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Introduction Adding grain refiner is an effective and practical way to refine Al alloy grains[1-3].
As an efficient grain refiner for Al and its alloys, Al-Ti-C grain refiner has a low tendency of "poisoning", and its production is pollution-free.
The minimum grain size that can be achieved is 100 μm.
The effective nucleation number of α-Al is also increased under the action of high intensity ultrasonic, which making the fading less likely to occur.
Greer, Grain refinement of Al alloys: Mechanisms determining as-cast grain size in directional solidification, J.

The important properties studied are moisture content, total clay content, grain fineness number, and grain shape.
Results obtained revealed that the river sand has average moisture content of 7.78 %, clay content of 3.20%, and grain fineness number (GFN) of 46.
Most mold sands should fall within 50-60 grain fineness number (GFN) or 220-250 microns average grain.
The grain distribution for each samples were obtained and the Grain Fineness Number (GFN) was calculated using the equation: GFN=Wn x SnWn (3) Where Wn is the weight of sand collected on each sieve and Sn is grain fineness coefficient.
This number classifies it under coarse grain size, which is still within the acceptable range of mold sand and suitable for metal casting application [7, 10, 14,15].

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

Mechanical Spectroscopy of Ultrafine Grained Copper I.S.
Increased amplitude dependent damping in ultrafine-grained copper is believed to be associated with a dislocation mechanism, rather than a grain boundary mechanism.
In Fig. 3b the grain size is also indicated for several temperatures.
At ε0 > 2.5×10-4, the values of IF depend on the number of cycles, see the arrow pointing from the n1 to the n7 cycle in Fig. 7.
This contribution drops with an increase in the grain size.

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.

One of the challenges to achieving a fine grain size in Mg-Al alloys has been to develop an effective and efficient grain refiner [2].
Whilst it is clear that UT can be effectively used to reduce the grain size in castings, there are a number of issues that need to be addressed before transferring the technology to gravity fed or low pressure die castings.
Fig. 3 shows two casting sections with an extremely fine grain structure at the bottom where UT was applied and a region of relatively coarser grain size in the bulk of the casting.
However, it is clear that there are a number of issues that need to be considered when applying UT to commercial castings.
UT was able to decrease the grain size further than SiC additions alone, whilst the SiC addition leads to a more extensive region of fine grains than UT alone.

In this study, the STSP is applied to grain refinement of an A5056 Al-Mg commercial alloy and the factors affecting the grain refinement are optimized.
The grain size tends to be smaller as the STSP temperature decreases: the average grain sizes are ~1.5 µm at 673 K, ~1.9 µm at 723 K and ~3.1 µm at 773 K.
The former leads to insufficient numbers of dislocations to create grain boundaries and the later makes it difficult to keep the grain size small.
Figure 6(a) shows that the microstructure at the slow cooling rate consists of fine grains and large grains with the average large grain size of ~5.5µm.
The SAED pattern indicates that the fine grains can be separated by high angle grain boundaries.

Introduction It is generally observed that the solid volume fraction and interface energies play an essential role in the morphological changes during sintering and determine directly parameters such as grain shape, grain-grain contact size and shape, grain coordination, contiguity and connectivity [1].
,ηps,s, is used to represent the different grain orientations of the solid phase particles, with ps the number of phase-field variables representing the solid phase, and one extra non-conserved phase-field variable, ηl, is used to represent the liquid matrix phase.
Later, the overall grain boundary area is further decreased via grain growth and Ostwald ripening.
It is related to the 3-D coordination number Nc and dihedral angle φ as [1] Cg = KNc sin(φ/2) with K a constant related to the grain size distribution.
The 3-D coordination number for each simulation is obtained as the average particle-particle contact number per particle from 3-D microstructure.

Grain boundary sliding.
Figure 1.h shows the grain boundary offsets that occur in grains orientated at an angle offset to the tensile direction, with the early start of accommodation by surface grain separation or grain emergence.
This was observed across a number of grids, as well as at various locations on the surface that had not been FIB milled.
Again, this was exhibited across a number of grids, and in surface areas not FIB milled.
The number and size of these defects were believed to vary with strain-rate.

Introduction The triple junction of grains is a linear defect, along which three variously oriented grains or three grain boundary surfaces are conjugated.
The grain boundaries are denoted by the bright dashed lines.
The grain boundaries are marked by thick gray lines.
As a result of rapid cooling, a large number of defects formed in the calculation block in addition to the grain boundaries: pores, vacancies, dislocations, disclinations.
The reason for the formation in polycrystals a large number of the strained triple junctions having a relatively "loose" structure with a high share of the free volume was elucidated in the study of crystallization in the three-dimensional molecular dynamics model.