Correlation between plasticity and fragility in Mg-based bulk metallic glasses with modulated heterogeneity

A correlation between the kinetic fragility index (m) and enhanced plasticity is presented in Mg-based bulk metallic glasses (BMGs) with modulated heterogeneity by both suitable minor addition and optimal cooling rate. As case study, with minor addition of Gd in Mg(65)Cu(7.5)Ni(7.5)Zn(5)Ag(5)Y(10-x)Gd(x) BMG, plasticity as well as glass-forming ability improves in a wide composition range (2.5 <= x <= 7.5 at. %). Furthermore, the cooling rate can affect the structural heterogeneity and the deformability of BMGs. With increasing diameters for the alloy x=5, the compressive fracture strain increases from 2.97% at d=1 mm up to 3.74% at d=2 mm and then largely decreases. In particular, the variation of heterogeneity, which can directly affect in the property of BMG, can be evaluated by comparing the m values reflecting the inherent structure of BMGs. This concept can be used as a means of guiding alloy design and processing to alleviate brittleness of BMGs. (C) 2008 American Institute of Physics.