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Grain refinement (with 0.06Ti) was also found to be beneficial to the elimination of hot tearing.
A., “The Columnar to Equiaxed Transition in Horizontal Direct Chill Cast Magnesium Alloy AZ91,” Light Metals, 911-917 (2001). ] noted that the grain refined alloys in their study formed equiaxed-dendritic grains, and gained resistance to hot tearing with moderate additions of grain refiner.
It is noticeable that a small number of dendrites exist in the microstructures of the casting produced without refiner.
With grain refinement, the grains are finer and more globular, with essentially no dendrites present.
One reason for the better performance of the grain refined material might be because fine grains are more ductile than the coarse grains, and therefore, the fine-grained material is free to compensate for strains by movement of both liquid and solid.

The inset shows the HEA exhibited significant increase in hardness after HPT and with increasing numbers of HPT turns.
A reasonably equiaxed grain structure was observed with an average grain size of d ≈ 60 nm in the HPT-processed Al-Mg system and after PDA the material demonstrated a homogeneous equiaxed microstructure with an average grain size of d ≈ 380 nm.
It should be noted that the error bar on each datum point represents the standard deviation of the total numbers of measurements of 20 tests but the error ranges are too small to recognize in the plot.
Specifically, PDA enables the production of an ordering of the defect structures within the grain boundaries leading to an equilibrium state without any significant grain growth [18].
Langdon, Twenty-five years of ultrafine-grained materials: Achieving exceptional properties through grain refinement, Acta Mater. 61 (2013) 7035-7059

Grain boundaries misorientation In Fig. 4, high angle grain boundaries (HAGB) (> 15º misorientation) and low angle grain boundaries (LAGB) (4 º < LAGBs < 15º) are depicted in red and green color, respectively.
Fig. 5 and Fig. 6 demonstrated that the distribution of grain boundary misorientation was affected by the processing temperatures and pass number (Fig. 7).
The yield stress (σy) increased with increasing the pass number in route A whereas it decreased with route Bc after four and six passes regardless of the processing temperatures (table 1).
The grain structure was more homogeneous at 473 K, and route Bc was the most effective for grain refinement.
The fraction of LAGBs decreased with increasing pass number in route A, and increased in route Bc, at 523 K.

This was mainly because of the hydrostatic extrusion which made AZ80 magnesium alloy within large numbers of dislocation tangles.
The figure 3 (b) shows microstructure and morphology of magnesium alloy after hydrostatic extrusion, although the grain size of solid solution was difficult to distinguish under an optical microscope, but it could be seen that grains were elongated and refined along the axis, and sub-grains increased at the same time appeared a large number of twins.
The organization constitution diagram of hydrostatic extruded AZ80 magnesium alloy showed the uneven deformation between grains with axial elongated grains and a large number of twins, and they caused the forming of lots of dislocation tangles and fiber structure.
The uneven deformation between grains or sub-grains, a large number of dislocation and vacancies caused by hydrostatic extrusion would generate residual stress.
(2) In the process of hydrostatic extrusion, grains were broken into many sub-grains in addition to generating slippage, and sub-grain boundaries were the lattice distortion zone where piled up a large number of dislocation.

As the cycle number increased, the pattern of the grains began to lose contrast, with the higher grains becoming sharper, distorted and thus looking more like crests.
The white and black dotes have been superimposed on the images to help finding identical grains in the two images In Fig. 3 to Fig. 5, a number of statistical values obtained from the same interferometry data as used to form the images in the previous figures are presented.
They exhibit small peaks and, for the same area analyzed, the wavelength remains essentially the same, irrespective of the number of cycles.
Arrows indicate steplike rumpling pattern associated with grain boundaries Discussion The observations of rumpling between different intermediate temperatures and 1150 o C and the dependence of the rumpling magnitude on the number of cycles is similar to that previously described by Tolpygo and Clarke [2].
At the grain structure level, the stress may be different according to the size of the grain.

Ultra Fine Grain via Friction Stir Processing of 7075-T6 Grade Aluminum Alloy M.
A number of studies, however, relate this process to the absorption of dislocations by substructure grain boundary [12,23].
Here the grains size dropped under 100 nm (between 0.35-0.6 µm).
Such a change lowered the grains size to less than 100 nm.
Lowe (Eds.), Ultrafine Grained Materials III, TMS (2004)

Also, the upward trend in monolithic construction is due to a number of technical and economic advantages: relatively low investment in the production base; lower in comparison with prefabricated structures, material consumption and labor costs and high performance [1, 2, 3].
In particular, the improvement of the grains shape by removing sharp and protruding corners can be achieved by rolling.
Removal of large open pores and cavities on the surface of aggregate grains, leading to cement overconsumption in concrete can be carried out by melting the surface of the grains; increasing the uniformity of grains in terms of strength and bulk density can be achieved by separation.
It should be noted that porous aggregates have a number of advantages: they have a developed rough surface, good adhesion to cement stone, the dust-like part is active with respect to cement, and porous differences are capable of creating self-vacuuming effect[6].
Strength Characteristics of Fine-Grained Lightweight Concrete Based on Tuff Waste At this point in time, there are a large number of formulas for predicting the compressive strength (cube strength) on various porous aggregates, depending on technological factors.

The paper is devoted to research of influence of “MC-Bauchemie” additions on the fine-grained concrete properties, namely compressive strength.
The results of testing of fine-grained concrete made on the basis of two different natural sands are presented.
Introduction Fine-grained concrete is a special type of heavy concrete in the production of which does not use a coarse aggregate.
Fine-grained concrete has its own characteristics: - composition homogeneity allows to achieve the maximum stone density which means high strength of structures; - the absence of coarse parts of aggregate gives the mix high mobility allowing them to freely pour into hard-to-reach places, densely reinforced structures; - the presence of a certain number of pores has a positive effect on the heat preservation; - low cost of the material (and the combination of components, change of proportions allows to obtain different technical characteristics of concrete as a result).
It should be also noted that the production of high-quality concrete including fine-grained one is not possible without the using of chemical additions [1-3].

Recent Advances and Unsolved Problems of Grain Boundary Diffusion Sergiy V.
Some unresolved problems of grain boundary diffusion – restrictions of Fisher-Gibbs model, refinement of the conditions for B- and C-regimes, relation between segregation (s) and enrichment (b) coefficients, grain boundary width, non-linear segregation effects on grain boundary diffusion – are discussed.
Grain boundary (GB) diffusion measurements are very sensitive to the structural state of GBs.
Grain boundary self-diffusion of Cu [13] is plotted by thick dashed (the B kinetics) and solid (the C kinetics) lines.
Conclusion A critical consideration of the present state of the art of GB diffusion gives rise to the conclusion that there still exist a large number of “hot” unresolved problems, which demands both experimental and theoretical (including computational) efforts

In the texture of AZ31B sheet, each grain has its c-axis almost parallel to the sheet normal.
Therefore, at the bending process of the sheet, basal slip system can not accommodate an in-plane plastic strain which is perpendicular to the c-axis of each grain.
In this study, an in-situ bending test of AZ31B sheet with a texture was conducted under a confocal scanning laser microscope to observe twinning by applying compression stress along a direction almost perpendicular to the c-axis of grains.
However, it is noted that the growth of twins is apparent while the number of twins is almost constant during plastic bending deformmation.
Twinning is expected to introduce grains having different crystallographic orientations.