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However, magnesium alloys exhibit poor room temperature ductility and formability because of hexagonal close-packed (hcp) crystal structure with limited number of operative slip systems [3], in comparison to other materials currently widely used such as steel and Al alloys.
It is indicated that a significant grain refinement was achieved during the first stage of rolling and the average grain size measured is about 4µm.
On the other side, the AZ31 alloy exhibits a bimodal grain size distribution after the first processing stage (ARB1), and a moderate fraction of relatively coarse non-subdivided grains coexist together with the newly formed fine grains.
Mechanism of Grain Refinement TEM observation (shown in Fig.2) further revealed the mechanism of DRX induced grain refinement in AZ31 alloy.
These submicro grain boundaries probably formed initially and locally at the as-received coarse grain boundaries in the shape of zigzag, and gradually developed toward the interior, then finally covered the whole grain.

The equiaxed grains have been elongated, and a large number of grains crashed under huge shearing force, even these small grains created by grains’ crashing were also elongated.
With the increasing of number passes, the amount of fine grains is increased greatly.
These grains appeared to be separated by high-angle boundaries in some areas because the diffraction rings are more obvious and the numbers of the rings are increased.
Fig. 6 Average micro-hardness of alloy each surface of copper alloy on different passes With the increasing of number passes, the micro-hardness values increased and the trend is obvious (as shown in Fig.6).
With the increasing of number passes, micro-hardness values increased gradually.

The grains were aligned in the same direction.
It can be seen from Fig. 2(b) and Fig. 2(c) that, due to the effect of grain size, the increase of annealing temperature leads to grain growth, the ratio of surface grain to internal grain increases, the proportion of surface grain increases, and the growth of twins depends on the decrease of interfacial energy.
At the same time, in the thermal insulation stage of annealing, a small number of grains will swallow up the surrounding small grains and grow rapidly, resulting in secondary recrystallization and the phenomenon of uneven grains.
Influence of grain size on mechanical properties.
(b) (a) torn grain Surface torsional torn grain (d) (c) surface torsional Fig. 4.

Introduction Nanometals, defined as pure metals or alloys having grain size reduced to below 100 nm, have been recognized as prospective for a number of structural applications due to their superior mechanical properties comparing to their conventional microcrystalline counterparts.
As a consequence, they have been a subject of extensive research which resulted in the development of a number of fabrication routes.
It should be noted that a number of SPD techniques, which allow obtaining unconventionally large strain, have been developed and successfully employed for grain size refinement in various metallic systems.
It should be noted large numbers of precipitates are uniformly distributed in the matrix.
Nano-consolidation produces larger grains (~500 nm in diameter) but more than 90% of grain boundaries are of high angle type.

The results show that the number of dislocations in Si wafers reduced obviously after annealing and Al gettering for 2 hours at 600～1100°C.
The proportion of Σ3 grain boundary increases.
A number of dislocations and grain boundaries in the UMG-Si can be decreased after proper annealing.
Grain boundaries.
This is because the sub-grains and small crystal grains are phagocytosed by sub-grain merger or eaten mechanism to form large angle grain boundaries during annealing.

The fraction and average spacing of HAGBs as functions of number of ARB cycles are plotted in Fig 2.
Also, shear bands spanning across a large number of grains are observed.
Fig. 3 Fraction of prominent texture components versus number of ARB cycles.
Fig. 2 Fraction and average spacing of HAGBs versus number of ARB cycles.
With the increasing number of ARB cycles, S component increases and reaches saturation after the sixth cycle.

The latter was counted as the fraction of grains with grain orientation spread below 1°.
The microstructure after annealing at 500 °C is characterized by fully recrystallized structure with a number of annealing twins.
Figure 2 shows the inverse pole figure (IPF), the grain orientation spread (Grain Orient.
Inverse pole figure (IPF) for the rolling direction with grain boundary misorientation distribution (q), grain orientation spread (Grain Orient.
Inverse pole figure (IPF) for the rolling direction with grain boundary misorientation distribution (q), grain orientation spread maps (Grain Orient.

Touge ground the ceramic with the superfine grain diamond cup wheel, and found the grain and grind depth affect on removal model [10].
The grains size decreased, the amount of grains in unit volume increased.
Grains micro-morphology show as fig 5.
The hm related to each grain force.
The every grain force composed the grinding force.

The oxygen tracer diffused quickly from the surface up to the grain boundary and then appeared as discontinuous steps at the grain boundary.
They found that non-doped BaTiO3 contained a higher number of oxygen vacancies than the La-doped BaTiO3.
Neither grain boundaries nor grain segregation were observed in any of the images.
One of the possible reasons for the blocking behavior could be the lower number of effective oxygen vacancies around the grain boundaries, compared to those in the grains themselves.
That is, the effective number of oxygen defects is reduced because of the formation of such complex defects.

Introduction Nano-metals, defined as pure metals or alloys having grain size reduced to below 100 nm, have been a subject of extensive research which resulted in the development of a number of fabrication routes.
As a result, a number of SPD techniques, which allow obtaining unconventionally large strain, have been developed and successfully employed for grain size refinement in various metallic systems.
This was already proved for a number of metals and alloys and is illustrated in Fig. 1 for those processed by HE.
It should, however, be noted that the improvement in tensile strength was much more significant (580 MPa and 310 MPa for nano- and microcrystalline samples, respectively). 260 280 300 320 340 360 380 400 420 1.0E+04 1.0E+05 1.0E+06 1.0E+07 Number of cycles to failure Stress [MPa] nano- micro 0.00E+00 1.00E-08 2.00E-08 3.00E-08 4.00E-08 5.00E-08 6.00E-08 7.00E-08 8.00E-08 9.00E-08 1.00E-07 1 2 3 resistivity [ΩΩΩΩm] Fig. 3 Wöhler curves for micro- and nanocrystalline 2017 aluminium alloy Fig. 4 Resistivity of CuCrZr alloy: 1 - coarse grained, precipitation hardened, 2 - dislocation boundaries, 3 - fine grained Corrosion Resistance An important consequence of the reduced grain size is a significant increase in the surface area of the grain boundaries per unit volume of the alloy.
As the nano-grain structure is formed, the resistivity becomes only slightly higher than in coarse grain materials.