Dislocation dynamics in vanadium: A nuclear magnetic resonance and transmission electron microscopic study

Pulsed nuclear magnetic resonance proved to be a complementary new technique for the study of moving dislocations in b.c.c. metals. From the motion induced part of the spin-lattice relaxation rate the mean jump distance of mobile dislocations has been measured in Vanadium as a function of temperature. The NMR experiments are combined with transmission electron microscopic investigations to reveal the static structure of defects in the samples. The NMR experiments show that the mean jump distance is nearly constant below 230 K whereas it decreases substantially above 230 to 300 K indicating a transition that marks two different mechanisms. NMR observations in combination with TEM support the physical picture that above the transition temperature dislocation segments are stopped between localized obstacles whereas below T c the lattice friction controls the plastic behaviour.