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The macrostructure of pure aluminum appears three different grain morphologies: the surface fine grains, the central columnar grains and the heart equiaxed grains.
When adding 0.3%Zr alone, the grains get slightly refined, the columnar grain area is reduced and the equiaxed grain zone is increased.
With 0.3%Ti added alone, the grains obtain obviously refined and all of the columnar grains transform into coarse equiaxed ones.
So, when 0.3%Ti or 0.3%Zr added alone，the Al3Ti or Al3Zr primary phases can effectively promote the grain refinement, and with the number of Al3Ti and Al3Zr particles increasing, the heterogeneous nuclei increases gradually in the melt and further promotes the grain refinement.
Thereby the grain refining effect of 0.3%Ti is better than that of 0.3%Zr, and the microstructure of the alloy completely transform into equiaxed grains, while the sample with 0.3%Zr still keep many columnar grains.

Sub-grains were found at the grain boundaries with little dislocations in the matrix after 27448 h service time.
With the increase of the service time under high temperature and high pressure, the island-like microstructure disappeared when the service time is 27448h and 31526h, and both the number and size of the carbides at the grain boundaries and the grain interior obviously increased.
There are a great number of dislocations in the grains and at the grain boundaries in the original T23 steel matrix as shown in Fig. 3(a), forming dislocation networks.
The number of the dislocations gets a relative reduction after running for 23872h compared to the original T23 steel.
However, there are a certain number of creep voids near the carbides at the grain boundaries.

Recently, ultrafine grained microstructures with a grain size of less than one micrometer were obtained after annealing of severely deformed alloys [3-6].
Despite the large number of studies on continuous recrystallization operating in various metals and alloys processed by large strain deformations, some characteristics of this mechanism, e.g. texture evolution, are not known in detail.
In this case, the grain coarsening takes place homogeneously without preferential growth of any individual grains.
Number Fraction, Ni / N 0.0 0.1 0.2 0.3 0.4 0 10 20 30 40 50 60 0.0 0.1 0.2 0.3 0.4 Misorientation, θ (deg) 0 10 20 30 40 50 60 0 10 20 30 40 50 60 ε = 2.0 ε = 4.4 ε = 2.0 625o C, 30 min ε = 2.0 625 oC, 2 hours ε = 4.4 625o C, 30 min ε = 4.4 625 oC, 2 hours Fig. 6.
The development of primary recrystallization associated with grain boundary migration over long distances results in a decrease in the total number of low-angle subboundaries, while the fraction of high-angle grain boundaries increases.

Transparent Fine-grained Oxide Ceramics G.
Keywords: Alumina, Spinel, Transparent, Fine-grained.
This behaviour is counter-intuitive as decreasing the grain size increases the number of grain boundaries from which scattering can occur.
TEM microsgraph of fine grained MgAl2O4.
The grain boundary scattering in RE-doped Al2O3 samples was exacerbated by the increased grain size distribution.

The ultrafine-grained materials produced by ECAP have a very high strength owing to their small grain size and high dislocation density [2].
The influence of the number of ECAP passes on the yield strength and the ductility is investigated for pure Cu up to an extremely high strain value of 29.
The yield strength and the maximum elongation as a function of the number of ECAP passes for pure Cu are plotted in Fig. 2a and the dislocation density and the crystallite size versus the number of ECAP passes are shown in Fig. 2b.
The larger fraction of high-angle grain boundaries facilitates grain boundary sliding which improves ductility [7].
Figure 2: The yield strength and the maximum elongation (a) and also the dislocation density and the crystallite size (b) as a function of the number ECAP passes for pure Cu.

