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As shown in Fig. 2, dynamically-recrystallized grains were observed near initial high angle grain boundaries before peak strain.
After hot compression up to 0.05 of true strain, recrystallized small grains seem to be formed first at triple junctions or at the point where slip band meets high angle grain boundary.
Journal Title and Volume Number (to be inserted by the publisher) 3 Fig. 2.
It implies that the controlling factor for DRX nucleation is not the matrix precipitate (�”) or grain boundary phase (�), but the strain rate, i.e. the dislocation accumulation rate on grain boundaries.
Variation of critical strain with Zener-Hollomon parameter at different initial grain size

For site-saturated reactions and random distribution of the grains, the microstructural path is described by: ( ) 3 2 1 1 ln1             − −= V V V V VBS (2a) 3/1 3 4 3       π = VN B (2b) where SV is the interface area between the recrystallized grains and the matrix and NV is the number of grains per unit of volume.
The interfacial area density per unit of volume separating recrystallized grains and the recovered matrix (Sv) was measured by optical microscopy superimposing a grid of straight lines on a planar section and counting the number of intercepts between the straight lines and the interfaces [7].
In consequence, the substructure developed within grains and the corresponding amount of stored energy varies significantly from one grain to another.
The nucleation of these grains is far from to be regarded random.
Therefore, a relatively small number of grains were measured that unavoidably led to the high scatter observed.

A multicomponent single-phase model of a working face in Yanzhou mining administration is modeled[1,2],and the temperature field is simulated by SIMPLE algorithm.The bi-directional coupling between droplets and air is simulated by the stochastic model.After simulating the two cooling schemes using air conditioner and spray cooler[3,4],the distribution of temperature is analyzed. 1 The stochastic model 1.1 The action of grains in flow field Grains are forced by friction,because of the difference in velocity.The mathematical description is the Stokes resistance law[5,6]: 3 (Re ) D k k k F d u u f  (1) Where DF represents the viscosity resistance; kd is the diameter of grains;  is the coefficient of viscosity of air; u is the absolute velocity of air; ku is the absolute velocity of grains; (Re ) Re / 24 k D k fC , where DC is the drag coefficient, if Re 1000k , 0.687 24(1 0.15Re )
Magnus force is caused by velocity gradient which pushes grains migrated laterally,Bubinow and Keller calculated the Magnus force of a whirl ball: 31 [1 (Re )] 8 M k k k k k F d u O      (2) Where MF is the Magnus force; k is the density of grains; k is the angular velocity of rotation of grains; (Re )kO is the error related to the Reynolds number.
While flying in a flow field with velocity gradient,a lift effect forcing the grains(Saffman force): 0.5 3.0844 kS k k k F m u u u D      (3) Where SF is Saffman force; km is the mass of grains.
When grains falling freely,the gravity should be considered: 31 6 g k k F d g  (4) Where gF is the gravity of grains. 1.2 The stochastic model The grains are supposed to be spherical.And each group of grains is supposed to move in its own orbit from the initial position.The impact of grains is ignored[7,8]Then the equation of motion of grains could be expressed as follows: , , , , ' ' ' (1 ) ki i ki k k i k D i M i S i g i rk k du u u m m g m F F F F dt           (5) Where rk is the relaxation time, 4 / 3 ' ' rk k p D i ki d C u u     .
According to the interaction model between grains and eddies,the interaction time intt should be less than the lifetime e of the eddy ,and the distance intL should be shorter than the space scale eL of it. 0.75 int 1.225 / et C k   , 0.75 1.5 int /eL L C k   (6) During the lifetime of an eddy,the fluctuation velocity keeps fixed: 2 '' ii uu (7) Where  is a random number from -1 to 1,which follows the standard normal distribution. 2 The turbulent model of the main phase The airflow in working face is steady and non-equilibrium,which satisfies the continuity equation,the momentum equation,the energy equation and the composition equation.The state parameters of airflow could be expressed as a general variable: '   ,where  represents the time-average value,and ' represents the pulsation value.In order to close the

The as-forged Ti-45Al-5Nb-0.3Y alloy is comprised of a large number of dynamic recrystallization (DRX) γ grains, curved and broken lamellae, and a small amount of remnant lamellae.
Furthermore, each of grains is comprised of lamellar microstructures (TEM image is shown in Fig.2b).
Metallographic examination shows that, after high temperature forging, the majority zone of the asforged Ti-45Al-5Nb-0.3Y alloy is comprised of a large number of dynamic recrystallization (DRX) γ grains, curved and broken lamellae, and a small amount of remnant lamellae (Fig.4a).
The DRX γ grain size reaches 1~2µm.
After holding at 1320℃,1340℃ for 30min and at 1370℃ for 15min, TiAl samples contain γ and α2 grains, and when it is furnace cooled to room temperature, the phase transformation of α → L (α/γ) → L(α2/γ) takes place in α grains.

