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The observed effect was explained by the replacement of the pearlite constituents by lower bainite in the grain boundary regions which produced a local strengthening of grain boundaries.
The average grain diameter (area fraction occupied by the grains with certain diameter) is calculated also for each individual sample orientation.
The grain size data in this work were obtained using a grain tolerance angle of 5°and the minimum grain size was chosen to be 2 measuring points which were at least a distance of 1µm apart.
It is assumed here that a larger number of grains per area unit (i.e. a smaller grain size) will provide a higher density of high angle grain boundaries and therefore increases the resistance against crack propagation.
It can be explained by the replacement of the pearlite constituents by lower bainite in the grain boundary regions which produced a local strengthening of grain boundaries and the grain boundary regions.

High-Pressure Influence on the Kinetics of Grain Boundary Segregation in the Cu-Bi System L.
The effect of pressure on the kinetics of grain boundary (GB) segregation in the Cu-50 at.
After further simplification one obtains ( )20 0 4ln 2 rDtr Dx J b= . (7) Total number of atoms diffusing into dislocations in the vicinity of a GB in a certain time t is then ( )∫ ∫ == t bd t d rDt dt' DxπLnJdt'LnπrN 0 2 0 0 0 4ln 2 ∆ , (8) where L is the dislocation length and nd is the dislocation number.
The specimens were investigated by means of Auger electron spectroscopy (AES) to determine the Bi amount at grain boundaries.
Grain boundary enrichment in dependence of pressure for Cu-50 at.ppm Bi.

Acicular ferrite has high misorientation angle boundaries and a number of sub-boundaries or high density of dislocations inside, which contributes to an excellent combination of high strength and toughness.
While granular bainite has a large grain size (approximately 40μm in width).
In terms of EBSD analyses data the average grain sizes of these specimens were 3.9, 4.4 and 2.9μm respectively, and the fractions of their low-angle grain boundaries were 14.1%, 21.4% and 21.4% respectively.
The other line (CD) with misorientation varied frequently between 0.5 and 2 degree within an acicular ferrite grain presented that the acicular ferrite contains a number of sub-boundaries, which can be also supported by Fig. 4.
Fig. 5 misorientation characteristics of acicular ferrite (a) orientation map, (b) misorientation between acicular ferrite grains and (c) misorientation inside acicular ferrite grain Conclusions Acicular ferrite formed within deformed austensite grains can be obtained in the hot rolled low welding crack susceptibility steel.

The as-cast ingots were cold-rolled into sheets 1 mm thick, which were annealed for 1.8 ks at 350℃, resulting in a fully recrystallized grain structure with a mean grain size of 41 µm.
boundaries, while the elongated grains are often subdivided by low-angle boundaries.
This map shows the presence of a number of boundaries with misorientation angles less than 2°, which further subdivide the grains into smaller units.
The dislocation density is, in general, higher in the elongated grains than in the equiaxed grains, as can be seen in Fig. 2(a).
Micrographs taken under such conditions were used for dislocation density measurements and it was found that the density within the equiaxed grains is 1.0 ×1013 m -2 and 3.5×1013 m -2 in the elongated grains.

