In situ high-energy X-ray diffraction study and quantitative phase analysis in the α+γ phase field of titanium aluminides

Yeoh, L. A.; Liss, Klaus-Dieter; Bartels, A.; Chladil, Harald F.; Avdeev, Maxim; Clemens, Helmut; Gerling, R.; Buslaps, T.

doi:10.1016/j.scriptamat.2007.08.021

Cited by 46 publications

(53 citation statements)

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“…Controversially, a large pressure dependence has been reported by Errandonea et al [48], which Zhang et al refute and interpret as a response to deviatoric stresses, occurring in their diamond-anvil cell. In alloys, especially titanium aluminides, lattice parameters and c/a ratios of both γ-and α 2 -phases depend strongly on the composition of each phase, which varies as a function of temperature and segregation in multi-phase systems [31,57,58]. Increasing 2c/a ratios of {1.60333, 1.60432, 1.60476} with increasing Al content in single-phase α 2 Ti-{24, 28.4, 33.3}Al have been measured by Dubrovinskaia et al [59].…”

Section: Crystallographic Anisotropy Disorder and Transformation Behmentioning

confidence: 99%

“…However, it is lacking even in a massively-transformed γ-phase [36]. It has been reported that γ always tends to order, and when disordered, it transforms to the α-/α 2 -phase [31]. Moreover, for alloys with no added nucleants, in situ temperature studies on cooling from the disordered α-phase consistently revealed significant undercooling below the α-transus, where the γ-phase should re-appear.…”

Section: Crystallographic Anisotropy Disorder and Transformation Behmentioning

confidence: 99%

“…A variety of alloys based on TiAl with additions of niobium has been developed in the so-called TNB alloy series [5,[25][26][27], where Nb substitutes Ti sites and eventually stabilizes the bcc-based β-phases. In the present study, we have investigated the TNB composition Ti-45Al-7.5Nb-0.25C, which has been produced through a powder-metallurgical route by Gerling et al [28] using gas-atomization and subsequent hot-isostatic pressing for 2 h at 200 MPa and 1553 K. It is obtained from the same series as extensively characterized by Chladil et al [29,30] and Yeoh et al [31], showing globular γ-TiAl/α 2 -Ti 3 Al grains with an average size of about 15 µm (see Figure 1b in [29]). In situ investigations revealed conventional transformation behavior for this Ti-45Al-7.5Nb-0.25C alloy, with T eu = 1453 K and T α = 1565 K, with an additional peritectic (α + β)-phase field at T per~1 500 K, but no (α + β + γ)-phase field has been observed.…”

Section: Introductionmentioning

confidence: 99%

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Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Liss

Funakoshi

Dippenaar

et al. 2016

Metals

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Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10-GPa range, and hence, it is necessary to investigate the phase diagrams of candidate materials under these extreme conditions. Here, we report on an in situ synchrotron X-ray diffraction study in a large-volume press of a modern (α 2 + γ) two-phase material, Ti-45Al-7.5Nb-0.25C, under pressures up to 9.6 GPa and temperatures up to 1686 K. At room temperature, the volume response to pressure is accommodated by the transformation γ → α 2 , rather than volumetric strain, expressed by the apparently high bulk moduli of both constituent phases. Crystallographic aspects, specifically lattice strain and atomic order, are discussed in detail. It is interesting to note that this transformation takes place despite an increase in atomic volume, which is due to the high ordering energy of γ. Upon heating under high pressure, both the eutectoid and γ-solvus transition temperatures are elevated, and a third, cubic β-phase is stabilized above 1350 K. Earlier research has shown that this β-phase is very ductile during plastic deformation, essential in near-conventional forging processes. Here, we were able to identify an ideal processing window for near-conventional forging, while the presence of the detrimental β-phase is not present under operating conditions. Novel processing routes can be defined from these findings.

