Kinetic and structural insights into the grain boundary phase transitions in Ni-Bi alloys

Bian, B and Taheriniya, S and Muralikrishna, GM and Godha, A and Makineni, SK and Sankaran, S and Straumal, BB and Du, Y and Wilde, G and Divinski, SV (2023) Kinetic and structural insights into the grain boundary phase transitions in Ni-Bi alloys. In: Acta Materialia, 245 .

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Abstract

Kinetic and structural changes associated with grain boundary phase transition induced by Bi alloying in dilute Ni–Bi alloys (0–0.3 at.% of Bi) are investigated in a concerted manner. Grain boundary diffusion of Ni in the Ni-Bi alloys is measured in Harrison's B- and C-type kinetic regimes applying the radiotracer technique and utilizing the 63Ni radioisotope. The measurements are performed across the single phase towards two-phase regions of the bulk phase diagram. In case of the single phase region it is the Ni(Bi) solid solution. In case of two phase areas these are Ni(Bi) solid solution + liquid Bi above 927 K or Ni(Bi) solid solution + NiBi below 927 K. Three distinct regions of the dependence of the Ni grain boundary diffusion rates on the Bi concentration are distinguished. A slight increment in Ni grain boundary diffusion is observed at lower Bi contents which is driven by Bi grain boundary segregation. Beyond a critical Bi concentration and still within the single-phase solid solution region, the Ni diffusivity starts to enhance dramatically with increasing Bi content. This is correlated with the appearance of multi-layer Bi segregation along the grain boundaries. It is substantiated by high-angle annular dark-field scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy measurements. At higher Bi concentrations, which corresponds to the appearance of a liquid layer of Bi at the grain boundaries, the Ni diffusivity attains the highest values. A serial of structural transitions between the different grain boundary phases is for the first time demonstrated to be accompanied by remarkable changes of the grain boundary diffusion rates. The present results highlight a close correlation between the atomic transport and structure modifications due to grain boundary phase transitions in the Ni–Bi alloys. Utilizing the present experimental results, a Ni–Bi grain boundary diffusion map is proposed.

Item Type:	Journal Article
Publication:	Acta Materialia
Publisher:	Acta Materialia Inc
Additional Information:	The copyright for this article belongs to Acta Materialia Inc.
Keywords:	Binary alloys; Bismuth alloys; Diffusion in solids; Energy dispersive spectroscopy; Grain boundaries; High resolution transmission electron microscopy; Phase diagrams; Scanning electron microscopy; Segregation (metallography); Solid solutions; Solidification, Diffusion maps; Grain boundary diffusion map; Grain boundary phase diagram; Grain boundary phase transition; Grain boundary phasis; Grain-boundaries; Grain-boundary diffusion; Radiotracer diffusion; Segregation, Nickel alloys
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	27 Jan 2023 08:37
Last Modified:	27 Jan 2023 08:37
URI:	https://eprints.iisc.ac.in/id/eprint/79533

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