Dynamic stored energy gradient induced oriented growth of subgrains in rapidly hot-extruded tungsten heavy alloys

Highly oriented lath-like subgrains decorated by numerous dislocation tangles and dislocation-free irregular grains were observed to prevail in a heavily hot-extruded fine-grained 93 W-4.9Ni-2.1Fe (wt.%) alloy. Except for such lath-like subgrains, there were also a considerable number of equiaxed strain-free grains visible in an extruded coarse-grained 93 W-4.9Ni-2.1Fe alloy. A mechanism in terms of a new concept designated as dynamic stored energy gradient was proposed to illustrate the formation of the lath-like subgrains that were actually created in extremely short time (only around 0.3 s) during hot extrusion. Due to the limited extrusion time, thermally activated diffusion of tungsten atoms was unlikely to play a decisive role in this process. It is found that there has been a significant driving force gradient at the growth front of the subgrains, which is believed to substantially promote directional annihilation of edge dislocation dipoles to develop the lath-shaped configuration of the subgrains in the extruded alloys. (C) 2013 Elsevier Ltd. All rights reserved.