Assistance with pyCalphad for NiTi-H System

[Ajayi Kehinde]

Thank you for developing pyCalphad—it has been very helpful for my research.

I am currently working with a NiTi TDB file, as my study focuses on hydrogen’s effect on the martensitic phase transformation in NiTi shape memory alloys, using both phase-field and macro-scale modeling.

After reviewing the documentation and watching your seminar videos on Youtube, I attempted to calculate and plot the equilibrium temperature (B2/B19') as a function of Ni mole fraction, varying from 0.48 to 0.52, which is near stoichiometry according to the TDB file and the paper I am referencing (dx.doi.org/10.1016/j.calphad.2013.02.004). However, I encountered several issues:

1. I could not pass an array of compositions to the equilibrium calculation; using a single value of composition, the calculation returned no equilibrium temperature, which seems unusual.

2. When debugging by printing the phases captured by the equilibrium function, only B19' appeared; BCC_B2, which is present in the TDB, did not show up.

Could you advise on how to resolve this issue?

Additionally, I want to plot site fractions versus Ni mole fraction at a fixed temperature. However, attempts to do so result in an error stating that Y cannot be output. Is this functionality possible, and if so, how can it be implemented?

Finally, I would appreciate your guidance on creating a TDB for the Ni–Ti–H system that could provide Gibbs energies for martensite and austenite. I have been unable to find an existing TDB for this system. Any advice or references would be greatly appreciated.

Thank you