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Recently, a novel and economical processing, i.e. combustion synthesis in high-gravity field, has been taken to prepare solidified fine-grained TiC-TiB2 composites [2-4].
Fig. 1 XRD pattern of solidified TiC-TiB2 composite (a) 500g (b) 1000g (c) 1500 g (d) 2000 g (e) 2500 g Fig. 2 FESEM microstructure of TiC-TiB2 composite prepared under different high-gravity acceleration (a) 500 g (b) 1500 g (c) 2500 g FESEM images and EDS results showed that a large number of randomly-orientated, fine TiB2 platelets were uniformly embedded in or around the irregular TiC grains, and Cr metallic phases were distributed between TiC and TiB2 phases, whereas a few of α-Al2O3 inclusions were also observed in the form of the isolated particles, as shown in Fig. 2 (a).
Although transgranular fracture took place in TiC grains, as shown in Fig 3(b), fracture behavior of TiC is completely different from that of α-Al2O3 inclusions.
As high gravity acceleration reached 2500 g, the ultrafine-grained microstructure with the average thickness of TiB2 platelets smaller than 1 μm was achieved.
FESEM fractographs showed that fracture mode of the ceramic presented a mixed one of transgranular fracture in Al2O3 inclusions and TiC grains with the intergranular fracture along TiB2 platelets, however, because of shrinkage cavities inside or around the Al2O3 inclusions, Al2O3 inclusions tended to develop the large crack sources, whereas TiC grains presented a classic cleavage fracture behavior.

The results show that Er can improve the feature of cast structure and decrease the grain size.
With increasing heating temperature, the dissolution of eutectic Mg17Al12 phase first took place, resulting in the primary dendritic grains coarsening into interconnected non-dendritic grains.
With heating continuously, the residual interdendritic γ-Mg17Al12 at the edges of the primary grains melted in succession and the primary grains separated into small polygon grains.
In the dendrite structure of AZ91D alloy, as shown in Fig. 1 (a), a large number of coarse γ-Mg17Al12 phase precipitates continuously along the grain boundary of α-Mg matrix to shows a net-like feature.
With heating continuously (Fig. 6(b)), the grain boundaries almost melted and the primary α-Mg grains segregated so as to form small irregular polygon solid particles.

It was studied the zirconia grains influences on platinum materials.
Crystal grains are finer grain size and homogeneous.
The results show the dispersion strengthened Pt materials fabricated by powder metallurgic method are dense, structure morphology is lath fibrous tissue, and the crystal grains are finer grain size and uniform.
The dispersion particles hinder the movement of dislocation to grain boundary, which makes the softening of platinum matrix obviously slow.
Fig. 4 The tensile strength of the comparison chart Strength is the ability to resist deformation of the material, which is controlled by the number of dislocations and dislocation movement.

The PMZ is rather narrow, only several grains wide.
The length of the cellular growth was approximately equal to the average grain size in the clad zone because the rate of the cellular growth from the semi-melted grains in the PMZ seems to be similar to that of the equiaxed grains in the CZ.
As a result, the grains in the CZ have a typical equiaxed shape.
A requirement is, of course, that the melt contains a sufficient number of seed crystals to facilitate heterogeneous nucleation of new grains ahead of the advancing solid/liquid interface.
No grain growth and coarsening are observed in the HAZ.

Table 1: Main cold rolling route parameters Final tube Mother tube dimensions fext - thickness Initial heat treatment e pass (%) (min-max) Total number of passes Total number of intermediate heat treatments e total (%) cumulative strain J37 18.3 - 1.25 1150°C-1h 22-24% * 6 2 76 K12 16.5 - 1.41 1250°C-0.5h 20-22% 6 3 76 K15 16.2 - 1.78 1200°C-3h 17-19% 8 3 80 *Except the first pass which corresponds to a cold work of e ~9% The obtained ODS ferritic grade has a nominal composition of Fe-14Cr-1W-0.3Ti-0.3Y2O3.
For K15 material, the reduction ratio per pass is lower (epass ~17-19%) and the total number of passes is larger (8 instead of 6).
Both cladding tubes exhibit an anisotropic microstructure with fine grains elongated in the working direction.
However, as illustrated by Fig. 4.b, there is a significant difference since in some areas of the K12 cladding tube microstructure presents a bimodal microstructure made up of both fine elongated grains and coarse equiaxal grains.
Fig. 3: TEM micrograph of J37 ODS cladding tube: elongated ferritic grains a) b) Fig. 4 : TEM micrographs of K12 ODS cladding tube: a) elongated ferritic grains, b) equiaxial ferritic grains As discussed in paragraph 3.3, this microstructural anisotropy induces anisotropic mechanical behaviour.

