Effects of Interstitial and Substitutional Alloying on Dislocation Structures and Mechanical Properties of Refractory Metals.

Mechanical testing in tension and compression has been done on single crystals of tantalum and tantalum-base interstitial and substitutional solid solutions involving a wide range of crystallographic orientations. These experiments were complemented by analyses of slip lines and dislocation structures by optical and high voltage electron microscopy, respectively. The research has established many aspects of the relative roles of the Peierls stress of extended screw dislocations and solution hardening in determining the low temperature strength of body-centered cubic materials. The major findings include (a) establishing the importance of the normal stress on low temperature strength of bcc materials; (b) determination of the large effects of solutes on the orientation dependence of yielding, the stress differential in tension and compression, slip and twin systems, and primary screw dislocation structure, distribution, density and cross glide; and (c) determination that the widths of extended screw dislocations in bcc materials are very small.