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Marx str., Ufa 450000 Russia, email: RZValiev@mail.rb.ru Keywords: superplasticity, ultrafin� -grain� d alloys, severe plastic deformation, grain boundaries Abstract.
Special attention is paid to microstructural dynamics, i.e. a grain growth and grain boundary sliding at low temperature and high strain rate superplasticity in ultrafine-grained alloys.
After heating up to temperature of superplastic testing there was some grain growth, but the mean grain size was still less than 0.3-0.5 µm (Fig. 1).
We observed a visible grain growth leading to an average grain size in gage section of about 1-2 µm.
Concluding remarks The applications of SPD techniques for processing of UFG structures have provided an opportunity to attain enhanced superplastic properties, namely low temperature and high strain rate superplasticity, in a number of alloys.

This size provides sufficient area for a number of indents located far from grain boundaries which may affect nanoindentation results [7].
At the same time, it still allows covering a large number of differently oriented grains by EBSD and nanoindentation in a reasonable time.
In order to obtain a reasonable statistics, a number of indents per grain ranged between 10 and 20.
All indents were located within the grain interior more than 1 μm far from grain boundaries to minimize their influence [7].
It may, however, change with increasing number of indents during the experiment due to sticking of the indented material to the indenter tip.

The grains produce fine grain strengthening effect.
The number of precipitated phases in the No. 3 joint is the least.
No. 4 joint has the largest number of second phases.
According to Figure 4(g), it can be seen that there are a large number of second phases distributed in the grain boundaries and within the grains, so the No. 4 joint has poor corrosion resistance.
And because the total number of grain boundaries increases, while reducing the degree of impurity atom segregation, it can also improve the electrochemical performance of the weld.

Part of the cell walls formed grain boundary and then small angle subgrain formed.
With the increase of current density, the number of the dislocation cell increases and the size decreases.
The dislocation cell has a tendency to move to the grain boundary.
With the increase of current density, the number of the dislocation cell increases and the size decreases.
The dislocation cell has a tendency to move to the grain boundary.

Bulk ultrafine-grained Nickel consolidated from nanopowders J.
HIP), thus preventing grain growth.
With increasing strain, the number of loops increases and the stress field of these loops hinders the emission of new dislocations from the grain boundaries.
As the dislocation emission from the grain boundaries is hindered in the SPS-processed specimen, the further plastic deformation is most probably mediated rather by grain rotation or grain boundary-related mechanisms such as sliding and/or decohesion.
The further deformation of the SPS-processed samples is probably mediated mainly by grain rotation and/or grain boundary-related mechanisms.

After the number of new grains in each time step is calculated, the location of these new grains is chosen randomly among the remaining liquid cells.
The grain number over the whole section could be measured.
As shown in table 2, grain number in a unit volume, Nv, was calculated from experimentally determined grain number in a unit area, NA, using Owadano's equation: 1/2 3/2 ( ) ( ) 6 v A N N π α= (12) where α=1.2 is a coefficient determined by material properties.
(a) Surface average grain size (b) Center average grain size Fig.9 Comparison of average grain size between experimental results and simulation results at the surface and the center of the three steps under different initial die temperatures Conclusions 1.
With the increase of initial die temperature, the grain size becomes larger.

Further analysis indicates that this difference is due to the number of grains in the direction of thickness of the material: more grains give more grain boundaries, which allows more strain of the grains.
Compared to this, the grains in forming zones are different.
Fewer grains mean fewer grain boundaries.
This procedure causes, that all grains within the forming area are strained, like the elongation of grains for Al99.5 with thickness of 100 µm.
Conclusion From the reported work it can be concluded: · The LDR in micro deep drawing is smaller than in macro deep drawing; · The forming limit of thin foils is lower that thicker foils; · The number of grains involved in the micro forming process affects the forming limit essentially.

The recrystallized grains have no strong preferred orientation about (0001), similar to the grains of growing. 1.
(a) and (c) show number frations, and (b) and (d) show area fractions.
The grain sizes are determined from the grain structure maps based on EBSD measurements.
Fig. 4 (a) and (c) show the number fraction of grains, and Fig. 4 (b) and (d) show the area fraction of grains, respectively.
However, Fig. 4 (c) shows that the number fraction of (0001) oriented grains decreases from 31.9% at annealed state to 27.5% at deformed state.

The relaxation times determined on the basis of impedance data were found to decrease with increasing atomic number of lanthanide.
The relaxation times at 20°C decrease with increasing atomic number of a lanthanide - from 2x10-4 and 2x10-2 s for Nd2/3Cu3Ti4O12 to 3x10-7 and 2x10-4 s for Dy2/3Cu3Ti4O12, for grains and grain boundaries, respectively.
The activation energies of resistances of grains and grain boundaries are close to those of dielectric relaxation.
At a given temperature, it increases with increasing atomic number of a lanthanide.
A higher resistivity of grain boundaries results presumably from reoxidation of copper ions during cooling, which occurs preferentially at grain boundaries, whereas the grain interior contains still Cu+ ions, responsible for a higher electric conductivity of grains.

The morphology of ultrafine grains formed is different from that of aluminum alloys.
The as-received copper showed a recrystallized structure with the average grain size of 63 µm in diameter.
This structural evolution of oxygen free copper with the number of ARB cycles is similar to the results of some aluminum alloys processed by the ARB [6, 7, 10].
It is found that the UFGs with grain diameter of about 250 nm have relatively equiaxual appearance.
The inhomogeneity in hardness for 1-cycle ARBed sample is 0 1 2 3 4 5 6 7 0 100 200 300 400 500 0 10 20 30 40 50 60 70 80 Elongation (%) UTS / MPa � Equivalent strain� UTS Elongation 0 1 2 3 4 5 6 7 0 100 200 300 400 500 0 10 20 30 40 50 60 70 80 Elongation (%) UTS / MPa � Equivalent strain� UTS Elongation Fig. 3 Changes in mechanical properties of the copper with the number of ARB cycles. 500nm Fig. 3 Dark field image of ultrafine grains developed in high purity copper by ARB process