Indentation size effect and dislocation structure evolution in (001) oriented SrTiO3 Berkovich indentations: HR-EBSD and etch-pit analysis

Javaid, Farhan; Bruder, Enrico

doi:10.1016/j.actamat.2017.07.055

Cited by 49 publications

(43 citation statements)

References 40 publications

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“…The gradient map of the Raman signal has its strongest intensity between the cross‐shaped {110} planes of high dislocation density (Figure b). The strain gradient is stronger closer to the dislocations and decreases over distances of several microns, in agreement with observations from Javaid et al The SHG signal correlates to the areas between these zones where strain gradients occur . Furthermore, the analysis of SHG images taken in the volume of the sample provides us with a picture of the structure of the dislocation planes.…”

Section: Resultssupporting

confidence: 92%

Second Harmonic Generation Investigation of Symmetry Breaking and Flexoelectricity Induced by Nanoindentations in SrTiO₃

Kolhatkar¹,

Nicklaus²,

Youssef³

et al. 2019

Adv Funct Materials

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Strain gradients induced by nanoindentations in bulk undoped strontium titanate (SrTiO 3 ) are investigated. After indenting a 850 nm deep pattern on the SrTiO 3 surface with a 8 GPa hardness and an 83 GPa indentation modulus by a Berkovich tip, the resulting deformation patterns are imaged by Raman spectroscopy and by second harmonic generation microscopy. Cross-shaped compressively stressed regions along the cubic SrTiO 3 primary slip planes are observed. These zones relax toward the unstrained bulk material through localized strain gradients on a length scale of several microns. Second harmonic tomography reveals the reduction of the crystal's centrosymmetry in the vicinity of the crosslike features due to a strain gradient. These results indicate the appearance of flexoelectricity following the nanoindentation process due to the creation of an inhomogeneous strain.

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Section: Resultssupporting

confidence: 92%

Second Harmonic Generation Investigation of Symmetry Breaking and Flexoelectricity Induced by Nanoindentations in SrTiO₃

Kolhatkar¹,

Nicklaus²,

Youssef³

et al. 2019

Adv Funct Materials

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“…Theoretically, these authors used a gradient plasticity framework in conjunction with a Hall-Petch approach to analyze the deformation curves and to establish criteria for slip transmission across GBs [7]. Zhang 3 et al [8] carried out nanoindentation on copper bicrystals and found that the hardness first increases and then decreases with increasing indentation depth. They pointed out that this phenomenon is related to the interaction between dislocations and GB.…”

Section: Introductionmentioning

confidence: 99%

Grain boundary effect on nanoindentation: A multiscale discrete dislocation dynamics model

Zhang

et al. 2019

Journal of the Mechanics and Physics of Solids

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Nanoindentation is a convenient method to investigate the mechanical properties of materials on small scales by utilizing low loads and small indentation depths.However, the effect of grain boundaries (GB) on the nanoindentation response remains unclear and needs to be studied by investigating in detail the interactions between dislocations and GBs during nanoindentation. In the present work, we employ a threedimensional multiscale modeling framework, which couples three-dimensional discrete dislocation dynamics (DDD) with the Finite Element method (FEM) to investigate GB effects on the nanoindentation behavior of an aluminum bicrystal. The interaction between dislocations and GB is physically modeled in terms of a penetrable GB, where piled-up dislocations can penetrate through the GB and dislocation debris at GBs can emit full dislocations into grains. In the simulation, we confirmed two experimentally observed phenomena, namely, pop-in events and the dependence of indentation hardness on the distance from GB. Two pop-in events were observed, of which the initial pop-in event is correlated with the activation and multiplication of dislocations, while the GB pop-in event results from dislocation transmission through the GB. By changing the distance between the indenter and GB, the simulation shows that the 2 indentation hardness increases with decreasing GB-indenter distance. A quantitative model has been formulated which relates the dependency of indentation hardness on indentation depth and on GB-indenter distance to the back stress created by piled-up geometrically necessary dislocations in the plastic zone and to the additional constraint imposed by the GB on the plastic zone size.

