Alloy design of gamma titanium aluminides based on phase diagrams

Hashimoto, Keizo; Kimura, Masao; Mizuhara, Y.

doi:10.1016/s0966-9795(98)00048-x

Cited by 52 publications

(21 citation statements)

References 6 publications

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“…The assignment of a phase to a composition observed was routinely corroborated by X-ray diffraction (XRD), though not in all cases the lattice parameter(s) were determined. The assignment of phase reactions used the strategy outlined earlier [18] and, in addition, could draw on the extensive information on variations of the phase homogeneity ranges available for Al-Cr-Ti between 1000°C and 1200°C in the form of isothermal sections (1000°C, [2,3,5] 1050°C, [6] 1150°C, [5] and 1200°C [19] ). Figure 1 shows the solid-state phase equilibria derived for 900°C (up to 75 at.…”

Section: Resultsmentioning

confidence: 99%

Reaction Scheme and Liquidus Surface of the Ternary System Aluminum-Chromium-Titanium

Chen

Weitzer

Krendelsberger

et al. 2009

Metall Mater Trans A

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The constitution of the ternary system Al-Cr-Ti is investigated over the entire composition range using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), differential thermal analysis (DTA) up to 1500°C, and metallography. Solid-state phase equilibria at 900°C are determined for alloys containing £75 at. pct aluminum and at 600°C for alloys containing >75 at. pct Al. A reaction scheme linking these solid-state equilibria with the liquidus surface is presented. The liquidus surface for £50 at. pct aluminum is dominated by the primary crystallization field of bcc b(Ti,Cr,Al). In the region >50 at. pct Al, the ternary L1 2 -type phase s forms in a peritectic reaction p max at 1393°C from L + TiAl. Furthermore, with the addition of chromium, the binary peritectic L + a(Ti,Al) = TiAl changes into an eutectic L = a(Ti,Al) + TiAl. This eutectic trough descends monotonously through a series of transition reactions and ternary peritectics to end in the binary eutectic L = Cr 7 Al 45 + (Al).

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Section: Resultsmentioning

confidence: 99%

Reaction Scheme and Liquidus Surface of the Ternary System Aluminum-Chromium-Titanium

Chen

Weitzer

Krendelsberger

et al. 2009

Metall Mater Trans A

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“…Summing up the atomic scattering lengths weighted by the respective phase factors for all atoms within the unit cell yields the structure factor F HKL which finally determines the intensity of the diffraction peaks. [37,38] If the elements are distributed randomly in the crystal lattice, a virtual atom with a mean scattering length is calculated. Intensities of single reflections are derived from the structure factors which in turn are calculated by summing up the mean atomic scattering lengths of the atoms in one unit cell and weighting them by an individual phase factor that depends on the position of the respective atom in the unit cell.…”

Section: High Energy X-rays and Neutronsmentioning

confidence: 99%

“…[24,37,40,41] One way of investigating phase fractions present at elevated temperatures is to perform conventional XRD on heat-treated and quenched specimens. A drawback of this method is that changes in the microstructure might occur during cooling which could potentially lead to erroneous results.…”

Section: Reviewmentioning

confidence: 99%

The Contribution of High‐Energy X‐Rays and Neutrons to Characterization and Development of Intermetallic Titanium Aluminides

et al. 2011

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Intermetallic γ‐TiAl based alloys are a novel class of lightweight structural materials that exhibit excellent high‐temperature strength while having low density. These properties make them ideal candidates for replacing dense Ni base alloys currently used in the temperature range from 550 to 750 °C. Therefore, extensive research activities were conducted during the last 20 years to make this innovative class of materials fit for service. In this task, diffraction methods have been an important tool for promoting the development of TiAl alloys. The ability to perform experiments in situ and to determine phase fractions even in cases where two phases are present in ultrafine lamellar structures are only two examples for applications in which diffraction methods are indispensable. In this work, a review is given concerning the use of diffraction methods in the development of TiAl alloys. Different methods are introduced and highlighted by examples. This review lists the advantages of diffraction experiments and critically discusses the limits of the individual methods.

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“…strong -phase former, and the formation of this phase seems to be resulted from a very limited solubility of W inTiAl. 11) To confirm further the formation of -phase by the implantation, detailed TEM observations were performed. Figure 3 shows a TEM bright field image of a cross section and diffraction patterns of the specimen implanted with Fe (50 keV, 10 21 m À2 ).…”

Section: Specimen Characterisationmentioning

confidence: 99%

Oxidation Resistance of TiAl Improved by Ion Implantation of Beta-Former Elements

2004

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TiAl coupon specimens were implanted with Fe, Mo, Ta or W ions and then cyclically oxidised with temperature varying between room temperature and 1200 K in a flow of purified oxygen under atmospheric pressure. The surface modification by the ion implantation was characterised by glancing angle X-ray diffractometry (GAXRD), Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). The oxidised specimens were examined by AES, GAXRD, X-ray diffractometry, scanning electron microscopy and electron probe microanalysis. The oxidation resistance of TiAl is significantly improved by the implantation of Mo, Ta or W ions with a dose of 10 21 ionsÁm À2at acceleration voltages ranging from 50 to 340 kV. The acceleration voltage has a small influence. The oxide scales consist predominantly ofAl 2 O 3 and are very adherent to the substrates even after 20 cycles (400 h). On the other hand, the implantation of Fe has a little effect. The significant effect brought about by the implantation is attributable to the formation of a thin -Ti phase layer in the modified area. Therefore, a possible explanation for the improved oxidation resistance is the formation of -Ti phase, which is a solid solution where diffusion of Al seems much faster than in -TiAl which has an ordered structure. The enhanced Al diffusion results in the formation of a thin but continuous Al 2 O 3 -rich layer in the scale during the initial oxidation stages. The enrichment of Al relative to Ti by the implantation was thought playing some role. The so-called doping effect of Mo, Ta and W is also contributing to the early formation of Al 2 O 3 -rich layers by retarding TiO 2 growth.

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Alloy design of gamma titanium aluminides based on phase diagrams

Cited by 52 publications

References 6 publications

Reaction Scheme and Liquidus Surface of the Ternary System Aluminum-Chromium-Titanium

Reaction Scheme and Liquidus Surface of the Ternary System Aluminum-Chromium-Titanium

The Contribution of High‐Energy X‐Rays and Neutrons to Characterization and Development of Intermetallic Titanium Aluminides

Oxidation Resistance of TiAl Improved by Ion Implantation of Beta-Former Elements

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