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Uniform fine-grained microstructures with the average grain sizes of 0.7 and 2.5 µm, are almost fully evolved at high ECAP strains at 250 o C and 450 o C, respectively, while ECAP at 300 o C (~0.6 Tm) leads to the formation of bimodal grain structure with fine grains of around 1 µm and relatively coarse grains of around 8 µm.
This picture becomes yet much more complicated by looking at some heavily-alloyed Al alloys, in which dynamic recovery is additionally inhibited by the presence of large number of dispersed particles and/or substitutional atoms in the solid solution [e.g. 13,4,6,8,9].
The other grain component is composed of relatively coarse grains of about 8 µm and the volume fraction of about 0.6.
A gradual increase in the number and misorientation of the boundaries of deformation bands and their conversion into HABs can result in the development of the new fine-grained structure through cDRX [13].
Coarse-grain formation at 300 o C.

Motion of Grain Boundaries: Experiments on Bicrystals Dmitri A.
Grain shape evolution and rotation behavior of grains with pure tilt and mixed <100> low angle boundaries.
In order to analyze the effect of the inclinational anisotropy of grain boundary energy on the grain shape evolution and grain growth kinetics molecular dynamics (MD) simulations were employed.
The dislocation content of these boundaries, therefore, was not characterized by the invariant dislocation number, but rather by the constant dislocation density that preserved essentially the grain boundary structure.
Concurrent grain boundary motion and grain rotation.

Grain orientation maps of slices determined by nf-HEDM at 25 mm intervals are presented and analyzed in terms of grain boundary misorientation angle.
Due to the limited number of grains observed, the automatic smoothing kernel estimation feature of MTEX was employed to reduce uncertainties in parameter selection [22].
Figure 1d shows the distribution of pores (number of pores) as a function of the pore volume.
Clearly, the largest number of pores is below the resolution of the current technique.
Most of the imaged grains are in the range of 5 mm to 20 mm, but some large grains, up to 100 mm are evident.

The grain size dispersion was 100 nm.
Thus, ρG increases when the grain size decreases, and the GND accumulates at the grain boundaries (GBs).
It should be emphasized that the numbers of the substructure units in Table 1 and Fig. 3 are the same.
An increase in numbers from 1 to 6 means a decrease in the size of the structural formation, within which there is an accumulation of dislocations (r, rS and rG).
The critical grain size is 250 nm.

For reducing the error, we take five square areas from the profile, and every square is 100mm2 on the profile, then calculate the grain number of the square.
The result is the average ration of grain number of five square and 100, and experimental results shown in Tab.1.
In addition, the effect of pulsed electric field on the Pb-Sn alloy grain size conform some law, and the pulse frequency has greater impact on the grain size, when the pulse frequency reach 25Hz, the grain size is maximum; The pulse voltage also has some effect on the grain size, when the pulse frequency reach 250V, the refinement is significant.
Based on the thermodynamics, we can know that this kind of salvation cluster is more stable than the solute and solution ones, and the number is also dominant.
The accumulated atoms and the cluster may reorganize and form new cluster with a bigger magic number, then the atom density far away from the cluster will become low.

At a strain of 0.8, an ultrafine equiaxed grained structure with mostly high angle grain boundaries was successfully obtained.
A combination of any two of the 12 variants gives rise to 5 different types (numbered as I-V in the present work) of high angle intervariant crystallographic interfaces/boundaries:, , , and forming through the variant selection mechanism during the martensitic phase transformation [10].
Similar to the mechanical twins formed inside the α' laths, a number of intervariant interfaces also had twin characteristics with the interface plane [12].
The newly formed refined grains had an average grain size of ~300 nm and their formation was found to be related to the alignment of α' laths with respect to the compression axis.
Closer microstructural examination around the strained laths (Fig. 3) revealed quite a number of low angle grain boundaries forming from the intervariant interfaces into the retained alpha laths.

Stress Generation During Grain Boundary Interdiffusion L.
We show that the inequality of intrinsic grain boundary diffusion coefficients of the two components leads to plating out of additional material at the grain boundary in the form of extra material wedge, which generates an elastic stress field in the vicinity of the grain boundary.
As pointed out by Hwang et al., “…the mass gained or lost by the unequal diffusion in the grain boundary is compensated for by a mass flow in a direction perpendicular to the grain-boundary plane…” [8].
We will further suppose that a total number of atoms of both components per unit area of the GB is constant: ; ; , (3) where d is the GB thickness.
Mishin: Fundamentals of grain and interphase boundary diffusion.

Introduction Equal channel angular pressing (ECAP) is the representative model technique of severe plastic deformation (SPD) refining the grain size of metallic materials down to the sub-µm level, so called ultrafine grained (UFG) materials.
In the flat area, individual grain did not appear explicitly, and grain boundary sliding (GBS) hardly occurred across the boundaries.
The flat areas seemed to be agglomerates of grains having low angle boundaries.
In addition, a number of boundaries were well-defined, and showed sharp offsets of marker lines.
The deformation mode was changed from dislocation viscous glide to grain boundary sliding by additional rolling resulting in the development of larger portion of high angle grain boundaries. 3.

Precipitation strengthening and grain refinement strengthening are the main strengthening mechanism in HSLA steels, precipitation strengthening and grain refinement strengthening accounted for more than 70% in all strength contribution[4].
Fig.1,2 show that a large number of dispersed fine precipitates appeared on ferrite matrix, grain boundary and dislocations, precipitate size on ferrite matrix is10 ~ 20nm, vanadium carbonitride was identified as precipitates through TEM diffraction spot calibration.
The grains degree of ferrite in core is 11.0 grade and their average size is 7.06 um while the grains degree of ferrite in interlayer is 11.5 grade and their average size is 5.86 um, and the grains degree of ferrite in fringe is 12.0 grade and their average size is 5.0um.
As the deformation temperature decreased, Ar3 point dropped, and then the stability of austenite reduced, induction phase changing of ferrite occurred when Ar3 coincided with the deformation temperature which refined the ferrite grain size and increased the content of ferrite, there were a large number of small equiaxed ferrites not only improving strength of materials but also keeping good shaping of materials.
Through adding adequate VN alloys and nitrify intensifying agent, a large number of the dispersed V(CN) precipitates(sized 10~ 20nm) are precipitated in the grain boundary, dislocation line and the ferrite matrix, precipitates of V (CN) accounted for 67.54% of the total vanadium in steel, effects of precipitation strengthening is significant.

For example, FSP of 99.999% aluminum leads to a minimum grain size of ~50 μm but much smaller minimum grain size of 3.5 μm is achieved in 99.99% aluminum [7].
FSP was conducted to investigate the minimum grain size of Al-0.01%Fe, which was compared with the grain sizes of other processed pure aluminums　[1-4, 7-8, 12-18].
A grain was defined an area surrounded by HAGBs, and the grain size (d) was defined the diameter of a circle with the same area as that of the grain.
However, the grain size remained almost unchanged over 1016 s-1.
Acknowledgements This work was supported in part by JSPS KAKENHI Grant Number 15K21294, the Light Metal Educational Foundation Inc., the Japan Aluminium Association, and the Nikki-Saneyoshi Scholarship Foundation.