“…Recently, several processing techniques existing metal forming processes have been designed such as continuous cyclic bending (CCB), twist extrusion (TE), equal channel angular pressing (ECAP), and so on. New techniques are often proposed, all of them rely on the idea that a high hydrostatic pressure is necessary to avoid cracking, for a review see [16][17][18][19][20][21][22][23][24][25]. Among these SPD methods, the HPT process is particularly noteworthy because it can produce finer grains, with a higher fraction of high-angle grain boundaries, than can the other SPD methods [5,8,[26][27][28][29].…”