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Methods Fine equiaxed Al-xCu (x=6, 8, or 15 wt% Cu) samples were produced by casting with Al-5Ti-1B grain refiner.
Based on direct in-situ imaging of the loading geometry and microstructure, different initial 2D packing fractions , , were generated in the DEM samples by slightly adjusting the size and number of cohesionless DEM grains.
After the onset, the percolating network was lost, and grains floated until they contacted grains at the top of the sample, as shown in Fig. 1a and b.
The new solid network created by the floating grains has a solid fraction , suggesting that 38% is the approximate percolation threshold for this irregular globular grain morphology.
In contrast, grains in the high solid fraction alloys pushed one another apart during grain rearrangement known as Reynold’s dilatancy [2].

The results show the following effects: the porosity number at the both sides of the welding seam fusion line may be decreased significantly by adding the high frequency pulse energy; The analysis to the high frequency pulse action mechanism has been carried out according to the above conclusions to provide the technology theory base for improving and enhancing the aluminum alloy welding joint performances.
Introduction After the molten pool has been solidified, the final mechanical properties and physical properties are closely related to the crystal grain sizes and microstructure defects during the crystallization process.
The uniform and tiny equiaxed grain structures may enhance the welding seam mechanical properties; on the other hand, the inhomogeneity of the non-tiny equiaxed grain structure and microstructures may significantly reduce the welding seam performances.
The crystal grains may be effectively refined through the heterogeneous nucleation [1], the physical field processing [2], the temperature control[3] and other methods; however, most of these methods may be difficultly applied due to the characteristics for the welding molten pool, such as the short residence time, the large temperature gradient, the high arc temperature and so on.
It may be seen from the microstructures near the welding seam fusion line before and after applying the high frequency energy that the porosity number and size are significantly decreased at the both sides of the fusion line after applying the high frequency energy. 150um 150um (a)Un-compound pulse energy (b) Compound pulse energy Fig.4 Microstructures of fusion-line Ultrasonic cavitations phenomenon can be induced when ultrasonic vibration is applied to the molten pool; the capitation bubble resonance frequency may be determined by the following equation [5]: (1) where: ƒ - the ultrasound wave frequency(kHz); d - the bubble diameter(cm);k- the specific ratio ,for the gas inside the bubble, k=cp/cv; p0 -the liquid static pressure(Pa); ρL -the liquid metal density(g/cm3).

The images indicated that annealed films were in orderly forms, where the nano sized grains were formed with a clear grain boundary.
This feature is very important, since the electromechanical responds can be arose from the orderly oriented grains.
The higher dielectric constant is due to the increasing number of domain population and its wall motion [4] hence improved crystallization process of the thin film after annealing.
When the grain size increase, the domain that carrying the dipoles will be increased as well [6].
The dielectric constant and grain size were found to increase with annealing temperature.

Introduction Nanocrystalline materials, are understood to be single- or multi-phase materials with a grain size smaller than 100 nm in at least one dimension.
Owing to the extremely small dimensions, nanocrystalline materials are structurally characterized by a large volume fraction of grain boundaries or interphase boundaries.
This may significantly alter a variety of physical, mechanical, and chemical properties compared to those of conventional coarse-grained polycrystalline materials [1].
The number of rings which represent nanocrystalline phases increases (see Fig.1.IV), when the crystallization degree increases.
The sample magnetization µ0M (measured at the field of H = 700 kA/m) slightly increased with the number of laser pulses and the laser energy density (1.20 T- 1.35 T).

The matrix deposition on both surfaces of the SiC fibers and nanowires induced smaller matrix grains in the nanowire-reinforced composite, and thus a higher hardness and elastic modulus than the conventional one after an ion irradiation.
On the other hand, the SiC matrix grows from both surfaces of the SiC fibers and nanowires and there are more impingements of the growth fronts due to a larger number of deposition sites in the WA-CVI composite.
This leads to a smaller grain size of the SiC matrix in the WA-CVI composite than that of the conventional counterpart as shown in Fig. 3.
Our supplementary irradiation studies on a single crystal SiC and CVD SiCs with various grain sizes suggest that a small-grained SiC has a higher resistance to an amorphization [5].
The matrix deposition from both surfaces of the SiC fibers and nanowires induced smaller matrix grains in the WA-CVI composite, and thus a higher hardness and elastic modulus than the conventional one after an ion irradiation.