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Section: Crystallographic Anisotropy Disorder and Transformation Behmentioning

confidence: 99%

Section: Crystallographic Anisotropy Disorder and Transformation Behmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Liss

Funakoshi

Dippenaar

et al. 2016

Metals

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“…The SEM investigations were carried out in backscattered electron (BSE) mode at an acceleration voltage of 15 kV on the specimens prepared by standard metallographic methods. A quantitative evaluation of the phases present as a function of temperature using HEXRD [6] was performed at the HARWI II beamline at the storage ring DORIS III at DESY in Hamburg, Germany, which is operated by the Helmholtz-Zentrum Geesthacht [7], where the beam defining an area of 0.5×0.5 mm 2 had a mean energy of 104.7 keV. Solid samples with a diameter of 5 mm and a length of 15 mm were rapidly inductionheated to 1000°C in a custom built furnace under Ar atmosphere, held at this temperature for 2 min and then continuously heated to 1350°C with a heating rate of 2 °C/min.…”

Section: Methodsmentioning

confidence: 99%

Phase Equilibria and Phase Transformations in Molybdenum-Containing TiAl Alloys

et al. 2011

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Molybdenum, being a strong stabilizer, is an important alloying element in TiAl alloys, since a significant volume fraction of the disordered bcc -phase at elevated temperatures improves the processing characteristics during hot-working. Unfortunately, the effect of Mo on the individual phases and their transition temperatures is not completely known but is necessary for designing engineering applications. In this paper, sections of the Ti-Al-Mo ternary phase diagram derived from thermodynamic calculations as well as experimental data are presented. Further, the phase transition temperatures given by the phase diagrams are compared with results from isothermal heat treatment studies, differential scanning calorimetry measurements and insitu high-temperature diffraction experiments. Combining all of these results, a revised phase diagram is proposed.

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“…HEXRD experiments were performed to investigate, for example, the site occupancy within the α/α 2 phase in a Ti-45Al-7.5Nb-0.5C (at. %) alloy [81]. A sudden rearrangement of the atomic site occupancies provided evidence for the disordering temperature of the α 2 phase.…”

Section: Neutron Diffraction Studies On Order/disorder Transformationmentioning

confidence: 98%

In Situ Characterization Techniques Based on Synchrotron Radiation and Neutrons Applied for the Development of an Engineering Intermetallic Titanium Aluminide Alloy

Erdely

Schmoelzer

Schwaighofer

et al. 2016

Metals

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Abstract:Challenging issues concerning energy efficiency and environmental politics require novel approaches to materials design. A recent example with regard to structural materials is the emergence of lightweight intermetallic TiAl alloys. Their excellent high-temperature mechanical properties, low density and high stiffness constitute a profile perfectly suitable for their application as advanced aero-engine turbine blades or as turbocharger turbine wheels in next-generation automotive engines. As the properties of TiAl alloys during processing as well as during service are dependent on the phases occurring, detailed knowledge of their volume fractions and distribution within the microstructure is of paramount importance. Furthermore, the behavior of the individual phases during hot deformation and subsequent heat treatments is of interest to define reliable and cost-effective industrial production processes. In situ high-energy X-ray diffraction methods allow tracing the evolution of phase fractions over a large temperature range. Neutron diffraction unveils information on order-disorder transformations in TiAl alloys. Small-angle scattering experiments offer insights into the materials' precipitation behavior. This review attempts to shine a light on selected in situ diffraction and scattering techniques and the ways in which they promoted the development of an advanced engineering TiAl alloy.

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In situ high-energy X-ray diffraction study and quantitative phase analysis in the α+γ phase field of titanium aluminides

Cited by 46 publications

References 14 publications

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Phase Equilibria and Phase Transformations in Molybdenum-Containing TiAl Alloys

In Situ Characterization Techniques Based on Synchrotron Radiation and Neutrons Applied for the Development of an Engineering Intermetallic Titanium Aluminide Alloy

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