Showing papers by "Mines ParisTech published in 1972"

Martensitic transformations induced by plastic deformation in the Fe-Ni-Cr-C system

Abstract: Martensitic transformations induced by plastic deformation are studied comparatively in various alloys of three types: Fe-30 pct Ni, Fe-20 pct Ni-7 pct Cr, and Fe-16 pet Cr-13 pct Ni, with carbon content up to 0.3 pct. For all these alloys the tensile properties vary rapidly with temperature, but there are large differences in the value of the temperature rangeM s toM d, which strongly increases with substitution of chromium for nickel or with carbon addition. Using the node method, it is found that the intrinsic stacking fault energy in the austenite drastically increases with temperature in all the chromium-bearing alloys investigated. This variation is consistent with the observed influence of temperature on the appearance of twinning or e martensite during plastic deformation. Very different α’ martensite morphologies can result from spontaneous and plastic deformation induced transformations, especially in Fe-20 pct Ni-7 pct Cr-type alloys where platelike and lath martensites are respectively observed. As in the case of e martensite, the nucleation process is analyzed as a deformation mode of the material, using a dislocation model. It is then possible to account for the morphology of plastic deformation induced α’ martensite in both Fe-20 pct Ni-7 pct Cr and Fe-16 pct Cr-13 pct Ni types alloys and for the largeM s toM d range in these alloys.

Structure and high temperature mechanical behavior of Ni-Ni3Nb unidirectional eutectic

Abstract: The structure and mechanical behavior of directionally solidified Ni-Ni3Nb eutectic have been investigated. The lamellar eutectic grows with the Ni-Ni3Nb interface semicoherent and, within experimental error, parallel to close-packed planes in both phases. When the temperature is lowered, supersaturation in the nickel-rich phase is relieved mostly by precipitation. Mechanical twinning is the typical deformation mode of the Ni3Nb phase and is also observed in the nickel phase between 700∮ and 1000°. The unusually high ductility of the regular structure below 600° is related to the high strain hardening rate due to mechanical twinning of the intermetallic and the difficulty of crack propagation.

Resistivite d'un niobium de haute purete de 20 °k a la temperature de fusion

Abstract: Resume Nous presentons les resultats d'une etude de la resistivite electrique d'echantillons de diverses provenances. Le degazage sous ultravide a permis d'obtenir des echantillons de grande purete. Particulierement, l'echantillon le plus pur a un rapport R 273,15 ° R 20,25 ° de 213; il a permis des mesures tres fines aux basses temperatures. La comparaison des echantillons dans toute l'echelle de temperature est permise par application de la regle de Matthiessen a 77,35 °K et 273,15 °K, la resistivite d'un echantillon de gros diametre servant de base. La regle de Matthiessen a ete verifiee de 63 °K a 300 ° K. Les resultats rapportes a l'echantillon le plus pur sont proposes: ils sont inferieurs a ceux trouves dans la litterature. Au-dela de 1500 ° K, la courbe de resistivite presente une courbure prononcee qui n'avait jamais ete signalee.

Limits of application for Wagner's oxidation theory

Abstract: The main quantitative results from Wagner's oxidation theory are recalled while the conditions of application of that theory are reviewed from the point of view of oxidation kinetics like those of chromium, zinc, and iron Bibliographical results on cobalt and copper oxidation and on cobaltous and cuprous oxides are quantitatively compared to Wagner's theory In the same, the validity of the cation self-diffusion coefficient determination by the parabolic constant is considered Finally, the modification of a rate equation to take a surface reaction into account is discussed

Influence de variations de température sur le comportement à l'oxydation du zirconium. Comparaison avec le cas du cobalt

Abstract: Des variations de temperature effectuees au cours de l'oxydation d'un metal ont un effet different sur la cinetique d'oxydation, selon le metal considere. Cette influence est discutee dans le cas du zirconium et comparee a celle observee dans le cas du cobalt, ces deux metaux se comportant d'une manie're differente. En effet, une diminution brutale de la temperature au cours de l'oxydation du zirconium entraine une acceleration marquee de l'oxydation. Par contre, dans le cas du cobalt, une telle variation de temperature a une influence negligeable sur la vitesse ulterieure de l'oxydation. Ces resultats sont discutes en termes de plasticite relative de l'oxyde et du metal.

Mathematical Models for Hydrologic Processes

Abstract: Models of simulation of groundwater flow in sedimentary basins are generally used for water-resources optimization problems; however, a byproduct of their building may be additional information on the structure of the basins themselves.