Cuza nr.13, Craiova, Romania, 200585, avictorczh@gmail.com, b stefan_iuly@yahoo.com Keywords: ferrite, ceramic materials, microwave heating, thermal-gravimetric analysis Abstract In this work there are presented the results of experimental researches which had the goal to establish the thermal effect of BaCO3 and α- Fe2O3 homogeneity mixture heated in microwave, used to processing barium ferrite W type by pyrosynthesis.There was used thermal-gravimetric analysis with a derivatograph reordered for microwave heating of samples containing iron oxides with different grain size.Experimental results emphasized that the microwave heating comparatively with resistor heating, lead to a lower synthesis temperature of hexaferrite of about 150 0 C , using oxides with grain size suitable to SBET= (7-10) m2/g.
They are used too in automotive industry and airspace vehicles.The hard ceramic materials are used in a large domains number .To produce these materials at industrial level the ceramic method [2,3].Other methods like the chemical methods as coprecipitation [1], SHS (self-propagating high temperature synthesis), hydrothermal method synthesis from aqueous sol-gel auto-combustion are used in laboratory because the need to use expensive raw materials and low productivity.
Material Purity[%] SBET [m2/g] Grain size range [μm] Average grain size Grain shape Density [g/cm3] Substance content [%] (SO4)2-[%] Length [μm] Thickness [μm] 1. α- Fe2O3 99,62 0,21 2,65 1,62-1,87 1,73 0,35 elongated 1,61 2. α- Fe2O3 99,37 0,36 7,53 0,84-1,39 1,12 0,19 elongated 1,29 3. α- Fe2O3 99,37 0,35 20,14 0,31-0,60 0,49 0,12 straight 1,04 4.
In Fig. 1 are shown comparatively the DTA curves traced for resistor and microwave heating for sample number 1.
The iron oxides morphology have an important influence of solid phase reaction process of barium ferrite W type, meaning that large and very small size grains, according to test results [4], reduce the components reactivity because: - the large size grain powders labelled by SBET= (2-5) m2/g have a reduced reactivity because of low number of contact points which represent reaction starting points are lower as size grain are larger; - the very fine powders with SBET= (10-20) m2/g induce a low reactivity because in heating process take place a fine particles concentration due to sintering process, and the number of point-like contacts are lower; - the optimal size grains regarding the solid phase iron oxides reactivity lie in range SBET= (6-8) m2/g.

We consider mono-phase grains illuminated by a beam smaller than the grain size.
The grain with the maximum value of N/M among the candidate grains was selected as the grain that occupies Q, where N is the number of detected diffraction spots from a grain and M is a normalization factor correcting orientation dependence of N.
From the orientation image, the orientation distribution in each grain and the mean grain size were estimated to be uniform and ∼ 60 µm.
To evaluate crystallographic rotation of each grain, typical coarse grains, G1-G7, were selected as shown in Figs. 3(e)-(k).
This work was supported by JSPS KAKENHI Grant Number 22760571.

The nanocrystalline silver powder and the amorphous powders of composition Ni49,5Ti20,5Nb15Zr15 (numbers indicate at%) were prepared by ball milling in the planetary Fritsch mill for 40 hours.
The grain size of silver crystals within powders drastically decreased after milling down to about 30 nm and only a small increase in the grain size up to 200 nm was observed after hot pressing.
The structure of tungsten has shown less defects and consequently less grain refinement than silver particles.
Change of mass Dm of the contact as a function of number of contact cycles of the composite based Ag- 20% NiNbTiZr measured for mobile and immobile contacts.
The silver grains grew only up to about 200 nm after hot pressing.

Fig. 2 shows variation in the erosion rate at room temperature with number of impacts on two different surfaces.
Initially the erosion rate on the coarse grain surface tends to decrease with an increasing number of impact and maintains constant values after about 10 impact events.
Erosion rate on the fine grain surface increases with increasing number of impact up to about 5 impact events.
Grain size dependence on the erosion of ceramics have been reported by many studies.[ 6 - 8 ] The erosion rates on both surfaces with respect to the number of impacts for higher temperature are shown in Fig. 2.
Fig. 2 Changes in erosion rate of the graded structures as function of the number of impacts for each tested temperature.

As shown in Fig. 2(a), the deformation of AlMg0.7Si alloy was performed by a large number of short-stroke pressing operations from four hammer dies; during the interval between strokes, the rotating and axially advancing of alloy was carried out by clamp.
(2) where D, F, A, N and P are average grain size, shape factor, area, the number and perimeter of grain, respectively.
Some solid grains are still connected to others and the grain boundaries are unclear in Fig. 5(a), so the average grain size and shape factor cannot calculate when the ARR is 20%.
In Fig. 7(c) and (d), when remelting time raises form 10 to 15 and 20 min, the grain boundaries are thicker, the solid grains are more independent and spherical, but the grains are large.
Then larger grains grow continuously and smaller grains dissolve fast due to the difference in curvatures of grains, causing the coarsening of solid grains.

The amount of deformation bands seems to increase with the number of ECAP passes, and their distribution becomes more homogeneous.
The initial grain boundaries are still distinguishable, however, the original grains become heavily deformed indicating the greater degree of grain refinement.
Sub-grain boundaries evolve within the grains/crystallite structure.
The quantity of these deformation bands increases with number of ECAP passes increasing degree of grain refinement. 2.
The increased dislocation density and a large number of grain boundaries allow faster diffusion.