A Dislocation-Scale Characterization of the Evolution of Deformation Microstructures around Nanoindentation Imprints in a TiAl alloy

Guitton, Antoine; Kriaa, Hana; Bouzy, Emmanuel; Guyon, Julien; Maloufi, Nabila

doi:10.20944/preprints201801.0183.v1

Cited by 2 publications

(1 citation statement)

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“…SEM is flexible essentially because of the large sample surface area that can be imaged, as compared to TEM. Moreover, in SEM, the nondestructive Electron Channeling Contrast Imaging ECCI imaging mode provides TEM-like diffraction contrast imaging of near-surface defects with a good accuracy [17][18][19][20][21] . In terms of length scales, centimetric bulk materials can be characterized, enabling statistical studies.…”

Section: Introductionmentioning

confidence: 99%

Electron channeling contrast imaging characterization and crystal plasticity modelling of dislocation activity in Ti21S BCC material

et al. 2021

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In this paper, an original approach is proposed to compare modeling and relevant statistical experiments using -Ti21S Body Centered Cubic (BCC) metal as a challenging benchmark. Our procedure allows the evolution of microstructural defects to be tracked in situ with excellent spatial resolution, while observing a bulk sample region sufficiently large to be statistically representative of the material. We identify multiple mechanisms such as slip transfer, slip traces, pencil glide, etc. We demonstrate that for small plastic strains ( < 0.25 %) under uniaxial tensile loading, the Schmid law is satisfied statistically. Under these circumstances, changes in Critical Resolved Shear Stress (CRSS) are minimal and accommodation of incompatible deformation between grains has not yet become important. The majority of the observed slip plane traces at the mesoscale corresponds to the {123} family. Fully automated while precise, the reported approach compares this data with four crystal plasticity models, and provides a methodology for similar analyses in other materials. * Corresponding author. X-Ray Diffraction HR-XRD, Electron BackScattered Diffraction EBSD…) that provide valuable atomic scale information, such as activation energies and critical shear stresses. However, one may argue that most multiscale strategies usually address only very specific cases, and that they are not necessarily statistically representative of the myriad of mechanisms that can occur in real polycrystals. For instance, one can cite HR-TEM [4] studies of special grain boundaries (structure, energy, migration under stress and temperature…) and their interactions with dislocations (emission, absorption, transmission…). Indeed, such available studies are far from covering the full range of possible grain boundary configurations in a real polycrystal. In addition, preparing and testing of thin foils for electron transmission-based techniques [5-7] (TEM, Transmission Kikuchi Diffraction TKD) can unfortunately affect the defect microstructure and the mechanisms investigated because of inherent size, strain rate, and external surface effects. Besides, these techniques do not provide enough data for statistical analysis of physical mechanisms.Experimental findings at an intermediate, mesoscopic scale, can be used to improve our knowledge of polycrystal plasticity and to improve models at the grain scale. They provide validation data for advanced numerical simulations that predict the mechanical behavior of polycrystals (strain hardening, ductility etc.

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Section: Introductionmentioning

confidence: 99%

Electron channeling contrast imaging characterization and crystal plasticity modelling of dislocation activity in Ti21S BCC material

et al. 2021

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Nanoindentation of γ-TiAl with Different Crystal Surfaces by Molecular Dynamics Simulations

Fan

Zhou

et al. 2019

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The periodicity and density of atomic arrangement vary with the crystal orientation, which results in different deformation mechanisms and mechanical properties of γ-TiAl. In this paper, the anisotropic characteristics for γ-TiAl with (100), ( 1 ¯ 10 ) and (111) surfaces during nanoindentation at 300 K have been investigated by molecular dynamics simulations. It is found that there is no obvious pop-in event in all load-depth curves when the initial plastic deformation of γ-TiAl samples occurs, because the dislocation nucleates before the first load-drop; while a peak appears in both the unloading curves of the ( 1 ¯ 10 ) and (111) samples due to the release of energy. Stacking faults, twin boundaries and vacancies are formed in all samples; however, interstitials are formed in the (100) sample, a stacking fault tetrahedron is formed in the (111) sample; and two prismatic dislocation loops with different activities are formed in the ( 1 ¯ 10 ) and (111) samples, respectively. It is also concluded that the values of the critical load, strain energy, hardness and elastic modulus for the (111) sample are the maximum, and for the (100) sample are the minimum. Furthermore, the orientation dependence of the elastic modulus is greater than the hardness and critical load.

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A Dislocation-Scale Characterization of the Evolution of Deformation Microstructures around Nanoindentation Imprints in a TiAl alloy

Cited by 2 publications

References 5 publications

Electron channeling contrast imaging characterization and crystal plasticity modelling of dislocation activity in Ti21S BCC material

Electron channeling contrast imaging characterization and crystal plasticity modelling of dislocation activity in Ti21S BCC material

Nanoindentation of γ-TiAl with Different Crystal Surfaces by Molecular Dynamics Simulations

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