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Since 1999 there has been a steady growth in conferences and topical workshops on nanotechnology and in parallel, comparable growth in the number of symposia on ultrafine-grained (UFG) metals.
This number compares with a total of 33 patent actions found in 2002 [5].
Ultrafine Grained Materials.
Ultrafine Grained Materials II.
Utrafine grained materials III.

Ultrafine grained (UFG) metals with grain sizes in the range of 10-1000 nm exhibit favorable mechanical properties including very high strength and ductility[7,8].
After 14h immersion, a number of cracks but no corrosion pits were observed on the surface of the HPT treated sample in Fig. 5c, while it can be seen that the corrosion pits enlarged and the corrosion products were dissolved on the surface of the as-cast samples in Fig. 5d.
Thus higher density of grain boundaries and the uniform redistribution of second-phase nanoparticles in the grain interiors would accelerate corrosion by forming more micro-electrochemical cells at the initial stage of corrosion between the second-phase nanoparticles and the matrix and at the grain boundaries.
However, as the second phase of the as-cast alloy mainly distributed along the grain boundaries, the pitting corrosion mainly occurred at grain boundaries; therefore the second phase came off grain boundaries after immersion for 14h (Fig. 5d). 4.
[9] Balyanov A, et al, Corrosion resistance of ultra fine-grained Ti, Scr.

Measurements of the size of the grains were made in these areas by seeking.
Installed that the number of SiC particles in the FSW AL25 + 18% SiC composite is more than twice compared to the base composite, though basically same particle volume fractions were observed in both conditions.
Comparative fracographic analysis of welded compounds performed by STP after tests showed that the kinks are caused by a fine-grained structure and a more plastic intra-grain nature of destruction (Fig. 6).
The size of the grain in the mixing zone is a value that is more dependent on the material (the presence of hardening particulate matter of aluminum oxide) and the cooling speed, as both temperature and deformation, which affect the size of the grain, increase with the intensification of the regime.
In addition, as the particle size increases, they increase the density of structure defects, the number of doubles and packaging defects.

Too much or too less of dopants (both Pr6O11 and TiO2) in the varistor cannot obtain regular shapes of ZnO grains, and the grain boundaries are neither clearly observed.
The results reveal that the Pr- and Ti-rich phases were distributed at grain boundaries, triple point junctions or embedded in ZnO grains, which is an inhibitor for ZnO grain growth.
The inhibitors for ZnO grain growth include the secondary phases PrTiO3 and Zn2TiO4, and the praseodymium ions segregated in the region of grain boundaries [8].
The increase of varistor voltage can be explained by the increase in the number of grain boundaries owing to the decrease of the average ZnO grain size [9].
This is attributed to the increase of the number of grain boundaries caused by decreasing average ZnO grain size.

The coarse grained tungsten carbides are mainly used in mining or drilling applications.
A reduction of the WC grain size, on the other hand, increases the hardness and improves other mechanical properties [7,8].
In the applied research of ultrafine cemented carbide, Liang Ping[9] and Yu Jiedong [10]et al. showed that ultrafine cemented carbide tool life improved several times over the conventional coarse grain cemented carbide; Pan Yongzhi [11], Kuai Jicai [12] and Zhang Hui [13] et al. indicated that grain refinement significantly reduce the friction coefficient of the ultrafine grain cemented carbide by the friction and wear testing.
Cutting Tool Material Tool materials that were selected for cutting test is YG6 and YG8 with the grain size 2 to 3μm as well as YG6U and YG8U with the grain size 0.2 to 0.3μm.
Thirdly, ultrafine WC/Co cemented carbide tools have a finer grain size, bigger grain surface area, larger volume fractions of grain boundaries twists and uniform distribution of binder phase Co, greater impeding the generation, motion and propagation of micro-cracks, so that the possibility of WC grain being removed reduce, the chipping of cutting edge is more difficult .

A large number of defective grain boundaries (GBs) existing in NC materials may act as "short-circuit" diffusion channels, so that atomic diffusion in NS materials is expected to be much enhanced relative to their coarse-grained counterparts.
Kolobov et al [6] noticed diffusivities of Cu in a NS Ni (with a grain size of about 300 nm, synthesized by means of severe plastic deformation) are about 4~5 orders of magnitude higher than those in the coarse-grained Ni.
Its basic principle is the generation of plastic deformation in the surface layer of a bulk material by means of a large number of repeated multidirectional impacts of flying balls onto the sample surface over a short period of time, resulting in a progressive refinement of coarse grains into the nanometer regime.
Actually, when the grain sizes are smaller than a critical value, dislocations will hardly be piled up in grains and the nanocrystallites become dislocation free [20].
The grain size can be refined to such a fine scale and with high diffusivity.

The best room temperature tensile strength and ductility were attained in specimens which had been heat treated to relieve stresses produced by the fabrication process but that had a minimum number of recrystallized grains [3].
Recovery should pronounce the <110> texture in rolling direction (RD) while recrystallization will generate a different texture [5] and reduce the number of single-fold dislocations thus decreasing the tensile ductility.
During recrystallization the first recrystallized grains in alloy A appear in bands at the grain boundaries between former grains.
Due to the smaller grain size and the less pronounced layered grain structure in the rolled state recrystallized grains occur with higher number, are smaller and more evenly distributed.
The average grain size has increased due to strong grain growth.

The reheating condition was optimized and the comparison between different routes and number of passes was investigated.
When the temperature rises to above solidus, the high- energy grain boundaries of these new grains are penetrated by liquid, leading to the fragmentation of original grains to small equiaxed grains.
The presence of liquid causes grain growth and spheroidization of the newly formed grains.
By increasing number of passes dendrites and interdendritic networks of lamellar eutectic silicon mix together and eutectic phase distributes in the structure resulting in reduced distances for diffusion.
Therefore, a grain boundary etchant is required to examine this phenomenon.

With the continuous martensitic transformation, the dislocation density increased further, which results in the formation of a large number of dislocation intertangles within the austenite grains.
According to grain size, the austenite grains can be divided into two parts: coarse ones and fine ones.
According to this, we assume that grains of different grain sizes come from different initial structure [18].
The coarse grains came from deformed austenite grains without phase transition.
In addition, as the amount of deformation increased, the austenite grains without strain-induced transition were elongated, and the dislocation density increased, providing a large number of austenite nucleation points during the annealing process, leading to grain refinement.

In this formula, M is one of the cations Li, Mg, Ca, Y and most rare earths with valance of +v, m is number of Si-N bonds in α-Si3N4 replaced by Al-N; n is the number of Si-N bonds in α-Si3N4 replaced by Al-O; and and x is the cation solubility (x=m/v) [1].
α-SiAlON grains, that contain a small amount of sintering additive are light gray β-SiAlON grains without any additive are black and the cation rich grain boundary phase appear white.
Some of the α-SiAlON grains are elongated which is believed to be a result of having a high amount of grain boundary phase.
After removing the grain boundary phase, individual α and β-SiAION grains were obtained for SEM and EDX analysis.
α-SiAlON grains are determined according to their morphologies since they are generally considered to occur in equiaxed grain morphology [8].