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ection II: Phase Diagram Evaluations

Al-Nd-Ti (Aluminum-Neodymium-Titanium) V. Raghavan

Recently, [2004Zho] determined an isothermal section at 500 °C for this ternary system, which depicts two ternary compounds found earlier by [1995Nie1,2].

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 (ErAltype orthorhombic), NdAl2 (C15, MgCu2-type cubic), bNdAl3 (stable between 1205 and 888 °C), aNdAl3 (Ni3Sn-type hexagonal), NdAl4 or bNd3Al11 (D13, Al4Batype tetragonal), and aNd3Al11 (aLa3Al11-type orthorhombic). Recently, [2006Sch] reviewed the Al-Ti phase diagram. The intermediate phases stable at 500 °C are: TiAl3 (tetragonal, space group I4/mmm), TiAl2 (HfGa2-type tetragonal), TiAl (L10, AuCu-type tetragonal), and Ti3Al (D019, Ni3Sn-type hexagonal). There are no intermediate phases in the Nd-Ti system. At 500 °C, (aTi) and (aNd) show very little mutual solubility.

Ternary Compounds Two ternary compounds are known in this system. NdTi2Al20 (denoted s1 here) is cubic, Fd 3m; Z = 8, a = 1.4704 nm [1995Nie1]. Nd6Ti4Al43 (denoted s2 here) is hexagonal, P63/mcm, Z = 2, a = 1.1124 nm and c = 1.8069 nm [1995Nie2].

Ternary Isothermal Section With starting metals of purity > 99.9 mass %, [2004Zho] arc-melted 150 alloys in Ar atm. The alloy samples were given a final anneal at 500 °C for 150 h and quenched in liquid nitrogen. The phase equilibria were studied with x-ray powder diffraction, scanning electron microscopy, and differential thermal analysis. The isothermal section at 500 °C constructed by [2004Zho] is shown in Fig. 1. The two ternary compounds s1 and s2 are present at 500 °C. The solubility of Ti in the binary phases of Nd3Al, Nd2Al and NdAl2 is up to 2.4, 3.5, and 16.1 at.% respectively. The solubility of Nd in Ti, Ti3Al, and TiAl is less than 1 at.%.

Fig. 1 Al-Nd-Ti isothermal section at 500 °C [2004Zho]. Narrow two-phase regions are omitted

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Journal of Phase Equilibria and Diffusion Vol. 29 No. 2 2008

Phase Diagram Evaluations: Section II References 1995Nie1: S. Niemann and W. Jeitschko, Ternary Aluminides AT2Al20 (A = Rare Earth Elements and Uranium; T = Ti, Nb, Ta, Mo, and W) with CeCr2Al20-Type Structure, J. Solid State Chem., 1995, 114, p 337-341 1995Nie2: S. Niemann and W. Jeitschko, Ternary Aluminides A6T4Al43 (A = Y, Nd, Sm, Gd-Lu, and U; T = Ti, V, Nb, and Ta) with Ho6Mo4Al43-Type Structure, J. Solid State Chem., 1995, 116, p 131-135

2004Zho: H. Zhou, Q. Yao, and S. Yuan, The 500 °C Isothermal Section of the Nd-Al-Ti Ternary System, J. Alloys Compd., 2004, 381, p 137-139 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 Calculations, Metall. Mater. Trans. A, 2005, 36A, p 3269-3279 2006Sch: J.C. Schuster and M. Palm, Reassessment of the Binary Aluminum-Titanium Phase Diagram, J. Phase Equilibria, 2