Ames Laboratory

About: Ames Laboratory is a facility organization based out in Ames, Iowa, United States. It is known for research contribution in the topics: Superconductivity & Magnetization. The organization has 1269 authors who have published 1669 publications receiving 51574 citations.

Additively manufactured hierarchical stainless steels with high strength and ductility

Abstract: 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.

A mathematical introduction to fluid mechanics

Abstract: Contents: The Equations of Motion.- Potential Flow and Slightly Viscous Flow.- Gas Flow in One Dimension.- Vector Identities.- Index.

Molecular Geometry Optimization with a Genetic Algorithm

Abstract: We present a method for reliably determining the lowest energy structure of an atomic cluster in an arbitrary model potential. The method is based on a genetic algorithm, which operates on a population of candidate structures to produce new candidates with lower energies. Our method dramatically outperforms simulated annealing, which we demonstrate by applying the genetic algorithm to a tight-binding model potential for carbon. With this potential, the algorithm efficiently finds fullerene cluster structures up to ${\mathrm{C}}_{60}$ starting from random atomic coordinates.

Superconductivity of metallic boron in MgB2.

Abstract: Boron in MgB2 forms stacks of honeycomb layers with magnesium as a space filler. Band structure calculations indicate that Mg is substantially ionized, and the bands at the Fermi level derive mainly from B orbitals. Strong bonding with an ionic component and considerable metallic density of states yield a sizable electron-phonon coupling. Together with high phonon frequencies, which we estimate via zone-center frozen phonon calculations to be between 300 and 700 cm(-1), this produces a high critical temperature, consistent with recent experiments. Thus MgB2 can be viewed as an analog of the long sought, but still hypothetical, superconducting metallic hydrogen.