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During the second aging at 200°C, the specimen ARB processed by 4 cycles always showed higher hardness than the specimen ARB processed by 8 cycles, though the increase in hardness was similar, independent of the number of ARB cycle.
However, the size of the fine grains was still less than 1mm.
It is considered that misorientation at grain boundaries was increased and grains were subdivided by severe plastic deformation.
Plate or rod-like precipitates having length of several tens nanometers were also observed on grain boundaries and within the grains.
In the specimen, the ultrafine grained microstructures fabricated by the ARB process kept fine grain sizes during the two-step aging

Introduction Twinning is an important deformation mechanism in most hcp metals because of an insufficient number of independent dislocation slip systems.
It is further seen that twinning proceeds in the studied parent grain families in accordance with the Schmid factors, i.e. the fastest in {10.0}|| grains, and slowest in {11.0}|| grains.
This post-yielding decrease in the AE activity has been previously attributed to the increasing number of dislocations and thus decreasing free length for dislocation movement as well as exhaustion of twinning activity [7].
That means that twins in one grain can lead to the nucleation of twins in neighbouring grains via an increase in the local stress at the grain boundary due to impinging on the grain boundary.
It stands to reason that a considerably higher number of twins nucleate at the onset of plasticity in the fine-grained alloy.

The addition of rare earth Ce can increase the number of hard phase and thus produce more crack initiations, so that the mechanical properties of HMn64-8-5-1.5 brass can be reduced.
Rare earth Ce is a common additive of refining copper alloy grain [7,8].
Fig. 2 Average size of HMn64-8-5-1.5 brass matrix grain with different content of Ce The addition of rare earth Ce into HMn64-8-5-1.5 brass can refine matrix grain, and the effect of refining grain can be more evident with an increase content of Ce.
It contributed to the formation of new grain nucleus, but not to the growth of grain [13,14].
The reasons of refining grain are as above.

The number of grains containing in-grain shear bands, increased with decreasing deformation temperature; after deformation at 600 °C or 550 °C bands were observed in every grain but at 750 °C or above, shear banding was detected only in some grains.
In-grain shear bands appeared to be intense in the g-fibre grains, but also grains with other orientations contained in-grain shear bands.
The highest number of nuclei formed at the original grain boundaries – especially at triple junctions, although nucleation also took place readily in the in-grain shear bands.
Reheating to 950 °C and immediate cooling was sufficient to produce large number of small recrystallized grains.
Evidently however, the number of grains containing in-grain shear bands decreased with increasing deformation temperature.

Materials A1 and B1 (Fig. 1(a)-(b)) have similar coarse grain size and elongated grain morphology, although, on average, the grains in the latter are coarser than in the former (97 μm vs. 83 μm from linear intercepts).
While material C1 (Fig. 1(c)) contains a number of coarse grains that are sometimes elongated, they are heavily outnumbered by small ones.
Fig. 4 shows a simplistic, schematic depiction of how post-cold-rolling grain sizes vary with the initial (grain) size and shape.
Fig. 4(e)-(g) represents circular grains.
Acknowledgements This research was carried out under the project number MC4.05238 in the framework of the Research Program of the Materials innovation institute M2i (www.m2i.nl), the former Netherlands Institute for Metals Research.

The grain size of surface ultrafine grains was characterized by X-ray diffractometry.
The grain size of surface ultrafine grains on SMATed Fe3Al was characterized by X-ray diffractometry (XRD) on XPERT-PRO diffractometer.
Based on the broadening of (220), (400) and (422) diffraction peaks, calculation showed the grain size of surface grains was about 35 nm.
The above phenomena are all attributed to the lower diffusion activation energy and higher diffusion coefficient which induced by the non-equilibrium defects and grain boundary in nanocrystallines, especially a large number of triple junction boundaries. 4.
Width of deformed layer, grain size of surface grains, phase constituents and microstructure of transition zone in SMATed-Fe3Al/Al and Fe3Al/Al diffusion bonded joint were studied to reveal the influence of ultrafine grains on the weldability of Fe3Al and Al dissimilar materials.

The number of total atoms was set to be 731640.
Thus, the MD calculations indicated that grain boundaries act not only as barriers for dislocation motion but also as dislocation sources, which implies that grain refining increases the number of dislocation sources.
The effect of increasing in the number of dislocation sources on the BDT behaviour will be discussed next, basing on the dislocation shielding theory.
Michot[22] pointed out that the BDT temperature depends on the number of dislocation sources and spacing along a crack front.
It is therefore concluded that the decrease in the BDT temperature by grain-refining is due to not the decrease in dislocation mobility with respect to short range barriers but the increase in the number of dislocation sources around the crack.

The study has revealed three structure types in the alloy: (1) a smooth shagreen-type structure (an orange peel), which turns into a stripe-like structure (2) in some areas, and a grain structure (3) to appear as lengthy thin layers with the width of 50-80 µm and an average grain size of 12.5 µm, the most probable size of grains is detected to be in the range from 10 to 15 µm, a preferred number of such grains is 31%.
It is noteworthy that an increased number of micropores are detected on the boundary between these types of structure.
There is a grain structure in several areas in the form of lengthy thin layers with the thickness varying from 50 to 80 µm and average grain size of 12.5 µm (Fig. 1 d).
The grain size distribution demonstrates the most probable dimension of grain to range from 10 to 15 µm.
An average grain size in the identified structure was determined to be 12.5 µm, the most probable size of grains ranges from 10 to 15 µm; that is 31% of all grains.

The cold working process multiplied the dislocations and led to the grain fragmentation.
The cold working process multiplies the number of dislocations in pc metal, which are arranged the network with a low angle misoriented cells within coarse grain interior at the center of the specimen where the moderate equivalent shear strain εv is .
The succeeding strains progress the fragmentation of grains.
The saturation of grain refinement is achieved by an equivalent strain of for nickel [1].
It is noteworthy that there are large angle grain boundaries for the uf microstructure.

The abrasive mixture was boron carbide powder with grain number F400/17, mixed with kerosene and machine oil with grain concentration equal to m = 0.25.
Normally those two surfaces interact indirectly via abrasive grains.
Grains are cutting tools during lapping.
Hence, the abrasive mixture used in this research was boron carbide powder, grain number F400/17, mixed with kerosene and machine oil with grain concentration equal to 0.25.
Normally two surfaces interact indirectly via abrasive grains.