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It is due to the grain refinement.
These grain refinement techniques of using of inoculate elements, such as Ti, Zr, and Cr, were reported by the number of researcher, and were applied on high pure or commercial pure aluminium [2-5].
The microstructure on longitudinal section of the alloy tube shows an equiaxed grain structure, but their grain size was different with Ti content.
This significant grain refinement is due to role of Ti as a grain growth inhibitor.
(b) Variation of grain size distribution with Ti content.

Grain size and morphology results show that the compounds have clear grain morphology and also nanoscale grain sizes.
The uniformly grain growth and rounded shape grains with very clear surface morphology were observed.
It is obvious that MR values of nano-structured samples (NCMO & NBMO) will be higher compare to the bulk samples due to enhanced spin-polarized tunneling through the increased number of grain boundaries in nano-structured materials.
The grain size, structural symmetry and surface morphology can be governed by the calcination temperature.
The TEM and AFM results confirm that the nanoparticles of the NCMO & NBMO samples and grains are arranged in chains.

The mean grain size of each state is 33.65um, 24.53um, 32.04um and 32.98um.
Yield strengthvaries with the grain size.
The smaller the grains are, the greater the total grain boundary is, and the more difficult is for the dislocations to traverse, resulting in the stacking of the dislocations.
Therefore, the fine-grained material with 1h cryogenic treatment has the highest strength.
Acknowledgements This work was supported by the key scientific and technological project of Chongqing (Project Number: CSTC, 2009AB4005).

The preferred ratio is defined as the number of cells in the preferred direction to the number of cells in the other (in two dimensions the preferred ratio is 2).
For each cell, a randomly allocated orientation number, q, was assigned to each grain.
The orientation number indicates primarily the orientation of a cell and maximum number of q was 936, which represents 936 texture components, which were equally distributed in orientation space.
The misorientation is obtained from the q numbers of the neighbouring grain where ∆q is the difference between orientation numbers of two adjacent grains and 10 < ∆ ≤ q q (12) In the present study, an adjustment of the nucleation criterion used in Raabe's study [28] was adopted.
The recrystallised grain grows continually until it impacts on the other growing grains.

It was found that the impact frequency represented by the number of balls from vials is an important parameter a milling process.
Average grain sizes evolutions with milling time in al type of milling condition are shown in fig. 6.
In the last stage of milling (between 8 and 16 h) the grain sizes is reduced from 35 nm to 22 nm.
It can be explained by number of balls which give the number of impacts and their velocity (higher in I than II and about the same in III and IV type of milling conditions).
This can be explained by higher number of ball – ball and ball – inner wall of vials impacts in case to use type I and III milling conditions (higher number of balls with 11 mm diameter).

Oxides materials with perovskite structure are well stabilized by its high dielectric constant (κ) that leads these classes of materials for a large number of technological applications.
On the other hand, the uS samples presents smaller and square grains, without a visible grain boundary phase formation as presented in the cS ceramics.
Figure 4 shows the EDS microanalyses of the a) grain and the b) grain boundary phase of the 1150/24h cS sample.
EDS analyses of a) grain and b) grain boundary of the sample presented in the Fig.3c.
The grain size of the cS samples was higher than those for uS samples, it can be due to the copper-rich phase formation in the grain boundary, which contributes to the grain growth.

In our previous studies, we proved that during abrasive machining the metal microvolume affected by abrasive grains accumulates energy.
A number of studies [3, 4, 5, 6, 7, 8, 9, 10, 11, 12] are devoted to the issues of metal machinability by abrasive tools.
Dyakonov has undertaken a number of studies that established a correlation between material machinability and the types of abrasive machining, processing restraints, and process system parameters.
We [26] proposed a method simulating the behavior of multiple abrasive grains in a grinding wheel.
It was experimentally proved that the number of measurements of the specific energy of metal dispersion by abrasive grains with various compositions and grain sizes does not exceed 10.

At the same time, the addition of Gr is beneficial to grain refinement and achieve "fine grain strengthening" [12].
Moreover, the addition of Gr also effectively hinders the grain growth, increases the grain boundary area, and increases its scattering effect on electrons as well, which result in a decrease in electrical conductivity.
Conclusions (1) There are a certain number of pores in the Gr/Cu composites prepared by powder metallurgy, and the number of pores increases with the increase of Gr content
There are a large number of dislocations and twins in Cu matrix
Mahmudi, Grain boundary strengthening in a fine grained aluminium alloy, Scripta Metallurgica Et Materialia. 5 (1995) 781–786

The results showed that composite coatings had a compacter and refiner surface than ordinary Pb-Sn alloy coatings; the addition of CNTs increased the number of crystal cores and changed the directions of crystal orientation, which resulted in a fine network structure.
The surface of the composite coatings had refine grains because of CNTs inclusion.
Crystal orientation even more cluttered for the increased number of CNTs, it is difficult for Pb-Sn alloy grains to grow up to the larger size, therefore, and it led to grain refinement.
(1) Homogeneously dispersed CNTs in the bath was the basis for access to high quality composite coatings, they increased the number of nucleation in the electro-deposition process, therefore, the composite coatings had more dense surfaces than ordinary Pb-Sn alloy coatings
(2) CNTs changed the direction of grain growth; it is difficult for grains to grow up to larger size, which led to grain refinement of composite coatings.

Elongation rate also fell over the first peak may be due to: non-uniform deformation within the grain and the grain boundary strength increases due to reduced.
This is why grain boundaries off consecutive sub-band structure of the phenomenon.
In addition a large number at the bottom of thick GP conditions for the¢ hzone formation at high-energy distortion field for formation of increased energy.
（a）24h, intragranular （b）24h, Grain Boundary （c）52h, intragranular （d）52h, Grain Boundary （e）76h, intragranular （f）76h, Grain Boundary （g）90h, intragranular （h）90h, Grain Boundary Fig.3 TEM images of 7050 aluminum alloy under various age states 4.
Lead to a large number of grain boundary phase of ¢ h thicken and gradually began to gather over a non-coherent system of h lower energy relative to the direction towards the development of grain boundary off consecutive sub-band structure of the phenomenon