SPD techniques work by imposing severe plastic strains on the material without significantly changing its overall dimensions. For instance, in [Equal-Channel Angular Pressing (ECAP)](), the material is pressed through a die with two intersecting channels of equal cross-section, causing intense shear strain that refines the grain structure. In [High-Pressure Torsion (HPT)](), a sample is subjected to high pressure while being twisted, leading to grain refinement through the severe shear deformation.
