Effect of partial crystallisation on mechanical properties of (Cu ₄₂Zr ₄₂Al ₈Ag ₈) _99.5Si _0.5 bulk metallic glass

The (Cu ₄₂Zr ₄₂Al ₈Ag ₈) _99.5Si _0.5 bulk metallic glass (BMG) rods, 3 mm in diameter, with different fractions of nanocrystalline phase were prepared by isothermal annealing the as cast BMG rods at the temperature within the supercooled temperature region for different time periods in vacuum respectively. The result of hardness and compression test revealed that the hardness and yield strength of compression test all exhibit an increasing trend with crystallisation fraction. The maximum 1990 MPa yield strength, 2100 MPa fracture strength and 5% failure strain occur at the 50% crystallised BMG sample (with an average size about 60 nm). This suggests that these homogeneous distributed nanocrystals embedded in the amorphous matrix may act as a network obstacle in the glassy matrix to restrict the propagation of highly localised shear banding, avoiding catastrophic shearing-off through the whole sample and result in improving the plasticity.