Cavity in CoMoOxSy Yolk–Shell Anodes to Co‐Enhance Capacity and Rate Capability in Sodium Storage

Sodium‐ion batteries (SIBs) have been recognized as the promising alternatives to lithium‐ion batteries for large‐scale applications owing to their abundant sodium resource. Currently, one significant challenge for SIBs is to explore feasible anodes with high specific capacity and reversible pulverization‐free Na⁺ insertion/extraction. Herein, a facile co‐engineering on polymorph phases and cavity structures is developed based on CoMo‐glycerate by scalable solvothermal sulfidation. The optimized strategy enables the construction of CoMoO_xS_y with synergized partially sulfidized amorphous phase and yolk–shell confined cavity. When developed as anodes for SIBs, such CoMoO_xS_y electrodes deliver a high reversible capacity of 479.4 mA h g^?1 at 200 mA g^?1 after 100 cycles and a high rate capacity of 435.2 mA h g^?1 even at 2000 mA g^?1, demonstrating superior capacity and rate capability. These are attributed to the unique dual merits of the anodes, that is, the elastic bountiful reaction pathways favored by the sulfidation‐induced amorphous phase and the sodiation/desodiation accommodatable space benefits from the yolk–shell cavity. Such yolk–shell nano‐battery materials are merited with co‐tunable phases and structures, facile scalable fabrication, and excellent capacity and rate capability in sodium storage. This provides an opportunity to develop advanced practical electrochemical sodium storage in the future.     

Spin‐Orbit Torque Switching of a Nearly Compensated Ferrimagnet by Topological Surface States

Utilizing spin‐orbit torque (SOT) to switch a magnetic moment provides a promising route for low‐power‐dissipation spintronic devices. Here, the SOT switching of a nearly compensated ferrimagnet Gd_x(FeCo)_1?x by the topological insulator [Bi₂Se₃ and (BiSb)₂Te₃] is investigated at room temperature. The switching current density of (BiSb)₂Te₃ (1.20 × 10⁵ A cm^?2) is more than one order of magnitude smaller than that in conventional heavy‐metal‐based structures, which indicates the ultrahigh efficiency of charge‐spin conversion (>1) in topological surface states. By tuning the net magnetic moment of Gd_x(FeCo)_1?x via changing the composition, the SOT efficiency has a significant enhancement (6.5 times) near the magnetic compensation point, and at the same time the switching speed can be as fast as several picoseconds. Combining the topological surface states and the nearly compensated ferrimagnets provides a promising route for practical energy‐efficient and high‐speed spintronic devices.     

Phase Transitions in Confinements: Controlling Solid to Fluid Transitions of Xenon Atoms in an On‐Surface Network

This study reports on “phase” transitions of Xe condensates in on‐surface confinements induced by temperature changes and local probe excitation. The pores of a metal‐organic network occupied with 1 up to 9 Xe atoms are investigated in their propensity to undergo “condensed solid” to “confined fluid” transitions. Different transition temperatures are identified, which depend on the number of Xe atoms in the condensate and relate to the stability of the Xe clustering in the condensed “phase.” This work reveals the feature‐rich behavior of transitions of confined planar condensates, which provide a showcase toward future “phase‐transition” storage media patterned by self‐assembly. This work is also of fundamental interest as it paves the way to real space investigations of reversible solid to fluid transitions of magic cluster condensates in an array of extremely well‐defined quantum confinements.