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Decrease in grain size after extrusion as compared to as-cast condition illustrates the fact that during hot extrusion, dynamic recrystallization takes place due to an accumulation of dislocations at the grain boundaries [21,24,26].
Fig.3 Variation of grain size of UTCB processed AZ31B nanocomposites in as cast and after extrusion [21,26].
It has been reported that uniform distribution of nanoparticles by UTCB technique in the Mg-matrix activates additional slip systems in otherwise limited number of slip systems of the Mg-alloys, resulting in improved ductility in the MMNCs.
Reinforcing particle acts as heterogeneous nucleating sites during solidification of MMCs, leading to the refinement of grain size.
Therefore, MMNCs exhibit higher grain size strengthening effect as per Hall–Petch relationship [16,25].

The time t50% is nearly linear dependent on initial grain size and s~1 [5, 6].
The evolution of the grain size after reheating and recrystallization can be calculated using an exponential growth equation [4].
The value p varies from a constant of -4 [2] to that depending on initial grain size -5,6 Dγ-0,15 [5].
Moreover precipitations of microalloying elements interact with grain boundaries and impede the growth of recrystallized grains.
The energy of a high angle grain boundary γGB is estimated to be 0,75 J/m2 [12].

Increasing the number of screw holes and traversing the tool along the center line of the screw hole are other possible methods for improving the strength of the interlock.
Fig. 5(b) shows the grain structure of the unaffected area.
It can be confirmed that a finer grain structure is achieved within the stir zone.
However, compared to the grain structure of the stir zone, a coarse grain structure was observed within the material that flowed into the screw hole.
Comparing the grain structure in Fig. 5(f) and Fig. 5(g) reveals that no change occurred in the SS400 grain structure.

The XRD analysis results showed that diffraction peak of Pd(111), Pd(200), Au(111) and Au(200) became sharp gradually with the extension of reaction time, crystalline phase composition and grain size of catalyst became bigger gradually.
Au-Pd bimetals are used as catalysts for a number of applications [2] [3] including vinyl acetate synthesis [4] and pollution control [5].
Au and Pd were determined to the mainly active group of catalyst through a large number of experimental comparison.
Table 1 Results of chemical analysis by AAS Number Au/Pd at ratio (theory) Au (wt%) Pd (wt%) Au/Pd at ratio (actual) 1 0.45 89.01 92.93 0.43 2 0.66 90.34 93.22 0.64 3 0.90 91.22 93.91 0.87 4 1.14 91.78 92.75 1.13 5 1.33 89.57 92.56 1.29 6 1.43 89.03 92.02 1.38 Catalytic activity evaluation.
This indicated that crystalline phase composition and grain size of catalyst became bigger gradually after reaction, it may be the mainly reason for declining of the catalytic activity.

The transition between fatigue failure and run-outs is shifted to higher lifetime with increasing R, and fine grained areas (FGAs) at the crack initiation sites only occur at R < -0.1.
Nevertheless, blade failures at high number of cycles still occur at corrosion pits or even at blade roots without environmental influence [1-5].
The resulting highly tempered martensitic microstructure features finely distributed Cr-carbides with diameters of around 100 nm along the martensite laths and the former austenite grain boundaries.
This was correlated with the observation of fatigue failure at cycle numbers far above 108 for R ≥ 0.1.
Göken, Influence of grain size and precipitation state on the fatigue lives and deformation mechanisms of CP aluminium and AA6082 in the VHCF-regime, International Journal of Fatigue, 33 (2011) 10-18

