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In the cerammed state, they present a number of advantages including control over dissolution rates and mechanical properties by altering the composition of the parent glass or heat treatment regime.
A novel coating method using a bioactive glass-ceramic has been developed that presents a number of potential advantages for the coating of medical parts.
(A) is a dark field image with the objective aperture on a mullite spot; SAD shows the presence of predominantly coarse grained mullite (appears lighter in the DF image) with some fine grained FAp (darker in the DF image) and a large amount of residual glass.
(D) is a dark field image of large columnar grains of titanium; the SAD image is along the [001] axis of the Ti grain.
(F) has large Ti grains and pores of unknown origin.

A combination of welding stresses and reduced ductility of an alloy due to melting of the grain boundary material, i.e., grain boundary liquation, results in intergranular cracking in HAZ.
Grain Boundary Segregation Mechanism.
Absorption of vacancies at grain boundaries during cooling from the elevated temperature after thermal processing can produce a concentration gradient of complexes, which would drive the complexes to diffuse from within the grain to the grain boundary region.
This results in vacancies associated with complexes being absorbed at the grain boundaries and a build up of excessive concentration of solute atoms in the vicinity of grain boundaries.
The number and length of cracks were observed to increase with an increase in the concentration of S and B.

The prior austenite grain size ranged between 50 ~ 60 μm as measured by linear intercept method.
Irrespective to the treatment duration, constant grain size was referred to the thermally stable carbides found along the austenite grain boundaries inhibiting the growth of austenite grains [5].
Fig. 9 shows the effect of increasing the ageing time on the mean grain size.
The influence of different aging times on average grain size.
Acknowledgments This work was supported by the National Science, Technology and Innovation Plan (NSTIP) strategic technologies program, within the project number (08-ADV-209-02) in the Kingdom of Saudi Arabia.

The fine grain is good for performance.
Fig.1 Schematics of suction casting and blade casting Result and discussion The Ti-47Al-5Nb-0.5Si alloy structure can be seen from the figure 2, and Ti-47Al-5Nb-0.5Si alloy structure has small grain size, with an average grain size of 20um or less, and some grains even smaller than 10um.
According Ti5Si3 phase distribution, it can be seen, the Ti5Si3 phase mainly in the grains, and there are a small number of Ti5Si3, which proved, formed during the solidification phase Ti5Si3 in addition to providing nucleation particles, but also hinder the grain growth during solidification, thereby grain refinement.
If more than B2 phase, the α grains are more susceptible to obstruction of the B2 phase on growing, while the β-phase stabilizing elements Nb, Nb elements are added, is conducive to the formation of the B2 phase, so that the grain size becomes thin.
Long term creep of TiAl + W + Si with polycrystalline and columnar grain structures [J].

It was found that the grain growth was restrained with the addition of Ba2+.
It is widely accepted that the transport properties in these polycrystalline ceramic varistors are mainly controlled by the electrically active grain boundaries between the semiconducting ZnO grains [4].
The l˚Cal defects on the grain boundary regions are ionized on both sides of the grain which gives rise to the depletion region.
The average grain size (l) is determined by the lineal intercept method, given by l=1.56L/MN, where L is the total line length on the micrograph, M is the magnification of the photomicrograph, 1.56 is the proportionality constant, and N is the number of the grain boundaries by lines[7].
This is mainly attributed to the increase in the number of grain boundaries caused by the decrease in the ZnO grain size.

In order to simulate the polyhedral grain nucleation in alloys, 3-D cell population growth processes are studied in space-filling periodic cellular systems.
This is due to the fact that materials characterized by cellular structures (froths, foams, tissues, grain aggregates in polycrystals, glasses) occur frequently in nature and in practice.
For this FTC system consisting of a finite set of cells the Euler-equation is valid in the following form : 0NFEV =−+− (1) where N is the number of cells (combinatorial polyhedra), F is the number of faces (interfaces), E is the number of edges, and V is the number of vertices, respectively.
The total number N of cells is N=∑ fN where Nf is the number of f-sided cells (f=4,5,... fmax).
The cell population growth algorithm based on inserted tetrahedra may be applied to simulate grain nucleation and growth processes occurring during solid state transformations in alloys with polyhedral microstructure (for example, abnormal grain growth and recrystallization processes).

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.

A number of particles near the surfaces of the cell wall are slug trapped during casting.
Large number of micro-pores (typically more than 1000 pores per part of a cell wall captured) is observed in the volume.
Large number of Zn- and Ti-bearing intermetallic particles is also observed in the reconstructed volume.
Grain boundary.
It seems most likely that stress singularity at free edges of grain boundaries (i.e. intersections between surface and grain boundaries) reduces apparent stress necessary for grain boundary fracture.

Introduction Nano-metallic materials [1] appeared in the mid-1980s, which are structurally characterized by nanometer-sized grains with a large number of grain boundaries, occupying over 50 percent of volume fraction.
As the grain size decreases, the volume fraction of grain boundaries is more and more, and whether grain boundaries activities dominate plastic deformation is not sure.
Whether there is an accessible relation between grain size and the wear resistance.
In fact, grain refinement could enhance the friction and wear resistance of materials.
Variation of the friction coefficient with the number of cycle for the SMAT Cu and the CG Cu samples against a WC-Co ball in mineral oil under the given test parameters: normal load of 50 N, frequency of 20 Hz, slip amplitude of 50 lm, and fretting cycle of 72,000 [26].

But they are strongly dependence on the number of CGP passes and the pressing modes.
However, nearly all of the investigations were focused on the microstructures evolution and grain refinement of the materials.
As can be seen in Fig. 1, the grains have been refined to submicron-meter level after four passes.
The difference in variation trend may be attributed to the difference in the rate of grain refinement [15].
In addition, the decrease in the dimple size should be associated with the grain refinement of samples processed by CGP [16,18-19].