The flow strength anomaly in metals and intermetallic compounds

In most materials, the flow strength due to plastic deformation decreases monotonically as a function of increasing temperature due to the influence of thermal activation on dislocation motion. However, there are a number of interesting and technologically-important exceptions to this general trend. For instance, berylium, a hexagonal close packed metal, exhibits an increase in the yield strength with temperature when single crystals are oriented for activation of prism slip. A large number of intermetallic compounds also exhibit an anomalous temperature-dependence of the flow strength, including most notably the cubic phases Ni3Al, CuZn, Cu3Au, FeAl, and the tetragonal phase TiAl. In these intermetallic compounds, the flow strength anomaly is exhibited even for polycrystalline microstructures. In most of these cases, the anomalous temperature dependence for yielding has been linked to non-planar dislocation core structure or dissociation which make simple glide of dislocations difficult. This paper is intended as a summary of the modeling and supporting microstructural observations which have been forwarded to explain these behaviors.