The rock samples include sand mudstone of under upper-group coal seam bed, limestone and medium-grained sandstone of lower-group coal seam roof.
Table 1 Physics-mechanical parameters of rocks Lithology Natural density r/g.cm-3 Uniaxial compressive strength sc /MPa Elastic modulus E/GPa Poission’s ratio m Cohesion C/MPa Angle of internal friction j /（°） upper group coal 1.37 5.44 5.00 0.412 1.75 29.60 sandy mudstone 2.57 77.59 39.16 0.166 15.9 46.20 medium-grained sandstone 2.55 84.70 10.31 0.146 8.90 59.61 limestone 2.61 119.27 67.10 0.294 24.31 43.96 Analysis of cracks development and water inrush danger from roof and floor during the course of mining lower-group coal seam Calculating the height of Water flowing fractured zone in coal seam roof Figure 1 Sketch of "Up Three Zone" after mining coal seam Academician Tianquan Liu put forward the "three zones" theory[14] in 1981, i.e after the workface being mined with longwall mining, according to the law of overlying strata movement and failure characteristics, the overlaying strata are divided into the caving zone, water flowing fractured zone and bending sinking
Table 2 Part borehole histogram columnar of M6 lithostratigraphic units buried depth (m) thickness of stratum (m) lithology Erathem System Series Formation Paleozoic Permian Lower Shanxi Formation 324.95 4.40 medium-grained sandstone 333.55 8.60 fine-grained sandstone 333.66 3.11 siltstone 340.30 3.64 4# coalseam 345.20 4.90 sandy mudstone 355.45 10.25 mudstone 359.95 4.50 siltstone 368.00 8.05 sandy mudstone 373.05 5.05 medium-grained sandstone Carboniferous Upper Taiyuan Formation 378.00 4.95 Limestone (L3) 382.50 4.50 medium-grained sandstone 385.70 3.20 siltstone 392.22 7.22 medium-grained sandstone 395.20 2.28 sandy mudstone 402.10 6.90 Limestone (L2) 403.55 1.45 siltstone 408.04 4.49 limestone (L1) 410.62 2.58 8# coalseam 414.30 3.68 fine-grained sandstone 418.54 4.24 medium-grained sandstone 422.22 3.78 9# coalseam 426.44 4.22 fine-grained sandstone 426.73 0.29 coalseam 429.25 2.52 fine-grained sandstone 434.45 5.20 siltstone 441.40 5.95 medium-grained sandstone 443.20 1.80
siltstone 447.45 4.25 medium-grained sandstone Middle Benxi Formation 448.45 1.00 siltstone 449.90 1.45 marl 451.70 1.80 fine-grained sandstone 457.35 5.65 aluminum mudstone 460.40 3.05 medium-grained sandstone 463.10 2.70 fine-grained sandstone 465.35 2.25 limestone 466.50 1.15 medium-grained sandstone 468.80 2.30 aluminum mudstone 473.50 4.70 limestone 476.25 2.75 siltstone 478.20 1.95 fine-grained sandstone 479.90 1.70 siltstone 481.25 1.35 marl 484.00 2.75 aluminum mudstone 484.85 0.85 marl 488.65 3.80 aluminum mudstone 490.30 1.65 pyrite ore stratum Ordovician Middle Fengfeng Formation 494.75 4.45 limestone 499.85 5.10 brecciola 502.60 2.75 limestone 506.55 3.95 marl 513.80 7.25 limestone 524.40 10.60 brecciola 527.80 3.40 gypsolith 536.25 8.45 limestone Calculating the depth of fractured zone in coal seam floor Yingbai Li argued that there are three zones in coal seam floor after mining, i.e mining damage zone in upper, water-resisting zone in middle, water-conductive zone
Table 4 Water inrush coefficients of lower-group coal seam’s floor under mining condition The number of hole Water pressure （MPa） Effective thickness of watertight stratum（m） Water inrush coefficient Ts（MPa/m） 133 2.74 67.74 0.040 77 4.28 69.36 0.062 366 4.54 68.33 0.066 368 5.73 81.21 0.071 134 4.33 39.12 0.110 Ms1 4.92 69.65 0.071 Ms4 5.62 71.05 0.079 Ms6 4.13 77.08 0.054 S6 4.66 66.75 0.070 Table 5 Critical water inrush coefficients of some mine districts [16] Name of mine district Fengfeng Jiaozuo Zibo Jingxing Water inrush coefficient Ts (MPa/m) 0.066～0.076 0.060～0.100 0.060～0.140 0.060～0.150 Conclusion In this paper, by rock physical and mechanical tests, and using "Up Three Zone" Theory of coal seam roof, "Down Three Zone" Theory of coal seam floor and “Water inrush coefficient” Theory, we have analyzed the water inrush risk while mining the lower-group in Shuangliu Coal Mine, a typical North—China—Type coalfield; and the conclusions and suggestions are as follows:

It can be seen that the structure is uniform; the grain size seems to be below 10 µm.
Fig. 7b shows a combination of small- and big- sized grains in longitudinal direction, whereby the small grains may indicate a beginning recrystallization process during the extrusion process.
After 6 h of annealing at 300°C, a relatively fine-grained structure can be obtained (Fig. 9c), whereby close to the outer tube-surface long stretched grains still can be found (Fig. 9d).
At 350°C annealing temperature and 12 h annealing time, a grain growth can be observed clearly.
Microstructure investigations show that at 350°C cavities can be observed (Fig. 10b), whereby the number of cavities seems to be higher compared to the non-annealed tube (Fig. 8b).

As soon as the given number of revolutions is performed, the drill stops automatically.
Gradually, the individual levels of the number of revolutions of both drill bits were tested.
When using a higher number of revolutions, the drill bit penetrated through the entire test specimen.
Based on the measured values, the compressive strength parallel to grain was calculated according to the standard calculation relationship.
Table 3 shows the results of compressive strength parallel to grain and the bending strength.

The grain size of TNTZ added with Y or Y2O3 is smaller than that of TNTZ.
Fig. 2 shows the microstructures of TNTZ with Y or Y2O3 additions subjected solution treatment, because the β phase grains in the alloys after cold rolling with the high rolling reduction are not apparent.
Moreover, the grain size of TNTZ with Y or Y2O3 additions shows smaller than that of TNTZ.
The low-cycle-fatigue life region means the number of cycles to failure is less than 105 cycles, and the high-cycle-fatigue life region indicates the number of cycles to failure exceeds 105 cycles.

Micrograph For the four grades, the micrographs in figure 1 reveal grains elongated in the rolling direction.
Austenitic grains are distributed in the ferritic matrix.
More over, many austenite grains display a strong deformed state.
However, it is worth noticing that the poles figures indicate the presence of coarse grains (see Fig. 1).
Indeed, the grain size has an effect on the number of crystallites measured per unit volume.