ASSESSED_SYSTEMS

ASSESSED_SYSTEM [descriptions on special treatments for specific assessed systems]*8000 !

This keyword can be included in the database definition file (the ***setup.TDB file). A maximum of 8000 characters after the keyword (to describe some special options when the DATA, GIBBS and POLY models deal with the existing systems with assessed data) is allowed until the exclamation mark (!).

Several ASSESSED_SYSTEMS keywords can be used in the same TDB file in order to have more lists of assessed systems. There is no limit to the number of the entries in the same TDB file.

The assessed systems in the database, and the special treatment options, are typed after the keyword. The elements (always in UPPER CASE) in each assessed system must be in alphabetical order and be separated by a hyphen, such as C-FE for the Fe-C binary system, and C-CR-FE for the Fe-Cr-C ternary system. A space must be between each assessed system. Information on assessed binary, ternary or higher-order systems may also be given in this way.

A ternary system like C-CR-FE does not imply that the binary C-CR, C-FE and CR-FE are assessed. There is no way to indicate partially assessed systems.

There is a field to give some descriptive information for a specific system, with various options about how to:
Reject or restore phase(s) from the current database in the DATA module;
Set major constituent(s) in the first composition set and to set a second composition set for a specific phase available in the current database in the GIBBS module; and
Calculate this specific system in the POLY module.
This is the facility used by the BIN (binary phase diagrams) and TERN (ternary phase diagrams) modules in the Thermo‑Calc software/database package.

The descriptive information must immediately follow the specific system name, and must be enclosed within parenthesis ( and ), and the left parenthesis must follow directly after the system, such as :

AL-NI(TDB +L12 ;G5 C—S:L12/NI:AL:VA ;P3 STP:.8/1200/1 STP:.2/600/1)

The syntax TDB means that the commands to the DATA module proceed, and +L12 in the example means that the phase called L12 should be restored (it has been rejected by default).

The directive ;G5 means that the following are commands to the GIBBS module. C_S: means creating a second composition set, after the colon follows the phase name and after the slash the major constituents.

After the directive ;P3 follows commands to the POLY module. STP: means setting a start point with the value of the X-axis first (composition for the second element in a binary system), the slash separates the Y-axis value (temperature), and possibly one or more directions (-1, 1, -2 or 2).

A summary of the allowed syntax is:

TDB accepts

+phase and -phase for restore/reject.
;G5 accepts
MAJ:phase/constituent-array for major constituents of the first composition set.
C_S:phase/constituent-array for a second composition set.
;P3 accepts
TMM:lt/ht for the low-/high-temperature limits (lt and ht; for instance TMM:500/4000) suitable for calculating phase diagrams and property diagrams of a binary system.
* for a default start point which is set as:
for a binary system: at the composition X(2^nd element)=.1234, temperature T=1100 K and with the default directions; or
for a ternary system: at the compositions X(2^nd element)=.1234 and X(3^rd element)=.1234 and with the default directions.
STP:x/t/d1/d2/d3 for a specific start point in a binary system which is set as at the composition X(2^nd element)=x and temperature T=t (in K), and with the directions d1, d2 and/or d3.
STP:x1/x2/d1/d2/d3 for a specific start point in a ternary system which is set as at the compositions X(2^nd element)=x1 and X(3^rd element)=x2 and with the directions d1, d2 and/or d3.
The direction(s) can be defined as -1, 1, -2 or 2. If no direction is specified, all default directions are used (meaning no ADD command is enforced in the POLY module).
If only one start point is specified, the direction(s) may be omitted; if more than one start points are specified, at least one direction for each start point must be given for all start points.

Each entry for a specific binary or ternary sub-system can be written in one or several lines (each line with 78 characters).

The directive ;P3 * is needed if the default start point should be used. If there is no P3 directive, the BIN or TERN module generates some 20 different start points in order to cover all possible compositions and temperatures (for a binary system) or all possible compositions (for a ternary system under any specific temperature).