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There are a number of fine grains having sizes of 0.5~2 μm due to the effect of chilling.
In Fig. 6(a) the grain consists of Mg crystal having a grain size of 5 μm.
The very fine grains with average grain size of 0.5 μm are observed in Fig. 6(a) and (b).
The Mg grain size is 7 μm.
Near the grain boundary, there also an amount of very fine grains with size of 0.3 μm.

The latter could result from higher stability and homogeneity of grain structure under straining due to less intense normal and/or abnormal grain growth [27].
These ultrafine grains compose dark regions in Fig. 1(b).
In fact, about one-hour static annealing at an optimum HSRSP temperature led to the normal grain growth in the grip section of the tensile samples and grain size increase to 2.6 mm only.
Fig. 4(b), virtually, supported this assumption, showing fine “relief grains” on the sample surface with size equal to the final grain size in the sample body.
The volume fraction of cavities does not exceed 5% even close to the fracture zone (Fig. 4(c)), due to a low number of sites for pore initiation, commonly attributed to coarse particles of second phases.

Because of this combination the silicon nitride ceramics have an especially high potential to resolve a wide number of machining problems in the industries.
The β-Si3N4 grains have an average grain size of about 4.5 μm and aspects ratios higher than 5.1 μm.
The intergranular phase located between the grains was revealed and created during the etching-off of the grain-boundary phase.
The SNYA2 composition showed the change of the average grain aspect ratio and grain volume fraction of 15 % additive, sintered at temperatures of 1850 °C, the same as for the amount of additive of 20 %: for both the grain aspect ratio decreased and the volume fraction of the grains increased.
Unlike for the aspect ratio and volume fraction of the elongated grains, no definite relationship exists between fracture toughness and grain diameter (grain width).

The results show that moderate introducing TiO2 in the process of the cordierite synthesis can easily make the crystal defects, but it can reduce the diffusion resistance of the particle, improve the particle diffusing speed and make the crystallinity of crystallization phase and grain size increase in sample.
The pattern of X-ray diffraction from sample from 1 # to 4 # shown in Figure 2.Through the observation except cordierite phase no other phase, with the addition of TiO2 increases, the sample of the phase composition that did not change significantly, TiO2 solid solution to cordierite phase.By means of X-ray diffraction diagram half tall wide and 2θ angular position parameter, using Scherrer calculator software, calculation sample of grain size.Selecting the cordierite phase in (110) crystal half tall wide and place 2θ angular position calculated grain size.By the software of X 'Pert Plus to calculate the sample crystallinity of crystalline phase, the additives are not the 1 # sample TiO2 crystallization of cordierite resort set k%, as the standard sample data to measure the crystallinity of the other samples.Calculation results in the list table 2 shows that with TiO2 introducing more volume, sample of crystallization phase, the crystallinity of TiO2 increases, when applied amount for
1%, sample is not join the crystallinity TiO2 1.2925 times.When TiO2 applied amount continue to increase to 2%,3%, sample of crystallinity decreased, respectively for not join TiO2 sample of crystallization of crystallinity 1.1995 times and phase 1.0515 times.When the introduction of TiO2 is 2%, the sample in the maximum grain size of crystalline phase.
Table2 Grain size and Crystalinity of cordierite in specimens specimen number FWHM / ° Grain size / nm Crystalinity / % 1# 1.0428 7.5643 k 2# 1.0057 7.5643 1.2925k 3# 0.9563 8.2483 1.1995k 4# 1.0454 7.5459 1.0515k FWHM——Full width at half maximum of characteristic crystal surface（110） Table3 Crystal spacing in (110), (202), (624) and lattice parameters of cordierite specimen number d(110) d(202) d(624) a/ 102pm b/ 102pm c/ 102pm α=β=γ/º lattice volume /106pm3 1# 8.5294 4.0994 1.6918 16.8483 9.8904 9.3851 90 1563.8995 2# 8.4751 4.1100 1.6878 16.5302 9.8714 9.4745 90 1546.0131 3# 8.5569 4.1056 1.6947 16.8660 9.9297 9.4007 90 1574.3758 4# 8.4742 4.1028 1.6912 16.8572 9.8028 9.3935 90 1552.2548 According to the diagram of X-ray diffraction provided the cordierite phase in (11), (202), (624) crystal spacing data, through cordierite orthogonal crystal system structure, calculate cordierite lattice constant change and lattice volume change.Table 3 is a impact table of the introduction
From the figure which is not join the TiO2 of the sample of #1 microscropic structure can be seen, the structure compact degree is poor, grain fuzzy, bonding is not ideal.

