Fracture and deformation of bulk metallic glasses and their composites

Bulk metallic glasses represent an exciting new class of materials with a wide range of potential applications. Plastic deformation of metallic glasses occurs by the formation of shear bands; however, the effect of stress state and the extent of local structural rearrangement during flow are under active investigation. In this work, we review our investigations of the mode II deformation and fracture behavior of a zirconium-based bulk metallic glass. The mode II fracture toughness was found to be ∼75 MPa√m, ∼4–5 times larger than the mode I toughness. This may be explained by the sensitivity of flow to normal stresses. The fracture and fatigue behavior of a BMG composite utilizing a ductile reinforcement phase has also been examined and compared with that of the monolithic alloy. The second phase blocks the propagation of shear bands and distributes the plastic deformation, resulting in extensive stable crack growth at stress intensities double the intrinsic toughness of the unreinforced glass. The composite also exhibits an improved fatigue endurance limit. Implications for future composite microstructures are discussed.