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Numerous reports are now available describing the application of HPT to a range of pure metals and simple alloys and excellent grain refinement were achieved using this process with the average grain size often reduced to the nanoscale range.
Inspections of Fig. 1 show several trends describing the hardness evolution through increasing numbers of HPT revolutions.
The higher values of Hv in the central region tend to decrease with increasing numbers of turns.
Close inspection shows these central regions of higher hardness extend through decreasing areas with increasing number of turns.
Third, there is a decrease in the hardness values over the disks when processing is continued to larger numbers of turns.

When sintered at 1450 oC~1500 oC, puncheon-like mullite grains were obtained and a higher temperature corres- ponded to mullite grains with larger size (Fig. 2b, c).
In Fig. 2c, both puncheon-like and sphere-like mullite grains could be observed.
Previous study [12,15] indicates that in spite of platy kaolinite [16], alumina grains can also act as the nuclei for the formation of mullite grains, which may explain the difference in morphology of mullite grains.
We also thank National Key Projects in the National Science & Technology Pillar Program under grant number 2011BAB03B08.
Messing, Development of textured mullite by templated grain growth, J.

With developing of nanocrystalline materials, there was a hope that superplasticity could be obtained in a number of pure metals.
Recently, it was concluded that superplastic behavior in pure nickel is not related to the presence of sulfur at grain boundaries or a liquid phase at grain boundaries.
Superplasticity is known as strong grain size dependent phenomenon.
The RQ nickel possesses an equiaxed grain structure with a mean grain size of 1-2 µm showing well defined grain boundaries.
Pshenichnyuk Superplasticity and grain boundaries in ultrafine-grained materials.

Results indicate that the abrasives with larger grain size and higher hardness can result in a higher material removal rate while the abrasives with smaller grain size and lower hardness can achieve a lower surface roughness value.
Generally, the cutting surface of SiC wafer machined by the diamond wire cutting machine is uneven and has a large number of the saw marks.
Effects of Abrasive Grain Size Fig. 4 Variation of Ra and MRR with Fig. 5 Surface morphology topography grain sizes of the wafers lapped by diamond abrasive (a) W14; (b) W7; (c) W3.5; (d) W1.5 The experimental results by using the different grain size of diamond abrasive are presented in Fig.4.
In the case of the same weight of abrasives and lapping pressure, the number of abrasives will decrease while the grain size increases.
Whereas, the number of active particles participating in lapping will increase while the grain size decrease.

This large number of papers is a convincing demonstration of the relevance of bulk ultrafine grained and nanostructured materials, produced by severe plastic deformation, to a wide range of researchers and engineers.
In fact, this community is growing, and the total number of articles in this edition is larger than that in the 2006 edition.
Significant progress has been made in this field; including all aspects of NanoSPD, such as an increased understanding of the mechanisms underlying grain refinement by severe plastic deformation, characterisation of the properties of SPD-processed materials, improvements in processing techniques, and their application.

A better contact condition stands for a stronger heat extraction from the melt, and will finally appear as a remarkable increase of primary α(Al) grains survived in the melt, which will conspicuously promote the spherical growth of the primary α(Al) grains. 1.
The shape factor of primary α(Al) grains was calculated as: F=4πA/P2 where A and P represent respectively the average area and perimeter of a grain.
The results prove that a low superheat can promote the transformation of primary α(Al) grain from a dendrite or a rosette to a spherical one.
But when the channel length increases to 400mm and 600mm, most of the primary α(Al) became to spherical and near-spherical ones with a slight number of rosette, as shown in Fig.2(c) and (g).
The scour effect can also reduce the temperature fluctuation and concentration gradient in the melt, finally appears a higher grain refinement.

For these alloys a grains with orientation of {111} and {100} grow much faster than grains {113} and particularly {110}.
For the ω-geometry, we have d=[(V p Phkl dβ ∆ω)/ 4πn] 1/3 (1) where V is the irradiated volume, p is the multiplicity factor, n is the number of crystallites with different orientations, Phkl is the pole density of the (hkl) reflection in the inverse pole figures, ∆ω is the measured angle range in the rocking curve, and dβ is the vertical divergence of the Xray beam.
Then the grain size value for this grain can be obtained from Eq. 1: di =[(V p Phkl dβ ∆ω)/ 4π] 1/3 (Si/ΣSi)1/3 (2) This approach [1] allows the determination of the fraction of recrystallized grains (fr) and of the grain size distribution for any grain orientation.
The grains with orientation of {111} and {100} grow much faster than grains {113} and particularly {110}.
At the same time the grain size of "textured" grains is much lower - (220) and (311) reflections on Fig.2b.

Introduction Some polycrystalline materials show very high tensile elongation prior to failure when a number of microstructural requirements are fulfilled [1].
As-quenched Zn-0.3Al alloy is composed of coarse-grained η-phases having a grain size ranging from 100 μm to 250 μm (Fig. 1(c)).
Furthermore, α-phase grains with ~110 nm are mainly located at the boundaries of η-phase grains having ~540 nm grain size [5].
ECAP leads to a significant grain refinement in the η-phase grains of Zn-0.3Al alloy.
The mean grain size of the η-phase grains is about 2 μm.

Micrographs were analyzed using standard image analysis software (KS 400, Kontron Electronics GmbH, Germany) to determine mean grain sizes and grain size distributions.
In consequence different microstructures were developed in each case: in particular the mean grain sizes, and grain size distributions differed.
The fracture toughness of the pure alumina (A3, 3.4 MPa.m1/2) corresponds at the mean grain size of 3.7 µm to MgSiO3-sintered alumina with 10 wt. % of silicate, and a similar mean grain size.
Further analysis revealed that the grain size distributions of all examined materials could be also described by a lognormal distribution function and the mean grain sizes and the grain size distribution widths were estimated by non-linear regression.
Acnowledgement The financial support of this work by the NATO Science for Peace Pprogramme, Project Number SfP-974122, and by the Slovak National Grant Agency VEGA, under the contract number 2/3101/23, is gratefully acknowledged.

Two populations of grains were studied, one textured (large grains or templates) with volume fraction f and texture factor r and one random (matrix small grains) with r = 1.
A bimodal microstructure dominated by a large number of interconnected large and anisometric grains is clearly observed.
For unseeded ceramics under the same processing conditions, only small plate-like and well-faceted matrix grains were observed, with a maximum grain size below 15 µm [8].
However, the final number of large anisometric grains for the samples sintered for > 2 h was greater than the initial number of templates, suggesting that new large grains are formed among the templates.
It is believed that the higher number of large grains, which are introduced in the stereological analysis, are probably responsible for the increase of the r parameter for samples with 2 and 24 h of sintering time. 0 10 20 30 40 50 60 70 80 90 0.0 0.2 0.4 0.6 0.8 1.0 Experimental March-Dollase fit Normalized Frequency θ (degree) 0.01 0.1 1 10 0.48 0.52 0.56 0.60 Texture Factor (r) Log Sintering Time (hours) Fig. 3.