Martensitic transformation in Fe-Mn-Si based alloys

The stacking fault energy (SFE) or the stacking fault probability plays an important role in the determination of the critical driving force ΔGγ→ε for the martensitic transformation fcc(γ)→hcp(ε) in ternary Fe-Mn-Si alloys, ΔGγ→ε increases with the content of Mn and decreases with that of Si. Thermodynamical prediction of Ms in ternary Fe-Mn-Si alloys is established. The fcc(γ)→hcp(ε) martensitic transformation in Fe-Mn-Si is semi-thermoelastic and the nucleation process does not strongly depend on soft modes. Nucleation of ε-martensite is not dominated by a pole mechanism. Based on the phenomenological theory of martensite crystallography, a shuffle on (0001)hcp planes is required when d111≠d0002. The derived principal strains for the Bain distortion are smaller, i.e. more reasonable than the values given by Christian. Alloying elements which strengthen the austenite, lower the SFE of the γ phase and reduce the TγN temperature may be beneficial to the shape memory effect (SME) of Fe-Mn-Si based alloys. (orig.)