Investigation of shape memory properties of FeMnSi alloys under mechanical and thermal effects

Some Iron-based alloys are very sensitive to the thermal and mechanical effects before andafter the transformation, and these effects may cause important changes on crystallographic,morphologic and mechanical properties or the other transformation parameters of the alloys. In thisstudy, the changes which occured on some transformation parameters of four FeMnSi alloys withdifferent composition due to the effects of various thermal and mechanical procedures have beeninvestigated by using X-ray diffraction, differential scanning calorimetry, mössbauer spectroscopy,transmission electron microscope (TEM), scanning electron microscope (SEM), EDAX analysis,optical metallography, tension tests, hardness measurements and bending tests. At the alloy specimenscooled to different conditions from high temperature γ phase region, the γ→ε, γ→ε→α′, γ→18Rmartensitic transformations were observed. The lattice parameters of fcc γ and hcp ε structures weredetermined and the changes occured upon to cooling rate on the lattice parameters were found. Fromthe differential scanning calorimetry, the austenitic and martensitic transformation temperatures weredetermined. The phase transformations and the magnetic properties of the sample were investigated byusing mössbauer spectroscopy. The phases in the materials were found by using the transmissionelectron microscope and the lattice parameters of these phases were investigated by electrondiffraction patterns. At the microscopic observations performed by two different methods; scanningelectron microscope and optical microscope, the grain structures of martensites in differentmorphology, precipitation phases and microcracs were observed. The compositions of the phases inthe structures are found were examined by using EDAX analysis. The shape memory properties of thespecimens were examined by using tension and bending tests. The changes which has occured on thehardness of the specimens by the effect of some thermal and mechanical processes were examined.With all these results the shape memory behavior of the alloys were examined.Key Words: FeMnSi alloys, shape memory effect, ε, α′ and 18R martensitic structure, cooling rateeffects, transformation temperatures, magnetic properties, martensite morphology, precipitationkinetics, stress-strain, Vickers micro hardness.