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Phase Diagrams 
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DTA Simulation

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Working Group
Bill Boettinger
Ursula Kattner
Kil-Won Moon
Schematic DTA apparatus and signals

Differential thermal analysis (DTA) measurements are a standard method of determining standard method of determining transformation temperatures of materials.  Accurate interpretation of these measurements is essential when they are used to infer the location of equilibrium phase diagram boundaries. The accuracy of the measurements is affected by the details of heat transfer within the measurement cell and by transformation kinetics. Simulations can provide understanding into how thermal events from transformations are reflected in the DTA signal and can enable more accurate interpretation of DTA results from samples with unknown characteristics. A heat flow model of a DTA and thermal characteristics obtained by fitting experimental results for a pure metal, the response of the DTA is modeled for the melting and solidification of alloys. 

As input to the calculation we use enthalpy vs. temperature values obtained for full equilibrium (lever law) and for Scheil freezing assumptions.  It should be noted that these are extreme cases.  DTA melting simulations, using the lever enthalpy-temperature relation, would apply to an alloy equilibrated prior to melting and where diffusion was adequate to guarantee spatial concentration uniformity of all phases during melting. DTA melting simulations, using the Scheil enthalpy calculations, would apply to a microstructure that was solidified and remelted with no solid diffusion. The melting of an equilibrated alloy as well as an as-cast sample requires an analysis of solid diffusion for both the freezing process and the melting process.


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Last modified: 15 August 2017