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The residual lattice strain, the crystallite size, the components of Gaussian and Cauchy functions of the X-ray line profile, determined by the Fourier analysis, are correlated for a better understanding of microstructural characteristics of a coarse and fine Y−Ba−Cu−O powder after explosive consolidation. The results are discussed taking into account the lattice defects generation, in particular, the twin formation in different crystallographic directions after shock loading.

The residual lattice strain, the crystallite size, the components of Gaussian and Gauchy functions of the line profile, determined by Fourier analysis, are correlated for a better understanding of recovery and recrystallization phenomena of Cu annealed after fast and conventional deformations. The density and distribution of the dislocations in the deformed starting material strongly influence the mechanisms of intermediate and high-temperature recovery as well as those of primary recrystallization.

The residual lattice strain and the crystalline size determined by Fourier analysis were measured for a better understanding of the mechanical properties of an ultralightweight metal matrix composite. An oriented SiC whisker reinforced aluminum alloy composite was examined. The microstructural characteristics were evaluated along different directions. Microhardness tests were carried out and correlated with the distribution and density of the microstructural defects.

Among all the solidification processings available for metal matrix composite (MMC) fabrication, the gas pressure liquid infiltration method, recently developed, is very simple and fast. The molten aluminum can be infiltrated either in a preform made up of a three-dimensional array of fibers (SiC whiskers), or in a porous ceramic network. The resulting microstructures present rather low dislocation densities and, short solidification times can avoid interface phase formation. A series of samples with different orientations and volume fractions of the reinforcement, i.e. with different porosity, were examined in order to investigate the reinforcing phase and convection effects on the nucleation and growth of the solid nuclei in the constrained environment existing between the preform fibers.

Eutectic structures of AgCu mixtures (71.90 wt% Ag) after melting and solidification in microgravity and on earth have been investigated by Barbieri and Patuelli. Results demonstrate morphological differences between rod-like and lamellar structures in specimens melted and solidified in μ-g and l-g. Spherical, rod-like and lamellar morphologies are also known in block copolymers, the molecules of which consist of lengths of two immiscible polymers attached to each other. We propose that in the absence of attachment between the components of the block copolymers, i.e. in blends (alloys) of the two polymers, the same morphological structures should be observed. In practice, in samples prepared on earth, the three characteristic morphologies are not observed. We suggest that phase separation in microgravity should lead to one or other characteristic morphology and that the observed morphology should correspond to a minimum surface area for the relative volume fractions of the two phases. We are therefore undertaking a series of experiments on polymeric and metallic mixtures to determine if the universality of the principle of minimization of interfacial area determines morphologies in systems not subject to interferences by factors involving gravitational effects.

In a previous model [1] the interfacial free energy of a flat solid‐liquid interface is influenced by gravity, that is the energy decreases when gravity decreases and it increases as gravity increases. In this paper the interfacial free energy gravity variations of inorganic(titanium) and organic(succinonitrile) are considered. The model also takes into account the effects of residual accelerations which may be present in space missions.

The structure and substructure changes in Al and dispersion-hardened Al alloy are studied after rapid deformation by explosion and slow conventional deformation (cross-rolling and compression) using X-ray diffraction analysis and transmission electron microscopy. Shock wave deformation generates a small dislocation density which does not produce any significant change in the microstructure as well as in the texture of Al and Al alloy containing a different concentration of Al2O3 particles (4 and 7%). After slow conventional deformation, in particular after cross-rolling, significant variations are observed due to the nonuniformly distributed high dislocation densities.

