The γ↔α′ martensitic transformation in Fe-Mn and Fe-Mn-Co alloys: experiments, thermodynamic analysis and systematics of driving forces

A study is presented of the γ↔α’ martensitic transformation (MT) in Fe-Mn-Co alloys. The work combines the experimental determination of the Ms and As temperatures with thermodynamic calculations based on Gibbs energy (Gm) models. The composition range investigated extends to the binary Fe-Mn system, which motivates detailed examination of the available MT data. This database is analyzed using independently established Gm functions, and the so-called resistance-to-start-the-transformation energies (RSTEs) are evaluated. A well-defined pattern of the differences between RSTEs for the forward and the reverse transformations is found, and a remarkable correlation for the composition dependence of the RSTE at As is reported. The need for further experimental and theoretical studies is emphasized.