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INTRODUCTION: The feasibility of producing ultra fine grain size microstructures in metallic materials via equal channel angular extrusion (ECAE) has been demonstrated in a number of pure metals and alloys, [1-4]. .
This deformation results in little to no dimensional changes of the sample, therefore an unlimited number of passes is possible, resulting in production of large strains in the material Deformation with such large strains can be utilized to produce grain refinement by one of several methods viz., grain fragmentation and rotation, dynamic recrystallization, or deformation followed by static recrystallization.
The sample was subjected to two and four extrusion passes with a 90° rotation and a 180° flip between passes A number of samples were subjected to post ECAE annealing in the alpha beta field to produce grain refinement by static recovery and recrystalization.
Langdon, The Process of Grain Refinement in EqualChannel Angular Pressing.
Effect of Route, Number of Passes and Initial Texture.

In addition, recovery influences precipitation through its effect on the number of potential precipitate nucleation sites (i.e. number of dislocations).
An indirect effect of precipitation is to deplete Nb form solid solution leading to a reduction in the solute drag the Nb exerts on the grain-boundaries of the recrystallizing grains.
The number of dislocation nodes, nc, was approximated as 0.5ρ1.5.
A number of authors have shown that the Zener approach, or a modified version of it, accurately captures the effect of a stable particle distribution on the growth of the recrystallizing grains [12, 16-18].
Accelerated coarsening of the particles located at the grain boundary will lead to a local reduction in the pinning force and the boundary is able to advance (locally) until it encounters a sufficient number of fresh particles which will ensure that the boundary is pinned again.

In order to achieve finer grains and better mechanical properties, multi-pass FSP was conducted to prepare fine-grained magnesium alloys.
Dadashpour et al. [7] investigated the effect of heat treatment and number of passes on microstructure and properties in AZ91C alloy.
The as-FSP alloy exhibited an increase in ultimate tensile strength (UTS) and elongation as the number of passes increasing due to finer grains and more dissolution of β phase (Mg17Al12).
After FSP, microstructures in SZ of AZ61 alloy are greatly refined into equiaxed grains with an average grain size of about 2.0 μm as shown in Fig. 1(c).
Mostafapour, Effect of heat treatment and number of passes on the microstructure and mechanical properties of friction stir processed AZ91C magnesium alloy, J.

In polycrystalline materials the development of local displacements along the grain boundaries happens in order to accommodate the plastic deformation in adjacent regions and to retain the grain-to-grain compatibility.
The higher solute diffusivity in the grain boundary regions leads to higher precipitate rates compared to the interior of the grains.
At this cooling rate the grain boundary precipitation is already present and small grain boundary particles (0.1 ÷ 1 µm) were formed along the grain boundaries.
When observing the outer surface of the hem in the sample quenched at 60°C/s, significant number of deformation steps representing the high amount of strain accumulated in the interior of the grains was found.
It was found to happen much faster than in the interior of the grains, which allows the formation of coarse (1 ÷ 5 µm) grain boundary particles in a very short time before any significant precipitation in the bulk of the grains can occur.

Each process was sampled five holes to determine the number of effective ear, rate of seed setting, empty and immature grain and 1000-grain weight in mature stage, and each process was also sampled 2 m2 for yield determination.
Total grain number increased with the increase of nitrogen fertilizer, and the treatment Ⅴ was the most, which had no significant differences with treatment Ⅰ (CK), Ⅳ, Ⅴ and Ⅵ, which indicated that the improvement of nitrogen application could increase the total number of solid grain but the increasing extent was not obvious after excessive nitrogen fertilization application.
Among the groups, the differences of spike weight, rate of total empty and flat grain and 1000-grain weight were not significant, which indicated that straw returning and nitrogen application amount had no significant influence on spike weight, rate of total empty and flat grain and 1000-grain weight.
With the increase of nitrogen application, Tianjing Zhao [12] thought total grain number per panicle, seed setting rate and 1000-grain weight declined gradually, while the effective panicles increased in general; Yuan cai Huang think [13] the panicles per unit area increased, but also results in a decrease in grain number per panicle, granulating rate and thousand seed weight.
This study thought the more and less amount of nitrogen both reduced effective panicles and the number of spikelets per square meters and had no impact on 1000-grain weight under the condition of straw returning while some scholars pointed that straw returning significantly reduced 1000-grain weight [8, 9], but this study found that the straw returning had no effect on 1000-grain weight. .For the studies on effects of straw returning on yield and yield components were also not the same, which may be due to the different returning way, soil, fertilization way, which need more research.

