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Therefore, this study provides important theoretical basis for the ultra-fine grain of bar rolling development.
Although parameters of fabricating ultra-fine grain can be gotten in previous studies, the barrier to produce ultra-fine grain bar was strong plastic.
The flat-oval/ off-round groove system proposed in this paper has feature of so great elongation coefficient that can reduce the number of rolling passes.
In the process of refining grain, the grain size depends on strain, temperature and strain rate, and the quantitative relationship was set up by a lot of research.
The result of research indicated that the grain size depends on Z() factor, and the bigger Z leads smaller grain size.

Packing density and coordination numbers of the grains in the sintered powder are analysed with application of computer simulation.
The parameters, most widely used in the description of the packing types, are: i. packing density defined as the ratio of volume of solids to the total volume of solid grains and voids; ii. the coordination number distribution which defines the coordination numbers appearing with various probabilities.
The program allows simulating the grain packing and related coordination-number distribution as well as a dependence between the both.
To eliminate the border effects the students make a series of calculations of the packing density (ρ) for various grain radii (R) and then draw the results in the ρ vs. �-1/3 scale (where N is a number of the grains in the given volume).
The screen of the results contains information about total number of the spheres in a given volume, packing density and the coordination number distribution (Fig. 3).

Experimental studies performed on a number of superplastic materials and review of literature indicates sliding of grain groups suggesting a process of cooperative movement of grains.
Movement of grain boundary dislocations associated with a step at the core causes coupling of sliding and grain boundary migration, and cooperative manner of grain sliding leads to a long range correlation in grain boundary migration.
Introduction: Cooperative Deformation Processes It has been shown in a number of superplastic (SP) materials [1-10] that grain boundary sliding occurs in a cooperative manner, i.e. groups of grains slide as blocks.
Cooperated sliding of grain groups is accompanied by cooperative grain groups rotation (CGBR), i.e. rotation of grain groups, and cooperated grain boundary migration (CGBS), i.e. correlated migration of sliding grain boundaries.
Coupling between CGBS and grain boundary migration can be attributed to motion of grain boundary dislocations associated with a grain boundary step resulting in relative grain displacement and grain boundary migration [8].

The grain abrasion resistance of the cladding layers is also discussed.
The grain abrasion resistance of the coating is also discussed.
While (b) and (c) show that the number of cracks and other defects are significantly reduced, the organization is relatively dense and the material uniformity is well improved.
Grain Abrasion.
The cladding layers consist of compact grains, little porosity and cracks.

Fig.1 Grain cumulative grading curve of different coarse-grained contents Test Result and Analysis Stress-strain relationship of materials with different coarse grain contents.
between coarse grain content and shear modulus G.
Shear planes of the specimen with a coarse grain content of 80% and 100% have no visible scratches, their compactness are poor , and a large number of rock block distribute on shear planes dispersedly.
Material with a coarse grain content of 70% means its framework is excellent, and fine grains fill in the coarse grain adequately, that let the compactness increase accordingly.
It is because that coarse grain cannot contact with each other perfectly and internal friction angles will become small when fine grains increase, while coarse grains will contact with each other perfectly and internal friction angles increase with the increase of coarse grain content.

Modeling Grain Boundary Mobility during Dynamic Recrystallization of Metallic Alloys F.
Introduction Grain boundary migration plays an important role in dynamic recrystallization because it is one of the main parameters controlling the final grain size after hot working of a material.
(The other solution, ρ = 0, corresponds to the nucleation of a new grain.)
The grain boundary mobility in particle and solute-containing metals undergoing DDRX is therefore obtained by combining Eqs. 7 (assuming here that its validity range extends up to M = 0) and 8a, viz., ( ) ( ) z z 0 m s 1 k M M 1 C C − ρ ρ = + α (9) Particle Size and Solute Concentration Dependence of Grain Boundary Mobility Assuming spherical particles, the Zener pressure is given by [4]: ( ) 2zP 2 n d= π γ (10) in which γ is the surface energy of the precipitates, n is the number of precipitates per unit volume, and d denotes their diameter.
In the cross-hatched area, the grain boundary mobility is zero.

Introduction Grain size effects in ferroelectric ceramics is of great importance due to the market demand for small-grain-size ceramics.
The average grain size for each sample was determined using the linear intercept method by counting at least 200 grains in SEM images.
Distinct grains and clear grain boundaries can be clearly observed in the ceramics.
Due to the same reason, the capacitance decrease for coarse grain samples is larger than that of samples with small grain sizes.
The decrease of the saturation polarization Ps with the increase of mechanical uniaxial stress indicates that the number of switchable ferroelectric domains decrease significantly under the uniaxial mechanical stress.

Disks of an AZ31 magnesium alloy were processed by High-Pressure Torsion (HPT) at 463 K to different numbers of rotations.
Most researchers estimate the amount of strain (ε) imposed to the material as a function of the thickness of the sample (t), distance to the center of the disk (r) and number of rotations (N): .
Different disks were processed to different numbers of turns.
This multimodal grain size distribution is attributted to the mechanism of grain refinement of magnesium alloys processed in the temperature range of ~400 – 600 K [2-4] which is characterized by slow consumption of coarse grains by the nucleation of fine grains along the grain boundaries.
This mechanism leads to multi-modal grain size distributions in the intermediate stages of grain refinement when the original coarse grains have not been completely consumed.

It is demonstrated that under the DCAP processing the material is strengthened faster, by lesser number of passes, and microstructure’s thermal stability is somewhat lower after ECAP compared to that after DCAP, although after equal number of passes ECAP results in a more homogeneous microstructure.
Along with these fine grains there are much coarser and anisotropic grains.
Local areas with fine submicron grains surrounded by high-angle grain boundaries are also observed.
Under the higher number of ECAP the structure gets more homogeneous, but after 8 passes the percolation porosity appears [4,5].
With the increasing number of passes the pronounced deformation bands are formed, and inside them there are subgrains of submicron sizes decreasing with the increase of the number of passes.

This can be simply explained by the significantly enhanced total grain boundary area in refined austenite leading to a larger number of nucleation sites for ferrite.
Particularly for case B a number of considerations have to be done.
During tempering a number of metallurgical effects take place as indicated in Figure 8.
There is evidence for the occurrence of this scenario in a number of alloy systems [17],[18].
In martensite a prior austenite grain contains a very large number of discrete laths of dislocated structure.