The evolution of dislocation structures in pure Fe during equal-channel-angular pressing was investigated. The effect of the formation of this dislocation structure upon deformation and fracture behaviors was also examined. The results showed that intensive dislocation cell blocks were present after one pass, and even more after subsequent pressings. The low-energy dislocation structures may have changed into high-energy dislocation structures during the last few pressings. The high-density array of dislocations played a significant role in strengthening. High-energy dislocation structures could cause materials to lose their work-hardening ability and exhibit a cleavage morphology of the fracture surface. Correct subsequent annealing treatments could lead to the evolution of high-energy dislocation structures into low-energy dislocation structures, while maintaining little grain growth. This change in the nature of dislocation structures permitted ultrafine-grained materials to achieve an excellent combination of high strength and high ductility.

Dislocation Structure and Deformation in Iron Processed by Equal-Channel-Angular Pressing. B.Q.Han, E.J.Lavernia, F.A.Mohamed: Metallurgical and Materials Transactions A, 2004, 35[4], 1343-50