Search results

The results indicate that LAGB's change to HAGB's as the increase of number of process.
The average grain size, aspect ratio of grains and fraction of HAGB's are shown in Table 1.
Aspect ratio of grains didn't change after aging treatment while grain size increased from 210 to 240 nm.
58 0.22 ARB/3cycles 300nm 0.4 58 0.22 ARB/3cycles 300nm Number of ARB cycle Vickers hardness, Hv 140 150 160 170 180 01 3 5 Number of ARB cycle Vickers hardness, Hv 140 150 160 170 180 01 3 5 why grain growth doesn't take place so much will be due to precipitates disturb the grain boundary migration effectively.
On the other hand, in ARB/aged ones, (c) precipitation hardening may be so effective, (d) bonding defects may disappear or decrease in number due to aging treatment.

Relationship between Fabrication Temperature and Microstructure Evolution The migration velocity (v) of grain boundaries can be given by the following equation [1]: (1) where A is the accommodation probability, Z is the average number of atoms per unit area at the grain boundary, Vm is volume of specific mol, Na is Avogadro’s number, h is Planck’s constant, R is the gas constant, T is absolute fabrication temperature, is the activation entropy, Qa is the activation energy, is grain boundary energy, and r is grain boundary curvature radius.
And its grain-boundary energy is J.
N is the sites number of the simulation domain. n is the solid-phase site number around one specific site.
The attempted N (total site number in the simulation system) times is regarded as one Monte Carlo Step (MCS).
The simulation time is expressed in term of the number of MCS.

When analyzed grinding process, Tönshoff et al. further studied undeformed chip thickness model after describing the three-dimensional and two-dimensional appearance of a large number of grinding chips[2].
In this paper, the grits are assumed to be perfectly conic, the grain diameter is normally distributed, and the spatial distribution of the grains is uniform in the wheel volume.
Suppose is the number of the grits simultaneously participated in the work on unit width contact arc length ，then .
In the experiments, the dimensions of the workpiece is 24mm*12mm*6mm, of which the material is steel 55. 3.1 Measurement of the inter-grain spacing The inter-grain spacing is one of the most important parameters in the analysis of grinding forces.
After calculation in Matlab7.1，the average inter-grain spacing of the CBN grinding wheel is obtained as：.

When the temperature increase to 400 ℃, with the grain boundary further nucleation, the increased small grain further refine the grain scales (figure 1 (c)), and small grain still mainly distributed around the grain boundary.
Dispersion particles can effectively pinning the grain boundaries and restricts grains grew up, which play an important role at the refine grain size.
Tiny grain appears not only in the grain boundary, but also in the grain, grain size scale further decrease.
Deformation temperature influence the second phase of alloy, the second phase size, number, distribution and the fracture mode.
With the deformation temperature increase to 480℃, grain size become small, the dimple number in the fracture increase gradually, and existing a number of the second phase particle in the dimple.

Macrostructure and calculation of grain size.
The grain size was defined as the grain numbers in unit area, i.e. squared 100 mm2 area from the center of section planes, and calculated the ratio of grain numbers in this area to 100.
Each group had 6 samples and averaged their values of the grain size.
Tab.1 Grain number of the samples at different superheated temperatures Temperature / °C EPM or No-EPM Grain number /mm2 700 EPM 1.89 750 No-EPM 1.15 750 EPM 2.31 800 EPM 1.44 It is obvious that the EPM of alloy melt at different superheated temperatures can make its casting structure change distinctively.
In addition, the observation of macrostructures denotes that the grain number of the EPM sample at 700°C (the superheated temperature is merely 40°C) is 1.89 mm-2, which is two times as much as that of the original sample; the equiaxed crystal grains in the center of the casting ingot increase obviously and also the gains more refining when the temperatures of EPM are 750°C, moreover their grain sizes are 2.31 mm-2, which are 2.3 times more than that of the original sample, here the effect of EPM is remarkable comparatively.

Through increasing the processing pass, further grain refinement can be achieved.
Fig. 3 (b) shows the microstructure in SZ of the single-pass FSP specimen, consisting of the coarse grain band and fine grain band.
After two-pass FSP, the grain is smaller than that of single-pass FSP.
Compared with BM, the number and intensity of β-Mg17Al12 diffraction peaks decrease a lot after FSP because they break up and part of them dissolve into the α-Mg matrix, which is in agreement with the microstructure observation (Fig. 3).
FSP can lead to a remarkable grain refinement in AZ91 magnesium alloy.

In many cases there are deep incursions of the secondary grain into the primary grain structure behind the macro-boundary.
In the vast majority of cases, no special character was evident for grain boundaries around the periphery of the secondary grains.
The secondary grains are marked with ‘S’.
The small triangular grains appear to be separated from the secondary grain but with a very acute junction.
The strongest selectivity of the Goss orientation will occur when the pinning strength is high since this will increase the number of neighbouring grains that must cooperate.

However, even for this material, significant changes of the porosity and grain structure are observed, where original grains of several µm diameter are divided into smaller grains of around 0.1 to 0.3 µm.
Pati of Combustion Engineering (C-E) and from Windscale hot laboratory on KWU fuels, observing significant number of µm size porosities at pellet rim [4].
Here "grain sub-division" is defined by observed fine grain formation and the definition does not include bubble formation nor swelling.
The sizes of the sub-divided grains are 150 to 200 nm which are the size range of the grains at the Cauliflower structure.
Number of cycles could be order of 104 to develop microstructures.

Fig.1 Example of whiskers that have grown from a tin-plated brass component Background Investigations into whisker growth date back at least 50 years [1] and have established a number of conditions relating to their growth: • Whiskers are single crystals of normal (tetragonal) tin structure [2]
The growth axes of a number of whiskers were determined by shaking these free in an ultrasonic bath and then depositing them on an SEM specimen holder for EBSD measurements.
This, as well as other local measurements demonstrates that there exist high angle grain boundaries between the whiskers and the grains from which they grow.
In virtually all cases the whisker is seen to end as a cone where a high angle grain boundary separates it from the tin grain(s) in the coating below.
By contrast, there is no evident grain growth in the coating layer, even over months of storage.

The number of guide trough is 6 to 10.
Condition of soybean accumulation: After observing in the warehouse, the number of cumulate grain piles in the squat silo is six, the distribution of grain piles is shown in Fig. 5.
By observation, we can know that the first grain pile is maximum, the next is the fifth grain pile, and the sixth grain pile is smaller than the fifth grain pile, but it relatively larger than the second, third and forth grain pile.
The main reason of the middle heap largest: The number of original design for branches are ten but the test use five branches at present.
That is to say, the blanking in the middle from one point finally become multi-point, grain and impurity can distribute in a number of grain piles.