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As the holding time is prolonged, the growing of the grain may change the intensity of the diffraction peaks.
The sample with 10 h holding time has an average grain size of about 30 µm.
A lot of remnant pores are found both at grain boundaries and in the grains (Fig. 5 (a)), accounting for a lower density (Table 1) and transparency (Fig. 3(a)) than those of other samples.
As the temperature holding time was increased to 20 h, the average grain size was increased to about 80 µm.
China under grant number 50272040, Fok Ying Tong Education Foundation under grant number 91046, and Youth Foundation of Science and Technology of Sichuan Province under grant number 03ZQ026-03.

The average values of grain size are shown in table 3.
They are less than or equal to the grains in the weld nugget.
The largest size of grains in the FSW joint is found in the native material.
Grain size of the material has a significant effect on strength properties of the material.
Czechowski, Effect of anodic polarization on stress corrosion cracking of some aluminium alloys, Advances in Materials Science, Vol 7, number 1/11 (2007), p. 13-20

Large lamellar grains caused serious damage in tensile tested specimens.
As shown in Figure 1, in FL tensile specimens, a number of large interlamellar cracks are produced before the final fracture, pointed by arrows 1, 2, 3, 4, 5 in Figure 1(a).
Therefore, the FL microstructure with large lamellar grain shows an inferior tensile strength than that of the DP microstructure with fine grains.
However, in a DP specimen, due to its fine grains it is easier to bypass the hard oriented grains and find the way through interlamellar cracks as shown in Figure 5 (b).
The crack tips seem to be blunted by slip of the lamellae along the grain boundary instead of by plastic strain inside the grain.

Bi4(SiO4)3 grains grew larger and the amount of vacancy increased along with the extension of holding time, while Bi4(SiO4)3 grains still presented a structure of partial ordering.
The structure of Bi4(SiO4)3 grains still presents a characteristic of partial ordering.
This may attribute to reassemble of smaller Bi4(SiO4)3 grains into a larger Bi4(SiO4)3 grain.
A large number of Bi4(SiO4)3 grains synthesized by rearranged SiO2 and Bi2O3 during the cooling process of glass melt in Bi2O3-SiO2 binary system.
When the Bi4(SiO4)3 become supersaturated it will crystallize on the surface of large Bi4(SiO4)3 grains.

The recrystal grains have the size of 20-40 micrometers.
The recrystallization-grain boundaries can be even seen at the edge of specimen, and the recrystallization grains are much finer.
Fig. 3(a) shows a section of 0.10 MPa specimen where we see the arrangement of grains is not compact.
Fig. 10 shows the section of a blade made of DZ4 superalloy and at the surface we see some incompact recrystal grains like as the grain produced by shot peening of low pressure and thermal anneal procedure.
It illuminates that the finer and compact recrystallized grains bring more triple junctions to materials, which are microstructural barriers to advance cracks along grain boundaries, and thereby lower the mean crack growth rate.

Special care being taken on the types of grain and their proportions in the geometry to give a statistically correct grains distribution.
Due to this, geometrical complexity of four-nodal elements allows them to capture geometrical features of the RVE to the optimum; various geometry types will contain various numbers of elements.
That means applied heat makes the connections between the grains to become weak which in turn causes the expansion of the grains and formation of dendrites in them.
These elongated grains are present in the weldment region as well as in the surrounding region and in other remote regions the grains are near equiaxed only reinforcing that heat does not play a very major part for grain formation in the far-field regions.
The disparity in the modulus values can be attributed to the grain size differences; Inconel 718 has a smaller grain size compared to vanadium as can be seen from Fig 3, leading to a higher modulus.

Approaching particle center gradually formed the grain boundary.
It can be seen from Table 1, the number of four groups ZTC's density was showed upward trend with the rise of sintering temperature, but there is no significant difference between four groups.
When the sintering temperature continues to rise, the grain size was grown up rapidly.
When sintering temperature is continually increased to 1610°C, the grains grow rapidly.
So a large number of grain size is more than the critical dimension.

The structure of drawn-wire after a series of section reduction, is characterized by a regular orientation of the grains « texture ».
Firstly recovery takes place and this is then followed by nucleation and growth of strain free grains.
For this work, a large number of drawn-wires specimens were chosen ( from 27 to 85 % of section reduction ).
We note, that elongated grains are almost replaced by the newly formed equiaxed grains (Fig.4a and 5a ).
The grain size is the same for a wire but it differs from drawn-wire to another, ( Fig.6 ) this depends on the rate of section reduction in the word, the finer grains are obtained for the higher reduced wires.

In the as-quenched state the material consisted of stress free grains of the disordered fcc-FePd solid solution with average grain size of about 133 microns [7].
The cold-deformed fcc-FePd exhibits 'mosaic'- or cell-structures with submicron sub-grain dimensions in a given prior fcc-grain inclusive of shear and micro-bands (e.g.
Bright-field TEM images and SEM show preferential nucleation of these essentially equiaxed new grains in the vicinity of and at prior fcc-phase grain boundaries (e.g. arrow in Fig. 2b) [5-7].
TEM diffraction patterns (not shown for brevity) obtained from these new orientation grains clearly identify them as single-variant or monolithic L10-FePd grains [5-9].
Acknowledgements The material presented in this article is based upon work executed by a number of undergraduate and graduate students and postdoctoral researchers and received support from the National Science Foundation under Grant No. 0094213.

The methodology of distinguishing subgrains formed during recovery process from the grains resulting from recrystallization was also presented in this study.
Individual areas are separated from each other with low angle grain boundaries, consisting of edge dislocations perpendicular to slip planes.
It was quite difficult to distinguish new grains formed during dynamic recrystallization from subgrains resulting from dynamic recovery (Fig. 6b,c).
Grains having small strain (Fig. 6e) and small crystallographic misorientation as well as high angle boundaries in relation to neighbouring grains (Fig. 6f), were considered as grains formed during dynamic recrystallization.
Financial support of the National Centre for Research and Development (project "High loaded tribological nodes for biomedical applications", number ID245467 in Applied Research Programme (PBS III) is gratefully acknowledged.