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In this case, ferrite grains in the range of 1-3µm were produced and a much more homogeneous distribution of these grains was present.
At least 200 grains were counted so as to give proper representation of average grain size and 95% confidence limits.
Clearly, ferrite grains present in sample deformed at 915 o C are coarser and distributed in a what seems a bimodal way with a population of grains of the order of 4-5 µm and another with grains around 10-11µm.
Less than 10% of the total number of grains counted was of sizes larger than 5µm.
It seems plausable then to conclude that SIT of γ into α grains generated finer and more uniform ferrite grains.

Indeed, the most streaking feature of these curves, illustrated for route C on figure 1, is the increasing ultimate stress with number of extrusions.
At 260°C the flow stress decreases with increasing number of passes: the maximum stress being 145 MPa for the non-extruded samples and 105 MPa after 8 extrusions (route C).
The grains size is of the order of 2 )m and corresponds to an upper limit for the mean grain diameter for as-extruded samples.
In order to measure the real grain refinement as a function of the number of extrusion passes, a dedicated tool was developed: it consist in analysing automatically the dot patterns obtained in TEM diffraction mode for successive points along a line (see the schematic dotted line in figure 4.a).
The yield stress at room temperature increases and the flow stress at 260°C decreases with increasing number of passes.

First, all annealed samples exhibited abnormal grain growth, which was manifested by the presence of large grains that were surrounded by regions of small grains (bimodal grain distributions).
(e) 250nm (a) 250nm (c) T T T 250nm (b) T T T 250nm (d) T T T In order to determine the average grain sizes and grain size distribution, a number of representative TEM micrographs were evaluated using a linear intercept method [10].
To ensure accurate and statistically meaningful counting of the number of intersections of a random line with the grain boundaries, a specially designed system for data acquisition and analysis was used.
The average grain sizes were estimated from 250 grains.
For example, samples annealed for 5h have grains with sizes of about 60 nm and 100 nm while for those annealed for 24h have a large number of grains with sizes larger than 100 nm.

Recently, with the advances in casting crystal growth technology, it is possible to grow large-grain or mono-like Si ingots in which the numbers of GBs could be greatly reduced [4-6].
Result and Discussion Fig. 1 mc-Si wafer with the presence of differently orientated grains and various grain boundaries.
We will focus on Grain No.1 (denoted as G1) and its four neighbour grains (G2-G5).
As small-angle grain boundaries are electrically active defects even at room temperature [18], it is necessary to avoid such kind of grains.
For lowering dislocation density, it is also necessary to reduce the number of “source” GBs.

Materials and Research Methods The objects of study were samples of VT20 alloy in ultrafine-grained (UFG), subfine-grained (SMG), fine-grained (MS), and mesopolycrystalline (MPC) states [1].
After annealing at a temperature of 820 ° C, the alloy has a grain structure with an average grain size of 16.4 μm.
One of the main structural features of ultrafine-grained titanium alloys is the predominant arrangement of dislocations in the boundary regions of grains in the absence of dislocation cells and loops inside the grain body.
During friction of the VT20 alloy with dav = 55.7 μm, not only the transfer of the sample material to the counterbody occurs, but also the formation of a large number of wear particles.
In the process of friction of samples with an ultrafine-grained structure, a significant number of wear particles are formed, in morphology and elemental composition similar to wear particles formed during friction of samples with a coarse-grained structure.

When the number of RPW cycle increased, the size of the Mg2Si particles decreased, and the grain size of the matrix alloy reached the minimum when 200 RPW cycles was used.
it shows that several different Mg2Si grains grew together and formed a cluster-like Mg2Si particles, and the interface between different Mg2Si grains was clearly observed, the SADPs of the A, B, C grains in Figure 5 (a) are shown in Figure 4(b), (c) and (d) respectively , according to these SADPS, we can conclude that the A, B, C grains are Mg2Si.
However, the grain size of the matrix alloy increased when the number of RPW cycles increased, according to Hall-Petch relationship, the increase in grain size will reduce the mechanical properties.
Therefore, taking the above factors, the Mg2Si/Mg-5Zn-2.5Er composite materials reached the optimum properties when the number of RPW cycle was 200.
(2) RPW deformation technique can be used to effectively refine the grain size of the Mg2Si particle and magnesium matrix alloy, when the number of RPW cycles increased, the size of the Mg2Si particle decreased, and the grain size of the matrix alloy reached the minimum when 200 RPW cycles was used

OM and TEM observation showed cryogenic treatment caused by the fibrous grains broken down and many grains with the size of 0.1~3µm These fine equiaxial grains can improve the strength and elongation of the Al-foil.
The grain size of O state with cryogenic treatment is larger than without cryogenic treatment.
From Figure 2(c) and (d), it is evident that there are many small sub-grains with the size less than 0.1mm among the large grains in the O state specimen before deep cryogenic treatment and these sub-grains disappeared and formed large grains with the size of 0.5mm after deep cryogenic treatment which means that deep cryogenic treatment cause the grains merged.
(3) The metallographs show that deep cryogenic treatment cause grains merged with larger size and transmission electron microscope shows that there exist many grains with the size of 0.1~3 mµ after deep cryogenic treatment.
Acknowledgements The authors gratefully acknowledge the financial support from Chongqing Science & Technology Commission (CSTC ) of China granted number 2005BB4108 References [1] F.

The structure of grains is defined by vertices with positions kr r where Nk ..1= (N - number of vertices in the structure).
The unit of time is defined as one Monte Carlo Step (MCS), which corresponds to N trials of position change for chosen vertices, where N is the total number of vertices in a map.
Such kind of behavior was observed in simulations obtained with the presented model (Fig. 3). 1000 2000 3000 4000 1000 2000 3000 4000 5000 6000 7000 8000 MCS Fig. 3 Plot of grain growth kinetics (average size of grains in function of time - MCS) 1,5 2 2,5 3 3,52,5 3 3,5 4 4,5 log(1+t) log N Fig. 4 Evolution of the grain number in time.
The circles define the linear region for which the slope defines grain growth exponent λ Number of grains N is also time dependent and obeys the following equation [11]: ( ) ( ) λ2 0 10 −       += t t NtN (6) This relation can be represented in a log-log plot in which the grain growth exponent λ determines the slope of the linear region.
In quite wide interval (number of grains changes from N=640 to 150) we can observe linear behavior for which the slope is -2λ = −0.93 ± 0.01, thus gives the grain exponent λ = 0.46 ± 0.01.

We aim to study grain boundary diffusion in tin by atomistic simulation.
Simulation of Sn Grain Boundary Diffusion.
Simulation models of Sn grain boundaries.
Grain boundary plane Tilt axis Cell size (a=5.95Å) Number of atoms (101) [010] 6.00a x 5.70a x 15.1a 3720 (201) [010] 6.00a x 5.89a x 14.8a 3840 (210) [001] 6.71a x 5.40a x 14.8a 4020 (310) [001] 6.32a x 5.40a x 14.8a 3720 Figure 2.
The MD simulations using the potential show that the effect of stress on Sn grain boundary diffusion depends on the type of grain boundaries.

At the annealing the atoms diffuse from the specimen's surface into the specimen by two ways, namely, directly into grains and much faster along grain boundaries.
Number 1 denotes component 1, and number 2 - component 2.
This model was used in a number of publications for the description of the Mössbauer data.
This was done in our grain-boundary diffusion model [23,24].
It was shown for a number of systems that the electron density on the Mössbauer nuclei localized in near-boundary areas of a matrix is lower than that in a regular lattice [12,28].