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Prior austenite grain boundaries hardly show in the pearlite microstructure without grain boundary phases.
When prior austenite grains reach a sufficient small size, only an individual colony to form in a single austenite grain [4].
The brittle fracture is common in coarse cementite largely because the cementite has a complex crystallographic structure and therefore possesses relatively small number of slip planes.
Large numbers of relatively homogeneous slips occur in both the cementite and ferrite during the deformation of fine pearlites.
Therefore, it appears that continued growth requires coalescence with another crack in the next grain at the common grain boundary.

A number of techniques have been developed to improve the processing to achieve high critical current densities Jc.
A number of practical applications would benefit from the possibility of employing a MgB2 conductor to realize DC windings that can be operated in persistent mode.
JC vs B improvement by MgB2 powder control One of the advantages of the ex-situ method is the possibility to control the properties of the MgB2 powders as grain size, purity, grain boundaries and crystalline stress.
In particular we have worked on the reduction of grain size by milling the powders.
The pinning force behavior is well described by grain boundary based pinning model, suggesting that the ball milling process increases the number of grain boundaries lowering the average grain size without any addition of lattice strain -0,1 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3 0,0 0,2 0,4 0,6 0,8 1,0 b1/2 (1-b) 2GBs pinning model H / H*K F / FPmax T = 5 K not milled Increased milling time -0,1 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3 0,0 0,2 0,4 0,6 0,8 1,0 b1/2 (1-b) 2GBs pinning model H / H*K F / FPmax T = 5 K not milled Increased milling time Fig. 9: Behavior of the normalized pinning force vs normalized magnetic field: a comparison with grain boundary pinning model is also reported.

The samples showed a high number of dislocations, and twinning was shown to be important to the yield asymmetry.
However, these processes have slower cycle times than HPDC and do not produce the fine-grained skin that protects high-pressure castings.
Microstructures in these fractured samples consisted of small, recrystallized grains, which are grouped around larger, non-recrystallized grains.
However, the number of recrystallized grains (and hence volume faction) increased with increasing strain.
Researchers at CANMET in partnership with the University of Erlangen have studied a number of processes to produce Mg metal composites.

In order to improve the piezoelectric performance of CBN, the Eu modification and texture method (templated grain growth, TGG) were applied in this material system.
The degree of the grain orientation is represented by Lotgering’s factor which calculated by the formula below: F= (P-P0)/ (1-P0) (1) Fig. 1.
The grains were aligned parallel to the tape casting direction and the grain size of textured samples is larger than that of the RO ceramics.
During sintering at high temperatures, the small equiaxed matrix particles were consumed by the large oriented templated particles, thus reduced the grain boundary area and the internal energy of the system.[11] Since grains preferentially grew along the surface of the templates, highly oriented grains were obtained.
Kucera, et al., Intrinsic and extrinsic size effects in fine-grained morpho- tropic-phase-boundary lead zirconate titanate ceramics, J Am Ceram Soc. 81 (1998) 677-688

The surface evolves toward equilibrium, which minimizes the total surface energy and grain boundary energy, by mass transport involving multiple diffusion paths; evaporationcondensation, surface diffusion, grain boundary diffusion and lattice diffusion.
The topological state of the pore channel is classified according to the number of grain boundaries Z , or the coordination number of a particle.
Beere [3] defined sintering force by considering force balance acting on a flat grain boundary plane, then the contribution of grain boundary tension was not included directly in his analysis.
The total energy is the sum of surface energy and grain boundary energy.
The grain boundary energy contributed to the sintering stress.

However, changes in phase distribution and grain morphology, or the accumulation of damage (cavitation) may compromise this assumption.
There have been a number of initiatives to improve this situation, including the use of ultrafine grained materials, modified alloy compositions and hybrid production techniques that combine an initial high strain rate deformation phase e.g. using hot drawing, with SPF [1, 2, 3] This paper focuses on the latter approach which uses an initially high strain rate to generate most of the deformation in a component and then makes use of the superplastic (SP) properties of a material to generate the more detailed geometry elements of the final shape.
Theoretically, the number of internal variables can be unlimited provided that the kinetics can be described by known equations.
The results of this process depend significantly on the algorithms used, and are very uncertain if a large number of parameters are used in the model.
Dunne, Modelling grain growth evolution and necking in superplastic blow forming, Intl.

Preparing fine grains or ultra fine grain of 7000 series Al alloy and reducing the segregation of the alloys is a very important direction for material engineers.
In addition, there are a large number of pores in both DC- TMPSF and AC- TMPSF 7075 Al alloy in Fig.2, whose dimension ranging from tens of to hundreds of microns.
There are two main reasons accounting for the formation of the equiaxed grains.
This is because the grains as the AC- TMPSF are fine and uniform.
Thus the fine grain strengthening effect is obvious.

Meanwhile, grain refinement of metal powders, the increase of grain boundary area and atomic diffusion rate, alloying elements could spread to titanium matrix when sintering.
The grain boundary energy and distortion energy around the defects were high.
Thus within the grains accumulated a large number of microdefects such as dislocations and vacancies.
It further transformed into subnetwork, and eventually refined grains.
This is due to the high energy ball milling, and crystal defects in the material increase, the number of priority areas of new phase nucleation increases.

This means in practice that there is a considerable reduction in the number of passes required for the formation of an ultrafine-grained structure.
In this condition, the microstructures of the alloys consisted of polyhedral grains with a mean grain size of ~80 µm.
For example, the ultimate strength, σB, of the Ti49.8Ni50.2 alloy increases with increasing numbers of ECAP passes at a temperature of 450 °C and reaches a maximum value of 1250 MPa after 8 passes while the yield strength increases by more than two times reaching a maximum of 1150 MPa.
This approach introduced in [7,29] is based on formation of ultrafine-grained structures with high-angle and non-equilibrium grain boundaries capable of grain-boundary sliding (GBS).
It should be stressed that recent experiments investigating deformation mechanisms in nanostructured materials have confirmed a number of the results of computer simulation [32,56,57].

Length of the grains is up to 2 micron.
And the diameter of the need-like grain is up to 500 nm.
When the needle-like grain grows to a few micron, and it will further grow in other directions and if the detritic grains met with other grains would stop growth.
The need-like grains grow from the center which is covered by nickel to the outer side.
The migration of NiSi2 precipitate from the rear to the front interface leaves behind a trail of needle-like Silicon grain.