Unusual Solidification Behavior of the Suction-Cast Cu-Zr-Al-Y Alloy Doped with Fe
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he first report on metallic glasses in 1960,[1] the minimum cooling rate, which is required to prevent crystallization of the melt, has gone down from ~106 K/s to below 1 K/s.[2,3] The extensive research on metallic glasses in the past decades enabled casting of fully amorphous parts well above 1 mm thick in many metalbased systems, including Zr-based,[3–5] Mg-based,[3,4,6] and Fe-based[3,4,7] alloys. Among bulk metallic glasses (BMGs), the Cu-based systems are very attractive due to their high glass-forming ability, high fracture strength, and relatively low costs of elements compared to other glass-forming systems.[8,9] BMG formers are multicomponent alloys with eutectic or close to eutectic compositions.[3,4] Using simple binary eutectic phase diagram, it is possible to predict different stable and metastable phases over the complete temperature range. The so-called freezing diagram
TOMASZ KOZIEŁ and KRZYSZTOF PAJOR are with the Faculty of Metals Engineering and Industrial Computer Science, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow, Poland. Contact e-mail: [email protected] PIOTR BAŁA is with the Faculty of Metals Engineering and Industrial Computer Science, AGH University of Science and Technology, Al. Mickiewicza 30, and with the Academic Centre for Materials and Nanotechnology, AGH University of Science and Technology, Al. Mickiewicza 30. GRZEGORZ CIOS is with the Academic Centre for Materials and Nanotechnology, AGH University of Science and Technology, Al. Mickiewicza 30. JERZY LATUCH is with the Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska Street 141, 02-507 Warsaw, Poland. Manuscript submitted October 18, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
(Figure 1) developed by John[10] is constructed by consideration of both, kinetic and thermodynamic factors. The T0α and T0β lines stand for temperatures at which a single-phase crystalline solid, α or β, has a free energy equal to that of liquid with the same composition. In the binary eutectic phase diagram, the T0α and T0β lie about half-way between liquidus and solidus lines and extend down to low temperatures. The TM and Tg temperatures correspond to a limit of shortrange diffusion and lack of diffusion (glass transition), respectively. Above TM, only long-range diffusion is feasible allowing the equilibrium phases to be formed and segregation may occur as the temperature drops.[10] If a molten alloy with a composition outside T0α–T0β range is undercooled below TM, massive transformation of liquid to solid phase with the same composition may occur. A fully amorphous phase of alloy within this composition range requires casting methods with much higher cooling rates, e.g., melt spinning. In contrast, between T0α–T0β lines, the massive transformation is not thermodynamically possible, as the free energy of a liquid phase is lower than of the corresponding solid, α or β. Continuous cooling of a melt within this composition range at a cooling rate equal or higher than the critical rat
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