Fracture of FeNiB-NiP amorphous bilayer ribbon

The study of failure surfaces of amorphous bimetal ribbons Fe40Ni40B20-Ni82P18 failed during tensile testing in the as-quenched and relaxed states (annealed at 250 °C) is presented. Two different fracture morphologies are observed on failed as-quenched samples: (i) near the maximum shear stress plane, shear ductile fracture with a typical vein pattern morphology is present, similar to the fracture surface morphology on monolayer amorphous metals, but with a different vein density typical for each layer; (ii) in some regions of the ribbon the upper NiP-based layer has failed by a shear ductile mechanism, while the lower, FeNiB-type layer shows ductile failure in the plane of maximum normal stress with typical chevron morphology. Relaxed samples show a tendency to embrittlement. Chevron fracture morphology in the maximum normal stress plane, typical of the fracture of relaxed amorphous monolayers, is present in both layers. The shear band width in amorphous alloy ribbons was estimated by quantitative fractography methods.