Elimination des defauts crees par laminage a tres basse temperature dans l'aluminium de haute purete

Abstract

The author has studied by electrical resistance measurements at 20.3°K the recovery of high purity aluminum deformed 97 % by rolling in liquid nitrogen and in liquid hydrogen. The increase in resistivity due to the defects is eliminated in four stages during successive isochronal anneals in the temperature range between 60 and 300°K. Each of these stages has been characterized by a temperature at which the rate of recovery is the greatest. A series of isothermal anneals at various temperatures has made it possible to study the kinetics of the combination and elimination of the defects as well as the determination of the average activation energy associated with the different recovery stages. Under the present experimental conditions, the aluminum employed recrystallizes below room temperature with an energy of activation of 0.56 ± 0.02 eV. This last stage is the only one whose position is greatly influenced by the temperature of deformation. The third and most important stage of recovery is characterized by a peak at about 190°K on the differential isochronal curves. The activation energy of the process is 0.56 ± 0.06 eV and the kinetics corresponds to that of a vanishingly small defect of infinite compressibility. This stage has been attributed to the migration of vacancies towards dislocations produced by cold working. Two peaks have been observed at about 125 and 80°K which are characterized by an average activation energy of 0.32 and 0.22 eV, respectively. The absence of a simple behavior in the recovery kinetics as well as a continuous variation in the energy of activation during these first two stages seems to suggest the superposition of several mechanisms for the elimination of point defects. A comparison between these ageing experiments at liquid nitrogen temperatures suggest that the first stages could possibly be due to the migration of interstitial defects.