Fracture toughness, fracture morphology, and crack-tip plastic zone of a Zr-based bulk amorphous alloy

DDThe elastic constants, fracture toughness, fracture morphology, and crack-tip plastic zone of a bulk amorphous alloy (bulk metallic glass), with the composition Zr-10AL-5Ti-17.9Cu-14.6Ni (at. pet), were investigated. The room-temperature fracture toughness reached values as high as 69 MPa rootm. However, it showed considerable scatter, which is, at least in part, due to microcrystalline regions in the castings. Controlled crack propagation could not be obtained in chevron-notched specimens. The fracture-surface morphologies of chevron-notched specimens varied as the crack advanced, and this effect is probably related to differences in the crack propagation rate. Controlled fracture resulting in featureless fracture surfaces was observed during in-situ transmission electron microscope (TEM) fracture experiments. The plastic zone of a fatigue-precracked bulk flexure specimen was examined in situ in an atomic-force microscope (AFM). Shear displacements up to 2 mum were found. The AFM observations did not reveal any cracks associated with the shear steps. Sectioning of shear steps using a focused ion beam (FIB) with a diameter of 5 nm also did not reveal any cracks.