Effect of annealing and irradiation on the evolution of texture and grain boundary interface in electrodeposited nanocrystalline nickel of varying grain sizes

2021 ◽  
Vol 426 ◽  
pp. 127770
Author(s):  
S. Julie ◽  
Manmath Kumar Dash ◽  
Nitin P. Wasekar ◽  
C. David ◽  
M. Kamruddin
Keyword(s):  
Grain Boundary ◽  
Nanocrystalline Nickel ◽  
Grain Sizes

An atom probe tomography study of grain boundary segregation in nanocrystalline Ni-W

2005 ◽  
Vol 903 ◽  
Author(s):  
Andrew Detor ◽  
Michael K. Miller ◽  
Christopher A. Schuh
Keyword(s):  
Grain Boundary ◽  
Atom Probe Tomography ◽  
Boundary Segregation ◽  
Atom Probe ◽  
Solute Segregation ◽  
Grain Boundary Segregation ◽  
Distribution Analysis ◽  
Grain Sizes ◽  
Composition Fluctuations ◽  
20 Nm

AbstractAtom probe tomography is used to observe the solute distribution in electrodeposited nanocrystalline Ni-W alloys with three different grain sizes (3, 10, and 20 nm) and the results are compared with atomistic computer simulations. The presence of grain boundary segregation is confirmed by detailed analysis of composition fluctuations in both experimental and simulated structures, and its extent quantified by a frequency distribution analysis. In contrast to other nanocrystalline alloys, the present Ni-W alloys exhibit only a subtle amount of solute segregation to the intergranular regions. This finding is consistent with quantitative predictions for these alloys based upon a thermodynamic model of grain boundary segregation.

Simulation of the interaction of plastic zone dislocations with the grain boundary at brittle-plastic transition temperatures in molybdenum

2021 ◽  
Vol 2021 (3) ◽  
pp. 77-85
Author(s):  
K. M. Borysovska ◽  
◽  
N. M. Marchenko ◽  
Yu. M. Podrezov ◽  
S. O. Firstov ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Grain Boundary ◽  
Plastic Zone ◽  
Grain Boundaries ◽  
Crack Tip ◽  
Dynamics Simulation ◽  
Density Of Dislocations ◽  
Grain Sizes ◽  
Pile Up

The (DD) method was used to model the formation of the plastic zone of the top of the cracks in polycrystalline molybdenum. Special attention was paid to take into account the interaction of dislocations in the plastic zone with grain boundaries. Structural sensitivity of fracture toughness was analyzed under brittle-ductile condition. Simulations were performed for a range of grain sizes from 400 to 100 μm, at which a sudden increase in fracture toughness with a decrease of grain size was experimentally shown. We calculated the value of K1c taking into account the shielding action of dislocations. The position of all dislocations in the plastic zone at fracture moment was calculated. Based on these data, we obtained the dependences of dislocation density on the distance from the crack tip thereby confirming significant influence of the grain boundaries on plastic zone formation. At large grain sizes, when the plastic zone does not touch the boundary, the distribution of dislocations remained unchanged. As grains reduce their size to size of the plastic zone, they start formating a dislocation pile – up near the boundaries. Dislocations on plastic zone move slightly toward the crack tip, but the density of dislocations in the middle of the grain remains unchanged, and fracture toughness remains almost unchanged. Further reduction of the grain size leads to the Frank-Reed source activation on the grain boundary Forming dislocation pile-up of the neighbor grains. Its stress concentration acts on dislocations of the first grain and causes redistribution of plastic zone dislocations. If the reduction in grain size is not enough to form a strong pile-up, density of dislocations on plastic zone increases slightly and crack resistance increases a few percent. Further reduction of grains promotes strong pile-up, dislocations move to crack tip, and its density on plastic zone increases. Crack is shielded and fracture toughness increases sharply. The calculation showed that the fracture toughness jump is observed at grain sizes of 100—150 μm, in good agreement with the experiment. Keywords: dislocation dynamics simulation, molybdenum, fracture toughness, grain size, plastic zone, brittle-ductile transition.

