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Corrosion resistance also increased with decreasing grain size in zirconium at high temperature when nanocrystalline grains were compared to coarse grains [4].
The number following the letter corresponds to the duration of heat treatment time (in minutes).
Figure 1 summarizes the average grain sizes investigated herein and indicates the impact of annealing/heat treatment upon grain size.
The large grains result from slow cooling rates, and the columnar grains form from directional cooling.
Corrosion current (icorr) versus grain size for pure Mg.

Therefore, the grain size becomes more and more uniform and thin, and the (SDAS) of aluminum alloy are more and more small.
While solidification pressure is 400 KPa, the grain size reduces further and the average of SDAS is 27.7 mm.
When solidification under 450 KPa, the number of grain is much more than others and the average of SDAS is 20.7μm.
So the dendrite may be broken as long as the feeding forces higher than strength of dendrite, which can make the number of the grain increase.
Acknowledgements This research was financially supported by Aeronautical Science Foundation of China (grant number: 2009ZE56015), and Jiangxi Education Department Science and Technology Project of China (grant number: GJJ10508).

While the specimens pressed via route A showed lamellar grain shapes those via route C or BC exhibited equiaxed grains.
Variation of the texture strength in Zr702 as a function of number of passes in ECAP via different routes.
The other routes, i.e., C and BC, either alternate the intensity or slightly weaken it with the number of passes.
Although grain refining down to the level of 0 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 35 Maximum f(g) value Number of passes Route A Route BC Route C0.2µm can be obtained by A, C or BC alike, the equiaxed grain feature is promoted most efficiently by route BC, which is attributed to increased random high angle boundaries due to intersection of shear strain paths caused by rotation of specimens between each pass.
Moreover, the intensity of the main texture components is also affected by the route of deformation; the intensity for route A increases while that for route BC or C decreases with the number of passes.

The granularity of diamond grains used was 60/70.
Furthermore, the total drilling hole number with the brazed and sintered core drill is 800 and 260, respectively, which means about 3 times in the life of the multi-layer brazed diamond core drill than in that of the sintered one.
Furthermore, the average total drilling hole number with the brazed and sintered core drills is 800 and 500, respectively.
But the grains quantity of the monolayer brazed diamond core drill with optimum grain distribution is only one-third of the multi-layer brazed Diamond grits Drag tails Drag tail Diamond Diamond pull-out cavities diamond core drill with random grain distribution, which means the utilization rate of diamond grain for monolayer brazed diamond core drill with optimum grain distribution is about 2 times than that of the multi-layer one with random grain distribution.
Table 3 Results of contrast machining performance evaluation Machining performance Multi-layer brazed diamond core drill with random grain distribution Monolayer brazed diamond core drill with optimum grain distribution Average spindle direction force［N］ 160 130 The total drilling hole number 800 500 Drilling hole number per diamond grit 2.6 5 Optimization Design of Multi-layer Brazed Diamond Tool Topography Considering that the absolute irregular distribution of grains is not a requirement of the grinding process, contrarily it will have a significant negative influence on the grinding process, our group put forward a new concept on the relatively regular and reasonable distribution of grains on the tool surface in accordance with different machining demands, and a creative idea of the optimization design of grinding tool topography in accordance with machining demands and grinding parameters as well as the optimization of grinding parameters

An intensive GBS, migration of grain boundaries, a considerable growth of grains, absence of dislocations in grain boundaries, dislocation substructure and gliding lines in grains were typical for their creep.
It stopped when a growth of grains stopped.
As can be seen, fine grain is not enough for SP.
Due to the above said, in grains there occurs dislocation structure, intensive gliding of dislocations, lines and bands of gliding are formed, a number of lattice dislocations in grain boundaries grows.
Then there grows a number of dislocations, approaching the boundaries.

Al-Ti-C grain refiner is a kind of grain refinement material that has excellent application prospect and is studied emphasisly[1-8].
After the columnar grain converges in the central area of refinement experiment mould, the grain growth terminates.
After the addition of Al5Ti0.25C grain refiner, columnar grain zone disappears completely (Figure 3(b)) and the columnar grain entirely transforms into equiaxed grain whose mean grain size is 180μm.
Thus it can be seen that Al-Ti-C grain refiner prepared under ultrasonic coupling has excellent capability in grain refinement.
Acknowledgements Authors thanks for the supports of The national natural science foundation of China（Fund number: 51174061）.

In addition, the number of austenite grains per unit area was evaluated.
In addition, the numbers of austenite grains per unit area under different strain were evaluated, and the results are shown in Fig. 3.
Fig. 3 Effect of strain on the number of austenite grains per unit area The schematic representation of dynamic strain – induced boundary migration is shown in Figure 4 (black lines: prior austenite grain boundary; red lines: dislocations).
The dislocation density within Grain A is relatively lower than that within Grains B, C, D or E, so the Grain A has a high growth driving force [20].
Grain E Grain A Grain D Grain C (c) (b) (a) Dislocations-free regions Grain B Fig. 4 Schematic representation of dynamic strain – induced boundary migration: (a) the initial austenite grain structures, (b) the distribution of dislocations after deformation, (c) the dislocations density driving austenite grain boundaries migration Conclusions 1.

Polyhedron in shape was dominated with obvious large numbers of pores on the surface.
When temperature was increased to 1100 oC, less numbers of pores were found and no appreciable change in grain size and shape was visible in comparison with the 1000oC sample.
This indicated well-sintered pellets and high grain compact.
Up to present, a number of papers had reported the possible mechanism of abnormal grain growth and corresponding measures taken to control large grain growth were also suggested[6-8].
This was believed to be due to the abnormal grain growth.

The grain size tends to be lowered as the ratio is close to the critical value.
The grain size was reduced from 50 µm to less 10 µm except at the center of the rod.
The grain size was reduced to ~1.5 µm and this fine-grained region covers from the outer edge to the region ~ 1 mm off the center.
It is apparent that grain refinement is effective when the STSP temperature is lower.
The former leads to insufficient numbers of dislocations to create grain boundaries and the later makes it difficult to keep the grain size small.

The research shows that the number of twinning crystal decreases, the number of the core of dynamically recrystallized grain increases, and the grain size become fine and isotropy by differential speed rolling with the increase of the reduction and the improving of the rolling temperature to some extent.
A great deal of fine grain are distributed at the converged place of big grain bound, which is the result of dynamical recrystallization as shown in Fig.4.
With the increase of the rolling temperature farther, when rolled at the temperature of 350˚C, the proportion of fine dynamically recrystallized grain increase evidently, but some twinning grain and coarse grain still exist as shown in Fig.6.
As a result, the orientation which produce compressing twinning grain decrease, and the inclination which produce compressing twinning grain decrease [4].
With the increase of the speed ratio, the number of compressing twinning grain decreases, and the number of short elongating twinning grain increases.