Deformation of lamellar TiAl alloys by longitudinal twinning

Edwards, Thomas Edward James; Gioacchino, Fabio Di; Muñoz‐Moreno, R.; Clegg, William

doi:10.1016/j.scriptamat.2016.03.004

Cited by 51 publications

(33 citation statements)

References 26 publications

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“…This causes the III T domain to be more confined in the physical pillar. This restriction probably inhibited the activation of the longitudinal twinning of III T [16,35], explaining why it was not seen in the experiment, as concluded previously [16,35,67]. Secondly, although EBSD shows that there was an occurrence of longitudinal twinning in lamella I M (Fig.…”

Section: Deformation Twinning and Its Influence On Mechanical Propertiessupporting

confidence: 57%

“…Because internal stress inherently relates to microstructures of constituent phases, it is important to study the relationships between microstructure and deformation in TiAl alloys. There have been a number of studies to understand such relationships via ex-situ and in-situ mechanical testing and electron microscopy (EM) [6,15,16]. However, complex microstructures make it difficult to interpret experimentally observed behaviour.…”

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confidence: 99%

“…Recently, micromechanical testing of TiAl alloys which are commonly used in aeroengines has proved helpful to extract the intrinsic mechanical properties of TiAl [11,28,33], and the small-volume specimen has made it practical to include detailed microstructure in CP-FEM. Moreover, the development of methods for mapping deformation in micromechanical testing [34] has helped linking the mechanical properties to the accumulation of plastic strain in individual lamellae [16,35].…”

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confidence: 99%

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Crystal plasticity analysis of deformation anisotropy of lamellar TiAl alloy: 3D microstructure-based modelling and in-situ micro-compression

Chen

Edwards

Gioacchino

et al. 2019

International Journal of Plasticity

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Detailed microstructure characterisation and in-situ micropillar compression were coupled with crystal plasticity-based finite element modelling (CP-FEM) to study the micromechanisms of plastic anisotropy in lamellar TiAl alloys. The consideration of microstructure in both simulation and in-situ experiments enables in-depth understanding of micromechanisms responsible for the highly anisotropic deformation response of TiAl on the intralamella and inter-lamella scales. This study focuses on two specific configurations of / 2 lamellar microstructure with the / 2 interfaces being aligned 25 and 55 to the loading direction. Microstructure-based CP-FEM shows that longituginal slip of super and ordinary dislocations are most responsible for the plastic anisotropy in the 25 micropillar while the anisotropy of the 55 micropillar is due to longitudinal superdislocations and longitudinal twins. In addition, transversal superdislocations were more active, making the deformation in the 25 micropillar less localised than that in the 55 micropillar. Moreover, the CP-FEM 2 / 42 model successfully predicted substantial build-up of internal stresses at / 2 interfaces, which is believed to be detrimental to the ductility in TiAl. However, as evidenced by the model, the detrimental internal stresses can be significantly relieved by the activation of transverse deformation twinning, suggesting that the ductility of TiAl can be improved by promoting transverse twins. IntroductionTitanium aluminide (TiAl) alloys have a density approximately half that of nickel-based superalloys [1] and specific strength that is comparable with nickel-based alloys up to temperatures as high as 700 o C [2], resulting in a potentially wide application of the alloys in aero-engines [3,4]. However, the application of TiAl alloys is limited by their low ductility, which is mainly due to the anisotropy of constituent microstructure in TiAl, and insufficient understanding of the microstructure-property relationships. In-depth understanding of the relationships would lead to wider applications of these lightweight alloys in aerospace, leading to the weight reduction, thereby, increase in the fuel efficiency and decrease in the CO2 emissions. Although there have been significant efforts in understanding the relationships between chemical composition, microstructure and mechanical properties of TiAl alloys, in particular regarding the TiAl lamellar microstructure [1, 5-7], there have been no detailed studies in which both in-situ mechanical testing and microstructure-based modelling are carried out to provide more insights into the direct relationships between constituent microstructures and mechanical properties. This present study aims to integrate modelling and in-situ tests to seek possible solutions to the low ductility of TiAl. The poor ductility of lamellar TiAl alloys is partly due to its strong plastic anisotropy because of the respective anisotropy of constituent phases. Lamellar TiAl alloys consist of two phases: -face centred tetragonal (f.c.t.) and ...

