MECHANICAL PROPERTIES OF REFRACTORY METALS AND ALLOYS.

The objectives of the research on the mechanical properties of refractory metals and alloys was to relate the fundamental nature and behavior of dislocations to the observed mechanical properties. The main emphasis has been on body-centered cubic metals and most of the work has utilized single crystals. A great deal has been achieved in advancing the understanding of the relationship of the properties of dislocations to the crystal lattice and hence to the mechanical properties. The most exciting aspects of this work relate to the high yield stress of bcc metals at low temperatures. This was variously interpreted as due to the intrinsic lattice friction stress the Peierls stress and to the interaction of dislocations with interstitial impurities. The Peierls stress can be thought of in more than one way, one of which the pseudo-Peierls stress involves a relaxation of the atoms near the core of a dislocation or, in other words, a local dissociation. These ideas can be used to explain many of the peculiar observations on slip in bcc metals, including multiple slip planes and slip asymmetry. Author