Microstructure evolution and plastic deformation of quinary Zr-Ni-Cu-Al-Co amorphous-crystalline hybrid alloy

An amorphous-crystalline hybrid microstructure was fabricated by adjusting the solidification mechanism of quinary Zr58Cu17Ni12Al11Co2 alloy. At low cooling rates below 1.2 x 104 K & sdot;s- 1, lamellar (Zr8Cu5 + Zr2Cu) eutectic growth dominated its solidification process, whereas Zr8Cu5 phase would grow independently at higher cooling rates. The critical cooling rate for amorphous transition was determined as 5 x 104 K & sdot;s- 1, beyond which the nucleation and growth of Zr8Cu5 phase were suppressed and liquid alloy transformed to amorphous phase. The compressive deformation mechanisms were modulated by such microstructure variation. Fracture analysis suggested that the tiny Zr8Cu5 grains formed in metallic glass induced the formation of multiple shear bands and thus promoted plastic deformation. Once grain size increased to 92.2 mu m, the fracture mechanism changed from intergranular fracture to transgranular fracture, which reduced the plastic deformation. The maximum plastic deformation attained 3 % at 1.2 x 104 K & sdot;s- 1 cooling rate, which was 3.5 times greater than that of pure metallic glass.