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The microstructure evolution during the ARB process was explained by grain subdivision.
Introduction High strengh of ultra fine grained metallic materials has attracted a number of researchers both in scientific and industrial fields.
In the previous studies about aluminium alloys and ferritic steels, it has been clarified that the mechanism for forming the ultra fine grain structure is grain subdivision [5-6].
(a) (b) (c) 0 1 2 3 4 5 6 0 5 10 15 Spacing of HAB Number of ARB cycles 0 1 2 3 4 5 6 0 20 40 60 80 100 LAB HAB Boundary fraction (%) Number of ARB cycles 0 10 20 30 40 50 60 0 10 20 30 40 Number frection (%) Misorientation angle (deg.) 0 10 20 30 40 50 60 0 10 20 30 40 Number fraction (%) Misorientation angle (deg.) 0 10 20 30 40 50 60 0 10 20 30 40 Number fraction (%) Misorientation angle (deg.)ARB processed OFHC copper at quarter thickness position.
It was demonstrated obviously that the grain subdivision progresses with increasing the number of the ARB cycle.

Although such force exists universally, it is too weak to fasten the diamond grains firmly between vitrified adhesive and diamond grain surface.
The numbers of grains falling out in each ways can be figured out by the fractography analysis with computer software aiding.
Under the first circumstance only the interface binding force plays the role, so the force equilibrium equation of grain falling out from matrix is: (1) where f1 is the pulling force of single grain (N), d the diameter of grain (M), σ1 the chemical combining strength (Pa).
(3) (4) where F is the external force loading in sample as tensile testing (N), n1 the number of grains fell out in the first way, n2 the number of grains fell out in the second way, n the total number of grains (n = n1 + n2), A the area of fracture surface (m2), A0 the area of porosity (m2).
Diameter of grains approximately equals the diamond products d50.

Thermally stimulated current (TSC) measurement provided the relative number of oxygen vacancies both on the cathode/ceramics interfaces and the grain boundaries.
At first glance, this result can be understood as an increase in the number of oxygen vacancies.
They also correlated the TSC peaks with two types of space charge formed by the electro-migration process of oxygen vacancies: within-grain (accumulation of oxygen vacancies on the grain boundaries) and across-grain (accumulation on the cathode/ceramics interfaces).
According to the Takeoka's report [7], these peaks can be assigned to the within-grain space charge and the across-grain space charge, respectively.
Therefore, in sample 3, both within-grain and across-grain space charges existed, implying that the electro-migration of oxygen vacancies is restricted by the grain boundaries.

Conventional wire drawing with a sufficiently high degree of deformation, a high number of passes and relatively low annealing temperatures also yields UFG NiTi alloys with fine microstructures, Fig. 1f.
With increasing number of cycles, a two-step transformation (B2→R, first peak on cooling, followed by R→B19', second peak on cooling) evolves.
In large grains there are only a few grain boundaries which act as obstacles for elementary lattice shear processes.
Although our study only provides a small number of data points, our results indicate that the required undercooling strongly increases with decreasing grain size, once the grain diameters fall below a threshold value of about 100nm.
This indicates that the material only partly transforms into B19' on cooling because a high number of grain boundaries acts as obstacles for the lattice shear processes which govern the martensitic transformation [4, 5].

GRAIN BOUNDARY SEGREGATION AND PRECIPITATION IN ALUMINIUM ALLOY AA6061 M.
These characteristics strongly depend on grain boundary phenomena, such as the size, distribution and chemistry of the grain boundary precipitates.
The number of grain boundary precipitates analyzed, the number of different random high-angle grain boundaries analyzed and the final standard deviation in the relative concentrations are listed as well.
Fig 2: TEM micrographs of grain boundary precipitates in AA6061: (a) Matrix (left grain) in [001]-projection (b) Matrix (left grain) in [011]-projection 4.
The measured [Mg]/[Si]-ratio of the precipitates at the grain boundaries is ~ 2.3.

Introduction A considerable number of reports have been published on the unconventional mechanical behavior of nano grain-sized materials due to the extremely high density of grain boundary area[1-7].
Change in tensile property of oxygen-free copper with respect to the number of (a) ECAP and (b) ARB process cycles.
A large number of dislocations began to be observed in the ECAPed specimen even after the first cycle.
Once the equiaxed grains formed, the dislocation density inside the grains appeared to decrease with further ECAP process.
The number of dislocations appeared to increase with further ARB process and nano-grains tended form although the normal direction to rolling plane.

A value for the average grain size along the whole cross section (diameter 250 mm) of 700 µm for the billet without grain refinement and 250 µm for the billet with grain refinement could be measured.
In this case the grain size distribution was inhomogeneous and the grain sizes ranged between 8 and 200 µm.
In theory recrystallization strongly depends on the forming temperature, the forming velocity, the number of defects and the microstructure [11].
The grain refined billets showed both finer grains and Mg2Si-precipitations.
Owing to the grain refinement 2.8 times smaller grain sizes and a homogeneous grain size distribution could be reached.

TEM observed that the small grains in 70-80 nm size were well distributed.
After an induction phase of calcined kaolin in the hydrothermal system, large numbers of Nanocrystalline of X zeolite molecular sieve were formed and became the growth unit.
Results and discussion Morphology evolution of small grain X zeolite.
The electron diffraction pattern of small grain zeolite is presented in Fig.2.
A large number of nanocrystal nucleus of X zeolite molecular sieve were formed and became the growth unit.

The pattern of deformation stages depends on the average grain size, defect structure of grains and their boundaries, internal stresses, texture and grain size distribution.
Sliding along grains boundaries and intergrain dislocation activity take place in the largest grains.
In materials with grain sizes less than 100 nm there are no dislocations inside grains, whereas in grains larger than 100 nm dislocations are present.
In these publications, analysis of a large number of s = f (e) dependences, for such materials as copper, cobalt, copper and aluminum alloys with grain sizes in the range of 12nm to 230 nm was performed.
To obtain the dependence presented in Fig. 3, a considerable number of s = f(e)dependences published by different researchers [2, 5-10] were evaluated by the authors of the present paper.

Most grains had high-angle grain boundaries with some boundaries exhibiting non-equilibrium characteristics.
Instead, a large number of ultrafine grains (50-150 nm, about 30 vol.%) were revealed to uniformly distribute at the triple grain junctions, leading to a fully dense bimodal microstructure.
On the other hand, instead of copious dislocations, deformation twins with a spacing of several tens of nanometers were revealed to form in a limited number of ultrafine grains (marked by the black arrow in Fig. 2 (d)).
Compared with the 1-pass sample, a prominent feature in the 3-pass sample was the formation of deformation twins within a large number of ultrafine grains of 50-150 nm, as shown in Fig. 3.
grain refinement.