Abstract
Fluctuation electron microscopy of bulk metallic glasses of CuZrAl(Ag) demonstrates that medium-range order is sensitive to minor compositional changes. By analyzing nanodiffraction patterns medium-range order is detected with crystal-like motifs based on the B2 CuZr structure and its distorted structures resembling the martensitic ones. This result demonstrates some structural homology between the metallic glass and its high temperature crystalline phase. The amount of medium-range order seems slightly affected with increasing Ag concentration (0, 2, 5 at.%) but the structural motifs of the medium-range ordered clusters become more diverse at the highest Ag concentration. The decrease of dominant clusters is consistent with the destabilization of the B2 structure measured by calorimetry and accounts for the increased glass-forming ability.
Highlights
MethodsThe discs were thinned to electron transparency using twin-jet electropolishing (Struers Tenupol-3) and a solution of methanol with 33% nitric acid at −25 °C
By analyzing the normalized variance curve V(k) calculated from the intensities of nanodiffraction patterns we find a pronounced MRO with crystal-like motifs based on the high-temperature crystalline B2 CuZr structure and its distorted structure resembling the martensitic ones
We propose that only a slight increase of the MRO with increasing Ag addition occurs and the increase of the normalized variance is mainly attributed to the presence of Ag as strong scatterer
Summary
The discs were thinned to electron transparency using twin-jet electropolishing (Struers Tenupol-3) and a solution of methanol with 33% nitric acid at −25 °C. This method yielded samples with large electron transparent regions and minimal damage and minimal thickness variation. Its three-condenser system allows for control of the semi-convergence angle to form rather parallel nanometer-sized electron probes. The semi-convergence angle was varied between 0.96, 0.62 and 0.49 mrad at a fixed spot size of 9 to form probes with a size of 1.2, 1.6 and 2 nm, respectively. To reach larger probe sizes with 2.5 and 3.2 nm, the spot size was changed to values of 7 and 6, respectively while keeping the semi-convergence angle at 0.63 mrad. The probe size was measured in vacuum before and after each experiment using a CCD camera
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