Niobium Silicide High Temperature
            <i>In Situ</i>
            Composites

Bewlay, B. P.; Jackson, M. R.; Gigliotti, M. F. X.

doi:10.1002/0470845856.ch26

Cited by 48 publications

(94 citation statements)

References 28 publications

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“…Current investigations focus on Nb-Ti-(Hf)-Si-Cr-Al in situ composites that consist of niobium solid solution, (Nb,Ti) ss , and Nb 5 Si 3 silicides, with/without the presence of a Cr-rich C14 Laves phase [4][5][6][7][8][9]. The presence of the Laves phase improves the oxidation resistance of the alloys but is detrimental to their fracture toughness.…”

Section: Introductionmentioning

confidence: 99%

“…The presence of the Laves phase improves the oxidation resistance of the alloys but is detrimental to their fracture toughness. Balance between fracture toughness and oxidation resistance can be achieved when the volume fractions of the phases are: 40-45% Nb ss , 45-55% Nb 5 Si 3 and 0-15% C14 Laves [4,5].…”

Section: Introductionmentioning

confidence: 99%

“…Optimum oxidation resistance can be achieved for alloy chemistries with Nb/(TiCHf) ratios in the range 1.8-2.1 and Si concentration in the range 17-19 at.%; such compositions offer also optimum creep strength [5]. The Cr and Al additions improve the oxidation resistance of Nb ss and Nb 5 Si 3 silicides [9], but are detrimental for the fracture toughness of the Nb ss [10,11].…”

Section: Introductionmentioning

confidence: 99%

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Study of the role of Ta and Cr additions in the microstructure of Nb–Ti–Si–Al in situ composites

Zelenitsas

Tsakiropoulos

2006

Intermetallics

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Niobium silicide-based in situ composites are Nb-base alloys with high Si content that have the potential for higher temperature capability than the Ni-base superalloys. Microstructure-property studies of these alloys have been the subject of many research programmes, where the differentiation between the aNb 5 Si 3 and bNb 5 Si 3 is usually not clear, even though it is essential to understanding the solidification of the alloys and the stability of their microstructures at high temperatures. In this work, the effects of Cr (5 or 8 at.%) and Ta (6 at.%) in the microstructures of as-cast and heat-treated Nb-24Ti-18Si-5Al in situ composites have been studied. The main phases observed in the as-cast and heat-treated (100 h at 1400 or 1500 8C) alloys were the niobium solid solution, (Nb,Ti) ss , the niobium 5-3 silicides, aNb 5 Si 3 and bNb 5 Si 3 , and a Cr-rich C14 silicide Laves phase. During solidification, Al additions promoted the formation of bNb 5 Si 3 , while the Cr additions caused the appearance of the C14 silicide Laves phase that was probably formed congruently from the remaining liquid. During heat treatment, the bNb 5 Si 3 phase transformed to aNb 5 Si 3 according to the reaction bNb 5 Si 3 /aNb 5 Si 3 C(Nb,Ti) ss . The Cr addition lowered the melting temperature of the alloys as liquation was observed after 100 h at 1500 8C in the two Cr-rich alloys. Ta and Cr retard the bNb 5 Si 3 /aNb 5 Si 3 C(Nb,Ti) ss transformation. Solid state diffusion was sluggish in the presence of Ta, but the Ta addition did not destabilize the three-phase equilibrium among (Nb,Ti) ss , aNb 5 Si 3 and the C14 silicide Laves phase, in the Nb-24Ti-18Si-6Ta-8Cr-4Al alloy. q

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study of the role of Ta and Cr additions in the microstructure of Nb–Ti–Si–Al in situ composites

Zelenitsas

Tsakiropoulos

2006

Intermetallics

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“…The content of newly generated Cr 2 Nb is 6 vol% in Alloy B. Consequently, different Cr contents have a slight effect on the size and silicide content in the alloys. It is well known that the alloying elements play an important role in the microstructure transformation for NbSi in situ composites [11][12][13]. In order to study the compositional distributions in the phases, EDS analysis was performed, and the results are shown in Table 2.…”

Section: Microstructural Characterization Of As-cast Alloysmentioning

confidence: 99%

Oxidation behavior of Nb–24Ti–18Si–2Al–2Hf–4Cr and Nb–24Ti–18Si–2Al–2Hf–8Cr hypereutectic alloys at 1250 °C

et al. 2015

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Nb-24Ti-18Si-2Al-2Hf-4Cr and Nb-24Ti-18Si-2Al-2Hf-8Cr alloys were prepared by arc melting in a water-cooled crucible under argon atmosphere. Microstructural characteristics and oxidation resistance of the alloys at 1250°C were investigated. The results show that, when the Cr content is 4 at%, the microstructures consist of (Nb,Ti) SS and Nb 5 Si 3 ; as Cr content increases to 8 at%, C14 Laves phase Cr 2 Nb is formed. The isothermal oxidation tests show that the oxidation kinetics of the two alloys follow similar features. The weight gains of the two alloys after oxidation at 1250°C for 100 h are 235.61 and 198.50 mgÁcm -2 , respectively. During oxidation, SiO 2 , TiO 2 , Nb 2 O 5 and CrNbO 4 are formed at first. Then, Ti 2 Nb 10 O 29 is formed after oxidation for 20 min and begins to change into TiNb 2 O 7 as the oxidation proceeds. SiO 2 is formed as solid state at first but later evolves into glassy state to improve the cohesion of the scale. After oxidation for 100 h, oxidation products consist of SiO 2 , TiNb 2 O 7 , Nb 2 O 5 and CrNbO 4 .

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“…[1][2][3][4][5][6] Recent research in Nb-Si composites has explored a variety of alloying additions such as Ti, Hf, Cr, Mo [7][8][9] both from the perspective of understanding phase stability of Nb solid solution, and the Nb 5 Si 3 phase, as well as balancing mechanical properties. For an accelerated understanding of the phase stability of these Nb-Si alloys, it is essential to develop the accurate thermodynamic database for the prediction of phase stability.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic and Microstructural Modeling of Nb-Si Based Alloys

Amancherla

Kar

Bewlay

et al. 2007

J Phs Eqil and Diff

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Nb-Si alloys have gained much attention over the last decade as the next generation alloys for high-temperature aero-engine applications due to their low density and improved mechanical properties. However, the microstructures of these alloys are quite complex and vary significantly with the addition of elements such as Ti and Hf. Hence, an improved understanding of the phase stability and the microstructural evolution of these alloys is essential for alloy design for advanced high-temperature applications. In the present paper, we describe the microstructural evolution modeling results of the dendritic and eutectic solidification of the binary Nb-16 at.% Si alloy, obtained using a Phase-Field simulations performed with MICRESS. The effect of parameters; such as heat extraction rate, the ratio of the diffusivity of the solute in liquid to solid, and the interfacial energy of liquid and solid interface, on the microstructural evolution during dendritic solidification is discussed in detail.

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Niobium Silicide High Temperature In Situ Composites

Cited by 48 publications

References 28 publications

Study of the role of Ta and Cr additions in the microstructure of Nb–Ti–Si–Al in situ composites

Study of the role of Ta and Cr additions in the microstructure of Nb–Ti–Si–Al in situ composites

Oxidation behavior of Nb–24Ti–18Si–2Al–2Hf–4Cr and Nb–24Ti–18Si–2Al–2Hf–8Cr hypereutectic alloys at 1250 °C

Thermodynamic and Microstructural Modeling of Nb-Si Based Alloys

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