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The volume of their application is currently about 70% of the total number of structural materials in the airframe [3].
In recent years, ultra-fine-grained aluminium materials have been of great interest to researchers of materials science.
This confirms the results of the well-known studies [5] that under the action of ultrasonic smoothing, the grain sizes of the source material are reduced to nano-sizes.
Therefore, subsequent studies should be conducted for a larger number of layers of experimental samples.
Grabovetskaya, et al, Grain boundary diffusion and properties of nanostructured materials, Novosibirsk, Nauka, 2001.

An increased performance is expected with increasing grain size because the number of efficient recombination centers, present at grain boundaries, decreases.
Due to preferential diffusion of phosphorus along grain boundaries when diffused emitters are used, EBIC measurements at grain boundaries are greatly influenced.
A possible explanation for a grain size dependent value of Sgb would be a changing local impurity concentration at the grain boundaries, arising from impurity segregation at the grain boundaries in combination with a changing grain size.
Other limitations may arise for example from the presence of small grains and a broad grain size distribution.
Acknowledgments This work was partly funded by the European Commission under contract number 019670-FP6IST-IP ("ATHLET").

According to the Copper Development Association (CDA), the brass with Cu 70% and Zn 30% can be known as Cartridge Brass [6,7] with the CDA number 260.
The number and size of the grains developed in a unit volume of the metal depends on the rate at which nucleation takes place.
The numbers of different sites at which individual crystals begin to form and the rate at which these crystals grow are both important and influences on the size of the grains developed.
Generally, rapid cooling produces smaller grains, whereas slow cooling produces larger grains.
In the present study, the grain size of brass in the sand casting is larger than the grain size of brass in the chill casting (Fig. 3).

The huge number of memories required to calculate the view factors for each surface cell against others makes it extremely complicated and difficult for the heat radiation calculation in directional solidification.
Fig. 5 Simulated grain evolution progress.
The simulated results show that a great number of tiny grains appeared at the bottom of the blade shortly after the beginning of the withdrawal progress.
When growing upwards, those grains with a better favorable crystal growth direction, which had a small angle with the heat flux direction, got larger chances to grow bigger and finally grew into several dozen of large columnar grains.
This shows the competitive grain growth progress during directional solidification, and reproduces the formation of the typical large columnar grains in the directional solidified turbine blade castings.

By drawing the several lines on the SEM image and the number of intersection was counted to determine average grain size.
The average grain size D can be measured by using equation below.
Experimental Outcome and Discussion Microstructural Evolution and Grain Size.
The grain size sample for 0.5wt% (a) and 0.4 wt% (b) of MnO2.
The spontaneous tetragonal to monoclinic phase transformation of grains takes place if the grain size is higher than critical value.

Nomenclature A Total cross-sectional area of the beam b Breadth of beam bpl Breadth of plank deck ca per Applied compressive stress perpendicular to grain cb par Basic compressive stress parallel to grain cg per Grade compressive stress perpendicular to grain cm per Mean failure compressive stress perpendicular to grain COVcper Coefficient of variaton for compressive stress perpendicular to grain COVfpar Coefficient of variation for bending stress parallel to grain COVvpar Coefficient of variation for shear stress parallel to grain COVUw Coefficient of variation for unit weight of the Nigerian grown Iroko cp per Permissible compressive stress perpendicular to grain E Modulus of elasticity for the Nigerian grown Iroko Emean Statistical mean value of modulus of elasticity Emin Minimum value of modulus of elasticity EN Statistical minimum value of E appropriate to the number of pieces N acting together F Form factor dependent on the cross-sectional shape of the
Forty test specimens of the Nigerian grown Iroko timber were prepared for each of the following tests; bending strength parallel to the grain, tensile strength parallel to the grain, compressive strength parallel to the grain, compressive strength perpendicular to the grain and shear strength parallel to the grain.
Figures 1 – 4 show the Nigerian timber test samples for compression parallel to the grain, bending parallel to the grain, tension parallel to the grain and shear parallel to the grain respectively.
(6) where EN is the statistical minimum value of E appropriate to the number of pieces N acting together (where N=1, EN becomes the value for Emin) and σ is the standard deviation.
From Ozelton and Baird [10] (30) where EN, is the statistical minimum value of the modulus of elasticity for the number of pieces acting together, Emean is the mean value of modulus of elasticity and N is the number of pieces acting together at a cross-section.

Although observed in various metals of diverse crystal structures, twinning is most prominent in hcp metals, which often have an insufficient number of slip systems to accommodate externally imposed strains [1].
While the twinned grains were refined due to sub-division by the twins, the untwinned grains, which had undergone only slip, had a largerthan-average grain size.
Hence, due to the high stored energy and the large number of high-angle boundaries, heavily twinned regions and particularly the regions of twin boundaries impinging to the prior grain boundaries become favorable nucleation sites for recrystallization.
Texture evolution during grain growth thus appears to arise from the size advantage of the recrystallized grains.
Vol. 50 (2002), p. 1245 12345678910 0 10 20 30 40 Overall specimen (a) Ave. grain size 3.9 µm Frequency [%] Grain size [µm] 12345678910 Grains with CRTC (b) Ave. grain size 3.1 µm Grain size [µm] 12345678910 Grains with RXTC I (c) Ave. grain size 4.2 µm Grain size [µm] 12345678910 Grains with RXTC II (d) Ave. grain size 4.3 µm Grain size [µm]

The result shows that due to the restriction by the Nb(CN) precipitates, the grain size in coarse grain heat affected zone (CGHAZ) at a heat input of 10 kJ/cm is 75 µm, which is half as that at the heat input of 40 kJ/cm.
Large numbers of experiments and production experience have shown that ferrite and pearlite are not sensitive to cold crack [2].
The microstructure in Fig.3(a) consists of primarily lath martensite, a number of M-A constituents, and some grain boundary ferrite (GBF) distributing along the prior-austenite grain boundaries.
Eq.(1) shows that grain boundary migration rate is much related with the solute concentration on grain boundary (cc) and the solute concentration before migration in matrix (c0).
This indicates that the GR.65 steel cannot inhibit the austenite grain growth effectively at high heat input, but the solute drag effect would play a significant role in controlling the grain size at low heat input. 2.

High-amplitude and thin-pulse electricity accelerated the nucleation and restrained the growth of the crystalline grains, and as a result nano-sized nickel grains homogenous in size were obtained, which are shown in Fig. 3(b).
The following explanation is as follows: (1) When pulse electricity was employed, existence of the pulse interval hindered the growth of the crystalline grains and changed the growth direction, thus prevented the grains from growing into bulks [4-6]. (2) The size of grains of the deposited layer depended on the velocity of nucleation and growth.
According to the theories in electrodepositing, when the cathode polarization is stronger, the rate of crystal nucleate will increase, and the number of nucleuses will multiple.
However, under the direct current electrodepositing condition, the cathode polarization is weaker, and the numbers of nucleuses are fewer, which will cause the grains to grow bigger and form a rough surface.
SEM shows that the average diameters of Ni grains and AlN particles are smaller.

And according to the optical micrographs, the mean grain size of the TM-addition alloy is much smaller than the base alloy, which is attributed to the grain refinement of TM.
The fine precipitates are formed in Co-, Ni-, Cr- and Fe-addition alloys with a larger number density distribution than the base.
The coarse precipitates are formed in Mn-, Y- and Gd-addition alloys with a smaller number density distribution than the base alloy.
Conclusions The grain size decreases for TM-addition alloys in this work, which is attributed to the grain refinement effect of TMs.
The decrease of the grains further increases the as-quenched hardness of TM-addition alloys.