Dislocation Dynamics in Deformed Tantalum
I. M. Robertson,* B. Lagow
Lawrence Livermore National Laboratory

High-purity group Va and VIa metals exhibit the so-called anomalous slip behavior at low temperatures (e.g., € K in Nb and 77 K in Ta). To understand this transition in deformation behavior, samples of high-purity tantalum will be deformed in situ in the transmission electron microscope as a function of temperature. Such studies will also yield direct information on the relative mobilities of edge and screw dislocations and their interactions with each other and with other obstacles as a function of temperature.

Interfacial Dynamics during Heterogeneous Deformation
I. M. Robertson,* L. Pawlowski
Battelle Northwest Laboratory

The techniques of in situ TEM deformation and hot-stage microscopy are being used to study the interaction of dislocations with grain boundaries, the operation of grain boundary dislocation sources, and the interaction of mobile grain boundaries with obstacles such as precipitates. These studies are being undertaken to provide an understanding of the physical processes controlling grain boundary cavitation, grain boundary sliding, grain boundary dislocation interactions, and grain nucleation at precipitates.