Studies on the formation of aluminides in heated Nb–Al powder mixtures

Sina, Hossein; Iyengar, Srinivasan

doi:10.1016/j.jallcom.2014.12.151

Cited by 30 publications

(11 citation statements)

References 32 publications

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“…It seems that as the aluminum melt reacts with titanium particles, some pores are left behind at the sites originally occupied by aluminum. Similar behavior has been attributed to the formation of pores during the synthesis of various aluminides from powder mixtures [31][32][33][34][35][36]. This is also in agreement with studies suggesting that the diffusion of aluminum atoms into titanium particles is the predominant mechanism governing the formation of titanium aluminides [21,22,[25][26][27].…”

Section: Tisupporting

confidence: 88%

“…Further, experimental data show that the combustion peaks in the DSC plots shift to higher temperatures on increasing the heating rate. The apparent activation energy of the product formation can thus be estimated using a nonisothermal analysis of DSC data [6,36,37]. For this purpose, model-free isoconversion methods are considered to be accurate and reliable enough to estimate the activation energy of thermally activated reactions [37,38].…”

Section: Timentioning

confidence: 99%

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Reactive synthesis and characterization of titanium aluminides produced from elemental powder mixtures

Sina

Iyengar

2015

J Therm Anal Calorim

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The formation of titanium aluminides in Ti-Al elemental powder mixtures containing 25, 50 and 75 at.% Al, has been studied using differential scanning calorimetry (DSC). Phase evolution in the mixture was followed by heating the compacted samples up to 1273 K at 7.5 and 15 K min -1 . The cooled samples were characterized using X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. The results showed that the primary combustion product in all the samples was TiAl 3 , and the combustion reaction occurred below the melting point of aluminum only in Ti-rich samples. In Alrich samples (75 at.% Al), TiAl 3 was obtained as a porous, single-phase product after combustion. In samples containing 25 and 50 at.% Al, the combustion reaction was incomplete and the unreacted titanium particles were covered by a layer of TiAl 3 . In these samples, other intermetallic compounds such as TiAl 2 , TiAl and Ti 3 Al were observed to form upon heating beyond the combustion peak and are attributed to the solid-state reaction between unreacted titanium and TiAl 3 . Heating the samples with 25 at.% Al to 1273 K for an hour led to the formation of a homogenous Ti 3 Al product, while a multiphase product with a dominant TiAl phase was observed in samples containing 50 at.% Al. Calculations based on DSC data show that the formation of TiAl 3 through the reaction between solid titanium and molten aluminum is associated with an apparent activation energy of 195 ± 20 kJ mol -1 and an enthalpy of -114 ± 5 kJ mol -1 .

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Section: Tisupporting

confidence: 88%

Section: Timentioning

confidence: 99%

Reactive synthesis and characterization of titanium aluminides produced from elemental powder mixtures

Sina

Iyengar

2015

J Therm Anal Calorim

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“…[4][5][6][7] Among the various compounds in the Nb-Al system (Figure 1), NbAl 3 with its high melting point (1680°C), low density (4.54 g/cm 3 ), is attractive as a potential material for high-temperature applications. 6,8 The applications of NbAl 3 include its use in turbine blades in aircraft engines or in stationary gas turbines. 1,9 However, despite its attractive features, its usage is limited by inadequate ductility at room temperature.…”

Section: Introductionmentioning

confidence: 99%

“…1,6,10 In-situ toughening is an alternative technique to enable a combination of brittle intermetallic phase with a ductile metallic phase in one step production. 11,12 Some conventional methods such as melting, casting and mechanical alloying techniques or self-propagating high-temperature synthesis (SHS) [7][8][9] developed electric current activated/assisted sintering (ECAS) technique has been used in this study. This system enables the cold formed compact obtained from uniaxial compression to be inserted into a container, which is heated by passing an electrical current.…”

Section: Introductionmentioning

confidence: 99%

Effect of holding time on the production of Nb-NbAl3 intermetallic composites via electric-current-activated sintering

Aybey¹,

Yener²,

İpek³

et al. 2017

Mater. Tehnol.

