EXPERIMENTAL MANIFESTATIONS OF THE LATTICE RESISTANCE STRESS IN ALUMINUM

The Bordoni relaxation in f.c.c. metals is generally attributed to the thermally activated nucleation of double kinks. From the peak features, the value σp of the Peierls-Nabarro (PN) stress can be obtained (ranging between 10-3 and 10-4 G, G being the shear modulus). Nevertheless, the studies of macroscopic plastic behaviour show that the macroplasticity of f.c.c. metals is not controlled by the existence of the PN stress. In fact, recent experimental results obtained in aluminium show that, in the temperature range of the Bordoni relaxation, the first dislocation motion is controlled by the existence of the PN stress. These results are the following: 1. (i) a thermally activated microdeformation stage takes place; 2. (ii) an important variation of the anelastic limit is observed, as a function of T; 3. (iii) the ultrasonic attenuation decreases with increasing bias stress ('stiffening' phenomenon); 4. (iv) at higher stresses, the attenuation increases with increasing bias stress and temperature ('softening' phenomenon). All these results, can be explained only by the existence of the PN stress in aluminium. © 1979.