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The HPT processing was conducted at RT under quasi-constrained conditions [3] under a pressure, P, of 6.0 GPa and a rotational speed of 1 rpm and through numbers of revolutions, N, up to 5 turns.
The initial microstructure of the as-extruded material before HPT consists of a bi-modal grain distribution with a fraction of >50% of coarse grains having ~25 µm surrounded by several finer grains having ~4-5 µm as shown in Fig. 1(a).
Thus, the evolution in grain structure depends on the initial grain size, the size of the new grains and the amount of imposed strain within magnesium alloys.
Fig. 4 Variation in strain-rate sensitivity for the Zn-Al alloy before and after HPT for increasing numbers of turns [13].
By contrast, the inset shows the HEA exhibited significant increase in hardness after HPT with increasing numbers of turns.

The borderline of the minerals (grains) is obviously, the shapes of mineral grains are most of ellipse, but abnormity, the size of the mineral grains are different.
And some small cracks in grains gradually disappear.
And in this phase, cracks basically develop along the mineral grains border.
The number of cracks determined by length is shown in Table 2.
We call Mn as ratio of cracks number.

Keywords: grain growth, triple grain junctions, grain boundaries, kinetics, nanocrystals, interfaces.
Triple Lines and Triple Line Tension in Polycrystals The grain boundaries (GB) in a polycrystal are high energy regions, in the sense that the energy of a (large) number of atoms at the boundary is larger by 1E∆ relative to the energy of N atoms in the bulk of the grains.
'N atoms at the TJ have energy larger by 2E∆ relative to the same number of atoms at the GB's.
The total excess energy E∆ of the polycrystal, relative to a perfect crystal with the same number of atoms is Fig. 1-Section of a symmetrical triple line, showing the grain boundaries (GB) and the triple junction (TJ).
The distribution, shown in Fig. 3, was truncated at 8.1/ =>< aa ; the initial number of grains was 10000 and the initial average diameter was = 1.

Compared with pure aluminum without any inoculant, although the macrostructure of the alloy only with 0.2%Sc can obtain slightly refined, the refining effect is not ideal due to the existence of large number of coarse columnar crystal.
Tnsile strength Rm /MPa Prcentage elongation A/% Hardness /HV 1# 43.53 42.30 22.40 2# 61.79 39.90 33.93 3# 51.13 40.07 31.66 4# 68.83 46.76 28.03 The grain refinement of aluminum alloys mainly depends on the number of the nucleus during nucleation and the speed of crystal growth in solidification process.
By analysis that the addition of Sc elements can increase the composition undercooking of the alloy and reduces the nucleation temperature in the center region of the melt to some extent, which prompts the nucleation rate increase and makes the number of equiaxed grains increased slightly in the center area.
So the grains of the alloy with 0.2%Sc can achieve a little refined, but the refinement effect is not desirable for the existence of a large number of columnar crystals.
Grain Refinement of Aluminium.

Based on the radiographs, the variations of equiaxed grain number and dendrite growth rate with time were measured and analyzed.
The dynamic processes of grain nucleation, free growth, grain interaction and impingement are of great importance to further understand the grain refining mechanism.
Fig. 4a shows the number of visible grains in the field of view (6 × 8 mm2) as a function of time.
It can be clearly seen that for the sample without the application of DC, the grain number increases gradually with time in the beginning and reaches a plateau (18) about 385 s later, while with DC treatment, the grains nucleate much later (about 850 s) compared to the condition without DC treatment, which indicates longer incubation time, and the grains number increases sharply to reach a plateau (163) only 175 s later.
Fig. 4 Time evolution of grain number and dendritic growth rate without and with the application of sequence DC. t = 0 reing is applied. presents the time when cool Fig. 5 shows an image of dendrite fragmentation, as denoted by a red square in Fig. 3c.

If the model represented a larger volume, with greater time an equiaxed grain structure would evolve from the original ribbon grains and normal grain growth would follow.
Journal Title and Volume Number (to be inserted by the publisher) 7 Deformation Structures Produced with Changes in Strain Path Microstructure Evolution.
In most commercial Al-alloys it is difficult to prevent grain growth when the starting grain size is submicron.
a b c d t = 0 t = 7 t = 22 t = 40 Journal Title and Volume Number (to be inserted by the publisher) 9 Continuous Recrystallization in Severely Deformed Alloys Severely deformed alloys contain elongated grain fragments with an average HAGB spacing (ω ≥ 15°) in the submicron range.
On Ultra-Fine Grained Materials, ed.

A relative number of grains with deformation twice as high as the average deformation of the sample has been obtained.
Each square cell of the grain grid here is a model of an individual polycrystalline grain.
The two-dimensional distribution allows defining a relative number of grains with an exhausted plasticity resource.
The relative number of grains with a strain, which is half times more than the average one, increases in a nonlinear way along with a higher reduction rate of the sample (Table 1).
The number of grains, deformations and stress-strain state of which correspond to the selected intervals, were recorded into table cells.

When the number of grains through the thickness is only 1 or 2, the deformation is quite inhomogeneous.
However, the grain number increase to 4 or 5, the plastic deformation is far more homogeneous.
When the number of grains through the thickness is 1 or 2, all grains are located in the surface area and thus only surface grains.
Once the number of grains over the thickness is more than 2, some of which are interior grains and thus interior grain appear.
(2) When the number of grains through the thickness is small, surface grains are in majority and the surface grains constraint dominates the overall roll force.

“P2” is expressed the occupation of the mass, which particle size is less than 5mm.To study the influence of fine particle content P2 on creep property, prepare five groups of samples with fine particle contents of 10%, 20%, 30% ,40% and 50% respectively to correspond to sample number G1, G2, G3, G4 and G5.
The number G0 represents the grain composition of the original soil sample.
Coarse and fine grains are evenly distributed and coarse grains form skeleton with 30% fine grain composition, contributing to high shear strength and small creep deformation.
Coarse grains cannot contact very well with fine grains with more fine grains, and more time is required to stable creep with small soil rigidity and α.
Coarse and fine grains are evenly distributed and coarse grains form skeleton with 30% fine grain composition, contributing to stable creep deformation in a short time and large α.

A further increase in hardness can be achieved by (3) taking advantage of spinodal decomposition for HPTed Al-Li-Cu alloy, in which nano-scale precipitates of δ’ phase are successfully formed within ultrafine grains, irrespective of the higher number density of grain boundaries.
Introduction In general, strengthening mechanisms of aluminum alloys include strain hardening, hardening by grain refinement (e.g. ultrafine-grained hardening), solid-solution hardening and precipitation hardening [1].
Fig.1 illustrates equivalent strain dependence of both the attained hardness and increment/decrement in hardness during aging (i.e. age-hardenability) for a number of age-hardenable aluminum alloys [3, 4].
The encircled numbers represent the improvement of hardness by our proposed three strategies to achieve concurrent strengthening.
The corresponding TEM microstructures reveal that Cu containing precipitates such as Q’ and Q phases are newly formed, resulting in the increased number density (thus volume fraction) of transgranular precipitates.