Theory of the tensile ductile-brittle behavior of poly-crystalline h.c.p. materials, with application to beryllium

Abstract A number of the h.c.p. metals, such as beryllium, are similar to other potentially brittle materials, most notably, steel, in that they all show in a certain range of temperature an abrupt change in ductility. In the h.c.p. case, the transition in behavior is reasonably sensitive to the polycrystal grain size. In the present study, an explanation is given for this dependence and for other variations in the ductile-brittle behavior in terms of the theory and experiments underlying the (Hall-Petch) stress-grain size equations. The theory for the behavioral change is connected in an important way with critical resolved shear stress measurements for various deformation systems in single crystals.