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In recent decades, severe plastic deformation processes have been developed to achieve this grain refinement.
Compressive torsion with various numbers of revolutions was applied to Al–Fe alloys at 373 K.
Five test pieces were machined and numbered (1) to (5) sequentially from the center outward, as shown in Fig. 2.
Thomson, Ultra-grained Al-5 wt.% Fe alloy processed by ECAP with backpressure, Mater.
Kanetake, Refinement of grains and second phases in aluminum alloys by compressive torsion processing, Steel Int.

Refining of aluminum matrix grain and second phase particles improves strength, stiffness and ductility.
In resent years, ultra-fine grains can be obtained by severe plastic deformation (SPD)[1-3].
By increasing the processing temperature, the number of fine particle was reduce (Fig.3 (b) and (c)).
However, matrix grain size was very fine because of uniform distribution of eutectic silicon.
These dimples would be caused by grain refinement of matrix.

In this formula, M is one of the cations Li, Mg, Ca, Y and most rare earths with valance of +v, m is number of Si-N bonds in α-Si3N4 replaced by Al-N; n is the number of Si-N bonds in α-Si3N4 replaced by Al-O; and and x is the cation solubility (x=m/v) [1].
α-SiAlON grains, that contain a small amount of sintering additive are light gray β-SiAlON grains without any additive are black and the cation rich grain boundary phase appear white.
Some of the α-SiAlON grains are elongated which is believed to be a result of having a high amount of grain boundary phase.
After removing the grain boundary phase, individual α and β-SiAION grains were obtained for SEM and EDX analysis.
α-SiAlON grains are determined according to their morphologies since they are generally considered to occur in equiaxed grain morphology [8].

The crevices between grains were partially sealed on the irradiated surface with 1 shot because the grain clusters on the irradiated surface was remelted in local region [Fig. 2(d)].
The diameter and the number of craters all decreased, and a few microcracks emerged on the irradiated surface originated from the crevices between the separated grains.
With increasing the shot number to 10, a large local region including more grains was remelted and the remelting region connected with the adjacent zone [Fig. 2(h)].
Note that some craters with diameter larger than 2 µm appeared on the remelting region not only originated from the grain tips but the grain boundaries on the non-irradiated surface.
After HIPIB irradiation at 1 shot, the tips of columnar grains were partially ablated, and the surface remelting led to rounding of column grains.

Grain size and Hardness of tested steel at different cooling rate.
The grain size of the tested steel were measured with average cut line method under different cooling rate, the curve of relationship between grain grade and cooling rate shows in Fig. 4.
The result indicates that the grain grade increases and grain size is fine with the increasing of cooling rate of Nb-Ti micro-alloyed s D460 ship plate steel.
When cooling rate is 0.5℃/s, the grain grade is 8.5; when cooling rate is 23℃/s, the grain grade is 12.
At lower cooling rate region, the reason is that Ferrite critical nucleation size decreases with increase of grain core number, the grain growing was restrained after phase transformation and cause the grain refined; at higher cooling rate region, the reason is that the early occurrence of Bainite transformation refines the γ grain and make later occurrence Martensite refine.

At the microscale, a small number of grains are directly involved in the forming process, so that size, orientation, and position of a single grain can influence the process[1-2].
The repeat number was 22.
The grains of the larger pin are more elongated while the grains in the smaller one are more rounded.
As recrystallization tends to round the grains, the grains in the smaller pin were rounded rather than elongated.
The grains in the larger pin were elongated, while the grains in the smaller one had rounded shapes.

Such sub-volumes are called pseudo-grains (Fig. 3).
It is seen from orientation tensor definition that such tensor has to satisfy a number of conditions: (2) Two-step homogenization scheme means that each pseudo-grain is homogenized by one of mean-field homogenization technique, and all pseudo-grain family is homogenized by Voigt scheme.
The failure of all RVE is determined by is weighted fraction of failed pseudo-grains in RVE: (3) Where - is the total number of pseudo-grains; - is the individual pseudo-grain weight, which reflects its relative contribution to the fiber orientation distribution; is a binary failure flag equal to 0 if the pseudo-grain is sane, and 1 if the pseudo-grain has failed.
Pseudo-grains failure model with failure indicator (3) and Tsai-Hill for transversely isotropic failure criterion in strain formulation (4) for pseudo-grains was used for failure prediction.
Such number of elements is necessary for accurate approximation of orientation tensors and to account thereby differences in orientation tensors over the sample’s volume.

Mishra et al.[2] prepared the grain size of nano-fine grain aluminum alloy, and the strength and ductility of the obtained aluminum alloy have greatly improved.
Therefore, when extrusion number of times is low, as shown in Fig. 2(a) and Fig. 2(b), CNTs in the copper matrix do not flow fully, the distribution areas are small, emerge more serious agglomeration of CNTs.
The one of possible reasons is that extrusion too much makes the grain deformation, with the presence of grain boundaries, the dislocations of the deformation grains were blocked in the grain boundary, the slip bands of each grain were also ended in the grain boundary.
Grains in compound region suffered from the tool strong stirring and intense friction bring in local high temperature during FSP, resulting in a large number of broken grains, the broken grains occurred dynamic recrystallization, along with the flow of plastics metal driven by the tool, the CNTs were evenly spread out in copper matrix.
The grain refinement introduced a large number of grain boundaries, while the presence of large number grain boundaries can significantly increase the scattering of electrons, thereby reducing the conductivity of the composite.

The mechanical anisotropy was measured by tensile testing after different numbers of ARB cycles.
Introduction Bulk ultrafine-grained (UFG) materials produced by accumulative roll bonding (for processing details see [1,2]) have very interesting mechanical properties [3] mainly because of a significant grain refinement (grain sizes smaller than 1µm).
With increasing number of ARB cycles an ultrafine-grained structure develops in the B layers by continuous recrystallization [8], while discontinuous recrystallization occurs in the A layers.
The laminates are labelled as AB_#, with # being the number of ARB cycles.
The global texture and the mechanical anisotropy change with increasing number of ARB cycles.

The processing route significantly affects the grain refinement and grain shape.
The number of ECAE passes was limited to 3.
However, a gradual decrease in the recrystallisation temperature could be noticed with increase in the number of ECAE passes.
[8] on route Bc deformed 5052 Al-alloy reveals that softening starts at a lower temperature for the material subjected to higher number of ECAE passes.
They also proposed that the heat release at a lower temperature is due to recovery in non-equilibrium grain boundaries.