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The average grain size of precipitated phases of the sample of 610°C×8h, 630°C×8h, 645°C×8h is 52nm, 72nm, 79nm, respectively, by the Scherrer formula.
On the other hand is due to grain growth with increasing the heat-treated temperature, the diffusion mechanism of the samples was changed for the grain coarsening; because the grain is larger, as a priority channel for grain boundaries diffusion less, thus, more difficult to form the passive film.
Moreover, with the increasing of crystal fraction and grain size, a large number of the separation phase appear in grain boundaries, which make grain boundaries priority dissolved, reduce the current efficiency and enhance the corrosion degree.

The number and morphology of these particles are important for the recrystallization, texture, grain size and mechanical properties of the manufactured products [1].
Microstructure observed in AlMnZr alloy sample, SEM imaging On the other hand, the sample of AlMnMgZr alloy was characterized by the presence of fine manganese precipitates concentrated mainly at grain boundaries.
In this alloy, nanometric lamellar precipitates were uniformly spread inside the grains (Fig. 3).
These precipitates were observed mainly at grain boundaries.
On the other hand in the case of an AlMnMgSiZr alloy sample the high volume of manganese containing precipitates was evenly distributed inside the grains.

Since then, a number of oxide and nitride ceramics have been developed for optical and other applications [2-8].
Light is scattered at interfaces (e.g., grain boundaries) where refractive indices are discontinuous.
Neither MgO nor AlN peaks was found due to their low amount and being amorphous in the grain boundary.
Conventional silicon nitride shows the large elongated grains of β-Si3N4.
Such defects are vacancies, dislocations, grain boundaries, pores and cracks.

The strength of Mg-RE alloys is achieved essentially by grain refinement strengthening at room temperature, and by dispersion strengthening at elevated temperatures.
However, many investigations have been made on grain refinement strengthening of rare earth in magnesium alloys, while only a few have been made on dispersion strengthening.
It increases the number of homogeneous nucleation, and refines the grain size. (2) Part Sm dissolves in Mg24Y5 phases, increases the stability and blocks the growth of Mg24Y5 phases.
In addition, during the solidification of the alloy, high melting point compound Mg24Y5 (the dissolved Sm enhances its stability) acts as a bar to the growth of α-Mg grain, and leads to further refinement of the grain size of the alloy.
Of course, additional strengthening mechanisms, grain refinement strengthening and solid solution strengthening of Sm also play important roles in strengthening the alloy.

A number of experimental studies on the variation of permeability with stress change in low permeability reservoir have been done, but few are involved in ultra-low permeability cores.
The permeability stress sensitive hysteresis of the microfracture cores is not obvious and the recovery degree of stress sensitive hysteresis is high in the unloading cycle for the grains were compacted in the process of shearing.
There are microfractures growing in the cores observed by cast thin section which contain interstratified microfractures, along strata distributed microfractures and grain marginal microfractures.
The experimental results showed that the permeability stress sensitive hysteresis in microfracture cores is not apparent and the permeability recovery degree is high in the unloading cycle due to the fact that grains were compacted in the process of shearing.

In this study, cold compacting (CP) and repeated plastic working (RPW) were firstly carried out for the mixture of Mg-Si powders, and the refinement of both Mg grains and dispersoids.
However; it causes some problems such as large Mg grains that reduce the strength and ductility of the composite.
As Figure 4 and Figure 5, effect of refinement owing to RPW process was explained. 0 2 4 6 8 10 0 50 100 150 200 RPW cycles /N Mean grain size /μm 2.5%Si 5%Si Extrusion Direction Fig.4 Optical microstructures of extruded AZ31-5%Si via CP(a), and RPW at 50cycles(b), 100cycles(c) and 200cycles(d).
Figure 6 shows a dependence of UTS and 0.2% proof stress on the number of cycle in RPW.
It is thought because of the influence of the refined Mg grains and the uniform distribution of fine Mg2Si occurred by RPW, and the results were agreed with the observation of microstructures shown in Figure 4.

The element Y is distributed mainly at the grain boundaries.
The atoms at grain boundaries are loose with more vacancies and other defects.
The segregation of Y atoms at grain boundaries will reduce the free energy, which is a spontaneous process in thermodynamics.
So Y atom is easy to gather at grain boundaries, and cause its uneven distribution.
That’s because (1) Y can refine grains; (2) Y element increased nitrides in strengthened layer; (3) Y has solid solution hardening effect.

SEM analysis showed a microstructure consisting of equiaxial granules at 700°C for 1 h and a uniformly dispersed network of very fine grains at 700°C for 2 h.
This concept has been utilized in a number of reactive melt casting techniques [4-6].
SEM analysis revealed that a microstructure consisted of globate granules at 700°C for 1 h and a uniformly dispersed network of very fine grains at 700°C for 2 h.
Residual stress field occurred around the nano-Al2O3 which strengthens grain boundary, so that crack can not grow along grain boundary but went through the grains.
The meandering and complex expansion path was a b hindered at many places in the grains, resulted in the increase of work of fracture.

Atomistic simulations, Intermetallic Compounds, Atomistic Potentials, Diffusion, Interfaces, Grain Boundaries, Phase Diagram Abstract.
The properties studied include lattice characteristics (elastic constants, phonons, thermal expansion), point-defect properties, atomic diffusion, generalized stacking faults, dislocations, surfaces, grain boundaries, interphase boundaries, and phase diagrams.
Indeed, processes like atomic diffusion, dislocation motion or grain boundary (GB) segregation require the ability to model large ensembles of atoms over extended periods of time.
It can be expected in other nano-size systems, particularly in nano-grained metallic polycrystals.
A number of mechanisms have been proposed, including sublattice diffusion, various cycles of vacancies, divacancies, anti-structural bridges, etc.

The development of microstructure in both single-and two-phase alloys ordinarily involves some type of phase transformation-an alteration in the number and/ or character of the phases.
These transformations can be divided into three classifications as: simple diffusion-dependent transformations in which there is no change in either the number or composition of the phases present; diffusion-dependent transformation where there is some alteration in phase compositions and often in the number of phases present, the final microstructure ordinarily consists of two phases and finally, diffusionless transformation where in a metastable phase is produced.
Most engineering calculations for structure are based on yield strength.When medium-carbon and medium-alloyed steels are annealed between the AC1 and AC3 and then water quenched, due to partial transformation taking place, a dual phase structure, i.e., a mixture embedded martensite islands within the grains of ferrite is usually obtained[6,7].
Figure 4 of third group of heat treatment shown increasing in martensite area comparison to ferrite areas, this will lead to increasing in the hardness and strength, it’s clear that grains dose not coarse as in first and second groups due to present of Ti, the addition of Ti to control grain growth during reheating and inhibit grain coursing during rolling.