Search results

The test samples used in this study are ground by vitrified bond diamond grinding wheels with different grain sizes.
And the grinding wheels with grain sizes of 25μm and 7μm were both used.
It is found that the surface of the glass-ceramics ground by grain size of W25 with rough surface has large numbers of dense pits.
For the ultra-precision grinding process, the material removal mechanism can be considered as the cutting of a single abrasive grain and the interaction of large numbers of closely spaced abrasive grains [5].
Two vitrified bond diamond grinding wheels with the grain sizes of 25μm and 7μm were both used, in order to research the influence of the abrasive grain size on surface and subsurface integrity during ultra-precision grinding.

It must be noted, among others, that the definition of a more complex model implies the use of an increased number of parameters.
This, inevitably, involves the use of a large number of model parameters, which then need to be known a priori as a function of composition, if alloy design is the aim.
This couple of time and temperature will be assumed to yield a perfectly homogeneous solid solution, but grain growth will occur, for which a first model will be used to calculate the grain size, d, using a classical growth law [8]: d=d02+g.t (1) with t the time and g the grain growth rate.
The effect of grain size will be expressed using the classical Hall-Petch law: ∆σGS=kd (3) where ΔσGS is the strengthening due to the Hall-Petch effect, k is the Hall-Petch coefficient (5538 MPa.nm1/2 for nickel [11]) and d is the grain size calculated by Eq. 1.
In an actual ICMS or ICME approach, on the one hand more complex models would be used, i.e. with more parameters in each model, and on the other hand a higher number of models may be integrated, also increasing the total number of parameters.

The grain size of about 1 µm was obtained in the Zn-0.3 wt.% Al alloy and a relatively coarse grain size of 10 µm was also obtained through a subsequent aging treatment.
According to the internal variable theory of structural superplasticity, the grain boundary characters of fine and coarse-grained materials were different from each other.
There have been an extensive number of reports on SSP in the various classes of materials including metallic materials, ceramics, and amorphous alloy [5-8].
A relatively coarse-grained material with the grain size of 10 µm was also prepared through a subsequent aging treatment of the fine-grained material to investigate the grain size effect.
This result strongly suggests that the character of grain boundary can also be changed with the severe grain refinement.

Fig.1 Schematic precipitate microstructure in Al-Li alloys Schematic precipitate microstructure in Al-Li alloys shows in Fig. 1[4],main precipitates include δ’ (Al3Li), β’, θ’ (Al2Cu), T1 (Al2CuLi), S’ (Al2CuMg), Al20Cu2Mn3, etc..One of the effective method of Improve Al-Li alloys’ properties is regulating the corresponding microstructure by multi-micro-alloying.A large number of researches have shown that trace amount of certain elements to add will significantly affect the microstructure and mechanical properties of Al-Li alloy, For example, changing the size,shape,distribution of the precipitated phase and the volume fraction or generating new strengthening phase,and refining grains, controlling recrystallization and grain orientation,etc. [5,6].
Fig. 2(a) shows 2A97T3 Al-Li alloy base metal microstructure, the major phase is α-Al, and the precipitates distribute and in the grains and grain boundaries.The heat affected zone(HAZ) is presented in Figure 2(b).Comparing the grain size between Fig. 2(a) and Fig.2(b),it shows that the grain size of HAZ is slight larger than of base metal(BM).
From the HAZ to BM,grain size shows no obvious difference,and the HAZ is rather narrow.
in this area,as well as the high surface activity of lithium,making nucleation rate very high, namely a large number of fine spherical equiaxed grains are formed in EQZ[8].Specifically,on the one hand, those suspended particles can reduce the wetting angleθ,on the other hand,the high surface activity of lithium may lower the surface tension coefficient σ,subsequently reduce the energy required for non-spontaneous nucleus,EQZ are developed in the end.
Fig.4 Microstructure of FZ（×500） (a) non-dendritic equiaxed grain zone（b）columnar crystal zone （c）columnar dendrite zone(d)equiaxed dendrite zone Fig.5 Schematic of crystallization of the welding joint A narrow band of EQZ which consists of spherical equiaxed grains is located between the partial melted zone (PMZ) and FZ,as shown in Fig. 4(a).

