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Accordingly, it was evident that multi-forging was very effective on grain refinement and grain size uniformity.
Reaching the mushy zone, liquid is formed by preferential melting at grain boundaries with high energy state, and penetrates into high angle boundaries of recrystallized grains.
The RAP microstructure consisted of equiaxed grains with the presence of liquid phase at some grain boundaries.
The increment of the multi-forging strain accelerates recovery and recrystallization kinetics and provides the larger number of recrystallization sites.
In addition to high angle grain boundaries, the liquid formed in grains can be penetrated into low angle boundaries formed by multi-forging at higher RAP temperature.

The grain refining effects of Al-Ti, Al-TiC and Al-Ti-C master alloys on commercially pure aluminum were compared, and the grain refinement mechanism of TiAl3 and TiC among master alloys was discussed.
With people’s increasingly deeper understanding of the phenomenon of grain refinement, they have put forward many ideas and theories of the mechanism of grain refinement.
Results and discussion The grain refinement effects of master alloys Al-Ti, Al-TiC and Al-Ti-C on pure aluminum.
When Ti wt% reaches 0.05%, with the increase in the addition amount of refinement agent, since TiAl3 particles added can exist stably for a long time in the melt and become cores of heterogeneous nucleation during crystallization of α-Al, thus the sample grains are refined significantly, until after the addition amount of refining agent reaches 0.07% of Ti wt%, when there exist in the melt a sufficient number of TiAl3 particles, the refining effect reaches a saturated state.
But with the extension of the heat preservation time, a large number of TiAl3 particles eventually dissolve, and only a small amount of residual TiAl3 becomes the core of aluminum nucleation.

Sandglass extrusion is an ultrafine grain size method.
Due to the repetitive and multiple extrusions, large strain can be accumulated and ultrafine grain size can be obtained.
Introduction Severe plastic deformation (SPD) is a kind of method for producing ultrafine grain size material.
This method can produce ultrafine grain size by SPD.
By using of this method, the ultrafine grain size material can be obtained.

The larger number of crystal nuclear are formed and the even shape and size grains are obtained.
By comparing with Fig.2 b),c),d), it can be obviously observed that crystal structure grows more even and regular and the number of grain grows more and the grain is refined.
It can be concluded from Fig.2 that slope length has significant effect on the grain number and shape of the alloy microstructure.
It can be observed that crystal structure grows more even and regular and the number of grain grows more and the grain is refined when the vibration voltage grows higher until to 80v.
So the broken arms can be new nuclear which increase the number of grain.

Aiming at the grain-size analyzing result of some shallow sea area sediments, calculates the grain-size parameter by graphical and moment methods separately, studies the correlation of the grain-size parameter results.
Median is the size when the grain content of the cumulated curve of grain distribution is 50%.
The mean size), at last, we can get the moment of distribution if the sum of the size product was divided by the number of grain size.
So we can make sure that the grain-size parameters derived from moment method are the parameters which can be got through the median of sediment grain size.
(8) Remark：—the frequency when the grain size is (standard)；—the grain size of the first i size bound(standard)；n —the sum of the size grouping.

Both of the master alloys remarkably reduced the size of α-Al grains, impeded the dendritic growth and promote the equiaxed growth of α-Al grains in Zn-50wt.
Two typical master alloys, Zn-45Al-5Ti-0.3C and Zn-45Al-4Ti-1C(the number before each element is its content in wt.% in the master alloys) , were produced in this study.
The α-Al grains in the three original Zn-50Al alloys without the addition of master alloy all present complex dendritic structure which contains a number of primary and secondary (and even some ternary) arms, with the length of primary arms exceeding 400μm at 690℃ and 200μm at 610℃(Fig.4(a)-(c)).
Grain refinement mechanism of Zn-Al-Ti-C master alloy.
When more TiC particles are added into Zn-Al melt through the master alloy, more α-Al grains are formed and smaller the α-Al grain size in a Zn-Al matrix.

In a micro metal forming process, it is possible that only a small number of grains are directly involved.
To investigate the effect of grain size on the CWR of micro copper rod, the study employed annealing techniques to enlarge grain size and the equal channel angular extrusion (ECAE) to refine the grains.
Grain Refinement Equal Channel Angular Extrusion.
Grain Size and Hardness.
The grain refinement clearly increased the strength of the copper.

The increasing number of ECAP passes influenced particularly homogeneity of microstructure and the number of high-angle grain boundaries (HAGB).
The EBSD data indicate that the number of high-angle grain boundaries (θ>15°) measured in the samples after ECAP and subsequent creep exposure is strongly dependent on the number of ECAP passes (Fig. 7).
In the areas with the higher number of HAGB the grain boundary sliding will be more intensive than in the surrounding areas [8].
The dependence of number of high angle grain boundaries on the number of ECAP passes.
The number of ECAP passes effects homogeneity of microstructure and the number of high angle grain boundaries.

The mechanism of grain refinement was discussed.
The number and the misorientation angle of kink bands evolved at low strains rapidly increase with deformation, finally resulting in development of new grains in large strain.
Namely, grain refinement from 22.3µm to 0.8µm can result in enhancement of grain boundary sliding taking place in such fine-grained structures [5], leading to reduction of flow stress as well as improvement of ductility.
The average grain size was about 0.36µm.
The average grain size decreases with repeated MDF during temperature drop, resulting in evolution of the minimal grain structure of 0.36µm in ∑ε=4.8 at 423K.

Analysis shows that GSS creep in geological and glacial materials can be accounted for in terms of four “universal”, mesoscopic scale constants of average values, γ0= 0.197, γB = 0.415 J.m-2, N = 8.9 and a = 0.166, where γ0 is the average shear strain associated with a basic boundary sliding event at the level of the atomistics, γB is the specific grain boundary energy (assumed to be isotropic),N is the number of boundaries that align to form a mesoscopic boundary glide plane and “a” is a constant that obeys the condition 0grain shape and size distribution in the material.
It is emphasized that in geological and glacial materials the grain size varies from extremely coarse to fine grain sizes.
The number and distribution of such free volume sites at a boundary will depend on its misorientation.
When the grain shape is irregular and there is a grain size distribution, “a” obeys the condition 0 < a <0.50 [8].
N (0number of boundaries that align to form a plane interface . γB (0<γB<1.5 Jm-2) is the specific grain boundary energy (assumed to be isotropic).