Abstract
A novel method for measurement of atomic interdiffusivity is applied to amorphous Cu-Zr close to its glass-transition temperature Tg. Sputter-deposited multilayers are examined in cross-section by transmission electron microscopy and energy-dispersive X-ray spectroscopy. Mapping the evolution of composition profiles gives the interdiffusivity, which is orders of magnitude higher than if coupled to the viscosity expected near Tg. Kirkendall drift of interlayer interfaces in both amorphous and supercooled liquid states (i.e. below and above Tg), and associated voiding in the liquid, show that the diffusivity of copper greatly exceeds that of zirconium. Amorphous Cu-Zr is known to show maxima in atomic packing density at sharply defined compositions. The comparison of the two compositions in the present work provides the first direct evidence that denser packing is associated with lower atomic interdiffusivity. The lower interdiffusivity is governed by a lower diffusivity of copper, and reflects a lessened degree of decoupling of the copper (fast) and zirconium (slow) diffusivities in an efficiently packed glass. The new insights help to understand issues ranging from glass-forming ability to the controlled generation of nanovoided structures.
Highlights
Alloys of late transition metals (LTM – Co, Cu, Fe, Ni) with early transition metals (ETM – Hf, Nb, Ti, Zr) are the bases of many bulk metallic glasses (BMGs)
In multilayers, when is short, the interdiffusion kinetics can be in the Nernst-Planck, rather than the Darken, regime [9]
Cross-sectional thin foils prepared from these samples are characterized by energy-dispersive X-ray spectroscopy (EDX) in transmission electron microscopy (TEM)
Summary
Alloys of late transition metals (LTM – Co, Cu, Fe, Ni) with early transition metals (ETM – Hf, Nb, Ti, Zr) are the bases of many bulk metallic glasses (BMGs). In such glasses, the LTM atoms are smaller and have diffusivities much higher than the ETM atoms [1,2,3]. Extensive studies of amorphous Ni-Zr multilayers [9,10] included finiteelement modelling of the composition profiles during interdiffusion This modelling showed effects of the diffusional asymmetry, but the inferred Kirkendall drift of the Matano interface between the layers was not directly observed
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
