The embrittlement and toughening of metallic glasses from nano-crystallization.

Metallic glasses with secondary crystalline phase have been reported to either enhance or degrade the global plasticity. Here, we employed molecular dynamics simulation to investigate a generic glass-forming system, in which crystal-glass composites can be obtained via in situ crystallization. Ex situ composite samples were also constructed by embedding perfect crystals into monolithic glasses in order to delineate the precise influences of the composite microstructure. Our simulations demonstrate both toughening and embrittlement effects due to nanocrystallization. The double-edged-sword role of nanocrystals is mainly controlled by elasticity mismatch between the crystalline phase and the glass matrix. The effects of volume fraction and the size of nanocrystals can be understood in the perspective of cumulative probability of shear bands formation and propagation being interfered by the presence of nanocrystals. [ABSTRACT FROM AUTHOR]