Matériaux nouveaux : les composites renforcés par les fibres

Cet article est un exposé général sur une nouvelle classe de matériaux : les composites renforcés par les fibres.Dans la première partie, l’auteur expose les principes théoriques qui sont à la base du développement de ces matériaux nouveaux. Ceux-ci se situent d’emblée au premier rang des matériaux modernes (à très hautes performances).Ils se basent sur une conception révolutionnaire (audacieuse) qui a toujours échoué par le passé, mais qui, aujourd’hui, peut se réaliser pratiquement.En théorie, il s’agit d’unir, dans une seule structure, deux ou plusieurs constituants individuels, dans l’espoir de retrouver dans le nouveau matériau composite les meilleures propriétés de chacun des constituants individuels sans en hériter leurs défauts.Les meilleurs composites sont, au surplus, pourvus de propriétés additionnelles nouvelles qu’aucun constituant individuel ne possède séparément. Celles-ci naissent spontanément lorsque l’association des constituants remplit bien les règles du « bon ménage ». Ce sont ces règles qui constituent les base du succès et l’auteur s’efforce de les dégager séparément.Dans la deuxième partie, on passe en revue les méthodes de fabrication qui ont été utilisées pour obtenir ces nouveaux matériaux, en insistant surtout sur les méthodes de fabrication des composites à matrices métalliques.Les méthodes de fabrication des composites par co-extrusion, développées par l’auteur, sont plus particulièrement décrites

On a model and on the mechanism of recrystallization of doped tungsten wires

The behaviour of drawn k, si and al doped tungsten wires to recrystallization, is completely different to that of other metals. The influence of the degree of deformation on the recrystallization temperature remains constant for a large increase in the amount of deformation and then suddenly increases sharply to very high temperatures for only a slight increase in the amount of deformation.Anglai

Some reflections and direct observations of imperfections in metals [a review]

On the occasion of the celebration of the 75th birthdary anniversary of one of the most prominent figures in the solid state field, it may be appropriate to stop a while and carry out an inventory of the manner in which our knowledge has evolved in this field over such a relatively short period.Anglai

Scanning Electron-microscopy of Liquid-metal Infiltration of Capillaries

The infiltration front of liquid metals (tin, lead, or copper) inside capillaries (iron, copper, or tungsten) after solidification of the infiltrant metal was examined using scanning electron microscopy. The existence of a precursor film ahead of the bulk liquid front was invariably revealed. The precursor film was seen to advance parallel to the solid walls of the capillaries, which indicates that the microscopic wetting angle of the film tends to zero. The microstructures observed at different stages indicate that the precursor film forms principally under the influence of the infiltrant vapour by a chain of elementary processes suggested to be adsorption, condensation, and surface migration of the condensed atoms on the solid walls. The vapour condensation observed in all the systems investigated is thus an important factor in the mechanism of capillary rise of liquid metals and the amount of condensation was observed to increase with increasing solubility of the solid in the liquid

The design of specific microstructures in order to obtain materials with desired properties

A new material has been prepared by a powder metallurgy process. It has been designed to exhibit good strength at both low and very high temperatures. After a critical evaluation of the most recent scientific and technological data (requirements), it was possible to formulate a `design philosophy' which then served as a basis for its preparation. The authors summarize first, the `basic philosophy' and then describe in some detail the complex structure of the material obtained with the aid of this philosophy. The paper is mainly concerned with the investigation of this complex structure. It appears to be a combination of several individual structures which were deliberately incorporated into the same material. It is then shown that the structure explains the mechanical properties of the material. As a final conclusion it is shown that powder metallurgy appears to offer high flexibility when it is necessary to synthesize desired structures in order to obtain a special behaviour in service, such as high temperature, strength, and stability.Anglai