J. W. Edington

Low-temperature diffusion in A1–7 wt. % Mg and A1–4 wt. % Cu alloys

Abstract Combined electron microscopy and electron energy analysis has been used to measure composition gradients near grain boundaries in aged Al-7 wt. % Mg arid A1–4 wt. % Cu alloys. The results show that the model due to Aaron and Aaronson (1968) describes satisfactorily the grain boundary precipitation process. Analysis of the development of the composition profiles associated with this precipitation has enabled low-temperature diffusion coefficients to be determined.

Microanalysis of Al-Li alloys containing fine 6′ (Al3Li) precipitates

Abstract Measurements of the plasma energy loss in aluminium alloys containing up to 12·9 at.% lithium are described. The energy loss of those alloys containing a fine dispersion of δ′ (Al3Li) precipitates can be explained in terms of direct superposition of the matrix and δ′ spectra. High-resolution microanalysis is possible when a fine dispersion of δ′ precipitates is present.

Measurement of Mg supersaturations within precipitate-free zones in Al-Zn-Mg alloys

Abstract An energy-analysing electron microscope has been used to measure directly the magnesium solute concentration profiles within the precipitate-free zones formed in aged Al-6% Zn-3% Mg alloys. The results are consistent with the proposals of Pashley, Jacobs and Vietz (1967), and Unwin, Lorimer and Nicholson (1969). Analysis of the resulting magnesium solute profiles has yielded low-temperature diffusion data for magnesium in the presence of zinc.

Slip systems in the intermetallic compound Ti3Sn

Abstract The slip process and deformation substructure in Ti3Sn have been studied using two-surface analysis together with transmission electron microscopy and computer image-matching. Despite the unusual occurrence of limited slip on the [001] {1100}, [0001] {11220} systems, there are only four independent slip systems and the material is not ductile. The relationship between the observed dislocation configurations and the estimated antiphase domain boundary energies is discussed.

Computer simulation of images of undissociated dislocations in hexagonal metals

Abstract The computer programme originated by Head (1967) has been modified for hexagonal crystal structures. Computed and experimental images have been matched for edge and mixed dislocations with Burgers vectors a/3 and lying in the basal plane of magnesium. The programme has been used to investigate the general form of dislocation images in common c.p.h. metals, allowing for elastic anisotropy. When g. b = 0 dislocations with Burgers vectors b = a/3 , a/3 and c and having particular line directions behave as if the material were elastically isotropic. For those combinations of Burgers vectors and line directions for which elastic anisotropy must be considered its effect is to lower the value of g. b ∧ u at which the change from invisibility to visibility occurs when g.b = 0.

Superposition effects in the energy analysing electron microscope

Abstract A simple analysis of superposition effects is described. Background intensity arising from carbon contamination and surface oxide film is shown to affect the accuracy with which peak position and therefore composition may be determined. Under some circumstances this effect is shown to be particularly important if the calibration and energy loss spectra are recorded on the same plate.

Microanalysis across grain boundaries in aluminium alloys

Abstract Solute concentration profiles have been measured across grain boundaries in aged Al-4-1 wt%Cu and Al-5-9 wt%Zn-3-2 wt%Mg alloys using the microanaly-tical techniques of combined electron microscopy/electron energy analysis (EMEA) and combined electron microscopy/X-ray microanalysis (EMMA). Agreement between the two techniques is good, provided sufficiently wide solute-depleted zones are developed to compensate for the relatively coarse spatial resolution of EMMA.

The variation of plasma energy loss with composition in dilute aluminium-magnesium solid solutions

Abstract Detailed measurements are described of the plasma energy loss in aluminum alloys containing up to ∼ 9 at. % magnesium. The measured dependence of the plasma energy loss on composition deviates from that to be expected from a rigid band model of alloying. A better fit to the measurements is obtained if the model is modified to take account of the influence of deep electronic band structure.

A study of the mechanism of loop growth in thin foils of an aluminium 3·0 at. % magnesium alloy using an energy analysing electron microscope

Abstract Parallel observations have been made of the plasmon energy losses and the growth of prismatic dislocation loops during annealing at 200°c of an aluminium 3·0 at. % magnesium alloy. It is shown that there is a continuous loss of magnesium during annealing and this supports the oxidation-vacancy emission loop growth mechanism suggested by Kritzinger, Dobson and Smallman (1967) to account for loop growth in aluminium-magnesium alloys. It is found that the rate of growth of loops varies by a factor of three from point to point within a given grain in the thin foil. This behaviour is explained in terms of local fluctuations in the efficiency of the oxide/metal interface for absorbing vacancies.

Microanalysis of splat quenched Al-Cu alloys

Abstract The variation of plasmon energy loss with composition in splat quenched Al-Cu alloys has been measured. The results have been used to perform microanalysis on several different microstructures in the as-splatted condition. The measurements demonstrate that there are no composition gradients near grain boundaries and that the matrix of both degenerate and radial eutectic structures is significantly supersaturated with copper.