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Also the acoustoplastic effect changes the kinetics of both dislocations and vacancies in the grain structure so that new secondary phases may precipitate in the vicinity of grain boundaries which are usually free of them and thusly possess lower strength.
It is common to identify three structurally different zones in the FSW joints on hot-rolled aluminum alloy sheets as follows: fine-grain stir zone (SZ) formed by the rotating pin, thermomechanically affected zone (TMAZ) with elongated coarse grains oriented with respect to metal flow in the SZ, heat affected zone (HAZ) and base metal (BM) with grains elongated with respect to rolling direction (Fig.2).
It follows from the results in Table 1 that mean solid solution SZ grains of both samples are of almost the same size.
The microhardness testing shows that UAFSW sample has more uniform distribution of hardness numbers across the zones (see Table 1) as compared to the FSW one and therefore this weld seam is more balanced in terms of strength.
At the same time the mean size of S-phase particles in FSW sample is lower by a factor of 1.7, i.e. these particles are distributed in higher number of grains.

It seems that the final size of the colonies at the end of the transformation is correlated to the number of α-alumina seeds in the starting γ-alumina powder.
But the above observations suggest that a grain rearrangement process is coupled with the phase transformation.
Unfortunately, at the end of the sintering, the microstructure is always composed of micrometric grains.
For higher contents, the excess of the dopant has to be rejected to the surfaces and grain boundaries of α-particles which grow at the expense of γ-grains.
To benefit from this effect and with the goal of producing sub-micrometric grain size dense ceramics using isothermal sintering, further work with controlled density of nucleation sites and co-doping to limit grain growth is planned.

Negative segregation at the bottom of ingot forms due to the interaction of solidification interface and equiaxed grains deposition during solidification.
Up to now, only a limited number of industrial investigations were reported in literatures.
In the porous region, the liquid velocity can’t be seen in Figs. 6(b) and (c) even if the liquid penetrate through the packed layer of the grains.
In the slurry region, the solid of equiaxed grains are free to move in the surrounding liquid and its velocity appears obvious in the ingot.
[3] M H Wu, A Ludwig, Modeling equiaxed solidification with melt convection and grain sedimentation—I: Model Description.

Results and Discussion Before ECAP the microstructure of the alloy had uniform equiaxed grains with the average size of about 9 µm.
It is seen that the ECAP route used gives rise to an ultrafine-grained structure of the alloy with the average grain size ~ 1-5 µm.
The observed changes in the texture are a consequence of the ECAP features and depend on the route of pressing chosen and the total number of passes.
At the same time, a pronounced microstructure refinement at the level of the grains and subgrains occurs.
This texture, in combination with the grain size refinement down to the average grain size of ~ 1-5 µm, is responsible for the observed improvement of ductility.

The extruded alloy exhibits the recrystallised grain size and excellent mechanical properties.
In recent years, a number of Mg-Gd alloys have been investigated which shown that Gd can be used to change mechanical properties with a wide range of alloy compositions and heat treatments by its large solubility of 23.49 wt % at eutectic temperature [4, 5].
Extrusion temperature effect on Mg-1.6Gd grain size.
This phenomenon is associated with the grain growth which the hardness value decreases with increasing grain size.
The extruded samples show an equiaxed recrystallized grain structure.

Presence of Goss grain colonies at about the quarter of the hot rolled sheet is probably, as it has already been suggested, at the origin of the Goss grain presence at the primary recrystallized state.
Many authors [2-6] have studied the influence of texture heterogeneities, grain boundary energy, grain size of Goss grains…, on the abnormal Goss grain growth from the primary recrystallized state.
These two orientations form high angles and CSL grain boundaries with the Goss grains, which favors their abnormal growth [7-13].
From these two tables it appears that the number of main orientations found by OIM® through the sheet thickness is obviously higher than that found by X-ray diffraction with which the texture is only determined at three places.
The large elongated grains are parallel to the rolling direction

To determine the maximum number of cycles N max (critical true strain) the cycles were repeated until the sample was broken.
The number of measurement points (in the range of 30149-54335) of EBSD analysis was adequate for the applied magnification and resolution of the microscope.
They are limited to the area of grain interior and only occasionally show tendency for getting beyond grain boundaries.
Yield strength and tensile strength of the copper strip after the number of passages equal to the one third of the maximum value is 350 and 360 MPa, respectively.
In the samples subjected to RCS process increase of hardness with increase of number of cycles is registered, however after maximum number of cycles slight decrease of hardness in the samples was observed in comparison to the samples subjected to 2/3 of the critical number of cycles, which can show presence of some critical value of deformation above which hardness increase is not observed, probably due to processes of dynamic recovery which decreases density of dislocations in the material.

Ni and Ni-15%Fe alloy deposits show nano-grain structure with the average grain size of 23 nm and 12 nm, respectively.
It has been found that nanocrystalline Ni-Fe alloys with grain sizes in the nanometre range show unusual magnetic characteristics.
Addition of an element which has more outer electrons than Ni, increases the mean number of electron spins per atom and consequently affects the spin magnetic moment per atom.
As expected, the addition of Fe to Ni increases magnetization as the number of dipole moments are added to Ni magnetic dipoles.
However, coercivity HC and permability m are strongly dependent upon the grain size, and in materials with grain sizes less than 50 nm, follow HC~ D6 and m ~1/ D6 relationships, described by the random anisotropy model [14].

Nucleation rate and number of precipitates in V and Nb-microalloyed steels Sebastián F.
The number of precipitates was calculated by integration of the nucleation rate expression.
The interaction of these two phenomena has been widely studied by a number of researchers, who have considered different variables such as the steel composition, strain, strain rate, austenite grain size and deformation temperature, among others.
On the other hand, the integration of equation (1) would give the number of precipitates per unit of volume (N).
Precipitate number vs. time.

AFM analysis presented different morphologies, showing that the coatings with 15 bilayers had an average grain size of 49 nm; while the 30-bilayer coating exhibited grain sizes of 99 nm.
This is due to the increase in number of bilayers with nanometric thicknesses, which, along with the applied voltage polarization, present a variation in the microstructure - evident in the reduction of grain size.
Grain size and roughness results are shown in Table 1.
Bilayer Grain size (nm) Roughness (nm) 1 113 ± 9 4.4 ± 0.5 8 39 ± 4 3.6 ± 0.5 15 49 ± 4 3.2 ± 0.5 30 99 ± 6 1.9 ± 0.5 The graph on roughness versus the number of bilayers is observed in Figure 2.
Vol 24, number 8, (1953), p 981-988