Etude par microscopie electronique de la decomposition de l'alliage Al-6,8 at.% Zn

Prediction of alloy precipitate shapes from first principles

“…Our strategy will hence be to assume that for Al-Zn a thermodynamic (rather than kinetic) description of size vs. shape might be appropriate, and examine the extent to which this does or does not agree with the measured distribution of sizes and shapes. We find that it does: Our calculations are quantitatively in excellent agreement with experimental results [11][12][13][14][15][16][17].…”

“…Of particular interest are the shapes and sizes of precipitates which are found to be strongly correlated: For example, Al 1−x Cu x alloys exhibit a transition of coherent precipitates from {100} planes of Cu atoms to Cu-Al-Al-Al-Cu thin platelet structures [9,10]. In Al 1−x Zn x , many experimental studies have been performed to examine the shapes and structure of precipitates [11][12][13][14][15][16][17] (due to the ability of Al-Zn to harden via precipitate heat-treatment). The Zn precipitates exhibit a remarkable series of shapes and sizes: Small precipitates tend to be spherical, until they reach a critical size R C of about 15-25 Å (dependent on the aging temperature) at which point they become ellipsoidal/plate-like with the short axis parallel to the [111] direction.…”

Classification of Markov chains describing the evolution of random strings

“…Our selection of structural parameters is related to previous experimental work (Laslaz andGuyot 1977, Luiggi et a1 1980b) in which samples from the same source and with similar heat treatments were studied. In particular we studied an A1-6.8 at.% Zn alloy (Luiggi et a1 1980b), attempting to identify the metallurgical states determined by electron microscopy.…”

“…The decomposition kinetics of an alloy in the first stage of aging appear to depend on the measurement technique used to study the demixing (Laslaz and Guyot 1977, Mimault et a1 1978, Gould 1971. This is reaffirmed in Luiggi (1979), where the anomalous evolution of the resistivity with time implies a time evolution of the size cp and/or of C,, but electron microscopy indicates constant values for both of these parameters, possibly implying demixing by means of spinodal decomposition.…”

Guinier-Preston zones in an Al-3 at% Zn alloy

“…zones is assumed to be spherical [ 2 to 51 as concluded from SAXS done with single crystals [a] or polycrystals [3], respectively, transmission electron microscopy (TEM) investigations [4] including the analysis of the surrounding of the matrix reflections of electron diffraction (ED), as well as from small-angle neutron scattering (SANS) [ 5 ] .…”