High-purity Aluminium Single Crystals Research Articles

Internal friction in high-purity aluminum single crystals

It is confirmed that the grain-boundary internal-friction peak (Kě peak) does not appear in high-purity aluminium (99.991 and 99.999 wt%) single crystals prepared by various procedures. This demonstrates conclusively that the Kě peak is originated by the grain boundaries in aluminium. In the case of 99.991 and 99.999 wt% aluminium single crystals prepared by the dynamic-annealing method, an internal-friction peak is observed for the first time at a temperature about 75 ° C higher than that of the grain-boundary peak when the frequency of vibration is about 1 Hz. This new internal-friction peak does not appear in 99.999 wt% aluminium single crystals prepared by growth with the zone-melting method. This peak seems to be originated by the climbing of dispersive dislocations in aluminium. Es wird bestätigt, daß das Maximum der inneren Reibung von Korngrenzen (Kě -peak) in hoch-reinem Aluminium (99,991 und 99,999 Gem.%)-Einkristallen, die nach verschiedenen Verfahren hergestellt werden, nicht auftritt. Dies zeigt schlüssig, daß der Kě -peak von den Korngrenzen im Aluminium herrührt. Im Falle von Aluminium(99,991 und 99,999 Gew.%)-Einkristallen, die mit der dynamischen Temperungsmethode behandelt werden, wird ein Maximum der inneren Reibung erstmalig bel einer Temperatur beobachtet, die etwa 75 ° C höher als die des Korngrenzenmaxi-mums ist, wenn die Schwingungsfrequenz etwa 1 Hz betragt. Dieses neue Maximum der inneren Reibung tritt nicht in Aluminium(99,999 Gew.%)-Einkristallen auf, die mit dem Zonenschmelz-verfahren gezüchtet werden. Das Maximum scheint von dem Klettern disprrsiver Versetzungen in Aluminium zu stammen.

The Effect of Microstructure on the X-Ray Integrated Intensity of High Purity Aluminium Single Crystals

The Effect of Microstructure on the X-Ray Integrated Intensity of High Purity Aluminium Single Crystals

Annealing Kinetics of Vacancies in Aluminum Single Crystals with Low Dislocation Density

Supersaturated vacancies were introduced in high purity aluminum single crystals with comparatively low dislocation densities by air-cooling from temperatures between 300°C and 400°C, and their decays during aging at 50°C were studied by means of the electrical resistance measurement. The S-shaped decay profile was observed clearly when the initial concentration of vacancies is low. The profile was explained by the clustering of vacancies, and the process is describable by a model which takes into account the association and dissociation of small vacancy clusters containing vacancies less than ten and their growth to larger clusters.

Anisotropy of the Apparent Resistivity in High-Purity Aluminium Single Crystals in Longitudinal Magnetic Fields

The longitudinal magnetoresistance of high-purity aluminium single crystals has been measured by point-contact four-probe method at 4.2 K in the magnetic fields up to 4 T. Squeezing effect of a current is recognized in all specimens, and anisotropy of the squeezing effect, which is induced by magnetic breakdown, is observed in specimens having specific orientations. The saturation values of the longitudinal magnetoresistance at 4.2 K along the principal axes [001], [111] and [011] are obtained as 0.36,0.8 and 1.1, respectively.

Preparation Method of High Purity Aluminum Single Crystals with Low Dislocation Density

The preparation method of high purity aluminum single crystal with low dislocation density has been investigated.The single crystals with dislocation dislocation density 5×102/cm2 have been obtained by the strain-anneal technique using the cooling rate changing method under vacuum. The densities and the Burgers vectors of dislocations were examined by X-ray projection topographs. The temperature range to be cooled very slowly has been determined by calculating the excess vacancy concentration and supersaturation in the specimens. The most optimum condition to obtain single crystals with low dislocation densities is obtained, if the specimens are cooled very slowly between 400°C and 150°C.

Unusual slip systems on high purity aluminium single-crystals

Unusual slip systems on high purity aluminium single-crystals

Positron lifetimes in voids and other defects in annealed, neutron-irradiated aluminum

Positron lifetimes were measured in neutron-irradiated high-purity aluminum single crystals, and companion small-angle x-ray scattering experiments were performed to determine the radius of gyration and volume fraction of radiation-induced voids. The lifetime data are consistent with a model in which positrons are trapped both in voids and in other defects which are tentatively identified as vacancy clusters bound to transmutation-produced silicon. The lifetime in the latter defects increased from 230 to 430 ps as the voids annealed out (around 306/sup 0/C), suggesting that the clusters grow in size as voids disappear. The lifetime in voids remained constant at (550 +- 30) ps.

Anisotropy of Anomalous Longitudinal Magnetoresistance in High-Purity Aluminium Single Crystals

Longitudinal magnetoresistance was measured in high-purity aluminium single crystals by point-contact four-probe method. Anomalous longitudinal magnetoresistance depending on the crystallographic orientations of a specimen was observed. This anisotropy is explained by the appearance of open orbits induced by magnetic breakdown.

