The influence of in situ formed precipitates on the plasticity of Fe-Nb-B-Cu bulk metallic glasses

Improved room temperature plasticity was achieved by microalloying Cu in a series of (Fe₇₁Nb₆B₂₃)_100-xCu _x (x = 0, 0.25, 0.5, 0.75, and 1) glass matrix alloys with tunable size and volume fraction of precipitates composed of α-Fe and Fe23B6 phases. When ∼10-nm-sized nano-scale precipitates are formed with a size comparable to the shear bandwidth by controlling the added content of Cu, the (Fe₇₁Nb₆B₂₃)_99.5Cu_0.5 alloy exhibits a maximum plastic strain of 4.3 ± 0.8% with pronounced multiple shear banding. A further increase in the size of the precipitates up to micrometer scale results in catastrophic fracture accompanied with irregular cracks, revealing that the fracture mechanism of the different alloys is controlled by the precipitate size.