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These types of steels often need to be added a large number of alloying elements, although the corrosion resistance can be improved, they have higher costs and it is not conducive to the promotion.
Some classical theories illuminated that the presence of grain boundary would block the dislocation movement, the grain was finer, the grain boundary was more, the block was more serious, and then the strength was higher.
For the whole substrate, there were a lot of segregation of impurities; the activity of the grain boundary was usually higher than that of the grain itself, so the grain boundary was prone to erode.
Compared to the coarse grain structure, the grain boundary area of the fine grain structure was much larger; therefore its activity of the substrate surface was higher, and its substrate was easier to erode.
From a thermodynamic point of view, the reaction free energy of the grain boundary was lower; the fine grain structure had more grain boundaries, so its surface reaction free energy was lower, and then it was easier to erode, as shown in the first corrosion cycle in Fig.4.

Atom probe tomography also allows the direct, local investigation of the grain boundary diffusion in any single grain boundaries.
Currently there are a number of reconstruction algorithms available, most of them are based on the model developed by Bas and coworkers [13].
The microstructure of these samples is very fine nanocrystalline with a grain size in the range of a few tens of nanometers.
Such small grain size means, that substructures of the GBs, such as TJs have a reasonably high volume fraction [23].
By contrast, the concentration dependence of the grain boundary diffusion in general high angle grain boundaries is very weak.

Microstructure investigation displayed an increment in average grain size of LSMO due to the grain growth promotion as the sintering temperature increased.
For polycrystalline manganites, their magnetic and electrical properties are strongly depend on the microstructure condition such as grain size, grain boundaries and grain porosity [6-9].
All samples showed high grain porosity.
At low sintering temperature, the average grain size is very small and thus leads to a large number of grain boundaries.
The increment of average grain size from LS650 to LS950 reduced the grain boundaries region and enhanced the grain connectivity.

The TEM-EDS profiles of (b) and (c) reveal that Lu 3+ ions is present in the grain boundary but not in a grain interior.
(b) Grain Interior Figure 4.
Figure 7 shows a grain boundary in TZP containing 5wt% SiO2 together with the EDS spectra across the grain boundary[23].
Since Zr 4+ and Si4+ ions are tetravalent, the number of vacancies formed near grain boundaries will increase with doping of lower valency cation.
Watanabe, "Grain Boundary Engineering in Ceramics; from Grain Boundary Phenomena to Grain Boundary Quantum Structures" ed. by T.

A general grain-boundary incremental/iterative algorithm, embedding the flow and hardening rules for crystal plasticity, is developed.
The key feature of the method is the expression of the micro-mechanical problem in terms of inter-granular variables only, resulting in a reduction of the number of DoFs, which may be appealing in multi-scale applications.
In the present work, a novel three-dimensional grain-boundary formulation for small strains crystal plasticity is described.
Formulation The grain boundary formulation for crystal plasticity is here described.
Furthermore, the polycrystalline problem is addressed using a multi-domain approach where each domain, also referred to as grain, is indicated by and its surface, also referred to as grain boundary, by .

It was found that the grain size and its distribution influence the property and microstructure of Si3N4 ceramics, namely, the relative narrow distribution of grain diameter in some extent and relative wide range of bimodal distribution of grain aspect ratio could improve the property of Si3N4 ceramics.
Minimums of 300 grains in each material were analyzed.
In these micrographs, the β-Si3N4 grains are observed clearly.
The addition amount of rare earth oxide, the heat-treatment temperature and the atomic number of rare earth element have key effect on the α→β transformation ratio of Si3N4 powder.
The grain-section diameter dominated the fracture toughness.

In particular, the effect of grain size and matrix content were examined.
It is shown, by comparing with real micrographs, that the method captures the features of real microstructures in terms of grain size distribution and grain aspect ratio.
A number of authors [3, 4] have generated finite element meshes directly based on actual microstructural images.
The real microstructures have a higher percentage of small grains than its numerical counterpart due to small fragmented grains.
(a) 40% grains (b) 50% grains (c) 60% grains (d) 40% grains (e) 50% grains (f) 60% grains Figure 3: The Von-Mises equivalent strain distribution in the numerical microstructures with (a-c) 5×5 grains and (d-f) 10×10 grains subjected to a normal traction of 100 MPa.

Introduction During welding of HSLA steel, austenite grain growth will inevitably results in poor toughness of the coarse grained heat-affected zone (CGHAZ).One method of alleviating this problem is to introduce fine dispersed particles, such as TiN, TiNb(C,N) into the steel.
These stable second phase particles are expected to pin the grain boundaries, thus restricting austenite grain growth [1-4].
More than 150 fields were examined and the number of particles analyzed was at least 1000 for every specimen.
The particle number per unit area changes from 42.88 to 3.144, the average particle diameter changes from 14.2nm to 24.6nm, see Fig.2b.
Effect of Ti addition on austenite grain growth kinetics of medium carbon V-Nb steels containing 0.008~0.18%N.

The extruded alloy exhibits the recrystallised grain size and excellent mechanical properties.
In recent years, a number of Mg-Gd alloys have been investigated which shown that Gd can be used to change mechanical properties with a wide range of alloy compositions and heat treatments by its large solubility of 23.49 wt % at eutectic temperature [4, 5].
Extrusion temperature effect on Mg-1.6Gd grain size.
This phenomenon is associated with the grain growth which the hardness value decreases with increasing grain size.
The extruded samples show an equiaxed recrystallized grain structure.

The influence of the reduction of the grain size on the fatigue resistance of various metals an alloys is described in a number of papers [2,6,7].
Quantitative metallography was employed to characterise the grain size.
The interior of elongated grains was fragmented by subgrains with low-angle boundaries.
For example, according to [9] the fatigue endurance limit of the notched coarse-grained Ti samples (αт=2.8) with the number of cycles to fracture 10 6 is only 262 MPa.
Another approach to increase the ductility and at the same time preserve high strength of UFG materials is the formation of a structure with bimodal grain distribution in which nanocrystalline grains provide strength and larger grains facilitate a high ductility during deformation [7].