Abstract
The ultra-small angle neutron scattering (USANS) measures the microscale structure of heterogeneity and the scattering from rough surfaces with small scattering volumes can be neglected. But this is not true in amorphous alloys. The small angle scattering from such surfaces is not negligible, regardless of scattering volume. However, we demonstrate that the unwanted rough surfaces can be utilized to determine the homogeneity and mass density of amorphous metallic glasses using the USANS and surface neutron contrast matching technique. The power law scattering of the homogeneous Cu50Zr50 amorphous alloy disappeared under the surface contrast-matched environment, a mixture of hydrogenated/deuterated ethanol having low surface tension against the metallic alloys, indicating that the scattering originated not from its internal structure but from the rough surface. This confirms the structural homogeneity not only at the atomic level but also on a larger scale of micrometer. On the other hand, the crystallized Cu50Zr50 alloy showed strong power-law scattering under the matching environment due to the structural heterogeneity inside the alloy. This technique can apply to the bulk samples when the transmission is high enough not causing multiple scattering that is easily detected with USANS and when the surface roughness is dominant source of scattering.
Highlights
Metallic alloys with robust glass forming ability, known as metallic glasses, consist of amorphous structure that is free of heterogeneities like crystalline phase, grain boundaries, and dislocations
Before determining the homogeneity and the mass density using Ultra-small angle neutron scattering (USANS), the structure of Cu50Zr50 metallic glass samples in the form of ribbons was checked by DSC thermal analysis and X-ray diffraction (Fig. 2)
The results demonstrate that the rough surface of amorphous metallic materials, which is a result of manufacturing process or intended purpose, can be used to determine the homogeneity and mass density of the bulk metallic glasses when the surfaces are sufficiently rough
Summary
Metallic alloys with robust glass forming ability, known as metallic glasses, consist of amorphous structure that is free of heterogeneities like crystalline phase, grain boundaries, and dislocations. Only limited information on the phase uniformity of metallic glasses is available in a wide range of length scales In this context, we have questioned whether the homogeneity of metallic glasses confirmed at the atomic and nanometer levels can be sustained at a much larger scale, at least up to the micrometer scale. We will show how the rough surface, which is not desired in most characterization methods, can be applied to determine the microscale homogeneity and the mass density of BMG alloys simultaneously using the unique contrast-matched USANS technique. For this purpose, USANS is more useful than SANS because only USANS can properly evaluate the typical micron-sized roughness. USANS is less sensitive to incoherent backgrounds than SANS
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