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GRAIN BOUNDARY SEGREGATION AND PRECIPITATION IN ALUMINIUM ALLOY AA6061 M.
These characteristics strongly depend on grain boundary phenomena, such as the size, distribution and chemistry of the grain boundary precipitates.
The number of grain boundary precipitates analyzed, the number of different random high-angle grain boundaries analyzed and the final standard deviation in the relative concentrations are listed as well.
Fig 2: TEM micrographs of grain boundary precipitates in AA6061: (a) Matrix (left grain) in [001]-projection (b) Matrix (left grain) in [011]-projection 4.
The measured [Mg]/[Si]-ratio of the precipitates at the grain boundaries is ~ 2.3.

The casting sample made without ultrasonic vibration exhibited coarse acicular grains of about 315 μm average grain size (Fig.2a).
Fig. 2 The microstructure of the samples treated at ultrasonic power of 0 kW(a), 0.6 kW(b), 1.2 kW(c), 1.8 kW(d) and 2.4 kW(e) According to the ultrasonic cavitation effect, a strong shock wave produced by the collapsed hole causes nonlinear mechanical damage to the cavitation bubbles near the solid phase, and repeated high-speed impacts lead to local damage to the solidphase, increasing the number of grains.
For non-wetting particles, the cavitation effect can easily produce, so in solidification front a continuous cavitation will repeatly generate, the formation of local cavitation heat pulse will continuously impact solidification front, the interface of particles will partially ablate, thereby the number of grains increases and the size of grain decreases, and the refined grain structure leads to increased hardness.
Thus, the growth rate of the crystal grains increases and the crystal grains are refined.
Ultrasonic treatment causes coarse grains to be refined, the number of large grains decreases significantly, and the size of grains is more homogenous.

In order to evaluate whether or not the proposed misorientation condition is obeyed, the number fraction dn of the experimentally measured distribution must be compared with the number fractions dr obtained for a random misorientation distribution.
The ratio dn/dr can be interpreted as the number intensity fi of the given reference misorientation ∆gr.
Tolerance [º] Number Fraction Nuclei [%] Number Fraction Grown Grains [%] Density Nuclei Density Grown Grains 5 0.37 6.49 0.37 6.46 10 2.46 23.4 0.30 2.89 15 11.7 67.5 0.43 2.47 Table 1 : Number fractions and number densities of nuclei and grown grains observed in a growth experiment on Fe-2.8%Si, before and after growth, respectively.
In the first example it was shown that the <110>26.5º orientation relation controls the selective growth of a number of nucleus grains, which grow at the expense of a single crystal matrix of a Fe-2.8%Si steel.
Conf. on Grain Growth, ICGG-3, Ed. by H.

The composite coating is a mechanical disordered composite; a large number of spheroidal ceramic grains are distributed in Ni base alloy matrix.
Because the thermal expansion coefficients and elastic modulus of Ni base alloy and spheroidal ceramic grains are different, there will be residual stresses in both ceramic grains and Ni base alloy in fabricating process.
V1 is the volume of the ceramic grain in two-phase cell.
Thermal expansion coefficients of two-phase cell For two-phase cell，Ni base alloy and ceramic grain are isotropy, the elastic constants of Ni base alloy and ceramic grain can be expressed as (8) Where, and, are Lame’s constants of Ni base alloy and ceramic grain respectively.
For the spheroidal ceramic grains, Sijkl can be determined by reference [7].

Observations on the as-extruded sample revealed the microstructure prior to HPT consisted of equiaxed grain with a grain size of ~20μm and Mg12Nd intermetallics along grain boundaries: this was determined by TEM in earlier work[9] as shown in Fig. 1.
Figure 2(d) shows the peripheral region of the same disk, where the microstructures of the α-Mg matrix are significantly refined after HPT processing through 1/4 turn although a small number of original grain boundaries are detected, as indicated by arrowheads.
With increase of numbers of revolutions, the initial grain boundaries and twins tend to be gradually lost as shown in Figs 2(b) and 2(c) for the microstructures taken from the central region of the disks after HPT for 1 turn and 5 turns, respectively.
Although the grain boundaries are generally ill-defined in Fig. 4(b), a limited number of small equiaxed grains with average grain size of ~200 nm are clearly visible using a higher magnification, as shown in Fig. 4(c) and (d) via bright-field and dark-field images, respectively.
The inhibition of deformation twinning is expected from easier accommodation of shear strain on many available grain boundaries and easier release of stress concentrations via non-basal slip, cross slip or grain boundary sliding with finer grain sizes.