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Section: Deformation Twinning and Its Influence On Mechanical Propertiessupporting

confidence: 57%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Crystal plasticity analysis of deformation anisotropy of lamellar TiAl alloy: 3D microstructure-based modelling and in-situ micro-compression

Chen

Edwards

Gioacchino

et al. 2019

International Journal of Plasticity

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“…Elsewhere, preliminary results by the present authors have shown from DIC strain mapping of deformed micropillars of TiAl lamellar stacks milled from individual colonies that by 10 % strain, bands of high shear strain develop near or at the lamellar interfaces [10]. Further, high temperature testing of micropillars is possible up to 630 °C ex situ [11], and using in situ equipment [12], up to 800 °C [13].…”

Section: Introductionmentioning

confidence: 59%

Deformation of lamellar γ-TiAl below the general yield stress

et al. 2019

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The occurrence of plasticity below the macroscopic yield stress during tensile monotonic loading of nearly lamellar Ti-45Al-2Nb-2Mn(at%)-0.8vol% TiB 2 at both 25 °C and 700 °C, and in two conditions of lamellar thickness, was measured by digital image correlation strain mapping of a remodelled Au surface speckle pattern. Such initial plasticity, not necessarily related to the presence of common stress concentrators such as hard particles or cracks, could occur at applied stresses as low as 64 % of the general yield stress. For a same applied strain it was more prominent at room temperature, and located as slip and twinning parallel to, and near to or at (respect.

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“…For high resolution DIC at room temperature, this can be achieved by the deposition of SiO 2 or Al 2 O 3 colloids [2,12,13], or metal nanoparticles (Pt, Au) [14,15], electron beam Pt deposition (suitable for small areas only) [16][17][18][19] and reconstructed metal thin films [1,20]. The latter, also referred to as thin film remodelling [1], is where a thin film is heat treated so that it breaks up into an array of particles.…”

Section: Introductionmentioning

confidence: 99%

Stable Speckle Patterns for Nano-scale Strain Mapping up to 700 °C

et al. 2017

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The digital image correlation (DIC) of speckle patterns obtained by vapour-assisted gold remodelling at 200 -350°C has already been used to map plastic strains with submicron resolution. However, it has not so far proved possible to use such patterns for testing at high temperatures. Here we demonstrate how a gold speckle pattern can be made that is stable at 700°C, to study deformation in a commercial TiAl alloy (Ti-45Al-2Nb-2Mn(at%)-0.8 vol% TiB 2 ). The pattern is made up of a uniformly sized random array of Au islands as small as 15 nm in diameter, depending on reconstruction parameters, with a sufficiently small spacing to be suitable for nano-scale, nDIC, strain mapping at a subset size of 60 × 60 nm 2 . It can be used at temperatures up to 700°C for many hours, for high cycle fatigue testing for instance. There is good particle attachment to the substrate. It can withstand ultra-sound cleaning, is thermally stable and has a high atomic number contrast for topography-free backscatter electron imaging.

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Deformation of lamellar TiAl alloys by longitudinal twinning

Cited by 51 publications

References 26 publications

Crystal plasticity analysis of deformation anisotropy of lamellar TiAl alloy: 3D microstructure-based modelling and in-situ micro-compression

Crystal plasticity analysis of deformation anisotropy of lamellar TiAl alloy: 3D microstructure-based modelling and in-situ micro-compression

Deformation of lamellar γ-TiAl below the general yield stress

Stable Speckle Patterns for Nano-scale Strain Mapping up to 700 °C

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