The aim of this paper is to evaluate the effect of high gravity on the solid-liquid interfacial free energy per unit area, σSL, of face-centered cubic metals. There is considerable ambiguity about the location of the solid-melt interface on an atomic scale. The atoms in the melt have a packing that is not too different from the corresponding solid and the densities of the two phases are comparable. Moving from solid to liquid through the interface, a region of gradual transition from solid to liquid is expected.1 It is reasonable to assume that the interfacial free energy per unit area may be due to the melt region considering that for a diffuse interface σSL is zero.2

The crystallite size, the residual lattice strain, the components of Gaussian and Cauchy functions of the line profiles obtained by Fourier analysis of X-diffraction lines, are correlated for a better knowledge of mechanical properties of infiltrated composites with ceramic reinforcements of different volume fractions (27, 19, 10%) and types (SiC whiskers, Al2O3 fibers and particles) after fast and slow deformation. The results are discussed taking into account the role of the reinforcing phase on the generation and relocation of dislocations along different crystallographic directions (111,200,220).

The solid-liquid interfacial free energy per unit area of a flat interface has been found to increase with decreases of temperature.

Some considerations are developed regarding possible effects of reduced gravity on liquid-solid interfacial free energies per unit area at constant temperature.

A comparison between the effects of slow and rapid deformation, shows that compression by explosion in Al and in Mg favours recovery-type rearrangement of dislocations into grain boundaries, with subsequent reductions of the long range internal stresses. Twins introduced in Zn by compression do not represent sites favourable for such rearrangement of the dislocations. Further in the deformation of Zn by explosion, twins do not contribute to glide, contrary to the behaviour in slow compression which is strongly conditioned by glide in the twinned zones.

Repeated load impulses added to constant load in creep tests lead to large fracture elongations. The phenomenon is interpreted by assuming that impulses activate new dislocation sources. In this way smaller plastic instabilites are obtained because of the more uniform deformation. The strain responses to the sudden stress increases are consistent with the existence of two high and low dislocation mobility stages. The abrupt deformations occurring during the load impulses are indicative of the high mobility one. Zusatzlich zur konstanten Belastung wahrend des Dauerstandversuchs angelegte wiederholte Belastungsimpulse fuhren zu grosen Verzogerungen des Bruchs. Diese Erscheinung wird durch die Annahme erklart, das die Impulse neue Versetzungsquellen aktivieren; auf diese Weise werden durch die gleichformigere Deformation kleinere plastische Instabilitaten erhalten. Die Dehnungs-response auf einen plotzlichen Spannungsanstieg ist mit der Existenz von zwei Zustanden mit hoher und niedriger Versetzungsbeweglichkeit konsistent; die plotzlichen Deformationen wahrend den Belastungsimpulsen zeigen den hochbeweglichen an.

Results obtained on a eutectic alloy of Ag-Cu after melting and solidification in μ-g are reported. In microgravity the specimens show a regular eutectic structure both lamellar and rod-like shaped and a dendritic one with random orientations and volume fraction higher than l-g. On earth, instead, they exhibit an irregular eutectic structure, almost completely lamellar and a dendritic one with preferential orientations. These differences are consistent with a considerable reduction of convection in the specimens treated in μ-g.

EBIC contrast in correspondence of the etch-pit rows from room temperature microhardness indentations and from polishing scratches are examined with and without successive mechanical and/or thermal treatments. According to the observations clean dislocations show no contrast, contaminated dislocations show contrast which may be treated by assuming suitable boundary conditions consistent with the existence of space charge cylinders around the dislocations. Contrast bands observed in correspondence of etch-pit rows after suitable treatments are related to point defects introduced together with the dislocations. Relative contrast of screw and edge character dislocations is deduced from the different visibility of half-loop arms. EBIC-Kontrast der Atzgrubenreihen von Zimmertemperatur-Mikroharteeindrucken und von Polierkratzern werden mit und ohne aufeinanderfolgende mechanische und/oder thermische Nachbehandlungen untersucht. Nach den Beobachtungen zeigen reine Versetzungen keinen Kontrast, kontaminierte Versetzungen zeigen Kontrast, der mit der Annahme geeigneter Randbedingungen konsistent mit der Existenz von Raumladungszylindern um die Versetzung behandelt werden kann. Kontrastbander, die in den Atzgrubenreihen nach geeigneten Behandlungen beobachtet werden, lassen sich Punktdefekten zuordnen, die zusammen mit den Versetzungen eingefuhrt werden. Der relative Kontrast der Versetzungen mit Schrauben- und Stufencharakter wird aus der unterschiedlichen Sichtbarkeit von Halbschleifenarmen abgeleitet.

