Theoretical investigation of phase transitions in the shape memory alloy NiTi

There remain a few unsolved problems when the ab initio approach was applied to study one of the most important binary shape memory alloys (SMAs), NiTi (nitinol), which is the starting material for alloying numerous multicomponent SMAs. This hinders the computational design of complex SMAs with desirable properties. In this Letter we report that including the electronic free energy in the Gibbs free energy nearly reduces by half the large errors in previously predicted martensitic transition temperatures, and the controversy on the ground state of NiTi is resolved by reaching the convergence in free-energy calculations. In addition, the present results demonstrate that the martensitic transition path in stoichiometric NiTi is directly from B2 to B19' without intermediate phases.

Automated summary

This study reports on the unresolved problems and proposed solutions when using the ab initio approach to study NiTi alloys. The results show that including the electronic free energy in the Gibbs free energy calculations significantly reduces errors in martensitic transition temperatures and resolves controversies on the ground state of NiTi. Additionally, it is discovered that the martensitic transition path in stoichiometric NiTi is directly from B2 to B19' without intermediate phases.