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The average size of grains is about 3μm and the grain shape is equiaxed.
A number of twinning was observed in γ as well as in α2 grains.
Taking account of the main feature of the room temperature deformation in TiAl alloy, namely, limited number of slip systems, such twinning facilitates stress relaxation, promotes the dislocation slip activity and improves the compatibility of deformation between grains.
During grain-boundary sliding, although the grains do not change shape, interstice between the grains can occur.
Meanwhile, a number of α2 grains break up into spots and are segregated or wrapped by γ colonies, as illustrated by Fig.8c and d.

The effects of grain-refine on the morphology and the grain size of the primary phase in semisolid A356 alloy were researched.
Most grains are rosette-like or particle-like, and there are few grains with dendritic-like structure.
The grain size of the primary phase is coarer with a little addition of Y2O3, about 47μm.
Disccusions Usually, RE elements have strong surface chemical activity, which can be absorbed on the grain interface, hindering the growth of grains, resulting in grain refinement, and thus playing the role of refiners [10-11].
There are strip-like or needle-like bright areas at grain boundaries, which should be the enriching area of Y theoretically, because the atomic number of Y is the largest among the elements (such as Al, Si, Mg, Y) contained in the alloy used in this test.

The grain boundaries were highlighted in 2(b).
Number 1 in the picture refers to grain boundaries and number 2 to some surface defects caused by the polishing process.
The orientation of the generated photo currents is perpendicular to the grain boundaries demonstrating the electrical activity of the grain boundaries.
As can be seen clearly the grain boundary below the indicated grain boundary in Fig. 6 (a) shows no electrical activity.
The top wafer of the corner ingot shows a higher strength of the measured magnetic fields and a higher number of electrical active grain boundaries in comparison to the top wafer of the center ingot.

The formation of these ranges was attributed to the existence of two different modes of domain wall motion each of which was related to the grain boundaries as well as the grain interior activity.
Further, in Fig 3 the evolution of the logarithmic,, number of counts v.s. strain for the same six predetermined threshold voltage values,, is also shown.
One can observe that for a certain critical strain value an increase in the number of counts occurs resulting in a transition point of the magnetic activity.
In Fig 4 the evolution of the number of detected counts with the squared threshold voltage, , for certain elastic tensile strains (stress), is presented.
Fig 5 shows the evolution of the logarithmic counts number,, with increasing , for the same applied elastic strains as in Fig 4.

During growth successive grain size enlargement takes place and leading to coarse grains in the range of several millimeters (Fig. 2).
Thus the grains do not seem to have any texture.
Grains with inclination angles less than 30 degrees prevail during growth because they laterally overgrow heavily off-oriented grains.
The reduced density of planar defects under optimized growth conditions could be since the number of carbon inclusions is strongly reduced and otherwise would cause defective growth.
This is the reason why grain 5 (Fig. 3, Table 1) led to a higher growth rate than grain 3 despite both grains are of 6H polytype with almost the same off-orientation but different inclination directions, <11-20> and <1-100> for grain 5 and grain 3, respectively.

This was because when the alloy was sensitized during 700~725℃, diffusion speed of chromium increased, the number of grain boundary carbides increased compared with 650℃.
The number of coarse carbide increased obviously, and network structure was formed, as shown Fig.5(c,d).
When alloy 690 was sensitized at lower temperature, alloying elements diffused slowly, carbides nucleated at dislocation tangle place in grain boundary, they grew up in the direction along the grain boundary, and expanded slowly in grain.
The primary cause was that the grain boundary migration driving force was insufficient in the sensitization temperature range, the grain size was remained basically stable.
When the solid solution temperature increased from 1050℃ to 1150℃, the grain size grew from 12μm to 58μm, the carbide didn’t occur in grain boundary and transgranular area

The numbering of the variants is proposed, as well as the misorientations between them.
Conversely, a method for calculating the parent hcp orientation from a sufficient number of inherited variants is proposed.
This limited number is due to the properties of the inverse orientation relation 1 g−∆ and the rotational symmetry elements of the hcp and tetragonal group.
Under this circumstance, a new analysis of the orientation relations and variant numbering must be made.
Lamellar colonies and Widmanstätten laths co-exist in a given grain.

.% Ca addition, the phase of Al2Y is refined obviously and the phase of Mg17Al12 has a dramatic decrease in number.
It can be observed that the Mg17Al12 phase is distributed in the grain interior and on the grain boundaries and that the second phase Al2Y is diffused in the intragranular [7].
After T6 treatment, blocky Mg17Al12 is discontinuously distributed at the grain boundaries and punctate Al2Y phase is unevenly distributed, mainly in grain.
Those are illustrated on the two respects: the grain growth is suppressed and the generation number of β(Mg17Al12) can be reduced, and the second phase particles are dispersed in the alloy.
It is well known that large numbers of β(Mg17Al12) phases can barely promote the high temperature mechanical properties of Mg-5.5Al-1.2Y alloy.

Quantitative analyses of the grain size were conducted using “Metilo” computer program.
This method requires conduction of large number of plastometric tests.
Changes in grain size in time function were calculated on the basis of dependence [7]: , (5) where: D(t) – average grain size in time function; X(t)s – fraction of recrystallized volume (X(t)D+X(t)s); DRX – grain size after dynamic and static recrystallization; Do – initial grain size.
The microstructure, after deformation at a temperature of 250°C, consists of fine dynamically recrystallized grains on primary grain boundaries and deformation twinnings (Fig. 2a).
Presence of high number of deformation twins was found.

At surface, where the crystallization of the grains is the most intensive, amount of the grains can reach about 77%.
The main advantage of the TRC technique is preferential grains growth [3].
The grains orientation was studied at surface as well as a cross-section of the strips.
During casting the high cooling rate forces the directional grain growth, which increases the number of preferentially oriented grains.
Thus, the lower amount of the preferentially oriented grains may be expected.