The average grain size was determined by EBSD data, and the grains less than 10 μm in diameter were considered to be dynamic recrystallized (DRXed) grains.
Most fine DRXed grains occurred surrounding original coarse grains, and a bit of DRXed grains occurred interior the coarse grains, which can be regarded as necklace structure.
In addition, the number of precipitated phases increased with the compression temperature increases.
Combining Fig. 2 (f) with Fig. 5 (e), it can be observed that amount of DRXed grains occurred not only in the grain boundaries but also interior the grains.
The grain refining mechanism is attributed to the increase of grain boundaries by DRX mechanism

The total number of precipitates is more than 300.
Compared with IA sample, WR sample has more small angle grain boundaries and smaller grain sizes of ferrite and austenite.
According to the analysis of EBSD image, the number of grains of each phase involved in the statistics is more than 200.
As shown in Fig. 5 (b), a small number of precipitates with large size are distributed at the ferrite phase interface.
The grain size is calculated by EBSD.

Description of the composites under investigation (N is the number of Nb filaments).
The finest grains are observed in the Zr-doped composite, while Zn and Mg do not result in any grain refinement.
It should be noted that with an increase of the number of Nb filaments up to several thousands columnar grains adjacent to the residual niobium are not observed as a continuous layer, which may result from shorter diffusion paths for Sn transferring from a bronze matrix.
Since the internal structure of the diffusion Nb3Sn layers and consequently the current-carrying capacity of a composite as a whole are extremely sensitive to a diffusion annealing regime, a number of different annealing schedules have been tested on composites with tubular Nb filaments in the present study.
For further optimization of structure and properties a number of other annealing regimes have been tested (see Table 1, samples 12-18).

The grain size of the hardened zone.
Table2 Grain size of samples along depth of hardened zone (scanning speed of 600 mm/min) sample number testing content beam power (W) the surface the layer close to the the substrate middle layer the substrate 1 the grain size rank 900W 10.6 10.2 8.5 2 the grain size rank 1000W 9.9 11.3 12.4 3 the grain size rank 1200W 9.2 11.4 11.3 4 the grain size rank 1300W 9.1 9.2 13 5 the grain size rank 1500W 8.5 11.8 11.8 9.1 Finer and more evenly distributed carbides would produce a better hardening effect [5,6].The macromorphology and microstructure of the hardened layers are investigated by the optical microscopy(OM) and scanning electron microscopy(SEM, FEI ESEM XL30).Table 2 shows the average grain size of samples along depth of hardened zone, the results presented in table 2 show that the surface grain is bulky, even to the substrate grain size rank No.8.5 ~ No.10.6;the grain size of middle layer and the layer close to the substrate is small, the grain size can be up to No. 11 ~ No.
13, the difference of the grain size of the substrate is small. the grain size of the laser hardened layer is more than two level above the substrate.
Carbide depleted zone and carbide enriched zone of austenite grain size is different, in the zone near the banding of the not soluble carbide, austenitic grain grow up is hindered, and in the banding of carbide depleted zone, austenitic grain is increasing sharply.
Acknowledgements This research was financially supported by the Natural Science Research Foundation of Department of Education of AnHui Province in China (Grant Number: KJ2012Z051, KJ2012B044) and the Doctoral Foundation of Anhui Institute of Architecture and Industry.

Most grains having a size less than 100 nm have sharp grain boundaries and are free of dislocations, i.e., no subgrains or dislocation cells were observed in these grains (see the inset in Fig. 4b).
Such straight and narrow grain boundaries are believed to be in an equilibrium state and are high angle grain boundaries (HAGBs) [10].
Hence, a large number of extrinsic dislocations exist in this GB region.
The excess dislocations within grains and near grain (Fig. 5a) or sub-grain boundaries make dislocation glide more difficult [16].
The smaller grain size indicates more grain or sub-grain boundaries are contributing to strengthening.

But the matrix grain size grows to a certain extent due to the abnormal growth of recrystallized grains.
There are a large number of low-angle grain boundaries inside the grains.
When the grain size is thick, compatible deformation capability of neighboring grains is weak.
When the grain is refined, although the number of slip systems in single grain does not increase, the number of grains increases around each grain.
There are a large number of dimples on the fracture.