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 ro om-temperature fracture toughness reached values as high as 69 MPa rootm. H owever, it showed considerable scatter, which is, at least in part, due to microcrystalline regions in the castings. Controlled crack propagation coul d not be obtained in chevron-notched specimens. The fracture-surface morpho logies of chevron-notched specimens varied as the crack advanced, and this effect is probably related to differences in the crack propagation rate. Co ntrolled fracture resulting in featureless fracture surfaces was observed d uring 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 m um were found. The AFM observations did not reveal any cracks associated wi th 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.