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A number of studies have been done to clarify the fatigue crack generation and growth mechanisms for high strength alloys [2].
The microcrack growth and/or coalescence model can excellently explain for a formation process of Stage I crack with a critical size where a process of microcrack growth involves a large number of cycles and not by its instantaneous spread.
The coplanar arrays developed in a grain under the cyclic softening impinge the grain boundary and produce steps and/or protrusions, which produces a strain-gradient in the neighboring grain as shown in Fig. 2. [8] Thus the strain incompatibility containing shear strain field at the grain boundary is believed to be developed and to act shear stress and tensile stress to the grain boundary plane, since the grain boundary plane is inclined to the applied stress axis.
In order to relax the internal stress due to strain incompatibility, therefore, a deformation or microcracking must occur between the neighboring grains, i.e. deformed grain, neighboring grain or grin boundary.
The multiple slips that developed in a considerable number of grains may promote homogeneous and multidirectional plastic deformation; further, the localized deformation and strain incompatibility at grain boundaries were believed to decrease as a result of the treatment.

The fracture modes at this aging temperature are mixed fracture mechanisms of dimple fracture and intergranular fracture, and the number of dimple fractures increases with time.
It can be seen from the figure that the die forging has not undergone recrystallization after 477℃/7.5h solution treatment, and there are a large number of fine sub-grains in the original grain boundaries.
The grains are elongated along the rolling direction, and undissolved second phase particles are dispersed inside the grains and at the grain boundaries.
Overall, the number of dimple fractures increases with time.
When the time was prolonged to 8h, the composition of intergranular fracture decreased significantly than before, and the number of dimples increased.

The mold surface was more smooth, and the number of stomata reduced .
At the same time , a cross-section was observed with the naked eye, the zinc alloy after solidification under pressure, compared to the material without pressure treatment, whose stoma number significantly reduced a lot.
At the same time, due to shorter crystallization time, which restricted the diffusion process of dendrites pressure made the growth of grains form smaller, thus played a grain refinement purposes.
The finer the grain is , the more plastic deformation can be spread in more grains, which will give more uniform plastic deformation, and the stress concentration is smaller; and the finer grain is ,the more interface it has, the more tortuous grain boundaries are; the more opportunities the grain interlocking have in the grains, the more difficult is conducive to the spread and development of cracks, at last ,the more tightening, the better strength and toughness will be.
Conclusion (1)In the casting process, the zinc alloy solidification with the nitrogen pressurized method could reduce shrinkage, its surface was more smooth, macroscopic density increased, with the number of stomata reducing

According to the experimental results, the solidification structure of hypereutectic high chromium cast iron was modified from large grains to finer grains with equiaxed crystals, by allowing the ECP to act on liquid.
According to the experimental results, the solidification structure of hypereutectic high chromium cast iron can be modified from coarse long rod-shaped large grains to finer grains with equiaxed crystals.
The number of times Lorenz force regularly repeated increasing with increasing frequency, so from the Fig. 3(b) we can see the average diameter of primary grain gradually decreased with increasing of pulse frequency, effects of the pulse width the same as the effect of pulse frequency.
The liquid-solid interface is unstable and the grains will grow anisotropically in its perferred crystallographic orientation, leading to get a large number of rod-shaped primary carbides grain, because Liquid conductivity greater than the Primary grain, the current flow around the primary grain, which leading to increased current density of the solid-liquid interface, so the liquid-solid interface is table and grains grow spherically.
Different conductivity of liquid and primary grain, which leading to increased current density of the solid-liquid interface, so the liquid-solid interface is table and grains grow spherically. 4. equivalent diameter of primary carbides was decreased initially and then coarsening as the increasing of electric voltage, the average diameter of primary grain decreased with increasing of pulse frequency and pulse width in this experiment.

The reheating condition was optimized and the comparison between different routes and number of passes was investigated.
When the temperature rises to above solidus, the high- energy grain boundaries of these new grains are penetrated by liquid, leading to the fragmentation of original grains to small equiaxed grains.
The presence of liquid causes grain growth and spheroidization of the newly formed grains.
By increasing number of passes dendrites and interdendritic networks of lamellar eutectic silicon mix together and eutectic phase distributes in the structure resulting in reduced distances for diffusion.
Therefore, a grain boundary etchant is required to examine this phenomenon.

With the increasing of original Cr3C2 content, the number and size of arborescent crystal increased obviously.
With the increasing of original Cr3C2 content, the number and size of arborescent crystal increase obviously.
On the surface of FGM, micro-score, deciduous and pulling-of TiC ceramic grains are observed, which is showing grain abrasion and plough ditch have happened.
Their FGM substrate is micro-cutted by deciduous TiC grain.
With the increasing of original Cr3C2 content, the number and size of arborescent crystal increased obviously.

The rapid formation of ultrafine-grained structures has been observed in materials susceptible to grain fragmentation upon plastic deformation.
The grain refinement in these steels is accelerated by mechanical twinning and/or strain-induced martensitic transformation [6, 7], leading to the fast development of ultrafine-grained structures at relatively small strains.
The rate of strain hardening gradually decreases with increasing the number of forging passes.
The structural changes are characterized by fast kinetics of grain refinement (Fig. 5b).
Miura, Ultrafine grain development in copper during multidirectional forging at 195K, Philos.

Each particle is assigned an independent orientation number q for distinguishing the individual state.
The neighbor interaction energies in the system given by (1) Here N is the total number of sites is the space; δ is the Kronecker delta; qi is the state of the grain or pore at the site i, and qj is the state of the nearest neighbor at site j.
First, a random grain site is chosen.
With annihilation of vacancies, the mass center of the adjoining grain moves to the grain boundary, thus giving densification.
Time in this model is measured in units of Monte Carlo step: 1MCS corresponds to N attempted changes where N is the total number of sites in the system [19].

Reg ar ding a known network topology, the problem of choosing links and switchers among alternatives different in reliability and cost is settled by a Coarse-grained parallel genetic algorithm, which maximize the network availablity within a fixed budget.
Among them, the coarse-grained model, also known as a distributed model or the island model, is the most adaptable and most widely used genetic algorithm parallelization model. coarse-grained model is the initial population of randomly generated according to the number of processors is divided into a number of sub-groups. various sub-groups are independent of each other on different processors the concurrent execution evolutionary operation, each after a certain evolution-generation between the various sub-groups will exchange certain individuals to introduce the good genes of the other sub-groups, the rich diversity of the various sub-groups, to prevent the occurrence of premature convergence. coarse-grained model less communication overhead, very suitable for running on the communication bandwidth the lower cluster system.
Migration strategy In the various implementations of the coarse-grained model, some choose the best individual subgroups outward "immigrants"; "immigrants" is selected at random.
Some algorithm to replace the population-migrant worst individual; some were replaced by randomly selected using the best individual to move out of the number of / worst individual is replaced by (herein referred to as the best / worst Standards) is the most commonly used, so this is the migration nem = 1 the optimal / worst criteria.
Using literature [7] the method of randomly generated three examples: Each time through the uniformly distributed in the (20, 80) of the random number generator (U (20, 80)) to generate 61 arc length dj.

Fig.5 Different angle shot of the fracture morphology Microanalysis Took sampling in the crack source pointed by arrow of zone 1 and numbered sample 1.
Took sampling in the fatigue source that pointed by arrow of zone 2 and numbered sample 2.
If hot rolling temperature was higher and grains were coarse, mischcrystal was formed easily [4].
Grain size was so uneven that central structure had mischcrystal phenomenon
(2) Carry on normalizing to refine grains and eliminate the widmanstatten structure and mischcrystal