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Introduction The mechanical properties of metals are determined by a number of factors but in practice the microstructural characteristics of the materials, and especially the average grain size, play a dominant role.
To avoid these uncertainties, it is easier in practice to adopt a procedure in which the strain is specified simply in terms of the number of turns, N, imposed on the sample [17].
The Nature of Grain Refinement During Processing by ECAP When metals are processed by ECAP, the microstructural characteristics depend upon the processing route and the numbers of passes through the die.
These increases in strength are consistent with the reductions in grain sizes from ~15-50 µm in the alloys prior to pressing to average grain sizes of <1 µm in all alloys after processing by ECAP.
The data in Fig. 10(b) show the maximum elongations are displaced to faster strain rates when the alloy is processed to larger number of passes, where this displacement occurs because the fraction of high-angle grain boundaries generally increases with increasing numbers of passes through the ECAP die [33].

As for the morphology of grain size, it was not homogeneous, small and big grains were in the specimen together.
The grain size of the as-ECAPed specimen was almost under 200 nm.
Further, although many small grains under 200 nm remained, annealing up to 550 o C increased the number fraction of grain size over 200 nm.
Histograms of grain diameter.
Annealing changed grain sizes of the specimens, the grain size of the 600 o C annealing specimen also became the largest of all annealed specimen.

The eutectic phase is characterized and quantified in terms of the development of eutectic cells size and number of eutectic cells.
Quantitative measurements were carried out on the fraction of solidified primary austenite (fγ), Secondary Dendrite Arm Spacing (SDAS), number of primary grains, eutectic cells (EC) size and number of EC.
To obtain the number of primary crystals, pictures of the etched DAAS sample were taken keeping the position of the camera and the sample fixed and varying the orientation of the light source in every shot to get the reflections of all grains.
The CET was identified and the number of and equiaxed grains obtained.
The number of EC per unit volume is in the range of those presented in the literature [13,14].

For grain size estimation Met-Ilo software was used [21].
Due to its specific morphology, grain boundaries in microstructure of massive phase gm are poorly or hardly visible, which practically makes it impossible to determine grain size in this phase.
At the same time, it should be short enough not to result in unintentional grain growth.
Effect of cycle number on the microstructure of Ti-47Al-2W-0.5Si alloy Fig. 9.
Effect of cycles number on the hardness of Ti-47Al-2W-0.5Si alloy The Ti-47Al-2W-0.5Si alloy after cyclic heat treatment conducted under optimum conditions for it was put to under-annealing (Stage 3) at the temperature of two-phase a+g area to obtain the expected grain refinement due to decomposition of defected massive phase gm caused by gm®a+g transformation.

When an austenite grain boundary intersects one or several TiN particles the pinning forces (FP) exerted by these particles impede the movement of the grain boundary.
FR and FP involves a number of difficulties, since the parameters upon which these forces depend are not easy to estimate.
The magnitudes of torsion, torque and number of revolutions have been transformed into equivalent stress and strain values using Von Mises criterion [3].
Austenite grain size and driving force for grain growth (Fd) at 1300ºC.
Shvindlerman: Grain Boundary Migration in Metals, Ed.

Vanadium is added to commercially pure Al as a grain refiner resulting in small grain size and improvement in its mechanical behavior and wear resistance, [5].
This may be attributed to the increase in the number of grains due to the refining effect and the activation energy of the corrosive media as follows: 1- Increasing the number of grains per unit area will cause more intergranular boundaries (surface area) exposed to the corrosive medium, this resulting in increasing the corrosion rate. 2- Increasing the temperature increases the activation energy of the corrosive media, thus promoting more attack on the solid surface through increasing the diffusivity of hydrogen ions towards the Al surface.
It shows the grain refinement effect of 0.112 wt % vanadium addition.
The grains are much finer than those of commercially pure Al (figure 6).
It shows that the grains and its boundaries are wiped off.

Since the early 90’s, number of research activities are carried out in the field of micro forming and micro extrusion.
The average grain size of the copper is 38 μm.
It is noticed that the grain size increases with the increase of working temperature and the grains are unevenly distributed in the billet.
Due to the presence of a large number of grain boundaries, the hardness is higher and requires higher deformation load and flow stress (Fig. 6) when compared to the heat treated metals.
During the process, it is observed that the grain refinement is possible only for a limited number of passes beyond which crack will propagate over the surface.

The grain size is erratic with elongated grains mainly in the centre regions.
The grain structure shows very large, slightly elongated grains at the centre, with equiaxed grains present at the edge.
The grain structure shows a small area of elongated grains in the centre, surrounded by fine equiaxed grains, although larger grains are situated at the edge.
Conversely the elongated grains present in the central region of both structures are more pronounced in specimen S2.4-650, where a lower annealing temperature has resulted in a lower number of recrystallised grains forming here.
The grain structure of specimen S2.4-750 shows large, slightly elongated grains at the centre, with equiaxed grains present at the edge.

A second microstructure parameter is the RB fraction, f, defined as the number of RB divided by the total number of boundaries.
The crack is allowed to propagate along grain boundaries only.
Instead, a discrete model is used, where nodes are placed in the grains centers and beam elements connect every pair of grains with common boundary.
This assumption is consistent with experimentally observed grain boundary behaviour (e.g
The failed grain boundaries are shown as non-transparent (blue and green in colour).

However, a bimodal character of the microstructure for RT processed sample with some significantly larger grains presented in the sample, and many non-equilibrium grains with low angle boundaries formed in larger grains (white lines in Fig. 1d).
It can be seen that the grain sizes of Mg were reduced to around 0.8 µm, including some smaller grain sizes of ~0.2 µm, as shown in Fig. 4.
Also, there are abundant dislocations are visible within grains, and some tangled dislocations near grain boundaries.
With an accumulation strain of around 4, almost all the twin boundaries were evolved to HAGBs, without twin formation in ultafined grain, and some dislocation sinks were accumulated by increased the number of grain boundaries [21].
In this study, the high fraction of {10-11}-{10-12} double twins deformation mechanism would give a large number of {10-11} variant interfaces, which can contribute to dynamic recovery at RT and absorb dislocations.