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It was therefore proposed to use FSW for grain refining of the parent material by putting a number of overlapping FS welds onto the edges of both parent plates prior to joining by fusion welding.
A number of technological measures have been evaluated in order to avoid liquation cracking of alloy 7085 EB welded joints.
Friction Stir Welding as Material Grain Refining Tool The results of metallographic examinations performed on a large number of alloy 7085 EB welds allowed it to be suggested that liquation cracking may be probably eliminated if the parent plate grain structure within the HAZ area could be changed from coarse into fine.
What was missing was a reliable method to provide such grain refining.
The EB weld, EBW / FSW boundary and FSW areas have fine grain microstructure.

Fig. 3 shows the corresponding morphology of austenite grains.
When the strain increases to 0.3, which corresponds to the peak stress, many dynamic recrystallization grains occur at the prior grain boundaries with zigzag shape, which refine the austenite grain size.
When the interruption time increases to 10 s, quite a number of newly formed austenite grains appear around the prior grain although some grains seem to be nucleated just at the quenching time.
With increasing the holding time, the newly formed austenite grains grow inside the prior grains and impinged each other, which leads to relatively small and homogeneous grain size (Fig. 5c).
Average grain size after held for 50 s is about 28μm, which is much smaller than the prior grain size.

At a given time, different from one (original) grain to another, some (sub)grains start to grow following an 'abnormal grain growth' pattern.
Journal Title and Volume Number (to be inserted by the publisher) (a) ED ND (b) ED ND Fig. 2.
The grain size distribution is bimodal, with all grains larger than 15µm belonging to the fraction of large grains.
ND ED Journal Title and Volume Number (to be inserted by the publisher) Table 1 Measured properties of EBSD scans from an 8pass ECAE sample for given annealing times.
The dislocation density inside the grains decreases, (sub)grain boundaries get a more equilibrated structure and some (sub)grain coarsening occurs.

However, after 5 cycles, grain growth occurred.
The reduction of the grain size after the ARB process proves the effectiveness of the process in the alloy; however, the re-growth of the grains with further cycles indicates that there is an optimum number of ARB cycle under the process conditions.
The low wear resistance of the ultra-fine grained Al alloy was attributed to its non-equilibrium and unstable grain boundary characteristics.
Wear rate vs. number of ARB cycles for 6061 aluminum alloy. 0 1 2 3 4 5 6 7 0 10 20 30 40 50 60 70 80 Wear Rate (1x10 -13 m3 /m) Number of Cycle Applied load : 1N Applied load : 2N Applied load : 4N Fig. 4.
Wear rate vs. number of ECAP passes for AZ61 magnesium alloy. 0 2 4 6 8 0 2 4 6 8 10 12 Applied load : 3N Applied load : 5N Applied load : 7N Wear Rate (1x10 -12 m 3 /m) Number of Pass

The deformation behaviour of Ni having different grain sizes and various grain boundary states are also considered.
The grain size and structural components were determined from the TEM images by counting at least 100 grain diameters.
The grains contain walls and cells (Fig.1b).
Groups of grains are displaced one relative to the other along grain boundaries.
Nonequilibrium grain boundaries with a high density of defects are a strong barrier to dislocation movement; and both the large number of grain boundaries and subgrains in UFG material after SPD provided for rapid deformation hardening.

Grain boundary diffusion, stresses and segregation Boris Bokstein National university of science and technology “MISIS”, Leninskiy prospect, 4, 119049, Moscow, Russia bokst@misis.ru Keywords: model of grain boundary diffusion, driving forces, stresses, segregation, computer simulation Abstract.
According to both models GB is a homogeneous thin slab of thickness δ between two infinite grains.
It can be connected with a large Fe-Fe coordination number (up to 3.5) in a liquid Al1-xFex alloys.
Fe-Fe coordination number in a liquid Al-Fe alloy and in GBs in Al-Fe alloy 3.
[13] Round table discussion “Grain boundary diffusion: experiments and modelling” DSS-2010, 1-4 June, Moscow.

A number of special boundaries form preferentially during solidification, and those with misorientations about a [110] axis, including low angle boundaries, are more likely to slide with thermal cycling.
Tin has a number of important forms of anisotropy that complicate its deformation behavior.
Since tin is tetragonal, it has a number of slip systems with different Burgers vectors and slip planes [10, 11].
Grain Boundary Sliding in Pure Tin.
After substantial grain growth, the large grain size led to greater amounts of shrinkage during cooling in grains having the c-axis more nearly aligned with the ND, which is most evident in the ledge along the lower (dark gray) grain at the bottom of the image.

Quantitative X-ray analysis of deformation microtexture within individual grains N.Yu.
Therefore, a set of MPF is available for an examined grain that is the basis for the following determination of the intra-grain ODF.
This set is presented by the L-dimensional vector of probabilities hPr determined according Eq. 2; L is the total number of p-cells throughout the set of the MPF used.
An obvious way to do that is to decrease the size of g-cell with respective increasing the number of the cells, N.
(8) Two main ways exist to improve the precision of the ODF determination: the increase of the dimension of the texture vector R and the increase of the number of MPF used.

It shows a lot of grains whose sizes lie in the range φ5~15 µm, and the grain boundaries between them.
In this process, it is necessary to repeatedly alternate the abrasive size from large to small to prevent the AlN grains from detaching as a result of grain boundary fracture.
As a result the number of effective cutting edges increases, and the Figure 2 Ultra-precision plane honing machine Grinding wheel with radial pattern Workpiece head Truing head Table 1 Main specifications of plane honing machine Workpiece head High stiffness double hydrostatic bearing Maximum workpiece diameter φ120mm Maximum rotation number 900rpm Constant feed rate and pressure feed back effective stroke 150mm Feed resolution 0.1µm Maximum machining force 200N Truing head Maximum rotation number 900rpm Servomotor control effective stroke 150mm Feed resolution 0.1µm Grinding wheel spindle High stiffness hydrostatic bearing Wheel diameter φ375mm Maximum rotation number 900rpm Table 2 Experimental conditions Workpiece AlN, 1-inch square, 6pieces Grinding wheel Radial pattern wheel Rough processing SD400B, SD1500B Feed rate: 3µm/min Finishing processing SD3000B, SD3000V, SD8000V Feed rate: 1µm/min Machining force Maximum 120N Grinding fluid
Fig. 7 shows the machining force and the number of effective cutting edges as calculated from the SEM images.
However, a vitrified bond wheel with small grain size such as SD8000V could cut AlN grains by transcrystalline fracturing.

Introduction Grain boundary engineering (GBE) evolved from "grain boundary design and control" [1-4] has proven to be an effective method for improving various properties of bulk materials.
Numerous studies have shown that these special grain boundaries, described in low  coincidence site lattice (CSL) grain boundaries (usually 29) possess special chemical, mechanical, electronic, kinetic, and energetic properties [5-11].
At the critical strain, some of the grain boundaries are distorted by extrinsic dislocation, which will induce the rapid growth of some grains when the materials are annealed at a high temperature.
Grain boundaries with 129 were regarded as special CSL boundaries, and Brandon's criterion was applied to determine the  number for all boundaries.
On the other hand, abnormal grain growth occurred under the effect of heat input.