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Rare earth element Y has a high melting point, and Y is added in the Mg-Al alloy which mainly through solid solution strengthening, precipitation strengthening and fine-grain strengthening to improve comprehensive mechanical properties.[8-10] Therefore, this article chooses Mg-6Al-1Zn-1.8Gd magnesium alloy as the research object, add a certain amount of rare earth elements Y (wt.0.9%) to improve its microstructure and mechanical properties.
It can been seen from Fig. 2 that the alloy grain size is uniformity, and some black dendritic crystal is distributed around the alloy grain boundary and in the grain.
Grain tiny helps to improve the alloy mechanical properties at room and high temperature.
At room temperature, tensile fracture surface has a large number of torn edges and cleavage steps, and has the nature of the cleavage or quasi cleavage, it is a typical brittle fracture.

As a result, the obtained sample represents a set of coalescent drops with a large number of pores.
The same sort of situation with the considerable diversity in grain particle sizes occurred with iron powder.
The powder grain shape is spherical and the range of particle dimensions is from 70 µm to 130 µm (Fig.2).
Due to the sample and substrate heating, poriness decreases and powder grains are melted more smoothly.
Thus, the diversity in average grain particle sizes of stainless steel over the dimensional ranges was not considerable.

Introduction Barium titanate (BT) as a ferroelectric material with perovskite structure has been extensively used in electronic industry including a number of dielectric, electro-optic and other electronic devices for its high dielectric constant and low losses.
The electrical properties such as permittivity, Curie temperature and phase assemblage have been found to be sensitive to the grain size and the characteristics of grain boundaries. [4] In recent years, first-principle calculations have been very successful in the study of BT materials, and greatly deepened our understanding of the origin of ferroelectricity. [5-6] From these investigations, it has been found that the ferroelectric instability occurs as a result of the delicate balance between long-range Coulomb interactions that favor the ferroelectric state, and the short-range forces that favor the cubic paraelectric phase. [7-8] To our knowledge, there is little investigation on the electronic structure of nanograin BT ceramics by first principle calculations, due to the difficult preparation of nano specimen.
We have calculated total density of states of BT ceramics so as to understand the difference of atoms distribution between different grain size BT ceramics.
And as for Ti 3d, there is one high peak around 0 eV, this means the covalent interaction between O 2p and Ti 3d is very strong in nanocrystalline BT ceramics, which means that there is hybridization between Ti 3d and O 2p, and this hybridization weakens the short-range repulsions and stabilizes the ferroelectricity, demonstrating the critical grain size of BT ceramics is below 50 nm, which is well consistent with our precious research on the critical grain size of nanocrystalline BT ceramics. [12] Conclusions In summary, we have performed FLAPW calculations to investigate the ferroelectricity of 50 nm BT ceramics.

The small grains as well as the high dislocation density result in a further lowering of thermal conductivity holding a high potential for future enhancement of ZT.
A rise in S means a rise in r and because of the Wiedemann Franz Law (with Lorenz number L = 2.44 x 10-8 WΩ/K2), le is dependent on r and vice versa.
Enhanced phonon scattering on grain boundaries and/or interfaces of a nanostructured material may offer a way to reduce lph [6-15].
We also will show the positive impact of HPT on transport properties, grain size and size distribution on some selected p- and n-type skutterudites.
The small grains as well as the high dislocation density result in low thermal conductivities.

The invited papers covered the following main items a) Volume Diffusion, b) Grain-boundary diffusion, c) Technical aspects and applications.
Special emphasis was given to new problems (diffusion in high Tc superconductors, diffusion in metallic glasses and nanocrystalline materials etc) and to the fields of diffusion in metals which have extended defects (dislocations, grain boundaries, solid-solid interfaces, particles of second phases with a stress field around them).
According to the final registration the number of participants was about 170 scientists from 20 countries.

