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Not nanocrystalline (grain size < 100 nm) but submicrocrystalline (grain/subgrain size of 0.2 - 0.3 µm) structure formed in this case.
The number of revolutions N varied as 1, 3, 5, 10 and 15 that corresponded to true torsion strains 3.2, 4.3, 4.8, 5.5 and 5.9 at half a radius.
Fig.1. {110}B2 X-ray line half-width vs number of revolutions N for alloys 2 (•), 3 (▲) and 4 (o) after HPT at RT.
Corresponding grain size changes are presented in Table 1.
In the non-aging alloy 1, the grain size abruptly increases and exeeds in many grains the upper grain size limit of 100 nm for a nanocrystalline structure, and the structure has to be referred to as the submicrocrystalline structure.

Irregular-shaped TiN and (Nb,Ti)C carbide formed during solidification and hot working process distributed in the grain interior and at the grain boundaries.
Annealing twins in the γ grains are observed.
The volume fraction and the number density of γ' precipitates at 750 oC is reduced compared to that observed at 700 oC.
The number density decreased with increasing the temperature is attributed to the higher solubility of Ti and Al in the γ matrix at higher temperatures [8].
It can be seen that, the outward growth nodules (Cr2O3) with irregular grains which seem to be a sand flower composed of many fine agglomerated grains.

A number of Al containing Mg alloys with single or combined addition of alloying elements such as Si, RE, Ca, Sr have been developed.
The hardness of Ca or CaO added alloys increase by grain refinement.
Summary The grain size is refined and also β-phase is reduced by Ca or CaO addition.
The hardness of Ca or CaO added alloys increase by grain refinement.
Addition of CaO results in the precipitation of C15 phase on the grain boundaries.

The average grain size and root mean square roughness were 250 and 7.04 nm, respectively.
We found the change of grain size corresponded to the root mean square roughness.
The circular-like grains with 20 nm width were observed with scanning electron microscopy (SEM) for as-deposited KNN thin films.
However, the grain size of thin films decreased for high oxygen concentration of 40% since many small grains forming at grain boundaries.
This result reveals that the number of oxygen vacancies of as-deposited KNN thin films at 25 and 40% oxygen concentration decreases.

Separating grain-boundary diffusion from grain-boundary migration It is quite well established that the main part of the grain growth that occurs during compaction takes place during the later part of the sintering cycle as schematically shown Figure 1.
In order to avoid grain growth during densification it is therefore necessary to enhance the densification kinetics and/or to depress grain growth kinetics.
Addition of a grain growth inhibitor is frequently used to suppress grain growth, implying that a higher sintering temperature can be used without noticeable grain growth.
Apparently, within temperature regime I there is no densification or grain growth, whereas in regime II densification occurs, accompanied by very limited grain growth, and within regime III fast grain growth occurs in a fully dense body [1].
It is certainly a draw back that it is not possible to record the exact sample temperature and in order to obtain reproducible results it is not only important to use the same sintering conditions but also to use the same configuration inside the reaction chamber, i. e. the same size and number of graphite spacers located between the die and the water cooled pressure pistons.

In fact the excess amount of Mg role of crystallite growth inhibitor in SnO2. this method is a simple ,inexpensive ,efficient and economic preparation for SnO2, MgSnO3 and Mg2SnO4 nanoparticles with adjustable grain sizes in the range of 3-44nm in high yield.
Morphology of the nanoparticles The Scanning electron microscopy images of TNO4, MST4 and MOST4 at 400ºC for 4h are shown in Fig.5, 6 and 7 respectively with different resolution .The SnO2 particles in Fig5a and 5b consists of very well-connected uniformly grains with a large number of open pores .The measured mean grain size of TNO4 from SEM is Mg13 nm.
A significant grain growth is observed for MgSnO3 and Mg2SnO4 after calcined 400ºc.
The average grain size remained close to 5 µm for strontium stannates (MgSnO3) and Mg2SnO4 nanoparticles.
The average grain sizes remained close to 1 µm .

