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With increasing of number of passes, grain refinement and the fraction of high-angle boundaries continued to increase, which in the end was ~ 40%.
After more number of passes, the grain size has slightly increased, which is indicative of recovery and recrystallization (no detailed study was undertaken here).
The EBSD analysis reveals that as number of passes increases, the fraction of high- angle grain boundaries increases.
Comparison of Fig. 4(b) (after 2 passes) with Fig. 4(c) (after 4 passes) reveals that the number of sub-grains formed has increased in the latter.
Number of passes.

It is widely accepted that the dominant deformation mechanism of fine-grained superplasticity is through grain boundary sliding (GBS) that occurs in fine-grained materials.
An equiaxial fine-grained microstructure with a grain size of 7.4 mm was obtained after FSP; however, this microstructure was unstable at high temperatures.
An equiaxed and fine-grained microstructure with an average grain size of ~7 mm was obtained by applying FSP [9] to this alloy.
The average grain size of SZ was estimated by linear intercept grain size method and was calculated by multiplying the average intercept length by 1.74 [23], which is correction factor [24]; the grain aspect ratio (GAR) was also calculated.
Acknowledgement This work was supported by the JSPS KAKENHI Grant Number JP15K06494, the JST A-STEP FS Stage Project Number 13409342, and the Japan Aluminum Association (JAA) Aluminum Research Grant FY 2010, 2011, 2015, and 2016.

This addition suppresses the variation in the ZnO grain size without reducing the grain size.
The varistor voltage increases with increasing number of ZnO grain boundaries between the electrodes.
Thus, to fabricate varistors with low breakdown voltages, it is necessary to reduce the number of ZnO grain boundaries between the electrodes.
Adding only Ba or Ti to Bi-based ZnO varistors promotes grain growth enabling large ZnO grains to be obtained [2].
The resistances to electrical degradation were markedly improved for the sample to which no Ba had been added and for the sample to which approximately 0.01 mol% Sb had been added with increasing number of ZnO particles with c-axes perpendicular to the pressured surface (the diffraction peak intensities for the (002) plane increased) [4].

The relation between the relative standard deviation of grain size and the ratio of twin number to grain number is obtained.
Fig.1 shows the influence of the ratio of twin number to grain number on the relative standard deviation.
The relation between the relative standard deviation and ratio of twin number to grain numbers of microstructures shown in Fig.4 are described in Fig.5.
The twins have obvious effect to grain growth inhibition, the mechanism is that the formed twins increase the mobility viscosity of 30 35 40 45 50 55 60 65 70 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Relative Standard Deviation Ratio of Twins and Grains Number (%) Fig. 1 The influence of Al2O3 content on standard deviations.
Fig. 5 The relation curve between relative standard deviation and ratio of twin number to grain number of microstructures described in Fig.4.

The material is described on a grain scale as a set of � (variable) spherical grains.
The model includes: (i) a grain boundary migration equation driving the evolution of grain size via the mobility of grain boundaries, which is coupled with (ii) a dislocation-density evolution equation, such as the Yoshie-Laasraoui-Jonas or Kocks-Mecking relationship, involving strain hardening and dynamic recovery, and (iii) an equation governing the total number of grains in the system due to the nucleation of new grains.
Description of Grain Properties When deterministic evolution equations (i.e., with no stochastic terms) are used, all grains of a given age τ have undergone identical evolution and therefore have the same diameter D and dislocation density .ρ Hence, all properties of the grains in the model are one-parameter distributions, and each grain is characterized by its age .τ The following functions can then be introduced: - the number of grains of age ,τ ( ),� tτ (number per unit volume and age time); - the plastic strain within the grain ( ) ( ),d , t tt u uτετ ε−= ∫ & in which the strain rateε& is assumed to be the same for each grain (per the classical Taylor isostrain crystal-plasticity assumption); - the strain hardening of the grain as represented by its dislocation density ( ),tρτ (length per unit volume); - the grain diameter ( ),.D tτ A number of constraints connect the various functions; e.g., the overall volume is constant at all times, i.e., ( ) ( ) 3 06
t t � t D tτ τ τ π ∀ = ∫ (1) Evolution of Grain-Property Distributions Several mechanisms contribute to the evolution of grain-property distributions: (i) Grain boundary migration.
ucleation of new grains.

The grain-boundary between ZnO grains was observed using HR-TEM.
Fabricated MLCVs were thickness of functional layer of 17 µm and the number of 7 grains between internal electrodes of Au, which have V1mA,=5.6 V and capacitance=100 pF.
However, we could not clearly distinguish the grain-boundary layer between ZnO grains from the observation.
The differences of atomic numbers among Zn,Sr and Co in the varistors seem to be relatively small.
The p-type compounds (SrCoO3) detected by EDS would be the layer of grain-boundary between ZnO grains (n-type).

In this fully recrystallized region the average grain size of the cube grains (dcube) is ≈ 20µm, compared to an average size d ≈ 10µm for all grains.
A significant number of twin boundaries, as shown by the thicker lines in the misorientation map of Fig. 1b, are also seen in the fully recrystallized samples.
Each simulation was carried out 10 times, using the same experimental starting microstructure in each case, but using different seed values for the random number generator.
For each grain the mean orientation was determined, and then assigned to each site within the grain.
Figure 5: Increase in cube volume fraction as a function of grain size increase during grain growth.

The experimental results show that, grain number per unit area of DIF increases with decreasing deformation temperature or increasing deformation amount; the grain size of DIF is not very sensitive to the deformation conditions; the volume fraction of DIF increases due to the increased grain number per unit area.
The curves of the volume fraction, grain number per unit area and mean grain diameter of DIF vs deformation temperature are illustrated in Fig.2.
The grain number per unit area will increases with nucleation rate of DIF.
The curves of the volume fraction, average grain diameter and grain number per unit area of DIF vs deformation amount are illustrated in Fig.4.
As the deformation amount increases, the grain number per unit area of DIF increases, with the nucleation site transitioning from grain boundaries to deformation bands inside the grains.

It is assumed that the pinning force must overcome the driving force for grain growth to prevent the abnormal grain growth.
(3) The number of precipitate particles is few.
Austenite grain structures were evaluated with an optical microscope to determine grain coarsening temperatures.
Grain coarsening behavior.
Grain coarsening behavior.

One of these processes reported in a number of experimental works is the paradoxial cementite dissolution [1, 2, 5–9].
The number of anvil rotations by HPT is given for each curve.
The derivative break at 210°C becomes invisible with increasing rotations number.
However, by increasing number of anvil rotations by HPT (i.e. with decreasing grain size), the Fe3C input into Js(T) curve flattened and disappeared (Fig. 4).
Yet, with increasing number of anvil rotations by HPT, the size of the cementite particles decreases drastically.