EBSD Overlap Master Patterns - EMsoft-org/EMsoft GitHub Wiki

EBSD Overlap Master Pattern Simulations

An overlap master pattern is an EBSD master pattern that is generated as a weighted average of two master patterns belonging to different phases for a given orientation relation (OR), or to the same phase with a given OR (think twins). The computation of such an overlap pattern is fast, since it is just a simple averaging procedure. The resulting master pattern file can be used by dictionary and spherical indexing programs.

To set up the simulation parameters, enter the following command:

EMEBSDoverlap -t

This will generate a template file in your folder: EMEBSDoverlap.template which you should rename to EMEBSDoverlap.nml. The template file contains the following parameters:

&EBSDoverlapdata
! template file for the EMEBSDoverlap program
!
! overlap mode  
!  'full' = generate a complete new master pattern file that can be used for indexing
!  'series' = generate a series of 21 overlap patterns for a range of volume fractions
 overlapmode = 'series',
! name of EBSD master files
 masterfileA = 'undefined',
 masterfileB = 'undefined',
!   - for EMsoft developers who have the EMsoft_SDK installed, 
!     the following parameter will be ignored;
!   - all other users will need to provide the full path to the 
!     h5copy program here
 h5copypath = 'undefined',
! name of HDF5 output file (either a small file containing the series or a full master pattern file)
 datafile = 'undefined',
! orientation relation vectors:
 gA = 0, 0, 1,
 gB = 0, 0, 1,
 tA = 1, 0, 0,
 tB = 1, 0, 0 ,
! the following two parameters can be used to define the orientation of the merged master pattern
! with respect to the cartesian crystallographic reference frame
! center axis for output master pattern
 PatternAxisA = 0, 0, 1,
! horizontal axis for output pattern
 HorizontalAxisA = 1, 0, 0,
! volume fraction of phase A  (only used for 'full' overlapmode)
 fracA = 0.5,
! effective new point group number for this overlap symmetry (-1 to use original symmetry of phase A)
!   valid choices are:
!   #1:    '1', #2:    '-1', #3:      '2', #4:    'm', #5:  '2/m', #6:   '222', #7:    'mm2', #8:   'mmm'
!   #9:    '4', #10:   '-4', #11:   '4/m', #12: '422', #13: '4mm', #14: '-42m', #15: '4/mmm', #16:    '3'
!   #17:  '-3', #18:   '32', #19:    '3m', #20: '-3m', #21:   '6', #22:   '-6', #23:   '6/m', #24:  '622'
!   #25: '6mm', #26: '-6m2', #27: '6/mmm', #28:  '23', #29:  'm3', #30:  '432', #31:  '-43m', #32: 'm-3m'
 newpgnum = -1,
/

The program can be operated in two modes: series mode will generate 21 overlap master patterns with a phase A volume fraction between 0 and 100% in steps of 5%; the resulting small HDF5 output file has stereographic projections of these overlap patterns in it and can be read by Matlab, IDL, HDFView, etc. This is useful for producing images of master patterns.

In full mode, the output file datafile will be a full-blown master pattern file useable by other programs. The user must define the master pattern files for phase A and B (could be the same master pattern file) as well as the orientation relation: the planes gA and gB are parallel, and the directions tA and tB are also parallel. Make sure that gA is normal to tA, and gB normal to tB. The resulting overlap pattern computed for a phase A volume fraction of fracA, can optionally be rotated by defining PatternAxisA, the normal to the pattern and HoriozontalAxisA, the horizontal direction (both in crystal components). Since the symmetry of an overlap pattern is usually lower than that of the constituent patterns, the user can optionally define the overlap pattern point group symmetry newpgnum; the template file provides the list of point groups for convenience. Leave this parameter set to -1 if you want the use the symmetry group of master pattern A.

The h5copypath parameter should only be set if you do not have the EMsoft_SDK (software developer toolkit) installed on your machine. You should search for the h5copy program, which is part of an HDF5 installation. This could be present, for instance, in a python anaconda package (typically in anaconda3/bin); in that case, the full path, including the program name, should be given as follows: h5copypath = '/fullpath/anaconda3/bin/h5copy'.

Once you have completed editing the parameters, save the namelist file and execute the following command:

EMEBSDoverlap filename.nml

As an example, we consider the Burgers orientation relation (BOR) between alpha and beta Titanium. The appropriate name list file would look like this (with comments removed):

&EBSDoverlapdata
masterfileB = 'path/Ti-alpha-master-8kV.h5',
masterfileA = 'path/Ti-beta-master-8kV.h5',
datafile = 'path/overlap.h5',
overlapmode = 'full',
gB =        0        0        1
gA =        0        1        1
tB =        1        1        0
tA =        1        1       -1
PatternAxisA = 0, 0, 1,
HorizontalAxisA = 1, 0, 0,
fracA = 0.5,
newpgnum = 2,
/

This assumes that the alpha and beta Ti master patterns have already been computed; the output file contains the merged master pattern for a 50-50% mixture of alpha and beta phases, with the beta phase in the standard orientation and the alpha phase rotated by the Burgers OR rotation matrix. An example overlap pattern would look like this:

Note that some of the bands are doubled up; the true symmetry of this pattern is monoclinic, with point group 5, but in the example above the symmetry is set to the lower order triclinic group bar-1. The monoclinic two-fold rotation axis lies along the diagonal from upper left to lower right, in the plane of the stereographic projection.