The fresh dislocations multiply from the Frank-Read sources within the grains, and pile up against the twin and grain boundaries of two kinds of specimens.
Although there were many annealing twins, the grown-in dislocations were quite uniformly distributed in the surface grains.
Fig. 1 Typical pile-up dislocations in Cu-6.8at%Al alloys etched under pulling in tension: (a) a stress of 17 MPa at a true strain of 0.05 %; (b) a stress of 26 MPa at a true strain of 0.1 %. 20µm (a) Tensile direction Twin boundary Grown-in dislocations Pile-up dislocations Grain boundary 50µm (b) Tensile direction Secondary slip plane Grain boundary Primary slip plane Although the number of dislocations in the pile-up groups became about two-thirds of that for tensile loading, the distance of them spread within the grains.
It was confirmed that the fresh dislocations multiplied from the Frank-Read sources within the grains, and piled up against the twin and grain boundaries of two kinds of specimens.
Compressive direction 20µm (a) Pile-up dislocations Grain boundary 20µm Compressive direction (b) Twin boundary Grain boundary Pile-up dislocations

Ø Modeling of chip formation Ø Modeling of chip formation force for individual grain Ø Modeling of ploughing force for individual grain Ø Modeling of Grinding force Modeling of chip formation The total grinding force can be deduced from the total number of active grains multiplied by the average grain force.
The static number of cutting edges depends on the grain size, wheel porosity and dressing condition.The static cutting edge density function is depicted as following[3].
When the cutting depth of grain t is available, the diameter of the equivalent grain can be determined from the geometry as follows
The equivalent grain diameter depends on the shape of the grain and depth of cut of the grain[3].
(31) Here is the number of active cutting edge, and are the normal and tangential forces on a single grain.

The corrosion potential and rate of depended on the feed direction and number of pass. 1.
As shown in Fig. 4-(b), route-A produces grains with high angle grain boundary.
The micro-hardness increases from 75 Hv to 190-210 Hv with increasing number of pass.
Deformation bands were more clearly observed as number of feeding increases.
Route-A produced grains with high angle grain boundary.

The effective output of heat is beneficial for the supercooling of melt, and then a large number Fig. 1.
When the whole melt reaches a certain degree of supercooling, a large number of grains will be produced in an instant.
In this stage, a large number of nucleation makes the grain density increase, and further makes the grain spacing smaller.
When a certain degree of supercooling is achieved, a large number of nucleation will occur in the melt.
It greatly reduces the size of grains in the melt and increases the number of critical nuclei when the melt reaches the uniform solid fraction in a shorter time, 4.

The heat treatments resulted in the formation of two phase (austenite-ferrite) ultrafine grained microstructures with average grain sizes of 0.9 to 1.2 µm, depending on the annealing temperature.
The use of medium manganese steels with a good formability will allow to reduce the number of components of the car, as well as to realize geometrically more complex parts, which also affect safety and environmental conditions.
The grain refinement leading to ultrafine grained microstructure can significantly increase the yield strength while ductility remains at a high level [9].
The cold rolled microstructure is mostly represented by austenitic structure with elongated grains along the rolling direction with average grain size of 1.7 µm.
The largest transverse direction of austenitic grains is about 10 µm.