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Furthermore, when the strain reaches a value of 4, a significant number of ultrafine grains have formed with the fraction of the HAGBs increasing continuously with strain.
A larger number of ultrafine grains were noticed in the region of higher strain, indicating that these grains are formed by a process of fragmentation/subdivision of initial grains.
It may be noted from Fig. 3(a) that even at a strain of 0.5, ultrafine grains, though few in number, have formed at the original grain boundaries and their volume fraction increases with increasing strain.
(I). purely elongated grains; (II). elongated grains with newly generated grains; and (III). newly generated grains.
Considering the large number of defects in ultrafine grained materials, it is appropriate to consider the grain boundary diffusion as the controlling mechanism of ferrite grain size, we obtain the relationship: ( ) 2/1 tDTH gb=α (3) The constant strain rate (ε& ) deformation at high temperatures can be divided into an amount of instantaneous plastic deformation (ε) and static annealing for a given period ( tt / ; εε=& ).

Impedance spectroscopy characterization indicated that the conductivity decreases as Cr concentration increases, probably due to Cr segregation at grain boundaries, which reduces grain size, increasing the number of resistive boundaries.
Table 2 presents the relative density and mean grain size of systems after sintering.
Increase in Cr concentration also leads to reduction of SnO2 mean grain size.
This decrease in mean grain size could be associated to segregation in the grain boundaries.
The Cr segregates at the grain boundary and appears to control sintering and grain growth rates.

Specimens with different grain dimensions, grain shapes, α/β phase ratios, densities were obtained by changing the heating rate and dwell time of SPS.
Both equiaxed and columnar β- Si3N4 grains are formed during sintering, but the thermal conductivity of Si3N4 ceramics is affected only by columnar grains.
Table 1 shows the statistic of equiaxed grains and columnar grains formed with different sintering conditions.
Considering the effects of the average diameter (Φ) and the number per area (N) of the columnar grains together, Fig. 5 shows the relationship of Φ×N and thermal conductivity of SPS sample.
Fig. 5 Relationship of Φ×N and thermal conductivity of SPS sample Table 1 Statistic of equiaxed grains and columnar grains formed with different sintering conditions Heating rate [K�s-1] Dwell time [min] Φe [µm] Φc [µm] Nc [µm-2] 2.5 2 0.46 0.16 0.06 2.5 5 0.49 0.21 0.17 5 2 0.41 0.20 0.21 5 5 0.45 0.44 0.24 Φe: Average diameter of the equiaxed grains; Φc: Average diameter of the columnar grains; Nc: Number of the columnar grains per area.

, (4) where, and are constants, (μm) the grain size of DRX, (μm) the average grain size, and (μm) is the initial grain size.
Additionally, lower dislocation density and distortion energy with smaller deformation and lower temperature leads to a lower number of nucleation on the blade rabbet (Point 1) and damper platform (Point 4).
The finer grain lies in the point 7 and the grain sizes are about 2.5(μm) after finish forging.
It can be seen that the grain in the blade is finer and uniform and the grain degree is up to 11.
The grain size number of DRX in the middle of blade body is 9~10 and the grain size number in the leading and back edge of blade body is 12~13.

A considerable number of dislocations exist in the grains and grain boundaries, which may accommodate a high density of strain energy.
The grain size distribution inserted was measured from a number of bright field and dark field TEM images by number-averaging the diameters of 200 grains.
The grain size ranges from 15 nm to 300 nm, and the average grain size is about 100 nm.
The SMAT sample shows smaller value as compared with coarse-grained one.
Figure 4 is the worn surface morphologies of SMAT Ti and coarse-grained counterpart.

Among the procedures devised for grain refinement, severe plastic deformation (SPD) has been proven capable of producing ultrafine grained (UFG) materials with sub micron grain size.
Increasing the number of ECAP passes an increase in hardness across the normal direction was observed.
The sample deformed by one ECAP pass at room temperature presented a large number of deformation twinning (Fig. 3a).
After HPT (Fig. 5d) the microstructure is characterized by both elongated and equiaxed grains which are separated by sharp grain boundaries as shown in the micrograph, and the diffraction pattern indicate a great misorientation between individual grains.
At 480 oC only a small number of crystals exhibit deformation twins; grains are equiaxed and with a amean diameter of 75 nm (Fig. 5e).

In this work, we grew Al1−xScxN thin films with different Sc concentrations by changing the number of Sc tips which were set on the Al target.
Fig. 2 shows the relationship between x and the grain size of Al1−xScxN films.
And with the Sc concentration increases, the grain size of Al1−xScxN films decreases.
It is reasonable to consider that Sc may cause the Sc–N phases forming and enwrapping the AlN grains, which restrict the growth of AlN grains.
In our cases, when AlN films are doped with Sc, the grain size and Eg decrease.

In this study, the effects of HIP treatment, WC grain size and content of βt phase on bending fatigue characteristics were investigated for fine and coarse-grained WC-6.7mass%βt-10.4mass%Co alloys （6.7βt(F) and 6.7βt(C) alloys） and fine-grained WC-20mass%βt-11.3mass%Co alloy (20βt(F) alloy) by comparing with the case of fine-grained WC-10mass%Co alloy（10Co(F) alloy） without βt phase.
In fatigue test, the stress in the range from 0 to maximum stress and with 10Hz frequency was applied up to fatigue failure and then S-N curves showing the relation between applied stress and number of cycles up to failure were obtained.
The fatigue strength of HIP-ed 6.7βt(F) alloy at a definite number of cycle was remarkably low in high stress range and nearly equal in low stress range, compared with that of HIP-ed 10Co(F) alloy.
(a), agglomerate of βt grains; (b), Co pool with a step-shaped form.
Conclusion The effects of HIP treatment, WC grain size and content of βt phase on bending fatigue characteristics were investigated for fine and coarse-grained WC-6.7mass%βt-10.4mass%Co alloys （6.7βt(F) and 6.7βt(C) alloys） and fine-grained WC-20mass%βt-11.3mass%Co alloy (20βt(F) alloy) by comparing with the case of fine-grained WC-10mass%Co alloy（10Co(F) alloy） without βt phase.

Introduction Nanostructured (ns) and ultra fine-grained materials exhibit higher strength and hardness, as well as excellent tribological properties compared to their coarse grained counterparts [1, 2].
Mishra et al. [6] compared the fretting behaviour of ns Ni (grain size of 8 nm) prepared by means of electrodeposition with that of bulk coarse grained polycrystalline Ni (grain size of 61 μm).
A gradient in microstructure i.e. finer grains in the surface and near surface regions and coarse grains in the bulk may be seen.
Figure 6 shows the variation of TFC with the number of fretting cycles for untreated and treated samples at 4.9 N normal load.
They reported that at a particular grain size (32 nm) the wear resistance was maximum and grain sizes above and below this size resulted in poor wear resistance.

In polycrystalline materials the development of local displacements along the grain boundaries happens in order to accommodate the plastic deformation in adjacent regions and to retain the grain-to-grain compatibility.
The higher solute diffusivity in the grain boundary regions leads to higher precipitate rates compared to the interior of the grains.
At this cooling rate the grain boundary precipitation is already present and small grain boundary particles (0.1 ÷ 1 µm) were formed along the grain boundaries.
When observing the outer surface of the hem in the sample quenched at 60°C/s, significant number of deformation steps representing the high amount of strain accumulated in the interior of the grains was found.
It was found to happen much faster than in the interior of the grains, which allows the formation of coarse (1 ÷ 5 µm) grain boundary particles in a very short time before any significant precipitation in the bulk of the grains can occur.