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A number of factors that may affect morphology of mullite nanocrytals synthesized from kaolin have been studied and discussed [2-4].
This change reflects a change inside mullite lattice that there is an increase in number of oxygen vacancies and a change in Si/Al molar ratio, thus affecting mulite composition and morphology.
Spherical crystals with only a few acicular crystals and have a relatively similar grain size (Fig. 5a, 5b, 5c, and 5d).
According to the theoretic growth unit model of negative ionic coordination polyhedral [9-10], the growth units are OH- complex compounds and their coordination number is the same as that of the cations contained within mullite crystals.
When the Si / Al ratio was high, the growth of mullite crystal in re-crystal process, in other word, was the growth of a certain amount of crystal seed of mullite whiskers in the mullite body of the precursor, which could act as the growing point of columnar crystal grains to grow into columnar and tabular crystal grains.

Continuous non discrete distribution function dn/d(ΔT) is used to describe the change of the grain density during nucleation. dn refers to the grain density increases with the increase of supercooling temperature ΔT, dn/d(ΔT) is determined by the Gaussian distribution function as follow[5]
As it can be seen from Fig. 5 and table 2, along with the rising of the heat transfer coefficient, grain number increases, primary phase morphology gradually changes from bulky isometric dendrite to small dendrites, the average grain size decreases.
Moreover, nucleation rate rises quicklier than crystal growth, so the ratio of the nucleation rate and crystal growth improves, which makes grain size small.
It provides grain nucleation and growth for favorable conditions
As it increases, the average grain size is smaller.

As shown in the below figure(see Fig. 1), according to statistics of a large number of samples, the growth bands can be summarized into three categories, respectively high transparent bright band (A2, B1, C1, C3), almost opaque dark band (D1) and normal band of the yellow color (A1, A3, B2, C2, D2).
Grain Morphology.
Fig. 2(a) shows the grain morphology of the normal bands, which is narrow grain extending their boundaries along the growth direction.
Fig. 2(b) and 2(c) show the grain morphologies of the bright band, both of them are the large grains, but the grain morphologies are obviously different, grains shown in Fig. 2(c) extend their boundaries in all directions, and their shapes are similar with that treated by hot isostatic pressing, but there are some small grains shown in Fig. 2(a) mixed among the big grains.
Fig. 3 Grain morphologies between transition bands, there are obvious change in grain morphologies between different bands.

The increase of the density of deformation bands divides the austenite grain into multiple grains of smaller size.
Therefore, the deformation accumulates in the austenite grains.
Development of incremental deformation processes is relatively complicated, because they include a large number of interconnected phenomena.
Tab. 2 First experimental part: F-ferrite, B-bainite, A-austenite, P-pearlite Interval of deformation [°C] Number of def. steps Micro-structure j [-] Grain size of ferrite [mm] Ferrite [%] Ret.
Ferritic grain about 2.1±0.9μm in size approaches the known physical limit of grain refinement by means of thermomechanical treatment.

These concentrations act as sources of damage initiators at the binder/carbide grains interfaces.
Metal matrix composites with ceramic grains are other examples of complex materials [4-8].
In particular, we analysed random internal structure of the metal matrix composites with ceramic grains.
It is particularly visible near the metallic binder(Co)/carbide grains (WC) interface.
This work was financially supported by Ministry of Science and Higher Education within the statutory research number S/20/2013.

When the stress gets the maximum value, the grains within the shear band begin to rotate, and dislocations in the grain interior begin to slip, which leads to shape changes of the grains, especially for elongation.
So grains will become flatter and longer.
We choose grains nearing the center of shear band as an aggregate.
A softening coefficient, which is proportional to strain in softening stage, is defined as: . (6) Here Ns is the number of softening grains with orientations parallel to shear band, Nt the total number of grains in the aggregate, εsoft the strain in softening stage, εu the strain corresponding to ultimate strength and εb the fracture strain at which material reaches to its limiting bearing ability.
The flow stress levels are generally higher in fine grain sized materials than in coarse grained materials.

Small particle size of reagents implies that sufficient number of crystal nuclei is provided in the mixture so that fine grain size of the product can be expected when sintered under appropriate conditions.
Phase fraction and the size of coherently diffracting domains (estimated grain size) were calculated.
Moreover, melting temperature of nanoparticles is decreased compared to coarse-grained material.
Thus, SPS of nanopowders allowed us to obtain fine grained nickel aluminide composite materials.
High homogeneity level of the powder mixture facilitated the initiation of the reaction in a larger number of points within the sample resulting in higher densification level in the sample as a whole.

Self-Diffusion along Grain Boundaries in Nickel Large uncertainties exist in the literature data concerning the grain boundary self-diffusion in nickel [8].
A dense twin network and/or presence of low-angle grain boundaries were identified as the probable causes.
Apparent Volume Diffusivities in Polycrystalline Magnesium Hexagonal metals are different from cubic metals in respect to the number of restricted slip systems and the activation of twinning.
Gust: Fundamentals of Grain and Interphase Boundary Diffusion (Wiley, Chichester 1995)
Kozma: Handbook of Grain and Interphase Boundary Diffusion Data (Ziegler Press, Stuttgart 1989)

Four total cracked bolts number of R1 to R8 on the same graph also show four distribution peaks.
Moreover, similar results can be obtained in Point Beach 2 unit as shown in fig. 2, which show a variation of cracked bolts number with the former number.
Fig. 1 Neutron irradiation damage and cracked bolts distribution in Tihange 1 unit [3] Fig. 2 The number of IASCC bolts distribution of Point Beach 2 unit with the fomer number In fact, according to the OER, irradiation fluence has been the key factor to judge whether a BFB should be replaced or not in engineering area.
RIS will cause the depletion of Cr at grain boundaries, along with enrichment of Ni.
It is inferred that Cr depletion at the grain boundary increases IASCC sensitivity.

In fact, the 2195 alloy during the artificial aging (AA) show that the microstructure evolution goes as follows: SSS→GP zone →δ′ (Al3Li), θ′, T 1→θ′(Al 2 Cu), T1(Al 2 CuLi) phase, and the number density increased and coarsening of θ′ and T 1 with prolonging of aging time[3].
At the same time, a large number of precipitated phases can be seen in the grain boundaries in the stress relaxation aging sample in the fig. 4 (a).
Wherefore it can be clearly seen that both nano-precipitates T1 and θ ' are uniformly distributed in the grain boundaries and the grains.
The results also show that in the stress relaxation aging, the precipitated phase precipitates uniformly at the grain boundary and in the crystal, reducing the strength difference between the grain boundary and in the crystal, and improving the elongation of 2195 Al Li alloy
Grain Boundary Precipitation and Fracture Behavior of Al–Cu–Li Alloys. 2018:217-23