Aluminum Loop Research Articles

Annealing kinetics of faulted loops in aluminium

Abstract The author derives a simple method for testing the annealing curves of the annealing kinetics of faulted loops and applies the result to a previous publication on the subject.

The effect of pressure on the annealing of dislocation loops in aluminium

Thin foils of quenched aluminium have been annealed at hydrostatic pressures up to 60 kb and temperatures up to 289°C. Observation by transmission electron microscopy before and after treatment has enabled a determination of temperature ranges within which dislocation loops anneal out at different pressures. It is found that the temperature required for annealing increases with pressure by between 1.26 and 2.62°C/kb, corresponding to an activation volume lying between 0.44 and 0.87 atomic volumes. This range accords with values for other f.c.c. metals and with values calculated firstly from the pressure variation of the melting temperature and secondly from expressions relating activation volume and entropy to activation energy. The work shows that the decrease in point defect mobility with pressure is a much larger effect than the increase in driving force. Two alternative general expressions have been derived for lines of equal annealing to predict the effect of pressure on diffusion controlled processes in any solid.

Faulted dislocation loops in quenched aluminium

Abstract Dislocation loops containing stacking faults have been observed in quenched aluminium using the electron microscope. It is found that lowering the quenching rate relaxes the stringent purity conditions governing the retention of faulted loops, such that a high proportion of the loops in oil-quenched aluminium (99·97 % purity) contain faults. The results are discussed in terms of the influence of quenching stresses on the stability of the faulted loop. A low quenching rate also favours double-faulting, in which a Frank sessile dislocation loop is nucleated on an existing fault. The stability of this defect is attributed to the lower stacking-fault energy of a double fault compared with that of two intrinsic stacking faults. Under the action of stress the outer fault of the double defect can sometimes be removed to produce a faulted loop within a prismatic loop. The annealing behaviour of the four different types of dislocation loop, i.e. prismatic, single-faulted, double-faulted and faulted prismatic loop, has been studied using the heating stage. The kinetic data have been analysed to deduce a value for the intrinsic and extrinsic stacking-fault energy of aluminium.

On the formation of {012} loops in quenched aluminium

Abstract The loop rotation mechanism of formation of {012} loops suggested by Makin and Hudson (1963) by the sequence, hexagonal Frank loop-hexagonal perfect loop-rhombus {012} loop, has been demonstrated experimentally. Quenching Al-1% Mg into silicone oil produces only hexagonal stacking-faulted loops. Heating of the foil in the polishing bath is probably responsible for much of the heterogeneity in the previously published literature on quenched loops in aluminium.

The Effect of Solute Concentration on the Formation of Loops in Aluminium‐Magnesium Alloys during Fission Fragment Irradiation

AbstractA study has been made of the effect of magnesium concentration (up to 0.5 at%) on the formation of dislocation loops in aluminium during fission fragment bombardment at 60 °C. Increasing magnesium content reduces the initial rate of increase of the total loop area with dose, but the loop area saturates at a higher level in more concentrated alloys. A concentration as low as 0.02% reduces the initial rate of loop growth by a factor of 4 to 5. Considerable attention has been given to the problems of obtaining accurate measurements of the loop area per unit volume in foils irradiated in the pre‐thinned state, and a number of corrections have been applied. An unusual surface denudation effect is observed. The results are explained in terms of the effect of trapping on the mobility of both the interstitial atoms and the vacancies.

The effect of quenching history, quenching temperature and trace impurities on vacancy clusters in aluminium and gold

Abstract It has been shown that in zone-refined aluminium, under specific quenching conditions, regions of stacking fault bounded by dislocation loops with a 1/3 [111] Burgers vector can be formed. The same type of defect can be produced by multiply quenching 99•995% aluminium. Repeated quenching therefore produces effects similar to those produced by increased purity. The observation of large, faulted loops in aluminium, a material assumed to have a high stacking-fault energy, is explained in terms of the difficulty of nucleating a Shockley partial dislocation to unfault the loop. The occurrence of such loops in the purest material only, is explained by postulating that in the purer material loop nucleation is more difficult than in a material of moderate purity. This results in some loops forming at low temperature, a condition which favours the formation of faulted loops. The purification produced by multiple quenching is discussed in terms of the sweeping out of impurities by the vacancies as they anneal out to the surface (the predominant vacancy sink in the present experiments). This [quench refining] effect has been confirmed in a parallel study of the effect of purity and multiple quenching on the type of clustered-vacancy defect in gold. In particular, it has been shown that the quenching temperature corresponding to the transition from the formation of stacking-fault tetrahedra to the formation of black-spot defects can be lowered by multiple quenching.

On interstitial dislocation loops in aluminium bombarded with alpha-particles

Abstract Electron transmission microscopy and selected area diffraction have shown that the dislocation loops in aluminium bombarded with 38 Mev alpha-particles lie generally upon the {110} planes with a [110] Burgers vector normal to the loop. These loops are only seen where the alpha-particles come to rest. The theory of diffraction contrast at dislocations (Hirsch et al. 1960) has been used to determine the sense of the Burgers vectors and shows that the loops are formed from interstitial atoms as previously inferred from their annealing behaviour (Barnes and Mazey 1960).

On the stability of quenched dislocation loops in aluminum

On the stability of quenched dislocation loops in aluminum

On The Behavior of Thermal Vacancies in Pure Aluminum

The results are reported of an investigation of quenched-in prismatic dislocation loops in super-purity aluminum. Some new effects have been observed: in particular, that loops tend to be grouped in clusters containing a surplus of loops of one orientation; that more than four loop orientations are realized; and that often pairs of similarly oriented and similarly shaped loops are present in the quenched material. It is concluded that vacancies aggregate into three dimensional clusters, containing from a few to a few hundred or even thousand vacancies, before being converted into prismatic loops.