A Review on Severe Plastic Deformation

In the recent years much attention has been paid to the development of ultra-fine grained and nanostructured materials due to their superior properties. Several severe plastic deformation (SPD) techniques have emerged in the recent years for producing ultra fine grained materials in bulk metals and alloys. Among the various SPD techniques proposed most of the methods are intended for processing bulk materials; very few methods like Equal-channel angular pressing (ECAP),High pressure torsion (HPT)technique ,constrained groove pressing (CGP) and repetitive corrugation and straightening (RCS) are capable of processing sheet materials. The requirement of stringent surface preparation the propensity of cracking due to de-lamination of accumulative roll bonded layersand formation of edge cracks limits the application of ARB processed sheets. Meanwhile in RCS process elongation of sheets causes strain inhomogeneity. The recently invented CGP process sans above mentioned problems is considered method for producing fine grained sheet materials for structural applications .A further defining feature of SPD techniques is that the preservation of shape is achieved due to special tool geometries which prevent the free flow of material and thereby produce a significant hydrostatic pressure. The presence of a high hydrostatic pressure, in combination with large shear strains, is essential for producing high densities of crystal lattice defects, particularly dislocations, which can result in a significant refining of the grains