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Microcracks propagation is evidently impeded by grain boundaries at low stress level and high stress ratio.
Detailed test procedures (stress level and stress ratio) and number of specimens are shown in the Table 2.
Microcracks slow down or stop near grain boundaries.The fact that microcracks have difficulty in traversing grain boundaries means that the crack plane has some favorable orientation with respect to the slip plane.
Microcrack propagation was clearly affected by the orientation of grains.
(4) Microcracks slow down or stop near grain boundaries.

However, the achievement of full density depends on a number of factors including the shape, size and plasticity of the particles, hydrostatic pressure applied, processing temperature, deformation rate and actual plastic strain experienced by the particles.
In the case of Al, it was thought to be related to easier recrystallisation at room temperature and decreasing number of pores acting to pin grain boundaries at the higher pressure [25].
The stability of the material was attributed to the presence of pores which pinned grain boundaries and thus prevented grain growth.
Although Fig. 5 Compressive stress versus strain curves showing increases in both strength and strain to fracture with increasing number of passes in Al consolidated from nanosized particles by ECAP at 400°C.
A number of promising materials with both enhanced strength and good ductility have been achieved.

Natural nanostructure in polycrystalline silicon was utilised for charging islands and its grain boundaries were modified by a multi-step annealing technique to form grain-boundary tunnelling barriers.
Subsequent annealing increases the grain-boundary tunnelling barrier height and resistance.
Introduction A single-electron transistor (SET) is a novel device where the on-off states can be formed by a single-electron, without any statistical fluctuation in electron number[1,2,3].
( ) �� � � �� � �−�� � � �� � �−�� � � �� � � = Tnk qV Tk qV m Tk qnVI B B B B P 2 sinh exp 2 2 2/1 * π (1) , where q denotes a carrier charge, m* an effective mass, kB the Boltzmann constant, VB a barrier height, T temperature, n number of grain boundaries, and V an applied voltage.
We found that the charging island is made of crystalline grains covered by an oxide GB barrier[4]

Controlling the grain size is also very difficult in the case of forgings.
In the present study, forged IN 718 alloy having 300 mm grain size is tested at room temperature (RT).
The material shows equiaxed grains with grain size varying from 150 mm to 290 mm.
The loop shape also significantly varied as the number of cycles increased.
Number of reversals.

This type of technology is based on the effect of adhesive friction between the rotating tool and the workpiece material, which has been well studied in a number of papers.
In the process of embedding into the surface of the tool blanks and conducting the process of friction stir welding a number of processes of plastic deformation, fragmentation and material flow along the tool contour take place [6].
In the stirring zone the material is mainly represented by submicrocrystalline equiaxial recrystallized grains.
In the channel, the zones of fine-grained structure and deformed structure alternate in layers and are rather heterogeneous.
The distribution of areas with different grain sizes in the structure is less heterogeneous.

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.
At the early stage of short cracks’ fatigue life, initiation is the main forms of fatigue damage (Figs.3 (b)-(d)), and the increasing in numbers of short crack instead of in length by the influence of the grain or phase boundary barrier.
The crack growth data are showed in Fig.5 and Fig.6, where x-axis is presented in two different life forms, one is the numbers of cycles; the other is the percentage of life.
The fatigue crack length at the plateau regions was 20~100mm, which equaled 1~5 grain boundary length.
The influence of barriers will not disappear until the crack length increases to 1~5 grain boundary length

Grain Size and Adhesion Strength of the V8C7 Coatings Produced In Situ Xin Wang1, Lisheng Zhong1*, Xi Zhang1, Yunhua Xu1,2, Hong Wu2, Yonghong Fu2 1School of Materials Science and Engnieering, Xi’an University of Technology, Xi’an 710048, China; 2Shaanxi Key Laboratory of Nano Materials and Technology, Xi’an 710055, China *zhonglisheng@xaut.edu.cn Keyword: In situ, V8C7 coating, Grain size, Adhesion strength.
The grain size of NbC is 350 nm on average.
Due to the microstructure by ultrafine-grained NbC, the hardness and elastic modulus of the coating are 21.1 GPa and 376.1 GPa, respectively.
When loaded to 70N, as shown in Fig. 6 (c), the number of lateral cracks on the bottom of the scratch obviously increased, and there are some cracks running through the bottom of the scratch.
As the number of cracks increases, the number of broken holes increases, the width of particle breakage area at the scratch edge increases.

The heat is inversely proportional with the alloy grain sizes.
Introduction For thousands of years the development of practical alloy systems has been based mainly on one principal element as the matrix, as in iron-based, copper-based, and aluminum-based alloys, limiting the number of applicable alloy systems, even though a substantial amount of other elements is incorporated for property/processing enhancement [1,2].
The fusion zone grain size is less than elsewhere, from the Fig.
Fig.5 Sample 5 after Welding Dendritic grain size is shown in Fig.6. a and b are the grain size of horizontal and vertical, respectively.
Four samples grain size were measured and draw the diagram of grain size versus heat, as shown in Fig.7(a) and Fig7(b).

However, regardless of the number of compression cycles, the centre of the sample looks undeformed.
In case of the samples deformed up to 4 hits, this zone is composed of large grains, which grain boundaries are mostly distinguishable.
With an increase in number of MAC cycles to 8, many parallel deformation bands appears in this zone.
The distinction between grain interiors and grain boundaries at zone of large plastic strains is almost impossible.
This clearly indicates the grain refinement process.

The specimens are numbered from sample 1 to sample 20.
After a fatigue crack initiates and begins to grow, every a certain cycles, the test is interrupted, the cycle numbers and short crack growth rates are recorded using the optical microscopy to take photos for specimen’s front edge at notch root.
For a polygon grain, drawing the grain’s circumscribed circle, and the circumscribed circle’s diameter is selected as the characteristic size of polygon grain, while for a rectangle grain, the length of rectangle’s diagonal is measured as the characteristic size of rectangle grain.
Using a statistical average method, the characteristic sizes of polygon grains and that of rectangle grains are individually measured, and the mean value of the characteristic sizes of polygon grains and that of rectangle grains are calculated as 0.15mm and 0.17 mm.
The mean size of polygon grains is approximately equal to that of rectangle grains, and the average value of polygon grain’s and rectangle grain’s characteristic size is calculated as 0.16mm, which is determined as the grain size of GH4133B superalloy.