Critical driving force for martensitic transformation fcc (γ)→hcp(ε) in Fe-Mn-Si shape memory alloys

By the application of Chou’s new geometry model and the available data from binary Fe-Mn, Fe-Si and Mn-Si systems, as well as SGTE DATA for lattice stability parameters of three elements from Dinsdale, the Gibbs free energy as a function of temperature of the fcc（γ） and hep（ε） phases in the Fe-Mn-Si system is reevaluated. The relationship between the Neel temperature of the γ phase and concentration of constituents in mole fraction, is fitted and verified by the experimental results. The critical driving force for the martensitic transformation fcc （γ）→ hep （ε）, △ G, defined as the free energy difference between γ and ε phases at Mof various alloys can also be obtained with a known M. It is found that the driving force varies with the composition of alloys, e. g. △ G= - 100.99 J/mol in Fe-27.0Mn-6.0Si and △ G= - 122.11 J/mol in Fe-26.9Mn-3.37Si. The compositional dependence of critical driving force accorded with the expression formulated by Hsu of the