In order to establish suitable processing windows for alloys, it is important to know their critical phase transformation temperatures such as: liquidus and solidus, A1, A3 and Martensite Start temperatures for steels, gamma prime / double prime solvus temperatures for Ni-Superalloys, beta-transus temperatures for Ti-based alloys, and so on. However, these values can be sensitive to differences in the heat-to-heat chemistries, resulting in wide variations, even over the allowable specification range of an alloy.
For existing alloys, process engineers will often look up these temperatures in handbooks or data sheets. However, these values rarely account for variations attributable to chemistry differences. Additionally, it can be difficult to capture the sensitivity experimentally without many costly and time consuming experiments.
One of the strengths of computational thermodynamics is the ability to quantify the variation of properties as a function of temperature or chemistry and predict the sensitivity associated with these variations. Such calculations can be easily made using the Uncertainty Calculation type in the Property Model Calculator in Thermo-Calc and the results visualized as a histogram or normal probability plot. Three such examples are illustrated below for alloy 718, Ti-6Al-4V, and a 4140 steel.
It should also be noted that similar calculations can be made to establish upper and lower temperatures to avoid certain deleterious phases, such as TCP phases, or to predict the volume fraction of certain phases at a specific operating temperature.
