Investigations on the Microstructure Evolution of Submicrocrystalline Metals Obtained by the Severe Plastic Deformation Method: A Review

Currently, submicrocrystalline (SMC) metals and alloys obtained using severe plastic deformation (SPD) techniques are of increasing interest to researchers. In the present work, we focus on the study of materials with a disorientation spectrum dominated by large-angle grain boundaries, i.e., not microfragmented, but nano-and micrograin materials-SMC materials in our terminology. The fundamental importance of the dominance of the high-angle grain boundaries (HAGBs) in the spectrum of grain-boundary disorientations is due to the exceptional role they play in the formation of the unique properties of SMC materials. As it will be shown in this paper, a special property of the HAGBs (in contrast to low-angle grain boundaries) is their ability to transition to a nonequilibrium state during SPD and to maintain this state for a certain time after deformation, which is the cause of many, if not all, special physical and mechanical properties of SMC materials.