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In addition, it is noted that the maximum elongation is displaced from 1.0 × 10 2 s-1 to 3.3 × 10-2 s-1 when the number of ECA pressings increases from 6 to 8.
A similar trend was noted in an Al-Mg-Li-Zr alloy [23] and it was attributed to the increase in the fraction of high-angle boundaries with increasing number of pressings.
There are two trends noted in Fig. 5: Firstly, the flow stress for the material decreases significantly after ECAP and decreases slightly with the increase of the number of passes.
This effect is the direct result of grain size reduction over ECAP.
Processing of ECAP at 473 K using an Al-7034 alloy results in an ultrafine grained microstructure having grain sizes reduced from ~2.1 µm to ~0.3 µm and breakup of precipitates of η-phase (MgZn2) from rod-shaped to smaller spheroid. 2.

The mean grain size is about 20 µm.
Moreover, grain fragmentation sets in (continuous dynamic recrystallization [5]) leading to a bimodal grain size distribution.
With increasing number of passes the mean grain size is reduced to the micron range.
The inclination decreases with the number of passes.
The inhomogeneity decreases with the number of passes.

In DOE full factorial technique, number of test, N is according to formula which is N = yx, where y is represent number of conditions and x is act as number of factors [4].
The grain size on the test specimen was measured by using AFM.
From Fig. 1, grain size of Sample 7 shows bigger than Sample 3.
From the results, effect of temperature and gas flow is positive when the average grain size at high level is higher than average grain size at low level.
Meanwhile, the effects of vacuum and RF power have shown negative when average grain size at high level is lower than average grain size at low level.

All ferrite grains are equiaxed and the average grain size is significantly reduced.
Their initial grain sizes of ferrite are all about 50 µm .
Fig.7 Effect of strain on number of recrystallized grains of ferrite in per area(a) and average recrystallized grain size(b) in the three steels deformed at 700 oC at 0.001s -1.
Fig.8 Effect of strain on number of recrystallized grains of ferrite in per area(a) and average recrystallized grain size(b) in the three steels deformed at 700 oC at 0.1s -1.
Fig.9 TEM image of the carbon replica of the Nb-microalloyed steel Fig.10 Effect of strain on number of recrystallized grains of ferrite in per area(a) and average recrystallized grain size(b) in the two steels deformed at 700 oC at 0.001s -1.

As a result, the toughness of welding seam increase with acicular ferrites number increases and acicular ferrites grain size decreases.
But in the HAZ, the grain growth coarsening is different with general grain growth.
High purity of CQ steel made the grain boundary migration and grain growth are easy.
It can be seen that there are a large number of inclusions, which was one of the important factors leading to cracks.
While grain growth in HAZ is serious, with average grain size 15μm, and unilateral width of heat affected zone 216um

For recrystallized grains orientations were assigned randomly from a list of grain orientations measured in an EBSD experiment.
Journal Title and Volume Number (to be inserted by the publisher) 3 Figure 2.
On the other hand, as the boundaries between recrystallized grains are mainly high misorientation (high angle grain boundary, HAGB) they tend to be associated with a high GB energy.
Journal Title and Volume Number (to be inserted by the publisher) 5 (a) (b) Figure 6.
Note however that a number of boundaries remain pinned along the original boundary of the band, as is often observed experimentally.

Thus, whereas conventional treatments may refine the grains to sizes of several micrometers, SPD processing is capable of producing grains having sizes within the submicrometer and nanometer ranges.
The grains produced in SPD processing are designated ultrafine grains (UFG) where UFG solids are defined specifically as “bulk solids having fairly homogeneous equiaxed microstructures with average grain sizes less than ~1 mm and with a majority of boundaries having high angles of misorientation.”
Within the range of UFG materials, submicrometer grain sizes refer to average grain sizes within the range from 100 to 1000 nm and nanometer grain sizes refer to average grain sizes of less than 100 nm.
This work provided a clear demonstration of the ability to achieve remarkable grain refinement in commercial metallic alloys with, as an early example, a reported grain size of ~0.3 mm in an Al-4% Cu-0.5% Zr alloy [9] at a time when the minimum attainable grain size in a comparable western alloy was of the order of ~3-5 mm [10].
These numbers reflect the considerable interest in ECAP around the world and the relatively small number of active HPT facilities.

L0 is the initial grain size.
L is grain size.
N is the sites number of the simulation domain. n is the solid-phase site number around one specific site.
The attempted N (total site number in the simulation system) times is regarded as one Monte Carlo Step (MCS).
The simulation time is expressed in term of the number of Monte Carlo Steps (MCS).

The material was considered as a composite of grain interior phase and grain boundary (GB) phase.
As soon as strain surpasses threshold value corresponding to ultimate strength, grains within shear band begin to rotate and dislocations in grain interior begin to slip, which leads to shape changes for grains, especially like elongation.
The following assumptions are made with shear band deformation mechanism stated above: (1) grains are spherical before unchanged, and grains’ sizes are identical; (2) grains with different orientations are randomly distributed; (3) rotational velocities for grains are same and synchronous; (4) rotational angle of grain is proportional to strain in the softening stage.
(3) where and are the number of softening grains with orientations parallel with shear band and the total number of grains in the aggregate, respectively; is the strain in softening stage, is the strain corresponding to ultimate strength and is the failure strain.
(7) FEM simulation for shear band The generated microstructure consists of 160 grains and the average grain size is 62 nm.

The number of layers includes all metal and ceramic layers.
Ni grains form big aggregates and distribute among Al2O3 grains.
The Al2O3 grain size in Al2O3 sample is about 0.4-0.7µm.
The grain size of Al2O3 in the (Al2O3+20wt%Ni) and (Al2O3+50wt%Ni) is about 0.3-0.5µm and 0.4-0.6µm.
According to the Hell-Petch formula, the strength will increase as the grain size decreases.