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The new fine grains appear mainly on the grain boundaries of highly elongated original grains at temperatures below 800°C, making a necklace like microstructure.
Nucleation of DRX grains at 700°C.
The new fine grains appear as cells in the network strain induced grain boundaries.
The number of strain induced grain boundaries increases with straining, leading to formation of new DRX grains, which form chains at the original grain boundaries (Fig. 3b).
Progressive development of the new fine grains at frequently serrated grain boundaries makes a mantle of RDX grains surrounding the original grains (Fig. 3d).

Thermal shock effectively promoted the fragmentation of the dendritic grains, providing a significant grain multiplication effect to refine the final solidification microstructure.
Compared with large body of work of crystal growth under stable conditions or the additions of various extrinsic grain refiners to promote heterogeneous nucleation, the intrinsic grain refinement due to dendrite fragmentation under more commonly found unsteady conditions are relatively neglected.
The model provides an initial step towards simulating intrinsic grain refining effects under highly transient conditions, and shows thermal pulses are extremely effective in increasing the number of solid particles per unit volume during solidification.
These parameters were chosen arbitrarily to demonstrate the model ability, and clearly a large number of conditions could be explored.
According to Figure 2, more than 200 dendrite fragments were created due to the thermal shock, ~20 times more than the number of the originally seeded crystals, although larger grains remained of approximately constant dimensions since primary dendrite arms were comparatively stable under these particular conditions.

The value of two characteristic diameters was recorded for each examined grain with the ratio of these characterizing the shape of the grain (some measurement results are shown in Table 3).
Both the mean grain size (~50-60 μm) and the scatter of grain size is greater in the case of the austenitic microstructure of the Grade X80Mo0 specimen than in the case of the Grade X80Mo2 specimen having a higher Mo content.
In the case of this latter specimen the mean grain size of the microstructure is only 25-35 μm and the grain size distribution is much more homogeneous.
Figure 11: The image of Grade X80Mo0 specimen taken with optic microscope (original magnification: 500x, reagent K) Figure 12: The image of Grade X80Mo2 specimen taken with optic microscope (original magnification: 500x, reagent K) Table 3: Austenite grain sizes Serial number of austenite grains investigated 1 2 3 4 5 6 7 8 9 10 11 12 X80Mo0 Austenite grain diameters (μm) 41.3 17.2 56.9 13.8 24.1 81 65 166 108 59 109 65.8 23.3 11.9 52.1 13.8 19.5 43.5 41.1 49 77 42 68 65.1 X80Mo2 Austenite grain diameters (μm) 12 41.4 29.2 26.3 34 11.8 31.6 13 33.7 10 28.5 12.2 11.3 40.4 26.6 16.1 23.7 8.8 27.7 10.6 30.4 6 26 9.7 Summary In the course of our experiments we have developed an etching procedure by means of which the austenite grains formed after roughing can be made visible in the case of Grade X80Mo0 and X80Mo2 microalloyed steels.
Vander Voort: Revealing Prior-Austenite Grain Boundaries in Heat-Treated Steels, 2010.

The mechanism of grain destruction by impact depends on the grain crystal structure.
The greatest changes in the grain composition were discovered in Sample 3: the total number of grains on the 200 and 250 μm sieves increased to 85%, the number of coarse grains on the 315 μm sieve decreased by 9%.
Table 3 data show that the abrasive paper made with normal electrocorundum grain heat treated at 1000°C in nitrogen atmosphere and subsequently air-cooled (Sample 1) have the best results in cutting performance, total metal removal and the number of grinding cycles up to the wear criterion compared to the mass-produced grain in Sample 4.
The effect of oxidizing atmosphere and thermal shock on the grain in Sample 3 allowed to increase the total metal removal figures by 37.8% and the number of grinding cycles achieved practically doubled.
When the grain of normal electrocorundum is heated in an oxidizing atmosphere to a temperature of 1000°C, followed by rapid cooling in water, a qualitative change in the properties of the grain takes place, which increases the performance characteristics of the abrasive paper: the increase in metal removal and the increase in the number of grinding cycles.

