Some evidence for ‘directional atomic pair ordering’ in a cobalt-based metallic glass

Time-of-flight neutron diffraction has been used to study structural anisotropy in a wide-ribbon sample of the multicomponent metallic glass Fe4Co67Cr7Si8B14 prepared by continuous casting. A planar sample held at 45 ° to the incident beam was examined by two stationary counters at 90 ° left and 90 ° right, so that the directional structure factors, Sl(Q), Sw(Q), St(Q) corresponding to the three orthogonal directions in the ribbon (length l, width w and thickness t) were determined. It was found that the directional Structure Factor St(Q) had stronger oscillations than Sl(Q) and Sw(Q). Comparison of the directional S(Q) with the total structure factors for FeB and CoB glasses suggest that the result may be tentatively associated with ‘atomic directional pair ordering’ of the Fe-Fe first neighbour pairs in the t direction. The diffraction data have been analysed in the context of the atomic level stress model of metallic glass structures.