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The average grain size (d) was determined by lineal intercept method [19], given by d = 1.56L/MN, where L is the random line length on the micrograph, M is the magnification of the micrograph, and N is the number of the grain boundaries intercepted by lines.
TiO2 is commonly used as the grain growth enhancer to achieve large grain growth [22, 23].
For low-voltage varistors, grain growth is desired to reduce the number of grain boundaries across the terminals of the varistor device.
Less number of grain boundaries will reduce the number of potential barriers and give rise to lower voltage across the terminals thus qualifying the varistors as a low-voltage model.
Grain junction properties of ZnO varistors, Appl.

Fig. 1 Microstructures of ZW61 alloy (a) as-cast, (b) hot extruded and (c) 8 passes ECAE processed Some large grains disperse in the matrix with small grains and a small number of second-phase particles of Mg3YZn6 (i.e. the dark particles) scatter along the grain boundaries.
In addition, a large number of strips oriented in the extrusion direction are present (Fig.1 (b)).
Lots of recrystallized small grains and some coarse grains are observed.
Liquid, indicated (c) (a) (b) by the presence of Mg3Zn6Y particles after quenching, has appeared both along grain boundaries and as tiny liquid pockets within the grains (Figure. 2 (a), (b) and (c)).
Obviously, with the increasing temperature, grain coarsens evidently.

The ablation depth is governed by the optical penetration depth, which is the inverse number of the absorption coefficient of the material at the laser wavelength.
The numbers of pulses irradiated were 8, 33, or 250 pulses depending on the irradiated energy.
The Ablation depth is obtained by dividing the numbers of pulses irradiated into the crater depth.
The BMG has no grain boundaries.
Hot electrons pass grain boundaries some times.

This definition again implicitly assumes uniformity in the overall grain size distribution.
Sequeira and Dunlop [1] and Rodrigo et al. [6] defined the skin as the region outside the mean hardness number across the specimen's thickness.
After testing the coordinates of the indentation points and hardness numbers were profiled into a 3D hardness surface map using a commercial software package (Surfer).
Figure 2a shows the fine grain structure that prevails along the surface.
The grains structure, however, is not fully uniform, as shown by the mixture of fine and large grains, Fig. 2b, and the presence of occasional microporosity, Fig. 2c.

Free-machining Cr-Mo structural steel, containing low-melting elements, has ASTM grain size of the number of 7–8.
The investigated steels containing low-melting elements had austenite grain size not larger than of the ASTM number 7 (Table 4).
The investigated steels containing low-melting elements had austenite grain size not larger than of the ASTM number 7 (Table 4).
Effect of tin, lead, boron, nitrogen and aluminium on austenite grain size Steel Element, % [Al], % ASTM grain size number 30KhM  0.04 8 AS30KhM 0.24 Pb 0.03 7 ASTs30KhM 0,23 Pb 0.04 8 AO30KhM 0.07 Sn 0.06 7–8 A30KhMAR 0.008 B, 0.008 N 0.02 7–8 Conclusion 1.
Free-machining Cr-Mo steel of the 30KhM type alloyed with low-melting elements has ASTM grain size number of 7–8.

For single pass the general form of the shear strain is given by [17]: , so that (7) where N is the number of passes.
The microhardness profile across the HPT disk for various numbers of turns is shown in Fig 6c.
By contrast, the grains at the edge are clear and grain interiors are almost dislocation free.
Both within and outside of these zones, the Al matrix grains were equiaxed with well-defined grain boundaries.
This suggests that the Si particles assist in grain refinement in the Al–7% Si alloy by pinning the grain boundaries and inhibiting grain boundary migration.

Optimization of Process Parameters for Unidirectional Solidification of Magnesium Alloy Ming Chen1,a Xiao-Dong Hu1,b Hong-yang Zhao1,c Dong-Ying Ju1,d University of Science and Technology Liaoning, Anshan, China 114051, 1a:cchen552@163.com,1,b:hulinas@sohu.com,1,c:zhy@ustl.edu.cn,1,d: dyju@sit.ac.jp Corresponding author: Dong-Ying Ju, E-mail: dyju@sit.ac.jp, Phone:86-412-5928052, Fax : 86-412-5929554 Keywords: unidirectional solidification, finite element method, phase field, columnar grain Abstract: The unidirectional solidification process of magnesium alloy needs to establish a specific temperature gradient in casting mold, the direction of crystal growth and heat flow are in the opposite direction in the unidirectional solidification.
The process can better control the grain orientation, and eliminate the horizontal grain boundary to obtain excellent performance of magnesium alloy.
(5) (6) The parametermeans the strength of anisotropy and is a mode number of anisotropy, for the magnesium alloy we assign the value of 6 to.
For the constant value of , which is according to the macro analysis result when cooling intensity is ~5000W/m2k and pulling speed is 0.1mm/s, we can see the developed columnar grain structure.
For the constant value of , it can be seen that the columnar grain structure is more developed, through the comparison of different value of , it can be known that the higher cooling intensity is, the more developed the columnar grain structure is, but it is hard to make the value less than 1.5 in the actual process, that needs very large cooling intensity.

From Fig. 2d it can be clearly seen that the grain structures are equiaxed with an average grain size of about 9.82μm.
It can hinder the grain growth during solidification.
According to the average grain size reduced, the grain boundary increased.
Dislocation slip can be strong impeded by a large number of grain boundary [19].
After solution treatment, a large number of lamellar tissues spreading to α-Mg matrix made the grain boundary fused and not continuous.

The scanning electron microscopy (SEM) experimental results indicated that: under the force, non-crystalline materials distorted, crystal faces were torn along grain boundaries and crystal grains were disrupted.
So crystal size became smaller, more grain boundaries and more voids were formed, which supplied more free space for the movement of crystal grains and chain segments.
Introduction Ultra-high molecular weight polyethylene (UHMWPE) is a linear polymer with number average molecular weight in the range from one to ten million.
So crystal size became smaller, more grain boundaries and more voids were formed, which supplied more free space for the movement of chain segments and crystal grains.
So crystal size became smaller, more grain boundaries and more voids were formed, which supplied more free space for the movement of crystal grains and chain segments.

At lower temperatures, it is followed by the medium-temperature stage accompanied by precipitation of grain-boundary alpha and the formation of coarse secondary alpha-lamellae.
The low-temperature stage has been established to be characterized by the formation of dispersed alpha-platelets within beta-grains.
In addition to the treatments, the number of specimens were furnace heated and then water quenched.
The second stage includes the formation and subsequent growth of grain-boundary α as well as growth of coarse secondary α platelets from the grain boundaries which are referred to as α**.
With an increase of the heating temperature from 880 to 920 °C, the number of transformation stages was found to increase.