UC Davis

The evolution of dislocation structure in pure Fe during equal-channel-angular pressing (ECAP) is investigated. Also, the effect of the formation of this dislocation structure on deformation and fracture behavior is examined. The results show that intensive dislocation cell blocks are present after one pass and even more after subsequent pressings. The low-energy dislocation structures (LEDS) may have changed into the high-energy dislocation structures (HEDS) in the final several pressings. The high-density array of dislocations plays a significant role in strengthening. The HEDS may cause the materials to lose work-hardening ability and show a cleavage morphology of the fracture surface. A proper subsequent annealing treatment will lead to the evolution of HEDS to LEDS while maintaining little grain growth. This change in the nature of dislocation structures allows ultrafine-grained materials to achieve an excellent combination of high strength and high ductility.