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The results also show that the grain boundary is a fast path for the oxygen diffusion in polycrystalline ZnO.
Results and Discussion Determination of the Bulk and Grain Boundary Diffusion Coefficients.
In order to estimate the grain boundary coefficient from the product D´δ, it was assumed for the grain boundary width the conventional value 9 of 1nm. 0 1000 2000 3000 4000 5000 6000 -1 0 1 2 3 4 Theoretical grain boundary diffusion profile Oxygen diffusion in polycrystalline ZnO T = 992oC PO2= 1 atm t = 3.06x104s lnC x 6/5 Fig. 4.
It is worth noting that the grain boundary diffusion coefficients are much greater than the bulk diffusion coefficients, which shows that the grain boundary is a fast path for oxygen diffusion in polycrystalline ZnO.
The results also show that the grain boundary diffusion is much greater than the bulk diffusion, which means that the grain boundary is a fast way for the oxygen diffusion in polycrystalline ZnO.

Under low normal stress condition, the pore among the fine gravel grain is too small to be filled by the fine grain during the process of direct shear.
Then, the interlocking action among the fine sand grain is broken by the shear stress, and the grain tumbles back and forth, which makes the volume expand.
Grain Breakage of Fine Gravel.
The volume of the fine gravel contacts obviously because the pore among the gravel grain is filled with the tiny grain under high normal stress condition.
The figure indicates that the number of the tiny grain increases after the grain breakage, which makes the fine gravel from bad gradation to good gradation.

Grain boundary precipitation is also not modelled.
Precipitation on grain boundaries The growth of grain boundary precipitates is modelled considering a collector plate approach [8,9] to account for the fact that precipitate growth rates at grain boundaries are too fast to be explained by volume diffusion alone [9].
Grain boundary and PFZ size evolution in the HAZ.
Evolution of a) homogeneous η volume fraction evolution with volume fraction of dispersoids, b) final η volume fraction in the matrix and on dislocations with varying dislocation number density, in the HAZ for 7449UA FSW.
A number of unknown physical parameters were calibrated using a combination of experimental techniques.

Texture weakening or randomization are desirable approaches to get high performance Mg alloy and a small number of cases having weak or non-basal textures have been reported recently for the Mg alloy sheets and extrusions[3-6].
Grains shown in Fig.2(d) are large deformed unrecrystallized grains.
Fig. 6(a) shows several long elongated grains (LEGs) and besides those grains the microstructure appear lots of fine equiaxed grains (FEGs).
With extrusion temperature increasing the number of LEGs decreases but that of FEGs increasing.
At 665K the elongation has been improved, which is ascribe to the homogenous grain distribution and the fine grain size.

The finer-grained copper was able to outperform (by between 4- to 16-fold) its coarser-grained counterpart under severe test conditions, but no advantage was observed when conditions were milder.
At such fine grain sizes, the volume of the material influenced by proximity to a grain boundary becomes significant [1-3].
In the present study, elemental copper powder, with average as-received grain size of 156 nm, was mechanically milled for 10 hr, reducing the grain size to about 25 nm.
There is also a marked difference between the degree of oxidation observed on the finer-grained and coarser-grained copper: the oxide on the former is more extensive, while that on the latter is sparse and patchy.
The greater number of reactive grain boundaries in the finer-grained 63 nm copper promotes oxidation, and the rate of formation of the oxide layer.

A large number of microcracks along grain boundaries of the equiaxed structure solder developed with increasing cycling, while for the dendrite structure solder, cyclic deformation took place along the direction of the maximal shear stress during fatigue tests and microcracks initiated and propagated along shear deformation bands.
The equiaxed microstructure of the Sn-3.8Ag-0.7Cu solder was composed of equiaxed tin-rich grains and needles or nodules of Ag3Sn phase and Cu6Sn5 intermetallic, as shown in Fig.1(a).
The size of most of the equiaxed β-Sn grains of the solder were in the range of 10~30 um.
For the SnAgCu solder with equiaxed structure, although some deformation in some grains was observed, a large number of microcracks developed along the grain boundaries, as shown in Fig.4(a).
Hence, the grain boundary sliding might be involved in development of the microcracks.

Introduction A large number of different processes have now been proposed for the severe plastic deformation (SPD) of metals, including equal channel angular extrusion (ECAE) [1,2], high-pressure torsion [3], and accumulated roll-bonding (ARB) [4,5].
It has been suggested that the transition to a continuous microstructural evolution is a result of the presence of a large number of high angle boundaries (HABs) in the system, with a figure of 70% HABs often quoted as the transition threshold [9].
The most direct parameter for following the microstructural evolution during annealing is perhaps the average grain size, or more usefully, the grain/cell size distribution.
During conventional recrystallization, nucleation and growth of new grains within a deformed matrix will lead to a bimodal grain size distribution.
For the ECAE ε ≈ 1 sample, annealing results clearly in discontinuous recrystallization, with a large number of non-randomly located nuclei.

Choose of transition metal as growth substrate is also very important because it could largely affect the number of graphene layers and produced defects [6].
Besides that, accurately controlling growth time is another key factor to determine the number of graphene layers[14].
The intensity of 2D band (~2663.9 cm−1) is found to lower than that of G band, which indicated a number of layers growth in most parts of the sample [17].
A, B and C region are corresponding to dark grain, light grain region and grain boundary of Cu.
It is also found that the growth of graphene is not related to different part of Cu including grain and grain boundary.

According to the theory of reference[13], the surface free energy σhkl for different surface orientation could be represented by the following expression: (1) Where ZL is the lateral coordination number, ZV the bulk coordination number. λ is the mean atomic distance, l0 the sublimation energy and NA the avogadro number.
The grain size is smaller than the films grown at higher temperature and the surface of grains are accidented.
Figure 2(b) and (c) exhibit very densely-packed grains and bigger grain size.
The grain size is smaller than the films grown at higher temperature and the surface of grains are accidented.
Figure 2(b) and (c) exhibit very densely-packed grains and bigger grain size.

In contrast to most grains, the EBSD map from the grain at the crack tip, Figure 4, distinctly shows the presence of lattice rotation ahead of the crack.
The grain deforms significantly where the crack enters the grain and the orientation rotates by about 5º from the original orientation.
Such a spread in orientation is also observed in grain 8.
Acknowledgements The author would like to acknowledge the EPSRC, Grant number EP/H022309/1, EP/H500375/1 and Rolls-Royce plc. under the TSB project ’Siloet’ TP NUMBER: AB266C/4 for funding and the Prof Lindsay Greer of the Department of Materials Science and Metallurgy, University of Cambridge for provision of facilities.
Energy of slip transmission and nucleation at grain boundaries.