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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.

It is noted that there exist elongated grain in both sintered samples.
In multi-step sintered sample, some elongated grain size is more than 10 µm, as shown in Fig. 4(a), but equi-axed grain is the main pattern in one step sintering specimens, shown in Fig. 4(b).
Which indicate that abnormality grain growth is easier to happen for multi-step sintering, the main reason perhaps is that holding at low temperature reduce the number of nucleation sites, lower the driving force for grain growth and slow the nucleation rate.
Therefore, multi-step sintering is necessary for dense Y-SiAlON grain development.
Contrast to one step sintering, multi-step sintering is favor to the Y-α-SiAlON grain development and densification and holding at low temperature can reduces the kinetics of crystal growth, which is helpful for elongated α-SiAlON development.

When the temperature further reduces to 100˚C, the β phase continues to extend inside grain, and the lamellar β phase is basically formed inside individual grain.
Cooling to 50˚C, the number of β phase increases dramatically, and the lamellar β phase evenly distributes inside most of the grain.
The main causes resulted from the fact that the crystal defect on the grain boundary was far more than inner grain, and the aluminum atom diffused easily.
So, the β phase would be easier to nucleate and grow on the grain boundary.
The β phase breadthwise nucleate and grow near the grain boundary, and then grows towards the neighbor grains with longitudinal direction.

Boron-doped diamond (BDD) films were grown with different grain sizes.
The constant interruption of the crystal evolution means there is a fundamental limit on the maximum grain size, and thus thick films can be grown with a small distribution of grain sizes [18,19].
The acceptor number can be calculated from the slope of the linear region of the Mott-Schottky plots (MSP) analysis [20,21] and the results of acceptor concentrations are presented in Table 1.
All films were grown with similar boron doping (30,000 ppm), thus, the grain size changed from micro to nanocrystalline further an increase in the number of diamond grains and consequently increases the doping.
This increased presence of boron in the grain boundary is not measured by MSP and thus decreasing the number of carriers for the films with 80 and 85% argon [20].

Grain size non-uniform, eutectic product along the grain boundaries or dendrite boundary discontinuous distribution with the crystal with black second phase particles precipitated by SEM and EDS spectrum scanning analysis shows ZK80 Mg alloy lamellar structures and granular middle mainly MgZn and MgZn2, as show in Fig. 3, the base body is relatively clean and coarse grains, about 70μm.
It can be seen from Fig.2 (b) that significant strip microstructure take place during extrusion process, and significantly elongated along the extrusion direction, at the same time, there are lots of needle shape twin organization and a small amount of secondary twin, part of the twinning occurred kink, coarse grains, the grain size of about 23μm；deformation at higher temperature, due to the low magnesium fault energy, sensitive to deformation temperature [7], the center of the extruded perform billets shows obvious dynamic re-crystallization(DRX) microstructure, and coarse dentrite is replaced by finer equiaxed grain with average size of 5.3 μm, part of the dynamic re-crystallization grain inclusions between serious deformation of grain.
According to Hall-Petch equation (), which is the yield stress, is of single crystal yield stress, K is a constant, d is grain size, strength of alloy increase with the decrease of the grain size, so the grain size larger influence on the strength of the magnesium and its alloys[8].
As can be seen from Fig.2(b) that there are lots of twins in extrusion ZK80 magnesium alloy, and extrusion preformed billets center for isometric obviously, the each grain internal possible slip band and twin belt and there are grain boundary and grain orientation to different between adjacent grain during die forging forming process，because of three to stress, the mechanical properties of ZK80 Mg alloy is improved obviously due to substructure change, twin microstructure disappear and obvious dynamic re-crystallization occurs, grain are refined greatly, the dislocation density increase under die-forging forming.
Grain-boundary sliding in AZ31 magnesium alloys at room temperature to 523 K[J].

According to the theory of reference[13], the surface free energy σhkl for different surface orientation could be represented by the following expression: (1) Where ZL is the lateral coordination number, ZV the bulk coordination number. λ is the mean atomic distance, l0 the sublimation energy and NA the avogadro number.
The grain size is smaller than the films grown at higher temperature and the surface of grains are accidented.
Figure 2(b) and (c) exhibit very densely-packed grains and bigger grain size.
The grain size is smaller than the films grown at higher temperature and the surface of grains are accidented.
Figure 2(b) and (c) exhibit very densely-packed grains and bigger grain size.

However, regardless of the number of compression cycles, the centre of the sample looks undeformed.
In case of the samples deformed up to 4 hits, this zone is composed of large grains, which grain boundaries are mostly distinguishable.
With an increase in number of MAC cycles to 8, many parallel deformation bands appears in this zone.
The distinction between grain interiors and grain boundaries at zone of large plastic strains is almost impossible.
This clearly indicates the grain refinement process.

We can see from surface of casting blank in picture 1 that, the grain is refined, zone of columnar crystal is reduced and equiaxed grain is enlarged.
From table 2 we can see that, when content of rare earth is 600ppm, the grain is refined obviously.
However, when content of rare earth exceeds a certain range, the grain is enlarged.
Table2 Comparison of the grain diameter Number of Sample Amount of rare earth added (PPm) Average Diameter of Grain (mm) Sample 1 0 0.165 Sample 2 70 0.078 Sample 3 84 0.062 Sample 4 112 0.071 Sample 5 140 0.090 Cu-Ag alloy casting blank without rare earth Cu-Ag alloy casting blank with rare earth Fig. 1: Macro-organization pictures of Cu-Ag alloy casting blank without rare earth and Cu-Ag alloy casting blank with rare earth 3.2.3 Effect of rare-earth addition on mechanical property and electrical conductivity of Cu-Ag alloy wire pole The reason why rare-earth element can enhance high-temperature plasticity of Cu alloy is mainly that, rare-earth element is a kind of active element which can react with low melting point impurity elements such as Pb, Bi, P and S in Cu alloy to produce high melting point compounds, which eliminates effect of harmful substances on grain boundary.
We can see from surface of casting blank in that the grain is refined, zone of columnar crystal is reduced and equiaxed grain is enlarged

Load Relaxation Behavior of Ultra-fine Grained Ti-6Al-4V Alloy Y.G.
In this study, superplastic deformation behavior of ultrafine-grained Ti-6Al-4V alloy was investigated on the basis of the inelastic deformation theory which consists of grain matrix deformation and grain boundary sliding.
To date, a number of grain refining processes are extensively reported to fabricate ultrafine-grained (UFG, below 1µm) materials, which lead to achieve superplasticity at low temperatures/high strain rates.
As shown in Fig. 4, the experimental data of CG samples (concave upward) were in good accordance with the lines drawn based on Eq. (3) with an exponent p value of 0.15, which is the same number found in earlier works on 7475 Al alloy and Ti-6Al-4V alloy.
The flow stress curves of UFG Ti-6Al-4V alloy changed their shapes at the intermediate strain rate region as compared to those of coarse grained microstructures, which was mainly attributed to the operation of grain boundary sliding with an aid of grain refinement via ECA pressings.

This is primarily due to the low grain size in the range between 5 and 100 nm and the resulting high number of grain boundaries.
In addition to residual stresses [5], also a high number of non-equilibrium vacancies are present [6].
The large number of grain boundary interfaces is a strong driving force for grain growth [7].
Θ 2Θ q grain sample ki kf Fig. 2: Schematic set-up of GIXRD.
The number of atomic planes, N, should be an integer.