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Results Grain Growth.
Recrystallization and Grain Growth.
Subsequent grain growth is affected by Nb in solution and Sarkar et al. [5] showed that the grain growth rate can be described by (5) where M is the grain boundary mobility, g is the grain boundary energy and P is an effective pinning parameter.
It is still required to develop more accurate grain size calibration relationships for these steels, i.e. currently laser-ultrasonic measurements have to be supplemented with a limited number of metallographic grain size measurements to benchmark the laser-ultrasonic data.
Even so, laser-ultrasonic measurements provide entire grain growth kinetic curves as long as the grain structure can reasonably be described with an average grain size.

In order to improve the accuracy of quantitative calculation of abrasive flow machining, the influence of geometrical parameters of abrasive grains on machining is analyzed by representing the geometrical shapes of abrasive grains with three parameters, namely height of abrasive grains, cone angle and wear height, establishing the calculation model of blunt conical abrasive grains for abrasive flow machining, deducing the force formulas of abrasive grains and calculating the maximum cutting depth in the event of smooth flow of abrasive grains in the boundary layer.
To solve this problem, researchers have made a large number of studies on the mechanism and quantitative calculation of abrasive flow machining in recent years, for instance, Haan put forward that the existence of decentralized pressure in abrasive flow machining can increase the cutting action of abrasive flow [1], Jain brought forward a calculation model of abrasive flow machining based on neural network method [2, 3], Gorana established the mechanical model of calculating the force of spherical abrasive grains, deduced the calculation formula of axial force and radial force, and made experimental verification and comparison [4], Kar, Tang Yong, Zhao Jia et al.
In the calculation model of the forces of abrasive grains, abrasive grains are surrounded by viscoelastic polymer carriers.
Position of the abrasive grain x = 20mm.
Fig. 4 Correlation between the grain size a Fig. 5 Correlation between the cone angle θ and cutting and cutting depth h of abrasive grains depth h of abrasive grains (Granularity remains unchanged) Fig. 6 Correlation between the wear height ∆a and maximum cutting depth h of abrasive grains Conclusions Three geometrical parameters, namely height of abrasive grains, cone angle and wear height, all have significant influence on the maximum cutting depth of abrasive grains, wherein the grain size parameter a has great influence and can be controlled by selecting different granularities of abrasive grains.

ECAP produced a grain size less than 1 mm, and FSP provides the formation of UFG structures with an average grain size ranging from 0.7 to 2.6 mm [3-8].
The size of the particles was estimated using at least five arbitrarily selected micrographs, the total number of individual measurements for each condition was ~1000.
The grains are completely separated by HABs (Fig. 4a, c, e and g).
The distributions of the grain sizes are shown in Fig.5.
The authors acknowledge with gratitude the financial support received through the German Academic Exchange Service (Funding program number 57048249, Research Grants for Doctoral Candidates and Young Academics and Scientists 2014/15).

The grain boundaries were found to have high number densities of nanoclusters as well as chromium and tungsten segregation which pin the grain boundary to minimize creep and grain growth.
The number density of the nanoclusters was so high that some impingement of the nanoclusters in the plane of the grain boundary was evident.
In addition to the high number density of nanoclusters, the grain boundary regions between the nanoclusters were also found to be enriched in chromium and tungsten.
In addition, significant numbers of nanoclusters are present on both grain boundaries and dislocations.
The grain boundaries were found to have high number densities of nanoclusters as well as chromium and tungsten segregation which pin the grain boundary to minimize creep and grain growth.

Aside from the average grain size of samples, the size of recrystallized grain reduced with the MAF pass number, too.
Fig.4(b) shows the numbers of MAF passes dependence of the average grain size of samples.
It could be observed that the grain size decreased with the pass number increasing.
With the pass number increasing, the following changes in microstructure can be observed: a) A large number of fine grains appeared after the first pass, which indicated the occurrence of DRX; b) The number of fine DRX grains increased with the pass number increasing; c) The size of recrystallizated grain reduced with the MAF pass number, which indicated that the DRX occurred in the recrystallized grains.
This is due to the volume fraction of dynamic recrystallization grains increased with pass number increasing, and the stretched deformed grains are depleted by finer recrystallized grains eventually. 4) YS, UTS and elongation of alloy increased with the pass number increasing.

The microstructure formed by severe plastic deformation is an unusual structure which can be hardly characterized only by the mean grain size especially after low number of ECAP passes.
The first, intersection count NL- the mean number of intersections between grain profile boundaries and unit lengths of random test lines.
The second, profile count NA - the mean number of grain profiles per unit area of the observation window.
An increase of the value of CVa on the microscopic level is influenced by higher number of fine grains present in the microstructure.
Thus, it is very difficult to determine quantitatively real grain size after low number of ECAP passes.

Introduction Grain boundaries are diffusion short circuits and consequently the major part of material transport will occur by grain-boundary diffusion in nanomaterials where a large amount of atoms can lie on grain or interphase boundaries (about 50% for a grain size equal to 5 nm; 20% for a grain size equal to 10 nm).
It is well known from classical treatments of grain- or interface diffusion that there are three different grain-boundary diffusion regimes: type A, B and C.
-In the A kinetics regime (Dv t) 1/2 >> d), the different diffusion zones overlap with each other resulting in a macroscopic homogeneous diffusing distribution which appears to obey Fick's law as for a homogeneous system with an effective diffusion coefficient (Deff) equal to an average of Dv and Db weighted in the ratio of the number of diffusing atoms in the grains to that in GB [9]: Deff = g Db + (1-g) Dv, (2) where g is the grain-boundary volume fraction (g ≈ δ/d; the factor of proportionality depends on the grain shape, but is in the order of unity).
In fact, owing to the high number of GBs and the synthesis conducted under UHV conditions, the grain boundaries must be purer in the first type of materials (not enough impurities to cover all grain boundaries).
Perraillon: Grain Boundary Structure and Kinetics, (R.

The images of iron contaminated grain boundaries in multicrystalline Si are obtained.
It is shown that the grain boundary XBIC contrast is 2-3 times smaller than the EBIC one.
The dependence of grain boundary XBIC contrast on the X-ray beam width is calculated.
As our estimation shows only about 20% of a total number of generated excess carries is collected due to the limited diffusion length value (25 mm).
EBIC (left) and XBIC images (right) of two grain boundaries in mc Si.

In order to control WC grain size and get a microstructure with fine grain size during the sintering process, WC grain growth in WC-Co cemented carbide was investigated.
The possible reason on the grain growth was showed which includes the normal grain growth (NGG) and the abnormal grain growth (AGG).
Ostwald ripening means large grains growing at the expense of small grains.
But the shape of WC solid grains is faceted, and abnormal grain growth (AGG) is often observed; a few grains grow exclusively while the growth of the other grains is suppressed.
It is observed that the grain size of WC increases rapidly with increasing temperature and there are more pores in number at 1150 o C than that at 1200 oC.

Ultrafine grain.
After the ECAP processing using 4 passes, equiaxed grains (~300 nm grain size) and elongated grains were formed for both samples.
To compare the degree of surface damage produced in these samples at the same number of stress cycling, OM photographs taken at nearly same numbers of cycling are shown.
Once this specific number of cycles had been exceeded, both the number and area of the damaged regions showed a significant rise.
The number of cycles required to initiate 0.03 mm-length crack is longer in DLP than OFC.