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Influence of number of passes in ECAP on superplastic behavior in a magnesium alloy Roberto B.
The flow behavior was found to vary with the number of passes of ECAP.
However, the values of the elongations varied substantially with the number of passes of ECAP.
Grain structure.
The number of passes of ECAP has a major influence on the flow behavior, the rate of grain growth and the evolution of the strain rate sensitivity during deformation. 4.

For interface controlled abnormal grain growth there may be a number of processes associated with atomic attachment at the interface that can be the controlling mechanism.
In the past decade, a number of researchers have invoked the idea of a non-linear relationship between driving force and grain boundary velocity to explain abnormal grain growth during nucleation limited interface controlled grain growth.[8-10,19-20] A schematic of this is shown in Fig. 4.
The nucleation limited interface controlled abnormal grain growth mechanism has been invoked to describe abnormal grain growth in single phase and pseudo-single phase systems.[16,21] Systems where only a small number of the grain boundaries contain a nanoscale intergranular film may be considered to be pseudo-single phase.
If the grain with the defect can not grow any faster than the normal grains then this grain can not grow abnormally.
Arrhenius behavior has been observed in alumina in a number of studies, where the driving force varied with temperature.[4,26,29-31] It then remains to explain how abnormal grain growth occurs by a diffusion controlled mechanism in pseudo-single phase alumina.

Development of GBS was experimentally observed during plastic strain of a number of UFG metals including copper [[] R.Z.
Most of grains coarser than 6 mm are elongated but due to their limited number they effect on the average grain aspect ratio weakly.
The number of twins does not rise.
In this case, the grain appears severely curved and a great number of straight dislocation glide lines are observed inside the grain.
Despite the limited number, coarse grains may occupy a noticeable part of the sample volume (0.27 and 0.46 prior and after tensile test, respectively).

Even, grain growth of <100>//ND textured grains is occurred as abnormal grain growth when <100>//ND textured grains are surrounded by <111>//ND fiber textured grains.
If we assume isotropic GB energies and mobilities, the phase field equation for the grain growth of the poly-crystalline microstructure is [1] (1) where the order parameter q(q=1,2,3, …, Q) represents the orientation state of a point in a polycrystalline system containing of Q grains, an integer q can be regarded as a number indicating a specific orientation of the grain, and the sum of all q values in a spatial point is conserved as 1 ( , , ) 1 Q q q i j k .
Then the number of phase coexisting in a given point is S.
The initial number of grains was 10054 with different crystallographic orientations (Euler angles).
Figure 2 Microstructures and pole figures of a polycrystalline structure composed of minor <100>//ND fiber (0.3% of total grain number) and major <111>//ND fiber texture.

In 2-dimensional case, the Betti numbers are consisting of two numbers.
The other is b1= H1(X), which is the number of holes.
Because the Betti numbers are invariant, the shape of the grain has nothing to do with the Betti numbers.
The number of b1 in the substrate area and HAZ area also has not changed except for the fine grains, but WMZ is decreasing.
The number of grains of more than 6µm2 seems to be the same of WMZ and HAZ.

The evolved substructures with nodes of the Fe precipitates gradually changed to new grains surrounded by low- and high-angle boundaries with increasing number of the repeated processes.
Introduction Numerous numbers of thermo-mechanical processes (TMPs) have been applied for grain refinement of bulky metallic materials.
Because RX normally involves grain coarsening due to grain boundary migration, lower limit of the minimum grain size seems to exist.
It is evident that fine grains were gradually evolved with increasing number of cycles.
Such slight grain coarsening took pace more significantly where fine grains were evolved in groups.

Introduction Migration of grain boundaries during grain growth generally proceeds under the capillary driving force provided by the boundary energy owing to a reduction of the total grain boundary area.
Due to the difference of susceptibility parallel and perpendicular to the c-axis with || > ||, the direction of the driving force pm was from grain 2 towards grain 1 (Fig. 1).
Mean grain size, number of grains and fraction of different grain subsets after annealing at 340°C for 90 min as obtained by orientation microscopy (EBSD in a SEM).
Field Total number of grains Subset Mean grain size, µm Number of grains Grain fraction both 82 1285 0.67 0 T 1925 (90°,20°,φ2) 81 656 0.34 (270°,20°,φ2) 83 629 0.33 both 100 1298 0.88 17 T 1471 (90°,20°,φ2) 99 444 0.30 (270°,20°,φ2) 100 854 0.58 As seen in Fig. 4, the magnetic annealing resulted in an asymmetry of the two major texture components.
Summary Magnetically induced migration of planar <> tilt grain boundaries in zinc bicrystals was measured, the absolute values of grain boundary mobility were obtained.

Here, a continuum microstructure is bitmapped onto a 2D square lattice, initially taking the form of a matrix populated with random numbers ranging from 1 to Q, with Q representing the number of probable orientations shown by the grains in the simulated microstructure.
At this juncture, a random number (r) is generated which is uniformly distributed between 0 & 1.
Fig 10 suggests the relationship of R(lim) with the percentage of particles (φ) interacting with the grain boundaries, in simulated microstructures. φ was computed, through coding, by counting the number of impurities physically in contact with the grain boundaries.
The number of MCS which resulted in grain growth stagnation is also given alongside and it peaks at KTs=0.4, the critical temperature.
They clearly demonstrate (i) the log-normal behavior of the grain sizes atFig. 12: Grain Size Distributions for pinned regimes at different values of KTs, at N=1000, Q=64 and f=0.1 various values of KTs, and (ii) that the number of grains at stagnation dwindles as KTs are increased, because of enhanced grain growth.

On the one hand, conventional optical analysis of the grain size distribution and neighbour numbers and on the other hand in-situ, high resolution continuous observation of microstructural development at high temperatures coupled with construction of time dependent crystallographic maps of the observed 2 dimensional polycrystal during grain growth.
The optical analysis allows large statistics but is limited in the number of characteristics that can be analyzed.
(a) (b) (c) Figure 3 The mean number of neighbours (S) of grains versus their relative area S/ from (a) optical experiments, (b) data from in-situ experiments at Tmax = 480 °C and (c) data from in-situ experiments at Tmax = 500 °C Several features that are not in accordance to the general theory of grain growth by von Neumann and Mullins which assumes isotropic grain boundary energy and mobility are observed.
These are: 1) The von Neumann-Mullins is not always satisfied (Fig. 4) Figure 4 Analysis of individual grains before and after heat showing the number of neighbours N versus change in grain area dS/dt.
Tmax = 480 °C, theat = 30 min., scale bar = 40 µm A) before heating, B) after heating. 6) Relative increase in number of grain boundaries that form traces of low index planes with heating.