In Situ NMR Study of Dislocation Jump Distance During Creep of Pure Sodium Chloride Single Crystals

Nuclear magnetic resonance pulse techniques were used in situ during creep of single crystals of NaCl to evaluate the contribution of mobile dislocations to spin relaxation. ²³ Na spin‐lattice relaxation rates were measured in the rotating frame ( T _1p ) during compression creep of single crystals of NaCl along the [110] direction at 473 K at an applied stress of 20 MPa. The relaxation rates were evaluated from the spin‐echo height following π/2, locking, and 64° pulse sequence. We describe here the experimental setup and methodology in evaluating the dislocation jump distance from NMR‐creep experiments. The height of the free induction decay decreased as soon as the load was applied followed by a gradual increase until the steady state was reached, at which point a saturation value was observed corresponding to the constant steady‐state creep rate. The mean jump distance of the mobile dislocations, evaluated from the ratio of the signal heights without deformation and during creep, decreased with time/strain, reaching a constant value during the steady‐state creep regime. The results are compared with the dislocation‐dislocation spacing, subgrain size, as well as the jump distance predicted from creep models.