High-resolution transmission electron microscopy investigation of diffusion in metallic glass multilayer films

SV Ketov and YP Ivanov and D Sopu and DV Louzguine-Luzgin and C Suryanarayana and AO Rodin and T Schoberl and AL Greer and J Eckert, MATERIALS TODAY ADVANCES, 1, 100004 (2019).

DOI: 10.1016/j.mtadv.2019.01.003

Lack of plasticity is one of the main disadvantages of metallic glasses. One of the solutions to this problem can be composite materials. Diffusion bonding is promising for composite fabrication. In the present work the diffusion process in glassy multilayer films was investigated. A combination of advanced transmission electron microscopy (TEM) methods and precision sputtering techniques allows visualization and study of diffusion in amorphous metallic layers with high resolution. Multilayered films were obtained by radio frequency sputter deposition of Zr-Cu and Zr-Pd. The multilayers were annealed under a high vacuum (10(-5) Pa) for 1 and 5 h at 400 degrees C, that is, well below the crystallization temperatures but very close to the glass-transition temperatures of both types of the glassy layer. The structural evolution in the deposited films was investigated by high-resolution transmission electron microscopy. It was observed that, despite the big differences in the atomic mass and size, Pd and Cu have similar diffusion coefficients. Surprisingly, 1 h of annealing results in formation of metastable copper nanocrystals in the Zr-Cu layers which, however, disappear after 5 h of annealing. This effect may be connected with nanovoid formation under a complex stress state evolving upon annealing, and is related to the exceptionally slow relaxation of the glassy layers sealed with a Ta overlayer. (c) 2019 The Authors. Published by Elsevier Ltd.

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