MTDATA – Phase Diagram Software from the National Physical Laboratory







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Calculation of primary phase fields and liquids valley for a ternary system at a fixed pressure

This application is used for the calculation of liquidus projections eg liquidus valleys and primary phase fields for ternary systems at a fixed pressure. Graphical output is produced as the calculations proceed showing the liquidus valley as calculated by MTDATA.

Before asking for the liquidus valley to be calculated it is necessary to define a datafile for the ternary system, to classify any phases required to be absent or identified as giving rise to miscibility gaps and to specify the pressure. All this can be set up using the normal APPLICATION commands within MTDATA. Also it is necessary to identify the liquid phase. eg:

set user_v(k_liquid) 3 !

and to define the range of temperatures to be covered by the scan for the liquidus valleys

range t 500 1200 1 !

The third value here represents the step size in temperature when following the valley. The best value to choose here depends on how flat the liquidus surface is likely to be. For a very steep liquidus surface a value such as 20 might be appropriate, while for a flat surface, a value of 1 might be best.

The start point for the calculations can be selected using the graphics cursor interactively or, before the "compute" command is issued, by setting the composition using the "set" command. Following the calculations the diagram may be labelled: entry of "l" (twice) or clicking the right mouse button in WinMT, will show the name of the phase in this region precipitating first from the liquid (the primary phase field). Entry of "t" (twice) near where three liquidus valley lines join, will provide the value of the temperature of the invariant reaction eg a eutectic, peritectic or transition temperature.

Liquidus projections may also be calculated using other MTDATA applications ie. LIQSECT and LIQCONT. These use different ways to delineate the liquidus valley are not limited to ternary systems.


Updated 7 May 2010