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Sub-grains were found at the grain boundaries with little dislocations in the matrix after 27448 h service time.
With the increase of the service time under high temperature and high pressure, the island-like microstructure disappeared when the service time is 27448h and 31526h, and both the number and size of the carbides at the grain boundaries and the grain interior obviously increased.
There are a great number of dislocations in the grains and at the grain boundaries in the original T23 steel matrix as shown in Fig. 3(a), forming dislocation networks.
The number of the dislocations gets a relative reduction after running for 23872h compared to the original T23 steel.
However, there are a certain number of creep voids near the carbides at the grain boundaries.

The longer the slope , the more the amounts of grain become,and the smaller size of grain get to be.
Great shear stress will be developed with the flow of melt under the action of violent vibration in the process of grain growth, which will break dendrite arm or grain of dendritic crystal, the broken grains become new nucleus of grain growth, which result in increase of amounts of grain.
It shows vibration can improve the alloy microstructure significantly, increase the grains in the number, decrease its size, spheroidize the microstructure which is better than those without vibration.
Conclusion (1) The longer the casting slope is, greater alloy grains in number is; smaller, more rounded shape and uniform two-dimensional grain size is
(2) Vibration can improve the alloy microstructure significantly, increase the grains in the number, decrease its size, spheroidize the microstructure.

Predictive theory for the grain boundary character distribution K.
Although we may be reasonably confident that small cells with small numbers of facets will be deleted, their effect on the configuration is essentially random.
An entropy based theory of the grain boundary character distribution.
Mullins. 2-Dimensional motion of idealized grain growth.
Smith "grain shapes and other metallurgical applications of topology".

The idea behind this technique is to develop a simple, economically viable, processing route by using the smallest number of rolling passes, with the largest possible strain per pass.
The material consists of coarse, equiaxed grains of average grain size equal to 95 microns.
Texture data must be interpreted with caution since, due to the large grain size of the starting microstructure, the number of grains measured may not be enough to have a good statistics.
It is well known that the number of active slip systems in Zr alloys is rather high at low homologous temperatures since both prismatic {10-10} and {10-10} as well as pyramidal {11-21} and {10-11} slip systems have been found to be active [12].
Summary In this work the potential of large strain rolling for grain refinement in a coarse grained Zr-Hf alloy has been investigated.

The size of the ferrite grain was 20-80 µm, the shape of the grains was polygonal.
In Fig. 2 and Fig. 3 they are indicated by numbers: 1 - evaporation crater; 2 - transition zone (zone of melting, phase transformations and quenching); 3 - heat-affected zone (zone of the original structure with various elements of grain boundary slippage - GBS).
Their schematic representation is shown in Fig. 2b, where they are designated by number 1 (shear bands, designated by number 2, were not observed in ARMCO pure iron, since they are characteristic, first of all, of fcc-metals).
In the above illustrations, the grain rotation can be observed in Fig. 3 c (grain B, at all boundaries of which accommodation zones are visible, as a result of which the grain acquires new outlines).
In Fig. 3 c, in the grain with the number 3 there are two boundaries, shown by arrows, which differ from all those described above in that they cannot be attributed to the boundaries that have undergone GBS.

Both materials possessed well defined high-angle grain boundaries.
Introduction There are a number of methods available for the manufacture of nanocrystalline metals, one of which is electrodeposition [1,2].
There have been a number of theories presented to explain internal stresses.
Dark field images were also used to determine the average grain size by counting at least 200 grain diameters for each material.
The addition of iron also caused a decrease in grain size.

At this time, the number of wearied and newly presented cutting edges arrives at homeostasis due to self-truing tendency.
A number of experiments performed in the past indicated that, for abrasive granule used in ultra-precision grinding, the grain diameter obey to truncated normal distribution, which means 99.7% of grains in grinding have size in [ max min, gg dd ].
Therefore, probability density function ( )gidP of grain diameter gid can be expressed as [4,8] ( ) max ggi min g 2 g ggi g 1 gi ddd; ;0 dd 2 1 exp 2 A dP <<                       − − = σ πσ (4) Where min gd and max gd is minimum and maximum grain size respectively, gσ is standard deviation and gd is mean which can be calculated by sieve number M and expressed as 1 2.15 − = Mdg [4,5,8], and 1A is test constant.
Numbers of such dressing tool topographies engage in the same place of abrasive, which work as an inerratic integral mode, made cutting edges equably at a certain level on the tool.
Hence, the grain protrusion number can be identified along with grain protrusion height hg by section height h and grain occurrence.

The results showed that the number and size of recrystallized grains increased with the increase of temperature at the same strain rate, and the number and size of recrystallized grains increased with the decrease of strain rate at the same temperature.
The dislocation increment rate will increase as the increase of strain rate at the same temperature, and a large number of deformation dislocations will be accumulated at the grain boundary soon, resulting in the increased of deformation resistance, so the peak stress will increase.
Microstructure Evolution and Recrystallized Grain Size of Mg-13Gd-4Y-2Zn-0.5Zr Alloy.
Therefore, the grain size model of dynamic recrystallized is as follows:
The grain size model of dynamic recrystallized is constructed as: .

At the same time, the grain shape becomes more round as the temperature of airflow increases, and the holes between the grains also become smaller.
Fig. 1a shows that the average grain size was 54 µm, and grain shapes were irregular when the gas was not heated; Fig. 1b shows that the average grain size was 50 µm, and grain shapes were more regular than Fig. 1a when the gas was heated to 50 °C; Fig. 1c shows that the average grain size was 43 µm, and grain shapes were round when the gas was heated to 100 °C; Fig. 1d shows that the average grain size was 39 µm, and grain shapes were more round when the gas was heated to 150 °C.
The number and the size of holes decreases with the growth of temperature.
Where, M is airflow Mach number, M = Vg / ag; Vg is gas velocity; ag is the local sonic.
The grain round progressively and sizes of the hole decreased.

The macrostructure of pure aluminum appears three different grain morphologies: the surface fine grains, the central columnar grains and the heart equiaxed grains.
When adding 0.3%Zr alone, the grains get slightly refined, the columnar grain area is reduced and the equiaxed grain zone is increased.
With 0.3%Ti added alone, the grains obtain obviously refined and all of the columnar grains transform into coarse equiaxed ones.
So, when 0.3%Ti or 0.3%Zr added alone，the Al3Ti or Al3Zr primary phases can effectively promote the grain refinement, and with the number of Al3Ti and Al3Zr particles increasing, the heterogeneous nuclei increases gradually in the melt and further promotes the grain refinement.
Thereby the grain refining effect of 0.3%Ti is better than that of 0.3%Zr, and the microstructure of the alloy completely transform into equiaxed grains, while the sample with 0.3%Zr still keep many columnar grains.