Modification of liquid/solid interface shape in directionally solidifying Al–Cu alloys by a transverse magnetic field Jiang Wang • Zhongming Ren • Yves Fautrelle • Xi Li • Henri Nguyen-Thi • Nathalie Mangelinck-Noel • Georges Salloum Abou Jaoude • Yunbo Zhong • Imants Kaldre • Andris Bojarevics Received: 17 April 2012 / Accepted: 9 July 2012 / Published online: 24 July 2012 Ó Springer Science+Business Media, LLC 2012 Abstract Al-0.85wt%Cu and Al-2.5wt%Cu alloys were directionally solidified under different transverse magnetic field (TMF) intensities to investigate the influence of TMF on the liquid/solid interface shape with respect to the var- ious length scales appearing (planar, cellular, and dendritic interfaces). Results show that planar and cellular interfaces tilt to one side and then level off with increasing TMF although the dendritic interface appears not to behave in this manner. In situ synchrotron X-ray imaging was applied during directional solidification of the Al-4wt%Cu alloy under a 0.08T TMF, revealing leveling of the initially sloped interface. Solute redistribution, caused by thermo- electric magnetic convection (TEMC), responds to the changes in the interface shape. Because different typical length scales should be used in estimating the velocity of TEMC for planar, cellular, and dendritic interfaces, the maximum velocity of the convection ahead of the interface is obtained under different TMF intensities; correspond- ingly, leveling of the interface’s degree of slop varies with TMF. Introduction As one of the determining factors of solid material prop- erties, microstructure is closely related to the solidification process [1]. Through its independent and precise control- ling of growth conditions, directional solidification has widely assisted experimental research in characterizing microstructure as a function of processing conditions [2]. The classical constitutional supercooling criterion [3] gave an upper stability boundary for a planar interface; the pioneering work of Mullins and Sekerka [4] gave a rigor- ous foundation for the onset of morphological instability when considering the interfacial energy and the perturba- tion wavelength. In addition to interfacial morphology, the shape of the liquid/solid interface in directional solidifi- cation is also crucial in the formation of the final solidified structure [5]. Interfacial shape strongly influences the generation and propagation of defects [6], the radial com- positional uniformity [7, 8], grain size, and orientation of phases [9]. Results from Chong and William [6] showed that convex shapes generally determined grain selection, and convex interfaces also enhanced twin generation. Arafune et al. [10] pointed out that planar interfaces were beneficial to single crystal growth and minimized disloca- tions during directional solidification. Although many factors influence interface shape, such as the relative thermal conductivity between sample and crucible, the temperature profile, and the growth rate, J. Wang  Z. Ren (&)  X. Li  Y. Zhong Department of Material Science and Engineering, Shanghai University, Shanghai 200072, People’s Republic of China e-mail: zmren@staff.shu.edu.cn J. Wang e-mail: wangjiang417@163.com J. Wang  Y. Fautrelle  X. Li  I. Kaldre SIMAP/EPM—Madylam, ENSHMG BP 75, 38402 St. Martin d’Heres Cedex, France H. Nguyen-Thi  N. Mangelinck-Noel  G. S. A. Jaoude Aix Marseille University, Campus Saint-Jerome, Case 142, 13397 Marseille Cedex 20, France H. Nguyen-Thi  N. Mangelinck-Noel  G. S. A. Jaoude CNRS, IM2NP, Campus Saint-Jerome, Case 142, 13397 Marseille Cedex 20, France I. Kaldre  A. Bojarevics University of Latvia/IPUL, Salaspils, Latvia 123 J Mater Sci (2013) 48:213–219 DOI 10.1007/s10853-012-6730-6