B-Nb (Boron-Niobium)

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Supplemental Literature Review: Section III

B-Nb (Boron-Niobium) H. Okamoto

References

The B-Nb phase diagram in [Massalski2] was recently updated by [2008Oka] and was based primarily on the work of [2003Bor] who examined the Nb-rich region of this system by means of scanning electron microscopy/backscattered electron image (SEM/BSE) and X-ray diffraction (XRD), and found that the eutectic reaction on the (Nb) side is not L ! B2 Nb3 þ ðNbÞ; as suggested by [Massalski2], but L ! BNb þ ðNbÞ; as suggested by [1969Rud]. After [2003Bor], [2005Nun] reported that the homogeneity range of B2Nb is approximately from 30 to 35 at.% Nb according to microstructural analysis of variously heat-treated B-Nb alloys. [2007Pec] calculated the B-Nb phase diagram based on [1969Rud], [1990Bol], [2003Bor], and [2005Nun]. The result is shown in Fig. 1. (Invariant reaction temperatures given in [2007Pec] disagree with this ﬁgure by up to -60 °C.)

1969Rud: R. Rudy, Compounds of Phase Diagram Data, AFML-TR65-2, Part V, Air Force Materials Lab., Wright Patterson AFB, OH 1990Bol: H. Bolmgren and T. Lundstrom, A New Binary Boride, Nb5B6, J. Less-Common Met., 1990, 159, p L25-L27 2003Bor: L.A. Borges, Jr., G.C. Coelho, C.A. Nunes, and P.A. Suzuki, New Data on Phase Equilibria in the Nb-Rich Region of the Nb-B System, J. Phase Equilb., 2003, 24(2), p 140-146 2005Nun: C.A. Nunes, D. Kaczorowski, P. Rogl, M.R. Baldissera, P.A. Suzuki, G.C. Coelho, A. Grytsiv, G. Andre´, F. Bouree´, and S. Okada, The NbB2-Phase Revisited: Homogeneity Range, Defect Structure, Superconductivity, Acta Mater., 2005, 53(13), p 3679-3687 2007Pec: R.M. Pec¸anha, F. Ferreira, G.C. Coelho, C.A. Nunes, and B. Sundman, Thermodynamic Modeling of the Nb-B System, Intermetallics, 2007, 15, p 999-1005 2008Oka: H. Okamoto, B-Nb (Boron-Niobium), J. Phase Equilib. Diffus., 2008, 29(2), p 201

Weight Percent Niobium 0 20

40 50

60

70

80

100

90

3200

3000

L 2800

2469°C 2400

B6Nb5

2000

B4Nb3

2200

B2Nb

Temperature, °C

2600

(βB)

B2Nb3

1800

BNb

(Nb)

1600 0

B

10

20

30

40

50

60

70

80

Atomic Percent Niobium

90

100

Nb

Fig. 1 B-Nb phase diagram

Journal of Phase Equilibria and Diffusion Vol. 29 No. 6 2008

539

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