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Reaction temperature and grain size.
In addition, the process of crystal nucleation is an exothermic process, the increasing of temperature will not helpful to the direction of nucleation reaction and make the rate of nucleation decreased, in this way the number of nuclei decreased in the reaction system, forming large grains easily (Fig. 2(b)).
Holding time and grain size.
Concentration of precursor and grain size.
With the increasing of the precursor concentration, the grain size gradually decreases, because there exists sufficient source of Al and Si during the nucleation and growth process, and the number of nuclei increases in the solution and the nucleation rate would be accelerated, resulting in the grain size smaller(Fig. 4(c)).

Role of Σ9 Boundaries in Abnormal Grain Growth of Goss Grains in Fe-3%Si Steel Approached by Solid-state Wetting.
In the previous approaches are based on the high mobility grain boundaries shared by Goss grains with other matrix grains.
Szpunar et al. [4]have proposed that Goss grains have a large number of high-angle grain boundaries with misorientation in 20-45o range.
In this mechanism, if Goss grain has a high fraction of low energy grain boundaries with matrix grains, it has high probability to occur SSW and grow abnormally.
Goss grain boundaries have low energy relations with CSL grain boundaries.

This paper examines the fabrication of ultrafine-grained materials using high-pressure torsion (HPT) where this process is attractive because it leads to exceptional grain refinement with grain sizes that often lie in the nanometer or submicrometer ranges.
Thus, Fig. 4(b) shows the presence of larger grains in the center of the sample and smaller grains at the edges.
More experiments are now needed to determine the effect of straining to higher numbers of turns.
These results confirm the gradual transition to a reasonably homogeneous hardness distribution with increasing numbers of turns.
Langdon, in: Ultrafine Grained Materials III, edited by Y.T.

Qualitatively, it could be stated that for 250°C, the number density of precipitates formed within the grain and at grain boundaries is higher with having finer distribution for the different aging times compared to 330°C.
Fig. 4 (a, b) compare the values of number density of precipitates developed both within the grains and at grain boundaries at varying aging times for 250°C and 330°C temperatures.
For instance, an increase of ~300 % and ~308 % in number density of precipitates formed inside the grain and grain boundary, respectively are obtained for over aging from 330°C to 250°C (Fig. 4).
Variation of the number density of precipitates for varying aging times at two different aging temperatures (250°C and 330°C) present (a) within the grain (continuous precipitates) and (b) at the grain boundary.
(The values of number density of continuous precipitates within the grain have been acquired from our previous work [7].

Moreover, the number of passes significantly improves the particle distribution.
The mean grain size decreases from 9.5 μm to 1.95μm for a 4-pass MMC.
They could achieve ultrafine grain size.
According to the results, it reveals that there is an optimum number of passes for refining the grains and increasing the pass number does not always yield to finer grains.
Furthermore the finest grains could be achieved with 4 passes FSP.

The properties of ultra-fine grained materials are superior to those of corresponding conventional coarse grained materials, being significantly improved as a result of grain refinement.
The specimens were processed for a number of passes up to nine, using a die channel angle of 110°, applying the ECAP route BC.
Considering the billet rotation, different processing routes are possible: route A with no rotation of the billet between consecutive passes; route BA when the billet is rotated counter clockwise 90° on even number of passes and clockwise 90° on odd number of passes; route BC when the billet is rotated counter clockwise 90° after every pass (Fig. 1, b); and route C with the billet rotated 180° after every pass [3].
Calculated accumulated equivalent strain evolution vs. number of passes.
Butu, Mechanical behavior and microstructural development of 6063-T1 aluminum alloy processed by equal-channel angular pressing (ECAP): pass number influence, JOM, 64 (2012) 607-614

The aim of our investigation is to clarify the effect of varying the duration of the heat treatment processes applying the same temperature, same strain rate and same number of cycles during the thermomechanical treatment.
In our investigations the parameters are as follow: grain tolerance angle 5°, minimum grain size 5 points.
It contains complex data about grain boundary network: the length of the grain boundaries, types of the boundaries, etc.
Beside the fraction of special grain boundaries, there is another approach to qualify the grain boundary characteristic.
If we need numerical comparison of the random boundary discontinuity level of the different specimens, we have to count the number of triple junctions (where three grain boundaries meet).

The results show that the microstructure which contains a number of cake shaped grain can be refined and homogenized by the feasible annealing holding time.
The most of these grains are irregular in nature.
But some recrystallized grains and caked grains can be easily observed in these micrographs in Fig.1(b).
A bimodal grain size distribution consisting of larger and finer grains has been observed after full recrystallization in Fig.1(d).
Conclusions 4.1 It is found that the ferrite grain size is grown up with longer annealing holding time at 850 ℃.The ferrite grains are fully recrystallized with 150s annealing holding time, the microstructure which contains a number of cake shaped grain can be refined and homogenized by the feasible annealing holding time. 4.2 It is known that the recrystallization can largely be effect by the annealing time .The change of strength for test steel is small when the annealing time is up to 150s.

There were few dislocations in the grains and in the plate - like shaped g’ precipitates, but a large number of the dislocations were observed around the interface of the plate - like shaped g’ precipitates.
The number of dislocations at the interface increases with increasing the stress.
In particular, a large number of dislocations which are tangled with each other are observed at the vicinity of the interface between the matrix and the plate - like shaped g’ precipitates at 180MPa.
A large number of dislocations is observed at the rafted g/g’ interfaces as well as in the matrix phase near the interface between the matrix and the plate - like shaped g’ precipitates (Fig.8-(c)).
It is supposed that the strain concentrates around the grain boundary in comparison with the grain interior, that is, the drastic creep deformation occurred at the vicinity of grain boundaries.

Grain boundary engineering has been well established.
Keywords: Grain boundary engineering, Fracture control, Grain boundary brittleness, GBCD, Triple junction, Magnetic field application.
One of the authors first introduced new grain boundary-related factors, so called "the grain boundary character distribution (GBCD)" and "the grain boundary connectivity" when he proposed the concept of grain boundary design and control [4], now widely termed "Grain Boundary Engineering"[6-10].
Now, we can determine the orientation and distribution of a huge numbers of grains and the characterization of grain boundaries in a polycrystal without much difficulty by using computer-aided and fully automated OIM, even for ceramics such as polycrystalline SiC with the average grain size of 2 µm, as shown in Fig. 1.
(a) SEM (b) OIM microstructure, not only the grain size ( i.e. the density of grain boundaries ) widely used in the past, and also the connectivity of grain boundaries with different characters.