Search results

(2) Where:- average grain size,- dynamic recrystallization volume fraction, - dynamic recrystallization grain size ,- initial grain size.
Grid number is 80000; the mould is arranged as a rigid body, the whole grid division number 10000.
Simulation results analysis Analysis of the temporal and spatial evolution of grain.
A large number of deformation occurs in the middle of the process, and most of the region is in the recrystallization temperature range, so a large number of dynamic recrystallization can occur at a high speed.
It can be seen that, time which happens a large number of dynamic recrystallization is at the beginning of the forging process.

In these simulations, the triple points of grains were joined by straight segments.
The Read-Shockley expression in Eq 4 is used for the grain boundary energy [7].
The brass microstructure did not evolve significantly even after several hundred thousand iterations, while the Goss structure showed a significant growth in sub-grains after a similar number of iterations.
The same is true for a very large number of boundaries in the Goss oriented deformed crystal.
[7] G Abbruzzese, K Lücke, A theory of texture controlled grain growth – I.

Recently, with the advances in casting crystal growth technology, it is possible to grow large-grain or mono-like Si ingots in which the numbers of GBs could be greatly reduced [4-6].
Result and Discussion Fig. 1 mc-Si wafer with the presence of differently orientated grains and various grain boundaries.
We will focus on Grain No.1 (denoted as G1) and its four neighbour grains (G2-G5).
As small-angle grain boundaries are electrically active defects even at room temperature [18], it is necessary to avoid such kind of grains.
For lowering dislocation density, it is also necessary to reduce the number of “source” GBs.

The grains are represented by vertices with position kr r , where Nk ...1= (N - number of vertices in structure).
Journal Title and Volume Number (to be inserted by the publisher) 3 Values of mobility mij and grain boundary energy ijσ depend on the misorientation angle φ between two adjacent crystallographic lattices.
The minimal distance ∆, allowed between adjacent vertices, is proportional to the mean size [8] defined as ><=∆ rα with: n A r total π 2 >=< (9) where Atotal is the area of the studied "sample", α=0.025 is a proportionality factor and n is the number of triple points in the examined structure.
Journal Title and Volume Number (to be inserted by the publisher) 5 Test of the model A preliminary test of the model consists in predicting the texture change during recrystallization.
The influence of grain boundary energy was also studied.

Materials and Research Methods The objects of study were samples of VT20 alloy in ultrafine-grained (UFG), subfine-grained (SMG), fine-grained (MS), and mesopolycrystalline (MPC) states [1].
After annealing at a temperature of 820 ° C, the alloy has a grain structure with an average grain size of 16.4 μm.
One of the main structural features of ultrafine-grained titanium alloys is the predominant arrangement of dislocations in the boundary regions of grains in the absence of dislocation cells and loops inside the grain body.
During friction of the VT20 alloy with dav = 55.7 μm, not only the transfer of the sample material to the counterbody occurs, but also the formation of a large number of wear particles.
In the process of friction of samples with an ultrafine-grained structure, a significant number of wear particles are formed, in morphology and elemental composition similar to wear particles formed during friction of samples with a coarse-grained structure.

(1) In the formula: g for the test number (1 ~ 9), Wk is the weight of a performance index, (yg)k for a round of testing of a performance index, (ymin)k is the minimum value of a performance index, Rk is the extreme differential value of a performance index, k take 1 to evaluate the tensile strength, k take 2 to evaluate the elongation rate, k take 3 to evaluate the hardness.
This could be regarded as the reference volume for grain refining and modification.
(b) Fig. 3 Optical micrographs of as-cast alloys:(a) master alloy; (b) grain refining and modification alloy Grain refining and modification had satisfied results (Fig.4).
Then they were distributed in the grain boundaries of plastic α-phase.
Further, porosity was significantly reduced after grain refining and modification.

Otherwise, the grain growth was inhibited.
The liquid phases of Ba6Ti17O4 and Ba2TiSi2O8 promoted grain growth due to high solution of BaTiO3 grains in the liquid phases.
In the literature [6], it is suggested that the grain size is the most smallest in BaTiO3 ceramics (x=2.0) since a large number of such seed grains formed during recrystallization in the final stage have little chance of growing to big grains.
However, BaTiO3 grain couldn't dissolve in Ba2Ti2SiP2O13, so that Ba2Ti2SiP2O13 restrained grain growth.
Otherwise, the grains were inhibited.

In addition, a large number of nano-γ'' phases were precipitated on the broadened grain boundaries of the near-surface regions.
As a result, a large number of newly generated dislocations accumulated in the vicinity of the grain boundaries and twin boundaries, causing the little migration of the grain boundaries and twin boundaries, which appeared as a slight change in grain shape on the EBSD map.
As the compression energy input was absorbed by the top-surface regions, the energy that transferred to the deeper regions gradually decreased, resulting in a decrease in the degree of deformation and the number of recrystallized ultra-fine grains in this region.
There was an ultra-fine strengthening layer in the near-surface regions and the degree of deformation and the number of recrystallized ultra-fine grains decreased with the increase of depth.
In addition, a large number of nano-γ'' phases (less than 100 nm) were precipitated on these broadened grain boundaries, as shown in Fig. 5b.

The analysis shows that the chilling effect of the inner channel wall precipitates a large number of primary silicon nuclei, and so the primary silicon grains are refined greatly.
As a result, a large number of primary silicon nuclei can be formed and a part of them may grow up along the inner wall surface.
Therefore, a large number of small primary silicon crystal nuclei or grains can survive in this melt.
If a large number of primary silicon grains appear in the A390 alloy slurry, the distance among the grains may be very much small and the mutual interference in the solute field and the temperature field can inhibit the excessive growth of the primary silicon grains, which makes the primary silicon grains significantly fine, as shown in Figure 1.
The chilling effect of the channel wall will become weaker and the number of primary silicon nuclei in the undercooled liquid area will decrease.

The corresponding selected area electron diffraction (SAED) pattern in Fig. 1 (a) was taken from an area of 4µm in diameter, diffraction rings are exhibited implying a large number of ultrafine subgrains/grains form in the diffraction area, however, quite discrete diffraction spots exist in the rings suggesting low-angle boundaries (LABs) and relatively coarse subgrains dominate in the structure.
Fig. 2 (c) shows the grain size distribution measured from dark field images, the mean grain size is 77nm, the largest fraction ranges from 60 to 80nm, while no grain size above 180nm is detected.
The 45 steel exhibits a homogeneous and finer grain size with HABs dominating.
By contrast, the pure iron exhibits an inhomogeneous ferrite structure, which consists of a large number of coarse subgrains with primarily LABs containing an excess of extrinsic dislocations.
HRTEM was used to detect the fine particles in the ferritic matrix, and a certain number of cementite particles with sizes around 10 nm or even smaller are resolved inside the ferrite grains.