THE RECOVERY OF THE ULTRASONIC ATTENUATION IN COPPER SINGLE CRYSTALS FOLLOWING SMALL PLASTIC DEFORMATION.
WATERVLIET ARSENAL N Y BENET LABS
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Copper single crystals of 99.9 purity were deformed about .5 in tension at temperatures in the range 332.5 to 368K. The ultrasonic attenuation was measured continuously after deformation at a frequency of about 17Mc. During the measurement the specimen was in the load-off condition and at the deformation temperature. It is found by use of the Granato, Hikata and Lucke recovery theory, that the Cottrell-Bilby t23 strain aging law is obeyed in the recovery of the ultrasonic attenuation. In most cases the use of an incubation time is required which differentiates between the time the deformation stopped and the time at which the t23 law seems to take effect. The recovery parameters for the three low temperature runs plotted against 1kT yield 1.0 plus or minus 0.2 ev as the activation energy for migration of the deformation-formed defect. The defect is therefore identified as the vacancy. It was possible to determine the approximate time after deformation stopped for which the pinning point density on the dislocations is a maximum. These times can be correlated with the times obtained by Birnbaums low temperature strain-aging technique. Author
- Metallurgy and Metallography