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This happens because the driving force for grain growth is the decrease in energy caused by the reduction of the number of grain boundaries per unit volume.
The total surface area of boundaries is decreased as grain size is increased, causing a reduction in the surface energy, i.e., when grains grow, the number of their boundaries is decreased and their total surface area energy decreases.
This is due to the number of grain boundaries.
It is clear then that the number of grain boundaries was probably the main cause for the difference found between the machining strengths in these two groups of specimens.
Coppini Index values are sensitive enough to characterize distinct values of machining strength in solid solutions with different number of grain boundaries; d. machining strength test may be performed preliminarily to discover the minimum number of steps in order to get more accurate results.

In many respects, diffusion, determines physical and mechanical characteristics for new materials with fine-dispersed matter and a large number of grain boundaries and phases.
With reduction of grain sizes the volume of material, presenting a grain boundary layer, increases.
This fact can be connected with the grain size decrease.
Acknowledgment This work was supported by Russian Foundation for Basic Research, grant number 13-01-00444.
Sauvage, et al., Grain boundaries in ultrafine grained materials processed by serve plastic deformation and related phenomena Mat.

Introduction The importance of understanding three-dimensional (3D) grain growth for controlling materials properties is well-recognized, and a large number of experimental and theoretical studies have investigated fundamental microstructural mechanisms associated with thermal processing.
Since the incident beam irradiates a large number of grains with different orientations as it penetrates the sample, many Laue patterns are superimposed in a single raw image (e.g.
During the data analysis, distinctive reconstructed Laue images containing rows of a large number of sharp Bragg peaks were observed at a few isolated locations superimposed on the fcc Al patterns.
The initial hot-rolled microstructure consists of many grains ~5-10 µm in size, and a large number of low-angle boundaries are observed in this (001)-textured sample.
After annealing at 355ºC, many small grains have been consumed, and only a few of the original grains are unchanged.

The lamellar grain fragments within a given region are most commonly comprised of only a limited number of texture components, either arranged alternately (e.g.
Considerable grain growth was first required before the lamellar grains spheroidised.
A number of investigations have predicted an increase in the density of LAGBs during grain coarsening when a strong texture is present in the starting material [14-16].
Following cryogenic PSC the deformation structures were dominated by bands of a limited number of texture components (Fig. 4a).
Because of the limited number of texture components in the deformed state, during annealing, lamellar grains with a growth advantage will expand sideways and eventually encounter a grain of a similar orientation, forming a new LAGB by orientation impingent.

The influence of low-temperature annealing (400°C during 1 hour) on the substructure parameters and phase composition of the surface layer depending on a number of cycles of ion implantation with annealing was shown in the research.
Ion implantation is considered as a significantly studied process for a number of titanium alloys [5-9].
Ti3N is situated in the octahedral interstices of the lattice, where the number of atoms of the tetranitride is approximately equal to the number of the titanium ones [18].
The conditions are created for grain boundary sliding and rotation of grains as a result of the local increase of the dislocation density and their pinning on the segregations of mixtures of oxygen and nitrogen in the boundaries of ultra-fine grains at subsequent deformation.
This approach to the controlled management of the grain boundaries structure and properties of ultra-fine grained materials was named as “grain boundary engineering” by Professor Ruslan Valiev [23].

The elements of oxide film consist of α- Fe2O3 with sphere grain of 5-50nm.
This phenomena is demonstrated that the composite abrasive grains in oxide film is a compound structure which is centered by abrasive grains, with α-Fe2O3,Fe(OH)3 surrounded.
Second, research the micro structure of oxide film, element, shape, grains size, and covering parcels situation of oxide film which surround abrasive grains, and the forming mechanism of composite abrasive grains.
Therefore, a layer of circular ring which center on abrasive grains and surrounded by α-Fe2O3 formed around the abrasive grains in cutting, namely composite abrasive grains.
Acknowledgements The research project was supported by the general program of the National Natural Science Foundation of China (Approval number of project: 51475147) and the Science and Technology key Project of the Education Department of Henan (Item Number: 13A460341) References [1] B.

The paper presents experimental data demonstrating the super-strength and “positive” slope of the Hall-Petch relation when passing from micro- to nanostructured state in a number of metallic materials subjected to severe plastic deformation.
In recent years our laboratory in close collaboration with colleagues and partners performed a number of investigations of unusual mechanical performance of SPD-processed Al and Ti alloys as well as in several steels [10,16-20].
Although it is possible to achieve the nanocrystalline structure with grain sizes less than 100 nm in a number of metals and alloys by means of HPT [23, 24], for SPD processing by ECAP and HPT it is typical to form ultrafine-grained structures with mean grain sizes within the submicrometer range so that, typically, the grain sizes are ~ 100-300 nm [21,23,24].
Non-equilibrium grain boundaries with dislocation arrays are typical of different materials after SPD processing, and their role in the mechanical behavior of UFG materials has been studied in a number of reports [23,27,28].
Figure 7 shows the data for a number of Al alloys presented in the form of the Hall-Petch relation in which the yield stress (σ0.2) is plotted against the inverse square root of the grain size (d-1/2) for the UFG Al alloy 1100 produced by ARB-rolling and consequent heat treatment [37] as well as for an ECAP-processed alloy Al-3%Mg alloy [38].

Moreover, the number of passes significantly improves the particle distribution.
The mean grain size decreases from 9.5 μm to 1.95μm for a 4-pass MMC.
They could achieve ultrafine grain size.
According to the results, it reveals that there is an optimum number of passes for refining the grains and increasing the pass number does not always yield to finer grains.
Furthermore the finest grains could be achieved with 4 passes FSP.

It was found that grain refinement decreased the grain size and made the grain morphology more globular.
Both of these affect the grain size and grain morphology.
It has been observed that grain size is reduced by increasing the growth restriction factor, Q, the nucleant potency, which is the inverse of the nucleation undercooling ΔTn, the number of nucleant particles and the cooling rate [7].
This leads to the grain morphology changing from large dendritic equiaxed (or columnar) grains, to grains which are cellular with the grains showing obvious dendrite arms but not extensive dendrite networks.
As well as reducing the grain size, grain refinement makes the grain morphology more globular.

It was found that the grain size reduction of the material, which was processed using a die with an angle of 90°,wassignificantly more than that of a die with angle of 120°for the same numbers of ECAE.
It was also mentioned that the specimens processed with route A had an elongated and banded structure and those with route C had larger number of equiaxed grains.
As received after the 2nd pass after the 4th pass after the 5th pass Fig.6: The microstructures of the extruded specimens at a magnification of 200 Fig.7: Variation in the grain size versus the number of passes Table 1: The Grain size of the material for different passes Sample ASTM micro-grain size number (n ) The number of grains per square inch (N ) Average grain size (µm ) As received 6 32 45 The1st pass 8 128 22 The2nd pass 8.6 369 13 The3rd pass 11 1024 8 The5th pass 13 4096 4 The6th pass 14 8192 2.8 The Fracture Toughness The toughness is a measure of the amount of energy a material can absorb before fracturing.
The impact energy absorption varied cubically with the pass number.
The impact energy absorption varied with respect to the number of passes.