Introduction A considerable number of reports have been published on the unconventional mechanical behavior of nano grain-sized materials due to the extremely high density of grain boundary area[1-7].
Change in tensile property of oxygen-free copper with respect to the number of (a) ECAP and (b) ARB process cycles.
A large number of dislocations began to be observed in the ECAPed specimen even after the first cycle.
Once the equiaxed grains formed, the dislocation density inside the grains appeared to decrease with further ECAP process.
The number of dislocations appeared to increase with further ARB process and nano-grains tended form although the normal direction to rolling plane.

Therefore, as the grain size decreases, the strength of the material increases.
From fig 4, we can see that the grain refinement takes place as the number of high angle boundaries increase with the number of passes and this is also an evidence for the attainment of high tensile properties obtained earlier.
The dislocation cell structure as depicted by the TEM micrographs shown in fig 4 clearly indicates that the dislocation density increases with the increase in number of passes which ultimately leads to the grain refinement and pore size reduction.
Variation of pore diameter with number of passes From figure it can be seen that the diameter of pore decreases with increase in number of passes and also the pore diameter reduction is more in pass 2A and 3A than that of 2C and 3C.
· The grain size decreases with the increase in number of passes thereby providing increase in tensile strength after each pass.

The pattern of deformation stages depends on the average grain size, defect structure of grains and their boundaries, internal stresses, texture and grain size distribution.
Sliding along grains boundaries and intergrain dislocation activity take place in the largest grains.
In materials with grain sizes less than 100 nm there are no dislocations inside grains, whereas in grains larger than 100 nm dislocations are present.
In these publications, analysis of a large number of s = f (e) dependences, for such materials as copper, cobalt, copper and aluminum alloys with grain sizes in the range of 12nm to 230 nm was performed.
To obtain the dependence presented in Fig. 3, a considerable number of s = f(e)dependences published by different researchers [2, 5-10] were evaluated by the authors of the present paper.

A number of models of the recrystallisation behaviour of IN718 have been developed [3-6] which are based on empirical observations of the relationships between strain, strain rate and temperature and the recrystallised volume fraction and grain size.
Set initial conditions Calculate if delta phase is present Increase grain set diameter Calculate dislocation density Recrystallising or growing Increase grain set diameter R G Set new number of dislocations Set dislocation density in new grains Nucleate new grains Calculate length of grain boundary available for nucleation Calculate partition ratios New increment Set new number of dislocations Set new dislocation density Stop Y N Set initial conditions Calculate if delta phase is present Increase grain set diameter Calculate dislocation density Recrystallising or growing Increase grain set diameter R G Set new number of dislocations Set dislocation density in new grains Nucleate new grains Calculate length of grain boundary available for nucleation Calculate partition ratios New increment Set new number of dislocations Set new dislocation density Stop Set initial conditions Calculate if delta phase is present
Increase grain set diameter Calculate dislocation density Recrystallising or growing Increase grain set diameter R G Set new number of dislocations Set dislocation density in new grains Nucleate new grains Calculate length of grain boundary available for nucleation Calculate partition ratios New increment Set new number of dislocations Set new dislocation density Stop Y N Figure 3.
At 1080 o C both models predicted the grain size to within one ASTM number however the volume fractions recrystallised were over predicted significantly.
At 1000 o C the volume fractions recrystallised were better at within 5% however the grain sizes were less reliable with some predictions being 2-3 ASTM numbers in error.

Biphasic Calcium Phosphate: preferential ionic substitutions and crystallographic relationships at grain boundaries T.
Biphasic Calcium Phosphate, Grain boundary, solid solution Abstract.
Numbers in ( ) correspond to estimated standard deviations.
Imaging at high magnification showed that the lattice lines are stopped at the interface (boundary line) between the grains without direct continuity (Fig. 3).
This study was supported by 7eme PCRD GAMBA grant number NMP3-SL-2010-24599 and 7th PCRD REBORNE grant number GA-241879/HEALTH-2009-1-4-2.