Annealing studies of voids in neutron-irradiated aluminium single crystals by positron annihilation

Abstract Positron lifetimes and the angular correlation of annihilation radiation in neutron-irradiated high-purity aluminium single crystals have been measured, and companion small angle X-ray scattering experiments made to determine the radius of gyration and volume fraction of radiation-induced voids. The lifetime data are consistent with a model in which positrons are trapped both in voids and in other defects which are tentatively identified as vacancy clusters bound to transmutation-produced silicon. The lifetime in the latter defects increased from 230 to 430 psec as the voids annealed out (around 306°C), suggesting that the clusters grow in size as voids disappear. The lifetime in voids remained constant at (550 ± 30) psec. Angular correlation results are consistent with the lifetime results. A magnetic quenching experiment showed less than 1% positronium formation in the voids. The results support the Hodges and Stott model of a surface state for a positron in a void.

Studies of voids in neutron-irradiated aluminium single crystals: I. Small-angle X-ray scattering and transmission electron microscopy

Abstract Small-angle X-ray scattering and transmission electron microscopy experiments have been performed on high-purity (99·9999+ %) aluminium single crystals that were neutron-irradiated to a fluenoe of 1·5 × 1021 n/cm2 (>0·18MeV) at 50°C. The volume changes determined by each technique are in reasonably good agreement. Evidence for scattering effects resulting from faceting of the voids is presented. Assuming a truncated octahedral void shape, the ratios of the third to the second moment of the distribution of void sizes determined by both SAXS and TEM are in excellent agreement. The effects of isochronal annealing on the swelling have been followed to near the melting point. The annealing-out of voids was clearly seen; no evidence was found for bubble formation at elevated temperatures.

Dislocation Damping in Macrosonic Fields

The damping of high-amplitude ultrasonic waves (macrosound) in the 40 kc/sec range is observed in high-purity aluminum single crystals at room temperature and at strains above ${10}^{\ensuremath{-}4}$. At strain amplitudes between ${10}^{\ensuremath{-}4}$ and ${10}^{\ensuremath{-}3}$, the decrement ranges from 1 to 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}2}$ and levels off at \ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}2}$ for strains above ${10}^{\ensuremath{-}3}$. The dependence of decrement on irradiation time shows a rapid increase at the beginning of irradiation ($\ensuremath{\alpha}$ region), a somewhat reduced damping over a longer period of time ($\ensuremath{\beta}$ region), and another increase in damping before termination of the experiment ($\ensuremath{\gamma}$ region). The data lie by about two orders of magnitude above those from previous observations on internal friction to which the Granato-L\"ucke theory and associated concepts apply. The present experimental conditions are discussed from the viewpoint of a refined model which accounts for the irreversible changes in dislocation structures caused by macrosonic irradiation and revealed by transmission electron microscopy. Indications are given of points requiring further study.

Uber die verfestigung von aluminium einkristallen (99,99% Al) und ihre deutung

To obtain a more complete survey of the work-hardening of high purity aluminium single crystals the orientation- and temperature-dependence of work-hardening was investigated. The study of the temperature dependence was limited to two temperatures (+ 21°C and −195°C). With the measurements of stress-strain curves observations of the surface patterns and X-ray asterism were combined. The results are as follows: The orientation dependence of work-hardening as well as that of the surface patterns depends on the amount of slip in additional glide-systems. By reason of an extensive study of the asterism a model for kink-band formation can be described. This is due to a piling up of dislocations at obstacles and their stabilization by micro-slip in a second glide-system. The deformation at −195°C showed the work-hardening of easy glide to be nearly independent on temperature in contrast to the further stages of deformation. After equal shear-strains the density of slip-bands is essentially greater at the lower temperature than at the higher one but they have a finer appearance. In the easy glide-stage asterism was found to be temperature independent as well. After larger deformations it is, however, smaller at the lower temperature than at the higher one.

Effect of Growth Imperfections on the Strength of Aluminum Single Crystals

The effect of growth imperfections on the critical resolved shear stress is investigated for high-purity (99.99+%) aluminum single crystals as compared with strain-anneal crystals. An apparatus for measuring strains of the order of 0.2 μin. is described. Using etch pits as an index, the critical resolved shear stress is found to be inversely proportional to the growth imperfections for a range of etch pit density ρ of 5 to 25×104/cm2. An elastic range is demonstrated; and prior plastic deformation is found to lower Young's modulus. The results are interpreted in terms of dislocation theory.

LXXXIII. Quench hardening in aluminium single crystals

Summary A large increase in the critical shear stress of high-purity aluminium single crystals can be achieved by water quenching, instead of furnace cooling, after annealing at a high temperature. This quench-hardening effect is insensitive to purity and is present in crystals of zone-refined aluminium. It increases rapidly with increase in the quenching temperature. The fully hardened state is reached, not instantly upon quenching, but only after ageing at room temperature. Various observations suggest that while quenching strains may be partly responsible for the hardening they cannot account for the whole effect, and that quenched-in vacancies also make an important contribution.

A study of the plastic behavior of high-purity aluminum single crystals at various temperatures

The plastic properties of extended aluminum (99.996) single crystals were investigated in the temperature range 77° to 353°K. Both the critical resolved shear stress and coefficient of shear hardening were found to increase with a decrease in temperature, and were consistent with the Schmid law of critical shear stress governing the initiation of the slip process. Measurements were also made on the density of slip bands, which was found to increase with decreasing temperature in a manner similar to the shear hardening coefficient. Some observations were made on the appearance of slip bands on etched and unetched electrolytically polished surfaces, and on the general complexity of the slip process.