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Introduction Nano-metallic materials [1] appeared in the mid-1980s, which are structurally characterized by nanometer-sized grains with a large number of grain boundaries, occupying over 50 percent of volume fraction.
As the grain size decreases, the volume fraction of grain boundaries is more and more, and whether grain boundaries activities dominate plastic deformation is not sure.
Whether there is an accessible relation between grain size and the wear resistance.
In fact, grain refinement could enhance the friction and wear resistance of materials.
Variation of the friction coefficient with the number of cycle for the SMAT Cu and the CG Cu samples against a WC-Co ball in mineral oil under the given test parameters: normal load of 50 N, frequency of 20 Hz, slip amplitude of 50 lm, and fretting cycle of 72,000 [26].

With the transformation of co-doped inhibitors’ content, the grain growth is inhibited and the grain size achieves 490 nm at 0.4% Cr3C2 / 0.3% NbC.
With its exceptional hardness, wear resistance and high mechanical strength, it is becoming very desirable for a number of applications.
Until now, the most successful way of controlling the WC grain growth is the addition of small amounts of WC grain growth inhibitors.
(a) (b) Fig. 1 SEM graphs of cemented carbides: (a) 0.4%Cr3C2+0.3%NbC; (b) without inhibitor As shown in Fig. 1, larger numbers of dark zones which may represent pores can be observed in (a) than (b), and the phenomenon will be studied in the next work.
Secondly, the presence of inhibitor NbC / Cr3C2 at the WC–Co interface prevents the transfer of the phase and stops the WC grains connected and growing, which results in the increased amount of the single WC grain, ensuring the inhibition of both normal grain growth and abnormal grain growth of the WC grains [14-19].

The grains in the heat-affected zone were relatively coarse.
It is seen that the microstructures of AZ31B magnesium alloy were mainly fine dynamic recrystallization grains, and there were small amount of coarse grains and elongated grains (Fig. 1 (a)).
Therefore, the crystal grains in the HAZ were relatively coarse (Fig. 1 (b)).
It is seen that there were a large number of dimples on the fracture surface of base metal, and the fracture mode belongs to the ductile fracture (Fig. 3 (a)).
The grains in the heat-affected zone were coarser, and the grains in the thermo-mechanical affected zone were relatively small and deformed.

Both HPT and ECAP are capable of imparting Von Mises strains up to two figures, depending on the number of turns, passes, or die geometry.
In this respect, Figure 15 of that paper [6] summarizes a large number of investigations correlating flow stress with grain size, over the range of d = 5 - 1000 nm.
However, this mechanism has also been considered as probable in a number of cases in which grain size was in the S-mc/coarse range.
However, the number of recent investigations in S-mc materials pointing out to grain boundary sliding as an operative mechanism appears to be growing; for instance internal friction Figure 3.
The authors show that grain size reduction led to a decrease in grain boundary diffusion activation energy, thus shifting the onset of grain boundary sliding to lower temperatures.

Exceptions are constituted by rather rare cases, when registered profiles of the X-ray line (hkl) are obtained as reflections from families of crystallographic planes {hkl} belonging to the same grain or to the group of grains with the same orientation.
Thus, the total number of points in obtained diagrams is equal to that in each GPF or in some of its region of interest.
The same number of points is contained in the correlation diagrams.
Grains with the too "spoiled" crystal lattice lose the ability to deform by means of crystallographic mechanisms, so that their final orientations prove to be occasional; texture minima contain only such grains.
Since the rolling texture of Ti-Ni single crystal is very sharp [8], its GPF contains a relatively small number of experimental points, but the indicated tendency is seen distinctly.

Recently, there has been significant attention on the fabrication of ultra fine-grained steel consisting of the finer ferrite grain size [2].
Finer ferrite grains can form due to the more nucleation site being available.
As a result, the ferrite grain is quite finer for the specimen 2.
This was attributed to the refinement of the ferrite grain size.
When cold heading steel is deformed, dislocations are produced in numbers proportionate to the degree of deformation.

The main result obtained by the application of such technique is that the hyperbolic flow of grains is the nature way during deformation, as well; this hyperbolic motion is assisted by dislocations dynamics and self accommodation of grains.
The grain size of 42.10 µm was measurement by using the mean linear intercept technique [8].
Here twelve grains were selected and identified with a number in order to follow their trajectory during deformation process.
As it is shown in the Figure 2, in all pictures in the Figure 1, twelve grains were selected and identified with a number in order to follow their trajectory during deformation process.
Also, it is obvious that the displacement of each grain is a function of their position.

Both the grain and grain boundary conductivities have been determined as a function of temperature in the range of 773-973 K.
The ohmic resistance value has been considered as a complex number which contains series of various electrical elements.
The grain and grain boundary separation can be slightly identified at lower temperature (673-773 K).
Influence of Grain and Grain Boundary on Electrical conductivity Though the sample has a larger grain size (~1-2µm), the ionic diffusion through grain boundaries (GDC-GDC and Ni-GDC, NiO-NiO) is more sluggish than grain interior.
Therefore NiO-GDC grain contacts are to be expected in Ni (50:50) composition at lower temperature (673-873K) whereas number of homo contacts can be higher than hetero contacts at higher temperature (823-973K) range in which grain resistance (RGi) may be predominant over boundary resistance (Fig. 9).

The number of AE events per minute is indicated as a bar chart on each graph (right-handed axes).
The number of AE events per unit of time for both rock samples tended to be higher under conditions of lower stress.
The amplitude and occurrence number of the AE signals might be a function of the amount of grain-boundary shear (mineral slip) between grains and/or the degree of resistance to deformation.
Acknowledgements This work was supported by JSPS KAKENHI [Grant-in-Aid for Young Scientists (B)] Grant numbers 22760651 and 24760691.
Oliver, Investigation of deformation twinning in a fine-grained and coarse-grained ZM20 Mg alloy: Combined in situ neutron diffraction and acoustic emission, Acta Mater. 58 (2010) 1503-1517

The addition of carbide-forming elements (such as Cr) leads to an increase in the number of grains containing shear bands after warm rolling, a change that can improve the formability of the steel after annealing [3-6].
Bulk texture Deformed grains Recrystallized grains Figure 3.
The common feature for both steels is that the grains nucleated at ferrite grain boundaries were larger than those nucleated within the grains (predominantly at the in-grain shear bands).
For both steels, the grain sizes of recrystallized γ-fiber grains were slightly larger than of α-fiber grains.
Calculations are based on the numbers of nuclei observed.