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In 1966, W.B.Morrison has succeeded in grain refinement to about 1.6µm in 0.13%C steel and showed that such a yielding behavior is taken over even in fine grained steel [1].
The grain refinement below 1.6µm is not so easy but ultra fine grained (UFG) iron has been obtained by consolidation of mechanically milled iron powder [2,3].
Grain size was controlled in the range between 15µm and 70µm.
Sub-number of samples (C30-1 or C30-2 etc.) means the lot number of heat treatment.
It is probably that carbon segregated at grain boundary plays a role to stabilize the dislocation emission site at grain boundary and this leads to the increase in ky.

The process parameters of ECAP (Channel Angle, angle of curvature, friction, number of passes, etc) influences major impact on the properties.
In all the above methods, the grain refinement to nano-scale grain structure in the bulk material is achieved by applying a severe plastic deformation.
Researchers have demonstrated a number of theoretical and experimental analysis on ECAP process [5-10], Fig. 1, to study the effect of process parameters on material behaviour.
Figure 6: Variation of MicroHardness with number of passes Figure 7: Variation of UTS with number of passes Tensile properties evaluated upto 2 passes of ECAP is depicted in Fig. 7.
Langdon, Ultrafine-Grained Materials: a Personal Perspective, J.

Micrograded grain structure.
So, the concentration distribution into carbide grain body is more gradually in comparison with grain boundaries.
It is well known that Ti-Nb alloys might undergo a number of phase transformations which can provide metastable phases [10].
In this system no precipitates inside grains were found.
Finally, a non-equilibrium structure consisted of complex carbide (Ti, Nb)Cx grains and β-(Nb, Ti) solid solution located on the grain boundary are formed.

A number of selective research about γ phase microstructure development of nickel-based single-crystal superalloys are scrupulously expounded further below.
Hao Chen and Xinbao Zhao [10,11] analyzed effect of repair conditions on stray grain formation, low angle grain boundaries, preferable epitaxial growth and crystallography-induced dendrite growth during single-crystal nickel-based superalloy AM3 component repair by laser cladding.
(2) where Γ is the Gibbs-Thomson coefficient, R is the dendrite tip radius, Pei is the Peclet number for i, mi is the liquidus slope, C0,i is the initial concentration for i, ki is the partition coefficient for i, ζc(Pei) is a function of the Peclet number, Iv(Pei) is the Ivantsov solution and Ghkl is the average temperature gradient near the dendrite tip.
Stray grain formation and solidification cracking are preferentially confined to vulnerable [100] dendrite growth region.
Epitaxial laser deposition of single crystal Ni-based superalloy: variation of stray grains.

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.

Grain size evaluation was performed using light microscope images and grain chord length measurements, samples of commercial WC-Co coarse and supercoarse grades being included into analysis for comparison purposes.
The international ISO 4499-1 standard recommends measurements of more than 200 grains; in the current analysis for each grade 561-924 grain chords have been measured on images of five fields.
Statistical (left) and geometrical (right) distributions of WC grain chord length in Co sintered carbide grade.
Statistical (left) and geometrical (right) distributions of WC grain chord length in NiMo2 sintered carbide grade.
Acknowledgements The article is based on the research project financed by NCN, project number 222/B/T02/2011/40.

Total grinding forces are defined by average number of grain in contact zone.
Calculation of cutting forces for single diamond grain.
The forces affecting a single worn diamond grain Fig. 1 shows: - reaction force of the machined material affecting the diamond grain on the wear area
The number of the cutting grains contacting the machined material can be calculated by the proposal of A.N.
Thus, for rough grinding the grain wear may be 30-40% from the average diameter of the grain, and for the finishing grinding – 10-20%.

The ultrafine-grained materials produced by ECAP have a very high strength owing to their small grain size and high dislocation density [2].
The influence of the number of ECAP passes on the yield strength and the ductility is investigated for pure Cu up to an extremely high strain value of 29.
The yield strength and the maximum elongation as a function of the number of ECAP passes for pure Cu are plotted in Fig. 2a and the dislocation density and the crystallite size versus the number of ECAP passes are shown in Fig. 2b.
The larger fraction of high-angle grain boundaries facilitates grain boundary sliding which improves ductility [7].
Figure 2: The yield strength and the maximum elongation (a) and also the dislocation density and the crystallite size (b) as a function of the number ECAP passes for pure Cu.

Superplasticity in Coarse-Grained Al-Mg Alloys E.
A number of mechanisms have been proposed for coarse-grained superplasticity [2, 5-7], although the actual mechanism has not yet been identified.
Grain size measurements were carried out to select suitably coarse-grained material (> 20 µm) for the tensile testing.
These etched samples were then examined optically to determine the grain size, amount of grain boundary movement, and deformed grain shape.
The arrows in Fig. 6(f) indicate the presence of the newly formed grains at the boundaries of the deformed grains.

The results of a considerable number of such measurements were averaged in view of the variations of angles between the foil plane and the plane in which dislocation exists.
The change of grain sizes (d) at a distance (l) from the sample rotation centre: (1) dislocation free grains; (2) grains containing dislocations; (3) grains with fragments; (4) average grain sizes;  is deformation degree Results and discussion Grain structure after THP.
It is known [3, 8-10] that in submicrolevel polycrystals the grains can be: 1) dislocation free grains; 2) dislocation grains which have a chaotic dislocation structure and 3) grains with dislocation fragmented substructure.
An average grains sizes were measured taking into account volume fraction of each type of grains.
The critical grain size here is the grains size if the dislocations inside the grain body are absent and remain only on their boundaries.