1.6 Production of atomic defects in metals by plastic deformation
This chapter discusses production of atomic defects in metals by plastic deformation. Annealing experiments indicate that vacancies and, to a lesser extent, interstitials are formed in metals during plastic deformation. To retain interstitials, the deformation must be performed near liquid helium temperature. The resistivity increase during plastic deformation (tensile or cold rolling) at temperatures below 78 K was found to depend nonlinearly on plastic strain. The parameters, A and a, describing the resistivity increase per plastic strain at various temperatures are tabulated. In an investigation on Cu single crystals at 4.2 K, a relation between resistivity increase and flow stress was observed. The results of several investigations indicate that the resistivity increase during low temperature plastic deformation is about half due to an increase in dislocation density and half due to the production of vacancies, while the contribution of interstitials is in the few percent range. The poor reproducibility of plastic deformation, the uncertainty about the underlying processes and the fact that other defects such as point defect clusters and dislocations are formed have prevented a more quantitative evaluation of these experiments in terms of point defect production. Recent investigations by PAS and thermal helium desorption spectroscopy (THDS) confirmed that predominantly vacancy defects are formed during plastic deformation, but have not given reliable, quantitative results on defect production.