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Introduction Although the first research on intercrystalline diffusion in nanocrystalline metals was carried out more than 20 years ago [1], up to the present time there is not a full understanding of specific features of the diffusion processes in such materials, and the number of studies dealing with the experimental investigation of diffusion in them is relatively small [2].
At the annealing the Mössbauer isotope atoms diffuse along grain boundaries.
As shown in [17-20] grains between agglomerates are the fastest diffusion paths in such materials while the diffusion properties of boundaries between nano-grains are the same as in coarse-grained materials.
As demonstrated by TEM in [28], grain sizes after such treatment are about 100 nm, and grain boundaries are wide and non-equilibrium, a complex diffraction contrast and moiré inside grains testifying high internal stresses.
At heating up to 873K grain sizes remain unchanged but recovery occurs, grain boundaries becoming thinner and straighter and grains clearing of dislocations, and at higher temperatures recrystallization starts with intensive grain growth.

Si and Mg2Si precipitated in the grain boundary of these two materials.
The weld penetration into the grain of the precipitates and a decrease in the precipitates on the grain boundaries can be considered as reasons for this improvement.
Moreover, an increase in the fine dispersion of the precipitate (Si, Mg2Si) in the grain and grain boundary were caused by the artificial aging treatment.
The fine grains are thought to be related to the increase in strength.
Forging of the artificially aged material produced fine grains and decreases the number of precipitates at the grain boundaries. 3.

Fine-Grained High-Strength Concrete N.P.
The structure of fine-grained concrete is studied.
Despite the larger optimal diameter of the metakaolin particles, stabilized by PVA after 8 minute ultrasonic dispersion, the number of the particles with the size of 11.2 nm is 44.3%, thus it being 4 times more than the metakaolin particles with the minimum diameter when stabilizing the suspension with S-3.
Structure of fine-grained concrete modified by PVA (a) and S-3 (b).
Goldenberg, Fine-Grained Concrete, MGSU, Moscow. 1998

Some elements, especially microalloying elements, segregate at grain boundaries, and this significantly retards grain growth.
The concentration profile across a grain boundary during grain growth can be calculated by coupling Eq. 1 and Eq. 2
During grain growth with velocity, v, it is natural that grain size increases gradually.
The total number of grid points for a calculation was 601.
Using this model, the concentration profiles across grain boundaries and grain size evolution were calculated.

Generally speaking, the burning area of grain changing with time is the key to the grain combustion simulation.
Wang et al uses 2D level set to simulate the anisotropic SRM grain burning[8], Qing [9] demonstrates the application of level set in grain burning surface calculation.
SRM grain surface regression simulation SRM grain is a kind of high-energy fuel which propels the whole missile to attack enemy target.
At last the whole grain will burn out.
It is found that two methods can get very close results except the end of the curve because of the number of finely triangles increasing.

The larger number of crystal nuclear are formed and the even shape and size grains are obtained.
By comparing with Fig.2 b),c),d), it can be obviously observed that crystal structure grows more even and regular and the number of grain grows more and the grain is refined.
It can be concluded from Fig.2 that slope length has significant effect on the grain number and shape of the alloy microstructure.
It can be observed that crystal structure grows more even and regular and the number of grain grows more and the grain is refined when the vibration voltage grows higher until to 80v.
So the broken arms can be new nuclear which increase the number of grain.

With the increase of the distance from the bottom of the starter block, the number of grains is gradually reduced, and the size of the grains gradually becomes larger.
With the increase of section height, the number of grain with an included angles that less than 15° between the <001> direction and the heat flux direction is increased.
The height of the starter block should be designed in the 13-36mm, which can ensure a certain number of grains to enter into the spiral part.
The number of grains in the spiral block is drastically reduced by the initial selection at (f) to (g) segments.
With the increase of the distance from the start block bottom, the number of grain decreases and the size of the grains become larger.

The first one is transformational grain refinement [1-3], wherein the austenite ferrite transformation is explored to obtain refined ferrite grains from a prior austenite grain structure.
There have been only a limited number of investigations to show that nanostructured materials, especially at room temperature, have high strain-rate sensitivity.
Even though a number of different approaches have been tried out to achieve both high strength and ductility in a sample, no investigations have been reported to see if it is possible to combine the different approaches to increase the strength and ductility further and also to check if some of the effects have a synergistic effect.
These newly formed ultrafine ferrite grains are surrounded by clear grain boundaries as evidenced by clear etching and are indistinguishable from the original ferrite grains judged from the intensity of etching.
The effects of precipitation strengthening were investigated by adding carbon to increase the numbers of cementite particles.

The transition is strongly grain size dependent, with the time to the transition decreasing with grain size.
For sliding frictional contact, the time to the transition is dependent on a number of extrinsic variables (load and speed) and intrinsic material variables, principally grain size.
The grain size is reasonably fine, however, there is a significant distribution in grain size.
Firstly, there has been differential wear between grains.
This means that, for a given time of operation, there will be greater dislocation activity in larger grain materials, leading to greater rotation of the grains and greater stress concentrations on grain boundaries [1,2,6].

Abrasive Grain Models.
Thus, the value of the grain volume has an influence on the distribution and consequently on the number of grains in the grinding wheel surface [5], which follows from Eq. 1 [7].
The number of grains in a defined volume NV can be calculated from the abrasive concentration C, the density of the cutting material ρg and the volume of the abrasive grain Vg.
While using the same grain size, the shape of the abrasive grain has significant effects on the grain's volume and the number of grains in a defined volume.
The distribution model and the concentration characterize the number of active cutting edges.