However, the metastable phase was commonly observed depending on the conditions due to the perspective of kinetics.
Accordingly, it is possible to calculate the driving force to calculate which phase will appear according to the temperature from the basis phase and its degree of appearance.
Ni-base superalloys can be an example of the application of the driving force.
Among the Ni-base superalloys, one alloy shows the η-Ni3Ti phase experimentally when heat treatment in high-temperature, another one alloy do not shows the phase.
For two different alloys, the driving force calculations result obtained like followings:
When looking at the picture above, it can be seen that the η-Ni3Ti phase (ETA) is more dominant than the γ’-Ni3Al phase (GAMMA-PRIME) in the left diagram. However, the right diagram shows the opposite trend.
Experimentally, the η-Ni3Ti phase appears in the alloy showing the left result, and the η-Ni3Ti phase does not appear in the alloy showing the right result.
In this way, calculating the driving force can predict the probability that the phase will actually appear for a phase that does not appear in the equilibrium phase diagram.
Recently, the 'Driving force' template has been updated in the Calphad module.
We will learn about how to calculate the 'Driving force' with video.
Driving force Template
Step 1. Select the elements of the system.
Step 2. Select the database which describes the system,
Step 3-1. Select the basis phase.
Step 3-2. Select the phase you want to know the degree of appearance.
Step 4. Determine the initial parameters to start drawing the Diagram.
At the 'Element', determine the ratio of Major element and other elements, determine the temperature at the 'Properties', and select 'Mol' or 'Weight'.
Step 5. After finishing the setting, enter the 'Job name' and click the 'Start Job!' button to start the calculation.
We can get the following data from this calculation.
The energy of the 'LIQUID' phase selected in Step 3-1 is regarded as zero, and the relative energy of the other phases to the basis phase is displayed.
If the driving force is positive, it means that the possibility of phase change is high, and if the driving force is negative, it is low.
Using the driving force template in the Materials Square Calphad module, you can perform driving force calculations simply with a few clicks.
In addition, the intuitive result graph allows you to predict at a glance the appearance probability of a phase that could not be observed in the equilibrium phase diagram.
Do you need more information?
[Materials Square] A Ternary phase diagram with Calphad module
[Materials Square] A Binary phase diagram with Calphad module
[Materials Square] A List of Equilibrium with Calphad module
[Materials Square] How to obtain 'Function Diagram' with Open Calphad module
 Y.-K. Kim et al., A numerical model to predict mechanical properties of Ni-base disk superalloys, Int. J. Plast. 110 (2018) 123–144.
Sign up for free and get $10.
This post is licensed under a Creative Commons Attribution-Nonprofit-ShareAlike 4.0 International License.