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Chen et al. [9] investigated the effects of inclusions, grain boundaries, and grain orientations on the fatigue crack initiation and propagation behavior of the 2000 series Al alloy.
The number of the cycle times was pre-set according to the conditions in experiments, the experiment would be interrupted if it reached the number, and then the middle surface short fatigue crack on notches would be observed and recorded, after that the experiment continued.
There were several cracks successively appeared during the preliminary stage of fatigue life, the cracks propagated along the slip band of the grains and most of them grown very slowly(Figs. 3(a)-(b)).
References [1] Deyan Yin, Huiqun Liu, Yuqiang Chen, etc, Effect of grain size on fatigue-crack growth in 2524 aluminum alloy, Int.
Xu, Effects of inclusions, grain boundaries and grain orientations on the fatigue crack initiation and propagation behavior of 2524-T3 Al alloy, Materials Science and Engineering A 580(2013) 150–158

The higher the linear velocity of the grinding wheel is, the more times the abrasive grain touches the ground metal layer per unit time.
While coefficient of heat conductivity of carbide is very little, the cutting heat focuses on a thin metal layer being ground which softens the surface layer of the cutting tool, so that the grinding wheel could planish and push-smear the surface Journal Title and Volume Number (to be inserted by the publisher) 53 and smooth the corrugation which is left over by a previous abrasive grain except grinding metal [3].
So if the granularity of the grinding wheel is smaller, there are more abrasive grains in unit volume.
Then at a certain grinding velocity, load of every abrasive grain will be relatively less under the same grinding conditions.
In the course of grinding, the scraping and ploughing of abrasive grain become dominant and the ground surface is pushed, smeared and smoothed.

A number of works have been done to study the influence of different factors on the performance of the XLPE cable insulation.
There are a number of different sizes of grains in outer specimen.
Meanwhile, the grain size of inner specimen in inside cable is significantly bigger than the grain size of inner specimen in outside cable.
Under the influence of stress and temperature, the grain size of outside specimens is oppositely lager, and the grain size of inner specimen is also larger.
The grain size of the outside samples is larger than that of the inside samples.

The grain boundaries of 6061 aluminum alloy are the weakest area and microcracks initiate at the grain boundaries parallel to tensile direction under shear stress.
There are a number of reports on ductile damage and ductile normal fracture, where the ductile normal fracture (based on the initiation, growth and coalescence of voids) and shear fracture (based on shear band localization) are addressed as two primary fracture forms for the ductile materials [2-5].
(2)The grain boundaries of 6061 aluminum alloy are the weakest area and microcracks initiate at the grain boundaries parallel to tensile direction under shear stress.

The parameters controlling the value of Eb are the grain size and barrier voltage (Vgb) according to the following equation: Eb = VgbNg (1) where the Ng is the average number of grains per centimeter [8].
The nonlinearity in the ZnO varistor is a grain boundary phenomenon where a Schottky-like barrier to majority charge carriers (electrons) exists in the depletion layers of the adjacent grains [1].
The negative surface charge at the grain boundary interface (electron traps) is compensated by the positive charge in the depletion layer in the grain on the both sides of the interface.
According to this assumption, Gupta and Carlson [10] proposed a grain boundary defect model for ZnO varistors.
As illustrating in Fig. 4, positively charged donors (Sni4+，VO2+，TaSn+, NbSn+) extending from both sides of grain boundary are compensated by negative charged acceptors (VSn4-, CoSn2− ) at the grain boundary interface.

Introduction Zirconium and hafnium-based ceramics (borides, carbides, and nitrides) display a number of unique properties, including extremely high melting temperature and hardness, low volatility, and high thermal and electrical conductivity.
For more SiC is located at the grain boundaries of ZrB2 and ZrC, it is more difficult for crack to extend.
Different with the crack propagation of ZS and ZSC5, for ZSC15, the propagation is rather straight because there are less SiC grains in ZrB2 and ZrC grain boundaries to resist crack propagation and make it deflect.
This remarkable decrease may be attributed to the less formation of SiC in ZSC15, as SiC generally acts as a grain-growth inhibitor at the grain boundary [3,11].
With less SiC formed, the grain of ZrB2 and ZrC will over grow and form agglomeration, the large grain size and inhomogeneous distribution is harmful to the strength of the composite.

Particularly in automobile electronics and semiconductor electronics, an increasing number of varistors are being used for low-voltage applications.
C0 and C are the capacitances per unit area of a grain boundary biased with zero and V volts, respectively.
Additionally, the presence of Ta2O5 generates molecular oxygen, which diffuse to the interfaces and will be absorbed at the grain boundary.
According to the analysis of Bueno, some metal atoms will facilitate the chemisorption of oxygen on the grain boundary [8].
These negative charged defects, ScTi−, diffuse to the grain boundary and promote the concentration of electron trap states at the interface.

The spotty textures indicate the large initial grain size.
The spread is associated with an increase in grain numbers due to fragmentation from the original larger grains by continuous recrystallization mechanisms.
The Gd containing specimen has a more refined substructure, and contains profuse serrated high angle grain boundaries, compared to the La containing case.
The latter substructure is characterized by larger microbands typical of hot deformed Mg [10], and a large number of elliptical grains with high angle grain boundaries that have further sub-divided into high angle parts.
The more continuous contours seen in all pole figures confirms the increase in number of grains, evidence of recrystallization.

Introduction Grain nucleation is an important phenomenon in polycrystalline materials such as metals, and most ceramics.
The critical nucleus size is defined as the number of atoms in a cluster with energy equal to the activation energy for nucleation.
By rotating the sample over a small angle ∆ω0 = 1.6° around an axis perpendicular to the beam, a number of grains give rise to diffraction spots on a 2D-detector.
Given the experimental conditions the radius of the smallest detectable grain is about 2 µm.
The nucleation rate is determined by counting the number of ferrite spots in the {200}- and {211}-rings on the detector as a function of time, since an individual spot originates from one individual ferrite grain.

Table 1 Chemical composition of the Mg-based alloy (mass fraction/%) Alloy Number Zn Mn Ce Mg 1# 1.80 0.95 0 Bal. 2# 1.92 0.91 0.19 Bal. 3# 2.12 0.93 0.28 Bal. 4# 2.06 0.92 0.39 Bal. 5# 2.14 0.91 0.57 Bal.
After extrusion, the grains of alloy are refined substantially.
This is because that Ce can refine grains.
On the one hand, the compounds formed by Mg and Ce distribute in the grains and grain boundaries, which inhibits the migration of grain boundary resulting in the refinement of recrystallization grains.
So the grains of alloy are obviously refined.