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In general, nanocrystalline ceramics with an average particle size of less than 50 nm can be simply described in a first approach as heterogeneous materials consisting of structurally ordered grains and a large number of interfaces being expected to show structural disorder.
In nearly all nanocrystalline ion conductors an enhanced diffusivity is found compared to that of their coarse grained equivalents.
line mirrors the number fraction of fast Li ions near the interfacial regions.
The corresponding onset for the coarse grained material is expected at much higher temperatures, i.e., at about 650 K.
If no mechanically induced phase transformations occur, solid state NMR techniques, like line shape analysis or NMR relaxation experiments, are highly suited to quantify the number fraction of the generated highly mobile ions as well as to study the dynamics of the two spin reservoirs separately, namely the slow ions in the interior of the grains and the fast ones in the interfacial regions.

But with the addition of alloying element, the tensile strength can be higher by solution strengthening and fine-grain strengthening and precipitation strengthening.
Serial Number ReL [Mpa] Rm [Mpa] Serial Number ReL [Mpa] Rm [Mpa] Y-1 365;370(367.5) 540;540(540) Z-1 360;355(357.5) 525;525(525) Y-2 375;370(372.5) 540;535(537.5) Z-2 355;365(360) 535;540(537.5) Y-3 360;365(362.5) 535;535(535) Z-3 350;375(362.5) 535;505(515) Table 5.
Impact toughness of weld joint(The numbers in brackets are the average value).
But with the greater increasing of weld heat input (such as serial number Y-2 and Y-3 using shielded metal arc welding method, and as serial number Z-2 and Z-3 using mixed active gas arc welding method), from Fig. 2 (b) and (c), and from Fig. 5 (b) and (c), it can be seen the quantity of bainite is decreased and crystalline grain size is become larger.
(1) In weld metal the quantity of bainite is decreased and crystalline grain size is become larger, and the impact toughness decreases when using the same welding method

There are several techniques has been exploited to refine the grain size in metals into nano-scale.
So far this technique has been utilized in a number of materials namely: Aluminum, Iron, Steels, Magnesium, Titanium and their alloys.
This generated a coarse-grained microstructure spanning the full sheet thickness.
(d) shows the orientations of the recrystallized grains in a <111> pole figure.
The extent of these events depends on the number of previous cycles.

The resulting stress amplitude vs. cycle number diagrams (SN curves) are shown in Fig. 2.
Very small equi-axed grains were found at the surface.
Some evidence of dislocation pile-ups at grain boundaries was found.
A few twins were found within individual grains.
Elongated near-surface grains Fig. 4.

Between the grain size and porosity of microstructures, grain size is more important parameter affecting the magnetic properties of ferrites.
Grain growth is closely related to the grain boundary mobility.
Recrystallization and grain growth involve the movement of grain boundaries.
The grain growth mechanism is compromised between driving force for grain boundary movement and retarding force of pores and inclusion during the sintering process.
Also the number of Fe3+ ions which will decrease on the A site and increase on B site by the same amount.

Introduction The increased use of rock as dimension stone in the last decades has lead architects and building designers to explore a wide number of diverse ways so to emphasize colour and texture variations within the same rock and among different ones.
Fine grained SPI granite (SPIGr), slightly altered Yellow San Martinho granite (YSMGr), and medium grained Arronches granite (ArrGr) and Cinzala granite (CinzGr) were excluded for experiment with that treatment.
Regarding textures, which in this particular case, are all granular, the grain size will mean more (fine grained) or less (coarser grained) contacts between grains, reflecting easiness (or not) to fluid penetration and salt crystallization in the rock.
As result, the appearance of fine fissures is observed as well as removal of mineral grains.
Rock types and surface average parameters (roughness and height) with standard deviations measured by AFM in 50×50μm scan areas (N is the number of averaged scans for each sample).

Fig. 2 Cutting simulation of several abrasive grain Fig. 3 Geometric shape of conic grain Fig. 4 Geometric shape of conic grain cutting edge Fig. 5 Inverted cone abrasives Single Abrasive Cutting Model Single abrasive cutting process.
Fig. 7 Force models of abrasive grain cutting Single abrasive cutting force model.
Effect of grain shape on cutting force in super abrasive single-grit tests, CIRP Annals-Manufacturing Technology. 1(1989)323-326
Waveform of grinding force for single grain grinding-grinding of a brittle material by a single abrasive grain (2nd report), Journal of Japan Society of Precision Engineering. 03(1993)515-520
Grinding mechanism based on single grain cutting simulation.

Preface Grain boundaries and interfaces are generally diffusion short circuits; consequently, the major part of material transport will occur by grain-boundary/interface diffusion in nanomaterials where a large amount of atoms can lie on grain or interphase boundaries (about 50% for d=5 nm and 20% for d= l0 nm; d is the grain size).
In the first chapter of this book (by Suzuki and Mishin) our present knowledge on the grain boundary (GB) diffusion mechanisms is summarized.
It is well known from classical treatments of grain- or interface diffusion that there are three different grain-boundary diffusion regimes: type A, B and C.
Another interesting question has been raised during the interpretation of the already existing data on grain-boundary diffusion in nanocrystalline materials: Whether the grain-boundary diffusion coefficients measured in these alloys are identical to those obtained in microcrystalline state or not?
We will see that there is an increasing number of experimental evidences that the above diffusion coefficients agree very well with each other, i.e. in most of the cases the structure of relaxed grainboundaries in nanocrystalline and polycrystalline samples is very similar.

The experimental results indicate that after ultrasonic impact, the grain boundary on the surfaces of AZ91D is obviously refined.
From the SEM appearances, we can see that with the increase of vibration impact time, the grain of the sample was gradually refined.
With the ultrasonic wave flushes, the surface grain refinement, with the growth of the flushing time, the degree of grain refinement increased.
The method of the ultrasonic wave flushes grain boundary was generating the local deformation strengthening on the surface.
A large number of tests confirmed that summed up polycrystalline material yield stress (or hardness) and the relationship between grain size.

Furthermore, no peak of Ga2O3 or V is observed, indicating that neither Ga2O3 nor V coats the nanowire surface, which proves that the ammoniaton reaction is complete and Ga2O3 has turned to GaN completely.In short, as seen from Fig.1, the crystalline of the GaN grains is at its best for the sample grown at 900 oC and a preferred orientation of the grain growth occurs.
The intensity of the (002) peak is weak for the sample grown at 850 oC because of the incomplete crystallization of the GaN grains at lower temperature.
When the ammoniating temperature is 950 oC, the number of the nanowires decreases sharply and the nanorods with the size of 260 nm in diameter appear.
And when the sample is ammoniated at 1000 oC, the nanowires disapear and only nanorods exist, which is caused by recrystallization of the GaN grains at the higher temperature.
However, the number of the GaN nanowires decrease and the nanorods appear when the ammoniating temperature is higher than 900 oC because of abnormal growth or recrystallization and decomposition or sublimation of the GaN grains at higher temperature.