Microstructure observation revealed that the grain sizes of the composites increased with increasing solution temperature and decreased with more severe deformation.
It can be seen that the grain sizes increases with increasing solution temperatures.
It can be seen that the microstructure under different solution temperatures are of equiaxed grain of different sizes, and that the grain sizes increases with increasing solution temperatures.
By compare Fig.2 with Fig.3, we can saw that grain sizes decreased with increasing deformation strains under the same temperatures.
Acknowledgement It is a project supported by natural science foundation of shanxi province China (project number: 2011011021-1).

It is known that the microstructural effects of the two mentioned processes can be distinguished because the creep type deterioration can cause cavities along the grain boundaries [2], while the fatigue process causes the appearance of micro and later macro cracks through the grains.
The diameter of the investigated middle part was 10 mm, the grain size of samples was in the range of 45-50 μm.
The grain size and shape do not changed, only the appearance of minor inclusions along grain boundaries can be observed in some samples.
Curves belong to 0, 250, 500, 750 and 1000 number of cycles.
Fig.5 Normalized relative phase angles vs. number of cycles.

It has been reported[7] that the ultrasonic attenuation coefficient(α) can be expressed in terms of the size of the grain(D) containing only one phase with no anisotropy.
The correlation between the average ferrite grain size in 0.16% C steel and the ultrasonic attenuation was plotted on a logarithmic scale(Fig. 2) to obtain the slope, m, which turned out to be approximately 2.03 instead of the value of 3 predicted by Eq.(3).
It is interesting to note that the same coercivity is obtained if the inter-lamellar spacing is the same, even though the prior austenite grain sizes(PAGS) differ from each other.
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G Fig. 2 Log-log plot of average ferrite grain size vs. ultrasonic attenuation.
The increase in the value of MBNrms in this material with increasing aging time can be attributed to the increase in the domain wall velocity, which is due to the decrease in the number of carbides resulting from their coarsening.

However, pernicious stray grain formation often occurs.
Multi-Scale Mathematical Model Procedure (1) Heat transfer model Significant difference of crystallization-independent shape of solid/liquid interface is attributed to a number of combinations of laser power and welding speed through thorough steady-state Rosenthal heat flow solution.
(1) where Γ is the Gibbs-Thomson coefficient, R is the dendrite tip radius, Pei is the Peclet number for i, mi is the liquidus slope, C0,i is the initial concentration for i, ki is the partition coefficient for i, ζc(Pei) is a function of the Peclet number, Iv(Pei) is the Ivantsov solution and Ghkl is the average temperature gradient near dendrite tip
Axis-symmetrical growth kinetics attenuate dendrite tip undercooling to counterbalance nucleation and subsequent growth of stray grain formation.
Numerical analysis of stray grain formation during laser welding nickel-based single-crystal superalloy part II: multicomponent dendrite growth.

Chevalier et al. [5] reported that LTD by the t-m phase transformation of zirconia grains starts on the surface upon contact with water.
Studies have reported that decreasing the grain size (GS) of t-zirconia reduces the thermodynamic force leading to t-m transformation.
The aging of zirconia has many consequences, including surface degradation with grain pullout.
In this phenomenon, adjacent grain boundaries (interface) cannot tightly control monoclinic grains because of volume expansion accompanying phase transformation.
Acknowledgement The authors thank the Universiti Kebangsaan Malaysia (UKM) and Ministry of Higher Education for their sponsorship under grant numbers GUP-2012-060 and FRGS/1/2013/SG06/UKM/01/1.