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“…The room and elevated temperature indentations were vibrational polished (Jean-Wirtz GmbH, D€ usseldorf, Germany) using 40 nm colloidal silica suspension (OP-S, Struers A/S, Ballerup, Denmark) to make sure the dislocation etch-pits associated with pileups extend below the surface. Our previous nanoindentation studies 15,16 conducted at room temperature on (001) STO single crystal confirmed that the etch-pits in dislocation pile-up extend well below the surface in half-loop shape along h110i 110 f g systems. However, for elevated temperature STO indentations, this additional polishing step was necessary to make sure that the dislocations etch-pits in pile-ups are not only limited to surface but extend well below the surface in <100> and <110> directions.…”

Section: Methodsmentioning

confidence: 61%

“…Moreover, only slip along the

false⟨ 110 false⟩ \{110\}

system was confirmed in these studies. Certain phenomenon, such as the indentation size effect (ISE), which is more pronounced at very small indentation depths was recently studied for the first time in (001) STO single crystals via direct observation of dislocations using etch‐pit and high resolution electron backscattered diffraction (HR‐EBSD) analysis. The independent measurements of Geometrically Necessary Dislocations (GNDs) gives a profound understanding of the physical basis of the ISE.…”

Section: Introductionmentioning

confidence: 99%

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Temperature dependence of indentation size effect, dislocation pile‐ups, and lattice friction in (001) strontium titanate

2017

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Nanoindentations with a Berkovich type indenter were performed on (001) strontium titanate (STO) single crystal at 25°C and 350°C, analyzing the influence of temperature on the indentation size effect (ISE) and dislocation structure around the residual impression. It is found that the STO exhibits an ISE, which is strongly reduced at 350°C compared to 25°C. The dislocation structure around the residual impression has been resolved using an etch-pit technique. At 25°C, the extension of the dislocation pile-ups were found to be shorter as compared to 350°C. This also correlates with the smaller size effects at 350°C. Peach-Koehler forces and the elastic-plastic indentation stress field were used to model the influence of the lattice frictional stress on the dislocation pile-ups. Based on an equilibrium position of the outermost dislocations, the average lattice frictional stresses were calculated to be 89 MPa and 46 MPa at 25°C and 350°C, respectively. K E Y W O R D Sdislocation etch-pits, elevated temperature, indentation size effect, strontium titanate

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Indentation size effect and dislocation structure evolution in (001) oriented SrTiO3 Berkovich indentations: HR-EBSD and etch-pit analysis

Cited by 49 publications

References 40 publications

Second Harmonic Generation Investigation of Symmetry Breaking and Flexoelectricity Induced by Nanoindentations in SrTiO₃

Second Harmonic Generation Investigation of Symmetry Breaking and Flexoelectricity Induced by Nanoindentations in SrTiO₃

Grain boundary effect on nanoindentation: A multiscale discrete dislocation dynamics model

Temperature dependence of indentation size effect, dislocation pile‐ups, and lattice friction in (001) strontium titanate

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Indentation size effect and dislocation structure evolution in (001) oriented SrTiO3 Berkovich indentations: HR-EBSD and etch-pit analysis

Cited by 49 publications

References 40 publications

Second Harmonic Generation Investigation of Symmetry Breaking and Flexoelectricity Induced by Nanoindentations in SrTiO3

Second Harmonic Generation Investigation of Symmetry Breaking and Flexoelectricity Induced by Nanoindentations in SrTiO3

Grain boundary effect on nanoindentation: A multiscale discrete dislocation dynamics model

Temperature dependence of indentation size effect, dislocation pile‐ups, and lattice friction in (001) strontium titanate

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Second Harmonic Generation Investigation of Symmetry Breaking and Flexoelectricity Induced by Nanoindentations in SrTiO₃

Second Harmonic Generation Investigation of Symmetry Breaking and Flexoelectricity Induced by Nanoindentations in SrTiO₃