Search results

Figure 1(a) shows the optical micrographs for the hot-rolled strip by TSCR process, the small equiaxed grains in surface, recovery grains in subsurface and center layer, inhomogeneous microstructure in the thickness contributed to secondary recrystallization [5].
In order to obtained more homogeneous microstructure and Continued to cold rolling, hot rolled strip of Hi-B steels were normalized, fig1(b) show the microstructure normalized, smaller grain and uniform equiaxed grains can be observed, because continuous recrystallization happened during normalizing, that is, interaction produced between dislocation and subgrains.
These microstructures are similar to those of twin-roll strips, it can be seen from fig.1(c), most of the equiaxed grains and a few columnar in thickness were observed in the twin-roll strip because of the faster casting rate and higher solidification point, the average grain size is bigger than that of the normalized by TSCR, because almost no reduction happened and higher temperature during twin-roll strip casting procedure, silicon promotes the grain growth, more quickly cooling rate more finer grains can be obtained.
However, the precipitations displayed disperse and fine distribution and had a spherical or close to spherical shape, the chemical analysis of a large number of precipitations using the TEM-EDS method was carried out.
(a) ingot soaked at 1150℃; (b) ingot soaked at 1200℃; (c) EDS spectrum of (b) (b) (a) Fig.5 TEM image showing morphology and EDS spectrum of inhibiter precipitation as-cast strip Conclusions (1) Under experimental conditions, smaller grain and uniform equiaxed grains can be observed for as-cast strip, which similar to the microstructure of hot-rolled strip normalized by TSCR, but the grain size is bigger for as-cast strip than that of normalizing

A steady decrease occurred in the number of [1012] tension twins as strain increased [4].
The number of twins and activated slip planes increases with the increases of elongation to 20%.
For the as-received sample, the images showed some relatively large grains mixed with small grains which is a bimodal grain structure shown in Fig. 4.
In both samples, the grains shape appeared to be equiaxed.
For air cooled sample, the grains size appeared was uniform whereas furnace cooled sample appeared to have a mix of large and small grains.

A conventional electroplated grinding wheel with abrasive grains distributed randomly was fabricated in the same way.
For this purpose, a mask mould with controlled micro-cavities is produced, and then the metal and abrasive grains are deposited onto the mask mount.
Herewith let S0 and SGi be the total area of wheel working surface and the cluster area of number i, respectively, the ratio of total abrasive area to working surface, η, a significant index for defining the cluster, can be expressed with the following equation: 0 (1) GiS S   (1) where SGi depends on the amount and granularity of abrasive grains.
As shown in Fig. 1, obviously in a certain area the amount of abrasive grains is in inverse proportion to its granularity.
Therefore, if the cluster is too small, there will be too little abrasive grains involving in grinding actions.

As can be seen in Fig.1(a), the average grain size of undoped Ba0.5Sr0.5TiO3 ceamics is ~1.5um, while the grain size of Mn-doped Ba0.5Sr0.5TiO3 with Mn concetration from 1 to 5mol％ in Fig.1(b)-(d) is~200nm,~1um,500nm according to the SEM analysis, respectively.
Considering the above analysis,we can see that the Mn doping could refine grains to a certain extent.
It is obvious that the samples comprised of well-connected regularly shaped and uniform grains when x=0.03,indicating a dense microstrcture.
loss tand values floated with different x values.When x=0.03,the dielectric loss tand reached minimum ,it may be caused by the formation of potential barriers at the grain boundaries by doping Mn2+.Besides,when the Mn2+concentration is small,it may cause reduction of Ti4+to Ti3+by neutralizing the donor action of oxygen vacancies.Oxidation of Mn2+intoMn3+or Mn4+throgh the reaction is accompained by the creation of oxygen vacancies,which decreases the number of oxygen vacancies and electron concentration and reduces the tand values[7].
Conclusion (Ba0.5Sr0.5)1-xMnxTiO3 ceramics were prepared via a new sol-gel method .Mn2+doping could not alter the basic crystal strcuture of Ba0.5Sr0.5TiO3 and they only improved the material properties as modified ions when x≤0.3.The (Ba0.5Sr0.5)1-xMnxTiO3 ceramics exhibited good dielectric properties (er =133 0,tand=0.03) at room temperature(25℃) and f =1KHz when x=0.03 sintered at 1250 ℃ for 2h, and the grains were regular and uniform ,indicating a dense microstrcture.

