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The Si3N4 porous ceramic contains a plurality of Si3N4 crystal grains with pores formed in grain boundary which forms a three-dimensional network structure.
A number of patents describe the preparation of porous silicon nitride ceramics since the 1980s, such as a porous silicon nitride ceramics can be prepared by adding gypsum or coarse silicon powder to the raw materials [1,2] and Matsuura et al. got porous silicon nitride ceramics by adding rare earth oxides to the raw material of the silicon nitride [3].
Fig.5 shows that the silicon nitride porous body comprises a body part and a pore part, where in the body part is formed by a plurality of b- Si3N4 crystal grains, the silicon nitride crystal grains with pores formed in grain boundary which forms a three-dimensional network structure.
Large aspect ratio b-Si3N4 grains may be easily formed, which can be seen in Figure 7.
(4) Large aspect ratio b- Si3N4 grains may be easily formed at vacuum furnace, compared with at Nitrogen atmosphere pressure furnace.

One option to produce an ultrafine grained microstructure is severe plastic deformation (SPD).
This is a top down method which begins usually with an initial coarse grained (CG) microstructure and leads to a break up of former grain boundaries and a production of very small new grains with high angle grain boundaries.
The softening annealed state offers spheroidal carbides in a homogeneous coarse grained microstructure with well-defined grain boundaries (Figure 2 a)).
After 6 rotations the grain boundaries have broken up and some new grain boundaries are visible in Figure 2 b).
It is obvious that the hardness increases with the number of rotations for both carbide morphologies.

The potential application range of coarse-grained commercial purity titanium is limited by its low mechanical properties.
A reduction of the grain size of titanium leads to a significant increase in its strength and hardness.
This paper is concerned with application of hydrostatic extrusion (HE) for fabrication nano-grained titanium.
Nano-grained Ti processed by hydrostatic extrusion (HE), reveals considerable increase in yield stress and tensile strength, when compared with those in the coarse-grain state.
Grain refinement of the titanium microstructure achieved by hydrostatic extrusion Process Initial grain size d2 [µm] Final grain size d2 [nm] Grain refinement Initial / Final Ø50mm → Ø3mm 15 65 230 Ø33mm → Ø5mm 20 55 365 Ø20mm → Ø3mm 160 60 2670 Ø12mm → Ø3mm 10 not fully - Fig 1.Structure of Ø50 Ti - initial state Fig 2.

(2) I-current; U-voltage; A-the effective cross-sectional area of the sensing material; Nd-the carriers density; VB0-the grain boundary potential; ε-permittivity of the material; T-temperature; kB-Boltzmann constant; Nbarr-the number of potential barriers.
Obviously, there is no activation source in dark, so the number of electron and hole pairs in dark is the smallest.
Consequently, the number of holes that actually react with as shown in eq.4 raises in the same order, too.
Then the width of the depletion layer decreases as a result of the decrease of the number of around the grain boundary.
And VB0 is the grain-boundary potential, Nbarr means the amount of grains of the material tested.

The application of pressure results in decreasing thermal activation and, thus, in the grows of number of dislocation sources and, finally, in the increase of DSH.
We show that the proposed model not only explains a number of known effects, but also suggests new ones.
One of the ways of increasing the intensity of substructure grain refinement is the increase of its amplitude [6].
As expected, we have some improvement of grain refinement (curve )(ed ), but structure failure has still increased (curve )(eθ ).
Varyukhin: In Ultrafine Grained Materials II, ed.

The grain refinement was assisted by the development of deformation twinning.
An early warm deformation leads to the elongation of original grains along the rolling direction (RD) and the development of large strain gradients within the grains.
At a maximum total strain (e=3), the deformation structure is composed of highly flattened austenite grains with transverse grain size of about 220 nm (Table 1).
The grain refinement was assisted by the deformation twinning, which resulted in rapid grain subdivision at relatively small strains, followed by shear banding.
Acknowledgements The financial support received from the Ministry of Education and Science, Russia, under Grant No. 14.575.21.0092 (ID number RFMEFI57514X0092) is gratefully acknowledged.

In addition, neighboring grains have different energies and these neighboring grains define the grain size.
According to it, two layers of grains and grain boundary form an inhomogeneous dielectric specimen.
Grain boundaries have low conductivity whereas the grains are more conductive.
It contains different mechanisms related to grains, grain boundaries and electrode contribution.
Nyquist plots at different temperature suggested that conduction mechanism in material was due to the increase in number of grains and thus the resistance.

The precipitation occurs at not only grain boundaries but also twin grain boundaries in the experimental steel.
The grain boundaries are clean, straight and thin.
This can be considered as follows: Large numbers of defects exist in material after cold deformation.
Cold deformation may cause dislocation pile-up at grain boundaries, and increase the distortion energy of grain boundaries, which can nucleate σ phase at grain boundaries and defect microstructures (deformation twin and slip band) accelerate the precipitation of σ phase inside grain.
The precipitation occurs at not only grain boundaries but also twin grain boundaries in cold-deformed Fe-18Cr-12Mn-0.48N steel

We can then assume that the nanocrystalline Pr2Fe14B inherited the structural features of the amorphous structure at least in the interfaces, because of the small grain size and the large number of interfaces.
The increase in the grain size lead to a slight decrease of the mean lifetime, which was elucidated in terms of grain boundary relaxation and atomic rearrangement during grain growth, inducing the changes of free volumes in amount and size.
The mean lifetime τm (▲) decreased with the annealing time (grain growth).
The second type defect will be gradually eliminated with increasing grain size.
A wide distribution of interatomic distances in the interfaces is expected due to the great number of different structures of the interface [10].

Multi-peak reflections and/or sharp change in the value of Ω indicate the presence of misoriented grains.
In order to study the overall crystalline quality of the substrates, rocking curves are measured in a large number of spots on the wafer surface, and a two-dimensional map is generated.
Multi-peak reflections and/or sharp change in the value of Ω indicate the presence of misoriented grains.
From this, the contribution from the sub-grain misorientation to the overall reflection broadening is approximately 49 arc-seconds.
Rocking curves measurements performed on a large number of substrates showed that different surface finish on different wafer faces could cause wafer warp and a small but detectable degree of lattice curvature.