The influence of modulation period on the microstructure and mechanical behavior of Al/Al2O3 nano-multilayers films

A series of Al/Al₂O₃ nano-multilayers with different modulation periods are prepared using magnetron sputtering method. The microstructure and mechanical property of multilayer films with different modulation periods are studied. The deformation mechanism is revealed. The results show that the Al layer in the multilayer film exhibited columnar crystal growth with a diameter of about 50 nm, while the Al₂O₃ layer had a distinct amorphous structure. As the modulation period is above 20 nm, the hardness of the multilayer film increases with the decrease of the modulation period, which conforms to the Hall-Petch relationship. When the modulation period is further reduced to 10 nm, the hardness shows a reverse Hall-Petch phenomenon of decrease. The toughness of multilayer films increases with the decrease of modulation period. As the modulation period decreases, the deformation behavior of the multilayer film changes from cracking of the Al₂O₃ layer combined with deformation of the Al layer to synergistic plastic deformation of the Al₂O₃ layer and Al layer. This transformation is the result of the competition between the interface stress affected zone (ISAZ) and the total shear stress ${\tau }_{\mathrm{tol}}$ applied to the Al₂O₃ layer.