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This causes porosity entrapping between grains due to the differences in morphology between β and α grains [5].
In the NA-SiC, the regions with high level of coarsening are accompanied by the regions with an increased number of large pores.
The elongated-shapes of grains are distinctly visible and contain small pores.
These samples are composed of exclusively elongated grains.
The shapes of the grains, similar in both samples, remain elongated but the aspect ratios in the ABC-SiC are significantly higher than that of the BC-SiC by accelerated elongated grain growth [6].

P/M superalloy has a lot of advantages such as ultra-fine grain, homogeneous microstructure, high alloy element content, high yield strength and high fatigue resistance at elevated temperature.
For as-prepared superalloy AA powders, the number of inclusions in per kg powder was about 20.
It is clear that button ingot mainly consists of the columnar grain and the equiaxed grain region, displaying a typical sequential solidification process.
Through the filter, the amount and number of inclusions can be reduced obviously.
It is calculated that the number of nonmetallic inclusions is about 0.166cm2/kg.

Due to the absence of grain boundaries, single crystal superalloys exhibit very good high-temperature properties.
As is known to all, total fatigue life is strongly influenced by a number of factors, such as loading mode, stress level and testing temperatures etc.
For instance, at the stress level of 335MPa, the numbers of cycles to rupture at 850°C and 900°C are identical, as can be seen in Fig.2.
In general, small cracks are prone to nucleate at the grain boundaries, persistent slip bands, inclusions or casting pores.
In this experiment, a SC superalloy SRR99 was adopted, in which grain boundaries ere removed.

Statistical analysis of 3D grain structures has been described elsewhere [5].
Serial sectioning can give detailed information of a specific grain and/or particle in all three dimensions.
Due to the limitations of the equipment and time constraints, serial sectioning is generally used to analyze only one or two grains.
The first is the number of times the coordinate falls within the image (Nx,y).
Use of MRSEC facilities under NSF grant number DMR-0520425 is also gratefully acknowledged.

Grain size is a key factor affecting physical and mechanical properties of polycrystals materials.
Grain size reduction in the metals and alloys can be achieved using Equal channel angular pressing (ECAP) method.
Grain size is a key factor affecting physical and mechanical properties of polycrystals materials.
The force required to form the tube increases as the number of bends increase The energies accumulated in the numerical simulation are shown in Fig. 11.
Acknowledgments This research with the Project Number of 65-34MS is funded by the King Abdulaziz City for Science and Technology.

Comparing with Fig. 1a, the size and number of twins in the material are different.
Most fine grains orient in <001> or <110> directions.
New grains will nucleate and grow, and form a fine grain zone.
The grain size is smaller than 200 nm.
This fine grain zone is a mixture of fine grains and carbides.

When cracking occurred, permittivity of specimens decreased with the number of cycles corresponding to the amount of mechanical damage.
As the number of cycles increased, the breadth of cracked region spread further.
After intergranular cracks initiated, the rise of the grain with a cracked boundary became prominent due to cyclic deformation.
Fig. 5 compares the permittivity normalized by an initial unit prior to testing and number of cycles under ∆E = ±400 V/mm.
(2) The permittivity of specimens decreased with the number of loading cycles.

Finally, mathematical expressions that relate the dependence with the Peclet number and inert particle diameter are proposed to describe the approximate size of the concentration boundary layer thickness.
Also in the understanding of certain mineralogical processes, such as the dissolution of plagioclase grains, during digenesis, modelling of the transport of aqueous Al by diffusion and convection around the grains may be required.
It is convenient to express the rate of dissolution in terms of the Sherwood number, , where is the mass transfer coefficient for the sphere.
It is possible to observe that the dimensionless concentration boundary layer thickness, at constant solute concentration and Peclet number, increases with , for .
Notation c Solute concentration ur ,uq Component of interstitial velocity vector c* Equilibrium solute concentration Pe Peclet number, c0 Background concentration PeL Axial Peclet number, C Dimensionless concentration PeT Radial Peclet number, d Inert particles diameter Pe’ Peclet number, d1 “Active sphere” diameter Sc Schmidt number, DL Axial dispersion coefficient Sh’ Sherwood number, Dm Molecular diffusion coefficient d Boundary layer thickness D´m Effective diffusion coefficient F Dimensionless potential function DT Radial dispersion coefficient Y Dimensionless stream function n Overall mass-transfer rate w Distance to the axis K Permeability in Darcy’s law h Enhancement factor k Mass transfer coefficient f Flow potential r Spherical coordinate q Spherical coordinate u Interstitial velocity vector y Stream function u0 Interstitial velocity e Bed voidage t Tortuosity References [1] C.Y.

Such observations can be explained by appealing to the conventional strain hardening from the large grains combined with the strengthening effect from the very small grains.
For example, Li and co-workers have published a number of papers on the tensile behavior of NC Ni-Fe alloys produced by electrondeposition[34-37].
Instabilities and ductility of nanocrystalline and ultrafine-grained metals.
Ultratough nanocrystalline copper with a narrow grain size distribution.
Grain size dependence of tensile behavior in nanocrystalline Ni-Fe alloys.

The formation mechanism of this microstructure is the new α plates selective nucleation and growth in combination with the smaller number of α plates within the α colonies ,which is decided by the cooling rate[15].
Moreover, the β grain boundaries α phase is a degree of brokenness caused by sufficient plastic deformation around the transus temperature.
In this regime, the crack tip plastic zone is generally smaller than the grain size resulting in the plastic deformation at the crack tip which is limited in a grain or a small scale with a faceted fracture morphology.
That is, coarser β grains containing high volume fraction of αplates andα colonies give more crack initiation and growth sites.
AVIC Beijing Institute of Aeronautical Materials, State Intellectual Property Office of the P.R.C., Patent number, ZL011312378, 2004