Influence of Thermal Treatment on Microstructure and Corrosion Behavior of Amorphous Fe 40 Ni 40 B 12 Si 8 Alloy
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AMORPHOUS alloys (known as metallic glasses, too) have been widely studied in the last fifty years due to their potential applications in various fields, including their use as high-frequency magnetic-shielding sheets, magnetic cores, fuel-cell separators, precision optical parts, aircraft parts, dental parts, brazing foils, etc.[1–9] Desirable and isotropic physical and functional properties of these materials result from their homogenous and isotropic structure, without long-range atom ordering. Iron-based amorphous alloys are well known for their soft-magnetic properties,[1,10–12] but their application is limited to some extent because of their propensity for corrosion, despite the fact that they exhibit better corrosion resistance than their crystalline counterparts. Addition of precious metals improves the corrosion resistance of the alloys,[13,14] but drawback of such alloys is their high cost, directing the scientific efforts toward more cost-effective alternatives. On the other hand, Ni as a non-noble and relatively inexpensive metal can improve anti-corrosion properties of Fe-based amorphous alloys if added in appropriate amounts, while retaining good soft magnetic properties, and providing high mechanical strength.[15–17] MILICA M. VASIC´, IVANA STOJKOVIC´ SIMATOVIC´, and DRAGICA M. MINIC´ are with the Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia. Contact e-mail: mvasic@ffh.bg.ac.rs TOMA´Sˇ ZˇA´K and NADEˇZˇDA PIZU´ROVA´ are with the Institute of Physics of Materials AS CR, Zˇizˇkova 22, 616 62 Brno, Czech Republic. Manuscript submiited May 4, 2020; accepted October 18, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
As a consequence of kinetic and thermodynamic metastability of amorphous alloys, they undergo microstructural transformations during thermal treatment or exposure to high pressures, or during prolonged activity under moderate conditions. Thermally induced microstructural transformations in amorphous alloys change their functional properties, where the favorable ones can be lost, or can be improved as in the case of formation of materials with combined amorphous/nanocrystalline structure with optimal nanocrystal size and volume fraction.[18,19] This makes them suitable as precursors for production of nanostructured and composite materials of desired properties. Corrosion resistance belongs to technologically important properties of the alloys determined by their microstructure. Speaking about corrosion phenomenon, the corrosion of amorphous and nanocrystalline alloys limits their practical application.[20–22] During the practical usage, amorphous and nanocrystalline alloys can be exposed to wet industrial atmosphere or marine atmosphere containing chloride ions,[23,24] resulting in a risk of their corrosion. In this sense, an investigation of the influence of crystallization on corrosion resistance of Fe-B-Si-Nb amorphous coatings in NaCl solution has shown deterioration of anti-corrosion properties with an increase in the amount of crystall
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