Invited reviewEffects of thermal and deformation on martensitic transformation and magnetic properties in Fe-17%Mn-4.5%X (XÂ =Â Co and Mo) alloys

- In this study, how to vary according to the third element of microstructure and crystallographic structure of martensitic transformations occurred by thermal and deformation effect in the Fe-Mn-X (X = Co, Mo) alloy also the magnetic properties were investigated. Microstructure and crystallographic structure have analyzed by micro photograph, electron diffraction pattern and X-ray analysis. And also, magnetic properties have investigated Mössbauer Spectrometers. The Mössbauer spectra show that the α¢ martensite phase has ferromagnetic character while γ and ε martensite phases have paramagnetic character.

In this study, the Co and Mo addition to Fe-Mn based alloys was investigated to observe its effect on martensitic phase transformation. Two types of martensite structure occurred from the surface observations made by SEM for Co-added and Mo-added alloys morphologically in austenite grain. With the help of TEM studies, it was understood that these martensite structures are ε (h.c.p.) and α′ (b.c.c.). TEM investigations showed that the orientation relationship between γ (f.c.c.) and ε phases corresponds to Shoji-Nishiyama type and between γ and α' phases corresponds to Kurdjumov-Sachs (K-S) type. In the SEM observations, the amount of these two types of martensite structure has been varied depending on the amount of deformation and the heat treatment temperature. In addition, Co and Mo effects were revealed in microstructure analyzes. By comparing the values of the lattice parameters obtained from the TEM and X-Ray observations with the values of those in the literature, it is shown how Co and Mo affect the lattice parameters of structure. The lattice parameter in Co-added alloy is aα′ = 2.8695 A° while Mo-added alloy is calculated as aα′ = 2.8567 A°. The type of martensitic transformation and the change of magnetic properties of alloys related to transformation rate were demonstrated by the analysis of the Mössbauer Spectrometer data. In particular, the change in the amount of α′ martensite changes the antiferromagnetism or ferromagnetism and the internal magnetic field values of the alloys.