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Fig. 3 also shows the variation of ρ as a function of the number of HPT revolutions.
Hydrogen absorption curves of the magnesium disks prepared by different number of HPT-turns.
As it is noticed form the plot, the maximum H-storage capacity increases with the number of the HPT-turns.
Horita, High-pressure torsion of palladium: Hydrogen-induced softening and plasticity in ultrafine grains and hydrogen-induced hardening and embrittlement in coarse grains, Mater.
Lendvai, Dislocations and grain size in ball-milled iron powder, Nanostr.

Large numbers of voids and cracks are present and relative density is a little lower.
Large numbers of voids and cracks are removed and relative density increases.
Fracture surface with the extruding temperature of 573K have large numbers of small dimples.
In addition, grain boundaries slide.
In the process of extruding, grain refining and grain growth simultaneously happen.

If there are other alloy elements or impurities, it maybe also form a ternary eutectic, its melting point lower than the number of binary eutectic, solidification temperature range should be even greater[10].
Semi-solid material of the microstructure of weld metal From Figure 2 and Figure3 we can see the changing of the aluminum alloy grains through the semi-solid processing and the grains are becoming smaller and more garden the whole grain.
Different grains have different bits to, known as anisotropy.
Thus, in a party up the grain raised on the most vulnerable.
Thus, relatively small grains.

The optical micrographs reveal the formation of fine grains.
Thus, a fabrication process is required with proper parameters to increase the interfacial bonding strength and to decrease the number of pores and thus mechanical properties will be improved.
Densification for ECAPed specimens increases with increase in milling time along with number of passes.
As, the number of passes increases for the20hr and 35hr milled powder, the hardness increases significantly.
Langdon, The principles of grain refinement in equal-channel angular pressing, Mater.

Precipitates cause a decrease in the effective grain boundary area and therefore in the associated surface energy, and this obstruction of the grain boundary motion or pinning effect of precipitates is much stronger than solute drag.
Normal grain growth would be completely inhibited when the grain size reached a maximum, given by the critical radius Rc = 4r/3f where r is the radius of the pinning particles and f their volume fraction.
According to the model of strain induced grain boundary migration [12], the recrystallisation driving force FR comes from the difference in dislocation density across the moving grain boundary separating two adjacent grains.
To carry out these calculations, the following data are needed: the stoechiometric ratio of the atomic weights of elements in the precipitated compound, the solubility product [23], Avogadro's number, the volume of unit cell of materials (compound and austenite), the number of atoms per unit cell and the atomic weights.
Mean particles size (d), standard deviation (σ) and number of particles per unit area of replica (Np).

And for stable Goss oriented grain, the orientation gradient increased slightly, but for meta-stable cube oriented grain, the orientation gradient increased dramatically.
And in spite of the same Taylor factor for both oriented grains, the dissipated averaged energy for cube oriented grain was higher than for Goss oriented grains, and the distribution width of dissipated work in cube oriented grain was also wider than that in Goss oriented grain.
With quaternion as orientation representing parameters [10, 12], the parameter mθ for describing intra-granular inhomogeneous deformation can be defined as following: ( )( ),i m i n θ θ =∑ q a (1) where ()iq is quaternion of the ith part in the grain, a is the quaternion of average orientation, n is total number of parts in the grain, ()( ),iθ q a is the misorientation between the ith part and average orientation. θm=0 means that the grain orientation is absolute uniform.
And even some parts of the grain rotated along two opposite directions, i.e., grain subdivision occur during plain strain compression.
The distribution width of PD in cube oriented grain is wider than that in Goss oriented grain.

A large amount of strengthening phases such as Mg3Zn6Y(I-Phase), Mg12ZnY(X-Phase) and MgZn2, which were massive, grainy and clavate, dispersedly precipitated from the matrix along grain boundary during ageing treatment at 225℃ after extrusion, and made the sliding of grain boundaries restrained, which resulted in an enhancement for mechanical properties to a great extent.
As can be seen, the average grain size of the as-cast is 50-60μm.
As can be seen from the graph, a large amount of strengthening phases which are block-like, grain-like and rod-like precipitate in the grain and along the boundary after being ageing treated.
While the grains grow obviously and the amount of precipitated strengthening phases decrease when the ageing time is as long as 28h.
Acknowledgements Thanks for “The General Program of Liaoning Province Committee of Education (program number: L2012035) and the 12th Five-Year” National Science and Technology Support Program (program number: 2011BAE22B01) for funding supporting the experiment.

The average size of grains is about 3μm and the grain shape is equiaxed.
A number of twinning was observed in γ as well as in α2 grains.
Taking account of the main feature of the room temperature deformation in TiAl alloy, namely, limited number of slip systems, such twinning facilitates stress relaxation, promotes the dislocation slip activity and improves the compatibility of deformation between grains.
During grain-boundary sliding, although the grains do not change shape, interstice between the grains can occur.
Meanwhile, a number of α2 grains break up into spots and are segregated or wrapped by γ colonies, as illustrated by Fig.8c and d.

The phase compositions of specimens were analyzed by X-ray diffusion and the tridymite crystal morphology and grain sizes were observed by SEM.
When adding 2.5% MoSi2, the precipitation of CaMoO4 phase reduces the O/Si ratio in the liquid phase, and promotes the generation of tridymite, so the number of tridymite increase, but the crystal size decreases.
When the O / Si ratio is about 2.16-2.23, the liquid will form a large number of silica tetrahedral anion complexes, their short-range order are similar to the crystal lattice structure of α-tridymite, so the tridymite crystallized from the liquid phase more easily[4].
It can be observed from the figures that each sample generated tridymite with different grain sizes and varying crystal growth degrees.
(2) The tridymite formation amount increases when adding a small amount of MoSi2, but the grain size decreases, and by adding the more MoSi2 adding, the finer tridymite grain growing.

In addition, as grain refinement, increased grain boundary carbides are evenly distributed in the grain boundary, thus greatly reducing the number of grain boundary carbides.
Austenite grain boundaries as in a number of nuclei formed, the austenite grain becomes a number of pearlite grain groups, reaching the purpose of grain refinement.
Austenite recrystallization, the nuclei in the cementite ferrite interface formation, the higher the dispersion of pearlite, the more austenite recrystallization nucleation, the more the number of pearlite grain groups, after the change, austenite grain increased, grain refinement[5].
Grain size have a great impact to the mechanical properties of the alloys, because the grain boundary disorder on the atomic arrangement, a number of impurity defects and grain boundaries on both sides of the bit to different, hindering dislocation from one grain to another the movement of grain, the finer the grain, the greater the grain boundary per unit volume, the greater the resistance to dislocation, the higher the strength of the material.
In this study, high-manganese steel of the blast-hardened have been carried out by micro-observation and X-ray diffraction analysis, It can be seen from figure 5, the two samples have shown a significant slip lines, and the samples with modified SiC nano-powders appear more slip-line the number of grains, even the emergence of a grain slip-line in different directions, and the hardened layer deeper.