IN-SITU NUCLEAR-MAGNETIC-RESONANCE STUDY OF DEFECT DYNAMICS DURING DEFORMATION OF MATERIALS

Nuclear magnetic resonance techniques can be used to monitor in situ t he dynamical behaviour of point and line defects in materials during d eformation. These techniques are non-destructive and non-invasive. We report here the atomic transport, in particular the enhanced diffusion during deformation by evaluating the spin lattice relaxation time in the rotating frame, T-1p, in pure NaCl single crystals as a function o f temperature (from ambient to about 900 K) and strain-rate (to approx imate to 1.0s(-1)) in situ during deformation. The strain-induced exce ss vacancy concentration increased with the strain-rate while in situ annealing of these excess defects is noted at high temperatures. Contr ibutions due to phonons or paramagnetic impurities dominated at lower temperatures in the undeformed material. During deformation, however, the dislocation contribution became predominant at these low temperatu res. The dislocation jump distances were noted to decrease with increa se in temperature leading to a reduced contribution to the overall spi n relaxation as temperature is increased. Similar tests with an improv ed pulse sequence (CUT-sequence), performed on ultra-pure NaCl and NaF single crystals revealed slightly different results; however, strain- enhanced vacancy concentrations were observed. The applicability of th ese techniques to metallic systems will be outlined taking thin alumin ium foils as an example.