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The M23C6 carbides precipitate preferentially at grain boundaries, and then coarsening remarkably with increasing aging time.
After aging, the number of twins structure is decreased even to be disappeared gradually with the aging time increase, it can be observed more precipitated phase which distributed in the interior of grain and grain boundary. as shown in Fig.2 (b).
There are also a small number of particles larger than 300nm inside the grains and at the grain boundaries.
After aged for 94 h, some newly formed M23C6 carbides are found to precipitate along the grain boundaries and in the interior of grains (Fig. 3(a)).
Besides the Cu-rich phase, also there are some precipitates of M23C6 carbides at the grain boundary during aging at 750℃ in 300h, the M23C6 carbides with small size can pin dislocation at grain boundary which can act strengthening function.

In order to fabricate billets with a fine-grained spherical microstructure in the semi-solid state, a number of fabrication methods have been proposed including cooling slope process [3,4], magnetohydrodynamic stirring [5], strain-induced melt activation (SIMA) route [6] and recrystallisation and partial melting (RAP) route [7].
As the temperature was 1250�C, carbides dissolved into the austenite grains and resulted in the one-phase austenite structure with grain size of 200µm as shown in Fig. 2b.
G: grain boundary; C: carbide; LF: liquid film; QL: grains from quenched liquid.
During the austenite growth stage, the combination of austenite grains swallowed some grain boundaries and entrapped and concentrated the alloying elements which once located on those grain boundaries.
Even clusters of small grains existed.

The results show that the alloys with small size, uniformly distribution and moderate number of carbides present a high stress rupture performance.
The fourth group elements mainly include Mg, Zr, B, which segregate to grain boundaries, fill vacancies and reduce grain boundary elements diffusion.
The blocky and strip MC type carbides rich in Ti and Mo distribute among the grains and grain boundaries.
(5) The grain boundaries easily turn into crack propagation path, so the grain size must be controlled.
The relationship of electron vacancy number and rupture life in C1023 alloys [J].

The effect of ultrasonic attenuation and phase velocity dispersion due to grain scattering is included in the predictions.
An inhomogeneous material is composed of numerous discrete grains, each having a regular atomic structure.
The elastic properties of grains are anisotropic.
For pulse echo set up, the voltage received at the transducer is given by Kim et al. [10] and is expressed as (1) where is the surface of the flaw or defect. k is the wave number and is the area of the transducer.
Panetta, Ultrasonic attenuation as influenced by elongated grains, Review of Progress in QNDE, 21(2003), 109-116

For the non heat treated samples, glassy regions were revealed, by centered dark field images, using diffuse scattered electrons, to be located at three and four point grain junctions.
Stress exponents near unity, related to grain boundary accommodation processes were obtained for low temperatures and for heat treated samples.
The deformation processes in these cases were correlated to stress concentrations at grain boundary and triple point junctions, caused by grains rotation and sliding, accommodated by cavitation.
For a series of materials in the Si-Mg-O-N systems it has been deducted that creep can occur by a number of mechanisms, including (6,19,20) diffusional creep, cavitational creep, grain boundary sliding accommodated by the elastic deformation of constrained grains and hardening due to compositional change induced by oxidation.
Clarke: Techinical Report, AFOSR Contract Number F49620-77- C-0072, (1978)

For instance, maximal grain-diameter equal to 0.16mm in the third group of stable 1 means that all grains in the specimens of the soil pattern were below 0.16mm.
It is thought that the influence of maximal grain-diameter on shear strength indirectly reflects the influence of grain-diameter range and grain grading.
The growth of maximal grain-diameter results in wider grain-diameter range and poorer grading to Gravel silty clay used in the experiment.
In contrast, the decrease of maximal grain-diameter results in narrower grain-diameter range and better grading.
The authors think that big grains grow constantly in number and so cohesion decreases while maximal grain-diameter enlarges; the change of internal friction has sensitivity because internal friction is determined by the irregular overturn movements of big grains on shear zone and the overturn movement of every big grain is different, hence shear strength has sensitivity to the change of maximal grain-diameter.

Mn doping had a more significant effect on the grain boundary than on the grain, suggesting that the grain boundary was more resistive than the grain.
The reduction in breakdown voltage (Vb) from 545 V (sample with 0.0% mol of borosilicate frit) to 188 V (sample with 3.0% mol of borosilicate frit) can be clarified by the increase of the average grain size from 5.7 μm (sample with 0.0% mol of borosilicate frit) to 29.3 μm (sample with 3.0% mol of borosilicate frit), resulting in lower numbers of grain boundaries for the sample with 3.0% mol of borosilicate frit and reduced p-n junctions.
The V-I nonlinear behavior of the varistor samples is a phenomenon of the grain boundaries between semiconducting ZnO grains.
The varistor breakdown voltage is directly proportional to the grain boundary number per unit of thickness and therefore to the inverse of the size of ZnO grain.
We suggested that the reduction in resistivity can be attributed to the reduced potential barrier between the ZnO grains resulting from a significant growth of grains in the samples after increasing doping amounts, which lead to a decrease in the number of grain boundaries between the ZnO grains and therefore reduced potential barrier.

In every sample 3 measurements were done and the mean was rounded to the nearest whole number. 1.
Mean grain’s cross sectional area varied from 1112 to 2262 µm2.
The presence of steel tubes did not affect significantly the grain size.
Fine grained microstructure - sample 4 (a), coarse grained microstructure - sample 6 (b) The mean volume fraction of eutectic areas varied from 0,44 to 2,70%.
Voids’ shape and distribution were typical for shrinkage porosity (longitudinal pores situated along grain boundaries and triangular voids at the junction of 3 grains).

The grain is coarse and cellular dendrite brochus is large.
The secondary dendrite arm spacing is 15~20 µm, average grain size (diameter) is 40~50µm, and the maximum grain diameter is 200µm.
By applying compound energy field, most of precipitations transform into Al( Fe, Mn) Si, whose number is larger than the number of (Fe, Mn) Al6.
The participations of plates under the compound energy field are relatively uniform, less in number and the participate phase Al( Fe, Mn) Si are dominated.
Potency of high-intensity ultrasonic treatment for grain refinement of magnesium alloys[J].

In the microstructure of normal direction (Fig.2-a) , much dendrite structure of initial primary phase are found, which are mainly coarse grain with rough and irregular boundary.
But due to the shearing action during the rolling process, little part of the coarse grain of primary phase are bended and broke into globular granules with smaller size.
Beside of high developed dendrite structure, in the microstructure of cross section of metallographic section without outside field (Fig.2-c) , a number of local-concentrated and plate shaped dendrite grain are formed, because of shearing action and limited floating space in the cross section direction.
Because of scour from the liquid phase and collision between the nucleus during the growing process, the new crystal nucleus are passivated and formed into spherical or rose-shaped dendrite grain finally, besides, the average grain size has been reduced greatly form 60-80 μm to 12-18 μm, showing that outside energy-field can make significant contribution to homogenization of the concentration field in rolling process.
To sum up, fine and uniform equiaxed grain will be obtained by cast-rolling process with composite outside energy-field.