Search results

Simulation of oxygen contaminated silicon grain boundaries in cluster approximation A.L.
Skaryna av. 4, Minsk, 220050 Belarus, fedotov@bsu.by Keywords: silicon, grain boundaries, oxygen, gettering Abstract.
Introduction Grain boundaries (GBs) in silicon attract cosiderable interest because of their gret technological value.
The majority of silicon polycrystals contain a number of oxygen atoms (~ 10 17-1018 cm-3) as a common impurity.
Cluster models of the grain boundary structure Cluster models of GBs have been constructed as follows.

The effect of condition on the grain boundary is numerically discussed.
The velocity gradient is additively decomposed into the non-plastic and plastic parts. . (1) The plastic part of velocity gradient is given by . (2) is the number of slip system, and a variable with the superscript denotes the value of a specific slip system .
In the case 1, is applied on the grain boundary, corresponding that dislocations cannot penetrate the grain boundary.
In the case 2, is subjected to the grain boundary.
In this case, dislocation cannot penetrate the grain boundary and piles up, resulting the strain gradient arises at a nearby grain boundary.

Grain refinements to the ultra-fine grained and even the nanocrystalline size regime have been achieved without formation of significant volume fractions of strain-induced martensite.
The mechanical strength enhancements in the linear plane-strain machined 316L have been attributed to grain refinement and stored strain.
Grain size refinement is an alternative strategy for strengthening.
This SAD pattern is consistent with a very large number of small grains, the majority of which is separated by high-angle grain boundaries (HAGB), being present in the associated microstructure imaged in Fig. 4b.
Fig. 5) confirmed a significant difference in grain size and grain size distribution for the 0˚-angle and 20˚-angle tool processing conditions at the tool velocities of 12.5cms-1 and 25cms-1, confirming prior reports [6].

The press rolling time is set by the wheel feed rate and the number of rolling coverage.
Abrasive grains hardly appear and project on the wheel surface.
SPa has a direct correlation with the projecting height of grain approximately.
The SPa of loading wheel surface with no projecting height of grain is about 0.8mm, and SPa is about 1mm larger than the projecting height of grain.
(1) The projecting state of abrasive grain on acting wheel surface can be investigated by analyzing SPa of wheel surface, SPa has a direct correlation with the projecting height of grain approximately

How a recovered dislocation structure gives rise to growing, strain-free grains has been debated for several decades.
Thus, a number of investigators have suggested that the strain-free nucleus must evolve from the recovered subgrain structure.
Journal Title and Volume Number (to be inserted by the publisher) 5 (a) (b) (c) Figure 2.
The probability of abnormal growth, Pabn, decreases as the critical angle θ* between low and high mobility boundaries increases (i.e. the number of high mobility boundaries decreases).
This model may be used to predict recrystallization nucleation frequency, as well as abnormal grain growth.

The amount of unidentified compound was much smaller than Al6Mn.Change in the number of DRX grains at the center of the extrudates under-extrusion with distance from the die mouth is shown in Fig3.
During hot-extrusion, the number of DRX grains in Meso10 alloy didn't change.
In Meso10-1.3Zr alloy, the increase in the number of DRX grains stopped 8mm rear from the die mouth, and DRX have stopped there.
Near the die mouth, the number of DRX grains hardly increased and it shows DRX didn't occur in each sample.
Fig.3 Change in the number of DRX grains at the center of the extrudates under-extrusion with distance from the die mouth.

The initial grain structure was equiaxed, but at low strains the grains become elongated in the torsion direction.
The origin of the increased complexity is from the number of possible events that can occur during deformation: austenite softening, ferrite softening, and deformation stimulated transformation.
There are a number of incomplete grain boundaries, i.e. isolated high angle grain boundary segments present in the larger ferrite grains.
Ferrite grain size and aspect ratio The changes in the ferrite grain size and grain aspect ratio, measured by linear intercept method, are shown in Fig. 5 at different strain.
Then with increasing strain from 1.5 to 2 ferrite grain size and grains aspect ratio simultaneously decrease.

An analysis of strength and ductility of ultrafine grained Al alloys R.
Over the last two decades a number of secondary processing techniques have emerged, with the primary aim of refining the microstructure to characteristic length scales near or below 1 µm.
This may be due to the more elongated grains and the lower fraction of high angle grain boundaries present in ARB alloys.
Micro-shear bands form during deformation and impinge on grain boundaries.
Effect of grain boundary character on ductility In addition to the important influence of grain size on ductility, the nature of grain boundaries also play a major role.

After T6 treatment, a large number of intermetallic compounds of Mg24Y5 with Y are precipitated from the alloy and the second phase has changed significantly in size and morphology which is uniformly and widely distributed in the grain and grain boundary with a good strengthening effect.
The grain formed by cooling of alloy liquid generally includes three categories: fine equiaxed grain on the surface, internal columnar grain and coarse equiaxed grain at the middle.
Since the grain boundary of equiaxed grain is long, impurities and defects are distributed dispersedly and the phase of different grain is different, its directivity of property is low and relatively stable.
At the same time, a small number of acicular compounds are also seen inside the grain which may be stable phase at high temperature left from cast structure and networking eutectic structure concentrated at the grain boundary of alloy after heat treatment completely disappears.
In meanwhile, after the casting second phase is discomposed, there is a large number of uniform and dispersed spot phases to precipitate which are an important factors of strengthening.

Unlike isothermal annealing, wherein grain growth increased with time, increasing number of repetitive annealing cycles showed formation of ultrafine grained recrystallised microstructure.
On the other hand, the subsequent process of grain growth mainly relies on the grain boundary energy because it occurs by grain boundary migration.
The grain size distribution analysis is shown in Fig. 4.
Nearly 50% of grains were of very fine size (< 2mm) when numbers of annealing repetitions, as shown by black and red data points in Fig.4, were less.
Figure 4: The plot shows the variation of grain size distribution with increase in repetitive annealing numbers.