Energetic design of grain boundary networks for toughening of nanocrystalline oxides

Bokov, Arseniy; Zhang, Shenli; Liu, Feng; Dillon, Shen J.; Faller, Roland; Castro, Ricardo H. R.

doi:10.1016/j.jeurceramsoc.2018.05.007

Cited by 25 publications

(36 citation statements)

References 47 publications

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“…To further study the possible mechanisms responsible for the inverse Hall‐Petch in these samples, an analysis was performed focusing on the observed side cracks formed during indentation. The increased grain boundary energy in nanoscale 10YSZ is expected to impact fracture toughness since higher energy boundaries are expected to be mechanically weaker . Analysis of the SEM images of the hardness indentation impressions shows significant differences when comparing samples with grain sizes larger and smaller than the size with maximum hardness (see Figure ).…”

Section: Resultsmentioning

confidence: 99%

“…As it has been demonstrated for the cubic YSZ system, La ions segregated at the interfaces can considerably decrease grain boundary energy and increase toughness of the entire grain boundary network. 12,15 Therefore, it could be expected that the increase in stability of grain boundaries can suppress the shear of grains and mitigate softening behavior, but this remains to be demonstrated.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

“…As the grains grow, the density of high energy grain boundaries decreases since these have higher driving force for movement, leaving an increased population of the more stable low energy grain boundaries in large‐grained samples. Such changes shall lead to higher energy boundaries at the nanoscale, which could translate into reduced strength (or toughness, or stability), since the strength of boundaries has been directly related to its energy in previous works, either considering its chemistry or the orientation of boundaries …”

Section: Introductionmentioning

confidence: 99%

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Size‐induced grain boundary energy increase may cause softening of nanocrystalline yttria‐stabilized zirconia

et al. 2019

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An increase in hardness with reducing grain sizes is commonly observed in oxide ceramics in particular for grain sizes below 100 nm. The inverse behavior, meaning a decrease in hardness below a critically small grain size, may also exist consistently with observations in metal alloys, but the causing mechanisms in ceramics are still under debate. Here we report direct thermodynamic data on grain boundary energies as a function of grain size that suggest that the inverse relation is intimately related to a size‐induced increase in the excess energies. Microcalorimetry combined with nano and microstructural analyses reveal an increase in grain boundary excess energy in yttria‐stabilized zirconia (10YSZ) when grain sizes are below 36 nm. The onset of the energy increase coincides with the observed decrease in Vickers indentation hardness. Since grain boundary energy is an excess energy related to boundary strength/stability, the results suggest that softening is driven by the activation of grain boundary mediated processes facilitated by the relatively weakened boundaries at the ultra‐fine nanoscale which ultimately induce the formation of an energy dissipating subsurface crack network during indentation.

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Section: Resultsmentioning

confidence: 99%

Section: Mechanical Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Size‐induced grain boundary energy increase may cause softening of nanocrystalline yttria‐stabilized zirconia

et al. 2019

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“…The presence of GBFs (or more general-GB complexions) strongly influences the grain growth as well as GB character distribution in oxides and metallic alloys [54,[56][57][58][59]63,75,76,79,80,83,106,[123][124][125][126][127][128][129][130][151][152][153][154][155][156][157][158][159][160]. It has been known for a long time that impurities can shift the borders between GBs with special and general structure and properties [142,143,220,221].…”

Section: Discussionmentioning

confidence: 99%

“…As a result, one can measure the thermal effect of GB phase transitions with the aid of a DSC [114,[148][149][150]. DSC also permits to observe the indications of GB phase transformations in nanocrystalline ceramics [151][152][153][154][155][156][157][158][159][160]. The GB phase transformations can also lead to abnormal grain growth and radical changes in the GB character distribution [54,[56][57][58][59]63,75,76,79,80,83,106,[123][124][125][126][127][128][129][130]151,[154][155][156][157][158][159].…”

Section: Introductionmentioning

confidence: 99%

Grain Boundary Complexions and Phase Transformations in Al- and Cu-Based Alloys

Kogtenkova

Straumal

Korneva

et al. 2018

Metals

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High-pressure torsion has been used to obtain the ultra-fine grained (UFG) state with a high specific area of grain boundaries (GBs) in Al-Zn, Al-Mg, Cu-Ag, Cu-Co, and Cu-Ni solid solutions with face-centered cubic (fcc) lattices. The UFG samples were heated in a differential scanning calorimeter (DSC). Small endothermic peaks in the DSC curves were observed in the one-phase solid-solution area of the respective phase diagrams, i.e., far away from the bulk solidus and solvus lines. A possible explanation of these endothermic peaks is based on the hypothesis of phase transformations between GB complexions. This hypothesis has been supported by observations with transmission electron microscopy and electron backscattering diffraction. The new lines of GB phase transformations have been constructed in the Al-Zn, Al-Mg, Cu-Ag, Cu-Co, and Cu-Ni bulk phase diagrams.

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Local Multimodal Electro‐Chemical‐Structural Characterization of Solid‐Electrolyte Grain Boundaries

Carr

Chen

et al. 2021

Advanced Energy Materials

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Typical models of polycrystalline ionic materials treat the grain boundary properties as single valued, without consideration of the full range of values that define the macroscopically measured average. Here a unique experimental platform suitable for local multimodal characterization of individual grain boundaries in bicrystal fibers is reported. A variation of three orders of magnitude in the grain boundary conductivity of ceria is observed, as measured across six individual bicrystals by both alternating current impedance spectroscopy and direct current (D.C.) linear sweep voltammetry. Nonlinear behavior of the D.C. measurements is consistent with resistance due to a space charge effect. Time‐of‐flight secondary ion beam spectroscopy reveals a correlation between grain boundary resistance and the concentration of impurities Si, Al, and Ca segregated at the grain boundaries, although the bulk concentrations of these impurities are negligible. Electron backscatter diffraction analysis of the crystal orientations suggests a correlation between the misorientation across the grain boundaries and grain boundary resistance. These correlations point towards a grain boundary resistance that arises from impurity‐generated space charge effects and variations in impurity concentration and hence resistivity driven by the energetics of impurity segregation to grain boundaries of differing surface energies.

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Energetic design of grain boundary networks for toughening of nanocrystalline oxides

Cited by 25 publications

References 47 publications

Size‐induced grain boundary energy increase may cause softening of nanocrystalline yttria‐stabilized zirconia

Size‐induced grain boundary energy increase may cause softening of nanocrystalline yttria‐stabilized zirconia

Grain Boundary Complexions and Phase Transformations in Al- and Cu-Based Alloys

Local Multimodal Electro‐Chemical‐Structural Characterization of Solid‐Electrolyte Grain Boundaries

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