In this study, the influence of Ti content on the microstructure of the martensite bcc α ), which was formed by thermal effect, was investigated by scanning electron microscope and transmission electron microscope observations, in Fe-30Ni-xTi (x = 0.8, 1.8, 2.6) alloys. The crystallographic orientation relationship between austenite fcc (γ) and thermally induced bcc (α ) martensite was found to be as (111)γ//(011)α (Kurdjumov-Sachs (K-S)), by the electron diffraction analysis. The martensitic transformation temperature (Ms) of α martensite was determined as -41• C, -62• C, and -76• C in the alloys with 0.8%, 1.8%, and 2.6% Ti concentration, respectively. The Mössbauer spectrometer analysis has been revealed by a paramagnetic character for the austenite phase and magnetically order character for α martensite phase. Hyperfine magnetic field, isomer shift and volume fractions of phases were determined by the Mössbauer spectroscopy.

It was noticed that this orientation relationships were compatible with the literature (Kurdjumov-Sachs and Shoji-Nishiyama orientation relationship). Precipitation phase (carbide) formation was observed in microstructure analyses. The changes in the magnetic properties of the alloys having different rates of Mn as a consequence of thermal effect phase transformations was investigated by using Mössbauer Spectroscopy. The internal magnetic field, volume fractions (transformation rates), isomer shift values and magnetic characteristics of the main and product phases were revealed by Mössbauer Spectroscopy. In the Mössbauer Spectrum, it was noticed that ε-martensite and γ-austenite structures showed paramagnetic single-peak, and α' -martensite showed ferromagnetic six-peaks.

In this study, the microstructure of thermal effective martensitic phase transformation observed in the Fe-30wt.%Ni-2.6wt.%Mo-Xwt.%Co (X = 0.8, 1.8) alloy was investigated morphologically and crystallographically by using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). In SEM studies, it was observed that the morphology of the martensite phase changed from lath and lenticular structure to massive structure with the addition of Co to the alloy. In addition to this, nano martensite formation was also observed as another effect of Co addition (figure 2c, d). Properties of lenticular martensite, electron diffraction pattern of austenite and martensite structures were given by TEM studies. According to the Differential Scanning Calorimetry (DSC) analysis, it was determined that the martensitic transformation temperature (Ms) significantly increased with the increase of the Co amount in the alloys. Also, by using Mössbauer spectroscopy, it was shown that the amount of martensite increased with the increase of Co amount and the magnetic order of the alloy changed accordingly.

In this study, structural and crystallographic properties of phase transformations in Fe-Mn-Mo-Si (Mn = 15.14 wt.% and 18.45 wt.%) alloys were investigated. The effects of heat treatment temperature on microstructure were investigated by Scanning Electron Microscopy (SEM) and Metallurgical Microscopy (MM). In addition to this, crystallographic properties of phase transformations were revealed by using Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) methods. In the samples subjected to heat treatment at 750 C, it was observed that bainite structure was formed in the alloy where Mn amount was low and ferrite structure in the alloy where Mn amount was higher. In addition, it was found that both alloys heat-treated at 900 C had the same microstructure (pearlite structure) in SEM and MM microscopy. At the same time, microstructure observations revealed that bainite and pearlite structures contain a mixture of ferrite and cementite. In the TEM studies it was revealed by electron diffraction pattern analyses that bainite and ferrite phase crystallized in b.c.c. structure and cementite phase in orthorhombic structure. → type transformation was observed for -bainite formation, and orientation relationship was found as (1 ̅ 11)  //(011)  , [101]  //[1 ̅ 11 ̅ ]  .

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