Slip character and the ductile to brittle transition of single-phase solids

A transition from brittle to ductile behaviour of single-phase polycrystals is shown experimentally to be a consequence of a change in slip character rather than of a change in yield stress. In the case of a b.c.c. Fe-Co alloy, deformation by planar glide induces brittleness, whereas the alloy is ductile if it deforms exclusively by wavy glide. For a series of copper-base solid solutions loaded in mercury, the degree of embrittlement increases with planarity of glide. The Cottrell-Petch equation can account for such behaviour provided the appropriate parameter, k y, is re-considered in terms of the number of operable slip systems and the propensity for cross slip.