Ultrahigh strength and high plasticity in TiAl intermetallics with bimodal grain structure and nanotwins

Edalati, Kaveh; Toh, Shoichi; Iwaoka, Hideaki; Watanabe, Masashi; Horita, Zenji; Kashioka, Daisuke; Kishida, Kyosuke; Inui, Haruyuki

doi:10.1016/j.scriptamat.2012.07.030

Cited by 102 publications

(73 citation statements)

References 37 publications

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“…In the present study, we investigate the influence of pressure on the formation of the ductile β-phase in γ-based TiAl alloys, which is not only of fundamental interest, but is also most relevant to modelling high-pressure deformation techniques, such as high-pressure torsion, in order to achieve severe plastic deformation [11][12][13][14][15] and high-pressure near-net-shape forging [16][17][18][19]. These deformation processes operate at pressures up to 7 GPa and forces exceeding 1 GN, respectively.…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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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“…Combinations of different SPD processing techniques are available to enhance the upper limit of mechanical properties of a specific alloy [9][10][11][12][13] but it is also important to study achieving superior properties by bonding dissimilar metals through a procedure such as fusion welding. Alternatively, processing by HPT was applied recently for the consolidation of metal powders and for fabricating dissimilar metallic systems based on aluminum and magnesium: for example, Al-Fe, 14 Al-Mg, 15 Al-Ni, 16 Al-Ti, 17 Al-W, 18,19 and Mg-Zn-Y. 20 Nevertheless, the practical difficulties associated with these processes include a requirement for a high processing temperature, 16,17,19,20 the need for a two-step process of cold/hot compaction prior to consolidation by HPT 18 and the inherent damage that may be introduced in the HPT anvils because of the stacking of fine hard powders in the depressions on the anvil surfaces.…”

Section: Introductionmentioning

confidence: 99%

Using high-pressure torsion to process an aluminum–magnesium nanocomposite through diffusion bonding

et al. 2015

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Disks of commercial Al-1050 and ZK60A alloys were stacked together and then processed by conventional high-pressure torsion (HPT) through 1 and 5 turns at room temperature to investigate the synthesis of an Al-Mg alloy system. Measurements of microhardness and observations of the microstructures and local compositions after processing through 5 turns revealed the formation of an ultrafine multi-layered structure in the central region of the disk but with an intermetallic b-Al 3 Mg 2 phase in the form of nano-layers in the nanostructured Al matrix near the edge of the disk. The activation energy for diffusion bonding of the Al and Mg phases was estimated and it is shown that this value is low and consistent with surface diffusion due to the very high density of vacancy-type defects introduced by HPT processing. The results demonstrate a significant potential for making use of HPT processing in the preparation of new alloy systems.

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“…Although most of these works are focused on HPT processing using bulk samples, consolidation of powders using HPT has recently received much attention [23][24][25][26][27][28][29][30] . The HPT method was recently applied for production of nanostructured intermetallics with ultrahigh strength and high ductility from their elemental constituents 33,34 . The method was applied to powder mixtures of the Al-Ni and Al-Ti systems and it was found that in addition to powders consolidation and grain refinement, nanograined intermetallics were formed.…”

Section: Introductionmentioning

confidence: 99%

Production of nanograined intermetallics using high-pressure torsion

2013

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Formation of intermetallics is generally feasible at high temperatures when the lattice diffusion is fast enough to form the ordered phases. This study shows that nanograined intermetallics are formed at a low temperature as 573 K in Al-25 mol% Ni, Al-50 mol.% Ni and Al-50 mol% Ti powder mixtures through powder consolidation using high-pressure torsion (HPT). For the three compositions, the hardness gradually increases with straining but saturates to the levels as high as 550-920 Hv. In addition to the high hardness, the TiAl material exhibits high yield strength as ~3 GPa with good ductility as ~23%, when they are examined by micropillar compression tests. X-ray diffraction analysis and high-resolution transmission electron microscopy reveal that the significant increase in hardness and strength is due to the formation of nanograined intermetallics such as Al 3 Ni, Al 3 Ni 2 , TiAl 3 , TiAl 2 and TiAl with average grain sizes of 20-40 nm.

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Ultrahigh strength and high plasticity in TiAl intermetallics with bimodal grain structure and nanotwins

Cited by 102 publications

References 37 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

Using high-pressure torsion to process an aluminum–magnesium nanocomposite through diffusion bonding

Production of nanograined intermetallics using high-pressure torsion

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