Search results

Fig.1 shows the clustered sand grains movement track.
This SUFA will take off only the sand grains which are satisfied critical velocity value of sand grains to jump.
With this contrary, on the sheltered lee-face, the sand grains have lots of open air and sand grains respectively relax, so fly far.
In this study, for the numerical simulation, the average clustered sand grain field density (2.65 g/cm3) and air stream field density (0.00129 g/ cm3) are assumed to be constant, and the average clustered sand field grain size and shape are set by the random number during the simulation in the whole field, then the whole sand field surface roughness are obtained automatically by using this manner.
However, for the detailed analysis needs to consider concrete influence factors and number of simulations results and should be compared with experiment.

SiC crystalline grain is round grain shape or ellipse shape, crystalline grain size is about 50nm and well-distributed on Si3N4 crystal boundary, small number of SiC crystalline grain exist in Si3N4 crystalline grain.
We find that SiC crystalline grain in Si3N4 crystalline grain is smaller than the grains on crystal boundary, most of them is under 20nm.
In Si3N4 single materials Si3N4 crystalline grain grow soundly, most of crystalline grain is long column shape, the ratio of diameter is 5-6, and there are unusual big crystalline grains.
This shows nanometer SiC crystalline gain can restrain the growth of Si3N4 crystalline grain effectively, especially SiC crystalline grain on Si3N4 crystal boundary which nail-picked on Si3N4 crystalline grain.
Fig.3 shows SiC crystalline grain nail-picked on Si3N4 crystalline grain.

No secondary phases were observed at the grain boundaries and triple grain junctions, which guaranteed good optical property of the sintered bodies.
Fig.5 (a) and (b) were the triple grain junction and grain boundaries of the specimen, respectively.
The grains were divided by straight grain boundaries and combined contiguously with each other without mini angle grain boundaries, which were helpful to the transmittance of transparent AlN ceramics.
The grain boundaries and triple grain junctions were clean, no secondary phase was observed.
Yu et al. [16] have pointed out that secondary phase and its distributions in the AlN grains would greatly decrease properties of AlN ceramics by the grain boundary phase layer which disrupted the continuous of AlN grains.

Introduction In polycrystalline materials, propagation of a cleavage crack from grain to grain is a complex process.[1] This is because cleavage occurs on well-defined planes and these planes in neighbouring grains do not usually meet in a line at their common grain boundary.
In addition there is a significant number of deformation twins formed on {10-12} planes ahead of the growing crack.
Hence the stepped cleavage has the effect of limiting the amount of grain boundary fracture that is required as cracks propagate from grain to grain.
This minimises the amount of grain boundary fracture needed to accommodate the mismatch between grains.
Accommodation at a grain boundary in low temperature fracture of Zn as the crack propagates from grain A to grain B is shown in (d).

The microstructure contained grains with an average size of 195 nm and 239 nm, respectively.
In the reported work HE was used to refine the grain size of 6082 aluminium alloy.
From the application and economic points of view it is important to minimize the number of extrusion passes required to achieve the required properties.
The grain sizes were determined using the stereological method and XRD analysis, which enabled the average grain size to be determined by measuring the full width at half maximum of the diffraction peak profile.
The nanometric-size of grains in the alloy's structure was confirmed by XRD analysis although The grain sizes were calculated as 195 nm in the multi-pass sample and 280 nm in the single-pass sample.

The individual grain orientation was measured by EBSD in a FEG-SEM.
A great number of needle-shaped δ phase distributed in the grain boundaries disappeared after solution treatment.
With the increasing of hot deformed temperature, the dynamic recrystallized grains become more uniform and the grain size increased.
The dynamic recrystallized grains are finer than the original ones.
Fig. 4 (c) shows the typical neck-structure of superalloys which there are many fine recrystallized grains around the big grains.

In order to obtain the high hot-strength in high-temperature service, the alloying degree of nickel-based superalloy is increasing which leads to the decreasing the stability of microstructure during the high-temperature and long-time service, and even a lot of TCP precipitation phase at the grain boundaries which leads to the appearance of the brittle failure in a large number of caused by catastrophic the phenomena of disastrous brittle failure[2].
A large number of dimples exist in tensile fracture without aging treatment.
The precipitation phases within the grain transform to grain boundaries during the long-term aging, which increase the size of precipitation phases at grain boundaries.
The needle-like precipitation phases along the grain boundaries or growing into grain can be observed.
With prolonging aging time, grain boundary precipitation phases continue to grow, the interface of precipitation phases and substrate replace a large number of grain boundaries.

Based on the results of cellular automaton, the transformation fraction of α phase is calculated with the number of lattice and isothermal phase transformation kinetic equation is also calculated with data of transformation fraction, and the effect of hot compression deformation parameters on phase transformation is also discussed.
For simplicity, the phase transformation process is divided into two stages, i.e., formation of initial microstructure and phase transformation process.The initial microstructure is created via a normal grain growth algorithm and dislocation density is uniform and identical for all primary grains.It is considered that the driving force for nucleation is provided by the variation of disloation density.The dislocation densityof a deforming matrix at every time step increases based on the dislocation density .If the dislocation density of a chosen cell exceeds the critical dislocation density,the cell becomes a nucleus for phase transformation.For a newly formed grain,the initial dislocation density is set to zero inside the grain,and increases as the grain grows with hot compressing deformation of the matrix.If impinge each other,the growing grains cease to grow in the impinging direction, but continue to grow in another direction with the increase of strain.When the dislocation density of
a phase transformation grain reaches the saturation value,the grain ceases to grow.And if all the phase transformation grains cease to grow,the phase transformation process terminates[7].
It is proposed in the present study that nucleation of phase transformation occurs only at grain boundaries.Nucleation of phase transformation is related to the accumulation of dislocation,and when dislocation densityexceeds the critical dislocation density,nucleation occurs at grain boundaries at a nucleation rate.For the hot compression deformation the critical dislocation densitycan be experssed as[9]: (4) Where M is the total number of CA cells,is the deformation temperature,and N is the number of phase transformation cells which varies as the function as well as m,where m is the strain rate sensitibity.
For a newly formed grain,the initial dislocation density is set to zero inside the grain and increases when the grain grows with continued deformation of the matrix.When the dislocation density of the phase transformation grain reaches the saturation value,the grain ceases to grow.The value ofcan be calculated by[9]: (5) Results and Discussion Microstrutural evolution of phase transformation.

Spherical grains are excessive alumina after burning or dissolvable phase.
The results showed that rod-like Crystal is very likely the CaCO3 and MgCO3 [9].The reactions are as follows: As shown in Fig. 3g the rod-like crystals become thick but the number of them is reduced after hydration for 24h.
Instead there appear a large number of mesh or beard shape crystals.
The stick big grains are not appeared.
The stick big grains are not appeared.

Thereby it reduces the number of shutdown to ensure the safe operation of the boiler and create the favourable vield and social benefits.
It clearly shows there is a clear boundary line and discontinuous columnar crystal in sample 1.The organization is uneven and there is a large number of bright coarse-grain on the left side.
And the grain is very small.
And the grain tapered from the inside out.
Then it is coarse-grained zone and fine-grained zone.