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A recently developed powder metallurgy processing technique -Electric Current Activated (Assisted) Sintering (ECAS) was employed to produce intermetallic Nb-NbAl3 composites. In this study, to produce Nb-NbAl3 in-situ intermetallic composites, Nb (99.8 % purity, less than 44 μm) and Al (99.5 % purity, less than 44 μm) elemental powders were mixed in the stoichiometric ratio corresponding to the Nb-Al phase diagram. The effect of different processing times, for (10, 30, 60) s, under maximum of 2000 A and 1.5-2.0 V, was investigated. Scanning electron microscopy and X-ray diffraction analysis were used to characterize the produced samples. X-ray diffraction studies revealed that the dominant phases are NbAl3 and Nb. Scanning electron microscopy examinations showed a dense microstructure with a very low amount of porosity and also a trace amount of residual aluminium. The microhardness of the test materials sintered for 60 s via electric-current-activated sintering was about 405 HV±46 HV0,05. Keywords: in situ composites, NbAl 3 aluminides, electric current activated sintering (ECAS) Pred kratkim razvita tehnika v metalurgiji prahov: sintranje, aktivirano z elektri~nim tokom (ECAS), je bilo uporabljeno za in situ izdelavo intermetalnega kompozita Nb-NbAl3. V {tudiji sta bila za in situ proizvodnjo Nb-NbAl3 intermetalnega kompozita zme{ana elementna prahova Nb (99.8 %~istost, delci manj{i od 44 μm) in Al (99.5 %~istost, delci manj{i od 44 μm), zme{ana v stehiometri~nem razmerju, skladno s faznim diagramom Nb-Al. Preiskovan je bil vpliv razli~nih~asov izdelave: (10, 30, 60) s pri toku maksimalno 2000 A in napetosti 1,5-2,0 V. Izdelani vzorci so bili karakterizirani z vrsti~no elektronsko mikroskopijo in rentgensko difrakcijo. Rentgenska difrakcija je odkrila, da sta prevladujo~i fazi NbAl3 in Nb. Vrsti~na elektronska mikroskopija je pokazala gosto mikrostrukturo z majhnim dele`em poroznosti in sledovi preostalega aluminija. Mikrotrdota preizkusnega materiala, sintranega 60 s, s sintranjem aktiviranim z elektri~nim tokom, je bila okrog 405 HV±46 HV0,05. Klju~ne besede: in situ kompoziti, NbAl3 aluminidi, sintranje aktivirano z elektri~nim tokom (ECAS)

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“…The high-temperature strength and BDTT decreased with the increase of Ni content, but the fracture toughness and oxidation resistance increased [22]. Although macroalloying, rapid solidification, grain refining and fabrication of composites can improve ductility and oxidation resistance for NbAl 3 , these methods seem to be insufficient for industrial applications [23]. Hence, we expect to find a new structure with excellent performance for NbAl 3 by using CALYPSO code [24].…”

Section: Introductionmentioning

confidence: 99%

Stable Properties of NbAl3 under High Pressure: Theoretical Predictions and First-Principles Calculations

Jiao

Liu

et al. 2016

Proceedings of the 4th 2016 International Conference on Material Science and Engineering (ICMSE 2016)

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Nb-Al alloy compounds are expected to be high temperature structural materials. However, the low toughness and poor oxidation resistance are the main obstacles to hinder Nb-Al intermetallics from applications. In this paper, a new monoclinic phase of NbAl 3 was proposed by particle swarm optimization. Structural and mechanical properties of monoclinic phase were investigated using the first-principles method. The calculated enthalpies suggested that the known tetragonal structure was more stable than monoclinic structure from 0 to 200 GPa, but the ductility of monoclinic phase was better than that of tetragonal phase.

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Studies on the formation of aluminides in heated Nb–Al powder mixtures

Cited by 30 publications

References 32 publications

Reactive synthesis and characterization of titanium aluminides produced from elemental powder mixtures

Reactive synthesis and characterization of titanium aluminides produced from elemental powder mixtures

Effect of holding time on the production of Nb-NbAl3 intermetallic composites via electric-current-activated sintering

Stable Properties of NbAl3 under High Pressure: Theoretical Predictions and First-Principles Calculations

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