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However, only a limited number of studies on the Kapitza resistance of grain boundaries have been reported [7, 8].
Yang et al. also studied the grain size effect and estimated the Kapitza resistance of grain boundaries in nanocrystalline YSZ.
Due to the similarity in transport mechanism, the classic Wiedemann-Franz law states that in pure polycrystalline metals, the following relationship holds: CWFL = κ / σT. (1) where CWFL ≈ 2.44×10-8 WΩ/K2 is known as the Lorenz number, κ is the thermal conductivity of a metal, σ is the electrical conductivity of the metal and T is the temperature.
In contrast to the large grains shown in Fig. 1, TEM micrographs of nanocrystalline nickel in Fig. 2 showed very small grains.
In nickel, thermal conductivity decreases with decreasing grain size while electrical resistivity increases over the same grain size range.

Grinding wheel consists of abrasive grains, bond and pore, and each abrasive grain is connected by bond-bridges.
It is considered that the contact stiffness of the grinding wheel in grinding operation depends on the number of the abrasive grain in contact with the workpiece.
If the support stiffness of single abrasive grain kgs and the number of abrasive grains in contact area can be obtained, the theoretical contact stiffness of the grinding wheel can be calculated by product of these values [2][3].
The number of abrasive grains in contact area can be obtained by multiplying a contact area between grinding wheel and workpiece A by abrasive grain density ng.
Here, the abrasive grain density ng for dressing lead 0.1, 0.5 and 1.0 mm/rev were used as 2.2, 1.6 and 2.0 grains/mm2.

The grain growth of metallic iron was investigated in detail.
As the reduction time elongated, the small grain of metallic iron gathered toward the larger one and grew up.
The metallic iron existed in the reduction products in the form of larger grains of metallic iron.
At the same time, it could be seen that the number of metallic iron particles of small size was more, which indicated that grain of metallic iron was in the growth stage, only part growing faster iron particles became lager one.
After restored 50min, metallic iron particles grew more uniform, existing in the form of larger grains of metallic iron.

Introduction The Nb solute atoms and precipitates pin the austenite grain boundaries and reduce the recrystallisation and grain growth rates, which leads to grain refinement and improved mechanical properties.
Nb(C,N) precipitates were shown to pin the grain boundaries stronger than Nb solute atoms [2 - 4].
To obtain the austenite grain size (equivalent circle diameter) distributions, 800-1000 grains were imaged using Leica DMRM optical microscope.
With a decrease in austenitising temperature, the Nb content in the austenite matrix, the Nb cluster size and number density and the Nb-C cluster number density all decreased, although the Nb-rich particle number density increased (Table 2).
Table 2 Summary of the parameters for Nb-rich precipitates and Nb-containing clusters Re-heating temperature [°C] 1100 1250 Deformation temperature [°C] 1075 975 1075 975 Nb in the matrix [wt %] 0.002 0.005 0.016 0.015 Nb clusters Maximum cluster size [number of atoms] 10 8 12 16 Maximum Guinier radius [nm] 2.1 1.4 1.6 1.7 Number density [×105 mm-3] 1.60 2.15 3.19 3.74 Nb-C clusters Maximum cluster size [number of atoms] 53 72 92 53 Maximum Guinier radius [nm] 3.0 3.6 4.1 3.0 Number density [×105 mm-3] 0.20 2.0 4.3 7.0 Nb-rich particles Average diameter (20-70 nm range) [nm] 26 22 29 29 Number density (20-70 nm range) [mm-3] 3.13 12.06 2.05 2.75 Austenite grain size [mm] 10 6 9 Partial recrystal.

Thermal annealing below 600℃, the movement of grain boundaries mainly led a reduce of the number of microvoids, and vacancy defects began to recover due to the growth of MgO nanoparticles after annealing between 600 to 900℃.
Compared with traditional bulk materials, volume fraction of grain boundaries in nano-ceramics is meaningful and thus open volume defects in grain boundaries play an important role.
The movement of grain boundaries might lead to decrease the number of microvoids below 600℃; and above 600℃, the particle size begins to grow and intensity decreases to about 0.5%, which indicates that most of microvoids are recovered or some microvoids agglomerate into larger pores.
The agglomerations of a number of nanoparticles were found.
For MgO nanocrystal, the total defect density decreases with the increasing annealed temperature, below 600℃, the movement of grain boundaries might lead to change the number of microvoids; above 600℃, the particle size begins to grow, associated with recovery of vacancy defects in the grain boundary region.

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.

The nanocrystalline silver powder and the amorphous powders of composition Ni49,5Ti20,5Nb15Zr15 (numbers indicate at%) were prepared by ball milling in the planetary Fritsch mill for 40 hours.
The grain size of silver crystals within powders drastically decreased after milling down to about 30 nm and only a small increase in the grain size up to 200 nm was observed after hot pressing.
The structure of tungsten has shown less defects and consequently less grain refinement than silver particles.
Change of mass Dm of the contact as a function of number of contact cycles of the composite based Ag- 20% NiNbTiZr measured for mobile and immobile contacts.
The silver grains grew only up to about 200 nm after hot pressing.

Fig. 2 shows variation in the erosion rate at room temperature with number of impacts on two different surfaces.
Initially the erosion rate on the coarse grain surface tends to decrease with an increasing number of impact and maintains constant values after about 10 impact events.
Erosion rate on the fine grain surface increases with increasing number of impact up to about 5 impact events.
Grain size dependence on the erosion of ceramics have been reported by many studies.[ 6 - 8 ] The erosion rates on both surfaces with respect to the number of impacts for higher temperature are shown in Fig. 2.
Fig. 2 Changes in erosion rate of the graded structures as function of the number of impacts for each tested temperature.

It is mainly of ferrites and a large number of uniformly distributed fine lath martensites.
Thereby a large number of grains were broken into sub-grains, resulting in a large number of nucleus during the process of recrystallization.
Thus, they were kept in the fine grain condition.
There appears reply recrystallization and grains growth, which is the main reason to promote MS1470 steel HAZ grains coarsening.
After the heat treatment, the average grains size becomes 10μm.

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.