INTERNAL FRICTION AND MODULUS MEASUREMENTS IN COLD-WORKED AND ELECTRON-IRRADIATED COPPER AT LOW FREQUENCIES

Abstract

The effect of cold-work and of 3 MeV electron irradiation on the internal friction and the shear modulus of polycrystalline copper was measured at 1 Hz. The general features of the results will be briefly discussed. Figure 1a gives the decrement as a function of temperature for the undeformed sample, the sample after 7 % cold-work at 78 °K, and the annealed sample. The main structure of the curve after deformation (filled circles) is the peak P2 at about 160 °K. The peak temperature is shifted to lower values by increasing plastic deformation and can be related to the dislocation density of the samples. For temperatures above 200 °K there is no pronounced structure, several damping processes seem to increase the background without yielding well-defined peaks. In particular, we cannot resolve that relaxation process, that was interpreted to be due to the relaxation of the -split interstitial. Figure 1b gives the corresponding decrement curves for a sample irradiated with 3 MeV electrons at 100 °K up to a defect concentration of 3 x 10-7. Between 120 °K and 330 °K the difference between the irradiated and the unirradiated sample gives a very broad peak. A 10 min. anneal at 360 °K reduces the radiation-induced increase of decrement completely above 100 °K, and the curve of the unirradiated sample is reproduced. The fact that here the irradiation increases the internal friction does not fit the commonly accepted views on dislocation damping. It must be assumed that the point defects themselves or in interaction with dislocations produce this very broad peak. This smeared-out increase of internal friction due to electron irradiation is very similar to that after cold-work, as can be seen by comparing the full-circle-curves in figure 1a and 1b.