8.13. Dislocation in HCP structure

_images/hcp_disl.png

( a ) A single crystal HCP sample and the four types of slip planes in the lattice. ( b ~ e ) Demonstrated squre-shaped dislocation loops on the basal, prismatic, the 1st order pyramidal and the 2nd order pyramidal slip planes in HCP atomic structures. In the figures ( b ~ e), atoms in perfect HCP lattice are not shown for clarity, and the remaining atoms compose the dislocation cores.

To create a dislocation loop withing a single-crystal magnesium (Mg) sampel, the following two steps are employed:

Step 1:

Use the tool in the subdirectory tools/Hcp to creat an HCP single crystal sample by running the following command in Terminal. This will produce an ASCII text file of the atomic structure in current directory: hcp_reg.lmp.

1Hcp 100 100 100 -x 2 -1 -1 0 -y 0 1 -1 0 -z 0 0 0 1 Mg

Step 2:

Open terminal, run the following command, and one square-shaped dislocation loop will be created on the basal slip plane.

1CryDisGen para_file hcp_reg.lmp

Parameter file

Content of the para_file:

 1#lines starting with '#' are comments
 2#dislocation loop is on the local xoy coordinate plane
 3#crystal region
 4Region
 5-x      2 -1 -1  0      # lattice orientation along x-axis
 6-y      0  1 -1  0      # lattice orientation along y-axis
 7-z      0  0  0  1      # lattice orientation along z-axis
 8-lat    3.209 5.241     # lattice constant
 9-pbc    1  1  1         # boundary condition flags along x/y/z-axex: '1' for pbc, '0' for non-pbc
10
11#dislcoation
12nLoop 1
13Loop
14-bv     1  1 -2  0      # orientation of Burgers vector
15-bs     1/3             # scaling coefficient of Burgers vector, e.g., 1/2 in [110]/2
16-dnorm  0  0  0  1      # normal direction of dislocation plane
17-dc     0  0  0         # center of dislocation loop
18-dr     30              # radius of dislocaiton loop
19-lx     null            # local x-axis on dislocation plane, and will be caculated by the code
20-ly     null            # local y-axis on dislocation plane, and will be caculated by the code
21-ndisl  4               # segments/vertices in a discretized dislocation loop

Important

In the above example, the parameter tags, -lx,-ly, both accept one argument null, which indicates that the local coordinate axes on the dislocation plane will be automatically set by the code.