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Öğe Comparison of thermally induced and deformation induced martensite in Fe-29% Ni-2% Mn alloy(Elsevier Science Sa, 2007) Güler, E.; Kirindi, T.; Aktas, H.The morphology and crystallography of maitensite either formed by cooling to subzero temperatures (thermal effect) or by compression deformation were compared for different austenite grain sizes of Fe-29% Ni-2% Mn alloy by transmission electron microscope (TEM). TEM observations revealed both epsilon and alpha' martensite formation within large grained austenite phases by thermal effect whereas only alpha' martensite formation was observed in small grained austenite phases. On the other hand, compression deformation effect caused only a' martensite formation in both small and large grained austenite phases of Fe-29% Ni-2% Mn alloy. Thermally induced alpha' martensite exhibited a lenticular morphology with partial twinnings that are peculiar to this kind of morphology. The crystallographic orientation relationship between austenite and thermally induced alpha' lenticular martensites was found to be as Kurdjumov-Sachs (K-S) type relationship. (c) 2006 Elsevier B.V. All rights reserved.Öğe Deformation induced martensite characteristics in Fe-29Ni-2Mn alloy(Taylor & Francis Ltd, 2008) Güler, E.; Aktas, H.Deformation induced martensite characteristics in the austenite phase of Fe-29Ni-2Mn alloy were studied for different austenite grain sizes of alloy. Scanning electron microscopy, transmission electron microscopy, Mossbauer spectroscopy and also differential scanning calorimetry techniques were applied to study in order to clarify the deformation induced martensite characteristics from morphological, crystallographical, magnetical and thermal points of view. Scanning electron microscope revealed that the increasing of deformation amount also increased the amount of existed martensite. Transmission electron microscope observations showed that the crystal structure of these deformation induced martensites morphology was lenticular plates with a bcc crystal structure. Also the magnetism of both austenite and martensite phases were determined with Mossbauer spectroscopy. Mossbauer spectrometer measurements showed paramagnetic character for austenite phases and ferromagnetic character for martensite phases in all samples. According to obtained differential scanning calorimetry cooling curves, deformation induced martensite start temperature M-d was found to be higher (-128 degrees C) for larger grained samples than for smaller grained samples (-135 degrees C).Öğe Effect of austenitization heat treatment on the magnetic properties of Fe-40wt% Ni-2wt% Mn alloy(Journal Of Univ Of Science And Technology Beijing, 2007) Buyukakkas, S.; Aktas, H.; Akturk, S.The effect of austenitization heat treatment on magnetic properties was examined by means of Mossbauer spectroscopy on an Fe-40wt%Ni-2wt%Mn alloy. The morphology of the alloy was obtained by using scanning electron microscopy (SEM) under different heat treatment conditions. The magnetic behavior of the non heat-treated alloy is ferromagnetic. A mixed magnetic structure including both paramagnetic and ferromagnetic states was obtained at 800 degrees C after 6 and 12 It heat treatments. In addition, the magnetic structure of the heat-treated alloy at 1150 degrees C for 12 It was ferromagnetic. With the volume fraction changing, the effective hyperfine field of the ferromagnetic austenite phase and isomery shift values were also determined by Mossbauer spectroscopy.Öğe Effect of homogenization temperature on the martensitic transformation kinetics in a Fe-32%Ni-0.4%Cr alloy(Elsevier Science Inc, 2008) Guener, M.; Gueler, E.; Aktas, H.Kinetic, morphological and some thermal properties of thermally induced and deformation-induced martensite were studied in a Fe-32%Ni-0.4%Cr alloy. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and compression deformation test techniques were used for these studies. SEM observations revealed the occurrence of both athermal and isothermal martensitic transformation kinetics for producing a lenticular martensite morphology for different homogenization conditions of the prior austenite phase. The DSC measurement results showed a fair agreement with those of previous studies on ferrous alloys. (C) 2007 Elsevier Inc. All rights reserved.Öğe Mossbauer studies on athermal martensite formation in an Fe-Ni-Mn alloy(Indian Academy Sciences, 2002) Aydin, A.; Güler, E.; Aktas, H.; Gungunes, H.In this study, austenite-martensite phase transformations which are formed by cooling effect in Fe-30% Ni-0.2% Mn alloy are investigated with Mossbauer spectroscopy and scanning electron microscopy. The single peak of the paramagnetic phase and the six peaks of the ferromagnetic phase of Fe-30% Ni-0.2% Mn alloy were observed in the Mossbauer spectrum. The internal magnetic field strength of ferromagnetic martensite phase was. determined as 33.8 T and the isomer shift values were determined as - 0.11 mm(.)sec(-1) and - 0.06 mm.sec(-1), respectively, for the austenite and martensite phases. In this alloy, athermal transformation was observed. The results obtained are in agreement with literature.