The result shows that adding Ce can significantly improve the corrosion resistance and damping capacity of AZ91 magnesium alloy; the grain refinement and secondary phase morphology modification can contribute to those properties improvement.
Subsequently, when the Ce contents are in range of 1-2%, the damping capacity decreased slightly, indicating that the number and size of Al4Ce phase in the alloy will increase the number of strong pinning points, which making the damping down.
For the 3%Ce, the damping value decreased remarkable might be due to the coarsen ofAl4Ce phase, resulting in moving the dislocation density decreased and the grain refinement will play a role [15].
In our tested alloys, AZ91+3%Ce have the best corrosion resistance.Ce not only the role of grain refinement, but also can play a role in purifying the melt to remove impurities in the alloys reducing the possibility of electrochemical corrosion
(2) With respective to the AZ91 magnesium alloys, the damping capacity of the ce added AZ91 alloys is better.. which is due to the grain refine and changes the morphology of second phase .

The thickness of columnar grains of each specimen shows some differences.
It was found that columnar grains increased in size towards the top of column in comparison with the bottom of it.
Figure 5 shows the number of column boundaries per same area for each ZrO2-4 mol% Y2O3 layers.
The number of column boundaries between columns decreased with increasing the coating thickness.
Number of column boundaries per 30 µm width as a function of coating thickness.

Presence of fine precipitates slows down recrystallization by subgrain boundary pinning, moreover grain boundary segregations modifies the grain boundary energy and therefore their mobility.
The coalescence with a neighbouring site belonging to the same grain is possible during this period.
Grain and Subgrain Growth Model The decrease of local energy due to the subgrain and grain growth is modelled by using the classical Read - Shokley approach for grain boundary energy )(θγ : the energy of low angle boundaries is calculated with the Read and Shokley equation and for the high angle boundaries (HAB) it is assumed that HABγ is constant ( HABγ =0.78J/m2 for pure iron).
The way to take them into account is to introduce the influence of grain boundary mobility (Eq. 6).
The other possibility used in some Monte-Carlo simulations is to assume that the probability of the state evolution depends on the grain boundary mobility for positive energy change: P(ik)=M(θ) (8) The influence of the condition chosen for the evolution way choice is revealed by comparing the recrystallized surface fraction and the texture of recrystallized zone for the same number of Monte Carlo steps for different probability choice (Fig. 3).

The grain sizes were estimated with reference to the ASTM standard [4].
Those factors favor the growth of equi-axed grains.
As a result, the structure becomes coarse equi-axed grains.
The grains of strip plate made by conventional horizontal continuous casting are coarse, which requires 7 hours or more annealing time to obtain needed re-crystallization grains size.
A large number of experimental results indicate that the service life of graphite mold can be extended from 168 hours to 334 hours.

Such dislocations accumulated in ultrafine grains play a significant role in the plastic deformation.
The number of ARB cycles was 6; such sample is referred to as 6C.
Thus, it is considered that the tangled dislocations accumulated during the ARB process are immobile without an external stress and contribute to the grain subdivision, leading to the ultrafine grained materials.
In contrast, it is natural to consider that the 6C-ARB sample with ultrafine grains that have few dislocations by annealing is hardly deformed, although there remains a question why generation of dislocations is so difficult for such ultrafine grained materials.
Such dislocations accumulated in ultrafine grains play a significant role in the deformation.

(1) where σ is the discrete parameter, xi refers to the difference between any given nominal grain diameter (di) and mean grain diameter(dmean), while xmax, xcmin and xwmin are for maximum grain, minimum cutting grain, minimum contacting grain, respectively.
(3) where NS is the average number of grains per unit area defined in literature [3], NTotal= b×vw×NS ,is the total number of grains passing through the grinding area per second, vs refers to the wheel speed, and A(x) is the chip cross-section area which has been defined in literature [6].
On the basis of the cutting force analysis of a single abrasive grain [3], the tangential sliding force of a single abrasive grain can be written as: ag O A(x) rox rx θ/2             1 css gw 0tc lvN av F
Hokkirigawa [7], the tangential sliding force of a single abrasive grain can be written as: 2 oxV tw rHF 
The number of the cutting and contacting grains is obtained by the statistical probability theory.