In-situ NMR investigation of strain, temperature and strain-rate variations of deformation-induced vacancy concentration in aluminum

Critical strain to serrated flow in sold solution alloys exhibiting DSA or Portevin-LeChatelier effect is due to the strain-induced vacancy production. Nuclear magnetic resonance techniques can be used to monitor in-situ the dynamical behavior of point and line defects in materials during deformation and these techniques are nondestructive and noninvasive. New CUT-sequence pulse method allowed an accurate evaluation of the strain-enhanced vacancy diffusion and thus the excess vacancy concentration during deformation as a function of strain, strain-rate ana temperature. Due to skin effect problems in metals at high frequencies, thin foils of Al were used and experimental results correlated with models based on vacancy production through mechanical work (versus thermal jogs) while in-situ annealing of excess vacancies is noted at high, temperatures. These correlations made it feasible to obtain explicit dependencies of the strain-induced vacancy concentration on test variables such as the strain, strain-rate and temperature. These studies clearly reveal the power and utility of these NMR techniques in the determination of deformation induced vacancies in-situ in a non-invasive fashion.