“…Although submicron grained materials can be successfully produced by most SPD processes, NC materials are obtained only by nonhomogeneous deformation processes with large strain gradients [12][13][14][15][16][17][18][19]. The basis of the SPD method is to increase the free energy of the polycrystals and generate much more defects and interfaces (grain boundaries) in various nonequilibrium processes such as high-pressure torsion [6,8,[20][21][22][23], ball milling [24][25][26][27][28][29][30][31][32][33][34][35], sliding wear [36,37], drilling [38][39][40][41][42], shot blasting and annealing [43][44][45][46], ultrasonic shot peening [15,[47][48][49][50][51][52] and air blast shot peening [16,17,…”