The first laser pass induces throughthickness strains close to yield, whereafter their magnitudes decrease with increased number of laser beam passes.
A comprehensive mapping of the longitudinal stresses as function of the number of laser passes is given.
As a result the grains in the HAZ were visibly refined.
In addition the grains in the region immediately below the top part of the HAZ (sub-region) are much smaller (approximate grain size less than 3µm).
Dynamic recrystallization in combination with phase transformation leads to grain refinement (3.7µm) in comparison to the grains in the near-surface region.

The absence of preferred misorientation angles between α-grains indicates that α-grains are not formed out of already solidified β-grains by a solid state phase transformation. 1.
For multiphase materials with a relatively complex phase diagram, undergoing a number of solid state phase transformations between solidification and room temperature, different powder particle sizes may provide snapshots of rapidly quenched non-equilibrium microstructures for different cooling rates.
Besides, numerous particles contain α-phase grain and β-phase grains as well.
The Ti-α-phase grains are usually supposed to be transformed out of Ti-β-phase grains [11].
The α-grains growing from the same parent β-grain are thus characterised by related misorientation angles.

Microstructure of Zn-1.0Cu-0.2Ti alloy before and after creep tests at 100℃ with the load of 60MPa for 48h is shown in Fig.3, it is seen that a large number of grains crack appears, which led to the formation of lots of trilateral and quadrilateral grains.
Grain crack and grain boundary sliding are associated with stress action.
Grain cracking frequently occurs inside the large grains.
Moreover, atoms diffuse from pressure grain boundary to tension grain boundary during creep tests of Zn-1.0Cu-0.2Ti alloy, deformation consequencely occurs independent for each grain toward tensile stress direction.
The grains' deformation was attributed to the synergistic action by grain boundary sliding among grains, otherwise excess vacancies will be created among pressure grain boundaries.

Obviously, the number of tests involved does not allow to make any general statement.
The effect of a 45° inclination to the grain direction was also investigated.
The number of spins required to fully develop that load, varies according to the timber modulus of elasticity (MoE).
Then, suddenly the grain rupture made the screw spin and the pressure go down to almost zero.
The inclination to the grain direction did not show a significant influence on the results.

During the solidification process of Al-Cu alloys, pulsed currents was added into the melted alloy in the crucible .The change of temperature curve and microstructure about the alloy was investigated in such conditions by temperature-recording instrument and optical microscope.The results showed that pulsed currents can shorten the temperature region of crystallization and refine the grains of the alloy,which crush the dendrite and make the solidification structure non-dendrite, presenting columnar and equiaxed grains which are distributed evenly and whose space between crystals are reduced.
It showed that adding alternating current, direct current or magnetic field during the process of solidification can refine grains and perfect organization structure, so it is paid close attention[1-5].Nevertheless, it has not been got an good agreement about the influence mechanism until now, so this technique is just in research phase and not be used widely.
However, with currents continuously increasing, initial crystallization temperature point of the alloy increased more distinctly, but the range of crystallization temperature enlarged together with pulse current amplitude, and corresponding organization began to merge and grow up into larger crystalline grain, at the same time, we found that grain size was larger as current value was higher by comparing figure3(d), figure3(f) and figure3(h). 2) Mechanism discussions When lots of similar solid agglomerate atoms exit in melted metal, they are short-range order and long-range disorder.
Moreover,because of the,larger agglomerate atoms can be cut or snapped, which increase the numbers of the small ones which can become nucleation center and make structure refined eventually. 3.CONCLUSION During solidification of alloys, adding of pulsed currents could refine grains and made dendrites present as columnar and equiaxed grains.
Controlling the growth of grains and making structure refined eventually were the other advantages.