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The use of process modelling has proven to be a useful tool in understanding the results from the extrusion experiments and limiting the number of interactions during extrusion. 1.
The low temperature to avoid grain growth limits the processing window (maximum temperature and time at maximum temperature) to which the powder can be exposed with modest or without grain growth.
High pressure is useful for consolidation, but there is limited number of commercially viable processes using high pressure.
Therefore, the effect of temperature rise on flow stress is believed to be not so high and its effect in grain growth is not significant.
Results from simulations runs have been used in helping to understand the extrusion experiments and to reduce the number of experimental tests required.

The average grains size and shape factor of solid grains were affected by melting mechanism and grain growth mechanism.
D=i=1N4AiπN (1) F=i=1N4πAiPi2N (2) where Ai and Pi are the area and the perimeter of the solid grains, respectively, and N presents the total number of solid grains.
As shown in Fig. 7(b), with the increasing of soaking time, the number of intragranular liquid droplets decreased, and large cloud-like solid grains were became into small spherical grains.
Differently, there were no intragranular liquid droplets in the microstructure and a large number of small isolated grains were formed.
Besides, it can be found that the number of recrystallized grains decreased and the size of them increased.

Size and number of the void at the position of the 10mm diameter increased further than that at R part of the 4mm diameter.
Figure 4 shows the grain boundary maps obtained by EBSD analysis for each specimen at R part.
In comparison with both specimens, the grain size in the specimen made from the carbon fixed chip became slightly finer.
However, size and number of the void of the magnesium-carbon alloy were less than those of the A91D magnesium alloy.
Fig.6 Macro observation of fracture surface in various number of cycles for each specimen.

Dimple and a number of torn edges appeared in the fracture surface after 4 passes of ECAP.
With the passes of ECAP increasing, the material got strong plastic deformation, resulting in a large number of dislocation and serious grain boundary distortions which produce more sub-grain to be recrystallization nucleus and produce the driving force for dynamic recrystallization.
The mechanical properties, except the relationship with matrix α-Mg, depends largely on the particle shape, size, number and distribution of Mg2Si phase [[] S.L.
For fine-grained materials, the stress can be distributed to more grains, thus reducing the stress of each grain.
The smaller grain sizes, the development of deformation coordination of the grain boundary.

The results shown that glass ceramic phase is CaNb2O6, grain size is about 30 nm, The two-stage controlled heat treatment is beneficial to control of the number and size of grains, thus affecting the transparency of glass ceramic and luminescence properties.
Fig.3 shows grain morphology, size and crystal distribution of grain in the residual glass phase.
Changes of particle size and distribution are evident along with the extension of heat treatment temperature. heat treatment temperature on the morphology control of microcrystalline glass is very important, with the extension of heat treatment temperature, the grain number increase gradually.
Heat treatment temperature too short will result in fewer grains and inadequate growth.
Heat treatment temperature is too long, and leads to grain growth is too large, appear gathered themselves together, and results in uneven distribution of grain size, transmittance drop too fast.

Note the sharp transition between the equiaxed grains from the top of one layer and the dendtritic grain growth that initiates at the bottom of the molten pool.
Instead, the grains grow continuously through the deposit layer boundaries in the intermediate region, with finer equiaxed grains in the final (top) layer.
Note that the depth of the molten pool during the preheat pass is the maximum depth that occurs, regardless of the number of subsequent layers deposited.
The width of deposit increases with increasing number of layers due to spreading of molten pool from build up of heat in deposit. 4.
After two layers, banding is clearly evident where the microstructure segregates with distinct regions of dendrites, columnar grains, and equiaxed grains.

When the sample annealed at 350℃ for 5s, the first recrystallized grains were observed in the vicinity of the grain boundary.
A large number of fine secondary particles in the as-homo specimen was formed in the Al matrix due to the effect of the homogenization treatment.
It can be seen that large deformed specimen with fine recrystallized grain are recrystallized faster than low deformed specimen with coarse grains.
In generally, the metal materials cause an increase in dislocation density and a decrease in crystallite size during deformation, and a large number of HAGB and LAGB are generated as the reduction rate increases.
When primary recrystallization is complete, the structure is not yet stable, and further growth of the recrystallized grains may occur by the migration of grain boundaries with the grain-boundary free energy as the driving force.

To some number of powder wire samples was added: nickel, cobalt and tungsten.
Grain size was defined by GOST 5639-82 under ×100 magnification.
Microstructure consist of martensite, which are forming inside the former austenite grains, and small amount retained austenite as separated islands and thin layers of δ-ferrite located on the former austenite grains borders.
Microstructure consist of martensite, which are forming inside the former austenite grains, and small amount retained austenite as separated islands and thin layers of δ-ferrite located on the former austenite grains borders. .
Per the results of calculations obtained dependencies, the adequacy of which was checked by actual values in index of the average approximation error: , (1) m - the number of observations; – calculated value of resulted index; – real value of resulted index.

SiC crystalline grain is round grain shape or ellipse shape, crystalline grain size is about 50nm and well-distributed on Si3N4 crystal boundary, small number of SiC crystalline grain exist in Si3N4 crystalline grain.
We find that SiC crystalline grain in Si3N4 crystalline grain is smaller than the grains on crystal boundary, most of them is under 20nm.
In Si3N4 single materials Si3N4 crystalline grain grow soundly, most of crystalline grain is long column shape, the ratio of diameter is 5-6, and there are unusual big crystalline grains.
This shows nanometer SiC crystalline gain can restrain the growth of Si3N4 crystalline grain effectively, especially SiC crystalline grain on Si3N4 crystal boundary which nail-picked on Si3N4 crystalline grain.
Fig.3 shows SiC crystalline grain nail-picked on Si3N4 crystalline grain.

No secondary phases were observed at the grain boundaries and triple grain junctions, which guaranteed good optical property of the sintered bodies.
Fig.5 (a) and (b) were the triple grain junction and grain boundaries of the specimen, respectively.
The grains were divided by straight grain boundaries and combined contiguously with each other without mini angle grain boundaries, which were helpful to the transmittance of transparent AlN ceramics.
The grain boundaries and triple grain junctions were clean, no secondary phase was observed.
Yu et al. [16] have pointed out that secondary phase and its distributions in the AlN grains would greatly decrease properties of AlN ceramics by the grain boundary phase layer which disrupted the continuous of AlN grains.