ECAE is the most promising severe plastic deformation (SPD) technique, and it is widely used to fabricate bulk ultrafine grain materials [9], compaction of powders [9-14], and mechanical property enhancement of tubular materials [15].
Fig. 1(b) shows the transverse cross-section of the MgB2 PITs after different number of passes via different routes of ECAE.
Table 1 shows the density of the compact before and after number of passes via different routes of ECAE.
Conclusions The MgB2 PITs with Fe tube were processed through number of ECAE passes via different routes: A, BA, C and BC.
Seow: Ultrafine Grain Materials IV, Edited by Y.T.

With increase of heat treatment temperature, structure of the plating transitioned gradually from amorphous state to crystalline state, and Ni3P crystal grain grown up, and it affect hardness of the plating.
Table 1 Uniform design scheme about heat treatment and hardness of Ni-P plating Serial number Index mark Factor 1 Factor 2 Hardness of plating / HV Heating temperature of / Heating time / h 1 586 200 2.0 2 775 250 3.5 3 930 300 5.0 4 1020 350 1.5 5 1100 400 3.0 6 1010 450 4.5 7 970 500 1.0 8 955 550 2.5 9 820 600 4.0 Fig.1 Morphology of electroless Ni-P plating Results and discussions Mathematical model is established according to law of metal phase transition and shown as expression (1): (1) Type: - Microhardness of the plating ( HV ); - Aging temperature (°C ); - Aging time ( h ); - Regression coeffcient.
Fig.4 (a) shows that structure of the plating is amorphous state when the aging temperature is 200°C and 250°C, but according to hardness number, there should be small microcrystal in the structure of the plating when the aging treatment was carried out at 250°C, which didn’t be detected by XRD.
Fig.4 (c) illustrates that full width at half maximum ( FWHM ) of diffraction peaks in XRD diffraction pattern narrow gradually with further increase of aging temperature, and crystal feature becomes more obvious, the grain size of Ni3P phase grow up gradually, which causes the hardness of the plating to decreas gradually.

It shows that local extrusion used in die casting production can not only achieve the aim eliminating shrinkage porosity and cavity of a casting but also can refine grain to improve the mechanical properties.
The feeding effect is better and microstructure is more density as the local extrusion force is stronger. 2) The analyze result of the tensile test and metallographic test shows that the local extrusion-die casting process can not only achieve the aim eliminating shrinkage porosity and cavity of a casting , but also can refine grain to improves its mechanical properties.
Guizhou technology committee industrial public relation project, the project number: Guizhou province (2012) NO.3004. 2.
Guiyang Industrial Public Relation Project, the project number: Guiyang (2012) NO.101-2-13 References [1] Wohlfahrt H: Giesserei Vol.86 (1999) NO.5, p. 73-75

On other hand, according to the similarity laws proposed by Yalin, in which the grain Reynolds number, dimensionless tractive force, Froude number and skin friction were adopted as similar criteria, the bed material of the distorted model experiments is restricted solely to lightweight material.
According to eq. (19), (24) and the definitions of discharge and Froude number (Fr), eq. (25) and (26) can be obtained.
Fig. 2 Grain-size distribution curves for model bed material Sand and lapilli were used as bed material in the model experiments.
The specific gravity and mean grain diameter are listed in table 2, and the distribution curves of the grain size of the bed material are shown in Fig.2.
The Chubetsu River has an average slope, I p, of 1/138, and its bed consists of small gravels with a mean grain diameter, dp, of 71mm.

Subboundary and grain-boundary strengthening is more effective as the nitrides are more stable than carbides, and they retard grain growth up to higher temperatures.
As compared to the base steel, nitrogen-alloyed steels have higher stresses at steady-state stage of deformation σss and finer recrystallized grains [5].
Decrease in the diffusion rate retards the dislocation climbing and grain boundary migration, and thus leads to a general retardation of the recrystallization while the hardening level is rather high.
Increasing the deformation rate up to 10 s -1 results in an increase in the number of structural defects, thus facilitating dynamic recrystallization and, as a consequence, σmax drop.
The fraction of recrystallized grains increases with strain rate decreasing and at high temperature, rising of the deforming forces.