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Introduction Grain refinement is desirable, especially for high performance applications.
There are few means available for grain refinement such as the addition of grain refiners (Chemical refinement) or through the application of external forces on a melt (Physical refinement).
Grain sizes were measured according to ASTM E112-96 [10].
[[The average grain size achieved when treated below the liquidus was around 102µm as compared to an average grain size of 43µm when the melt was treated above the liquidus, challenging the idea of achieving a fine grain size by implementing below liquidus shearing i.e. in the semi-solid region.
St.John, An analysis of the relationship between grain size, solute Content and the potency and number density of nucleant particles, Metall Mater Trans A, 36 (2005) 1911-20

It has a 'trap' effect on the hard large grains that can prevent defect effectively on the surface of the workpiece which is caused by large grains.
But the practical grain size is not uniform, when the larger grains from abrasive or the debris which come off from workpiece into the machining zone, the load is borne by small number of large grains if using the hard tool plate (cast iron, copper, tin etc.), which will lead to the workpiece's cutting depth increased and then form scratching or pit damages (Fig. 1b).
When the large grain enters into the machining zone, grains surrounding the large grain may generate position displacement to form 'trap' space (Fig. 3), and the large grain and abrasive will be at same high.
Therefore it can avoid surface defect of workpiece caused by large grain.
The equipment used to test roughness is Mahr Perthometer S2 (vertical resolution: 0.8 nm, sampling numbers: 11,200).

Both of the master alloys remarkably reduced the size of α-Al grains, impeded the dendritic growth and promote the equiaxed growth of α-Al grains in Zn-50wt.
Two typical master alloys, Zn-45Al-5Ti-0.3C and Zn-45Al-4Ti-1C(the number before each element is its content in wt.% in the master alloys) , were produced in this study.
The α-Al grains in the three original Zn-50Al alloys without the addition of master alloy all present complex dendritic structure which contains a number of primary and secondary (and even some ternary) arms, with the length of primary arms exceeding 400μm at 690℃ and 200μm at 610℃(Fig.4(a)-(c)).
Grain refinement mechanism of Zn-Al-Ti-C master alloy.
When more TiC particles are added into Zn-Al melt through the master alloy, more α-Al grains are formed and smaller the α-Al grain size in a Zn-Al matrix.

Al-Ti-B master alloy is a good grain modifier, and can play better refinement of the aluminum grain.
The corrosion specimens were taken from the gearbox itself, and the series of the sample was numbered A, B and C depending on position in the gearbox.
The more the number of nucleation, the smaller of the grain was.
If the grain was very small, there would be more grains in a certain volume.
The number of grains increased in a certain volume after modification, which resulted that the number of the grain boundaries increased.

A huge number of three-dimensional micro cuttings are performed with different shape of grains.
A number of grinding experiments with a single abrasive grain were performed [1, 2, 3].
On the other hand, a number of finite element models had been presented to describe the metal cutting processes [4, 5].
Single Grain Cutting Model There are mainly three aspects which influence the results of single grain cutting, grain, workpiece and cutting parameters, as show in Fig. 1.
It is regarded cutting with ball-shape grain.

Somewhat different assumptions are accepted for non-equiaxial grains.
Prolate grains were inclined with respect to the extrusion direction. 2.
Grains were relatively thin plates parallel to the rolling plane.
ASTM grain size number is defined as G = 3.322 log - 2.954, which gives 16.6 for the Al sample and by extrapolating the ASTM Tables ending at G = 14.3 we find a good agreement concerning the above estimated values of NV and NL.
[4] ASTM E-112: Standard Methods for Determining Average Grain Size.

Introduction The application of magnesium alloy sheets are limited by their generally poor plasticity and stamping formability at ambient temperature due to a lack of sufficient number of slip systems associated with hexagonal close-packed (hcp) crystal structure and also a strong basal texture developed in rolled process [1, 2].
The average grain size is about 25 μm.
It can be clearly seen that grains are significant refined with a few of origin coarse grains embedded in new grained structure, the average size of fine grains is about 3 μm. q and Sq change discontinuously at the places correspond exactly to the grain boundaries, it is shown that new grains are mostly separated by high angle boundaries (> 20 degree).
New grains with high angle grain boundaries are developed.
Grain size is reduced to about 3 μm and the volume fraction of new grains reaches to about 0.8 after 8 passes

Introduction The grain size of a metal has a large effect on its properties, and the refinement of the grain size has many technological benefits.
Recently, the product of ultrafine-grained structure with a grain size of about 1µm or lower in various steels has been actively studied.
One is that a heavy deformation is applied to the matrix phase before transformation in order to introduce a large number of nucleation sites for transformed product.
Recrystallized γ grains are pinned by finely dispersed α particles and then maintain fine grain size (1～2µm).
On the other hand, most of α grains are subgrains surrounded by low-angle boundaries in the fine-grain region as shown in (e).

The calculation shows that the maximum number of dislocation emission increases with the increase of applied stress, as shown in Fig. 4, which also illustrates the variation of the maximum number with the grain size .
It is clearly shown that the decrease of the grain size can decrease the value of the maximum number of the dislocation.
It means that void growth can hardly occur for small grain sizes.
The maximum number of edge dislocation emitted from the surface of nanovoid as a function of grain size in nanocrystalline materials.
The void growth depends on the applied remote stress and the grain size.

As a result, ultra fine-grained austenitic single structure with the grain size of about 0.6µm was obtained.
Then, it was concluded that the tensile properties markedly deteriorate when the number of grains existing in the diameter direction becomes smaller than about 5.
Tensile Properties of Ultra Fine-Grained Wire.
However, the proof stress of the ultra fine-grained thin wire is comparable to that of bulk material which has the identical grain size.
This is due to the fact that the number of grains existing in the diameter direction becomes much larger than 5 by ultra grain refinement, although the wire is very thin.