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Flow-induced elastic anisotropy of metallic glasses

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Sun, YH 
Concustell, A 
Carpenter, MA 
Qiao, JC 
Rayment, AW 


As-cast bulk metallic glasses are isotropic, but anisotropy can be induced by thermomechanical treatments. For example, the diffraction halo in the structure function S(Q) observed in transmission becomes elliptical (rather than circular) after creep in uniaxial tension or compression. Published studies associate this with frozen-in anelastic strain and bond-orientational anisotropy. Results so far are inconsistent on whether viscoplastic flow of metallic glasses can induce anisotropy. Preliminary diffraction data suggest that the anisotropy, if any, is very low, while measurements of the elastic properties suggest that there is induced anisotropy, opposite in sign to that due to anelastic strain. We study three bulk metallic glasses, Ce65Al10Cu20Co5, La55Ni10Al35, and Pd40Ni30Cu10P20. By using resonant ultrasound spectroscopy to determine the full elasticity tensor, the effects of relaxation and rejuvenation can be reliably separated from uniaxial anisotropy (of either sign). The effects of viscoplastic flow in tension are reported for the first time. We find that viscoplastic flow of bulk metallic glasses, particularly in tension, can induce significant anisotropy that is distinct from that associated with frozen-in anelastic strain. The conditions for inducing such anisotropy are explored in terms of the Weissenberg number (ratio of relaxation times for primary relaxation and for shear strain rate). There is a clear need for further work to characterize the structural origins of flow-induced anisotropy and to explore the prospects for improved mechanical and other properties through induced anisotropy.



Metallic glass, Anisotropy, Elastic properties, Non-Newtonian flow, Anelasticity

Journal Title

Acta Materialia

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Elsevier BV
Engineering and Physical Sciences Research Council (EP/I035404/1)
Engineering and Physical Sciences Research Council (EP/I036079/1)
Natural Environment Research Council (NE/F017081/1)
This research was supported by the Engineering and the Engineering and Physical Sciences Research Council, UK (grant EP/I035404/1). Y.H.S. acknowledges support from a China Scholarship Council (CSC) scholarship. The authors thank Z. Lu, H. Y. Bai and W. H. Wang for the supply of the Ce65Al10Cu20Co5 and La55Ni20Al25 metallic glasses.