XRD, SEM and EDS results showed TiB2-TiC composites were mainly composed of the fine-grained microstructures of TiC matrix in which a large number of the fine TiB2 platelet grains were dispersed uniformly, whereas there discontinuously dispersed the ε-carbides with the enrichment of Ti atoms, and a few of isolated, irregular α-Al2O3 grains and Al2O3-ZrO2 colonies were also observed at the boundaries of the eutectic microstructures.
Except for the extremely high temperatures required for densification of the materials, the microstructures obtained by the tranditional processings can be fine-grained, but are rarely characterized by crystal grains finer than 1μm [3].
Furthermore, it was observed by FESEM that a number of fine platelets were embedded in TiC matrix, as shown in Fig. 4.
Fig. 4 The TiB2 platelet grains in TiC matrix of T80.
However, because of higher concentration and faster diffusion of C relative to B in liquid Ti alloy as well as the growth isotropy of TiC, TiC grows far faster than TiB2 does, so that the TiB2 platelets are completely surrounded by TiC grains, as shown in Fig. 4, and the final microstructures that a number of TiB2 platelets are embedded in TiC matrix are achieved.

It is believed that the refinement of the coating structure at low nitrogen pressures is associated with a larger number of atoms/molecules depositing on the substrate with higher energies, thus enhancing the adatom mobility and nucleated cluster formation in the coatings.
The number and kinetic energy of the depositing atoms/molecules have been considered the factors that determine the adatom mobility and formation of the nucleated clusters in the thin films.
When a large number of atoms/molecules approach the substrate with higher depositing energies, the nucleation rate will be enhanced and coatings with smaller grain sizes develop.
The value of ko was considered as the limiting grain size for grain refinement under specified deposition conditions.
Similar grain size reduction was evident in the current study of (Cr,Al)N coatings.

Each plot was selected 10 spikes and calculated indoor after drying, the test indicators contain spike diameter, spike length, the number of rows, and kernel number per row, grain number and so on.
The maturity test results showed that which compared with the CK, the number of kernels per row with mulching was increased by 9.0%~9.9%, and 7.4%~14.6% increased in grain number.
Table 2 The agronomic traits effect of whole film mulching in different treatments (2010) treatment Spike diameter. spike length the number of rows kernel number per row grain number grain moisture content (CFM) (CFM) (row) (grain) (grain) (%) WFM 4.84±0.05 15.47±0.12 14.8±0.4 34.53±3.00 508.5±38.58 22.4±1.35 CFM 4.91±0.07 15.87±0.60 15.6±0.8 34.80±2.42 542.6±63.21 22.4±0.62 CK 4.79±0.30 14.67±1.27 14.93±0.9 31.67±4.43 473.4±35.10 23.4±1.25 The grain yield of the test in 2011a showed in Figure 3 and the water use efficiency showed in Figure 4.
Because of less precipitation in the late growth stage (grain filling stage) and adequate light and heat resources, spike diameter, kernels per row, grain number and kernel weight differences of the different treatment are not significant (Table 4).
Film mulching laid the foundation for the grain yield.

Average squared output error (ASE) decreases with increase of the hidden node number.
The irregular blocky carbide ((Cr0.4Mo0.2W0.2Ni0.1Ti0.08Co0.02) C(1)) with bright contrast indicates that this phase contains elements having higher atomic numbers.
During thermal exposure, particles near grain boundary merge into layer of the grain boundary, which plays the main role in the grain boundary coarsening.
Although interface between the M23C6 particles and layers is not obvious, the cores with dim contrast in the grain boundary should be M23C6 particles due to light elements having lower atomic numbers in composition.
This prevents dislocations from piling up against grain boundaries and in consequence inhibits stress concentration on grain boundaries, when dislocations move to grain boundary.

A BCC layer with a nano grain structure appeared in the vicinity of the MM powder surface.
Therefore, a BCC layer formation from austenitic matrix is a specific phase transformation, and is attributed to the rise of the grain boundary energy by the nano grain formation.
Result of such a large hardness decrease in the surface of MM powder after annealing at near the room temperature indicates an existence of a huge number of defects, such as vacancy and interstitial atom, by the SPD-PM Process.
Nano grain refinement proceeds by way of nano layer structure [3,7,10].
Such a near room temperature diffusion is attributed to high density vacancy introduced by SPD process and increase of the grain boundary area for the grain refinement.