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Low-temperature casting, ultrasonic vibration, and mechanical or electromagnetic stirring have been utilized to obtain fine as-cast grain structures.
As mentioned above, pulse electric current will segregate at the tips of columnar grain toward liquid phase on solid-liquid interface.
With the splitting of grain boundaries, the number of the columnar grains will increase, which makes the cellular spacing decrease, indicated clearly by comparing the morphology of the longitudinal section of the specimens with or without PED treatment in Fig.2.
Chakraborty, Effect of grain refinement on wear properties of Al and Al-7Si alloy.
Mater., Colony(Grain) size reduction in eutectic Pb-Sn castings by electroplusing. 31 (1994) 1691-1694

In the cerammed state, they present a number of advantages including control over dissolution rates and mechanical properties by altering the composition of the parent glass or heat treatment regime.
A novel coating method using a bioactive glass-ceramic has been developed that presents a number of potential advantages for the coating of medical parts.
(A) is a dark field image with the objective aperture on a mullite spot; SAD shows the presence of predominantly coarse grained mullite (appears lighter in the DF image) with some fine grained FAp (darker in the DF image) and a large amount of residual glass.
(D) is a dark field image of large columnar grains of titanium; the SAD image is along the [001] axis of the Ti grain.
(F) has large Ti grains and pores of unknown origin.

In the model, it is assumed that each material point contains a number of crystal grains and the properties of a material point ( )• are given by the averaging of all grains; ( ) ( )∑= •=• M k k M 1 1 (7) wher M is a number of crystal grain at each material point.
In each case, the results converge almost same response with increasing of number of elements or grains per element.
Fig. 4 Flow stress of FCC material with different numbers of grains per element (extended Taylor model with 8(2x2x2) elements is utilized). extended Taylor model presents stiffer response when the number of grains increases as shown in Fig. 6.
Meanwhile, the results in Fig. 8 show that 0.2% proof stress increases respect to the number of grains per element.
The effects of the number of elements and the number of grains in the extended Taylor model are discussed.

The mean grain-lamellar colony size 512 mm was transformed to fully lamellar structure containing g and a2 phases having the mean grain size 229 mm.
Grain size was calculated from the measured average grain area.
Only at grain boundaries (see Fig. 3b) discontinuous coarsening of new gamma grain with thick lamellae morphology can be observed.
Eutectoid transformation affects grain size only negligibly (discontinuous coarsening).
The principal effect on the grain size has recrystallization in the alpha phase region. 3.

Upon straining, the number of twinned grains and twins per grain increase steadily.
Most of the grains are twinned at e ~ 3%.
Fig. 2 (a) Twin number fraction as a function of the highest Schmid factor for twinning of active twin variants; (b) Twin frequency of type (v(1)…v(12)) of active twin variant.
Interestingly, this plot also shows that twins appeared in grains over a wide range of m, i.e. they also appeared in grains oriented less favorably for twinning.
GB grain boundary; TT twin tip.

Among the methods capable of producing such structures a certain number (e.g. inert gas condensation, ball milling, rapid solidification techniques) result in production of powders and thin ribbons which must be subsequently consolidated.
Some of these samples were subjected to severe plastic deformation (SPD) by high pressure torsion described in [4] under pressure 6GPa and number of rotations N=5 for additional structure refinement.
Average grain size in these samples varies from 0.5 to 0.7 μm.
Domain walls do not limit separate grains, but encircle a lot of disoriented grains and form “exchange” domains.
Superposition of DS with image mode shows that in smaller grains domain walls are pinned at grain boundaries.

The DRX grain size increases as strain rate decreases.
In this way, the microstructure such as DRX grains and sub-grains could be observed and analyzed on a Tecnai G 2 20 TEM.
At 250°C, there are a large number of high density dislocation tangling in grains, leading to the forming of dislocation cells(Fig.1a).
As ε& increases to 0. 1s-1, the grain size decreases and the grain boundaries of DRX tend to straight, revealing that the DRX grains grew up to some extend(Fig.2b).
The grain size of DRX increases with decreasing strain rate.

Decreasing grain size usually results in the mechanical properties improvement.
Final product properties are strongly dependent on the ECAP process parameters, such a temperature, type and number of passes and pressing rate, and also on the structure of the initial material.
In the case of AZ91 magnesium alloy the ultra-fine grained microstructure remains stable bellow 300 °C while increased temperatures (350 °C and 400 °C) leads to gradual grain coarsening [8,9].
Enhanced corrosion resistance of ultra-fine grained magnesium alloys prepared by SPD techniques was studied, however still only limited number of works describing the corrosion mechanism is available [4, 11, 12, 14, 15].
There are areas with small grains with the average grain size of 3.3 ± 0.5 µm with large amount of small Mg17Al12 particles, and areas with larger grains, with the average grain size of 9.9 ± 4.5 µm where the density of small Mg17Al12 particles is low.

The formation of Mg2Sn precipitates during the dynamic recrystallization process may retard the dynamic recrystallization and slow down the grain growth by precipitation pinning effect at the DRX grain boundaries, resulting in a finer grain size.
Also at 300 ºC, the grain size is much lower in AT33 than AT32.
At 350 ºC, the DRX grain sizes are similar.
During deformation, new grains form along the initial boundaries, but stop at a certain size, allowing new layers of DRX grains to form of the same size.
Conclusions The main results from this study can be summarized as follows: · Peak stress and peak strain increase with increasing number of precipitates

From this point, the mechanical performance of TWIP steels can be improved through tailoring their twinning behavior by means of adjusting the grain size and morphology because the two factors will contribute to varied number and configuration of twins and dislocation pile-ups [5].
In the present study, a directional solidification technology was utilized to obtain TWIP steel samples with specially oriented grains and beneficial grain boundary morphologies.
The former possesses an equiaxed grain microstructure with uneven sizes ranged from around 200mm to 400mm while the latter shows a typical columnar grain microstructure distributed in parallel.
Depending on the solidification rate, the diameter of columnar grains was changed from about 200mm to 400mm, in which the medium solidification rate, i.e. 120μm/s, resulted in the finest columnar grains while relatively low or high solidification rate made the grains coarse.
It should be noted that there are several annealing twins in the equiaxed grains but there are not in the columnar grains.