The texture of diffusion-grown HfAl3 layers

Maas, Jh Jan; Bastin, GF Giel; Vanloo, Fjj; Metselaar, R Ruud

doi:10.1016/0022-5088(83)90232-1

Cited by 9 publications

(10 citation statements)

References 5 publications

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“…These Si atoms react with the substrate Nb atoms at the growth front, i.e., the NbSi 2 layer-substrate interface, to form further NbSi 2 phase. There is experimental evidence that Si diffusion is much faster than metal diffusion in transition metal disilicides such as NbSi 2 , MoSi 2 , WSi 2 , VSi 2 and TaSi 2 [30,31]. In fact, Salamon and Mehrer [32] have shown that the tracer diffusion of 71 Ge in MoSi 2 is orders of magnitude faster than 99 Mo.…”

Section: Discussionmentioning

confidence: 98%

Microstructure and High Temperature Oxidation Performance of Silicide Coating on Nb-Based Alloy C-103

2010

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The microstructure and oxidation resistance of NbSi 2 coating formed on Nb-based alloy C-103 by a pack siliconization process have been studied. The as-formed coating consists of an outer NbSi 2 layer and an inner Nb 5 Si 3 layer. A NbSi 2 -Nb 5 Si 3 two-phase zone is also present between the above two layers. Weight-change data obtained under isothermal and cyclic oxidation in air at 1100 and 1300°C, suggests that the coating gives oxidation protection up to about 4 h. The oxide scale that formed on the coating during oxidation exposure consists of an outer glassy silica layer and an inner Nb 2 O 5 -silica mixed layer. Nb 2 O 5 phase is also present in the outer silica scale in the form of elongated particles. Oxidation protection is achieved primarily by the presence of the glassy silica layer on the surface. Spallation of this layer during thermal cycling causes significant reduction in the protective life of the coating.

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Section: Discussionmentioning

confidence: 98%

Microstructure and High Temperature Oxidation Performance of Silicide Coating on Nb-Based Alloy C-103

2010

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“…Here we discuss the impact of extra freedom on the 1d-APD in detail [19][20][21][22][23]47] to assess the stability of D0 22 -TiAl 3 at elevated temperature, using n = 8 series as an example. Assuming that there is one 1d-APD in this configuration, then this structure has (a) an formation energy of about −0.070 eV/cell or −0.009 eV/TiAl 3 with respective to that of D0 22 , (b) freedom of configurations, w = 8 due to the fact that such 1d-APD may occur for each TiAl 3 unit in the cell.…”

Section: Discussion: 1d-apd In D0 22 -Tial 3 Chain and Configurationmentioning

confidence: 99%

“…Tang and co-workers performed first-principles calculations for some one-dimensional long period structures (1D-LPSs) based on the cubic L1 2 -TiAl 3 [45,46]. In the present manuscript, we have analysed systematically the existing TiAl 3 phases and predicted various stackings by application of the one-dimensional antiphase domain (1d-APD) model [19][20][21][22][23]47] based on the D0 22 structure using ab initio density functional theory (DFT). We also performed DFT calculations with hybrid-functional correction for the three known TiAl 3 (L1 2 , D0 22 and D0 23 ) phases.…”

Section: Introductionmentioning

confidence: 99%

An ab initio study on stacking and stability of TiAl3 phases

Fang

Fan

2018

Computational Materials Science

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TiAl 3 persists in many Al alloys and plays a detrimental role in solidification of related melts. Knowledge about TiAl 3 phases and phase relations is of importance to get some insight into the solidification processes, the microstructures and the properties of Al alloys. In this manuscript, we present a systematic study of the basic structures of TiAl 3 with aid from ab initio density functional theory (DFT) calculations. The study confirms that the ground state of TiAl 3 has the D0 23 structure, whereas the observed D0 22 type is a metastable phase. The calculations have identified the stability of a series of stacking composed of both D0 22-and D0 23-TiAl 3 units. At elevated temperature, the equilibrium configuration contains neither pure D0 23 nor pure D0 22 but will consist of a combination of the TiAl 3 cubes arranged to minimise its Gibbs energy. Stacking default investigation reveals a large energy barrier for the D0 22 ↔ D0 23 transition. The obtained information sheds some light on the rich variety of the experimental observations in Al alloys, and further to understand the complex titanium aluminides and their thermo-structural properties.

