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For that reason, the number of crystallites reduces during the growth until, finally, a few large grains, associated with the faster growth rate, exist at the top of the ingot.
Only in the 2300 °C sample, large grains, which belong to the 15R variety, are observed (Fig. 3-a).
In the 2000 °C sample, due to a smallest grain size, some statistics could be performed.
The grains consist of two polytypes, 60 % of which correspond to 3C and 40 % to 6H.
Of course, other 6H grains have the c-axis almost parallel to the growth direction, as shown in Fig. 5.

The fusion zone of the welds were mainly composed of columnar grain structure. 1 Introduction Underwater welding is one important repairing and maintenance technology for the structures and facilities used in offshore and sub-sea, and it is also widely used for repair of components and structures damage caused by fatigue and mishandling in nuclear power plants [1-2].
Table 4 The orthogonal test factors and levels factors voltage current Welding speed number A B C D 1 1 1 1 1 2 1 2 2 2 3 1 3 3 3 4 2 1 2 3 5 2 2 3 1 6 2 3 1 2 7 3 1 3 2 8 3 2 1 3 9 3 3 2 1 Fig .2 The appearance of the welds 3.2 Hardness measurements For each weld sample, hardness(HV) was measured on the cross section of the weld specimens.
Fig. 4(b) showed that the massive proeutectoid ferrite located in the grains boundary of columnar crystals.
Fig. 4(c) shows the mocrostructure of HAZ near fusion zone and coarse grains of eutectoid ferrite grains precipitated along the austenite grain boundary due to welding thermal cycles.

The a-phase will form initially along grain boundaries and, at a later time, will heterogeneously nucleate within the b grains.
The resulting button was solution treated in a vacuum at 840°C for 66 h to increase the grain size and minimise the number of grain boundaries and subsequently quenched into water.
Under these conditions the particles themselves cannot be resolved, and the contrast is attributed to the coherent strain fields surrounding them Fig. 1(b).) shows a denuded zone where the decomposition products are reduced drastically in number density within a narrow zone (~ 300 nm) on both sides of a grain boundary.
Scanning transmission electron microscopy (STEM) has been carried out to analyse the atomic number contrast of the incipient decomposition products.
Nevertheless, a long-range cooperative change of crystal lattice could be identified in a number of cases.

Simultaneously, scale growth occurs by the inward diffusion of oxygen and outward diffusion of aluminum along the grain boundaries (GBs) in response to their respective chemical potentials.
The GBs used to determine the oxygen GB diffusion coefficients are labeled with numbers in the map.
The data (numbered 1~3) from the 18O line profile along the numbered GBs in Fig. 1 are comparable to the calculated curve.
The GBs used to determine the oxygen-GB self-diffusion coefficients in Fig. 3 are numbered in the map.
The GBs used to determine the oxygen-GB self-diffusion coefficients are numbered in the map.

Introduction At present the method of severe plastic deformation (SPD) is widely used for obtaining ultrafine- grained (UFG) materials with the average grain size of a few tens-hundreds of nanometers.
In this regard, the microstructure is changed in the SPD process, in particular, the grain size is decreasing, the dislocation density and the misorientation between the adjacent grains are increasing, etc. [1-3].
This fact was explained by the limited number of slip systems in HCP metals [10].
It was determined that the increase of the ECAP passes in number is followed by the weakening of the crystallographic texture intensity.
Relative activity of slip and twinning systems (a) and the average active systems per grain (b) depending on the strain degree.

The stoichiometric of precursors were diluted in deionized (DI) water, for the La2O3 was dissolved using nitric acid to form La(NO3)3 solution and the number of citric acid are 1: 1.2 compared by total metal ions.
The average grain size of all samples was determined by taking the average value of the diameter from six different grains.
The results reveal that Ba substitution increases the average grain size of the samples until it reaches its largest grains in x = 0.10 sample.
Ba substitution also affected the average grain size of the samples with the largest grain found in x = 0.10 sample.
Greater Ba composition does not further increase the average grain size of the samples.

The platelets then grow rapidly in number and after 90min they seem to occupy nearly the entire surface (Fig. 2c).
(c) Fe22Cr2Al oxidized at 900°C for 1h, platelets formed on Fe oxide grain boundary grooves.
Grain growth reduces the total interfacial area of the grain boundaries intrinsic to the platelet polycrystalline-network but does not change the shape of the platelet.
One important characteristic implied by this convexity of the grain boundaries is that each incoming platelet will experience an intrinsic grain Fig. 6.
Intersections and recrystallization in platelets grown after 500h oxidation at 900°C Shrinking Grain boundaries Grain growth in a platelet Twining Intersections platelet 80nm Fig. 7.

We have shown experimentally that increase in fineness of grind leads to growth in the number of active centers.
The formation of agglomerates is affected by the number of balls, involved in the process that determines the flow of energy, supplied to the powder particles.
Increased number of balls leads to increase of the generated energy stream.
However, in coatings, which after MA have smaller powder particle size (TiNiNb, TiNiMo), the grain size is more evenly distributed.
Fig. 4 The grain size distribution and the percentage of powder materials after HVOF of SME powder materials.

The SEM results revealed that the grains of SiC-phase in as-fabricated silicon carbide were flaky-like or globular-like.
The similar grains flocked together.
The crystal grains of SiC mostly existed as flaky or globular and a very few needle-like shapes.
Fig.2 (b) showed the micro-morphology of SiC grains.
Gas-gas reaction between SiO(g) and CO(g) likely produced needle-like grains [14].

The average grain size, maximum grain size, minimum grain size and grain boundary width are tabulated in Table 1.
MG ductiltity εfMGmax , εfMGmin 0.06, 0.006 Constant of Eq. 5, α' 0.5 Average grain size 50 µm Maximum/minimum grain size 70 µm, 25 µm Grain boundary width 1.0 µm Results and Discussion Creep Rupture Life.
Furthermore, it is found that the first failed element (fully damaged) occurs at the grain boundary, at the juncture between the grains.
Based on metallurgical investigation [9], large numbers of creep voids are clearly observed around the notch area and main crack.
The voids then grow due to the coarsening of the precipitates, grain boundary sliding, and movement of the grain structure.