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.

Despite the general inertness of gold, finely dispersed gold nanoparticles on suitable oxide supports can demonstrate remarkable catalytic activity for the epoxidation of propene or the oxidation of CO, for example. [1][2][3][4][5][6][7] Gold-based catalysts have potential applications in automotive emission control, because unlike platinum or palladium catalysts, they remain active at low temperatures (room temperature).[8] While various support materials, particle synthesis routes, and deposition techniques have been investigated over the years, [9,10] the mechanisms responsible for the catalytic activity are still under debate, because of the complexity of the particle-support interactions and the reaction pathways.Research to date has shown that the particle size, type of support material, and particle-support contact structure play major roles. [6,11,12] In contrast to supported gold catalyst systems, unsupported systems, such as gold powder, have not yet drawn much attention, although remarkably high catalytic activity for CO oxidation has been attained with such systems. [13] Moreover, unsupported gold catalysts allow the relevant catalytic mechanisms to be more easily understood and also make new applications accessible. Herein, we demonstrate that high catalytic activity is not necessarily linked to the presence of finely dispersed particles. Nanoporous gold with a spongelike morphology, formed through the selective leaching of silver from a gold-silver alloy, [14][15][16] has an unexpectedly high catalytic activity for CO oxidation at ambient pressures and temperatures down to À20 8C. Sintering can hamper the catalytic applications of gold particles; in contrast, nanoporous gold has good thermal stability, and its morphology can be easily reproduced.The spongelike morphology of the nanoporous gold used herein consists of interconnecting ligaments with diameters[*] Dr.

Although actuation in biological systems is exclusively powered by chemical energy, this concept has not been realized in man-made actuator technologies, as these rely on generating heat or electricity first. Here, we demonstrate that surface-chemistry-driven actuation can be realized in high-surface-area materials such as nanoporous gold. For example, we achieve reversible strain amplitudes of the order of a few tenths of a per cent by alternating exposure of nanoporous Au to ozone and carbon monoxide. The effect can be explained by adsorbate-induced changes of the surface stress, and can be used to convert chemical energy directly into a mechanical response, thus opening the door to surface-chemistry-driven actuator and sensor technologies.

Point design targets have been specified for the initial ignition campaign on the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)]. The targets contain D-T fusion fuel in an ablator of either CH with Ge doping, or Be with Cu. These shells are imploded in a U or Au hohlraum with a peak radiation temperature set between 270 and 300 eV. Considerations determining the point design include laser-plasma interactions, hydrodynamic instabilities, laser operations, and target fabrication. Simulations were used to evaluate choices, and to define requirements and specifications. Simulation techniques and their experimental validation are summarized. Simulations were used to estimate the sensitivity of target performance to uncertainties and variations in experimental conditions. A formalism is described that evaluates margin for ignition, summarized in a parameter the Ignition Threshold Factor (ITF). Uncertainty and shot-to-shot variability in ITF are evaluated, and sensitivity of the margin to characteristics of the experiment. The formalism is used to estimate probability of ignition. The ignition experiment will be preceded with an experimental campaign that determines features of the design that cannot be defined with simulations alone. The requirements for this campaign are summarized. Requirements are summarized for the laser and target fabrication.

We describe the fabrication of ultralow-density carbon nanotube (CNT) foams that simultaneously exhibit high electrical conductivities and robust mechanical properties. Our approach utilizes carbon nanoparticles as a binder to crosslink randomly oriented bundles of single-walled CNTs. The resulting CNT foams are the stiffest low-density nanoporous solids reported and exhibit elastic behavior up to strains as large as ∼80%. The use of the carbon binder also allows bulk electrical conductivity to be maintained at low densities.