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Homogeneous and ultra-fine grain (UFG) structure enables the materials high strength.
In a harmonic structure, the coarse-grained (CG) areas (“Core”) are surrounded by a three-dimensional continuously connected network (“Shell”) of ultra-fine-grained (UFG) matrix.
Each milling pass was completed in 10-15 minutes and the milling time was decreased with an increasing number of passes.
Figures indicate grain size distribution images by EBSD.
As can be seen in (b), the shell is composed of randomly oriented fine grains.

Rotation of grains leads to emergence of high local internal stresses.
Rotation of grains leads to emergence of high local internal stresses (fig.3).
So, high chemical activity of gallium turns this technological task into a sufficiently complicated process which depends on the number of both positive and negative factors.
Mass transfer of gallium into Al alloy between grain (SEM).
The diffusion results in an intense growth of grains sizes and volume of the detail, in shifting of old grain boundaries and formation of new ones.

Due to the smallness of the grain size, these NS metallic materials are usually several times stronger than their coarse-grained (CG) counterparts [1-3].
Based on measuring more than 300 grains, the calculated average grain size from the relative number frequency is approximately 22 nm.
Sample Grain size [nm] RTTLN σσ /2 Ref.
On the other hand, due to the strength rise with decreasing the grain size - Hall-Petch relation, the absolute strength rise is much more remarkable at smaller grain size.
As the grain size is reduced to the nano scale, the grain boundary (GB) related activities, such as grain boundary sliding and grain rotation, start to contribute to the plastic deformation significantly [11].

Determination of the parent grain orientation.
When a sufficient number of variants are considered, there is a unique common potential parent orientation which is the searched parent orientation gp [1].
As a result, gp is obtained when the three following conditions are simultaneously met: 1- the variants are inherited from the same parent grain; 2- the number of variants is sufficient; 3- the OR (Δg0) is known.
Insufficient number of variants.
When the number of variants gathered is not sufficient (condition 2), the variants are equally related to several potential parent orientations.

Also, the effect of holding time on the cavity damage was examined with the number of cavities.
Both number and size increased with increased holding time.
Relationship between cavity number and size with various holding times.
As is shown in Fig. 8, cavities were observed along the prior austenite grain boundaries, and the intergranular damage is believed to be caused by these cavities.
Cavity of crack growth path and cavity at grain boundary with various holding times.

The decomposition of tempered martensite lath was retarded after adding a number of alloying elements such as Cr, Co, W, Mo, V, according to observations by transmission electron microscopy.
It also shows that the fine dispersion secondary carbide precipitates along the martensite grain surface and grain boundary.
The decomposition of tempered martensite lath was retarded after adding a number of alloying elements such as Cr, Co, W, Mo and V, and it would result in better tempering resistance.
A number of alloying elements being added to steel makes the decomposition of tempered martensite lath retarded, which will cause the better tempering resistance.
The decomposition of tempered martensite lath was retarded after adding a number of alloying elements.

The ratio of the traversing rate to the rotation rate, i.e., tool advance per revolution (Table 1; the designators are only serial numbers), is essentially the same for these two samples; accordingly the SZ microstructures are similar and have been discussed in previous reports [19, 20].
Convergent-beam electron diffraction (CBED) patterns were taken from each α phase grain in a region of contiguous grains and the patterns were then analyzed to determine unambiguous lattice orientations of the grains.
The grain-to-grain lattice disorientation accuracy was then ~0.4º.
The boundaries in this image are shown in the tracing of the boundaries in Fig. 3(b) in which the line width corresponds to the grain-to-grain disorientation angles from TOCA analysis.
At this temperature 1 - 10 µm κiv particles will persist in α grains.

However, overlapping of grains in the thin foil prevents direct examination of the boundaries between the grains.
During these investigations we have encountered a number of issues with the examination of nanocrystalline materials using APT.
Quantification of the local composition around the grain boundaries can be achieved a number of ways.
This approach can provide a greater number of counts for analysis compared to specifying selected volumes, increasing the confidence in the results.
Dotted lines show the grain boundaries.

Some �-Si3N4 grains are converted into columnar £ -Si3N4 grains with a high aspect ratio, and improve the fracture toughness of the new silicon nitride ceramic tool.
The additives were yttria (Y2O3) and lanthana (La2O3) with a grain size of 1.0-1.5 µm.
Then the �-Si3N4 grains grew into columnar grains in one crystalline direction at the high fabrication temperature.
The tool-life by fracture was measured with the impact number on the tool tip before tool fracture.
Three inserts for each tool material were used and the average impact number was then taken and plotted in Fig.3.

Through the mechanical analysis about the sand grain in the downstream of the pipe, the critical condition about of scour start is derived.
Through the mechanical analysis about the sand grain in the scour hole, the maximal scour hole depth is got.
And they point out that the KC number is the major parameter to control the scour hole depth in regular wave.
The sediment grain can be assumed as sphere, so ,d is the medial grain diameter.
So the seepage force can be written as: (4) The submerged weight of the sediment grain, W is (5) Where, s is the specific gravity of sand grains (), is the specific weight of sand grains, is the specific weight of water[19].