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Phase Diagram Evaluations: Section II

Al-B-Rh (Aluminum-Boron-Rhodium) V. Raghavan

Recently, [2006Kim] determined an isothermal section at 1000
C for Rh-rich alloys of this system. No E21, Rh3AlBtype of ternary compound was found.

Binary Systems There are two intermediate phases in the Al-B system: AlB2 (C32, AlB2-type hexagonal) and AlB12 (AlB12-type

tetragonal). The Al-Rh phase diagram [2006Kho] (see Fig. 1 under Al-Pd-Rh) depicts the following intermediate phases: Rh2Al9 (D8d, Co2Al9-type monoclinic), Rh1-xAl3 (orthorhombic, denoted O1 or e16 Þ; RhAl3 (orthorhombic, denoted O2 or e6 Þ; Rh2Al5(c) (space group Pm3, cubic), Rh2Al5(h) (D811, Co2Al5-type hexagonal), Rh3Al7 (monoclinic, denoted V), and RhAl (B2, CsCl-type cubic). The tentative B-Rh phase diagram [Massalski2] depicts two compounds: Rh7B3 (D102, Fe3Th7-type hexagonal) and RhB1.1 (B81, NiAs-type hexagonal).

Ternary Isothermal Section On the basis of a limited number of experiments, [2006Kim] constructed an isothermal section at 1000
C for Rh-rich alloys of this system as shown in Fig. 1. Threephase fields of (Rh) + RhAl + Rh7B3 and RhAl + Rh7B3 + RhB are seen. No E21-type ternary compound Rh3AlB was found.

References

Fig. 1 Al-B-Rh [2006Kim]

partial

isothermal

section

at

1000
C

2006Kho: V.G. Khoruzhaya, K.E. Kornienko, P.S. Martsenyuk, and T. Ya. Velikanova, Phase Equilibria in the System Al-Rh, Poroshk. Metall., 2006, (5-6), p 48-56 in Russian; TR: Powder Metall. Met. Ceram., 2006, 45(5-6), p 251-258 2006Kim: Y. Kimura, K. Iida, F.G. Wei, and Y. Mishima, Phase Equilibria in the T-Al-C (T: Co, Ni, Rh, Ir) and T-Al-B (T: Rh, Ir) Systems for the Design of E21-Co3AlC Based Heat Resistant Alloys, Intermetallics, 2006, 14, p 508-514

Journal of Phase Equilibria and Diffusion Vol. 29 No. 1 2008

43