The as-deposited films did not show clear grain boundaries, but after thermal annealing, grains grow and form nanocrystalline structure with a grain size of 8 nm.
Color code indicates the coordination number.
The size of a grain is about 8 nm.
For perfect fcc crystals, the coordination number is 12.
Wang: Theoretical tensile strength of an Al grain boundary.

The dislocation of crack tip,grain boundaries and different grain orientations have great influence on the path of crack growth, which can make cracks bending.
As shown in fig. 1, a number of small black spots dispersed and distrubuited in A7075 alloy with a bit gray in the grain, which may be caused by oxide inclusion or precipitation phase of grains and grain boundries.
Meanwhile, there is a deformation in the grain boundary junction, even appearing parts of the grain layer fracture.
In order to achieve a balance of free energy in the fatigue process, cracks may be initiated at grain boundaries or junction of grain and matrix.
When fatigue cyclic number was 4000 times (6c), the primary crack completely formed with the secondary micro-cracks initiation in the peripheral.

Introduction Nanocrystalline materials consisting of nanometer-sized crystalline contain a large number of interfaces such as grain boundaries and triple junctions, and thus, a large volume fraction of atoms are associated with the intercrystalline region [1].
Results and Discussion The occurrence of grain growth in the specimen resulted in the change of crystallographic textures as follows.
The texture evolution that takes place during annealing can be attributed to relatively faster growth of the <111>//ND grains than the <100>//ND and other oriented grains.
TEM and OIM analysis were used to obtain the grain size for the as-deposited and annealed specimens.
When the mechanical properties were measured by means of the nanoindentation test, the annealed specimen exhibited a lower hardness due to grain growth and a higher elastic modulus due to the high density of the <111>//ND grains in comparison of the as-deposited specimen.

There is a bimodal structure which large and small grains staggered in the microstructure.
Meanwhile, with the ultrasonic powers increased, the grains become more spherical and finer.
The hardness of the alloys under pressure, ultrasonic vibration and compound field are higher than gravity cast because of small grain size resulting grain boundary strengthening.
It can be seen that large number of porosity and the coarse β-Fe phase dispersed among α-Al dendrites in produced by gravity cast alloy, as shown in Fig.5a.
Moreover, the nuclei formed at the interfaces of cavity and melt would be re-distributed into the melt due to the strong string by acoustic streaming, offering large numbers of nucleation sites throughout the bulk melt.

As the concentration of Fe2+ ions increases the number of oxygen vacancies increases, and this increases the sintering rate, lowering the maximum temperature of densification [13].
As can be seen in Fig. 3, the SFO1OOSiC sample (SrFe12O19), appears to have a liquid phase on the grain and also across the grain, as can be observed in other samples, but further studies are needed for confirmation.
In the BFO90 sample there was not any change in grain size, while in the sample SFO100 the dopant made a decrease in size of the grains.
Table 3: Grain size variation of the samples with and without additives, sintered at 1000 °C/2h.
In the BFO100 and BFO15 samples, there was a significant growth in the grains, while in the sample BFO90 the grains remained practically the same size and the sample SFO100 had a decrease in grain size.

Through the analysis and research of cultivated land area change rate and grain yield rate and rate of urbanization.
Discusses the relations between and among population, cultivated land and grain production, Put forward some countermeasures and Suggestions.
Cultivated land, population and grain output correlation analysis Population, cultivated land and grain problem is the most specific population, ecology, economic relations is one of the most practical aspect, is the most basic in the relations between man and nature of a link, as the middle part of the relationship between the cultivated land grain production reality ability has a very important role.
Cultivated land is the material foundation to solve the problem of food and the food is the material base of existing of population, the number of people to a great extent, determines the relationship between the development and utilization of cultivated land condition, and influence the development of economy and society.
Based on the food security of China's grain demand forecasting and cultivated land resources allocation research [J].