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The top surface comprises equiaxed grains, and columnar grains are observed in the cross-section.
As the grains grew larger, the grain boundaries became more obvious, as shown in Figs. 4 (a) and 4(b).
The number of these structures increased with time, and their growth was intertwined and overlapping.
Additionally, the number of particles in each rod-like structure also depended on the reaction time; it was diffusely molded between the particles, and joined together.
The morphology of the cross-section comprises columnar grains and the top surface is composed of grains that are almost equiaxed grains.

The modification of liquid metal by electric pulse (EP) is a novel method for grain refinement.
These tests experimentally testified Wang's electric pulse modification (EPM) model that was built only by phenomenology and hereby the mechanism of grain refinement resulting from EPM is further elucidated.
So the present work focuses on the structure changes of the liquid aluminum remelted from EP-modified casting in order to experimentally examine Wang's EPM model and hereby illuminate the mechanism of grain refinement resulting from EPM.
Structural Parameters EP-Modified Unmodified Atomic density 0.0529 0.0531 Correlation radius (rc)[nm] 0.925 0.780 Average atom number per cluster (�at) 174 119 Coordinating number (�s) 9.063 8.546 The nearest neighbor distance (r1)[nm] 0.285 0.285 It is especially significant for the investigation of EP-modified liquid aluminum structure at 750°C, since at this temperature, the liquid aluminum was EP-modified and the optimal grain refining effect was obtained.
Large numbers of stable nucleus lead to inevitably the refinement of solidification structure.

Quantitative analyses of the grain size were conducted using “Metilo” computer program.
This method requires conduction of large number of plastometric tests.
Changes in grain size in time function were calculated on the basis of dependence [7]: , (5) where: D(t) – average grain size in time function; X(t)s – fraction of recrystallized volume (X(t)D+X(t)s); DRX – grain size after dynamic and static recrystallization; Do – initial grain size.
The microstructure, after deformation at a temperature of 250°C, consists of fine dynamically recrystallized grains on primary grain boundaries and deformation twinnings (Fig. 2a).
Presence of high number of deformation twins was found.

The average grain size D was determined by Mendelson intercept method [11], which is based on the SEM micrographs using D=1.56×C/(MN), where C is the random lines length on the micrograph, M is the magnification of the micrograph, N is the number of the grain boundaries intercepted by the lines.
Therefore, it is attributed to the increase number of grain boundaries caused by the decrease of ZnO grain size.
As a result, the ZnO grain size decreased.
Cerium mainly segregated at the grain boundaries.
CeO2 acted as an inhibitor of ZnO grain growth due to the decrease of average grain size with increasing CeO2 content.

Theoretical analysis Fig. 1 the heat source position From micro view, a large number of the grains rub and cut the surface of the workpiece, causes the grinding heat.
There are three heat source positions around the grain.
They are in the grain-workpiece (wear plane), chip-workpiece (shear plane) and chip-grain interfaces, as shown in the Fig. 1.
vs vw grain The chip and grain interace chip C D A B The grain and workpiece interface The chip and workpiece interface The heat generated in grinding process can be expressed as following: tot w sh gc q q q q = + + （1） Comparing with heat generated in grain-workpiece and chip-workpiece interface, the heat generated in chip-grain interface is so small, so it can be ignored.
The heat partition between the grain and workpiece interface.

Journal Title and Volume Number (to be inserted by the publisher) 3 Steel C Si Mn P S Cr Al N Nb Ti DIN EN 10084 0,14 - 0,19 ≤ 0,40 1,00 - 1,30 ≤0,035 ≤0,035 0,80 - 1,10 - - - - 16MnCr5+Nb 0,19 0,23 0,74 0,011 0,012 1,19 0,041 0,026 0,045 0,001 Table 1 Chemical composition of the investigated steel, mass content in %.
This gives improved grain size stability at higher temperatures that has been confirmed by grain growth investigations.
The grain size distribution is given by means of the cumulative frequency of grains belonging to different ASTM classes; the approximate average grain size is represented by the 50% cumulative frequency.
Figure 4 Calculated nitride and carbide precipitates. 700 600 500 400 300 200 100 0 700 600 500 400 300 200 100 0 NbC NbN TiN AlN 1000 1200 1100 Temperature, °C Mass fraction of precipitates, ppm Journal Title and Volume Number (to be inserted by the publisher) 5 ening temperature (GCT) is associated to the following limit in this investigation: all grains must be of ASTM size 5 or finer; grains of ASTM size classes 4 and 3 are tolerated up to a total volume fraction of 10%; grains of ASTM size class 2 or coarser are not permissible [6/10].
The grain size stability at elevated temperatures is attributed to a sufficient amount of precipitates which guaranty a grain boundary pinning.

Microstructural parameters covered included the morphologies of martensite, the sizes of the prior austenite grains, grain sizes and grain boundary misorientations, and the number density and size of precipitates.
Results and Discussion Number density, size and chemical compositions of NMIs.
The total number of NMIs decreased by 7% as a result of ESR.
The number of NMIs per mm2 in all size ranges decreased as a result of ESR except the number of NMIs per mm2 in the size range 6-10 µm which remains unchanged.
Using Image J software, the numbers and sizes of all precipitates were calculated.

The fatigue behavior of metals is strongly governed by the grain size variation.
In many microcrystalline (mc) and ultra-fine grain (ufc) metals and alloys, strengthening with grain refinement has traditionally been rationalized on the basis of the so-called Hall-Petch mechanism [2, 8].
Here the increased resistance to plastic flow is explained as depending on the pile-up of dislocations at grain boundaries and to the mechanism associated with the much more difficulty of the slip transfer between adjacent grains.
Even if a grain refinement leads to an increase in the number of cycles to failure at the same stress levels investigated, the results for very close microstructures results a strong function of the ductility.
The dislocation generation and locks formation is larger as decreasing grain size because of the grain boundary density, in this way the more the structure is fine the more such phenomenon is pronounced and the hardening increases as decreasing the grain size.

As illustrated in Fig. 2, the microstructure of AF, QF, GB, and DP exhibited irregular-shaped grains, and the EBSD analysis was applied to estimate corresponding effective grain size.
The effective grain was mainly composed of high-angle boundary.
There are general two methods to define effective grain size of microstructure.
The other one is equivalent diameter, which can be estimated by equivalent the irregular-shaped grain to circle, and the diameter of circle is regarded as effective grain size [11, 12].
The dimples and tearing rides involved in the fracture surface were typical features of ductile fracture, implying that large number of energy was consumed during fracture.

For the sintered Ni, the 3D reconstructed volumes revealed the grain connectivity, necks formation and particle rearrangement in the densification process.
MgB2 is characterized by transparent grain boundaries being also a light, non toxic and relatively cheap compound composed of just two elements.
The synthesis of this material suffers from a number of drawbacks, related to the volatility and oxidation of Mg which hinder the precise control of the stoichiometry and impurification features.
By post-processing the reconstructed volume data one can derive valuable local and statistical information such as grain sizes, contact area, number of contacts between grains, density variation, etc.
This allows the determination, by visual navigation inside the reconstruction, the determination of the number of inter-filament contacts.