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“…Because of its distinct crystal structure, composition, lattice parameter and so misfit, D0 22 Ni 3 V may exhibit a different morphology to L1 2 Ni 3 Al as well as different coarsening kinetics and strengthening effects [12,13,14]. D0 22 Ni 3 V has lattice parameters of a = 3.543 Å, c = 7.221 Å [15], compared to those for metastable D0 22 Ni 3 Nb of a = 3.62 Å, 25 c = 7.41 Å [7].…”

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confidence: 99%

“…The Ni 3 V phase offers some advantages over Ni 3 Nb as it is thermodynamically stable and 30 has a different lattice misfit, δ. Given δ = 2(a γ −a γ )/(γ +a γ ) and a γ = 3.51 Å, δa γ -a N i3V ∼ 0.9%, and δa γ -c N i3V ∼ 2.8%, in contrast to δa γ -a N i3N b ∼ 3.1%, and δa γ -c N i3N b ∼ 5.4%, taking the lattice parameters given earlier for Ni 3 V [15] and Ni 3 Nb [7]. Further, it is possible to have controlled precipitation of L1 2 Ni 3 Al with optimised volume fraction and size before producing D0 22 Ni 3 V 35 at a lower temperature.…”

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confidence: 99%

A nickel based superalloy reinforced by both Ni3Al and Ni3V ordered-fcc precipitates

et al. 2019

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A nickel based superalloy has been designed where the fcc γ Ni matrix is reinforced by two different ordered-fcc intermetallic compounds, γ L1 2 Ni 3 Al and γ D0 22 Ni 3 V. Primary ageing at 900 − 1000 • C precipitated spherical L1 2 Ni 3 Al, whose volume fraction and size were controlled by altering the ageing temperature and time. Secondary ageing at 700 • C for 1 − 1000 h precipitated D0 22 Ni 3 V laths. The duplex precipitation increased hardness by up to 85 HV, with ∼ 500 MPa compressive proof strength maintained at 800 • C. Electron microscopy studied the Ni 3 Al precipitation and confirmed the form of the secondary Ni 3 V precipitates and their long term stability.Nickel based superalloys are widely used due to their combination of strength, creep, toughness, environmental resistance and microstructural stability in the 650 − 1200 • C interval [1,2]. Such alloys exploit the two-phase field that exists within the Ni-Al binary system to produce microstructures comprising a γ face-centred cubic (fcc) A1 (Strukturbericht designation) matrix, Figure 1a, 5 reinforced with γ L1 2 Ni 3 Al ordered-fcc intermetallic precipitates, Figure 1b. A variety of additional phases are used in multicomponent (∼ 10) commercial superalloys, including other intermetallics as well as carbides and borides. However, there is an additional ordered-fcc D0 22 γ phase, Figure 1c, that can be exploited in superalloys, e.g. Inconel 718 [3], which is also being explored in 10 other alloy systems [4,5,6]. Unfortunately, the D0 22 Ni 3 Nb phase in Inconel 718 is metastable [7,8] decomposing into the δ Ni 3 Nb D0 a orthorhombic P mmn phase [9, 10]. The Ni 3 X type intermetallics adopt a number of stable crystal structures as the X element is changed due to differing formation energies. For Ni 3 X intermetallics with X = Nb, Ta, Mo the stable structure is D0 a , while for 15 X = Ti the D0 24 structure is adopted, and with X = Al and Si the traditional γ * Corresponding

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The texture of diffusion-grown HfAl3 layers

Cited by 9 publications

References 5 publications

Microstructure and High Temperature Oxidation Performance of Silicide Coating on Nb-Based Alloy C-103

Microstructure and High Temperature Oxidation Performance of Silicide Coating on Nb-Based Alloy C-103

An ab initio study on stacking and stability of TiAl3 phases

A nickel based superalloy reinforced by both Ni3Al and Ni3V ordered-fcc precipitates

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