Search results

Cu, Cu2O, SiC), the spheroids can be viewed as individual "grains".
This movement causes contact of the shell with the kernel and of a large number of spheroids.
SEM image of nano grains in the sintered compact.
It is obvious that the spheroids are composed of nano grains, i.e., nano Cu and SiC grains.
It should also be noticed that although no apparent grain growth is found in Fig. 4, neck growth and grain-boundary development do occur in the present case.

The grain size distribution, the shape factor, the clay content and the acid demand value were determined.
Compared with the base sand, the grain size of the reclaimed sand is almost no difference.
But the coal dust is less effective on the grain size distribution and the shape factor.
More attention should be paid to the mechanical reclamation cycles, including keeping the grain size distribution and the shape factor in the stable level, the acid demand value and the clay content decrease resulting from the number increment the reclamation cycles.
Compared with base sand, the grain size and the shape factor of the reclaimed sand is almost no difference.

All samples comprised of rather round BaTiO3 grains with wide grain size distribution.
The number of these Al-rich needle-like grains increased with the Al2O3 content.
The particular microstructure tended to reside particularly at the grain boundaries of the BaTiO3 grains and seemed to link the grains of BaTiO3 together, especially in the samples with small content of Al2O3 additions (3-5 mol%).
In general, the free energy of grain boundaries is higher than that of grains and thus, the grain boundaries may act as obstacles to dislocation slip which can strengthen the material.
In this investigation, the addition of Al2O3 particles could also significantly reduce the grain size which led to more grain boundaries and then provided more obstacles to dislocation pile-up in the adjacent grains.

A lot of residual surface cracks were observed to perpendicular to the bending stress, but the number of cracks dramatically decreases with decreasing λ and almost become zero when λ=50 nm.
For a coarse grain, dislocation activities or dislocation structures can develop and evolve within grains to refine grains.
When the grain size decreases to nanoscale even submicron scale, the typical dislocation behavior is transformed to grain boundary dislocation creation and annihilation due to the limited dislocation capacity in such small grains [21,22].
As schematically shown in Fig. 10(b), it is suggested that a large number of dislocations would interact with the interface to form an interface roughening region (IRR).
Fig. 10 (a) Plastic pileup around the microindentation in the λ=50 nm Cu/Au multilayer indicates no evident feature of grain deformation except for characteristics of grain rotating and grain boundary sliding, like aligned grain boundary indicated by red arrows.

It can be seen that the microstructure was very homogeneous and full of equiaxed grains.
The frequency values of high angle grain boundaries (HAGB > 15 o) and low angle grain boundaries detected by EBSD method were 83% and 17%, respectively.
On the other hand, the numbers of twins were greatly reduced, when the sheet were rolled at the 50% reduction ratio, although twins and DRXed grains still co-existed similar to the microstructure at the 30% reduction ratio.
Large strain rolling (70 and 85%) by one pass decreased the grain size down to around 2 mm.
The decrease of the volume fraction of the <0001>//ND texture components is attributed to the grain refinement and the DRXed grains produced by the high plastic energy.

And the spatial morphology of grain structure is some different along the thickness of the forging.
In the grain boundary map, coarse black lines represent high angle grain boundaries (>15°), fine black lines (10-15°) and fine red lines (2-10°) represent low angle grain boundaries (2-15°).
It is shown that the microstructure is characterized by elongated grains and some low angle boundaries in the elongated grains.
In Fig.2 few small size grains with high angle boundaries in big size elongated grains shows that the small size grains may be recrystallized grains, and the substructured grain are dominant in both near surface and in the center layer of the forging.
In addition, the alloy also contains a certain number of dislocations formed during pre-compression process.

A change of grain boundary configuration in classical vertex model is found by the calculation of vertex velocities.
However, this model was applied only to the simulation of grain growth.
The structure of grains is defined by a set of vertices (triple points) with positions →kr where k=1,..., N (N is the number of vertices in a model sample).
Configurational energy associated with the chosen vertex →ir (before changing its position) can be denoted as: )AEr( H ijij j ijij before i + = ∑ → γ (1) where: γij is the grain boundary energy of the segment between vertices i and j, Eij is the stored energy inside a grain adjacent to boundary i,j (right hand rule is applied) and Aij is the area of a grain adjacent to the segment.
At the very beginning of simulation, new nuclei are placed within randomly chosen grains.

But the roles of grain boundaries in porous samples are negligible [5].
The number of holes in the CuO2 planes decreased (hole-filling effect) due to the excess oxygen that is not enough to compensate the variation of the charge in the system [8].
In the case of sample b, superconducting grains seem not properly linked and these grains are considered responsible for the low Bi-2223 phase.
In sample d, the grains become smaller and randomly distributed, which indicates a weaker link between grains as compared to the pure low-density sample.
The destruction of the superconducting properties in BSCCO extremely depends on the hole numbers in CuO2 layers.

However, HPDC products possess low mechanical properties resulting from a substantial number of porosity during die-filling and the solidification in the die cavity.
Some recrystallized grains preferentially nucleate like-chain at grain boundary, and proceed to form fine equiaxed grains of the fully recrystallized microstructure when the annealing time is increased to 30 min, as shown in Fig.8 (a)-(b).
For the annealing at 673K, only the recrystallization of α-Mg is completed in several minutes, accompanying the apparent grain growth (grains averaging 23 μm), as shown in Fig6 (d) and Fig.8(d).
However, the recrystallized grains grow apparently due to the high migrating rate of grain boundary at high annealing temperature.
With increasing annealing time, grain growth of α-Mg matrix is slight due to pinning of β-Mg17Al12 phase which forms at grain boundary.

A great number of studies have been undertaken to improve the mechanical properties of sintered HA.
The yield was ball milled at 250 rpm for 30 min to ensure even size grains.
As temperature increases pores coalescence, the number of pores decreases while the average pore size increases.
Higher temperature leads to exaggerated grain growth accompanied by grain coalescence.
Exaggerated grain growth accompanied by grain coalescence promotes weak mechanical strength and increase brittleness.