The corrosion tests results indicate that there is a potential difference between grains and grain boundaries due to the precipitation of chrome carbide at grain boundaries, resulting in pitting corrosion occurred preferentially at grain boundaries, consequently, the corrosion resistance of Ni-based alloys is reduced.
Data showed that [10] when more higher solution heat treatment temperature, the grain boundries lost the pinning effect of original precipitated phase and the grain size growing up quickly.
There exist a mass of long strips or flake precipitated phase in intragranular as shown in Figure 5a, the number increase relatively with temperature increasing[11].
The TEM observed that the flake phase at grain interior was M6C, and the continuous-chain phase at grain boundary was M23C6 (Figure 6).
It can been seen from TEM that new carbide phase M6C was observed, and the number of M6C phase increased obviously and formed easily at high temperature.

The sample serial number and the roasting situation are given as following Table 1.
The sample serial number and the roasting situation are given as following Table 1.
Table.1 The sample serial number and the roasting situation Sample number Roasting temperature Roasting situation 1# 800 Ceramic crucible inwall non-adhesion 2# 850 Ceramic crucible inwall non-adhesion 3# 900 Ceramic crucible inwall non-adhesion 4# 950 SG abrasives sticks light powdery on the clay crucible inwall, may wipe off 5# 1000 SG abrasives sticks the quantity on clay crucible's inwall to increase, the partial crystal grain adherency, cannot wipe off completely 6# 1150 SG abrasives in clay crucible the adherency basically is the crystal grain, cannot wipe off 7# 1200 SG abrasives in clay crucible the adherency is the crystal grain, cannot wipe off Fig.1.
It could be seen that the ceramic corundum (SG) abrasives big grain edges and corners are unusual clarity, and the grains crack increases, even a part of grains already have break.
Some grains with small edges and corners present to matrix, in addition, the grains present some liquid organize.

High Temperature Deformation of Cast ZW11 Magnesium Alloy with Very Large Grain Size K.P.
However, the resultant alloy developed a very coarse grained microstructure with a grain size in the range of 2,600 to 4,000 μm (2.6-4.0 mm).
The numbers associated with the contours represent efficiency of power dissipation in percent and the shaded areas represent flow instability regimes.
The numbers for the contours are efficiencies of power dissipation and the shaded areas are flow instability regimes.
The developed microstructures reveal complete recrystallization and the grain sizes are in the range of 30-60 μm, with finer grains corresponding to higher strain rates of deformation.

Influence of grain size distribution in the cross section was also investigated.
Considering that the sample is loaded perpendicular to the cross section, stress in the cross section should be: (3) where is the stress of the layer, is the area fraction of the layer in the cross section, and is the number of layers.
In conventional polycrystalline material, fine grains can exhibit high yield stress because of the enhancement of obstacle to dislocation motion at grain boundaries.
As the grain size decreases to the order of nanometers, the grain boundaries will tend to slide [18].
In addition, it should be noted that the formation of nanostructures from coarse-grained polycrystals involves various dislocation activities and development of grain boundaries during SAMT [4].

It enables to distribute uniformly the total working contact along the abrasive tool and owing to that, a greater number of active grains is involved in stock removal, which corresponds the value of the effective working contact.
Abrasive grains were fixed using the binder of glasscrystalline structure (Fig.3).
bonding bridge abrasive grain bonding bridge Figure 3.
Microstructure of bonding bridges fixing the abrasive grains.
The microcrystalline structure of abrasive grains, with particles not exceeding 0.1 µm, under such conditions makes it possible to produce a large number of active tool points on the working surface of grinding wheel, which causes the power consumption to remain on the almost constant level.

A coarse-grained parallel model has been used to implement the PLCA.
According to the nature of the population structure and the mechanisms of reproduction, the parallel model for PEAs can be classified into three main types: master-slave model, fine-grained model and coarse-grained model [11].
In the coarse-grained model the whole population is divided into several subpopulations (Fig.1c).
Obviously, the communication overhead increased linearly as the number of processors increased.
A coarse-grained parallel model is used to implement the PLCA.