Deformation mechanisms in natural dolomite mylonites from a detachment system (Mt. Hymittos, Greece)

2021 ◽  
Author(s):  
Mark Coleman ◽  
Bernhard Grasemann ◽  
David Schneider ◽  
Konstantinos Soukis ◽  
Riccardo Graziani
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Boundary Migration ◽  
Size Reduction ◽  
Greenschist Facies ◽  
Normal Faults ◽  
Grain Boundary Migration ◽  
Grain Sizes ◽  
Subgrain Rotation ◽  
Middle Unit

<p>Microstructures may be used to determine the processes, conditions and kinematics under which deformation occurred. For a given set of these variables, different microstructures are observed in various materials due to the material’s physical properties. Dolomite is a major rock forming mineral, yet the mechanics of dolomite are understudied compared to other ubiquitous minerals such as quartz, feldspar, and calcite. Our new study uses petrographic, structural and electron back scatter diffraction analyses on a series of dolomitic and calcitic mylonites to document differences in deformation styles under similar metamorphic conditions. The Attic-Cycladic Crystalline Complex, Greece, comprises a series of core complexes wherein Miocene low-angle detachment systems offset and juxtapose a footwall of high-pressure metamorphosed rocks against a low-grade hanging wall. This recent tectonic history renders the region an excellent natural laboratory for studying the interplay of the processes that accommodate deformation. The bedrock of Mt. Hymittos, Attica, preserves a pair of ductile-then-brittle normal faults dividing a tripartite tectonostratigraphy. Field observations, mineral assemblages and observable microstructures suggests the tectonic packages decrease in metamorphic grade from upper greenschist facies (~470 °C at 0.8 GPa) in the stratigraphically lowest package to sub-greenschist facies in the stratigraphically highest package. Both low-angle normal faults exhibit cataclastic fault cores that grade into the schists and marbles of their respective hanging walls. The middle and lower tectonostratigraphic packages exhibit dolomitic and calcitic marbles that experienced similar geologic histories of subduction and exhumation. The mineralogically distinct units (calcite vs. dolomite) of the middle package deformed via different mechanisms under the same conditions within the same package and may be contrasted with mineralogically similar units that deformed under higher pressure and temperature conditions in the lower package. In the middle unit, dolomitic rocks are brittlely deformed. Middle unit calcitic marble are mylonitic to ultramylonitic with average grain sizes ranging from 30 to 8 μm. These mylonites evince grain-boundary migration and grain size reduction facilitated by subgrain rotation. Within the lower package, dolomitic and calcitic rocks are both mylonitic to ultramylonitic with grain sizes ranging from 28 to 5 μm and preserve clear crystallographic preferred orientation fabrics. Calcitic mylonites exhibit deformation microstructures similar to those of the middle unit. Distinctively, the dolomitic mylonites of the lower unit reveal ultramylonite bands cross-cutting and overprinting an older coarser mylonitic fabric. Correlated missorientation angles suggest these ultramylonites show evidence for grain size reduction accommodated by microfracturing and subgrain rotation. In other samples the dolomitic ultramylonite is the dominant fabric and is overprinting and causing boudinage of veins and relict coarse mylonite zones. Isolated interstitial calcite grains within dolomite ultramylonites are signatures of localized creep-cavitation processes. Following grain size reduction, grain boundary sliding dominantly accommodated further deformation in the ultramylonitic portions of the samples as indicated by randomly distributed correlated misorientation angles. This study finds that natural deformation of dolomitic rocks may occur by different mechanisms than those identified by published experiments; notably that grain-boundary migration and subgrain rotation may be active in dolomite at much lower temperatures than previously suggested.</p>

Intergranular Corrosion Behavior of 00Cr12 Ferritic Stainless Steels Containing Cerium

2013 ◽  
Vol 690-693 ◽  
pp. 133-138
Author(s):  
Ya Bo Li ◽  
Fu Ming Wang ◽  
Xiao Nong Cheng
Keyword(s):  
Grain Boundary ◽  
Corrosion Behavior ◽  
Stainless Steels ◽  
Intergranular Corrosion ◽  
Optical Microscope ◽  
Mechanism Analysis ◽  
Chromium Depletion ◽  
Ferritic Stainless Steels ◽  
Boundary Density ◽  
Grain Sizes

Intergranular corrosion behavior of 00Cr12 ferritic stainless steels with different amounts cerium was evaluated. For this evaluation, electrochemical measurements - polarization curves - were obtained for tested materials, and optical microscope was used to observe corrosive microstructure. Experimental results shows: cerium reduces grain sizes and improves intergranular corrosion resistance of test materials. Through mechanism analysis: cerium reduces grain sizes, increases grain boundary density, therefore might improve distribution aspects of carbides and nitrides, chromium depletion situation near grain boundary would be improved, this work worth further study.