The FESEM micrographs exhibit that the film deposited on Si substrate presents the best uniformity and that on Ti substrate has smallest grain size and film thickness, with titanium element detected in the EDS spectra.
The tantalum wires are used as the hot filaments, the parameters of which have been optimized in order to obtain uniform temperature field distribution on the wafer substrate surface in previous study (filament number=6, diameter=0.8mm, filament separation=17mm, filament-substrate distance=9mm) [11].
It can be observed that all the BDD films exhibit similar rugged surfaces on which well-faceted diamond grains distribute, among which that on Si substrate present the most uniform grain size and orientation.
It should be noted that the grain size and film thickness on Ti substrate are much smaller than others, indicating the lowest nucleation and growth rate of BDD films on Ti substrate amongst the four varieties of substrates discussed in the present study.
The diamond film on Si substrate presents the most uniform grain size and orientation and that on Ti substrate exhibits much smaller grain sizes and film thickness, meaning the lowest nucleation and growth rate.

Composite microstructure consisted of α(Mg) globular grains with size of about 60 μm and volume of 7-10% surrounded by mixture of proeutectic magnesium solid solution with irregular shape and average size of 12 μm as well as fine eutectic mixture (α(Mg) + β-Mg17Al12).
It consists of irregular grains with the average size of 195 um, in which the (Mg17Al12 with α(Mg)e) eutectic is present inside and around them.
The differences in the size of grains are connected with melting of particles due to the highly dynamic and unstable processes such as laboratory experiments, inconstant temperature profile as well as diffusive phenomena, e.g. coarsening by Ostwald ripening.
The grains were surrounded by (i) the mixture of proeutectic α(Mg)p with the irregular shape and average size of 15 μm, which were formed directly from the liquid phase (Fig. 2b) and (ii) the fine eutectic consisted of α(Mg)e and β-Mg17Al12 to be seen among the globular grains in Fig. 2a and in the highly magnified micrograph in Fig. 2b.
It is well known that the YS, of a composite is the stress required to operate dislocation sources and is governed by the presence and number of all the obstacles that restrict the motion of dislocations in the matrix.

F, the system total free energy (Eq. 4), is the driven force for the evolution, and its reduction is achieved by the multiple mechanisms of mass transport and structural relaxation (surface diffusion, grain boundary diffusion, volume diffusion, vapor transport, and grain boundary migration).
Qi is the activation energy, kB is Boltzmann constant, and T is the absolute temperature, and MGB=MGB0exp-QmkBT is grain boundary (GB) mobility, and δGB the GB thickness.
Parameters Value Parameters Value Volume molar, Vm 7.012 ,m3mol Volume activation energy, Qv 2.6 ,eV Surface energy, γs 2.41 ,Jm2 Grain boundary activation energy, Qb 0.58 ,eV Grain Boundary, γGB 1.06 ,Jm2 Surface activation energy, Qs 2.21 ,eV Volume diffusion pre-factor, Dov 2.0 ,cm2s Migration activation energy, Qm 0.171 ,eV Grain boundary diffusion pre-factor ,Dob 0.127 ,cm2s Grain boundary mobility, MGB0 5.53.10-8 ,eV Surface diffusion pre-factor, Dos 4.103 ,cm2s Results and Discussion Theoretical Model Validation.
· The introduction of the effect of gravity on the model makes the computational modeling of the solid-state sintering process more realistic, although it doesn't have much influence on a small number of particles.
Yu, “Three-dimensional phase field sintering simulations accounting for the rigid-body motion of individual grains,” Comput.

This is generally attributed to the high negative rake angles presented by the abrasive grains, extremely small chip size, and considerable rubbing between the abrasive grains and the work material.
The friction heat caused at the grain-workpiece interface has attracted a lot of research in the field of grinding hard and brittle materials[2,3].
The monolayer brazing diamond tools can improve the bonding strength due to the chemical metallurgical reaction between the matrix and grains.
The size of diamond grains were 500–600 µm.
The function f(ξ) can be written as: (5) where , A0 is the average single grain-workpiece contact area and , γ a geometric grain shape parameter, αg the thermal diffusivity of the grain, and r0 the radius of circular grain contact.