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Microhardness evolution as a function of pass number.
The microhardness evolution as a function of pass number is shown in Fig. 7.
Irrespective of material and pass number a similar microstructure evolution during annealing was evident characterized by the emergence of new larger grains in the deformed structure (Fig. 8a, b).
In general, the hardness decrease became faster with growing number of passes.
Apparent activation energy for discontinuous recrystallization vs. pass number.

Both grains are α-Mg grains.
For the convenience of later description, this larger grain is called α1-Mg, smaller grain is called α2-Mg.
Due to the long growth time, the grain size is large.
These nuclei form large number of small size α2-Mg grains under the effect of rapid cooling.
With the enhancement of pressure, the number of bright white phase on LPSO structure increases gradually.

At 400oC grain growth took place yielding a bimodal microstructure with mean grain size of 9 microns.
The grain size was reduced to 1.5 um and 9 µm respectively.
At 400oC the distribution is bimodal and grain boundaries are decorated with small grains indicating the process is controlled by dynamic recrystallization.
Smaller grains decorate the interface between larger grains.
These larger grains have a recovered inner structure and collars of small grains at the high angle interfaces.

Homogeneous and ultra-fine grain (UFG) structure enables the materials high strength.
In a harmonic structure, the coarse-grained (CG) areas (“Core”) are surrounded by a three-dimensional continuously connected network (“Shell”) of ultra-fine-grained (UFG) matrix.
Each milling pass was completed in 10-15 minutes and the milling time was decreased with an increasing number of passes.
Figures indicate grain size distribution images by EBSD.
As can be seen in (b), the shell is composed of randomly oriented fine grains.

Recently, a large number of papers have been published in which an attempt has been made to quantify the relationship between the structure and properties of steel [1].
In many studies, (e.g. [2, 3]), it is noted, for example, that the most studied effect in the process of hardening is the effect of grain grinding.
The dependence of the yield strength on grain size is well described by the Hall–Petch relationship.
A similar dependence of grain size (d-1/2) was used to describe the viscosity as a function of the brittle transition temperature [4, 5].
However, in turn, the sizes of primary grains are determined by the sizes of dendritic crystals.

After the test, the number of load cycles were recorded and plotted on a graph as a dependence of frequency change from number of cycles (Fig. 2).
Thereby plastic deformation originated preferentially in grains that had appropriate crystallographic orientation, deformation evoked deformation strengthening in some grains resulting in higher values of microhardness in those grains in comparison with those grains where plastic deformation did not occur.
Cyclic loading generated plastic deformation in the grains close to the main crack but also in those grains that were further from the crack.
On the other hand there were also grains where plastic deformation did not occur.
This was given by the inappropriate orientation of grains against the applying stress.

Ni and Ni-15%Fe alloy deposits show nano-grain structure with the average grain size of 23 nm and 12 nm, respectively.
It has been found that nanocrystalline Ni-Fe alloys with grain sizes in the nanometre range show unusual magnetic characteristics.
Addition of an element which has more outer electrons than Ni, increases the mean number of electron spins per atom and consequently affects the spin magnetic moment per atom.
As expected, the addition of Fe to Ni increases magnetization as the number of dipole moments are added to Ni magnetic dipoles.
However, coercivity HC and permability m are strongly dependent upon the grain size, and in materials with grain sizes less than 50 nm, follow HC~ D6 and m ~1/ D6 relationships, described by the random anisotropy model [14].

Further studies have demonstrated that a number of different high shear deformation processes can transform the near surface microstructure and generate an ultra-fine grain structure [9-11].
The higher magnification image shows the fine grains generated by grinding.
The high density of grain boundaries within the very fine grain structure of the deformed layers results in a highly superficial corrosion attack and fast lateral propagation of corrosion under paint films.
In the dark filed image, the hardening phase precipitates can be seen to be present in the large grain below the deformed surface layer, while no such precipitates are present within the very fine grains in the surface.
This may be achieved by using treatments that enhance the natural, protective oxide layer, e.g. anodising, or by a number of chemical conversion treatments.

After the ECP treatments, some fine β precipitates appear along the α phase grain boundaries and in grain interiors, as shown in Fig. 2 (b) and (c).
Hereafter, we denote the ECP induced β precipitates located along the α grain boundaries βGB, whereas those located in the α grain interiors βGI.
That means the β precipitates obeys the K-S OR when formed along the α grain boundaries, or the N-W OR when formed in the α grain interiors.
TEM bright field images of crystal defects along α grain boundaries and in α grain interiors.
Guo, Grain refinement and formation of ultrafine-grained microstructure in a low-carbon steel under electropulsing.

Because the number of components fabricated by the high temperature carburizing to shorten the heat treatment time has gradually been increasing, the utilizing range of such steel is rapidly reducing.
All austenite grains are stable, as reported by Krauss [5].
In spite of omitting isothermal heat treatment, no abnormal austenite grain was found.
Note austenite grains in the samples of test 1; a), arrows in above graph indicate the censored and test 2; b).
grain was found in Fig. b).