Abstract: Based on the equal channel angular pressing(ECAP), why there is considerable difference between different metals in evolution of fine grained microstructure under same process conditions is investigated. Influences of lattice structures and stacking fault energy(SFE) on the mechanism of grain refinement and ultra-fine or nano-structured grains plastic deformation are put forward in severe shear deformation during ECAP. Experiments are conduced on face-centered cubic lattice pure copper with medium-low SFE, and body-centered cubic lattice medium carbon steel with medium-high SFE. Room-temperature pressing process and route Bc are adopted. Experimental results indicate that in bcc metal with medium-high SFE the formation of ultra-fine and nano-structured grains are caused by dislocation slip and intercross slip and in fcc metal with medium-low SFE the formation of ultra-fine grains is caused by dislocation slip plus twinning during severe shear deformation in ECAP process. The higher the stacking fault energy of metal is, the greater the effect of intercross dislocation slip, the quicker the speed of grain-refining will be during severe shear deforming. The homogeneous high angle boundary ultra-fine grains can be achieved in the steel through four passes and in the copper through eight passes by ECAP.

Key words: Equal-channel angular pressing (ECAP), Grain-refining, Severe shear deformation, Stacking fault energy (SFE), Ultra-fine grains(UFG)