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In addition, the grain-refining was another researching emphasis, in which rare earth [2] and Al-Ti-B master alloy [3] were used to refine grain in Al alloy.
In addition, La and Ce are the surface active element to reduce the interface tension of liquid alloy and to decrease the nucleation power (Gibbs energy) of the grain, in which the critical nucleus radius decreases and the formation of nucleus is easy to increase the number of nuclei in the melt [6].
Besides those Al-RE compounds, there are a number of α-Al grains in the reaction product, in which the grains have the fine size when the reaction just finishes so that they can sever as the nucleating site for primary α phase during the solidification of Al alloy.
Finally, there are some primary α phase with non-round-like and the coarse columnar grains.
Lu, Effective nucleation particles in grain refining of Al-Ti-B master alloy, The Chinese J.

The microstructures show that the deformed grain structure is inhomogeneous, that caused the grain sizes and grain orientations in HAZ to become different.
The energy E (Joules) in a rectangular laser pulse of peak power V (kw) and width τ (ms) is given by: τ⋅= VE (1) The mean outer power is equal to the number of Joules issued by the laser in one second.
During laser forming, temperature increased to the limit below the surface melting, the grain structure is deformed inhomogeneously, leading to the formation of zones with different grain sizes and grain orientations.
And the grain size is not same in the different layer, the size of the grains in the upper layer is smaller than that in the bottom layer because of the affection of the overlapped laser spot.
The size of the grain is not same in the heat affected zone.

Calcium and strontium can refine the grain size and the secondary phases.
With the increase of calcium, reticular Al2Ca phase distribute at the grain boundaries.
Linear intercept method described in ASTM standard E112-88 was used to evaluate the grain size.
It clearly shows that the grain size of AM80 alloy decreases with increasing quantity of Ca added.
Kainer: US Patent number: 6139651, 2000

This may due to the precipitation of fine b phased grains.
This may due to the precipitation of fine b phased grains.
This may be due to the size and distribution of precipitates of b phased grains.
This may due to the precipitation of fine b phased grains.
Acknowledgement This research was financially supported partially by the Strategic Young Researcher Overseas Visiting Program for Accelerating Brain Circulation (grant number: R2403), funded by the Japan Society for the Promotion of Science (JSPS), for which the authors wish to express their gratitude.

The bainitic ferrite laths become longer and narrower with increasing niobium content and cooling rate, and niobium also shows a tendency to decrease polygonal ferrite grain size. 1.
Introduction A large number of studies have been made on transformation behaviors [1-3] and microstructural characteristics [4-6] of ultralow carbon microalloyed steels containing niobium.
The specimens were compressed at 1150℃ up to total 40% at the strain rate of 10/sec to refine austenite grain size by recrystallization without NbC precipitation.
The decease in Bs temperature is attributed to the following two factors: (1) Nb atoms segregate at prior austenite(γ) grain boundaries and suppress bainite nucleation by decreasing the grain boundary energy; (2) shear growth of the bainitic ferrite [1] becomes difficult due to the solution hardening of Nb in γ matrix.
The ferrite grain size and pearlite amount slightly decrease with increasing Nb content.

There are mainly two kinds of flow in liquid phase: either from the region with relatively large hydrostatic compressive stress to the region with relatively small hydrostatic compressive stress or from the grain boundaries perpendicular to the compressive axis to the grain boundaries with a certain directional angle to the compressive direction.
As for the alloy with characteristics of thixotropy, when the shear rate is constant, its apparent viscosity will decrease with increasing the shear time, which makes shear stress decrease continuously, and when the shear stress is removed, the apparent viscosity will recover its original number.
Otherwise, liquid phase may also shift due to different forced states in continuous grain boundaries or the changing of volume resulting from deformation.
It is possible for the liquid phase to flow to the region with tensile stress under the condition of normal compressive stress or to flow from the grain boundaries perpendicular to the compressive axis to the grain boundaries with a certain directional angle to the compression direction, as shown in Fig.4.
(4) The higher the strain rate, the more uniformity the microstructure, otherwise, the lower the strain rate, the more serious the segregation of solid-liquid phase. 3) Liquid phase may flow from the regions with relatively large hydrostatic compressive stress to the regions with relatively small hydrostatic compressive stress, or flow from the grain boundaries perpendicular to the compression axis to the grain boundaries with a certain directional angle to the compression direction.

Most of the diameter of Ceramic grains are in the range of 0.5-5 μm, existing some amorphous phase among the grains.
Backscattered electron SEM of 5000 times surface image of samples Z1 and Z2 are respectively shown in Fig.1 ‘a’ and ‘b’, we can see brighter grains distributed evenly in the surface of synthetic zircon with size from 0.5 μm to 5μm, and there is some darker glass phase in the middle of these grains, the grains may be (Zr, Ce)O2 and (Zr, Ce) SiO4 crystal, the amorphous phase is SiO2, the glass phase in sample Z1 is more than Z2 obviously, and the crystal grains distribution in Z2 is more tight, indicating better crystallinity.
On the grain of sample Z1, distributing a small amount of small another brighter particles, its may be crystals containing Ce.
Main mineral composition of dots 1, 2 in dark area in Fig.2 is SiO2 with lower average atomic number, and a small amount of ZrO2 and Ce2O3; While the points 3,4T in bright area contain more ZrO2, meanwhile, content of Ce more than dark area.
Surface of attained samples is smooth, with density of 3.9 g/cm3, and greater shrinkage of 22% pre and post sintering, the lower compression force, the higher shrinkage.②The zircon ceramic form is composed of dense grains with size of 0.5 μm, existing a spot of micro-holes, and containing some glass phase in middle of these grains.③The gel after washed by ammonia, crystals of (Zr, Ce)O2 and (Zr, Ce)SiO4 can be obtained with fewer impurities, and better crystallinity.

This definition does not include the microstructure, i.e. the position of the grains in the material.
After 45min heat treatment single peaks corresponding to individual recrystallized grains occur (fig.2a).
The slit was 0.1mm and very small grains are imaged.
Bigger grains are seen as longer streaks with the streaklength corresponding to the grain diameter in scanning direction (transverse direction).
The Recrystallization of AlMn1 Investigated by Pole Figures by onal Orientation-Location Space with Hard X[6 [7 Number.

The study of the applying of equal channel angular pressing(ECAP) method on grain refinement by acquiring great plastic deformation was widely investigated [3-5].
So sub-micron even nanometer microstructure will be gained, and the strength and plastics will be improved greatly with fine grains.
The model mesh took auto-meshing method, and the number of node, the number of element and the number of polygon on surface were 1256, 8000 and 1562, respectively.
Stress and strain distribution of cross section of the sample is not uniform, so the dimension of grain after single pressing pass is not equivalent.
On the contrary, it is necessary to choose large mould angle for the material with high deformation resistance to accumulate strain by adding the pressing pass number.

At increasing strain, the distance between the original grain boundaries will eventually be in the order of magnitude of the subgrain size.
The same material condition has been used for FSSW experiments in prior investigations to allow for a direct comparison of the evolved microstructure according to the same initial microstructure, which showed elongated grains dependent on the prior rolling with an average grain size of 81.7 µm [10].
The torsion axis is clearly visible in horizontal direction (a), in which the original large grains are only twisted.
In the microstructure investigations, higher strained areas can be identified by zones of smaller grain size, see Fig 4.
The grain refinement in both cases takes place through ongoing lattice rotation and formation of new grain boundaries during the process.