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It is also well known that the grain size refinement leads frequently to remarkable improvement of their strength [1].
The present investigation addressed to make clear the relation between the flow stress and the grain size for pure Mg and AZ31 alloy polycrystals at the wide range of temperatures.
Five kinds of average grain sizes ranging from 43 to 172µm for pure Mg and from 16 to 35µm for AZ31 alloys were selected for mechanical testing.
According to the original definition by Armstrong et al. [10], the prominent decrease of ky at elevated temperatures is considered to be associated with the contribution of non-basal slip to the basal slip mainly operated at room temperature, reducing the value of orientation factor which is related to the number of slip system.
Fig. 6 shows the relation between the ratio εer/εt and the strain εp at 293K for AZ31 alloys with the grain size of 35µm, together with pure Mg having those of 43, 60 and 172µm.

On the other hand, the number of particles in the coarsening system decays with the coarsening time.
The normal GG is driven by interfacial free energy on the grain boundary.
Applying the approach in DCPC theory to the case of grain growth, one describes the size of a grain by the radius R of an equivalent circle or sphere that has the same volume as the grain.
Hillert, On the Theory of normal and Abnormal grain growth, Acta Metall., 13 (1965), 227-238
Udler, Two-dimensional grain growth: topological aspects, Adv.

Besides, doping of a trace of Sr2+ ion can help promoting the growth rate of ferrite material crystal grain, the permeability of ferrite materials will increase.
According to the content of Sr2+ ion, the samples are numbered as S0, S1, S2, S3, S4 and S5.
Under the pressure of 130Mpa, press the grains into annuluses with 7mm outside diameters and 3mm inside diameters.
As the doping quantity continuing to increase, fracture surface of sample S4 showed that when doping quantity x=0.8, sample grains appeared excessive growth, dim grain boundaries, abundant pores, and obvious defects, microstructures presented obvious over sinter feature.
Growth of crystal grains are promoted, average size of the crystal grains grew, the whole sintered body became more dense, which is beneficial to movement of domain boundaries.

Besides, doping of a trace of rare-earth ion can help promoting the growth rate of ferrite material crystal grain.
According to the content of Gd3+ ion, the samples are numbered as A0, A1, A2, A3, A4.
Under the pressure of 130Mpa, press the grains into annuluses with 7mm outside diameters and 3mm inside diameters.
From the picture of doped sample A2(x=0.025), we can get that adequate Gd3+ doping (x≤0.025) obviously improved the growth of grains, and as doping quantity of Gd3+ ion, average size of the grains increase obviously, grains largen gradually in the width direction, the length-width ratio decreased, the porosity decreased, the grains became more dense.
While as the doping quantity continued to increase, impure phase grains appear in sample A3 (x=0.050) as seen in the fractograph, and the grain boundary becomes dim.

Several attempts to resolve the problem of ductility through alloying, grain refinement and grain boundary elimination have been made [1,2,3,4].
Demand for sub-grain sized microstructural development in NiAl have arisen since refined grain size had been shown to have a dramatic effect on tensile ductility at 673 K [5].
The grain size of cast NiAl was determined by the mean intercept method and the average grain size was found to be about 30 �m, which is in agreement with other reports [3,7].
Many of the grain boundaries are likely to be low angle ones because a large number of grains exhibit the same contrast even after tilting the specimen over several degrees in TEM operation.
Grain refinement hardening 2.

At grain size level, the domain walls motion imposes the intensity of magnetization.
The macroscopic properties depend essentially on the synthesizing process and the grain size.
The average grain sizes of the composite constituents are: ferrite nanograins of 0.8 - 4.7 μm; ferroelectric nanograins of 400 - 600 nm, with the ferromagnetic particles dispersed at the piezoelectric matrix grain boundaries [2].
(In the GHz region, the grain sizes are much smaller than the skin depth.)
The electromagnetic parameters values depending strongly of the synthesizing method and implicitly on sintering temperature (at 1280°C–1300°C the phase structure is stable) and average grain size.

At 0% and 0.2% manganese, intermetallic compounds which have lamellar structure are observed on grain boundaries, but these lamellar compounds are not rarely observed in 0.4 to 0.8% manganese billets.
As the manganese content becomes high, the number of Al-Mn intermetallic compounds becomes large.
At 0.2 to 0.4% manganese, the number of surface cracks is smaller than that of 0% manganese alloy.
The grain size of 0% manganese extrusion is large, and grain size of the extrusions at 0.2 to 0.8% manganese is small.
But, there is no difference in grain size in the range of 0.2 to 0.4 % manganese.

The glass sheet substrates we used (24 mm×12 mm×0.2 mm in size) were only ultrasonically cleaned, because after that they could exhibit a strong adsorption affinity for metal ions and it was unnecessary to be etched by an air plasma in order to increase the number of OH-groups [4].
XRD and SEM (figure 1,2) measurements indicate that the Fe3O4 ferrite films have a single spinal phase structure with well-crystallized columnar grains growing perpendicularly to the substrates.
And all the unirradiated and irradiated Fe3O4 thin films have a single spinal phase structure with polycrystalline columnar grains growing perpendicularly to the substrates.
When the Kr26+ ion fluence is low, Hc increases, mainly because the number of grain boundaries increases significantly and then the grain boundaries act as pinning sites of magnetic domain [5,6], which are the results of heavy ion irradiation causing hidden tracks makes the lattice defects much more and the grain size of our samples much smaller; on the contrary, Ms decreases, mainly because heavy ion irradiation could order the magnetic moments of the Fe3O4 thin films, and the magnetic moments tend to arrange along the film plane.

Introduction The dislocation slip and mechanical twinning, being two kinds of fundamental deformation modes in polycrystalline metals or alloys, govern not only the mechanical properties such as work hardening and tensile plasticity, but also the micromechanical behavior such as grain orientation rotation and evolution of local stress.
Generally speaking, the twin nucleation required for a higher level of stress on some grains with the preferred orientation to exceed the critical resolved shear stress (CRSS), which is proposed by Thamburaja, et.al [3].
The length-to-width ratio for the investigated sample, assembled by 50 grains, is 2:1 as shown in Fig. 1.
The random orientations are assigned to each grain, which is discretized by four meshes with four integration points in each mesh.
Acknowledgments This work was supported by National Science Foundation of China under grant number 51231002 and Pacific Northwest National Laboratory with contract number DE-AC05-76RL01830.

In the field of engineering soil can be divided into detritus, sand soil, fine grained soil.
The density of crushed stone can be defined by qualitative method in the open usually, the density of pebble can be defined according N120,the hammered number of the super heavy dynamic penetration.
Sand soil is the content of grain size that is greater than 2mm does not excess 50% of the total quality and content of grain size which is greater than 0.075mm excess 50% of the total quality.
The fine grain soil is content of the grain size that is larger than 0.075mm does not excess the 50% of the total quality.
suspended capillary water when the ground water decrease rapidly from the fine grain layer to the coarse grain layer, due to the capillary force the capillary water should keep back in the fine grain layer and do not connect with the ground water. 3. climate.