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Phase Diagram Evaluations: Section II

Al-Nd-Si (Aluminum-Neodymium-Silicon) V. Raghavan

Recently, [2001Lon1] and [2001Lon2] reported an isothermal section at 500
C for this ternary system in the Nd-lean region.

Binary Systems The Al-Nd phase diagram, reassessed with new additional experimental input by [2005Gao], shows the following intermediate compounds: Nd3Al (D019, Ni3Sn-type hexagonal), Nd2Al (C23, Co2Si-type orthorhombic), NdAl (ErAl-type orthorhombic), NdAl2 (C15, MgCu2-type cubic), aNdAl3 (Ni3Sn-type hexagonal), bNdAl3 (stable between 1205 and 888
C), NdAl4 or bNd3 Al11 (D13, Al4Ba-type tetragonal), and aNd3 Al11 (aLa3 Al11 -type orthorhombic). The Al-Si phase diagram is a simple eutectic system with the eutectic reaction at 577
C and 12.2 at.% Si. The Nd-Si phase diagram [Massalski2] depicts the following intermediate phases: Nd5Si3 (D8l, Cr5Si3-type tetragonal), Nd5Si4 (Si4Zr5-type tetragonal), NdSi (B27, FeB-type orthorhombic), Nd2Si3 (C32, AlB2-type hexagonal), aNdSi2 (aGdSi2 type orthorhombic), and bNdSi2 (Cc, ThSi2-type tetragonal).

Ternary Isothermal Section With starting metals of 99.99% Al, 99.9% Nd, and 99.999% Si, [2001Lon2] arc-melted or induction-melted 260 alloys under Ar atm. After homogenization, the alloys were given a final anneal at 500
C for 7 days and quenched in water. The phase equilibria were studied by metallography, electron probe microanalysis, and x-ray powder diffraction. The isothermal section constructed by

[2001Lon2] at 500
C is shown in Fig. 1. The ternary compound labeled d by [2001Lon2] at NdAl1.75Si0.25 is an extension of the binary compound NdAl2 with the MgCu2type cubic structure [1967Ram]. The compound NdAl1.25Si0.75 (or Nd4Al5Si3, denoted s1 here) has a homogeneity range of NdAl1+xSi1-x (0 £ x £ 0.4) [2001Lon1]. The compound of fixed stoichiometry NdAl2Si2 (denoted s2 here) 3m1 has the La2O2S-type of structure with space group P and lattice parameters a = 0.423 nm and c = 0.671 nm [1984Gsc].

References 1967Ram: A. Raman and H. Steinfink, Crystal Chemistry of AB2 Structures. I. Investigations on AB2 Sections in the Ternary Systems RE-Al-Si, -Ge, and -Sn, Inorg. Chem., 1967, 6(10), p 1789-1791 1984Gsc: K.A. Gschneidner and L. Eyring, Handbook on the Physics and Chemistry of Rare Earths, 1984, Vol. 7, NorthHolland, Amsterdam, p 140 2001Lon1: Z. Long, Y. Zhou, Y. Zhuang, R. Chen, and J. Liu, Isothermal Section (500
C) of Phase Diagram of Nd-Al-Si Ternary System, Trans. Nonferrous Met. Soc. China, 2001, 11(2), p 278-280 2001Lon2: Z. Long, Y. Zhou, Y. Zhuang, R. Chen, J. Liu, and X. Wang, Phase Relations in the Nd-Al-Si System at 500
C, J. Alloys Compd., 2001, 325, p 190-193 2005Gao: M.C. Gao, N. Unlu, G.J. Shiflet, M. Mihalkovic, and M. Widom, Reassessment of Al-Ce and Al-Nd Binary Systems Supported by Critical Experiments and First-Principles Energy Calculation, Metall. Mater. Trans. A, 2005, 36, p 3269-3279

Fig. 1 Al-Nd-Si isothermal section at 500
C [2001Lon2]. Narrow two-phase regions are omitted

Journal of Phase Equilibria and Diffusion Vol. 28 No. 6 2007