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Grain Refinement of Magnesium Alloys by CONFORM: A Continuous Severe Plastic Deformation Route?
The average grain size was measured as ~150 µm.
Near the rod surface (Fig. 4d), the texture is significantly weakened by a number of peak orientations with the basal poles aligned 43°, 53°, 67° and 90° to the ED.
This grain size non-uniformity impeded the development of conventional superplasticity through grain boundary sliding, resulting in the early failure of the specimens [7].
Compared to ECAP, the CONFORM process has the following advantages: 1) the process is operated in a continuous manner, so very long products can be readily produced and the production rate is very high; 2) cast rods can be directly used as the feedstock, no prior extrusion is needed; 3) the grain refinement effect is higher than ECAP, so less number of processing passes may be needed to achieve the same grain size; 4) the CONFORM machine is commercially available in the market and can be readily used for industrial production.

Grain boundaries of approximately 500 grains were delineated manually with Adobe Illustrator software on digitised TEM bright field images to determine the grain size distribution.
Larger grain size can be obviously seen in sample A.
It is clear that high current densities promote the grain refinement.
As oxide nucleation in the grain boundary region is easy, decreasing the grain size increases the number of surface oxide nucleation centers, resulting in an increase in the nucleation rate of NiO.
The scales on various grains grow at significantly different rates.

Compared with 20MnSi, steel 20MnSiV boasts much finer microstructure, and large numbers of nanometer precipitates exist in the specimens of 20MnSiV.
Formation of Widmannstatten structure is caused by many reasons, such as chemical composition (carbon content), austenite grain size and cooling rate.
Grain refinement hardening effect can be described by well known Hall-Petch equation (3) where: d is the average ferrite grain size; is constant and its value is 0.55 (17.4N/mm3/2) for HSLA steels.
It can be seen from Fig.3 that large number of nanometer particles exist in 20MnSiV steel, which can provide strong precipitation hardening effect.
(2) A large number of nanometer particles exist in 20MnSiV steel, but this kind of particles can hardly be observed in 20MnSi steel

In most cases, coarse crystal grains are included in aluminum casting alloy.
The two problems arise because of the existence of the coarse crystal grains.
For an accurate estimation of the stress measurement by neutron diffraction, a sufficient number of crystal grains must exist in the gage volume.
However the casting materials usually include coarse crystal grains.
The diffraction profiles frequently disappear due to the existence of coarse crystal grains.

The grains that are intersected by the domain boundary S and the internal grains that are not intersected by S.
Each grain is bounded by a boundary uj,wherej =1]p§ and p§ denotes the number of grains.
The boundary of each grain is divided into the contact boundary uj¢ , indicating the contact with a neighbour grain boundary and into the free boundary ujfl¢, indicating the grain boundaries that coincide with the domain boundary S.
Hence for every grain:Figure 1: Artificial microstructure generated by a quasi-random generator with randomly distributed material orientation for each grain.
uj = ujfl¢ } uj¢ (1) For the internal grains ujfl¢ = a and thus uj = uj¢ .Thereforeujfl¢ exists only on boundary grains resulting to p§S j=1 ujfl¢ = S.

Grain Boundary Segregation and Grain Boundary Wetting Arkady Vilenkin The Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem, 91904, Israel Keywords: grain boundary segregation, grain boundary dynamics, grain boundary wetting Abstract.
Different hatching represents different grains.
LA Diffusion along Grain Boundary.
Grain Boundary Shape Function and Velocity.
In order to obtain simple algebra, we have made several numbers of assumptions.

To measure the average grain of CCS according to GB 6394-36 [12], three views are taken in the selected region of observation position, one hundred grain size is test in each view.
The more number contained in grain is, the smaller its size is [11].
Its grain only grew, and not to be equiaxial.
The results show that the grain size in cross section of a-Fe phase is from 2 mm to 21 mm, small size grain is enhanced with the increase of the drawing deformation.
[12] The testing method of metal average grain.

The pre-existing He bubbles within and around the grain boundary region have a major effect on the number and distribution of surviving Frenkel pairs.
When He bubbles are located around the grain boundary, the number of surviving vacancies/SIAs decreased by 23% to 60% compared to models without He bubbles.
It is worth noting that the number of vacancies is roughly equal to the number of interstitials, so from this point on, we'll report only the vacancies numbers.
For models with He bubbles near the grain boundary (i.e., W-He-AGB and W-He-BGB), the number of residual vacancies reduced significantly compared with W models.
Wei, A comparative study on the in situ helium irradiation behavior of tungsten: Coarse grain vs. nanocrystalline grain, Acta Mater 147 (2018) 100–112

The effects of centroidal process on the distributions of grain size and number of grain corners, facet and edge are analysed.
In microforming process, as the specimen size approaches the dimension of grain size, there are a small number of grains locating in the specimen as shown in Fig. 1 [3].
The number of grain with the average volume increase significantly as shown in Fig. 5b, which indicates the centroidal process make the grain size more even.
As the influence of CS on the geometrical features, Fig. 6 shows the distributions of the number of corners, facets and edges per grain Nc, Nf and Ne.
The analysis indicates that the distributions of grain size and number of geometrical features per grain including grain corners, grain facets and edges appear towards a value of the steady-state polycrystalline structure.

However, the microstructure evolution during HPT has been examined in details for restricted number of pure metals and alloys [1-3].
The numbers indicate the misorientation in degrees.
Second, the boundaries of some grains acquire an ability to migrate; new grains involving annealing twins and low dislocation density consume grains with size less than 100 nm that contain high density of lattice and grain boundary dislocations.
Fig. 5. a- Effect of strain on microhardness and recrystallized grain size after annealing at 500°C, 1 h of a Ni-20%Cr alloy. b - Schematic drawing for variation of structural mechanisms responsible for new grain development during annealing of cold-worked Ni-20%Cr alloy, where Nn – number of recrystallizing nuclei, Ns – number of strain-induced grains/subgrains.
In contrast, at lower strains, the number of nanoscale grains evolved is very restricted.