Journal of Alloys and Compounds 480 (2009) 295–298 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Effect of melt convection on the secondary dendritic arm spacing in peritectic Nd–Fe–B alloy K. Biswas a,∗ , R. Hermann a , H. Wendrock a , J. Priede b,c , G. Gerbeth b , B. Buechner a a Leibniz Institute for Solid State and Materials Research (IFW) Dresden, P.O. Box 270116, D-01171 Dresden, Germany b Forschungszentrum Rossendorf (FZR), Institute of Safety Research, P.O. Box 510119, 01314 Dresden, Germany c Applied Mathematics Research Centre, Department of Mathematical Sciences, Coventry University, Priory Street, Coventry CV1 5FB, UK article info Article history: Received 9 November 2008 Received in revised form 16 January 2009 Accepted 24 January 2009 Available online 6 February 2009 Keywords: Peritectic solidification Nd–Fe–B Secondary dendritic arm spacing Melt-convection abstract Dendrites are one of the major microstructural constituents of peritectic alloys. In the present work, the effect of melt convection on the secondary dendritic arm spacing (SDAS) and volume fraction of properitectic -Fe was investigated during solidification of stoichiometric Nd–Fe–B alloys using the forced crucible rotation technique. The resulting microstructure of the alloy in consideration of melt convection has been investigated using scanning electron microscopy and optical microscopy. The average SDAS was determined for each sample from the whole cross-section of the cylindrical test samples using image analyzing software LEICA QWIN. A detailed statistical analysis of the spacing distribution was performed on the basis of the variation of SDAS values, averaged from about 80 to 120 dendrites in different zones. The -Fe volume fraction, measured by vibrating sample magnetometer (VSM), reduces with increasing crucible rotation frequency. Similarly, the SDAS values decrease with increasing rotation frequency. These results are explained from the viewpoint of a reduced melt convection state under steady forced crucible rotation leading to a reduced effective mass transfer coefficient. © 2009 Published by Elsevier B.V. 1. Introduction Peritectic solidification has drawn huge attention in both exper- imental and theoretical studies due to the wide application field of many peritectic alloys [1,2]. Extensive investigations have been done to understand the solidification behaviour of the properitec- tic phase, the morphology of properitectic phase, and the evolved microstructures for different peritectic alloys. Especially, Ti–Al- based alloys and Nd–Fe–B-based rare earth permanent magnets exhibit attractive properties like high strength at high tempera- tures and excellent hard magnetic properties, respectively [1–3]. The change in volume fraction and morphology of the properitec- tic phase is the topic of prime importance as these microstructural parameters play an important role in determining the magnetic and mechanical properties of Nd–Fe–B [4] and Ti–Al alloys, respectively [5]. However, there is still a lack of understanding of the transforma- tion mechanisms and the influences of many aspects such as melt convection during peritectic solidification which plays an impor- tant role concerning magnetic and mechanical properties [6–7]. ∗ Corresponding author. Current address: Glass Technology Laboratory, Central Glass and Ceramic Research Institute, 196, Raja S.C. Mullick Road, Kolkata 32, India. Tel.: +91 9748051040; fax: +91 33 2473 0957. E-mail address: kk.biswas@gmail.com (K. Biswas). The dendritic structure, which is commonly observed in peri- tectic microstructure, is a key microstructural feature and is characterized by the primary and secondary dendritic arm spac- ing (SDAS). Numerous studies have been done during the last years to investigate the effect of convection during directional solidifi- cation experiments on the primary and secondary dendritic arm spacings of several alloys like Sn–Pb, Al–Cu, Pb–Sb systems [8–10]. But little is known about the influence of natural or forced con- vection on the microstructure development of peritectic alloys. There is no report on the effect of melt convection on the SDAS of properitectic phase of any alloy during conventional solidification process. In comparison with the amount of work done on the measure- ment of SDAS as a function of cooling rate, there is relatively little information on the effect of other solidification parameters like effective mass transfer coefficient and fluid flow velocity on SDAS. Solidification studies have been reported with a view to charac- terize primary dendrite arm spacing ( 1 ), secondary dendrite arm spacing ( 2 ) and dendrite tip radius (R) as a function of initial alloy solute concentration (C 0 ), growth rate (V) and temperature gradi- ent (G) ahead of the microscopic solidification front together with extensive theoretical studies [11,12] and models [13–19]. Langer and Müller-Krumbhaar [14] have carried out a detailed numeri- cal analysis of the wavelength of instabilities along the sides of a dendrite. 0925-8388/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.jallcom.2009.01.106