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It was found that the more plastic deformation imposed in a single pass, the more ultrafine grains with high angle grain boundaries are achieved.
Two routes A and BC were adopted up to a total number of 4 passes in the present work.
The number of cycles at failure was recorded at the applied stress amplitude.
Fig.9 Dependence of the stress amplitude on the number of cycles to failure for ECAPed samples (2A and 2BC; present) and coarse grained(CG Al and 8BC; Ref. [8]).
Concluding Remarks The microstructure and Mechanical characteristics of the ECAPed 1050 Al alloy using two routes A and BC was examined in the present investigation and the following conclusion can be drawn: 1- The ECAP process via route BC to two passes resulted in fine cell size and relatively higher angle of misorientation. 2- The compressive strength is usually higher than that of tensile strength for same number of passes for both routes. 3- The tensile and compressive strength is usually higher for route BC compared to route A for same number of passes. 4- The value of uniform elongation is low, though the total elongation is as high as 18%. 5- The number of dimples on the fracture surface decrease with the refinement of grain size. 6- Route Bc exhibited higher fatigue strength under HCF condition compared to route A, for the same number of passes.

Aside from the average grain size of samples, the size of recrystallized grain reduced with the MAF pass number, too.
Fig.4(b) shows the numbers of MAF passes dependence of the average grain size of samples.
It could be observed that the grain size decreased with the pass number increasing.
With the pass number increasing, the following changes in microstructure can be observed: a) A large number of fine grains appeared after the first pass, which indicated the occurrence of DRX; b) The number of fine DRX grains increased with the pass number increasing; c) The size of recrystallizated grain reduced with the MAF pass number, which indicated that the DRX occurred in the recrystallized grains.
This is due to the volume fraction of dynamic recrystallization grains increased with pass number increasing, and the stretched deformed grains are depleted by finer recrystallized grains eventually. 4) YS, UTS and elongation of alloy increased with the pass number increasing.

Such grains were called "parent"-grains because they are formed during primary recrystallization.
The average number of the special boundaries per one "parent"-grain decreases with increasing complex stacking fault energy, the energy of the antiphase boundaries and the ordering energy [2].
The grain boundary ensemble parameters, namely, the proportion of the "parent"-grains without special grain boundaries, the average number of the special boundaries per one "parent"-grain, the fraction of the twins S3 in the spectrum of the special boundaries and the average relative energy of the special boundaries depend on the long-range order degree (Fig. 2).
An increase in the "parent"-grain fraction without special grain boundaries with increasing long range order degree leads to a decrease in the average number of special boundaries per one "parent"-grain (Fig. 2b).
The dependences of the "parent"-grain proportion not containing a special boundary (a), the average number of special boundaries per one "parent"-grain (b), the twin boundary S3 proportion in the special boundary spectrum (c), the mean relative energy of the special boundaries (d) on the long-range atomic order degree degree (Fig. 2c) cannot to be explained by the influence of the stacking fault energy on the special boundary spectrum.

Ultrafine grain.
After the ECAP processing using 4 passes, equiaxed grains (~300 nm grain size) and elongated grains were formed for both samples.
To compare the degree of surface damage produced in these samples at the same number of stress cycling, OM photographs taken at nearly same numbers of cycling are shown.
Once this specific number of cycles had been exceeded, both the number and area of the damaged regions showed a significant rise.
The number of cycles required to initiate 0.03 mm-length crack is longer in DLP than OFC.

A grain growth simulation based on the concept of grain boundary migration driven by the radius curvature has been tested to study the abnormal grain growth (AGG) of the Goss grains in silicon steels in presence of particles.
The grains with a radius jR greater than nR ( nRjR > ) resist to the normal (abnormal) grain growth.
The transition probability from one orientation number to another is given by: T         > > ≤ < = 0)ΔEornRij(R 0 0)ΔEandnRij(R 1 p (11) Where E∆ is the energy variation.
The black grains correspond to the Goss grains.
The large size grains resist AGG and the Goss grain shape becomes anisotropic.

(c) TEM image of WC grains in WC-36Ni3Al Fig.3.
However, round grains in WC-36 vol%Ni3Al composites are more often observed in the largest grains of the Ni3Al binder alloys.
These two families of prismatic planes can have a different affinity to carbon because W atoms on each plane have a different number of W–C bonds [11].
So the WC grain growth is inhibited and finer small WC grain will exist in Ni3Al rich binder alloys.
Hardmetals with “rounded” WC grains[J].

In the last decades a lot of research focused on ultrafine grain microstructures (grain size lower than 5 µm).
With increasing the accumulated strain, pancaking of deformed grains increase and so the number of nucleation sites for ferrite increases.
Heavy Austenite Deformation The mechanism of Heavy Austenite Deformation has been investigated by means of a number of tests on samples of steels 30MnB4 and 18MnB2, deformed of 50 % at temperature Ar3+70°C at two different strain rates (1 s1 and 30 s1) and two different prior austenite grain size (10 µm and 50 µm).
Increasing strain rate is not effective on grain size refining: on the contrary, ferrite grain size tends to increase when strain rate rises.
Microstructure of steel 30MnB4 with UF ferrite grain size 3.3 µm.

The dependence on the grain orientation of the alignment of planar dislocation boundaries in plastically deformed metals has been investigated by examining grains of S orientation ({123}<63-4>) in cold-rolled polycrystalline aluminum.
One concern with TEM investigations however is that the number of grains that can be analysed is somewhat limited.
In this way we are able to show a clear correspondence between the boundary alignment and the grain orientation.
This high volume fraction of rolling texture orientations allows a large number of grains with S orientations to be examined in the samples.
At this moderate reduction the EPBs can be easily recognized while the grain rotations are sufficiently small to allow identification of the original grain boundaries from the ECC and EBSD images.

The grain boundaries were found to have high number densities of nanoclusters as well as chromium and tungsten segregation which pin the grain boundary to minimize creep and grain growth.
The number density of the nanoclusters was so high that some impingement of the nanoclusters in the plane of the grain boundary was evident.
In addition to the high number density of nanoclusters, the grain boundary regions between the nanoclusters were also found to be enriched in chromium and tungsten.
In addition, significant numbers of nanoclusters are present on both grain boundaries and dislocations.
The grain boundaries were found to have high number densities of nanoclusters as well as chromium and tungsten segregation which pin the grain boundary to minimize creep and grain growth.

Different methods are available for grain refinement of metals and alloys e.g. grain refinement by rare earth elements and severe plastic deformation, SPD, methods.
To determine the grain size and the general microstructure of ZA22 and its microalloys, cylindrical specimens of 10 mm diameter and 10 mm height were machined from each, mounted on araldite, then ground using successive grit numbers of silicon carbide paper, followed by polishing with one micron diamond paste, and finally etched using (5% HNO3 + 3% HCl+4% HF+88% H2O) solution for 20 seconds and the Metallurgical examination was carried out using the optical microscope type (NIKON108).
Hence it improves its formability and reduces the number of stages required for forming the alloy at large process strain in excess of the plastic instability strain.
Birch: The Effect of the titanium Boron Concentrations on Aluminum Grain Refining Alloy.
Zaid: Poisoning of Grain Refinement of Some Aluminum Alloys (Seventh, Cairo Intern.