Search results

The plastic deformation is mainly dominated by the grain boundary atom slide.
The molecular dynamics (MD) model boxes are fixed as 8.58nm×8.58nm×8.58nm before relaxation, and the numbers of atoms contained in the samples are all about 50000.
The grain centers placed in the MD model boxes are 16, 27, 64, 125 respectively for four samples, and corresponding average grain sizes are 4.32nm, 3.55nm, 2.66nm and 2.13nm.
The abnormal mechanical properties are attributed to the high fraction of grain boundary atoms, and the plastic deformation is mostly carried out through atomic sliding on grain boundary and grain rotation.
The movement vectors of atoms on grain boundary are obviously different from that of atoms interior grain, the similar atomic vectors in a same grain end at grain boundary.

The in-line transmission increases with a decrease in grain size.
Ceramics are polycrystalline materials composed of crystallized grains.
It is thought that the existence of grain boundaries has little relationship to light scattering or the scattering at grain boundaries can be neglected [10].
The scattering coefficient of birefringence is given as follows [11]: (13) Here, Ngr is the number of grains, rgr and Qgr are the radius and scattering efficiency factor of a grain.
Effect of grain size on in-line transmission at wavelength λ= 0.5μm.

For Si content ≥10.7%, grain sizes gradually reduced with annealing temperature increasing.
As Si content increased (CrAlSi3.7N, Fig. 1(b)), the size of and number of micro-hole reduced.
When the Si content ≥ 6.3%, the micro-hole basically disappeared and the grain distributed uniformly.
The effect of annealing temperature on grain size of CrAlSi8.6N and CrAlSi10.7N coatings are shown in Fig. 2.
The grain size of CrAl(Si)N coatings gradually decreased with Si content increasing.

At the meantime, another reaction between Si and B4C occurred, resulting in the formation of β-SiC as well as a new boron carbide phase in which the ratio of B to C was changed from 4 to a higher number.
The large boron carbide grains in the sample fired at 1450oC (Fig. 4(b)) maintained a similar grain size compared to the original B4C grains (45µm) with rounded corners.
Microcraks were observed in the boron carbide grains as highlighted in Fig. 4(b), indicating these grains were products of the reaction between B4C and silicon and a significant volume expansion was produced during the reaction, which was accommodated by the resultant boron carbide grains rather than by grain movement and the voids in the green body.
The corresponding JCPDS card numbers of the above mentioned phases are 06-0555 for B4C, 19-0178 for B12(C,Si,B)3, 73-1708 for β-SiC, 80-0018 for Si and 71-0097 for B49.9C1.82 respectively.
The grain size of the identified B4C was much smaller than the average size of the B4C starting powder, suggesting it to be a remainder of an originally large grain that had been mostly reacted.

To date, Mg alloys have been significantly inhibited by their low formability resulted from the hexagonally close-packed crystal structure and insufficient number of slip system.
SDC is independent of grain size, and allows low-cost superplasticity when compared to GBS[5].
After static recrystallization during 2-hour annealing treatment at 430˚C, as shown in Fig. 1 (b), equiaxed grains were well developed with an average grain size of d = 16 mm, which is larger than the typically required grain size of d < 10 mm for grain boundary sliding superplasticity.
Fig. 4 (b) and (c) show the coarse grains and uneven grain distribution near the fracture, resulted from dynamic recrystallization and grain growth.
The coarse grains and the cavities caused the premature failure of the material.

However, a number of studies have found recrystallization nuclei in orientations that were not expected from measurements on deformed structures.
Electronmicroscopy Observations Within recent years there have been a number of investigations into the local orientation is deformed metals and the development of recrystallization nuclei [4-22].
A smart way to avoid the uncertainty discussed above concerning "below-surface grains" possibly leading to nucleation of grains with orientations not seen at the surface is to work with columnar grained sample - i.e. samples where the surface grains extend through the entire sample thickness.
Recrystallization and Grain Growth.
Rex and Grain Growth 2 nd, eds.

Ultrasonic waves exert time-dependence forces on crystal lattice defects resulting in a number of different phenomena such as self-organization of dislocation ensembles [7], dislocation reactions [8], multiplication of vacancies [9], etc.
One can see a minor grain growth after annealing at 130°C with the resulting mean grain size d » 0.24 μm.
Noticeable changes occur in the microstructure of nickel annealed at 150°C: there is a significant grain growth, some individual grains with size of d » 1.5 μm appear in the ultrafine-grained matrix with mean grain size of d » 0.3 μm (see Fig. 1, c).
The structure consists of dislocation-free equiaxed grains having mean grain size of d » 320 nm.
Reduction of the distortion and excess energy of grain boundaries supresses the grain growth.

Results and discussion Effect of the substrate on surface morphology and grain size.
As can be seen in Fig.1, comparing with substrate for T4-CA material, crystalline grains of substrate for T2.5-BA material are larger and coarser, and low-density grain boundaries.
For CA material and the secondary cold rolling for CA, DR-8CA the grain of an even smaller grains along the rolling direction of the extension of the trend of a higher density of grain boundaries, which was mainly due to use of secondary cold rolling processes, reduction ratio of 20% ~ 40%, resulting in a number of grains have been extended, and even crushed [3-4]. ①T4-CA ②DR-8CA ③T2.5-BA ④DR-8BA ② 50μm ④ 50μm ① 50μm ③ 50μm Fig.1 Metallographic structure of TFS black sheet ① ② ③ ④ Fig.2 Surface morphology of the TFS products under different annealing/rolling modes The surface morphology of TFS products is observed by SEM corresponding to metallographic structure for T4-CA, DR8-CA, T2.5-BA, DR8-BA, as shown in Figure 2.
Grain size of TFS products surface for BA is more coarse, dense, and less porous.
This was mainly because that the different modes of annealing and rolling affect the surface of the substrate grain size, which led to significant differences in the grain boundary.

This wire tool with resinoid diamond grains (grains diameter about 20~40µm) is used to cut silicon ingots.
The abrasive diamond grain should be the same size as the SiC grain being used in free abrasive wire sawing.
In the manufacturing process, diamond grains are first stirred into SiC grains.
After selecting factors, their desired number of levels is determined.
The smaller grain size, the better kerf width.

Because of this, weld property is improved , effect of precipitation strength is strong and can refine grain.
Laminar fine ferrite grains is obtained in the subsequent rapid cooling process.
The grain size is very small obviously, as figure 2 shows.
Large number of nanometer particles can be observed in the experimental steel.
As show in Figures 4 and 5, we can see a large number of nano-size precipitates containing Ti in the finished steel.