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The results indicate that a great deal of ultra-fine grains appear in CNTs/AZ31 Alloy Composites just after one pass of ECAP; With the increase of pass number, the proportion of ultra-fine grain increases.
Coarse grains with a few fine grains in the composites prior to ECAP were shown in Fig. 3(a).
As is presented in Fig.4, with different number of ECAP passes, the grain size evolutes.
Since the grain size decreased monotonously with the number of passes, other factors, besides grain sizes, should be considered.
With increasing the number of ECAP passes, the initial coarse grained structure in the as-extruded material is transformed gradually into an ultrafine-grained microstructure with an average grain size of 2µm by 4 ECAP passes

The differences of elongation in three directions are related to the number and morphologies of M/A islands and the ferrites.
In this paper, the grain misorientations are used to identify grain boundaries and grain size.
However, the number of 1-2μm grains of the former is more than the latter, while that of larger than 2μm is less than the latter.
Furthermore, when the plastic deformation or cracks propagates through grain boundaries by one into another grain, the relatively more grain boundary of fine grains can effectively suppress crack.
The ratio of large-angle grain boundaries to small-angle grain boundaries at 90°direction is the largest.

We developed a multilayer system formed by introducing a number of thin silicon oxide layers into the polycrystalline silicon layer.
The number, and the thickness, of the buried silicon oxide layers determine the gettering properties of the multilayer structure.
If the number of buried oxide layers is low then the thickness of the single polycrystalline silicon layers is significantly greater than the lateral grain size.
In order to optimize the thickness and number of the buried oxide layers we prepared a number of structures.
The number of buried oxide layers was varied from 3 to 9.

Therefore, it is speculated that the increase in the FWHM for the spinel particles is due to the increase in the numbers of fine spinel particles at grain boundaries and triple points.
On the other hand, it has been reported that the electrical degradation characteristics of varistors are improved by removing the extra interstitial Zn2+ ions in ZnO grains near grain boundaries by thermal annealing and decreasing the number of Zn2+ ions moving into or across the grain boundaries [1,4].
Therefore, it is speculated that thermal annealing changes the number of interstitial Zn2+ ions in ZnO grains or the crystal structure and the particle size of Bi2O3 or spinel particles.
From these results, it is considered that the increase in α after electrical degradation caused by thermal annealing has a slight correlation with the number of interstitial Zn2+ ions in ZnO grains.
Therefore, it is speculated that the increase in the FWHM for the spinel particles is due to the increase in the numbers of fine spinel particles at grain boundaries and triple points.

However, fabrication of homogeneous UFG microstructures having high-angle grain boundaries by ECAP is a complex problem since the number of passes and the selected ECAP route can be very important parameters of the processing.
The relative fraction of high-angle (θ > 15°) grain boundary population has progressively increased with increasing number of ECAP passes - Fig.5.
In Fig.7 the tensile data are summarized as a function of the number of passes.
With increasing number of ECAP passes this difference decreases.
The coexistence of a dislocation climbing process and grain boundary sliding in creep of ECAP material may explain the observed decrease of the creep resistance with increasing number of ECAP passes (Fig.8).

There is a large number of methods for severe plastic deformation (SPD).
The grain size slightly differed between the samples, and different area dimensions and step sizes were chosen to maximize the number of data points and still get a good statistical results.
Fig. 3 (b) presents the grain boundary map of the same sample.
The commercial Al-1050 grain size is approximately 150μm [11].
EBSD results: (a) Texture and (b) Grain boundary maps (black: HAGB, green:LAGB); (c) grain size distribution and (d) grain boundary misorientation distribution of Al 1050 processed to 24 passes by CCDF.

It is influenced by grain boundary plane; one of twelve {110}β planes in the neighboring β grains, which is most parallel to the grain boundary plane, is preferentially chosen as the close packed plane for the K-S relation.
The interfacial sliding occurred and a large number of cavities were formed at the interface (2) / 'β γ while coherent interface (1)/ 'β γ was stable against deformation even at high temperature.
Figure 4 shows change in the number of irrational ( / ')β γ boundaries in Ni-36at%Al Fig. 2 Variation in fracture stress with K Sϕ −∆ at ( (2)/ ')β γ interface boundary.
The dynamic recrystallization accompanied by the bulging of grain boundaries occurs at high Z and small new grains are formed by pinching-off from the serrated parts of initial grains.
In contrast, at low Z the equiaxed fine grains surrounded by high angle boundaries are homogeneously formed due to the geometric dynamic Fig. 4 Number of irrational / 'β γ boundearies with deviation angle from the K-S relation in Ni-36at%Al annealed at 1123K.

With its effect, grain boundaries are bent, distorted or cut off, which contributes to complete grain refinement, and the grain size is less than1μm.
Between two laths, sub-grains, tiny grains and strain-induced precipitated carbides emerge in large numbers, which make composition distribution more uniform.
During dislocation cross-slip, grains are refined to generate grain boundary strengthening.
Sub-grains formed by high dislocation density generate sub-grain strengthening.
(3) The finer the tempered martensite grains are, the easier sub-grains will form during deformation.

Since grain subdivision occurs by movement and accumulation of dislocations, grain refinement by plastic deformation should proceed more efficiently in systems, e.g. fcc metals, with a larger number of active slip systems (or slip systems that can become active).
This result indicates that grain refinement by plastic deformation proceeds more efficiently in systems with a larger number of active slip systems.
The numbers indicate hardness values in GPa, gray color indicates results from the literature.
Numbers indicate the RCR repetitions.
However, this peak did not sharpen after a large number of passes.

Introduction It is generally observed that the solid volume fraction and interface energies play an essential role in the morphological changes during sintering and determine directly parameters such as grain shape, grain-grain contact size and shape, grain coordination, contiguity and connectivity [1].
,ηps,s, is used to represent the different grain orientations of the solid phase particles, with ps the number of phase-field variables representing the solid phase, and one extra non-conserved phase-field variable, ηl, is used to represent the liquid matrix phase.
Later, the overall grain boundary area is further decreased via grain growth and Ostwald ripening.
It is related to the 3-D coordination number Nc and dihedral angle φ as [1] Cg = KNc sin(φ/2) with K a constant related to the grain size distribution.
The 3-D coordination number for each simulation is obtained as the average particle-particle contact number per particle from 3-D microstructure.