APPLICATION OF THE CURRENT NOISE TECHNIQUE TO THE INVESTIGATION ON DISLOCATIONS IN METALS DURING PLASTIC-DEFORMATION

A current noise due to dislocation processes in aluminum film samples has been put in evidence during plastic deformation. Burst-type dislocation generation and annihilation processes have been observed, showing the discontinuous character of plastic flow and the presence of strong correlation effects on dislocation dynamics. Noise behavior shows a strong enhancement of the dislocation generation and annihilation events with increasing temperature, a fact which accounts for the material softening at high temperature. The stress-strain behavior of the metal film upon cyclic deformation is obtained from the noise results; in particular it is possible to detect the very beginning of plastic deformation of the metal and the temperature dependence of the elastic limit. The behavior of the dislocation density during cycling can also be obtained. Such a behavior of the dislocation density during cycling can also be obtained. Such a behavior is accounted for by a theoretical model where the competing effects of generation and annihilation of dislocations are evidenced through a balance equation. It can be concluded that current noise yields more detailed information on plastic deformation than usual acoustic noise emission methods and can be easily applied to nondestructive mechanical testing of integrated circuits metallizations.