2,806 research outputs found
Direct observations of nucleation in a nondilute multicomponent alloy
The chemical pathways leading to gamma-prime(L1_2)-nucleation from nondilute
Ni-5.2 Al-14.2 Cr at.%, gamma(f.c.c.), at 873 K are followed with radial
distribution functions and isoconcentration surface analyses of direct-space
atom-probe tomographic images. Although Cr atoms initially are randomly
distributed, a distribution of congruent Ni3Al short-range order domains (SRO),
=0.6 nm, results from Al diffusion during quenching. Domain site occupancy
develops as their number density increases leading to Al-rich phase separation
by gamma-prime-nucleation, =0.75 nm, after SRO occurs.Comment: 5 pages, 4 figure
Direct Measurement of 2D and 3D Interprecipitate Distance Distributions from Atom-Probe Tomographic Reconstructions
Edge-to-edge interprecipitate distance distributions are critical for
predicting precipitation strengthening of alloys and other physical phenomena.
A method to calculate this 3D distance and the 2D interplanar distance from
atom-probe tomographic data is presented. It is applied to nanometer-sized
Cu-rich precipitates in an Fe-1.7 at.% Cu alloy. Experimental interprecipitate
distance distributions are discussed
Effects of solute concentrations on kinetic pathways in Ni-Al-Cr alloys
The kinetic pathways resulting from the formation of coherent L12-ordered
y'-precipitates in the g-matrix (f.c.c.) of Ni-7.5 Al-8.5 Cr at.% and Ni-5.2
Al-14.2 Cr at.% alloys, aged at 873 K, are investigated by atom-probe
tomography (APT) over a range of aging times from 1/6 to 1024 hours; these
alloys have approximately the same volume fraction of the y'-precipitate phase.
Quantification of the phase decomposition within the framework of classical
nucleation theory reveals that the y-matrix solid-solution solute
supersaturations of both alloys provide the chemical driving force, which acts
as the primary determinant of the nucleation behavior. In the coarsening
regime, the temporal evolution of the y'-precipitate average radii and the
y-matrix supersaturations follow the predictions of classical coarsening
models, while the temporal evolution of the y'-precipitate number densities of
both alloys do not. APT results are compared to equilibrium calculations of the
pertinent solvus lines determined by employing both Thermo-Calc and
Grand-Canonical Monte Carlo simulation.Comment: Submitted to Acta Materialia, June, 200
A Flight Investigation of the Spinning of the F4B-2 Biplane with Various Loads and Tail Surfaces
A flight investigation of the spinning of the F4B-2 single-seat fighter airplane was made for the purpose of finding modifications that would eliminate dangerous spin tendencies exhibited by this type of airplane in service. The effects on steady spins and on recoveries of changing the loading, enlarging the fin areas, changing the elevator plan form, and raising the horizontal surfaces, were determined
k-core organization of complex networks
We analytically describe the architecture of randomly damaged uncorrelated
networks as a set of successively enclosed substructures -- k-cores. The k-core
is the largest subgraph where vertices have at least k interconnections. We
find the structure of k-cores, their sizes, and their birth points -- the
bootstrap percolation thresholds. We show that in networks with a finite mean
number z_2 of the second-nearest neighbors, the emergence of a k-core is a
hybrid phase transition. In contrast, if z_2 diverges, the networks contain an
infinite sequence of k-cores which are ultra-robust against random damage.Comment: 5 pages, 3 figure
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