Microstructure and oxidation behavior of Nb–Mo–Si–B alloys

Behrani, Vikas; Thom, Andrew J.; Kramer, M. J.; Akinç, Müfit

doi:10.1016/j.intermet.2005.03.007

Cited by 71 publications

(45 citation statements)

References 28 publications

(38 reference statements)

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“…Most of the research so far has been focused on Mo-Si-B alloys [1,2] even though some investigations have also evaluated related systems. [3][4][5] In terms of the current knowledge of phase equilibria concerning the Nb-B, Nb-Si and Si-B binary systems, the following information should be mentioned: Borges Jr. et al [6] have reevaluated the Nb-rich region (0-50 at.% B) of the Nb-B system and reported important discrepancies with respect to the phase diagram shown in, [7] with their proposed phase relations being close to those from Rudy et al [8] In fact, Rudy's diagram lacks only the Nb 5 B 6 phase found by Bolmgren and Lundstrom. [9] Solidus temperatures in the Nb-B system are expected to be higher than approximately 2050°C for alloys containing up to 66.7 at.% B and at 1700°C the following solid phases should be stable: Nb ss (ss-solid solution), Nb 3 B 2 , NbB, Nb 5 B 6 , Nb 3 B 4 , NbB 2 and bB.…”

Section: Introductionmentioning

confidence: 99%

Isothermal Section of the Nb-Si-B System at 1700 °C in the Nb-NbSi2-NbB2 Region

Nunes

Júnior

Coelho

et al. 2011

J. Phase Equilib. Diffus.

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Me-Si-B (Me-metal) alloy systems have been evaluated to aid the development of ultra high temperature structural materials. In the present work, the phase relations at 1700°C in the Nb-NbSi 2 -NbB 2 region of the Nb-Si-B system have been experimentally determined. The alloys were prepared via arc melting and powder metallurgy routes. All samples were characterized via scanning electron microscopy (SEM) and x-ray diffraction (XRD) and selected samples were also scanned via wave-length dispersive spectroscopy (WDS). The high B solubility in the aNb 5 Si 3 phase has been confirmed with solubility range larger than that proposed in the 1600°C isothermal section of Nowotny et al. (Aufbau und Zunderverhalten von Niob-Bor-SiliciumLegierungen, Mon. Chem., 1960, 91, p 975-990). In contrast to Nowotny's isothermal section, it has been observed that the D8 8 -phase should be nearly stoichiometric with composition close to 57Nb35Si8B (at.%). It was also found that the D8 8 -phase does not equilibrate with NbB 2 -phase at 1700°C. A negligible Si solubility in the boride phases as well as that of B in NbSi 2 has been noticed.

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Section: Introductionmentioning

confidence: 99%

Isothermal Section of the Nb-Si-B System at 1700 °C in the Nb-NbSi2-NbB2 Region

Nunes

Júnior

Coelho

et al. 2011

J. Phase Equilib. Diffus.

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“…[3] But, their low fracture toughness and thermal-expansion anisotropy need to be improved before the alloys can find practical applications. This was the motivation of recent studies [4][5][6][7] to incorporate Nb into the MoSi-B system to improve mechanical properties while retaining oxidation resistance. The Nb-Si-B system offers the possibility of ductile-phase toughening, since Nb metal can coexist in equilibrium with boron-containing silicides.…”

Section: Introductionmentioning

confidence: 99%

Chlorination treatment to improve the oxidation resistance of Nb-Mo-Si-B alloys

Behrani

Thom

Kramer

et al. 2005

Metall Mater Trans A

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Recent studies have shown that the quaternary Nb-Mo-Si-B system is not oxidation resistant. The difference in oxidation resistance between Mo-Si-B and Nb-Mo-Si-B may be interpreted in terms of the volatility of the metal oxide that forms. MoO 3 evaporates from the surface scale at about 650 °C, leaving a porous borosilicate glassy scale. Nb 2 O 5 persists as a rapidly growing condensed phase that overwhelms the ability of the borosilicate glass to form a protective layer. In the present work, a novel chlorination process was employed to selectively remove Nb 2 O 5 from the scale of the quaternary alloy as volatile NbCl 5 . A Nb-Mo-Si-B alloy was studied with a nominal composition of 63(Nb,Mo)-30Si-7B (at. pct) with Nb/Mo ϭ 1:1. The alloy consisted of a three-phase microstructure of (Nb,Mo) 5 Si 3 B x (T1)-(Nb,Mo) 5 (Si,B) 3 (T2)-(Nb,Mo) 5 Si 3 B x (D8 8 ). The oxidation behavior of these alloys in air was studied both before and after chlorination. Results showed that Nb 2 O 5 can be selectively removed from the scale to leave a borosilicate-rich scale, which then forms a dense scale after heat treatment at 1100°C in argon. The oxidation rate of the chlorinated alloy was about one-third that of the unchlorinated alloy under identical conditions. Alloy oxidation during heating to the test temperature was studied, and a plausible mechanism for the formation of porosity in the oxide scale has been offered.

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“…This is borne out when we consider that alloys with less D8 8 volume fraction showed improved oxidation behavior [60].…”

Section: Oxidation Behaviormentioning

confidence: 97%

“…Single phase Nb 5 Si 3 has been observed to oxidize rapidly resulting in the formation of a thick voluminous scale [67]. Consequently, studies have been carried out by boron doping of Nb-Si alloys [60,61,68]. From these studies, it appears that the T2 phase has better oxidation resistance than the other phases present in the system.…”

Section: Oxidation Behaviormentioning

confidence: 99%

Microstructures and oxidation behavior of some Molybdenum based alloys

Ray

2011

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Microstructure and oxidation behavior of Nb–Mo–Si–B alloys

Cited by 71 publications

References 28 publications

Isothermal Section of the Nb-Si-B System at 1700 °C in the Nb-NbSi2-NbB2 Region

Isothermal Section of the Nb-Si-B System at 1700 °C in the Nb-NbSi2-NbB2 Region

Chlorination treatment to improve the oxidation resistance of Nb-Mo-Si-B alloys

Microstructures and oxidation behavior of some Molybdenum based alloys

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