Internal friction and dynamic modulus measurements are carried out on amorphous electross deposited NiB and NiP alloys with different metalloid concentration from room temperature up to the starting temperature of the crystallization processes. In this temperature range, characterized by “structural relaxation” one or two anelastic peaks depending on the alloy composition are observed. The influence of annealing and quenching on these peaks is studied together with the evaluation of the activation energies and of the relaxation times. Some possible elementary mechanisms at the origin of these peaks are discussed, also in connection with models recently proposed to explain the nature of the anelastic and magnetic relaxation peaks observed by other author, in the same temperaure range, on different amorphous alloys obtained with other techniques. The correlation of the peaks observed with the structural relaxation processes is also examined. Messungen der inneren Reibung und des Elastizitatsmoduls werden an amorphen elektrolos aufgebrachten NiB- und NiP-Legierungen mit unterschiedlicher Metalloidkonzentration im Bereich von Zimmertemperatur bis zur Einsatztemperatur des Kristallisationsprozesses durchgefuhrt. In diesem Temperaturbereich, der durch „Strukturrelaxation” gekennzeichnet ist, werden ein oder zwei anelastische Maxima in Abhangigkeit von der Zusammensetzung beobachtet. Der Einflus von Temperung und Abschreckung auf diese Maxima werden untersucht und die Aktivierungsenergien und Relaxationszeiten bestimmt. Einige mogliche elementare Mechanismen uber die Ursache dieser Maxima werden diskutiert auch im Zusammenhang mit kurzlich vorgeschlagenen Modellen zur Erklarung der anelastischen und magnetischen Relaxationsmaxima, die von anderen Autoren im gleichen Temperaturbereich an verschiedenen amorphen Legierungen mittels anderen Techniken beobachtet werden. Die Verknupfung der beobachteten Maxima mit den strukturellen Relaxationsprozessen wird ebenfalls untersucht.

Results of melting and solidification experiments in μ-g of sintered aluminum powder alloys (with 4 pct and 7 pct of A12O3) are presented. Thin oxide films have been used as tight containers which remain adherent during melting and solidification. Convective motion in melted metals in μ-g are indicated from observations of the oxide particle distribution after melting and solidification. Effects of Marangoni convection are always observed in relatively large cylindrical samples, 5 mm diameters, melted and solidified in μ-g. Thin disc-shaped samples do not present evidence of convective motions in μ-g. Even in the absence of convective motion in the thin samples, some particle aggregation occurs, depending on the interactions with the solidification front and conditioned by diffusion controlled critical radii for capture in the solid.

Comparative observations were carried out on the plastic deformation characteristics of cold-rolled and recrystallized S.A.P. sheets, particular attention being given to the apparent and true activation volumes and energies. The higher flow stresses of the cold-rolled specimens are interpreted on the basis of a dislocation sink and emission model, by assuming that the sink rate is conditioned by the dislocation tangles pinned against the grain boundaries. Recrystallized sheet strength and dislocation emission processes are discussed in terms of conservative climb and backstresses due to dislocations pinned by the oxide particles.

Comparative examinations have been carried out on Al and ERGAL specimens deformed by compression either fast or slow. The high-strain-rate compressions were obtained by explosive. The dislocation structures have been examined by transmission electron microscopy and by Fourier analysis of the X-ray diffraction lines. Crystalline textures were also determined. After fast deformation smaller interaction energies appear among the dislocations with comparable total densities because of the accumulation in grain boundaries. The results have been interpreted by assuming that the loads which are reached in the shock and reflected wave fronts give rise to generations or multiplications of the dislocations on levels more differentiated than by slow compression.