“…Several fabrication methods have been introduced to offer various heterogeneous structured materials with balanced strength and ductility, such as the gradient structure produced by surface mechanical attrition [ 11 , 12 , 13 ], the hetero-lamellar structure produced by cold rolling and annealing [ 2 , 14 , 15 ], and the harmonic structure produced by powder metallurgy [ 16 , 17 , 18 , 19 , 20 ]. Mechanical milling, a metallurgy technique, has been applied for microstructure modification [ 21 , 22 ].…”