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Bulk metallic materials possessing uniform grain structure with average crystallite sizes below 100 nm and grains limited by high-angle boundaries can be formed by a number of methods [2].
The first set consists of the samples after plastic deformation and the annealing at 575°С, 100 h (the numbers from 1 to 6).
Grain boundaries in ultrafine grained materials processed by severe plastic deformation and related phenomena, Mater.
Plasticity and grain boundary diffusion at small grain sizes, Adv.
Semionkin, Mössbauer Spectroscopy of Grain Boundaries in Ultrafine-Grained Materials Produced by Severe Plastic Deformation, Bull.

The relation between the grain size of 16MnR steel and the fractal dimension of fatigue fracture, and the relation between the grain size of 16MnR steel and the fatigue mechanical properties were discussed.
The grain sizes of material were also measured with the comparison method.
There were also the relation between fracture fractal dimension and grain size, The fracture fractal dimension Dm can be estimated according to the grain size G.
There were also the relation between fatigue mechanical properties and grain size, The fatigue mechanical properties Ji can be estimated according to the grain size G.
Acknowledgement The research work is supported by Nature Science Foundation of Anhui Province Education Department (Grant Number:KJ2009A126).

The results show that the number of dislocations in Si wafers reduced obviously after annealing and Al gettering for 2 hours at 600～1100°C.
The proportion of Σ3 grain boundary increases.
A number of dislocations and grain boundaries in the UMG-Si can be decreased after proper annealing.
Grain boundaries.
This is because the sub-grains and small crystal grains are phagocytosed by sub-grain merger or eaten mechanism to form large angle grain boundaries during annealing.

A significant grain refinement was observed by using the solute Ta together with stochiometric grain refiner (Al-2.2Ti-1B).
The grain size in Alloy 1 is about 700 µm.
The measured grain size in Alloy 2 is about 223 µm, while the measured grain size in Alloy 3 was approximately 140 µm.
The grain size can be refined to be less than 140 µm, which is much smaller than the grain size that can be achieved using Al-5Ti-1B grain refiner. 2.
StJohn, An analysis of the relationship between grain size, solute content, and the potency and number density of nucleant particles, Metall.

Thus, for a large initial grain size, grain refinement can be achieved at low values of Z.
To solve this problem, Derby proposed [10-11] the following correction for a large number of materials: 10 1 3/2 <            < b D µ σ (3) Sakui et al. [12] and Sakai et al. [13] demonstrated that the critical condition for the transition from single peak to multiple peak curves corresponds microstructurally to D0 = 2 Dss.
When the initial grain size D0 is smaller than Dss, multiple peak dynamic recrystallization is predicted, which leads to grain growth; while for initial grain sizes larger than Dss, a grain refinement associated with a single peak dynamic recrystallization is predicted.
This can be explained because a fine grain size provides a great number of nucleation sites, which in turn favours dynamic recrystallization.
This grain size can be related to the initial grain size, as in the literature there is mention of a transition between grain growth and grain refinement once the initial grain size is equal to twice the size of the steady-state.

Measurement of plastic zone dimensions after different number of cycles of deformation show that plastic zone size increases during the first stage of cyclic deformation (until definite number of cycles are completed), and then remains unchanged.
The cracks form on slip bands inside grains or on grain boundaries.
Former austenite grain after 500 cycles. b.
However, after definite number of cycles further growth is ceased.
The maximal number of slip bands are oriented to the macrocrack at an angles 30-60o . 5.

Introduction Nano-metals, defined as pure metals or alloys having grain size reduced to below 100 nm, have been a subject of extensive research which resulted in the development of a number of fabrication routes.
As a result, a number of SPD techniques, which allow obtaining unconventionally large strain, have been developed and successfully employed for grain size refinement in various metallic systems.
This was already proved for a number of metals and alloys and is illustrated in Fig. 1 for those processed by HE.
It should, however, be noted that the improvement in tensile strength was much more significant (580 MPa and 310 MPa for nano- and microcrystalline samples, respectively). 260 280 300 320 340 360 380 400 420 1.0E+04 1.0E+05 1.0E+06 1.0E+07 Number of cycles to failure Stress [MPa] nano- micro 0.00E+00 1.00E-08 2.00E-08 3.00E-08 4.00E-08 5.00E-08 6.00E-08 7.00E-08 8.00E-08 9.00E-08 1.00E-07 1 2 3 resistivity [ΩΩΩΩm] Fig. 3 Wöhler curves for micro- and nanocrystalline 2017 aluminium alloy Fig. 4 Resistivity of CuCrZr alloy: 1 - coarse grained, precipitation hardened, 2 - dislocation boundaries, 3 - fine grained Corrosion Resistance An important consequence of the reduced grain size is a significant increase in the surface area of the grain boundaries per unit volume of the alloy.
As the nano-grain structure is formed, the resistivity becomes only slightly higher than in coarse grain materials.

Due to the Hall-Petch effect, ultrafine grained (UFG) metals possess a number of improved properties such as 3-4 times higher yield strength and 2-3 times higher ultimate tensile strength (compared to an annealed material) [4]; the high cycle fatigue is also improved [5].
Other applications just take advantage of the small grain size and the increased amount of grain boundaries.
It has been mainly utilised in its isothermal forging form to refine grain structure in Ti-6Al-4V [25].
The first conference publication of the idea took place in 2007 [38] and since then there have been a number of publications describing further development of the method and experimental results [39-48].
TEM observations revealed elongated grains (due to route A), with the average grain/subgrain size after 8 passes of about 450 nm (Fig.15). 500 nm Fig. 15: TEM image of Al 1070 plate subjected to 8 passes of I-ECAP (route A).

The limited number of active deformation systems in hexagonal close packed (HCP) structure of Mg alloy lead to their poor formability at room temperature, which restricts the application of wrought magnesium alloys.
It can be noted that Al2Ca intermetallics locate in the grain boundary in slabby shape with reticulation structure for the as-cast Mg-11Al2Ca master alloys in the Fig. 3(a), whereas large number of Al2Ca phases are well-distributed in a particle or rod-shaped in the Mg matrix for as-extruded Mg-11Al2Ca master alloys in the Fig. 3(b).
Therefore, as-extruded master alloys are employed to study grain refinement behavior in this study, which would expect to have a better grain refining efficiency.
When adding a small amount of master alloys, grain will decrease in some degree, but the extent of grain size decreasing starts to slow down with further addition.
Grain size of AZ31 and AZ61 with different levels of the addition Mg-11Al2Ca The grain refinement mechanism of Al2Ca in Mg-Al based alloys.

In addition to the macroscopic grain subdivision, microscopic grain subdivision also occurred within the matrix to form an ultrafine grained structure in the single crystal specimen after high strains.
Introduction It is well known that severe plastic deformation (SPD) of bulky metallic materials can produce ultrafine grained (UFG) microstructures having submicrometer grain size.
It is an effective way to use a single crystal having no initial grain boundary as the starting material for SPD, in order to get a deeper understanding of grain subdivision.
Additionally, several numbers of deformation bands inclined at about 20 degrees to the rolling direction (RD) were also observed within the deformed matrix and the bands subdivided the crystal.
Many fine "grains" surrounded by high-angle boundaries can be seen.