(a) What is the configuration of a tilt
boundary with 38.94 degree angle in Aluminum?
(b) What is the combined effect of tensile stress
and temperature on an Aluminum cell with this grain boundary?
What defects do these conditions form in the cell?
adesh.zip
:Click HERE to Download a DEMO version of ADESH
(ADESH works on PC-DOS. You will need the pkunzip.exe utility for this zipped file.)
Answer
ADESH produced following results in a few hours (on a PC with a 486
micro-processor).
Figure 1
(a) Figure 1 shows the atomisitc configuration
of a grain boundary in aluminum cell.
This is a tilt grain boundary with an angle of 38.94 degrees.
The grain boudnary is vertical and perpendicular to the screen.
A repeat block of atoms can be seen along the grain boundary.
The repeat blocks mark the coincidence sites.
The repeat block consists of an atom attached to a five atom ring.
Figure 2
After imposing a tensile stress on the above cell (in Figure 1),
the cell was relaxed at 600K using Monte-Carlo relaxation
technique. ADESH was used for this purpose.
The total CPU time required for this exercise was about five hours
(on a PC with 486 micro-processor).
There are several areas in this cell which show non-ideal
atom arrangements. Voids and dislocations were observed
in the relaxed cell.
The dislocations are perpendicular to the screen.
They can be recognized by following the planes of atoms.
Extra half planes indicate the dislocation. Void is
self explanatory.
Following defects formed in this cell:
- A void at the grain boundary little below the center of the cell.
- A nucleation of another void at the grain boundary
can be seen in the upper half of the cell.
- From the nucleating void at the grain boundary, dislocation
is being created and it is migrating in the
right grain.
- A pair of dislocations with opposite signs are also seen
in the bottom half of the left grain.
Questions? Comments? Suggestions?
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