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A better contact condition stands for a stronger heat extraction from the melt, and will finally appear as a remarkable increase of primary α(Al) grains survived in the melt, which will conspicuously promote the spherical growth of the primary α(Al) grains. 1.
The shape factor of primary α(Al) grains was calculated as: F=4πA/P2 where A and P represent respectively the average area and perimeter of a grain.
The results prove that a low superheat can promote the transformation of primary α(Al) grain from a dendrite or a rosette to a spherical one.
But when the channel length increases to 400mm and 600mm, most of the primary α(Al) became to spherical and near-spherical ones with a slight number of rosette, as shown in Fig.2(c) and (g).
The scour effect can also reduce the temperature fluctuation and concentration gradient in the melt, finally appears a higher grain refinement.

As the Na2O was added up to a maximum of 2 mol%, the number of abnormal grains and the grain size increased.
All the grains (the abnormal and the matrix grains) have faceted boundaries as shown in Fig. 1 and 2.
The 5 mol% Na2O sample consists mostly of equiaxed matrix grains and no abnormal grains are present.
Comparing 0 and 0.5 with 1 mol% Na2O excess samples, it can be seen that the number of abnormal grain increases with Na2O addition.
Therefore, the number of grains that show abnormal growth is increased.

Values of E were obtained from compression and tension parallel to grain, and static bending tests.
Brazilian Code ABNT NBR 7190: Design of Timber Structures [6], in its Annex B, specifies three tests in order to determine the longitudinal modulus of elasticity: compression parallel to grain; tension parallel to grain and static bending.
After static bending tests, specimens were extracted for testing in compression parallel to grain (15cm × 5cm × 5cm) and tension parallel to grain (45cm × 5cm × 2cm), both performed obeying the requirements of Brazilian Code ABNT NBR 7190 [6].
Fig. 1 Extraction of specimens for tension and compression parallel to grain tests Table 1 shows the number of specimens tested in static bending, tension and compression parallel to grain, for the six wood species used in this study, totalizing 297 tests.
Table 1 Number of specimens per species of wood and type of test.

On the middle of guide roller, a large number of grid shaped cracks were observed only on the surface.
In addition, element content of Cr was a little higher, which easily leads to chromium carbide precipitating along grain boundary and weakens the binding force between grains.
Grain boundaries were evident along direction of cracks propagation.
Hard and brittle carbides distributed on the grain boundaries.
Therefore, the cracks extended along grain boundaries and became intergranular cracks.

But the grain size increases somewhat with further addition of Al5Ti1B.
Grain size can influence the precipitation kinetics and grain boundaries are preferential places for precipitate nucleation [8].
As shown in Fig. 1c, the volume fraction of grain boundaries of Al-5wt.
The grain size increases somewhat with further addition of Al5Ti1B.
The grain refinement of α-Al is mainly resulted from the existence of a large number of heterogeneous nuclei.

As shown in Fig. 2(a), the deformation of AlMg0.7Si alloy was performed by a large number of short-stroke pressing operations from four hammer dies; during the interval between strokes, the rotating and axially advancing of alloy was carried out by clamp.
(2) where D, F, A, N and P are average grain size, shape factor, area, the number and perimeter of grain, respectively.
Some solid grains are still connected to others and the grain boundaries are unclear in Fig. 5(a), so the average grain size and shape factor cannot calculate when the ARR is 20%.
In Fig. 7(c) and (d), when remelting time raises form 10 to 15 and 20 min, the grain boundaries are thicker, the solid grains are more independent and spherical, but the grains are large.
Then larger grains grow continuously and smaller grains dissolve fast due to the difference in curvatures of grains, causing the coarsening of solid grains.

Macrostructure in the transverse (a), longitudinal (b) section of the tube, lining-out and Vickers hardness impressions (c) (without magnification) Analysis of the macrostructure showed that it is homogeneous in both the transverse and longitudinal section (Fig. 1, a, b) and has a 1-2 grain size number according to the grain size scale of the macrostructure of titanium alloys [15].
In these areas, grains elongated along the extrusion direction with 4th elongation scale number according to [8].
At the same time, the presence of a small number of elongated grains indicates that recrystallization processes are not fully completed.
This structure refers mainly to 2-3d structure scale number, according to the scale of microstructures of α-alloys [12].
This led to the formation of a more homogeneous and fine-grained structure with 1-2 and 2-3 structure scale number according to the scales of macro- and microstructures of titanium alloys, a two-component tangential texture (0001)TD<100>ED and (0001)TD<110>ED and hardness – 155 HV.

This in-turn causes grain recrystallization and refined zone.
They also find increase in abnormal grain growth with an increase in number of pass of FSP.
El-Rayes et al.[9] found that 100 % overlapping of FSP lead dynamic recrystallization with equiaxed grains as number of passes of FSP are increased in case of Al alloy 6082.
A series of FSP runs were conducted perpendicular to the rolling direction at constant process parameters with varying number of FSP passes.
The number of FSP passes are carried out according to Table 1.

The Comparative Effectiveness of Nb Solute and NbC Precipitates at Impeding Grain Boundary Motion in Nb-Steels Christopher R.
The recrystallization process (and the subsequent grain growth) largely controls the final grain size of the material and in alloys such as ferritic steels, this is the primary means to control the mechanical properties of the alloy.
A fine grain size can be achieved by maximizing the nucleation rate of recrystallization and minimizing the growth rate (or boundary migration velocity) during recrystallization and grain growth.
The solute drag effect, on the other hand, reduces the mobility of the boundary in a non-linear manner depending on velocity and depends on a number of parameters such as the binding energy of solute to the grain boundary (Eb), the diffusivity of solute across the boundary (D trans ) and the mobility of the boundary in the absence of solute (M0).
In both ferrite and austenite, a grain boundary energy, γ, of 0.6 J/m2 is used.

It is shown that combination of strain effects leads to possessing the ultra-fine grain structure in carbon wire.
Besides, products made of modern materials can be processed technologically in a number of different ways.
Ultrafine grain structure forming is one of the most promising methods of steel properties improvement [4-9 etc.].
Combination of operations reduces their total number while the number of semi-product transformations does not change.
Biswas, Ultra-fine Grain Materials by Severe Plastic Deformation: Application to Steels.