Search results

Grain boundary diffusion, stresses and segregation Boris Bokstein National university of science and technology “MISIS”, Leninskiy prospect, 4, 119049, Moscow, Russia bokst@misis.ru Keywords: model of grain boundary diffusion, driving forces, stresses, segregation, computer simulation Abstract.
According to both models GB is a homogeneous thin slab of thickness δ between two infinite grains.
It can be connected with a large Fe-Fe coordination number (up to 3.5) in a liquid Al1-xFex alloys.
Fe-Fe coordination number in a liquid Al-Fe alloy and in GBs in Al-Fe alloy 3.
[13] Round table discussion “Grain boundary diffusion: experiments and modelling” DSS-2010, 1-4 June, Moscow.

The observed grain boundary diffusion phenomena can be classified as C-type diffusion.
The need for a simpler, more straightforward evaluation method is also dictated by the increasing number of different diffusion experiments carried out in thin film systems, by measuring composition profiles e.g. with SIMS, AES [8,9,10] or SNMS [1,2,3] techniques.
Thus the effective GB diffusion coefficient of intermixing decreases with increasing time (as was indeed observed in [2] at 593 K) and all of them are smaller than the value belonging to the number calculated from the first appearance.
The volume fractions of the grain boundaries and the Ta-penetrated layer of grains (the volume penetration depth, in the lack of Ta bulk diffusion data in Cu, was estimated from the Cu self diffusion data [18] and about 0.5 nm was obtained [2]) are approximately 5%, supposing a grain size of 10 nm in Cu.
Supposing 40 nm grain size and C-type kinetic regime the average Si concentration in the grain boundaries are estimated to be about 83 %.

AFS Grain Fineness Number: From the sieve analysis the AFS grain fineness number (GFN) of the base sand was determined.
This parameter is the number which corresponds to the sieve number, in the set of sieves used in the test, through which all the grains would just pass if they were of the same size.
The dredged sand had rounded grains.
Rounded grains produce densities about 8-11% higher than angular grains [8].
The grain fineness number (GFN) of mould sands ranges from 40 to 220, the higher numbers representing fine sands [13].

The sheets are subjected to total number of three passes of CGP and further processing could not be continued due to initiation of cracks.
The ambiguity in grain size measurement arising from the non-equiaxed nature of deformed grains is minimized by measuring the number of intercepted grains from superimposition of grids on the image in different orientations (00,450,900).
Table 1 Estimated average grain sizes and tensile properties of CGP processed nickel sheets CGP Pass number Average grain size (mm) Yield strength (MPa) Tensile strength (MPa) Tensile elongation (%) Annealed 37±8 58 349 46.2 1 21±4 558 571 7.4 2 16±5 618 641 4.6 3 12±4 394 594 16 Microhardness evolution.
The variation of microhardness profile with increasing number of CGP passes is summarized in Fig.3b.
Grain sizes decreased continuously with increasing number of passes.

Introduction Grain-oriented silicon steel is a soft magnetic material that is used as the core material in electrical transformers.
The global movement in energy saving and environmental protection has aroused deep interest in the properties and total transformer performance of grain-oriented silicon steel [1-3].When grain-oriented silicon steel is produced using CSP technology, the sufficient solution and refining precipitation of inhibitors during rolling, cooling and heat-treating, are conducive to the formation and development of grain-oriented texture of secondary recrystallization grains, conducive to the improvement of magnetic properties, but also conducive to the improvement of surface quality and dimensional accuracy.
Experimental procedure The starting material was grain oriented silicon steel, whose chemical composition was illustrated in Table 1.
The designed idea was to make experimental steel dynamic recrystallization, which made grains refined.
A large number of AlN inhibitors whose sizes were effective separated out by controlling the cooling after normalizing and AlN in normalized plate was separated out in the light of certain habit plane, which tended to be separated out in the form of bundle parallel to each other.

However, fabrication of homogeneous UFG microstructures having high-angle grain boundaries by ECAP is a complex problem since the number of passes and the selected ECAP route can be very important parameters of the processing.
The relative fraction of high-angle (θ > 15°) grain boundary population has progressively increased with increasing number of ECAP passes - Fig.5.
In Fig.7 the tensile data are summarized as a function of the number of passes.
With increasing number of ECAP passes this difference decreases.
The coexistence of a dislocation climbing process and grain boundary sliding in creep of ECAP material may explain the observed decrease of the creep resistance with increasing number of ECAP passes (Fig.8).

TEM observed that the small grains in 70-80 nm size were well distributed.
After an induction phase of calcined kaolin in the hydrothermal system, large numbers of Nanocrystalline of X zeolite molecular sieve were formed and became the growth unit.
Results and discussion Morphology evolution of small grain X zeolite.
The electron diffraction pattern of small grain zeolite is presented in Fig.2.
A large number of nanocrystal nucleus of X zeolite molecular sieve were formed and became the growth unit.

With its effect, grain boundaries are bent, distorted or cut off, which contributes to complete grain refinement, and the grain size is less than1μm.
Between two laths, sub-grains, tiny grains and strain-induced precipitated carbides emerge in large numbers, which make composition distribution more uniform.
During dislocation cross-slip, grains are refined to generate grain boundary strengthening.
Sub-grains formed by high dislocation density generate sub-grain strengthening.
(3) The finer the tempered martensite grains are, the easier sub-grains will form during deformation.

Therefore, it is speculated that the increase in the FWHM for the spinel particles is due to the increase in the numbers of fine spinel particles at grain boundaries and triple points.
On the other hand, it has been reported that the electrical degradation characteristics of varistors are improved by removing the extra interstitial Zn2+ ions in ZnO grains near grain boundaries by thermal annealing and decreasing the number of Zn2+ ions moving into or across the grain boundaries [1,4].
Therefore, it is speculated that thermal annealing changes the number of interstitial Zn2+ ions in ZnO grains or the crystal structure and the particle size of Bi2O3 or spinel particles.
From these results, it is considered that the increase in α after electrical degradation caused by thermal annealing has a slight correlation with the number of interstitial Zn2+ ions in ZnO grains.
Therefore, it is speculated that the increase in the FWHM for the spinel particles is due to the increase in the numbers of fine spinel particles at grain boundaries and triple points.

Before diamond grain tack-on operation, ultrasonic agitation can make grain dense and guarantee nice contact between substrate and grains.
Diamond grain numbers per unit area were computed as grain density.
Grain Density.
Then in second stage, quick electroplating with high current density can be carried out with application of ultrasonic agitation. 0 5 10 15 20 25 30 No.1 No.2 No.3 No.4 Buildup scheme Grain numbers 0 100 200 300 400 500 Agitation No agitation Tool type Grinding ratio Fig.3 Diamond grain density of tools Fig.4 Grinding ratio Grinding Ratio.
Before diamond grain tack-on operation, ultrasonic agitation can compact grains and guarantee the nice contact between substrate and grains.