Search results

The anisotropy of the individual crystals, however, is smoothed out only in the presence of a large number of grains having a random distribution of orientations.
Its magnitude depends upon the statistical distribution of grain orientations – the "crystallographic texture" or, more simply, the texture.
Local variations in texture, as well as the arrangements and types of grain/phase boundaries, may give rise to inhomogeneous material properties.

Sub-micron crystalline silver grain structure were observed using SEM micrographs.
Fig.5(a) shows a uniform small grain with diameter around 100 nm.
The facetted grain shown in Fig.5(b) to 5(f) appear to be nonuniform in grain sizes.
Fig.5(f) shows a higher facetted grain sizes with average grain sizes around 450 nm.
Our results agreed well with others studies [6-9] which report that as the sputtering power increases, the number of energetic atoms and mobility of atoms on substrate surface increases resulting in deposited films became more facetted with larger facetted grain sizes.

It is found that Pr affects the grain size, electrical properties and the dielectric properties of the TiO2-based varistors.
A number of low-voltge varistor materials were reported such as TiO2, SnO2 and SrTiO3 ceramic[4-6].
It can be seen that the grain sizes increase with the increase of dopant concentration, meaning that the dopant can promote growth of grains.
But as a whole, the shape of the grains is almost the same.
Where is the number of grains per unit length and the voltage barrier width.

Initial microstructure contains 100 grains.
This number of the grains correspondents to the average grain size about 80 mm.
The changes of average grain size for entire process can be seen in Fig. 2f.
Depending on temperature, strain and strain rate, the different grain size were obtained.
These parameters influence on the number of new grains and their growth rate.

Nonetheless, a number of negative consequences tend to be possible [2].
While flame heating until 3550C, it was observed that the morphology of the grains retained austenite as evident in Figure 2a, and thus, changes not from the initial grain structure.
In the Figure (1a), shows the Micrograph of initial grain structure and average hardness plots (1b) of the same grain structure at room temperature as HRC 29.
(Slightly higher than those obtained on the initial grain structure).
Figure 4 shows average hardness as HRC 24, 29 29.3 as results; on surface grain structure after flame heated to 550⁰C, on surface of initial grain structure before flame heating and on grains beneath the surface of flame heated samples to 550⁰C respectively.

It is shown that dielectric properties of these materials may be modified by a combination of different BTS powders as well as layers number.
Combinations of powders were 0-15, 2.5-15, 7-15, 2-7-10-12 and 2.5-7-10-12-15 (numbers designate mol% of Sn in BTS).
BTS ceramics have been electrically studied as a function of temperature, Sn contents, as well as a function of number of layers.
The grain size is between 20 and 40 µm.
There is an obvious difference in the grain shape between barium titanate sample (polyhedral grains) and BTS ceramics (spread and burst grains).

When the fraction recrystallized, Xrex, is determined, the grain size in the recrystallized regions can be calculated as where is the total number of nuclei.
Here NCube is the number of nuclei formed on old cube grains, NGB the number of grain boundary nuclei and NPSN the number of nuclei from particle stimulated nucleation.
The different nucleation sites are treated independently, so that the total number of active nucleation sites, number of potential nucleation sites and nucleation rate per unit volume respectively, are sums over s = GB, Cube and PSN.
The extended volume fraction of recrystallized grains (which is a key concept of the JMAK-approach), with time-dependent nucleation, is the integral of the volume 4p/3[r(t’,t)]3of grains nucleated at t’ times the number of grains nucleated at t’: , (7) where V and d* are the growth rate and initial diameter of recrystallized grains as given, by Eq. 4 and Eq. 5.
The number of sub-grains that will nucleate during the time dt is the number of available potential nucleation sites (that have not started to grow) , times the increase of overcritical subgrains during time dt.

A modulus of elasticity of 225 GPa and a Poisson number of 0.28 had been used for calculating residual stresses for the (211) reflection.
The results were still quite noisy, which was attributed to bad grain statistics.
The number of diffracting grains is small in this case not only because of the small beam size but also because of the small divergence of the beam coming from an undulator.
Since beam intensities are much higher than at neutron instruments, a large number of points can be measured within short time.
Moreover, in many cases measures have to be taken to improve the grain statistics.

The starting materials were α-Si3N4 powders with average grain size of approximately 0.5 µm, purity 99.5%, and TiC nanoparticles with average grain size of 140 nm, purity 99.8%.
A minimum number of five specimens was tested for each experimental condition.
The sub grain boundaries formed around the TiC nanoparticles were observed inside the β-Si3N4 grains, which is assumed to cause some grain refinement.
The microstructure of the composite was characterized by fine, elongated β-Si3N4 grains, with larger TiC nanoparticles located at grain boundaries, while the smaller ones trapped inside the β-Si3N4 grains.
The intragranular TiC nanoparticles led to sub grain boundaries and consequently the strengthening by grain refinement.

And the failure mechanism is that NiMoB crystallized and grains grew after annealing at high temperature, a large number of Cu grains passed through NiMoB film via grain boundaries and then reacted with Si substrate and oxygen, causing the generation of highly resistive Cu4Si and CuO.
In Fig.4(d), grains were larger after annealing at 500°C.
There were many small grains generated in the grain boundary.
Fig.4(e) shows the surface appearance of NiMoB/Cu/NiMoB/SiO2/Si films after annealing at 550°C, it could be seen that the grains were so large, small grains which generated after annealing at 500°C grew up and generated more, which indicated that a lot of Cu grains have passed through the diffusion barrier layer, and the NiMoB film failed completely.
The failure mechanism of NiMoB film is that the barrier layer crystallized and generated large grains, a lot of Cu grains passed through diffusion barrier layer by grain boundaries, and reacted with the Si substrate and O2 to generate Cu4Si and CuO with high resistivity.