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In both cases a strongly refined structure is visible, with different sizes and forms of grains, wherein grains of ca. 100nm size prevail.
The occurrence of grains and/or sub-grains sized ca. 20÷30nm or even smaller was confirmed by HRTEM (Fig. 2b).
The high-energy mechanical milling is a process generating a large number of defects and causing the refinement of the crystalline structure.
The occurrence of solid solution of aluminum with nanometric grains has been confirmed thanks to HRTEM.
Acknowledgment The presented research project was funded by the National Science Centre based on the decision number DEC-2011/03/B/ST08/06076.

Table 1 provides the serial number and the corresponding compositions of the aluminum alloys.
It can be observed that the grains in alloy 1 are slightly coarser than those in the other three types of alloys, while the grain size of the other three alloys remains similar.
As can be observed, the alloy grains are elongated and flattened along the extrusion direction, forming a fibrous microstructure.
The decrease of Zr in alloy 1 would lead to the decrease of the number of the Al3Zr phase particles that hinders grain boundary movements and causes recrystallization.
After extrusion, the alloy grains have a primarily fibrous morphology.

The ferrite grain size distribution was bimodal in all steels.
This might originate from a smaller prior austenite grain size in the Mo- and Nb-microalloyed steels related to the effect of solute atoms and precipitates on the retardation of austenite grain growth in these steels.
Steels Average ferrite grain size, μm Second phase fraction, % Particles Hardness, HV <5 μm range >5 μm range size, nm number density, μm-2 MoNbV 2 ± 1 8 ± 2 14 ± 5 25 ± 6 0.8 ± 0.2 293±11 NbV 2 ± 1 8 ± 2 11 ± 3 28 ± 10 1.3 ± 0.84 265±8 High V 3 ± 1 10 ± 5 9 ± 2 40 ± 13 0.5 ± 0.1 285±10 Particle precipitation was studied using SEM imaging and EDS (Figure 4).
The presence of Mo in the MoNbV steel increased Nb solubility in austenite, which could refine the (Nb,Mo)(C, N) precipitates and reduce their number density with respect to the NbV steel (compare 25±6 nm and 28 ± 10 nm of average particles size in the MoNbV and NbV steels, respectively; 0.8 ± 0.2 μm-2 and 1.3 ± 0.84 μm-2 of particles number density in the MoNbV and NbV steels, respectively, Table 3).
Yang, et al., Ultrafine grained austenite in a low carbon vanadium microalloyed steel, J.

Fig. 4 shows grain size variation during rolling as a function of number of pass.
And the measured grain sizes as a function of number of rolling pass were plotted in Fig. 8.
a b Fig. 4 Grain size of modified Properzi c ast and rolled AZ31 alloy plates as a fu nction of number of pass. 0246810 0 10 20 30 40 50 60 70 80 90 number of pass Grain size(?
a: cast-rolled; b: homogenized /machined-rolled 6 10 12 18 homogenized -rolled Fig. 7 Microstructures of as-HCC cast and as-rolled AZ31 alloy plates. 0 2 4 6 8 10 12 14 16 18 0 10 20 30 40 50 60 70 80 90 number of pass Grain size(?
) ascasr RD ascasr TD annealed RD annealed TD Fig. 8 Grain size of HCC cast and rolled AZ31 alloy plates as a function of number of pass.

As known, ultrasounds are mechanical waves which, when applied to liquid metals, increase the number of solidification nuclei, so that the cast products show superior mechanical performances, as a consequence of the finer grain structure.
Between 1950 and 1990 researches were aimed at using low frequency vibration to create fragments of the solid phase under formation during solidification, increasing in this way the number of heterogeneous nuclei [2, 3].
Currently, researches on ultrasound treatment (UST) of liquid alloys are especially addressed to the evaluation of its effects on degassing and grain refinement.
However, grain refinement and degassing can not guarantee high performances of castings.
In both US and not US treated microstructures a strong variation of the chemical composition from the center of the grain to the boundary is present, as can be inferred from the different color gradation.

When tin content was increased over 10 wt. %, the deterioration of ITO conductivity as associated with segregation of the Sn ions at the grain boundaries and the conversion of Sn 4+ to Sn 2+ which behave as acceptors. 3.3 Change in layers number The thicknesses of the resulting films were observed to increase with multiple dipping although the relationship between film thickness and number of repeated cycles is not quite linear[13].But the important reduction of the sheet resistance with the number of deposited layers can be explained by the increase of the total film thickness.
Fig.2 shows the variation of sheet resistance as a function of layers number.
It indicates a better percolation between grains in the inner layers, due to densification process.
The increase in carrier concentration may be due to an increase in the diffusion of Sn atoms from interstitial locations and grain boundaries into the In cation sites.
(3) As layers number arising, the thickness increases and the resistivity of films reduces form 482 to 117 Ω/□

The latter quantity depends on the grain misorientation.
The alloys were then grain refined with 0.4 wt% Al-TiB2 master alloy.
The high temporal resolution allowed us to obtain a sufficient number of diffraction patterns during solidification.
With an average grain size of 120 μm and a gauge volume of 0.5 x 0.5 x 7.5 mm3, the number of irradiated grains is approximately 2’000 thus providing good statistics.
At the grain level, this corresponds to a succession of agglomeration/decohesion between grain clusters.

When the grain size of metal and alloys decreases to submicro, turned into the ultrafine-grained (UFG) metallic materials, the materials might exhibit a good combination of mechanical properties [1].
It has led to the development of operations to reduce the grain size.
It shows a characteristic dimple-like ductile fracture with a large number of tear ridges and dimples.
Compared with unidirection rolled, the number of dimples of MWE sample is more and the size of dimples is smaller, as shown in Fig. 7. 4.
Valiev, Structure and mechanical properties of ultrafine-grained metals, Mater.

Results furthermore indicate defect stabilization by hydrogen trapping not only for vacancy-type defects but also for dislocations and grain boundaries.
Methods known to enable the fabrication of bulk nanocrystalline materials immediately from the coarse-grained source materials belong to the family of SPD [1].
These changes were interpreted to arise from a large number of vacancies which formed in the lattice during the combined heat and temperature treatment.
Furthermore, they concentrate at grain boundaries, thereby forming a net-like arrangement.
Summary The presence of interstitial H brings about an increase in the total number of defects created during low-temperature HPT in Pd.

The strengthening mechanisms which are operative in bainite are very well known: small bainite packet, small width of the laths, dislocation density and size and number of carbide particles (Fe3C), among others.
When the austenite grain size is relatively large, each grain is transformed into several bainitic packets, until finally, when the austenite grain is relatively small, each grain will be transformed into one single bainitic packet.
Austenite grain size (Dg) and bainitic packet (Db) at different austenitisation temperatures.
The number of ferrite laths measured was more than 200 and their size distribution is shown in Fig. 4.
Two different grain boundary misorientation tolerance criteria were considered: a 15° misorientation between grains (Fig. 7-b) and a 5° misorientation.