A COMPUTATIONAL STUDY ON THE DEFORMATION OF NANOCRYSTALLINE NICKEL

2009 ◽  
Vol 23 (06n07) ◽  
pp. 1517-1522
Author(s):  
JIANQIU ZHOU ◽  
SHUN LI ◽  
NAN XU
Keyword(s):  
Finite Element ◽  
Grain Boundary ◽  
Finite Element Model ◽  
Computational Study ◽  
Equivalent Plastic Strain ◽  
Element Model ◽  
Boundary Phase ◽  
Nanocrystalline Nickel ◽  
Strain And Strain Rate ◽  
Log Normal

A phase mixture based finite element model was developed and the deformation of nanocrystalline nickel was studied in this paper. Monocrystalline grain interior phase and amorphous grain boundary phase were applied in the finite element model respectively. The digital topological model, which followed the Log-normal distribution, was generated by a systematic method. The experimental strain and strain rate hardening behaviors and severe nonlinearity phenomena of nanocrystalline nickel can be predicted very well by the numerical simulation. By presenting evolution process of Mises stress and equivalent plastic strain, we found shear localization phenomenon and much faster plastic deformation in grain boundary phase. These result in the relatively lower ductility of nanocrystalline nickel compared with that of coarse-grain counterparts.

Effects of Microstructure on Cavity Nucleation in Creeping Ceramics Containing Viscous Grain Boundary Phase

2008 ◽  
Vol 368-372 ◽  
pp. 1084-1087
Author(s):  
Chao Wang ◽  
Jun Liang ◽  
Yang Liu ◽  
Jie Cai Han
Keyword(s):  
Stress Concentration ◽  
Grain Boundary ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Critical Stress ◽  
Local Stress ◽  
Viscosity Coefficient ◽  
Boundary Phase ◽  
Cavity Nucleation ◽  
Grain Sizes

A theoretical model considering the distribution of the grain sizes and grain-boundary ledges was developed for cavity nucleation in creeping ceramics containing viscous grain boundary phase. The critical stress involving the effects of various shapes of cavities and viscosity coefficient (η) for cavity nucleation was presented. Then, the local stress concentration factor concerning different distributions of grain-boundary ledges was calculated and discussed. The results showed that various shapes of cavities and η are not the main influencing factors on the critical stress. The stress concentration factor increases with the increase of grain-boundary ledge size or the density. Therefore, it would be liable to cause cavity nucleation at gain boundary when the density of grain-boundary ledges is high and the size is large.

Hillocks on half-micron aluminum lines

1991 ◽  
Vol 6 (9) ◽  
pp. 1817-1819 ◽  
Author(s):  
Carey A. Pico ◽  
Tom D. Bonifield
Keyword(s):  
Grain Boundary ◽  
Large Scale ◽  
Boundary Diffusion ◽  
Al Alloy ◽  
Grain Sizes ◽  
Integrated Devices ◽  
Hillock Formation ◽  
New Type ◽  
Hillock Growth ◽  
Bamboo Structure

A new regime of hillock growth has been observed in patterned Al98.5 W.%Si1.0 Wt.%-Cuo0.5 wt.% films. The “surface” hillock and “side” hillock, which have been seen previously, form on patterned metal lines having linewidths greater than the larger Al alloy grain sizes (∼3 μm). None is seen on the fabricated lines having linewidths between 0.9 and 2 μm where long-range grain boundary diffusion cannot occur because of its bamboo structure. However, a new type of hillock, the “line hillock”, occurs in structures having linewidths of 0.6 μm. The presence of this last type of hillock is inconsistent with the current understanding of hillock formation and may present severe restrictions on the down-sizing of ultra–large–scale integrated devices.

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