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As the grain size is small, the grain boundary fraction cannot be neglected and we will study properties of both grain boundary and core grain by Mössbauer spectrometry, which is appropriate to study the specific problems of nanometer range [26].
More the number of samplings is and more the powder is contaminated.
However, it is well known that the MA process gives a distribution of the grain size, which should give a paramagnetic contribution for grains having the smallest size and a magnetic contributions for the largest grains.
For the mean grain size obtained by MA (about 10nm), the grain boundaries can be estimated to approximately 20 % of the total volume.
This fraction can be estimated using a simple spherical grains model assuming grains as a spherical crown of mean δ/2 width (grain boundary) surrounding the spherical grain core of mean diameter d.

There is a number of factors which can affect the DRX namely: the chemical composition of the alloy, the grain size at the beginning of the deformation, the deformation mode (Fig. 2) and the applied thermomechanical cycle [3,7-9].
Determining the onset of DRX via of metallographic observation techniques involves putting a great effort on the implementation of a large number of tests and sample preparation.
Kuc et al. [32] reported Eq. 9 by applying stereology simultaneously with a quantitative description of the shape and size of grains in polycrystalline materials.
A strong influence of average grain size (the mean area of grain plane section, the mean grain volume and the variability factor of the grain volume) on the peak stress was observed.
Zhu and colleagues [33], in order to obtain a homogeneous distribution of ultrafine grain size in strip finish rolling processes, state that the critical strain for initiation of DRX is given by Eq. 10.

Because nano-Al2O3 particles contribute to providing more nucleation particles and can effectively limit the growth of grains for the nickel grains.
It shows that [111] direction is the preferred orientation for grain growth of Ni.
Figure 2 demonstrates that the added nano-Al2O3 can transform the growth mode of Ni grains prepared by pulse electro-deposition and results in the transformation of the preferred orientation for Ni grain.
The number and size of pores on the coating surface have increased compared with the coating achieved at 0.5g.L-1 nano-CeO2 content.
When the nano-CeO2 amount increases to 6.0g.L-1, it is observed that the difference in Ni grain size has increased with number of pores (Figure 3d).

It is common to obtain the FLD experimentally by measuring at critical areas, the major and minor strains from deformed circles that have been previously electroetched or imprinted on the surface of specimens from a number of different types of formability tests.
These effects are usually divided into two distinctive categories: “grain size effect” to describe the interactive effect of the grain size of the material, which is a dominant effect at micro scales; and ‘‘feature/specimen size effect’’, which depends on the process/test, referring to the size of the feature/specimen and the smallest feature to be obtained, or in other words, an indicator of the manufacturability.
The grain sizes were measured using an optical microscope and maintained constant throughout the experimental work.
The grain sizes d were measured using a commercial image editing software ImageJ.
Fig. 5 shows an almost linear evolution of the effective stress for both M and N numbers, presenting a similar trend to other observations reported in the literature [4] at similar stress levels for stainless steels, however, it will require improvements on the apparatus and experimental techniques to control the grain size in order to obtain more conclusive results.

But there are still some broken and coarse block product distributed at the grain boundary or in the interdendritic regions.
In the meantime, there are a large number of ultrafine dot-like particles in the homogenized alloy ingot, and the distribution of them are heterogeneous.
There are some ultrafine dot-like particle-free zones at the grain boundary or in the interdendritic regions which is the the end of solidification zone, or in the centre of dendrite arms which is the preliminary solidification zone during casting process (as shown in Fig. 1 (b)).
It can be seen that the grain shape of the solution-treated plate that hot-rolled from homogenization ingot is coarse and equal-axis (as shown in Fig. 5 (a)), the grain shape of the solution-treated plate that hot-rolled from homogenization-free ingot is almost fine fibrous (as shown in Fig. 5 (b)).
Because the larger number of fine, dispersive and homogeneous AlFeMnSi particles can inhibite the recrystallization behavior of α-Al matrix.

As can be seen from microstructures presented in Fig.2, the nucleation of austenite occurs preferably at the ferrite-cementite interface in pearlite colonies and to a less extent at ferrite grain boundaries due to lack of cementite particles on ferrite grain boundaries after coiling at a high temperature.
The more uniform distribution of carbon containing phases, cementite particles in particular, together with a much smaller size of ferrite grains are responsible for a larger number of austenite nuclei in the steel after a low CT.
Regardless of the higher volume of recrystallized ferrite grains in the steel coiled at a higher CT, the nucleation of austenite is more intense in the steel after a low CT.
Holding at 740 oC accelerates the recrystallization of ferrite promoting the formation of austenite nuclei at recrystallized ferrite grain boundaries (Fig.4).
The higher volume of recrystallized grains and enhanced dissolution of cementite during holding results in an increased number of austenite nuclei, which in turn assists the formation of more uniform refined microstructure in the steel coiled at a higher temperature.

Austenite nucleates at ferrite-ferrite grain boundaries or ferrite-cementite boundaries.
Spheroidization reduces the number of sites available for austenite nucleation.
Figure 2e (LCR 1019M) shows evidence of unrecrystallized grains from a combination of equiaxed, “clean” grains and pancaked, deformed grains [8].
It is possible that Ac3 is reduced at 1000 °C/s because of the greater driving force and the greater grain boundary area (due to smaller grain size) that provides nucleation sites in the final period of austenitization.
Furthermore, the Andrews equation is limited to a small number of elements and compositional ranges.

Researches on material properties were mainly focused on impurity elements (such as P, S, Mn elements), yield strength and grain boundary carbide [5-11].
Some M-A islands are semi-continuous and nearly parallel and they tend to grow along grain boundaries, which accords with the characteristics of granular bainite.
Some M-A islands distribute irregularly and grow up across grain boundaries, which corresponds to the characteristics of granular structure [14].
The grain size of three rotor steels were statistically rated through the three-circle intercept method.
Results show that the grain size numbers of 25Cr2Ni2MoV steel and 26NiCrMoV10-10 steel are 7.5~8.0 grade with a corresponding average diameter of 22.5~26.7μm and the grain size number of 30Cr2Ni4MoV is 6~7 grade with a corresponding average diameter of 31.8~44.9μm, which indicates that the grains of all three rotor steels are relatively fine and uniform.

The use of a wheel with fine abrasives is effective in improving the quality of surface roughness and reducing the thickness of a damaged layer, due to the increasing number of active grains.
The dropping of dull abrasive grains prevents both the increase of lapping force and loading of swarf.
Moreover, large grains can fall into the plate and support approximate load with other abrasives of plate, which is called 'trap' effect.
Surface roughness is tested by Mahr Perthometer S2 surface roughness measuring equipment, scan length 5.6mm, sampling number 11200, vertical resolution 0.8nm.
The dropping of dull abrasive grains prevents both the increase of lapping force and loading of swarf.

MF is one of the severe plastic deformation (SPD) techniques, which used to refine the grains size up to nanostructure size.
The grain refinement has high effect on several material properties such as strength, fatigue and superplasticity (2).
It should be noted here that the number of hardness measurements were 30 point distributed randomly on the material surface.
The refining process is exist and the grain size decreases as shown in Fig (4).
However we estimate the existing of grain refinement by considerably increas in yield stress according to Hall-Petch relationship