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Plasticity of Copper with small grain size Y.
It was observed that at intermediate grain size stress relaxation shifts from unit to partial dislocations both nucleated at grain-boundaries and finally in the extreme refinement of the grains a radical change occurs with relaxation at the grain-boundary regions.
The stress concentration depends on the number of dislocations in the pile up ; combining the pile up length to the grain size leads to the Hall-Petch law:τs ∝∝∝∝ Gb d , where τs is the yield strength.
(b) Ultrafine grains have grain size below the critical dislocation mean free path, though (c) pile-up of dislocations and grain-boundaries sources still exist.
The grains are separated by low, high angle grain boundaries and twins.

Equal-channel angular pressing (ECAP) is used to convert coarse grain into ultrafine grain (UFG).
It is clear that the grain structure is not homogeneous but a mixed one of coarse grains and relatively small grains.
It can be found that the microstructures after 4 passes in 100°, 110° and 120° die via route Bc still consist of a considerable number of large grains and an un-uniform grain structure.
Plot showing the effect of die angle on shear strain after different number of passes Indeed, the die angle has effect on the microstructure produced.
A large number of grains are initially in the so-called hard orientations with small Schmid factors and deformation is difficult in them.

The number and the size of the recrystallized grains generally increase as the annealing temperature increases.
The total number of grains used for this calculation were as follows: 2663 grains at 790°C, 1144 grains at 850°C, 1037 grains at 900°C and 954 grains at 950°C.
The number of grain boundaries used for the calculation was 650 and 512 for Goss and {111}<112> orientations, respectively.
Average grain diameter of grains with various orientations with annealing temperature during the progress of grain growth.
Consequently, {111}<112> grains have a much higher frequency of high angle grain boundaries than Goss grains.

The larger grain size, the smaller crack growth rate, though the static strength was decreased with increase in grain size.
The influence of grain size on the crack growth is complex.
For example, ultra fine-grained carbon steels have an excellent crack growth resistance, though the resistance is not influenced by grain size in conventional grained steels [2].
The relation between the logarithms of a crack length and the number of cycle can be approximated by a straight line, when the crack length is small.
The larger grain size, the smaller crack growth rate, though the static strength was decreased with increase in grain size inversely.

Not only cedar pollen in Japan but grass and birch pollens in North Europe [1-4] actinomycetes and fungal spores in US [5, 6] cause allergic symptom, and the number of allergy sufferers increases all over the world.
grains and orbicle substance.
The room has no open window, and therefore the total number of pollen grains is conserved.
In the present study, removal efficiency is fraction of the number of removed pollen grains to all of traced particles that are distributed uniformly in the room.
The bottom numbers indicate the flow rate [m3/min] The alphabet S stands for the smaller device width of 400 mm and L stands for the larger divice width of 450 mm.

Rods were subjected to ECAP using a die with a channel-intersection angle of F = 110° at a temperature of 400°C with the number of passes amounting to 8.
Ultra fine-grained (UFG) – ECAP; 3.
Annealing for 1, 10 and 100 hours results in the increase in the number of peaks at cooling and heating which attests to a multi-stage transformation in these states.
Due to this, no new peaks are formed during annealing of UFG and NC states at 400°С for a period from 1 to 100 hours and the number of MT steps remains the same.
The temperature is 40°С, number of cycles 20. a) CG state, b) after ECAP, c) after HPT and annealing 400°C, 1 hour Thus, grain refinement of Ni50.7Ti49.3 alloy with application of SPD techniques results in emergence of the pseudoelastic effect at a temperature close to that of a human body.

There are number of refinement mechanisms proposed over the years for grain refinement.
The cavitation induced dendrite fragmentation hypothesis assumes that the shock waves generated from the collapse of bubbles lead to fragmentation of dendrites, which are redistributed through acoustic streaming, thereby increasing the number of crystals.
When ultrasonic intensity is increased to 4 kW/cm2 increased grain refinement is observed and grain size is reduced further to 17 μm.
This hypothesis assumes that the shock waves generated from the collapse of cavitation bubbles cause fragmentation of the dendrites, which are then redistributed through acoustic streaming, thereby increasing the number of crystals and hence refining the grain size.
As a result of grain refinement, the grain boundary area is increased.

INFLUENCE OF GRAIN SIZE ON THE THERMAL DIFFUSIVITY OF Pt-SnO2 CERAMIC M.M.
The grain coarsening is mainly attributed to sintering [6].
In bigger grain size samples, phonons would encounter less number of grain boundaries, presenting a longer apparent mean free path.
As shown in Fig.4, the inclusion of 0.5 wt% Pt in SnO2 (Sample B) inhibits the grain growth as it produces smaller average grain size.
This can be attributed to the reduction in the number of grain boundaries blocking the heat flow path.

The three-stage bolt forming using the ultra-fine grained specimens was carried out to check formability of the material.
The improved mechanical strength achieved by the ECAE is due to grain refinement since strength of materials was known to be proportional to the reciprocal of the square root of the grain size according to the empirical Hall-Petch equation [4].
Recently, high strength M4 bolts were manufactured using the ultra-fine grained AA6061 processed by the ECAE without heat treatment and formability of the ultra-fine grained specimen was investigated by Choi et al. [9].
In experiments of the ECAE, three different routes A, Bc and C up to four passes were applied to investigate the effect of processing routes and the number of passes on microstructural change and its homogeneity.
However, Vickers microhardness value was more homogeneous in the ultra-fine grained bolt than in the conventional one.

There are 3 stages: reordering of dislocations and formation of sub grains, nucleation of grain boundaries and finally grain growth.
This P2 grain boundary peak is absent in single crystals and the peak position depends on the grain size.
Starting with a single crystal, the introduction of a small number of dislocations by cold deformation leads to different relaxation mechanisms.
The sub grain boundaries disappear and the misorientation between adjacent grains increases.
At the same time the dislocation density in the grains decreases as grain boundaries absorb residual dislocations.