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Micrograded grain structure.
So, the concentration distribution into carbide grain body is more gradually in comparison with grain boundaries.
It is well known that Ti-Nb alloys might undergo a number of phase transformations which can provide metastable phases [10].
In this system no precipitates inside grains were found.
Finally, a non-equilibrium structure consisted of complex carbide (Ti, Nb)Cx grains and β-(Nb, Ti) solid solution located on the grain boundary are formed.

Superplasticity in Coarse-Grained Al-Mg Alloys E.
A number of mechanisms have been proposed for coarse-grained superplasticity [2, 5-7], although the actual mechanism has not yet been identified.
Grain size measurements were carried out to select suitably coarse-grained material (> 20 µm) for the tensile testing.
These etched samples were then examined optically to determine the grain size, amount of grain boundary movement, and deformed grain shape.
The arrows in Fig. 6(f) indicate the presence of the newly formed grains at the boundaries of the deformed grains.

Microstructure characterization indicated that a large number of tiny grains are distributed around the large grains.
The majority of these grains are equiaxed grains, and the few twins could be observeded.
It can be seen from Fig. 4, the grain size of rolled AZ31 magnesium alloy sheet is not uniform, that a large number of tiny grains are distributed around the larger grains.
For the recovery and recrystallization of magnesium alloy sheet occur after hot rolling, the majority of grains are the equiaxed grains, and the twins almost disappear.
A large number of tiny grains are distributed in large grains.

This result indicates better crystallinity and structural ordering of ZnO in the grain and grain boundaries.
The reduction in breakdown voltage can be clarified by the increment in the average grain size after the sintering process, thus reducing the numbers of grain boundaries between the electrodes and causing the reduction ‘p-n junctions’.
The V-I nonlinear behavior of the ZnO disc is a phenomenon of the grain boundaries between semiconducting ZnO grains.
The breakdown voltage of varistors is directly proportional to the number of grain boundaries per unit of thickness and inversely proportional to the size of ZnO grain.
This reduction results from a very high growth of grains in the ZnO nanoparticles after sintering, which decreases the number of grain boundaries between the ZnO grains, thus reducing the potential barrier.

This was mainly because of the hydrostatic extrusion which made AZ80 magnesium alloy within large numbers of dislocation tangles.
The figure 3 (b) shows microstructure and morphology of magnesium alloy after hydrostatic extrusion, although the grain size of solid solution was difficult to distinguish under an optical microscope, but it could be seen that grains were elongated and refined along the axis, and sub-grains increased at the same time appeared a large number of twins.
The organization constitution diagram of hydrostatic extruded AZ80 magnesium alloy showed the uneven deformation between grains with axial elongated grains and a large number of twins, and they caused the forming of lots of dislocation tangles and fiber structure.
The uneven deformation between grains or sub-grains, a large number of dislocation and vacancies caused by hydrostatic extrusion would generate residual stress.
(2) In the process of hydrostatic extrusion, grains were broken into many sub-grains in addition to generating slippage, and sub-grain boundaries were the lattice distortion zone where piled up a large number of dislocation.

The ultrafine-grained materials produced by ECAP have a very high strength owing to their small grain size and high dislocation density [2].
The influence of the number of ECAP passes on the yield strength and the ductility is investigated for pure Cu up to an extremely high strain value of 29.
The yield strength and the maximum elongation as a function of the number of ECAP passes for pure Cu are plotted in Fig. 2a and the dislocation density and the crystallite size versus the number of ECAP passes are shown in Fig. 2b.
The larger fraction of high-angle grain boundaries facilitates grain boundary sliding which improves ductility [7].
Figure 2: The yield strength and the maximum elongation (a) and also the dislocation density and the crystallite size (b) as a function of the number ECAP passes for pure Cu.

The process parameters of ECAP (Channel Angle, angle of curvature, friction, number of passes, etc) influences major impact on the properties.
In all the above methods, the grain refinement to nano-scale grain structure in the bulk material is achieved by applying a severe plastic deformation.
Researchers have demonstrated a number of theoretical and experimental analysis on ECAP process [5-10], Fig. 1, to study the effect of process parameters on material behaviour.
Figure 6: Variation of MicroHardness with number of passes Figure 7: Variation of UTS with number of passes Tensile properties evaluated upto 2 passes of ECAP is depicted in Fig. 7.
Langdon, Ultrafine-Grained Materials: a Personal Perspective, J.

Under high zinc application (5 mg kg-1) the grain zinc content increased by 61%.
Increasing nitrogen application under low zinc fertilizer, the grain zinc mainly comes from the root zinc uptake.
Therefore, the plant nitrogen nutrition may have great effect on wheat zinc absorption, transport and grain zinc accumulation through affecting the number of substances and activity of the above protein and nitrogen-containing ingredients.But so far, researches of the nitrogen fertilizer on plant micronutrients (such as zinc) are rarely reported.
Figure 1 The straw zinc remobilization ratio of wheat plant 2.4 The analysis of grain zinc From table 3 that we can see that when Zn application is 0.2 mg kg-1, the grain Zn mainly comes from absorbing Zn from the soil; when Zn application is 5 mg kg-1, the grain Zn mainly comes from straw Zn.
At grain formation process, the accumulation zinc will be given priority to transfer to the grain, used for the formation and development of grain.

In contrast, for the smallest initial grain size (166 µm) both magnitudes are similar.
If softening processes develop before precipitation occurs, the number of precipitate-nucleation sites (dislocations) will be reduced and the onset of precipitation retarded.
In contrast, increasing the grain size, a reduction in the number of sites available for nucleation of recrystallised grains will lead to longer recrystallisation times.
In the case of the smallest grain size the major density of sites available for nucleation (grain boundaries) leads to recrystallisation start earlier comparing to the above case.
Some level of softening can be reached through recovery processes until the precipitate number density exceeds some critical value and recovery stops.

It is believed that the refinement of the coating structure at low nitrogen pressures is associated with a larger number of atoms/molecules depositing on the substrate with higher energies, thus enhancing the adatom mobility and nucleated cluster formation in the coatings.
The number and kinetic energy of the depositing atoms/molecules have been considered the factors that determine the adatom mobility and formation of the nucleated clusters in the thin films.
When a large number of atoms/molecules approach the substrate with higher depositing energies, the nucleation rate will be enhanced and coatings with smaller grain sizes develop.
The value of ko was considered as the limiting grain size for grain refinement under specified deposition conditions.
Similar grain size reduction was evident in the current study of (Cr,Al)N coatings.