High Magnetic Field-Induced Formation of Banded Microstructures in Lamellar Eutectic Alloys During Directional Solidific
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exhibit a wide variety of microstructures and unique properties, making them useful for applications in many fields and resulting in eutectic solidification being the subject of numerous investigations.[1,2] Eutectic growth involves the formation of interfacial patterns during solidification. The basic structures are generally both lamellar and fiber, which are considered characteristic of high-purity alloys.[3] In addition, eutectic microstructures are much finer than those of dendrites and can therefore improve mechanical properties. The stability of eutectic structures against single-phase formation is generally described by a coupled zone, which represents a regime of composition and undercooling conditions in which a eutectic microstructure can form. The stability of eutectic structures remains a topic of interest. The primary model for a coupled zone was proposed by
XI LI, Professor, is with the State Key Laboratory of AdvancedSpecial Steels, Shanghai University, Shanghai, 200072, P.R. China,and also with SIMAP-EPM-Madylam/G-INP/CNRS, UJF, PHELMA,BP 75, 38402 St Martin d Heres Cedex, France. Contact e-mail: [email protected] ZHONGMING REN, Professor, is with the State Key Laboratory of Advanced Special Steels, Shanghai University. YVES FAUTRELLE, ANNIE GAGNOUD, and RENE MOREAU, Professors, are with SIMAP-EPMMadylam/G-INP/CNRS, UJF, PHELMA. Manuscript submitted April 23, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
Tammann and Botschwar.[4] The theoretical models of the coupled zone have been developed by Hunt and Jackson,[5] Burden and Hunt,[6] Kurz and Fisher,[7] and Trivedi and Kurz.[8] Although many aspects of steady-state growth are well understood, experimental and theoretical knowledge remains incomplete regarding the range of stability for even simple lamellar structures at off-eutectic melt compositions. A banded structure is a type of instable structure that has been observed in the directional solidification of peritectic and eutectic alloys.[9–11] Several quantitative theories have attempted to explain the growth of various kinds of banded structures,[12,13] but ambiguities remain regarding their formation mechanism. Recently, high magnetic fields have been extensively applied during material preparation and solidification process, leading to many interesting phenomena:[14–16] The application of high magnetic field during directional solidification significantly affected the growth of the dendrites in Al-based alloys.[17,18] However, little work has examined the effect of high magnetic field on morphological stabilities and banded structures of eutectic alloys during directional solidification. The aim of this work is twofold: (1) to investigate the effects of high magnetic field on banded structures in eutectic alloys and (2) to fully understand the formation mechanism of banded structures in eutectic alloys. We selected Pb-Sn and Al-Al2Cu eutectic alloys with typical lamellar structure to investigate the effect of high magnetic field on a lamellar eutectic during directional
Fig. 1—Longitudinal structures in di
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