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Hence, the SPS technique can suppress grain growth during the sintering processing.
As shown in Fig. 3, in contrast to the submicro-grained composites, many fine cavities are observed to form at multiple grain junctions in the nano-composites.
Using the SEM micrographs, the grain size was determined by counting the number of grains.
Assuming the grains to be spherical, the average grain size, d, was determined to be 1.225 times the apparent grain size, which was calculated from the average cross sectional area per grain [12].
The grain size is almost similar to the particle size of the staring powder, suggesting that grain growth during the sintering is highly limited.

During annealing, the microstructure is characterized by a mixture of increasing amounts of recrystallized grains and decreasing amounts of strain hardened grains.
The maximum grain diameters of the recrystallized grains were measured by image analysis in metallographically prepared samples.
Recrystallized grains having the largest grain size were assumed to be the first nucleated.
Temperature (°C) Alloy 1 Alloy 2 Alloy 3 Alloy 4 375 0.0009849 0.0003108 0.0002475 0.0001979 500 0.0007502 0.0007039 0.0006003 0.0004295 In metallographically prepared samples, the number of grains recrystallized (N) by image analysis was also found as a function of annealing time.
Acknowledgements The authors gratefully acknowledge the financial support of the Scientific Research Projects Coordination Unit of Kocaeli University (Project number: 2013/072).

Penelle1,2,c 1 Univ Paris-Sud, UMR8182, ICMMO, Laboratoire de Physico-Chimie de l'Etat Solide, Orsay, F-91405 2 CNRS, Orsay, F-91405 a denis.solas@u-psud.fr, b Thierry.baudin@u-psud.fr , c Richard.penelle@u-psud.fr Keywords: Asymmetrical rolling, Fe-36%Ni, Texture, Grain refinement.
Finally, a simple model was developed in order to establish the condition to obtain either shear texture or grain refinement.
It is reasonable to consider that grain refinement is related to dislocation accumulation when = 0.
With this condition, the latent hardening is high and one could expect to enhance the grain refinement.
As a consequence, the asymmetrical rolling could be used to generate shear texture but also grain refinement depending on the deformation path and the amount of shear deformation.

In case of martensitic SS 420, segregation of P and Cr along the grain boundaries at this temperature range has been shown to cause grain boundary embrittlement [3].
A number of wide cracks were visible with the naked eye on the valve seat surface and these cracks had propagated across the thickness.
A number of wide cracks were present in the failed valve seat.
Grain dropping and fine cracks propagating along the grain boundaries are clearly evident.
In addition, all the cracks observed in the valve seat (Fig. 2 and 3(b)) were along the grain boundaries indicating grain boundary embrittlement.

Any process decreasing the number density of precipitates thus immediately leads to lower creep resistance.
No primary and secondary particles could be found; prior austenite grain boundaries are noticeable.
The annealed condition (specimen 3, Fig. 2c) reveals martensitic structure with distinct prior austenitic grain boundaries.
Mean austenite grain size was measured to be approximate 22µm.
The opposite holds for MC: a significant number was found via TEM, although simulations predicted a smaller fraction of 0.01%.

It shows that Sc additions can refine the grain size and change the growth morphology from dendrite to small equiaxed grains.
There are more equiaxed grains and fine grains when the content of Sc was 0.2wt.%.
Elongations (δ) of 1#~5# alloy 2.3 Analysis and discussion According to the theory of non-homogeneous nucleation, the refinement of as-cast alloy grains depends on the nucleation particles number of unit melt and the role of effective nucleation particles.
Therefore the effect of grain refinement is enhanced significantly.
Thus the alloy grains were refined and the strengthening effect of fine-grain is apparent.

Introduction Due to the large number of industrial applications involved, the study of the austenite decomposition reactions has been an important research topic in physical metallurgy.
Whereas, when the volume fraction of ferrite was low, the grain size was taken as the average value over at least 50 measurements of individual grains.
The number of nucleation sites was taken proportional to the austenite grain boundary area per unit volume: N = N0 /dγ where dγ is the austenitic grain size and N0 is the number of sites available for nucleation by unit interfacial area.
The physical model has only one parameter to be adjusted empirically, i.e. the number N0 of sites available for nucleation by unit interfacial area.
Left: Ferritic grain size as a function of the cooling rate.

The results showed that the substrate temperature obviously influenced the grain size of ZAZO films.
Due to the increasing of Al and Zr concentrations into ZnO lattice, the Al ions created an abundance number of free electrons in the ZnO lattice, and in turn, the electrical conductivity increased.
The ZnO thin film deposited at 200℃ is poorly crystallized and has a small grain size.
With increasing of Al concentration into ZnO lattice, the Al ions create an abundance number of free electrons in the ZnO lattice, and in turn, the electrical conductivity increases [13, 25].
In addition the grain size reaches to the maximum of 14.67nm at 250 ◦C and then decrease.

Zirconium sheet also complete recrystallized at the annealing temperature of 580℃ but the crystalline grain has the tendency of growing.
Zirconium and zirconium alloys show impressive corrosion resistance in harsh corrosive medium such as most of the organic acid,  inorganic acid, strong base and a number of the molten salt.
From figure 1(c) and 1(d), it can be obtained that the grain grown up as novel and orthoscopic equiaxed grain perfectly, and the average size of grain was about 10μm.
In this situation, the reasons of the grain growth phenomenon were that large grain swallowed small grain and the total system free energy declined after grain boundary migration.
When the annealing temperature was up to 580 ℃, the recrystallization was also acquired, but the difference is that the grain was grown up.

The fine structure produces a considerably large number of grain boundaries in the material.
In addition, the bonding strength between grains may be very strong, because there are no secondary phases or impurities in the grain boundary.
The sizes of the cBN grains of specimens obtained at temperatures lower than 2300 °C are small, less than 0.5 µm, however, the cBN grains rapidly become larger above 2400 °C.
Most of the grains grow as large as 5 µm or more at 2600 °C.
The fine-grained high-purity polycrystalline cBN has a fine structure and has no secondary phases or impurities in the grain boundary.