Dislocation Dynamics In B.C.C. Metals: A Nuclear Magnetic Resonance and Transmission Electron Microscopic Study

Abstract

ABSTRACTPulsed 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 dislocationshas 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 K to 300 K indicating a transition that marks two different mechanisms. NMR observations in combination with TEM support the physical picture that above that transition temperature dislocation segments are stopped between localized obstacles whereas below Tc the latticefriction controls the plastic behaviour.