This is primarily due to the low grain size in the range between 5 and 100 nm and the resulting high number of grain boundaries.
In addition to residual stresses [5], also a high number of non-equilibrium vacancies are present [6].
The large number of grain boundary interfaces is a strong driving force for grain growth [7].
Θ 2Θ q grain sample ki kf Fig. 2: Schematic set-up of GIXRD.
The number of atomic planes, N, should be an integer.

These boundaries correspond to high-angle grain boundaries.
The area fraction of Cube oriented grains was largest when the area fraction of recrystallized grains reached 100 % in each alloy.
Therefore, Therefore, the <0 0 1> grains shown in Fig. 9 are considered to recover more easily and grow more preferentially than other grains.
Cube oriented {0 0 1}<1 0 0> grains in aluminum alloys is considered to be able to grow preferentially similarly to <0 0 1>grains.
In　MZ alloy homogeneized at 590 ℃, the number of recrystallized grains immediately after the deformation is smaller than M alloy.

A large number of subsequent efforts on ceramics as well as single-crystal samples were made to explain the universal dielectric properties of CCTO based on respective experimental results, and revealed additional features, such as dipolar relaxation, relaxor behavior and strong non-linearity [2-5].
The polygonal grains and an unobvious bimodal distribution of grain size have been observed.
Ceramics with small grains has higher grain boundary concentration, corresponding to higher compression on grains, than that with large grains[4, 16].
Inset is the Arrhenius plots for the conductivities of grain and grain boundary.
Complex impedance analysis has been used to distinguish the resistance between grains and grain boundaries.

The grains of the matrix were finer in Mg2Si-L than in Mg2Si-H.
The matrix microstructures in Fig.2 consist of equiaxed grain structure with the average grain sizes of 12.1 µm and 7.0 µm for Mg2Si-H and -L, respectively, where lower working temperature contributed to the grain refinement in the matrix as discussed in the previous report [3].
Surface crack length, 2c, is shown in Fig.4 as a function of cycle ratio, N/Nf, where N is number of cycles and Nf the fatigue life.
S-N diagram. 104 105 106 107 50 100 150 200 Number of cycles to failure Nf Stress amplitude σ (MPa) Mg2Si/AZ31-H Mg2Si/AZ31 composite Mg2Si/AZ31-L Extruded AZ31 Mg2Si-H Mg2Si-L Fig.5.
It could be attributed to finer grains in the matrix and higher bonding strength of Mg2Si/Mg interfaces

Increasing the brazing time also enhanced the formation of grain boundary boride.
Higher brazing temperature and/or longer brazing time favored boron transport along grain boundary.
The grain boundary provided a high diffusivity path for boron diffusion, and formed the stable borides along grain boundaries during brazing.
Higher brazing temperature and/or longer brazing time enhance boron transport along grain boundary.
Acknowledgements Authors gratefully acknowledge the financial support of this research by Ministry of Science and Technology, Taiwan (Contract number MOST 103-2221-E-002-213-MY3).

As shown in Fig. 4(a), from the perspective of the metallographic structure, the base stock of the Hastelloy C-276 cylindrical part prior to the power spinning process is made of single-phase austenites (grain fineness number: 4-5) including a considerable amount of twins.
Fig. 4(c) shows the metallographic structure of the annealed base stock with a thickness reduction rate of 79%, which is similar to the case prior to power spinning in its grain fineness number and grain shape.
It can be seen that while the thickness reduction rate increases, the grains in the base stock are refined to a greater extent and arranged more neatly and more densely, leading to higher strength and lower plasticity.
Both the number and the size of corrosion pits increase as the thickness reduction rate grows, and its corrosion resistance after the power spinning process as well as the internal stress-relieving annealing treatment is obviously higher that that of raw materials.
Conclusions The impacts of the power spinning process on the cylindrical part can be summarized as follows: The firs, the grains in the base stock and the weld zones of the Hastelloy C-276 cylindrical part are refined during the power spinning process at room temperature, causing higher grain directivity and strength and lower plasticity.