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It can be seen that the grain size decreases as Bi content increases, which is in agreement with previous studies that Bi is a grain refiner for zinc.
Fig.4 plots the average grain size based on measurement of the grains from the microscopic photos.
There is about order of magnitude reduction of grain size with addition of 500 ppm Bi compared to pure zinc.
The fact that grain size decreases with Bi concentrations is an indication that the amount of irregular lattice sites is increased at the density of grain boundaries, where the atoms are poorly aligned, per area is increased.
Conclusions 1.Small amount of Bi addition results in a reduction of grain size or number of grains per unit area. 2.Solid particles enriched with Bi are formed on the surface mostly located alone the step edges of the crystal planes. 3.The exchange current for zinc reaction increase with addition of Bi because the surface becomes more active with addition of small amount of Bi as the number of active sites increases with Bi as indicated by 1.

It is suggested that a larger size of grain boundary precipitates(GBPs) can nucleate the hydrogen bubble and reduce the hydrogen concentration in the grain boundary and improve the HE resistance [4-6].The present article takes advantage of modified retrogression and reaging treatment based on subpeak aging differ from traditional RRA scheme, through which optimized microstructure with larger matrix precipitates(MPt), coarsened grain boundary precipitates(GBP) and appropriate precipitates free zone(PFZ) is achieved.
Table 1 Aging heat treatment schedules of AA7085 solutionized bars Test number First Step Second step Test number First Step Second step Third step A1 120°C /12h 160°C /0.5h A7 120°C /12h 160°C/8h A2 120°C /12h 160°C /2h A8 120°C /12h 160°C /2h 120°C /12h A3 120°C /12h 160°C /3h A9 120°C /12h 160°C /3h 120°C /12h A4 120°C /12h 160°C /4h A10 120°C /12h 160°C /4h 120°C /12h A5 120°C /12h 160°C /5h A11 120°C /12h 160°C /5h 120°C /12h A6 120°C /12h 160°C /6h A12 120°C /12h 160°C /6h 120°C /12h Properties tests and Microstructural characterization.
As is shown in Fig.8, the A4 tempered condition can provide a larger size of grain boundary precipitates (GBP) to nucleate the hydrogen bubble, then reduce the hydrogen concentration in the grain boundary and improve the HE resistance.
The precipitates of GP zones and η/ phase in grain matrix confirm the high strength of the alloy at this state.
Ardell and Park suggested that coarsening of grain boundaries precipitates was responsible for the improvement to the improvement of SCC resistance[4].

The non-conserved variable was adopted to describe the local structure or grains orientation.
Property Value Units Grain boundary mobility prefactor (ϑ0GB) 1.95⋅ 10-6 [m4⋅J-1⋅s-1] Grain boundary mobility activation energy (QGB) 0.23 [eV⋅atom-1] Grain boundary energy (γGB) 4.42 [eV⋅m-2] Surface energy (γS) 1.06 [eV⋅m-2] Surface diffusion activation energy (Qs) 0.751 [eV⋅atom-1] Surface diffusion prefactor (D0S) 0.26⋅10-4 [m2⋅s-1] Volume diffusion activation energy (Qv) 2.19 [eV⋅atom-1] Volume diffusion prefactor (D0Vol) 0.74⋅10-4 [m2⋅s-1] Grain boundary diffusion activation energy (QGB) 0.58 [eV⋅atom-1] Grain boundary diffusion prefactor (D0GB) 1.95⋅10-9 [m2⋅s-1] Molar volume (Ω) 1.182⋅10-29 [m3] Fig. 1.
The interface width was selected equal to the grain boundary thickness.
Grain boundary diffusion was considered equal to DGB=0.1⋅Dsurf [11].
Material properties were converted in non-dimensional numbers using a length scale l0=1⋅10-6 m, a time scale t0=1 s and an energy scale e0=1⋅109 eV, selected in consistency with the dimensions of the problem under consideration.

The effects of ultrasonic processing on structure, i.e. grain size and porosity, are studied using metallography and 3D X-ray tomography.
It is important to understand that the solubility of hydrogen in liquid aluminium is not a constant or a fixed number.
The number and size of the bubbles along with forced convection seems to be the main parameters of the process [2].
Nevertheless, the grain structure of an A380 alloy did refine somewhat (from 2 to 1.5 mm) as it is shown in Fig. 4.
Grain structure of A380 alloys before (a) and after (b) 2 min ultrasonic degassing.

The average initial grain size was measure and found to be 35 µm.
Ferrite grain boundaries have also become comparatively more defined as compared to Fig. 3(b) indicating that some precipitation at grain boundary has also taken place.
Further, reduction in surface energy can be achieved by decreasing the number of iron carbide particles from a large number of small particles to small number of large particles.
This is followed by appreciable breakdown of iron carbide platelets and also precipitation at grain boundaries.
It is observed that by this treatment the precipitates have coarsen and they are aligned at grain boundaries.

The fuel for the new system which is atomized into micron grade fog grain with ultrasonic system, increases the fuel and air mixing contact area, make the fuel mix more uniform.
With the decrease of the particle size, the number of surface atomic increases rapidly, as shown in fig. 2.
Fig.2 Diagram of fuel particles atomization When the particle size is10 nm, the number of surface atoms are 20% to the total number of full grain atoms; When the particle size is 1 nm, the surface atoms percent increases to 99%; At this time , almost all about 30 atoms are on the surface[3].

To determine the grain size of the TWIP steel Le Pera etchant was used.
The grain sizes were determined according the ISO 643:2012 standard in the heat affected zone, weld material and base material as well, the grain sizes were also converted to ASTM E112-12.
The TRIP steel side of the joint suffered greater grain coarsening in the HAZ.
The grain size of the BM increased from ~Ø 3 μm to Ø 50 μm in HAZ2 and to Ø 76 μm in HAZ1.
Russo Spena), grant number: TN2001.

Higher density of oxygen vacancies results in increased number of hydroxyl groups and hence, TiO2 nanoparticles exhibit enhanced photocatalysis.
High density of oxygen vacancies implies the presence of large number of unpaired electrons leading to large space charge polarization within the grain boundaries and consequently high dielectric constant.
The oxygen vacancies present within the grains traps electrons from the semiconducting grains and results in space charge polarization.
The highly conducting grain in T1 separated by a highly insulating grain boundary enhances e¢.
This indicates that the relaxation processes for both grain and grain boundaries in sample T1 and T2 are non-Debye type and the conductivity takes place through hopping of charge carriers.

These precipitates exert a pinning effect on grain boundaries retarding or even completely stopping softening processes.
In fact due to the lower solubility in ferrite a significant number of Nb precipitates were found in this phase.
With respect to the dependence of t0.5 on the different parameters and taking into account the limited number of data, literature reported relationships were assumed herein.
This behaviour can be attributed to the competition between recrystallization and phase transformation as both processes share the prior austenite grain boundaries as nucleation sites for recrystallized and ferrite grains.
Therefore first consumption of austenite grain boundaries by ferrite grains could prevent to some extent the occurrence of recrystallization.

A several number of investigators have measured and reported the values for the Young’s modulus (E), as shown in TABLE 1.
Micro-electroforming Ni material is anisotropic and with heterogeneity of grain size [22].
Distribution of grain size affects significantly on deformation behaviors, so it is necessary to study grain size distribution.
Micro-electroforming Ni samples with smaller average grain size have bigger surface hardness.
The material with smaller grain size has bigger yeild strength [30].