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Introduction Ultra-fine grained materials (UFG) and nanocrystalline materials have been receiving significant attention due to their improved strength.
Therefore, the tensile deformation behavior and the mechanisms operating plastic deformation have been an object of many investigations as the ductility can be significantly improved via manipulation with the various deformation mechanisms especially severe plastic deformation (SPD).A requirement of large plastic strain for the grain refinement and the difficulties in producing long length products in ultrafine grained Al alloys limits the use of SPD.
Similarly, conventional rolling process cannot be used to produce UFG Al alloys due to its high stacking fault energy and the reduced driving force available for recrystallization [1].Accordingly, the cryogenic deformation would require less plastic deformation for achieving ultrafine grains, compared to the SPD processes executing at ambient or elevated temperatures [2].Cryogenic rolling and subsequent annealing has generated mixture of equated grains and elongated sub grains, exhibiting a good combination of uniform elongation and high strength [3].The bimodal structures of ultrafine grains obtained by cryorolling, in pure metals such as copper, possess good combination of both ultra high strength and ductility as reported in the literature [4-7].The rolling of pure metals and alloys in cryogenic temperature suppresses dynamic recovery and promotes the formation of higher density of dislocations as compared to room temperature rolling.
These dislocations act as driving force for the initiation of large number of nucleation sites during annealing, forming the sub microcrystalline, or ultrafine grain structures [8-10].

Chemical refinement doesn't avoid dendritic structures, has no effect over intermetallic phases and is not able to decrease grain size to values below 200 μm [5,6].
If the melt temperature is low enough to avoid dissolution of the nuclei, embryos life time is long enough to promote the development of large number of globular grains with grain size less than 40 μm [12].
Fig. 1 shows the experimental set-up used to perform ultrasonic grain refinement/modification.
Optical microscope (OM) and Scanning Electron Microscope (SEM) with quantitative metallographic analysis capability were used to evaluate shape and grain size of constituents.
US treatment promoted the formation of a mixture of globular and coarse rosette like a-Al grains with average size around 150 mm.

As a result of such hightemperature annealing the samples possess a sharp cubic crystallographic texture {100}<100>, grain size of 0.2 mm, and contain (according to [3]) an optimal amount of the "fresh" defects.
The number of cycles upon CTMT was equal to that in [9]; the holding time at a temperature below Tc was close to optimum in accordance with data [7].
After the recrystallization annealing and accelerated cooling (HTA) the grains are free from precipitates (Fig. 2a).
In our case, the grains have ρ ~ 108 cm-2 because of the alloy has been cooled accelerated.
FPD go through grain boundaries and the body of Treatment Нс (А/m) HTA 17.8 HTA+TMT 8.4 HTA+CTMT 7.1 grains, Fig. 2c.

The concentration of Al2O3-doping in the films was controlled by changing the number n of Al2O3 chips pasted on the surface of Co2FeSi target.
With the increase of Al2O3 chips n, diffraction peak is gradually widen, indicating a reduction of the grain size of the films.
The grain refinement will give rise to an improvement of soft magnetic property.
This can be attributed to the grain refinement discussed above.
Herzer, Grain structure and magnetism of nanocrystalline ferromagnets, IEEE Trans.

Slightly misoriented grains can be observed in this alloy, with selective area diffraction (SAD) pattern typical for a single-phase wurtrzite material with clear arcs confirming some misorientation between the grains (Fig. 1a-inset).
Note the formation of crystalline grains.
Darker areas are grains of GaAs:N.
They are surrounded by more randomly distributed grains of GaN:As.
Presence of the GaAs:N is also confirmed by Z-contrast microscopy (Fig. 3b) showing brighter contrast from the elements with larger atomic number Z, in this case As.

Grains are moderately weathered and altered, with good-poor sorting, medium psephicity, pore cementation and point-line contact.
Grains are moderately weathered and altered, with good-poor sorting, medium psephicity, pore cementation and point-line contact.
Surplus intergranular pores Grains around primary intergranular pores are cemented; result in shrinkage of primary intergranular pores.
Dissolved pores Dissolved intergranular pores Pores formed after intergranular grains are denuded.
Number of porosity samples is 1080.

Dx= 8M/ a3NA (3) where M is the molar mass, NA is the Avogadro’s number.
The average grain size of the different composition is listed in Table 1.
Relatively dense material formation is apparent in the sample with a remarkable change in grain size.
The resistivity of the ferrites in general, depends on different factors such as the density, porosity, grain size etc.
n = NADmPFe / M (6) where NA, Dm and M are the Avogadro’s number, mass density and molecular weight of the corresponding sample, respectively and PFe is the number of iron atoms in the formula CoFe2-2xZrxMnxO4 (0.1≤ x ≤0.4).

We can see easily from Fig.3 (a) to (c) that the size of grains increases with time, but the number of grains is roughly the same.
It can be easily seen from Figs.3 (a), (d) and (g) that the difference in grain size and coverage on the substrate.
The grain size (~250 nm) in Fig.3(d) is smaller than that (~500 nm) in Fig.3(a) but bigger than that (~180 nm) in Fig.3(g).
Generally speaking, a higher overpotential corresponds to a higher nucleation rate, leading to a bigger coverage and smaller grain size.
It can be seen from Fig.5(a) that sample S1 is very rough and consists of big sheet like grains, in which the grain boundary can be clearly seen under FESEM.

Nevertheless, in this paper, we made a large number of measurements to investigate the distribution of germanium in silicon ingot after a dynamic process of industrial ingot casting.
The very low temperature of the top lead to greater sized grains but bad crystallization on the top.
Some defects such as grain boundaries, dislocations, metallic and other impurities induced precipitation etc. act as active recombination centers of carriers in silicon wafers.
The number of dislocations in a given dislocation cluster also increase upwards in the ingot#.
Silicon grains initially nucleate at the bottom of the quartz crucibles and a large number of grain boundaries and dislocations existed.

Driven by a number of industries, there are strong demands in the combined improvement of properties.
The main strengthening mechanisms in Mg alloys are grain size refinement, precipitation and solid solution hardening.
In this sense, Zr and Al play a central role in grain size reduction from 1000 μm in pure Mg to 50-100 μm, when Zr (up to 1 at%) or Al (up to 12 at%) are added.
This effect can be explained in terms of the Interdependence theory [3], relating the growth restriction factor Q with the final grain size Dgb by the Equation (3): (3) Where Q = Xi m (k-1), Xi is the solute concentration, m is the slope of the liquidus line from the binary phase diagram, k is the partition coefficient, and a and b are constants related to solute atom diffusion, the undercooling temperature and the growth rate of grain nuclei.
Although there are a number of studies focused on characterizing yield strength in terms of Hall-Petch, results display scattered information.